draft-ietf-issll-atm-mapping-02.txt   draft-ietf-issll-atm-mapping-03.txt 
INTERNET-DRAFT Mark W. Garrett, INTERNET-DRAFT Mark W. Garrett,
Bellcore ISSLL WG Bellcore
Expires 26 September 1997 Expires: 25 January 1998
Marty Borden, Marty Borden,
New Oak Communications New Oak Communications
Interoperation of Controlled-Load and Guaranteed Services with ATM
<draft-ietf-issll-atm-mapping-02.txt> Interoperation of Controlled-Load Service and Guaranteed Service with ATM
<draft-ietf-issll-atm-mapping-03.txt>
Status of this Memo Status of this Memo
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Abstract Abstract
Service mappings are an important aspect of effective interoperation This document provides guidelines for mapping service classes, and
between Internet Integrated Services and ATM networks. This document traffic management features and parameters between Internet and ATM
provides guidelines for ATM virtual connection features and technologies. The service mappings are useful for providing
parameters to be used in support of the IP integrated services effective interoperation and end-to-end Quality of Service for IP
protocols. The specifications include IP Guaranteed Service, Integrated Services networks containing ATM subnetworks.
Controlled-Load Service and ATM Forum UNI specification, versions
3.0, 3.1 and 4.0.
These service mappings are intended to facilitate effective end-to- The discussion and specifications given here support the IP
end Quality of Service for IP networks containing ATM subnetworks. integrated services protocols for Guaranteed Service (GS),
We discuss the various features of the IP and ATM protocols, and Controlled-Load Service (CLS) and the ATM Forum UNI specification,
identify solutions and difficult issues of compatibility and versions 3.0, 3.1 and 4.0. Some discussion of IP best effort service
interoperation. over ATM is also included.
Table of Contents Table of Contents
0.0 What's New in This Version ......................................... 3 0.0 What's New in This Version ......................................... 3
1.0 Introduction ....................................................... x 1.0 Introduction ....................................................... 3
1.1 General System Architecture .................................... x 1.1 General System Architecture .................................... 5
1.2 Related Documents .............................................. x 1.2 Related Documents .............................................. 7
2.0 Discussion of ATM Protocol Features ................................ x 2.0 Major Protocol Features for Traffic Management and QoS ............. 8
2.1 Service Category and Bearer Capability ......................... x 2.1 Service Category and Bearer Capability ......................... 8
2.1.1 Service Categories for Guaranteed Service ................ x 2.1.1 Service Categories for Guaranteed Service ................ 8
2.1.2 Service Categories for Controlled Load ................... x 2.1.2 Service Categories for Controlled Load ................... 9
2.1.3 Service Categories for Best Effort ....................... x 2.1.3 Service Categories for Best Effort ....................... 10
2.2 Cell Loss Priority Bit, Tagging and Conformance Definitions .... x 2.2 Cell Loss Priority Bit, Tagging and Conformance Definitions .... 12
2.3 ATM Adaptation Layer ........................................... x 2.3 ATM Adaptation Layer ........................................... 13
2.4 Broadband Low Layer Information ................................ x 2.4 Broadband Low Layer Information ................................ 13
2.5 Traffic Descriptors ............................................ x 2.5 Traffic Descriptors ............................................ 13
2.5.1 Translating Traffic Descriptors for Guaranteed Service ... x 2.5.1 Translating Traffic Descriptors for Guaranteed Service ... 14
2.5.2 Translating Traffic Descriptors for Controlled Load Service x 2.5.2 Translating Traffic Descriptors for Controlled Load Service 17
2.5.3 Translating Traffic Descriptors for Best Effort Service .... x 2.5.3 Translating Traffic Descriptors for Best Effort Service ....19
2.6 QoS Classes and Parameters ..................................... x 2.6 QoS Classes and Parameters ..................................... 20
2.7 Additional Parameters -- Frame Discard Mode .................... x 2.7 Additional Parameters -- Frame Discard Mode .................... 22
3.0 Discussion of IP-IS Protocol Features .............................. x 3.0 Additional IP-Integrated Services Protocol Features ................ 22
3.1 Handling of Excess Traffic ..................................... x 3.1 Path Characterization Parameters for IP Integrated Services .... 22
3.2 Use of AdSpec in Guaranteed Service with ATM ................... x 3.2 Handling of Excess Traffic ..................................... 23
3.3 Use of Guaranteed Service Adspec Parameters and Slack Term ..... 24
4.0 Discussion of Miscellaneous Items .................................. x 4.0 Miscellaneous Items ................................................ x
4.1 Units Conversion ............................................... x 4.1 Units Conversion ............................................... x
5.0 Summary of ATM VC Setup Parameters for Guaranteed Service .......... x 5.0 Summary of ATM VC Setup Parameters for Guaranteed Service .......... x
5.1 Encoding GS Using Real-Time VBR ................................ x 5.1 Encoding GS Using Real-Time VBR ................................ x
5.2 Encoding GS Using CBR .......................................... x 5.2 Encoding GS Using CBR .......................................... x
5.3 Encoding GS Using Non-Real-Time VBR ............................ x 5.3 Encoding GS Using Non-Real-Time VBR ............................ x
5.4 Encoding GS Using ABR .......................................... x 5.4 Encoding GS Using ABR .......................................... x
5.5 Encoding GS Using UBR .......................................... x 5.5 Encoding GS Using UBR .......................................... x
5.6 Encoding GS Using UNI 3.0 and UNI 3.1. ......................... x 5.6 Encoding GS Using UNI 3.0 and UNI 3.1. ......................... x
6.0 Summary of ATM VC Setup Parameters for Controlled Load Service ..... x 6.0 Summary of ATM VC Setup Parameters for Controlled Load Service ..... x
6.1 Encoding CLS Using ABR ......................................... x 6.1 Encoding CLS Using ABR ......................................... x
6.2 Encoding CLS Using Non-Real-Time VBR ........................... x 6.2 Encoding CLS Using Non-Real-Time VBR ........................... x
6.3 Encoding CLS Using Real-Time VBR ............................... x 6.3 Encoding CLS Using Real-Time VBR ............................... x
6.4 Encoding CLS Using CBR ......................................... x 6.4 Encoding CLS Using CBR ......................................... x
6.5 Encoding CLS Using UBR ......................................... x 6.5 Encoding CLS Using UBR ......................................... x
6.6 Encoding CLS Using UNI 3.0 and UNI 3.1. ........................ x 6.6 Encoding CLS Using UNI 3.0 and UNI 3.1. ........................ x
7.0 Summary of ATM VC Setup Parameters for Best Effort Service ......... x 7.0 Summary of ATM VC Setup Parameters for Best Effort Service ......... x
7.1 Encoding Best Effort Service Using UBR ......................... x 7.1 Encoding Best Effort Service Using UBR ......................... x
7.2 Encoding Best Effort Service Using Other ATM Service Categories x
8.0 Acknowledgements ................................................... x 8.0 Acknowledgements ................................................... x
Appendix 1 Abbreviations .............................................. x Appendix 1 Abbreviations .............................................. x
REFERENCES ............................................................. x References ............................................................. x
AUTHORS' ADDRESSES ..................................................... x Authors' Addresses ..................................................... x
0.0 What's New in This Version 0.0 What's New in This Version
Corrections to VC setup parameter tables. New sections on path characterization parameters (Section 3.1), and
on handling of excess traffic (Section 3.2) have been added. The
Deleted specific QoS parameter values in tables. sections on translating traffic descriptors (Section 2.5) and QoS
paremeters (Section 2.6) have been substantially revised. Minor
Section 3.1 on handling of excess traffic. improvements were made in the mapping tables in Sections 5, 6, 7.
1.0 Introduction 1.0 Introduction
We consider the problem of providing IP Integrated Services [1] with We consider the problem of providing IP Integrated Services [1] with
an ATM subnetwork. This document is intended to be consistent with an ATM subnetwork. This document is intended to be consistent with
the rsvp protocol [2] for IP-level resource reservation (although it the rsvp protocol [2] for IP-level resource reservation, although it
is, strictly speaking, independent of rsvp, since GS and CLS services is, strictly speaking, independent of rsvp, since GS and CLS services
can be supported through other mechanisms). In the ATM network, we can be supported through other mechanisms. In the ATM network, we
consider ATM Forum UNI Signaling, versions 3.0, 3.1 and 4.0 [3, 4, consider ATM Forum UNI Signaling, versions 3.0, 3.1 and 4.0 [3, 4,
5]. The latter uses the more complete service model of The ATM 5]. The latter uses the more complete service model of the ATM
Forum's TM 4.0 specification [6, 7]. Forum's TM 4.0 specification [6, 7].
This is a complex problem with many facets. In this document, we This is a complex problem. In this document, we focus on the service
focus on the service types, parameters and signalling elements needed types, parameters and signalling elements needed for service
for service interoperation. The resulting service mappings can be interoperation. The resulting service mappings can be used to
used to provide effective end-to-end Quality of Service (QoS) for IP provide effective end-to-end Quality of Service (QoS) for IP traffic
traffic that traverses ATM networks. that traverses ATM networks.
The IP services considered are Guaranteed Service (GS) [8] and The IP services considered are Guaranteed Service (GS) [8] and
Controlled Load Service (CLS) [9]. We also treat the default Best Controlled Load Service (CLS) [9]. We also treat the default Best
Effort Service (BE) in parallel with these. Our recommendations for Effort Service (BE) in parallel with these. Our recommendations for
BE are intended to be consistent with RFC 1755 [10], and its revision BE are intended to be consistent with RFC 1755 [10], and its revision
(in progress) [11], which defines how ATM VCs can be used in support (in progress) [11], which defines how ATM VCs can be used in support
of normal BE IP service. The ATM services we consider are: of normal BE IP service. The ATM services we consider are:
CBR Constant Bit Rate CBR Constant Bit Rate
rtVBR Real-time Variable Bit Rate rtVBR Real-time Variable Bit Rate
nrtVBR Non-real-time Variable Bit Rate nrtVBR Non-real-time Variable Bit Rate
UBR Unspecified Bit Rate UBR Unspecified Bit Rate
ABR Available Bit Rate ABR Available Bit Rate
(Note, Appendix 1 provides definitions for all abbreviations.) In In the case of UNI 3.0 and 3.1 signalling, where these service are
the case of UNI 3.0 and 3.1 signaling, where these service are not not all clearly distinguishable, we identify the appropriate
all clearly distinguishable, we identify the appropriate available available services.
services.
The service mappings which follow most naturally from the service The service mappings which follow most naturally from the service
definitions are as follows: definitions are as follows:
Guaranteed Service -> CBR or rtVBR Guaranteed Service -> CBR or rtVBR
Controlled Load -> nrtVBR or ABR (with a minimum cell rate) Controlled Load -> nrtVBR or ABR (with a minimum cell rate)
Best Effort -> UBR or ABR Best Effort -> UBR or ABR
For completeness we provide detailed mappings for all service For completeness we provide detailed mappings for all service
combinations and identify how each meets or fails to meet the combinations in Sections 5, 6, 7) and identify how each meets or
requirements of the higher level IP services. The reason for not fails to meet the requirements of the higher level IP services. The
restricting mappings to the most obvious or natural ones is that we reason for not restricting mappings to the most obvious or natural
cannot assume now that these services will always be ubiquitously ones is that we cannot predict how widely available all of these
available. A number of details, such as treatment of packets in services will be as ATM deployment evolves. A number of details,
excess of the flow traffic descriptor, make service mapping a such as the difference in service definitions and the treatment of
complicated subject, which cannot be expressed briefly and accurately packets in excess of the flow traffic descriptor, make service
at the same time. mapping a relatively complicated subject.
The remainder of this introduction provides a general discussion of The remainder of this introduction provides a general discussion of
the system configuration and other assumptions. Section 2 considers the system configuration and other assumptions. Section 2 considers
the relevant ATM protocol elements and their effects as related to the relevant ATM protocol elements and their effects as related to
Guaranteed, Controlled Load and Best Effort services (the latter Guaranteed, Controlled Load and Best Effort services (the latter
being the default "service"). Section 3 discusses a number of being the default "service"). This section discusses features of the
important features of the IP services and how they can be handled on IP services as well; we chose to organize the main discussion by ATM
an ATM subnetwork. Section 4 addresses a few miscellaneous problems features only because ATM is more complex in structure. Section 3
which are neither distinctly IP nor ATM. Section 5 gives detailed VC discusses a number of remaining features of the IP services and how
setup parameters for Guaranteed Service, and considers the effect of they can be handled on an ATM subnetwork. Section 4 addresses an
using each of the ATM service categories. Section 6 provides a issue (units conversion) that is neither distinctly IP nor ATM.
similar treatment for Controlled Load Service. Section 7 considers Section 5 gives the detailed VC setup parameters for Guaranteed
Best Effort service. Service, and considers the effect of using each of the ATM service
categories. Section 6 provides a similar treatment for Controlled
Load Service. Section 7 considers Best Effort service.
This document is only a part of the total solution to providing the This document is only a part of the total solution to providing the
interworking of IP integrated services with ATM subnetworks. The interworking of IP integrated services with ATM subnetworks. The
important issue of VC management, including flow aggregation, is important issue of VC management, including flow aggregation, is
considered in [12]. We do not consider how routing -- QoS sensitive considered in [12,18,19]. We do not consider how routing, QoS
or not -- interacts with the use of VCs, especially in the case of sensitive or not, interacts with the use of VCs. We expect that a
multicast (or point-to-multipoint) flows. We expect that a
considerable degree of implementation latitude will exist, even considerable degree of implementation latitude will exist, even
within the guidelines presented here. Many aspects of interworking within the guidelines presented here. Many aspects of interworking
between IP and ATM will depend on economic factors, and will not be between IP and ATM will depend on economic factors, and will not be
subject to standardization. subject to standardization.
1.1 General System Architecture 1.1 General System Architecture
We assume that the reader has a general working knowledge of IP, rsvp We assume that the reader has a general working knowledge of IP, rsvp
and ATM protocols. The network architecture we consider is and ATM protocols. The network architecture we consider is
illustrated in Figure 1, below. An IP-attached host may send unicast illustrated in Figure 1. An IP-attached host may send unicast
datagrams to another host, or may use an IP multicast address to send datagrams to another host, or may use an IP multicast address to send
packets to all of the hosts which have "joined" the multicast "tree". packets to all of the hosts which have "joined" the multicast "tree".
In either case, a destination host may then use RSVP to establish In either case, a destination host may then use RSVP to establish
resource reservation in routers along the internet path for the data resource reservation in routers along the internet path for the data
flow. flow.
An ATM network lies in the path (chosen by the IP routing), and An ATM network lies in the path (chosen by the IP routing), and
consists of one or many ATM switches. It uses VCs to provide both consists of one or more ATM switches. It uses SVCs to provide both
resources and QoS within the ATM cloud. These connections are set resources and QoS within the ATM cloud. These connections are set
up, added to (in the case of multipoint trees), torn down, and up, added to (in the case of multipoint trees), torn down, and
controlled by the edge devices, which act as both IP routers and ATM controlled by the edge devices, which act as both IP routers and ATM
interfaces, capable of initiating and managing VCs across the ATM interfaces, capable of initiating and managing VCs across the ATM
user-to-network (UNI) interface. The edge devices are assumed to be user-to-network (UNI) interface. The edge devices are assumed to be
fully functional in both the IP int-serv/RSVP protocols and the ATM fully functional in both the IP int-serv/RSVP protocols and the ATM
UNI protocols, as well as translating between them. UNI protocols, as well as translating between them.
ATM Cloud ATM Cloud
------------------ ------------------
H ----\ ( ) /------- H H ----\ ( ) /------- H
H ---- R -- R -- E --( ATM Sw -- ATM Sw ) -- E -- R -- R -- H H ---- R -- R -- E --( ATM Sw -- ATM Sw ) -- E -- R -- R -- H
H ----/ | ( ) \ H ----/ | ( ) \
| ------------------ \------ H | ------------------ \------ H
H ----------R H ----------R
Figure 1: Network Architecture with hosts (H), Figure 1: Network Architecture with Hosts (H),
Routers (R) and Edge Devices (E). Routers (R) and Edge Devices (E).
The edge devices may be considered part of the IP internet or part of When considering the edge devices with respect to traffic flowing
the ATM cloud, or both. This is not an issue since they must provide from source to destination, the upstream edge device is called the
capabilities of both environments. The edge devices have normal RSVP "ingress" point and the downstream device the "egress" point. The
capability to process RSVP messages, reserve resources, and maintain edge devices may be considered part of the IP internet or part of the
soft state (in the control path), and to classify and schedule ATM cloud, or both. They process RSVP messages, reserve resources,
packets (in the data path). They also have the normal ATM and maintain soft state (in the control path), and classify and
capabilities to initiate connections by signaling, and to accept or schedule packets (in the data path). They also initiate ATM
refuse connections signaled to them. They police and schedule cells connections by signalling, and accept or refuse connections signaled
going into the ATM cloud. An IP-level reservation (RESV message) to them. They police and schedule cells going into the ATM cloud.
triggers the edge device to translate the RSVP service requirements The service mapping function occurs when an IP-level reservation
into ATM VC (UNI) semantics. (RESV message) triggers the edge device to translate the RSVP service
requirements into ATM VC (UNI) semantics.
A range of VC management policies are possible, which determine A range of VC management policies are possible, which determine
whether a flow should initiate a new VC or join an existing one. VCs whether a flow should initiate a new VC or join an existing one. VCs
are managed according to a combination of standards and local policy are managed according to a combination of standards and local policy
rules, which are specific to either the implementation (equipment) or rules, which are specific to either the implementation (equipment) or
the operator (network service provider). Point-to-multipoint the operator (network service provider). Point-to-multipoint
connections within the ATM cloud can be used to support general IP connections within the ATM cloud can be used to support general IP
multicast flows. In ATM, a point to multipoint connection can be multicast flows. In ATM, a point to multipoint connection can be
controlled by the source (or root) node, or a leaf initiated join controlled by the source (or root) node, or a leaf initiated join
(LIJ) feature in ATM may be used. Note, the topic of VC management (LIJ) feature in ATM may be used. Note, the topic of VC management
and mapping of flows onto VCs is considered at length in another and mapping of flows onto VCs is considered at length in other issll
issll working group draft [12]. working group drafts [12,18,19].
Figure 2 shows the functions of an edge device, summarizing the work Figure 2 shows the functions of an edge device, summarizing the work
not part of IP or ATM abstractly as an InterWorking Function (IWF), not part of IP or ATM abstractly as an InterWorking Function (IWF),
and segregating the control and data planes. (Note: for expositional and segregating the control and data planes. (Note: for expositional
convenience, policy control and other control functions are included convenience, policy control and other control functions are included
as part of the admission control in the diagram.) as part of the admission control in the diagram.)
IP ATM IP ATM
____________________ ____________________
| IWF | | IWF |
skipping to change at page 7, line 7 skipping to change at page 7, line 9
It is not possible to completely separate the service mapping and VC It is not possible to completely separate the service mapping and VC
management functions. Several illustrative examples come to mind: management functions. Several illustrative examples come to mind:
(i) Multiple integrated-services flows may be aggregated to use one (i) Multiple integrated-services flows may be aggregated to use one
point-to-multipoint VC. In this case, we assume the IP flows are of point-to-multipoint VC. In this case, we assume the IP flows are of
the same service type and their parameters have been merged the same service type and their parameters have been merged
appropriately. (ii) The VC management function may choose to appropriately. (ii) The VC management function may choose to
allocate extra resources in anticipation of further reservations or allocate extra resources in anticipation of further reservations or
based on an empiric of changing TSpecs. (iii) There must exist a based on an empiric of changing TSpecs. (iii) There must exist a
path for best effort flows and for sending the rsvp control messages. path for best effort flows and for sending the rsvp control messages.
How this interacts with the establishment of VCs for QoS traffic may How this interacts with the establishment of VCs for QoS traffic may
alter the characteristics required of those VCs. See [12] for alter the characteristics required of those VCs. See [12,18,19] for
further details on VC management. further details on VC management.
Therefore, in discussing the service-mapping problem, we will assume Therefore, in discussing the service-mapping problem, we will assume
that the VC management function of the IWF can always express its that the VC management function of the IWF can always express its
result in terms of an IP-level service with some QoS and TSpec. The result in terms of an IP-level service with some QoS and TSpec. The
service mapping algorithm, which is the subject of this document, can service mapping algorithm can then identify the appropriate VC
then identify the appropriate VC parameters, whether the resulting parameters, whether the resulting action uses new or existing VCs.
action is initiation of a new VC, the addition/deletion of a leaf to
an existing multipoint tree, or the modification of an existing VC to
one of another description.
1.2 Related Documents 1.2 Related Documents
Earlier ATM Forum documents were called UNI 3.0 and UNI 3.1. The 3.1 Earlier ATM Forum documents were called UNI 3.0 and UNI 3.1. The 3.1
release was used to correct errors and fix alignment with the ITU. release was used to correct errors and fix alignment with the ITU.
Unfortunately UNI 3.0 and 3.1 are incompatible. However this is in Unfortunately UNI 3.0 and 3.1 are incompatible. However this is in
terms of actual codepoints, not semantics. Therefore, descriptions terms of actual codepoints, not semantics. Therefore, descriptions
of parameter values can generally be used for both. of parameter values can generally be used for both.
After 3.1, the ATM Forum decided to release documents separately for After 3.1, the ATM Forum began to release documents separately for
each technical working group. The Traffic Management and Signalling each technical working group. The Traffic Management and Signalling
4.0 documents are available publically at ftp.atmforum.com/pub. We 4.0 documents are available publically at ftp.atmforum.com/pub. We
refer to the combination of traffic management and signalling as refer to the combination of traffic management and signalling as
TM/UNI 4.0, although specific references may be made to the TM 4.0 TM/UNI 4.0, although specific references may be made to the TM 4.0
specification or the UNI SIG 4.0 specification. specification or the UNI Signalling 4.0 specification.
Within the IETF area, related material includes the work of the rsvp Within the IETF, related material includes the work of the rsvp [2],
[2], int-serv [1, 8, 9, 13, 14] and ion working groups [10, 11] of int-serv [1, 8, 9, 13, 14] and ion working groups [10, 11]. Rsvp
the IETF. Rsvp defines the resource reservation protocol (which is defines the resource reservation protocol (which is analogous to
analogous to signaling in ATM). Int-serv defines the behavior and signalling in ATM). Int-serv defines the behavior and semantics of
semantics of particular services (analogous e.g., to the Traffic particular services (analogous e.g., to the Traffic Management
Management working group in the ATM Forum). Ion defines interworking working group in the ATM Forum). Ion defines interworking of IP and
of IP and ATM for traditional Best Effort service, and covers all ATM for traditional Best Effort service, and covers issues related to
issues related to routing and addressing. routing and addressing.
A large number of ATM signaling details are covered in RFC 1755 [10], A large number of ATM signalling details are covered in RFC 1755
e.g., differences between UNI 3.0 and UNI 3.1, encapsulation, frame- [10], e.g., differences between UNI 3.0 and UNI 3.1, encapsulation,
relay interworking, etc. These considerations generally extend to IP frame-relay interworking, etc. These considerations generally extend
over ATM with QoS as well. Any description given in this document of to IP over ATM with QoS as well. Any description given in this
IP Best Effort service (i.e. the default behavior) over ATM is document of IP Best Effort service (i.e. the default behavior) over
intended to be consistent with RFC 1755 and it's extension for UNI ATM is intended to be consistent with RFC 1755 and it's extension for
4.0 [11], and those documents are to be considered definitive. In UNI 4.0 [11], and those documents are to be considered definitive.
some instances with non-best-effort services, certain IP/ATM features In some instances with non-best-effort services, certain IP/ATM
will diverge from the following RFC 1755. The authors have attempted features will diverge from the following RFC 1755. The authors have
to note such differences explicitly. (For example, best effort VCs attempted to note such differences explicitly. (For example, best
are taken down on timeout by either edge device, while QoS VCs are effort VCs are taken down on timeout by either edge device, while QoS
only removed by the upstream edge device when the corresponding rsvp VCs are only removed by the upstream edge device when the
reservation is deleted.) corresponding rsvp reservation is deleted.)
RFC 1821 [15], represents an early discussions of issues involved RFC 1821 [15], represents an early discussion of issues involved with
with interoperating IP and ATM protocols for integrated services and interoperating IP and ATM protocols for integrated services and QoS.
QoS.
2.0 Discussion of ATM Protocol Features 2.0 Major Protocol Features for Traffic Management and QoS
In this section, we discuss each of the items that must be specified In this section, we discuss each of the items that must be specified
in the setup of an ATM VC. For each of these we discuss which in the setup of an ATM VC. For each of these we discuss which
specified items and values may be most appropriate for each of the specified items and values may be most appropriate for each of the
three integrated services. three integrated services.
The ATM Call Setup is sent by the edge device to the ATM network to The ATM Call Setup is sent by the ingress edge device to the ATM
establish end-to-end (ATM) service. This setup contains the network to establish end-to-end (ATM) service. This setup contains
following information. the following information.
Service Category/Broadband Bearer Capability Service Category/Broadband Bearer Capability
AAL Parameters AAL Parameters
Broadband Low Layer Information Broadband Low Layer Information
Calling and Called Party Addressing Information Calling and Called Party Addressing Information
Traffic Descriptors Traffic Descriptors
QoS Parameters QoS Class and/or Parameters
Additional Parameters of TM/UNI 4.0 Additional Parameters of TM/UNI 4.0
We will discuss each of these, except addressing information, as they We discuss each of these as they relate to the translation of GS and
relate to the translation of GS and CLS to ATM services. Following CLS to ATM services. We do not discuss addressing at all, since it
the discussion of the service categories, we discuss the tagging and is (at least presently) independent of QoS. Following the section on
conformance definitions for IP and ATM, since the policing method is service categories, we discuss tagging and conformance definitions
implicit in the call setup. We then continue with mappings of the for IP and ATM. These do not appear explicitly as set-up parameters
other parameters and information elements. since the policing method used is implicit in the call setup.
2.1 Service Category and Bearer Capability 2.1 Service Category and Bearer Capability
The highest level of abstraction distinguishing features of ATM VCs The highest level of abstraction distinguishing features of ATM VCs
is in the service category or bearer capability. Service categories is in the service category or bearer capability. Service categories
were introduced in TM/UNI 4.0; previously the bearer capability was were introduced in TM/UNI 4.0; previously the bearer capability was
used to discriminate at this level. used to discriminate at this level.
In each version of the ATM specifications, these indicate the general These parameters indicate the general properties required of a VC:
properties required of a VC: whether there is a real-time delay whether there is a real-time delay constraint, whether the traffic is
constraint, whether the traffic is constant or variable rate, the constant or variable rate, the applicable traffic and QoS description
applicable traffic and QoS description parameters and (implicitly) parameters and (implicitly) the complexity of some supporting switch
the complexity of some supporting switch mechanisms. mechanisms.
For UNI 3.0 and UNI 3.1, there are only two distinct options for For UNI 3.0 and UNI 3.1, there are only two distinct options for
bearer capabilities (in our context): bearer capabilities (in our context):
BCOB-A: constant rate, timing required, unicast/multipoint; BCOB-A: constant rate, timing required, unicast/multipoint;
BCOB-C: variable rate, timing not required, unicast/multipoint. BCOB-C: variable rate, timing not required, unicast/multipoint.
There is a third capability, BCOB-X, but in the case of AAL5 (which A third capability, BCOB-X, can be used as a substitute for the above
we require -- see below) it can be used interchangeably and two capabilities, with its dependent parameters (traffic type and
consistently with the above two capabilities. timing requirement) set appropriately. The distinction between the
BCOB-X formulation and the "equivalent" (for our purposes) BCOB-A and
BCOB-C constructs is whether the ATM network is to provide pure cell
relay service or interwork with other technologies (with
interoperable signalling), such as narrowband ISDN. Where this
distinction is applicable, the appropriate code should be used (see
[5] and related ITU specs, e.g., I.371).
In TM/UNI 4.0 the service categories are: In TM/UNI 4.0 the service categories are:
Constant Bit Rate (CBR) Constant Bit Rate (CBR)
Real-time Variable Bit Rate (rtVBR) Real-time Variable Bit Rate (rtVBR)
Non-real-time Variable Bit Rate (nrtVBR) Non-real-time Variable Bit Rate (nrtVBR)
Unspecified Bit Rate (UBR) Unspecified Bit Rate (UBR)
Available Bit Rate (ABR) Available Bit Rate (ABR)
The first two of these are real-time services, so that rtVBR is new The first two of these are real-time services, so that rtVBR is new
to TM/UNI 4.0. The ABR service is also new to TM/UNI 4.0. UBR to TM/UNI 4.0. The ABR service is also new to TM/UNI 4.0. UBR
exists in all specifications, except perhaps in name, through the exists in all specifications, except perhaps in name, through the
``best effort'' indication flag and/or the QoS Class 0. "best effort" indication flag and/or the use of QoS Class 0.
The encoding used in 4.0 is consistent with the earlier versions. The Service Category in TM/UNI 4.0 is encoded into the same signalled
For example, the Service Category is indicated solely by the Information Element (IE) as the Bearer Capability in UNI 3.x, for the
combination of the Bearer Capability and the Best Effort indication purpose of backward compatibilty. Thus, we use the convention of
flag. referring to Service Category (CBR, rtVBR, nrtVBR, UBR, ABR) for
TM/UNI 4.0 (where the bearer capability is implicit). When we refer
to the Bearer Capability explicitly (BCOB-A, BCOB-C, BCOB-X), we are
describing a UNI 3.x signalling message.
In principle, it is possible to support any foreseeable service In principle, it is possible to support any service through the use
through the use of BCOB-A/CBR. This is because the CBR service is of BCOB-A/CBR. This is because the CBR service is equivalent to
equivalent to having a ``pipe'' with specified bandwidth/timing. having a "pipe" with specified bandwidth/timing. However, it may be
However, it may be desirable to make better use of the ATM network's desirable to make better use of the ATM network's resources by using
resources by using other, less demanding, services when available. other, less demanding, services when available. (See RFC 1821 for a
(See RFC 1821 for a discussion of this [15].) discussion of this [15].)
2.1.1 Service Categories for Guaranteed Service 2.1.1 Service Categories for Guaranteed Service
There are two possible mappings for GS: There are two possible mappings for GS:
CBR (BCOB-A) CBR (BCOB-A)
rtVBR rtVBR
GS requires real-time support, that is, timing is required. Thus in GS requires real-time support. Thus in UNI 3.x, the bearer class
UNI 3.x, the bearer class BCOB-A (or an equivalent BCOB-X BCOB-A (or an equivalent BCOB-X formulation) must be used. In TM/UNI
formulation) must be used. In TM/UNI 4.0 either CBR or rtVBR is 4.0 either CBR or rtVBR is appropriate. The use of rtVBR may
appropriate. In both cases, GS would use a value of CLR
appropriately low for the link (i.e., such that congestion losses are
dominated by losses due to bit errors). The use of rtVBR may
encourage recovery of allocated bandwidth left unused by a source. encourage recovery of allocated bandwidth left unused by a source.
It also accomm odates more bursty sources with a larger bucket It also accommodates more bursty sources with a larger token bucket
parameter, and permits the use of tagging for excess traffic (see burst parameter, and permits the use of tagging for excess traffic
Section 2.2). (see Section 2.2).
Neither the BCOB-C bearer class, nor nrtVBR, UBR, ABR are good Neither the BCOB-C bearer class, nor nrtVBR, UBR, ABR are good
matches for the GS service. These provide no delay estimates and matches for the GS service. These provide no delay estimates and
cannot guarantee consistently low delay for every packet. cannot guarantee consistently low delay for every packet.
Specification of BCOB-A or CBR requires specification of a PCR. The Specification of BCOB-A or CBR requires specification of a peak cell
PCR should be specified as the the token bucket rate parameter, with rate (PCR). In these cases, PCR is the nominal clearing rate with
appropriate conversion from bytes to cells (accounting for overhead), jitter toleration (bucket size) CDVT, which is generally small.
of the GS TSpec. For both of these, the network provides a nominal
clearing rate of PCR with jitter toleration (bucket size) CDVT,
specified in a network specific manner (see below).
Specification of rtVBR requires the specification of two rates, SCR Specification of rtVBR requires two rates, PCR and SCR. This models
and PCR. This models bursty traffic with specified peak and average bursty traffic with specified peak and sustainable rates. The
rates. With rtVBR, it is appropriate to map the PCR to the line rate corresponding ATM token bucket depth values are CDVT, and CDVT+BT,
of incoming traffic and the SCR to the GS TSpec bucket rate. The ATM respectively.
bucket sizes are CDVT, in a network specific manner, and CDVT+BT,
respectively for the PCR and SCR parameters (see below).
2.1.2 Service Categories for Controlled Load 2.1.2 Service Categories for Controlled Load
There are three possible mappings for CLS: There are three possible good mappings for CLS:
CBR (BCOB-A) CBR (BCOB-A)
ABR ABR
nrtVBR (BCOB-C) nrtVBR (BCOB-C)
Note that under UNI 3.x, only the first and third choices are Note that under UNI 3.x, there are equivalent services to CBR and
applicable. The first, with a CBR/BCOB-A connection, provides a nrtVBR, but not ABR. The first, with a CBR/BCOB-A connection,
higher level of QoS than is necessary, but it may be convenient to provides a higher level of QoS than is necessary, but it may be
simply allocate a fixed-rate ``pipe'', which should be ubiquitously convenient to simply allocate a fixed-rate "pipe", which we expect to
supported in ATM networks. However unless this is the only choice be ubiquitously supported in ATM networks. However unless this is
available, this will probably be wasteful of network resources. the only choice available, this will probably be wasteful of network
resources.
The nrtVBR/BCOB-C category is perhaps the best match, since it
provides for allocation of bandwidth and buffers with an additional
peak rate indication, similar to the CLS TSpec.
The ABR category with a positive MCR aligns with the CLS idea of The ABR category with a positive MCR aligns with the CLS idea of
``best effort with floor.'' The ATM network agrees to forward cells "best effort with a floor." The ATM network agrees to forward cells
with a rate of at least MCR, which should be directly converted from with a rate of at least MCR, which should be directly converted from
the token bucket rate of the TSpec. The bucket size parameter the token bucket rate of the receiver TSpec. The bucket size
measures approximately the amount of buffer required at the IWF. parameter measures approximately the amount of buffer required at the
IWF. This buffer serves to absorb the bursts allowed by the token
bucket, since they cannot be passed directly into a ABR VC.
The nrtVBR/BCOB-C category can also be used. The rtVBR category can The rtVBR category can be used, although the edge device must
be used, although the edge device must choose a value for CTD and CDV determine a value for CTD and CDV. Since there are no corresponding
as a matter of local policy. IP-level parameters, their values are set as a matter of local
policy.
The UBR category does not provide enough capability for Controlled The UBR category does not provide enough capability for Controlled
Load. The point of CLS is to allow an allocation of resources, which Load. The point of CLS is to allow an allocation of resources, which
is facilitated by the token bucket traffic descriptor, and is is facilitated by the token bucket traffic descriptor, and is
unavailable in UBR. unavailable with UBR.
2.1.3 Service Categories for Best Effort 2.1.3 Service Categories for Best Effort
All of the service categories have the capability to carry Best All of the service categories have the capability to carry Best
Effort service, but the natural service category is UBR (or, in UNI Effort service, but the natural service category is UBR (or, in UNI
3.x, BCOB-C or BCOB-X, with the best effort indication set). A CBR 3.x, BCOB-C or BCOB-X, with the best effort indication set). A CBR
or rtVBR clearly could be used, and since the service is not real- or rtVBR clearly could be used, and since the service is not real-
time, a nrtVBR connection could also be used. In these cases the time, a nrtVBR connection could also be used. In these cases the
rate parameter used reflects a bandwidth allocation in support of the rate parameter used reflects a bandwidth allocation in support of the
edge device's best effort connectivity to the far edge router. It ingress edge device's best effort connectivity to the egress edge
would be normal for traffic from many source/destination pairs to be router. It would be normal for traffic from many source/destination
aggregated on this connection; indeed, since Best Effort is the pairs to be aggregated on this connection; indeed, since Best Effort
default IP behavior, the individual flows are not necessarily is the default IP behavior, the individual flows are not necessarily
identified or accounted for. CBR may be a preferred solution in the identified or accounted for. CBR may be a preferred solution in the
case where best effort traffic is sufficiently highly aggregated that case where best effort traffic is sufficiently highly aggregated that
a simple fixed-rate pipe is efficient. Both CBR and nrt-VBR provide a simple fixed-rate pipe is efficient. Both CBR and nrt-VBR provide
bandwidth allocation which may be useful for billing purposes. An bandwidth allocation which may be useful for billing purposes.
ABR connection could similarly be used to support Best Effort
traffic. The support of data communications protocols such as TCP/IP An ABR connection could similarly be used to support Best Effort
is the explicit purpose for which ABR was specifically designed. It traffic. Indeed, the support of data communications protocols such
is conceivable that a separate ABR connection would be made for as TCP/IP is the explicit purpose for which ABR was designed. It is
conceivable that a separate ABR connection would be made for
different IP flows, although the normal case would probably have all different IP flows, although the normal case would probably have all
IP Best Effort traffic with a common egress router sharing a single IP Best Effort traffic with a common egress router sharing a single
ABR connection. ABR connection.
The rt-VBR service category may be considered less suitable, simply The rt-VBR service category may be considered less suitable, simply
because both the real-time delay constraint and the use of SCR/BT add because both the real-time delay constraint and the use of SCR/BT add
unnecessary complexity. unnecessary complexity.
See specifications from the IETF ion working group [10, 11] for See specifications from the IETF ion working group [10, 11] for
related work on support of Best Effort service with ATM. related work on support of Best Effort service with ATM.
2.2 Cell Loss Priority Bit, Tagging and Conformance Definitions 2.2 Cell Loss Priority Bit, Tagging and Conformance Definitions
An ATM header carries the Cell Loss Priority (CLP) bit. Cells with Each ATM cell header carries a Cell Loss Priority (CLP) bit. Cells
CLP=1 are said to be ``tagged'' and have lower priority. This with CLP=1 are said to be "tagged" or "marked" and have lower
tagging may be done by the source, to indicate relative priority priority. This tagging may be done by the source, to indicate
within the VC, or by a switch, to indicate traffic in violation of relative priority within the VC, or by a switch, to indicate traffic
policing parameters. Options involving the use of tagging are in violation of policing parameters. Options involving the use of
decided at call setup time. tagging are decided at call setup time.
A Conformance Definition is a rule that determines whether a cell is A Conformance Definition is a rule that determines whether a cell is
conforming to the traffic descriptor of the VC. The conformance conforming to the traffic descriptor of the VC. The conformance
definition is given in terms of a Generic Cell Rate Algorithm (GCRA), definition is given in terms of a Generic Cell Rate Algorithm (GCRA),
also known as a "leaky bucket" algorithm, for CBR and VBR services. also known as a "leaky bucket" algorithm, for CBR and VBR services.
(UBR and ABR have network-specific conformance definitions. Note, (UBR and ABR have network implementation-specific conformance
the term "compliance" in ATM is used to describe the behavior of a definitions. Note, the term "compliance" in ATM is used to describe
connection.) the behavior of a connection, as opposed to "conformance", which
applies to a single cell.)
The network may tag cells which are non-conforming, rather than The network may tag cells that are non-conforming, rather than
dropping them only if the VC is set up to request tagging and the dropping them if the VC set-up requests tagging and the network
network supports the tagging option. When congestion occurs, a supports the tagging option. When congestion occurs, a switch must
switch must attempt to discard tagged cells in preference to the attempt to discard tagged cells in preference to discarding CLP=0
discarding of CLP=0 cells. However, the mechanism for doing this is cells. However, the mechanism for doing this is completely
completely implementation specific. Tagged cells are treated with a implementation specific. The behavior that best meets the
behavior which is Best Effort in the sense that they are transported requirements of IP Integrated Services is where tagged cells are
when bandwidth is available, queued when buffers are available, and treated as "best effort" in the sense that they are transported when
dropped when the resources are overcommitted. bandwidth is available, queued when buffers are available, and
dropped when resources are overcommitted. ATM standards, however, do
not explicitly specify treatment of tagged traffic. Providers of GS
and CLS service with ATM subnetworks should ascertain the actual
behavior of ATM implementation with respect to tagged cells.
Since GS and CLS services require excess traffic to be treated as Since GS and CLS services require excess traffic to be treated as
Best Effort, the tagging option should always be chosen (if best effort, the tagging option should always be chosen (if
supported) in the VC setup as a means of ``downgrading'' non- supported) in the VC setup as a means of "downgrading" the cells
conformant cells. However, the term ``best effort'' seems to be used comprising non-conformant packets. However, the term "best effort"
with two distinguishable meanings in the int-serv specs. The first can be interpreted in two distinct ways. The first is as a service
is that of a service class that, in some typical scheduler class that, in some typical scheduler implementations, would
implementations, would correspond to a separate queue. Placing correspond to a separate queue. Placing excess traffic in best
excess traffic in best effort in this sense would be giving it lower effort in this sense would be giving it lower delay priority. The
delay priority. The other sense is more generic, meaning that the other sense is more generic, meaning that the network would make a
network would make a best effort to transport the traffic. A best effort to transport the traffic. A reasonable expectation is
reasonable expectation is that a network with no contending traffic that a network with no contending traffic would transport the packet,
would transport the packet, while a very congested network would drop while a very congested network would drop the packet. A packet that
the packet. A packet that could be tagged with lower loss priority could be tagged with lower loss priority (such as with the ATM CLP
(such as the ATM CLP bit) would be more likely to be dropped, but bit) would be more likely to be dropped, but would not be reordered
would not normally be transported out of order with respect to the with respect to the conforming portion of the flow. Such a mechanism
conforming portion of the flow. Such a mechanism would agree with would agree with the latter definition of best effort, but not the
the latter definition of best effort, but not the former. former. This interpretation is left to the implementation.
In TM/UNI 4.0 tagging does not apply to the CBR or ABR services. There are three conformance definitions of VBR service (for both
However, there are three conformance definitions of VBR service (for rtVBR and nrtVBR) to consider. In VBR, only the conformance
both rtVBR and nrtVBR) to consider. In VBR, only the conformance definition VBR.3 supports tagging and applies the GCRA with rate PCR
definition VBR.3 supports tagging and applies the GCRA with PCR to to the aggregate CLP=0+1 cells, and another GCRA with rate SCR to the
the aggregate CLP=0+1 cells, and another GCRA with SCR to the CLP=0 CLP=0 cells. This conformance definition should always be used with
cells. Thus this conformance definition should always be used in a VBR service supporting IP integrated services. For UBR service,
support of IP integrated services. For UBR service, conformance conformance definition UBR.2 supports the use of tagging, but a CLP=1
definition UBR.2 supports the use of tagging, but a CLP=1 cell does cell does not imply non-conformance; rather, it may be used to
not imply non-conformance; it may be a hint of network congestion. indicate network congestion.
Once an ATM connection is established, and the particular conformance In TM/UNI 4.0 tagging does not apply to the CBR or ABR services.
definition is determined, the resulting policing action is mandatory. More precisely, the conformance definitions listed in TM 4.0 for CBR
Since the conformance algorithm operates on cells, when mapping rates and ABR do not use tagging. Since conformance definitions are
and bucket sizes from IP services to corresponding ATM parameters, a network specific, it may be possible that implementations of CBR or
correction needs to be made (at call setup time) for the ATM ABR with tagging can exist. Wherever an ATM network does support
segmentation overhead. Unfortunately this overhead, as a ratio, tagging, in the sense of transporting CLP=1 cells on a "best effort"
depends on packet length, with the overhead largest for small basis, it is a useful and preferable mechanism for handling excess
packets. Thus the appropriate correction could be based on minimum traffic.
packet size, expected packet size, or otherwise in a network specific
manner, determined at the edge device IWF. See Section 4.1.
It is always better fo the IWF to tag cells when it can anticipate It is always better for the IWF to tag cells when it can anticipate
that the ATM network would do so. This is because the IWF knows the that the ATM network would do so. This is because the IWF knows the
IP packet boundaries and can tag all of the cells corresponding to a IP packet boundaries and can tag all of the cells corresponding to a
packet. If left to the ATM layer UPC, the network would inevitably packet. If left to the ATM layer UPC, the network would inevitably
carry some cells of packets which are worthless, because some other drop some of the cells of a packet while carrying others, which would
cells from those packet are dropped due to non-conformance. then be dropped by the receiver. Therefore, the IWF, knowing the VC
Therefore, the IWF, knowing the VC GCRA parameters, should always GCRA parameters, should always anticipate the cells which will be
anticipate the cells which will be tagged by the ATM UPC and tag all tagged by the ATM UPC and tag all of the cells uniformly across each
of the cells uniformly across each affected packet. affected packet.
2.3 ATM Adaptation Layer 2.3 ATM Adaptation Layer
The AAL type 5 encoding must be used, as specified in RFC 1483 and The AAL type 5 encoding must be used, as specified in RFC 1483 and
RFC 1755. AAL5 requires specification of the maximum SDU size in both RFC 1755. AAL5 requires specification of the maximum SDU size in both
the forward and reverse directions. Both GS and CLS specify a maximum the forward and reverse directions. Both GS and CLS specify a maximum
packet size as part of the TSpec and this value shall be used as the packet size as part of the TSpec and this value shall be used as the
maximum SDU in each direction for unicast connections, but only in maximum SDU in each direction for unicast connections, and for
one direction for point-to-multipoint connections, which are unidirectional point-to-multipoint connections. When multiple flows
unidirectional. When more than one flow aggregated into a single VC, are aggregated into a single VC, the M parameters of the receiver
the TSpecs are merged to yield the largest packet size. In no case TSpecs are merged according to rules given in the GS and CLS specs.
can this exceed 65535 (or, of course, the MTU of the link).
2.4 Broadband Low Layer Information 2.4 Broadband Low Layer Information
The B-LLI Information Element is transferred transparently by the ATM The B-LLI Information Element is transferred transparently by the ATM
network between the edge devices and is used to specify the network between the edge devices and is used to specify the
encapsulation method. Multiple B-LLI IEs may be sent as part of encapsulation method. Multiple B-LLI IEs may be sent as part of
negotiation. The default encapsulation LLC/SNAP [16] must be negotiation. The default encapsulation LLC/SNAP [16] must be
supported as specified in RFC 1577 and RFC 1755. Additional supported as specified in RFC 1577 [17] and RFC 1755 [10]. See RFC
encapsulations are discussed in RFC 1755 and we refer to the 1755 for information on additional encapsulations.
discussion there.
2.5 Traffic Descriptors 2.5 Traffic Descriptors
The ATM traffic descriptor always contains specification of a peak The ATM traffic descriptor always contains a peak cell rate (PCR)
cell rate (PCR) (in each direction). For variable rate services it (for each direction). For variable rate services it also contains a
also contains specification of a sustainable cell rate (SCR) and sustainable cell rate (SCR) and maximum burst size (MBS). The SCR
maximum burst size (MBS). The SCR and MBS form a leaky bucket pair and MBS form a leaky bucket pair (rate, depth), while the bucket
(rate, depth), while the bucket depth parameter for PCR is CDVT. depth parameter for PCR is CDVT. Note that CDVT is not signaled
Note that CDVT is not signaled explicitly, but is determined by the explicitly, but is determined by the network operator, and serves as
network operator, and serves as a measure of the jitter imposed by a measure of the jitter imposed by the network.
the network.
Since CDVT is not signaled, and is presumed to be small, the leaky Since CDVT is generally presumed to be small (equivalent to a few
bucket traffic descriptor (TSpec) of the Internet service cannot cells of token bucket depth), and cannot be set independently for
always be directly mapped into PCR/CDVT parameters. Additional each connection, it cannot be used to account for the burstiness
buffering is needed at the IWF to account for the depth of the permitted by b of the IP-layer TSpec. Additional buffering is needed
bucket. at the IWF to account for the depth of the token bucket.
The Burst Tolerance is related to MBS (see TM 4.0 for details). The ATM Burst Tolerance (BT) is equivalent to MBS (see TM 4.0 [6] for
Roughly, they are both expressions of the bucket depth parameter that the exact equation). They are both expressions of the bucket depth
goes with SCR. The units of BT is time while the units of MBS is parameter that goes with SCR. The units of BT is time while the
cells. Since both SCR and MBS are signalled, they can be computed units of MBS is cells. Since both SCR and MBS are signalled, they
directly from the IP layer traffic description. The specific manner can be computed directly from the IP layer traffic description. The
in which resources are allocated from the traffic description is specific manner in which resources are allocated from the traffic
implementation specific. Note that when translating the traffic description is implementation specific. Note that when translating
parameters, the segmentation overhead and minimum policed unit need the traffic parameters, the segmentation overhead and minimum policed
to be taken into account (see Section 4.2 below). unit need to be taken into account (see Section 4.1 below).
In ATM UNI SIG 4.0 there are the notions of Alternative Traffic In ATM UNI Signalling 4.0 there are the notions of Alternative
Descriptors and Minimal Traffic Descriptors. Alternative Traffic Traffic Descriptors and Minimal Traffic Descriptors. Alternative
Descriptors enumerate other acceptable choices for traffic Traffic Descriptors enumerate other acceptable choices for traffic
descriptors and are not considered here. Minimal Traffic Descriptors descriptors and are not considered here. Minimal Traffic Descriptors
are used in ``negotiation,'' which refers to the specific way in are used in "negotiation," which refers to the specific way in which
which an ATM connection is set up. Very roughly it works like this, an ATM connection is set up. To illustrate, roughly, taking PCR as
taking PCR as an example: A minimal PCR and a requested PCR are an example: A minimal PCR and a requested PCR are signalled, the
signalled, the requested PCR being the usual item signalled, and the requested PCR being the usual item signalled, and the minimal PCR
minimal PCR being the absolute minimum that the source edge device being the absolute minimum that the source edge device will accept.
will accept. When sensing the existence of both minimal and When sensing the existence of both minimal and requested parameters,
requested parameters, the intermediate switches along the path may the intermediate switches along the path may reduce the requested PCR
reduce the requested PCR to a ``comfortable'' level. This choice is to a "comfortable" level. This choice is part of admission control,
part of admission control, and is therefore implementation dependent. and is therefore implementation dependent. If at any point the
If at any point the requested PCR falls below the minimal PCR then requested PCR falls below the minimal PCR then the call is cleared.
the call is cleared. Minimal Traffic Descriptors can be used to Minimal Traffic Descriptors can be used to present an acceptable
present an acceptable range for parameters and ensure a higher range for parameters and ensure a higher likelihood of call
likelihood of call admission. Whether anything more specific about admission. In general, our discussion of connection parameters
Minimal Traffic Descriptors needs to be said here is left for further
study (FFS). In general, our discussion of connection parameters
assumes the values resulting from successful connection setup. assumes the values resulting from successful connection setup.
The Best Effort indicator (used only with UBR) and Tagging indicators The Best Effort indicator (used only with UBR) and Tagging indicators
are also part of the signaled information element (IE) containing the are also part of the signaled information element (IE) containing the
traffic descriptor. In the UNI SIG 4.0 traffic descriptor IE there traffic descriptor. In the UNI 4.0 traffic descriptor IE there is an
is an additional parameter, the Frame Discard indicator (see Section additional parameter, the Frame Discard indicator, which is discussed
2.7). below in Section 2.7.
2.5.1 Translating Traffic Descriptors for Guaranteed Service 2.5.1 Translating Traffic Descriptors for Guaranteed Service
For Guaranteed Service there is a peak rate, p, a source Tspec rate, For Guaranteed Service the source TSpec contains peak rate, rate and
r_s, a receiver Tspec rate r_r, and an Rspec rate, R. The two Tspec and bucket depth parameters, p_s, r_s, b_s. The receiver TSpec
rates are intended to support receiver heterogeneity, in the sense contains corresponding parameters p_r, r_r, b_r. The (receiver)
that different receivers can accept different rates representing Rspec also has a rate, R. The two different TSpec rates are intended
subsets of the sender's traffic. In this document we leave this to support receiver heterogeneity, in the sense that receivers can
feature for further study (FFS), and assume the two Tspec rates are accept different rates representing different subsets of the sender's
always identical. The Tspec rate describes the traffic itself, and traffic. Whenever rates from different receivers differ, the values
is used for policing, while the Rspec rate (which cannot be smaller) will always be merged appropriately before being mapping into ATM
is the allocated service rate. A receiver increases R over r to parameters.
reduce the delay.
Note that when the sender and receiver TSpec rates r_s, r_r differ,
there is no mechanism specified (in either rsvp or the int-serv
specs) for indicating which subset of the traffic is to be
transported. Implementation of this feature is therefore completely
network specific. Hence the ambiguity in how policing and scheduling
use the two rates is an inherent and currently unresolved issue in
IP-IS technology.
The receiver TSpec rate describes the traffic for which resources are
to be reserved, and may be used for policing, while the Rspec rate
(which cannot be smaller) is the allocated service bandwidth (or
strictly speaking, a lower bound on this). A receiver increases R
over r_r to reduce the delay.
When mapping Guaranteed Service onto a rtVBR VC, the ATM traffic When mapping Guaranteed Service onto a rtVBR VC, the ATM traffic
descriptor parameters (PCR, SCR, MBS) can be set within the following descriptor parameters (PCR, SCR, MBS) can often be set cannonically
bounds: as:
R <= PCR <= min(p, line rate) PCR = p_r
r <= SCR <= PCR SCR = R
0 <= MBS <- b. MBS = b_r.
Note that a receiver can choose R > p to lower the delay. This There are a number of conditions that may lead to different choices.
leaves the first equation somewhat subject to interpretation. If a The following discussion is not intended so much to set hard
receiver chooses R > line rate, it seems clear that the admission requirements, but to provide some interpretation and guidance on the
control would simply reject the reservation. bounds of possible parameter mappings. The ingress edge device
generally includes a buffer preceeding the ATM network interface.
This buffer can be used to absorb bursts that fall within the IP-
level TSpec, but not within the ATM traffic descriptor. The minimal
requirement for guaranteed service is that the delay in this buffer
may not exceed b/R, and the delays within the ATM network must be
accurately accounted for in the values of Adspec parameters C and D
advertised by the ingress router (see Section 3.3 below).
The edge device has a buffer preceding the ATM network which must be In general, if either an edge device buffer of size b_r exists or the
sufficient to absorb bursts arriving faster than they can be admitted ATM maximum burst size (MBS) parameter is at least b_r, then the
into the ATM network. For example, parameters may be set as PCR = R, various rate parameters will generally exhibit the following
SCR = r, MBS = b. The edge device buffer of size b would absorb a relationship:
burst sent at any IP-level peak rate. Although this buffer exists,
the ATM network must accept bursts at rate PCR, at least R, to ensure
that the edge device delay is no greater than b/R. Since this buffer
is not in the ATM network, its delay is not included in D_ATM.
For GS over CBR, the service rate is mapped to the PCR parameter, r_r <= SCR <= R <= PCR <= APB <= line rate
using the same constraint for PCR given above. The edge device again
requires adequate buffering to accommodate the TSpec bucket depth and r_r <= p_r <= APB
ensure delay before entering the ATM network of no more than b/R. If
PCR is greater than R, the buffer requirement may be relaxed APB refers to the General Characterization Parameter,
accordingly. AVAILABLE_PATH_BANDWIDTH, which is negotiated in the Adspec portion
of the PATH message. APB reflects the narrowest bottleneck rate
along the path, and so is always bounded by the local line rate. The
receiver must choose a peak rate no greater than APB for the
reservation to be accepted, although the source peak rate, p_s, could
be higher, as the source does not know the value of APB. There is no
advantage to allocating any rate above APB of course, so it is an
upper bound for all the other parameters.
We might normally expect to find R <= p_r, as would be necessary for
the simple mapping of PCR = p_r, SCR = R given above. However, a
receiver is free to choose R > p_r to lower the GS delay [8]. In
this case, PCR cannot be set below R, because a burst of size b
arriving into the buffer must be cleared at rate R to keep the first
component of GS delay down to b/R. So here we will have PCR = R.
In the case R <= p_r, we may still choose R <= PCR < p_r. The edge
device buffer is then necessary (and sufficient) to absorb the bursts
(limited to size b_r) which arrive faster than they depart. For
example, it may be the case that the cost of the ATM VC depends on
PCR, while the cost of the Internet service reservation is not
strongly dependent on the IP-level peak rate. The user may the have
an incentive to set p_r to APB, while the operator of the IP/ATM edge
router has an incentive to reduce PCR as much as possible. This may
be a realistic concern, since the charging models of IP and ATM are
historically different as far as usage sensitivity, and the value of
p_r, if set close to APB, could be many times the nominal GS
allocated rate of R. Thus, we can set PCR to R, with a buffer of
size b, with no loss of traffic, and no violation of the GS delay
bound.
A more subtle, and perhaps controversial case is where we set SCR to
a value below R. The major feature of the GS service is to allow a
receiver to specify the allocated rate R to be larger than the rate
r_r sufficient to transport the traffic, in order to lower the
queueing delay (roughly) from b/r + C_TOT/r + D_TOT to b/R + C_TOT/R
+ D_TOT. To effectively allocate bandwidth R to the flow, we set SCR
to match R. (Note it is unnecessary in any case to set SCR above R,
so the relation, SCR <= R, is still true.) It is possible to set SCR
to a value as low as r_r, without violating the delay bounds or
overflowing the edge device buffer. With PCR = R, a burst of size b
will be buffered and sent into the ATM network at rate R, so the last
byte suffers delay only b/R. Any further traffic will be limited to
rate r_r, which is SCR, so with the arriving and departing rates
matched, its delay will also be no more than b/R.
While this scenerio meets the GS service requirements, the penalty
for allocating SCR = r_r rather than R is that the delay in the ATM
network will have a component of MBS/SCR, which will be b/r rather
than b/R, contained in the D term advertised for the ATM sub-network
(see further discussion in Section 3.3 below). It is also true that
allocating r instead of R in a portion of the path is rather against
the spirit of GS. As mentioned above, this mapping may however be
useful in practice in the case where pricing in the ATM network leads
to different incentives in the tradeoff between delay and bandwidth
than those of the user who buys IP integrated services.
Another point of view on parameter mapping suggests that SCR should
merely reflect the traffic description, hence SCR = r_r, while the
service requirement is expressed in the QoS parameter as CDV = b/R.
Thus the ATM network may internally allocate bandwidth R, but it is
free to use other methods as well to achieve the delay constraint.
Mechanisms such as statistical flow/connection aggregation may be
implemented in the ATM network and hidden from the user (or parameter
mapping module in the edge router) which sees only the interface
implemented in the signaled parameters.
Note that this discussion considers an edge device buffer size of
b_r. In practice, it may be necessary for the AAL/segmentation
module to buffer M bytes in converting packets to cells. Also an
additional amount of buffer equal to C_sum + R D_sum is generally
necessary to absorb jitter imposed by the upstream network [8].
With ATM, it is possible to have little or no buffer in the edge
router, because the ATM VC can be set to accept bursts at peak rate.
This may be unusual, since the edge router normally has enough buffer
to absorb bursts according to the TSpec token bucket parameters. We
consider two cases. First, if PCR >= p_r, then MBS can be set to b_r
and no buffering is necessary to absorb normal bursts. The extra
buffering needed to absorb jitter can also be transferred to MBS.
This effectively moves the buffering across the UNI into the ATM
network.
For completeness, we consider an edge router with no burst-absorbing
buffers and an MBS parameter of approximately zero. In this case it
is sufficient to set the rate parameters to PCR = SCR = max (R, p_r).
This amounts to peak-rate allocation of bandwidth, which will not
usually be very cost effective. One reason for mentioning this case
might be that IP routers and ATM switches differ so substantially in
their buffering designs that IP-level users typically specify much
larger burst parameters than can be handled in the ATM subnet.
Peak-rate bandwidth allocation provides a means to work around this
problem. It is also true that intermediate tradeoffs can be
formulated, where the burst-absorbing buffer is less than b bytes,
and SCR is set above R and below p_r. Note that jitter-absorbing
buffers (C_sum + R D_sum) can not be avoided, generally, by
increasing ATM rates, unless SCR is set to exceed the physical line
rate(s) into the edge device for the flow.
For GS over CBR, the value of PCR may be mapped to the Rspec rate R,
if the edge device has a buffer of size b_r. With little or no burst
buffering, the requirements resemble the zero-buffer case above, and
we have PCR = max (R, p_r). Additional buffers sufficient to absorb
network jitter, given by C_sum, D_sum, must always be provided in the
edge router, or in the ATM network via MBS.
2.5.2 Translating Traffic Descriptors for Controlled Load Service 2.5.2 Translating Traffic Descriptors for Controlled Load Service
Controlled Load service has a peak rate, p, a Tspec rate, r, and a The Controlled Load service TSpec has a peak rate, p, a "token
corresponding bucket depth parameter, b. The ATM traffic parameters bucket" rate, r, and a corresponding token bucket depth parameter, b.
for nrtVBR service category are constrained by The receiver TSpec values are used to determine resource allocation,
and a simple mapping for the nrtVBR service category is given by,
r <= SCR <= PCR <= min(p, line rate) PCR = p_r
0 <= MBS <- b. SCR = r_r
MBS = b_r.
For ABR VCs, the Tspec rate would be used to set the minimum cell The discussions in the preceeding section on using edge device
rate (MCR) parameter. The bucket depth parameter does not map buffers to reduce PCR, increasing buffers to reduce PCR and trading
directly to a signalled ATM parameter, so the edge device must have a off between such buffers and MBS, apply generally to the CLS over
buffer of at least b bytes. nrtVBR case as well. Extra buffers to accommodate jitter accumulated
(beyond the b_r burst size allowed at the source) must be provided.
For CLS, there are no Adspec parameters C and D, so the estimation of
such buffers is an implementation design issue.
For CBR, the Tspec rate sets a lower bound on PCR, and again, the For ABR VCs, the TSpec rate r_r is used to set the minimum cell rate
(MCR) parameter. Since there is no corresponding signalled bucket
depth parameter, the edge device must have a buffer of at least b_r
bytes. Since the actual transfer rate can vary substantially with
ABR, the buffering should not be made so large that the, in an
attempt to avoid loss, that delays exceed higher-layer timeouts,
e.g., TCP retransmission.
For CBR, the TSpec rate r_r sets a lower bound on PCR, and again, the
available buffering in the edge device must be adequate to available buffering in the edge device must be adequate to
accommodate possible bursts. accommodate possible bursts of b_r.
The requirement for CLS that network delays approximate "best-effort
service under unloaded conditions", is interpreted here to mean that
an allocation of (at least) r_r, resulting in the last byte of a
burst of size b_r having delay approximately b_r/r_r, is sufficient.
A network element e.g., with no cross-traffic, work conserving
scheduling and output link rate of r_L might provide delays in the
range from M/r_L to b_r/r_L, which may be much better.
2.5.3 Translating Traffic Descriptors for Best Effort Service 2.5.3 Translating Traffic Descriptors for Best Effort Service
For Best Effort service, there is no traffic description. The UBR For Best Effort service, there is no traffic description. The UBR
service category allows negotiation of PCR, simply to allow the service category allows negotiation of PCR, simply to allow the
source to discover the smallest physical bottleneck along the path. source to discover the smallest physical bottleneck along the path.
(The ingress edge router should set PCR to the ATM line rate, and may
wish to make use of the returned value when the VC is set up.) Often
a service provider will want to statically configure large VCs with a
certain bandwidth allocation to handle all best effort traffic
between two edge routers. ABR, CBR or nrtVBR VCs are appropriate for
this with traffic parameters set to comfortably accommodate the
expected traffic load. See [10,11].
2.6 QoS Classes and Parameters 2.6 QoS Classes and Parameters
In TM/UNI 4.0 the three QoS parameters may be individually signalled. In UNI 3.x the quality of service is indicated by a single parameter
These parameters are the Cell Loss Ratio (CLR), Cell Transfer Delay called "QoS Class," which is essentially an index to a network
(CTD), and Cell Delay Variation (CDV). In UNI 3.x the setup message specific table of values for the actual QoS parameters. In TM/UNI
includes only the QoS Class, which is essentially an index to a 4.0 three QoS parameters may be individually signalled, and the
network specific table of values for these three parameters. A signalled values override those implied by the QoS Class, which is
network provider may choose to associate other parameters, such as still present. These parameters are the Cell Loss Ratio (CLR), Cell
Severely Errored Cell Block Ratio, but these are less well understood Transfer Delay (CTD), and Cell Delay Variation (CDV) [6].
and accepted compared to the basic loss, delay and jitter parameters
mentioned here. The ITU has recently included a standard set of A network provider may choose to associate other parameters, such as
parameter values for a (small) number of QoS classes in the latest Severely Errored Cell Block Ratio, with a QoS Class definition, but
version of Recommendation I.356, October 1996. The network provider these cannot be signalled individually. The ATM Forum UNI 3.0, 3.1
may choose to define further network-specific QoS classes in addition and TM 4.0 specs, following prior ITU specs, give vague qualitative
to these. The problem of agreement between network providers as to definitions for QoS Classes 1 to 4. (QoS Class 0 is well-defined as
the definition of QoS classes is completely unaddressed to date. We "no QoS parameters defined".) Since our mapping is based on these
will adopt a convention expressed in UNI 3.x, that assumes that QoS specifications, we generally follow this guidance by setting QoS
class 1 is appropriate for low-delay, low-loss CBR connections, and Class value to 0 for UBR and ABR (as required), 1 for CBR and rtVBR
QoS class 3 is appropriate for variable rate connections with loss and 3 for nrtVBR. Note that the QoS Class follows the ATM service
and delay roughly appropriate for non-real-time data applications. category, and not the IP service, to avoid combination that are
unlikely to be supported. For example, if only nrtVBR is available
for GS, then choosing QoS Class = 1 would probably result in
connection failure, rather than a way to add real-time behavior to an
inherently non-real-time service.
The ITU has recently included a standard set of parameter values for
a (small) number of QoS Classes in the latest version of
Recommendation I.356, October 1996. Network providers may choose to
define further network-specific QoS Classes in addition to these.
Note that the QoS class definitions in the new I.356 version may not Note that the QoS class definitions in the new I.356 version may not
align with this model. align with the model we follow from the UNI specs. Apart from these
definitions, the problem of agreement between network providers as to
the definition of QoS Classes has not, to our knowledge, been
addressed.
Since no IP layer counterparts to these ATM QoS parameters exist in The ATM QoS parameters have no explicitly signalled IP layer
any of the IP services, they must be set by policy of the edge counterparts. The values that should be signalled in the ATM network
device. The QoS classes can be chosen relatively easily. QoS class are determined by knowledge of certain network characteristics and
1 should be used with Guaranteed Service and QoS class 3 should be the IP service definitions.
used with Controlled Load Service. Best Effort Service always gets
QoS class 0, which is unspecified QoS by definition. There are two
issues which amount to the same thing: First, the choice of
individually signalled parameter values (under TM/UNI 4.0) for GS and
CLS is the edge device policy. The second issue is choosing
parameter values for the two QoS classes, which is the ATM network
policy. If the same network operator controls both, then these
problems are identical; if not, an agreement to make the values
identical would be extremely desirable.
Note that we have mapped QoS class 1 and 3 onto Guaranteed and The ingress edge router must keep a table of QoS information for the
Controlled Load service respectively. This is regardless of what set of egress routers that it may establish VCs with. This table may
service category is used. So when running CLS over a CBR pipe, it be simplified by using default values, but it will probably be good
would not be inappropriate to use QoS class 3. This leaves the delay network practice to maintain a table of current data for the most
unspecified (or much looser than with QoS 1). These comments should popular egress points. An ATM network generally needs to have some
be taken as preliminary, as these issues are far from clear, and way to propose initial value for CDV and CTD, even if changed by
industry consensus should be sought. negotiation; so by positing such a table, we are not creating any new
design burden. Cached information can be updated when VCs are
successfully established, and to the extent that IP-layer
reservations can wait for VCs to complete, the values can be refined
through iterated negotiation. In general the construction of this
table is implementation specific.
Both GS and CLS require that losses of packets due to congestion
should be minimized, so that the loss rate is approximately the same
as for an unloaded network. The characteristic loss behavior of the
link-layer medium not due to congestion (e.g., bit errors or fading
on wireless channels) determines the order of the permitted packet
loss rate. The ingress edge device will choose a value of CLR that
provides the appropriate IP-level packet loss rate. The CLR value
may be uniform over all egress points in the ATM network, or may
differ, e.g., when wireless or satellite ATM links in the path. The
determination of CLR should account for the effects of packet size
distribution and ATM Frame Discard mode (which can change the
effective packet loss rate by orders of magnitude, given the same
underlying cell loss rate [20]).
The ingress router will also tabulate values for the Minimum Path
Latency (MPL) and estimated queueing delays (D_ATM) for each egress
point. The latter will be used as part of the Adspec "D" parameter
for GS, but its use here applies to CLS as well. MPL represents all
non-congestion related delays, including propagation delay. D_ATM
accounts for the variable component of delays in the ATM network.
(It may depend on parameters such as CDVT, etc.) Hence, when a VC is
set up, the delay-related QoS parameters are given by
CDV = D_ATM
CTD = D_ATM + MPL.
(CDV and CTD may be increased by the slack term in GS, see Section
3.3 below.) For rtVBR, the value of CDV will generally have a
component of MBS/SCR analogous to the b/R term in the delay of GS
service. It may have other components that depend on the ATM switch
implementation. In cases where the ATM network uses statistical
resouce allocation methods, it may be possible to establish VCs with
CDV less than MBS/SCR. This capability should be reflected in the
D_ATM values advertised in GS and used to determine CDV in for VCs
supporting both GS and CLS.
It is interesting (and perhaps unfortunate) to note that in a typical
GS/rtVBR service, the delay bound advertised can contain two
components of b/R instead of one. Consider the case where SCR = R
and MBS = b. Parekh's theory, which is the basis of the GS delay
formula [8] states that the b/R delay term occurs only once, because
once a burst of size b has been served by a congested node at rate R,
the packets will not arrive at a subsequent node as a single burst.
However, we can't tell if this bottleneck will occur in the ATM
network or elsewhere in the IP network, so the declaration of CDV
must account for it. Once CDV is set, the ATM network can impose
that delay. Since the delay b/R can also occur elsewhere, it cannot
be removed from the first term of the GS delay formula. The ATM b/R
delay component appears in the third term, D_tot. See Section 3.3
below for more on GS Adspec parameters. This effect may be
unapparent when the ATM network employs more efficient statistical
resource allocation schemes.
2.7 Additional Parameters -- Frame Discard Mode 2.7 Additional Parameters -- Frame Discard Mode
In TM/UNI 4.0 ATM allows the user to choose a mode where a dropped TM/UNI 4.0 allows the user to choose a mode where the ATM network is
cell causes all cells up to the last remaining in the AAL5 PDU to be aware, for the purpose of congestion management, of PDUs larger than
also dropped. This improves efficiency and the behavior of end-to- an ATM cell (i.e., AAL PDUs that correspond in our context to IP
packets). This facilitates implementation of algorithms such as
partial packet discard, where a dropped cell causes subsequent cells
in the AAL5 PDU to be dropped as well. Several other applicable
buffer management schemes have been proposed [20, 21].
Frame discard can improve efficiency and the performance of end-to-
end protocols such as TCP, since the remaining cells of a damaged PDU end protocols such as TCP, since the remaining cells of a damaged PDU
are useless to the receiver. For IP over ATM, Frame Discard should are generally useless to the receiver. For IP over ATM, Frame
always be used in both directions, if available, for all services. Discard should always be indicated, if available.
3.0 Discussion of IP-IS Protocol Features 3.0 Additional IP-Integrated Services Protocol Features
3.1 Handling of Excess Traffic 3.1 Path Characterization Parameters for IP Integrated Services with ATM
(Placeholder for text.) This section discusses the setting of General Characterization
Parameters (GCPs) at an ATM egress edge router. GCPs are signalled
from source to destination, and modified by intermediate nodes using
the Adspec portion of PATH messages in rsvp. The GS-specific Adspec
parameters are discussed below in Section 3.3. These parameters are
denoted as <x,y> where x is the service and y is the parameter
number. Service number 1 indicates default or general parameter
values. Please refer to [22] for definitions and details.
Reiterate that whole packets should be tagged, See Section The IS break bit <1,2> should, of course, be left alone by
2.2. implementations following these guidelines (as they are presumably
IS-aware). Similarly, the router should always increment IS_HOPS
<1,4>. The GS and CLS service-specific break bits, <2,2> and <5,2>
respectively, should be set if the support of the service is
inadequate. In general GS is adequately supported by CBR (BCOB-A)
and rtVBR service categories, and not adequately supported by UBR,
ABR and nrtVBR because delays are not controlled. CLS may be
adequately supported by all service categories except UBR (or Best
Effort in UNI 3.x). See Sections 5, 6 for further discussion.
3.2 Use of AdSpec in Guaranteed Service with ATM For GS, the ATM network must meet the delay performance advertised
through the Adspec parameters, MPL, C, and D. If it cannot
predictably meet these requirements, the GS break bit should be set.
Similarly both break bits should be set if reservations are honored,
but sufficient resources to avoid congestion loss are not allocated
in practice. If the service break bits are not set, then the
corresponding service hop counters, <2,4>, <5,4>, should be
incremented.
The AdSpec is a feature of Guaranteed Service which allows a receiver The Available Path Bandwidth (APB) parameters <x,6> indicate the
to calculate the worst-case delay associated with a GS flow. Three minimum physical bottleneck rate along the path. This may be
discoverable in an ATM network as the negotiated PCR value for a UBR
VC along the path. This value should be corrected for AAL, ATM and
physical-layer headers, as necessary, to reflect the effective IP
datagram bandwidth. With ATM, it is possible that there is some
policy limitation on the value of PCR, below the physical link
bottleneck. In this case, the advertised value of APB (in general
and for each service if different) should reflect this limit, since
excess traffic beyond this rate will be dropped. (Note that there is
no tagging of traffic in excess of PCR for TM/UNI 4.0.) These values
should generally be cached by the ingress router for the set of
egress routers that it typically needs to establish VCs to. The
Adspec parameters <x,6> are only adjusted down, to reflect the
minimum as the composed value.
In the case of a multipoint VC, the value of several parameters can
be different for each egress point. In this case, the IWF at the
egress routers must correct these values in PATH messages as they
exit the ATM network. This is the only case where the egress router
needs to operate on rsvp control messages. (A similar correction
must be implemented for any non-rsvp set-up mechanism). The
parameters that require such correction are specifically the
Available Path Bandwidth (APB), the Minimum Path Latency (MPL), the
Path MTU (although for ATM/AAL5 this may typically be constant), and
the ATM-specific components of the GS Adspec parameters C_ATM and
D_ATM.
The ingress router table must store values for the ATM-network MPL
<x,7> for the various egress points. The composed values <x,8> are
formed by addition and forwarded along the path. In the cases where
ATM routing chooses different paths for VCs to a given egress point,
depending on the service category, the table will generally reflect
different values for each service. If the ATM network is very large
and complex, it may become difficult to predict the routes that VCs
will take once they are set up. This could be a significant source
of misconfiguration, resulting in discrepencies between GS delay
advertisements and actual results. The RSpec Slack term may be
useful in mitigating this problem.
AAL 5 will support any message size up to 65,535 bytes, so setting
the AAL SDU to the receiver TSpec M parameter value should generally
not be a issue. In the PATH Adspec, however, the PATH_MTU parameter
<x,10> for each service should be set to 9180 bytes, which is the
default MTU for AAL 5.
3.2 Handling of Excess Traffic
CLS requires and GS recommends that network elements transport
traffic in excess of the TSpec parameters whenever physical resources
(bandwidth, buffers and processing) are available. While excess
traffic should be supported on a best effort basis, it should not
interfere with the QoS (delay and loss) of conforming CLS and GS
traffic, nor with normal service of non-reserved best effort traffic.
There are several solutions with ATM: the most attractive is to use a
VBR service category (with an appropriate conformance definition) and
tag excess traffic as low priority using the CLP bit. This avoids
reordering of the flow, but requires care in the design of the egress
router scheduler. To avoid reordering, the excess traffic would be
queued with confoming traffic. A threshold must be used to ensure
that conforming traffic is not unnecessarily delayed by the excess.
Also, for GS, the extra delay that would be incurred due to excess
traffic below the threshold would have to be accurately reflected in
the delay advertisement. Note that the egress router should
uniformly tag all the cells of each non-conforming packet, rather
than letting the ATM network apply tagging due to ATM-level non-
conformance.
There is no requirement in ATM standards that tagged cells, marked
either by the user or by policing, must be transported if possible.
Therefore, the operator of an edge router supporting IP-IS should
ascertain the actual behavior of the ATM equipment in the path, which
may span multiple administrative domains in the ATM network. If
tagged cells are simply dropped at some point, regardless of load,
then the operator may consider setting the break bit, at least for
CLS service.
The other solutions generally involve a separate VC to carry the
excess. A distinct VC can be set up for each VC supporting a GS or
CLS flow, or, if many flows are aggregated into a single QoS VC, then
another VC can handle the excess traffic for that set of flows. A VC
can be set up to handle all excess traffic from the ingress router to
the egress point. Since the QoS of the excess traffic is not
particularly constrained, the design is quite flexible. The service
category for the excess-traffic VC may typically be UBR or ABR,
although one could use CBR or nrtVBR if the excess traffic were
predictable enough to know what rate to allocate. (This wouldn't
normally be expected for excess traffic, though.)
Whether a separate VC is used may be influenced by the design of the
router scheduler. The CLS spec suggests two possible
implementations: one where excess traffic shares the Best Effort
class scheduler allocation, but at lower priority than other best
effort traffic. The other where a separate allocation is made. The
first would allow excess traffic to use the same VC as normal best
effort traffic, and the second would suggest a separate VC.
TM/UNI 4.0. does not support tagging of traffic in excess of PCR.
Although UNI 3.x does have a separate PCR parameter for CLP=0 cells
only, we do not recommend using this feature for reasons of
interoperability. This restricts CBR VCs to use solutions other than
tagging. The value of PCR can be set higher than necessary for
conformant traffic, in an effort to support excess traffic on the
same VC. In some cases this may be a viable solution, such as when
there is little additional cost imposed for a high PCR. If PCR can
be set as high as APB, then the excess traffic is fully accommodated.
3.3 Use of Guaranteed Service Adspec Parameters and Slack Term
The Adspec is used by the Guaranteed Service to allow a receiver to
calculate the worst-case delay associated with a GS flow. Three
quantities, C, D, and MPL, are accumulated (by simple addition of quantities, C, D, and MPL, are accumulated (by simple addition of
components, one for each network element) in the PATH message from components corresponding to each network element) in the PATH message
source to receiver. The resulting values can be different for each from source to receiver. The resulting delay values can be different
unique receiver. The maximum delay is then found by for each unique receiver. The maximum delay is then computed as
delay <= b/R + C/R + D + MPL delay <= b_r/R + C_TOT/R + D_TOT + MPL
The Maximum Path Latency (MPL) includes propagation delay and any The Minimum Path Latency (MPL) includes propagation delay, while
other unavoidable system delays. (We neglect the effect of maximum b_r/R accounts for bursts and C and D include other queueing,
packet size and peak rate here; see the GS specification [8] for the scheduling and serialization delays. (We neglect the effect of
more detailed equation.) The service rate requested by the receiver, maximum packet size and peak rate here; see the GS specification [8]
R, can be greater than the sender's Tspec rate, r. The effect of the for a more detailed equation.) The service rate requested by the
larger R is to allocate more bandwidth and, through this equation, receiver, R, can be greater than the TSpec rate, r_r, resulting in
lower the packet delay. The burst size, b, is the leaky bucket lower delay. The burst size, b_r, is the leaky bucket parameter from
parameter from the Tspec, and is not changed by the receiver in the the receiver TSpec.
Rspec.
The values of C and D which a router advertise will depend on both The values of C and D that a router advertises depend on both the
the particular packet scheduling algorithm used in the router, and router packet scheduler, and the characteristics of the subnet
the characteristics of the subnet attached to the router. We assume attached to the router. Each router (or the source host) takes
here that each router (or the source host) takes responsibility for responsibility for its downstream subnet in its advertisement. For
its downstream subnet only. If the subnet is a simple point-to-point example, if the subnet is a simple point-to-point link, the subnet-
link, then the subnet-specific parts of C and D will account for the specific parts of C and D need to account for the link transmission
link transmission rate and MTU. An ATM subnet is more complex. rate and MTU. An ATM subnet is generally more complex.
The edge router will always have an internal packet scheduler, which For this discussion, we consider only the ATM subnet-specific
will contribute to C and D. For this discussion we consider only the components, denoted C_ATM and D_ATM. The ATM network can be
ATM subnet-specific components. We further assume that the ATM represented as a "pure delay" element, where the variable queueing
network will be represented as a "pure delay" element, contributing a delay, given by CVD is captured in D_ATM, and C_ATM = 0. It is
component to D, but not to C. The reason for this is that C would possible to use C_ATM only when the ATM service rate equals R. This
depend on details of the cell scheduling algorithm inside the ATM may be the case, for example with a CBR VC with PCR = R. Usually it
switches, which is not known by the edge device, where the AdSpec will be simpler to just advertise the total delay variation (CDV) in
parameters are accumulated. (In the special case where the edge D_ATM.
device does have enough information to modify C, it would not be
precluded.) Generally the delay behavior of the whole ATM cloud may
be expressed abstractly as a fixed constant D_ATM.
Since the AdSpec values are incremented before any reservation is As discussed in Section 2.6, the edge router keeps a table with
made, the edge device must have some knowledge about the VC which values of MPL and D_ATM for each egress router it needs to share VCs
would be set up in case a reservation were made. This does not with. The values of D_ATM contribute to the D parameter advertised
really add to the complexity of the device, since it must also have by the edge router, and should accurately reflect the CDV that the
this information in order to make an intelligent VC setup request. router will get in a VC when it is set up. Factors that affect CDV,
For example, the edge device may have a cached table with the such as statistical multiplexing in the ATM network, should be taken
propagation delay and a reasonable additional delay budget, from into account when compiling data for the router's table. In case of
which it composes a value of CTD for the VC setup. The device may uncertainty, D_ATM can be set to an upper bound.
learn such information through VC setup negotiation, and, indeed,
there may be no other way to obtain that information. However, it
seems reasonable that these values would be cached for later use when
new VCs to the same egress router need to be established.
Therefore, we will presume a table with values of MPL (which includes
propagation delay) and expected queueing delays for each possible
egress edge device. (How such a table is maintained is
implementation specific.) The latter quantity is simply D_ATM, the
value added to the AdSpec D term to account for the ATM network.
When a RESV message arrives, causing a VC to be set up, the requested When a RESV message arrives, causing a VC to be set up, the requested
value for CTD should then be given by values for CTD and CDV can be relaxed using the slack term in the
receiver RSpec:
CTD = D_ATM + MPL + S_ATM. CTD = D_ATM + MPL + S_ATM
CDV = D_ATM + S_ATM.
The last term, S_ATM is the portion of the slack term applied to the The term S_ATM is the portion of the slack term applied to the ATM
ATM portion of the path. Recall that the slack term [8] is positive portion of the path. Recall that the slack term [8] is positive when
when the receiver can afford more delay than that computed from the the receiver can afford more delay than that computed from the
AdSpec. The ATM edge device may take part (or all) of the slack term Adspec. The ATM edge device may take part (or all) of the slack term
to relax the delay constraint on the ATM VC. The distribution of S. The distribution of delay slack among the nodes and subnets is
delay slack among the nodes and subnets is network specific. network specific.
An important detail to note is the relationship between the b/R term Note that with multipoint VCs the egress edge router may need to
of the (Internet) delay and the corresponding MBS/SCR in the ATM correct advertised values of C and D. See discussion in Section 3.1.
network, when using a VBR VC. The term b/R accounts for the delay
experienced by the last byte of a burst, of size b, which encounters
a congested node. In the simple ideal case, where the scheduling
algorithm emulates a fixed rate server, at rate R, the delay of the
last byte is b/R. Once this occurs, the stream has been smoothed,
and such a delay will not occur at later congested nodes, as long as
they also serve at rate R. The form of the delay equation expresses
this ideal behavior with C and D acting as error terms. Now, since
the delay which smooths the burst can occur outside of the ATM cloud,
the b/R term cannot include any delay within the ATM cloud. However,
a burst of size MBS is permitted to enter the ATM network, and it may
be served at a rate no greater than SCR. We might reasonably expect
a queueing delay of MBS/SCR to occur at a congested ATM switch. If
the ATM network will impose this delay, then it must be included in
the value of D_ATM advertised. If the ATM network can increase its
bandwidth allocation (e.g., due to CTD being lower than MBS/SCR), to
decrease this delay, then this behavior should be reflected in the
value of D_ATM. So, the information from which the edge device
determines D_ATM must reflect an accurate abstraction of the actual
behavior of the ATM network. To the extent that D_ATM is approximate
(and it must be an upper bound on the actual delay), it reduces the
chance that the VC setup will succeed, and/or increases its cost.
4.0 Discussion of Miscellaneous Items 4.0 Miscellaneous Items
4.1 Units Conversion 4.1 Units Conversion
In the integrated services domain, bucket sizes and rates are All rates and token bucket depth parameters that are mapped from IP-
measured in bytes and bytes/sec, respectively, whereas for ATM, they level parameters to ATM parameters must be corrected for the effects
are measured in cells and cells/sec. of cell headers, AAL headers and segmentation of packets into cells.
At the IP layer, bucket depths and rates are measured in bytes and
bytes/sec, respectively, whereas for ATM, they are measured in cells
and cells/sec.
Packets are segmented into 53 byte cells of which the first 5 bytes Packets are segmented into 53 byte cells of which the first 5 bytes
are header information. For are header information. For
B = number of Bytes, B = number of Bytes,
C = number of cells, C = number of cells,
a rough approximation between the token bucket parameters (rate and a rough approximation between the token bucket parameters (rate and
bucket depth) is bucket depth) is
skipping to change at page 21, line 39 skipping to change at page 28, line 33
5.0 Summary of ATM VC Setup Parameters for Guaranteed Service 5.0 Summary of ATM VC Setup Parameters for Guaranteed Service
This section describes how to create ATM VCs appropriately matched This section describes how to create ATM VCs appropriately matched
for Guaranteed Service. The key points differentiating among ATM for Guaranteed Service. The key points differentiating among ATM
choices are that real-time timing is required, that the data flow may choices are that real-time timing is required, that the data flow may
have a variable rate, and that demotion of non-conforming traffic to have a variable rate, and that demotion of non-conforming traffic to
best effort is required to be in agreement with the definition of GS. best effort is required to be in agreement with the definition of GS.
For this reason, we prefer an rtVBR service in which tagging is For this reason, we prefer an rtVBR service in which tagging is
supported. Another good match is to use CBR with special handling of supported. Another good match is to use CBR with special handling of
any non-conforming traffic. any non-conforming traffic, usually through another VC, since a CBR
VC will not accommodate traffic in excess of PCR.
Note, in all cases the encodings assume point to multipoint Note, these encodings assume point to multipoint connections, where
connections, where the backward channel is not used. This is done to the backward channel is not used. If the IP session is unicast only,
be consistent with rsvp, which generally assumes a multicast then a point-to-point VC may be used and the IWF may make use of the
scenerio. If a specific situation does not involve multicast, then backward channel, provided that the QoS parameters are mapped
the IWF may make use of the backward channel in a point-to-point VC, consistently for the service provided.
provided that the QoS parameters are mapped consistently for the
service provided.
5.1 Encoding GS Using Real-Time VBR (ATM Forum TM/UNI 4.0) 5.1 Encoding GS Using Real-Time VBR (ATM Forum TM/UNI 4.0)
AAL AAL
Type 5 Type 5
Forward CPCS-SDU Size parameter M of TSpec Forward CPCS-SDU Size parameter M of receiver TSpec
Backward CPCS-SDU Size 0 Backward CPCS-SDU Size 0
SSCS Type 0 (Null SSCS) SSCS Type 0 (Null SSCS)
Traffic Descriptor Traffic Descriptor
Forward PCR CLP=0+1 Note 1 Forward PCR CLP=0+1 Note 1
Backward PCR CLP=0+1 0 Backward PCR CLP=0+1 0
Forward SCR CLP=0 Note 1 Forward SCR CLP=0 Note 1
Backward SCR CLP=0 0 Backward SCR CLP=0 0
Forward MBS (CLP=0) Note 1 Forward MBS (CLP=0) Note 1
Backward MBS (CLP=0) 0 Backward MBS (CLP=0) 0
BE indicator NOT included BE indicator NOT included
Forward Frame Discard bit 1 Forward Frame Discard bit 1
Backward Frame Discard bit 1 Backward Frame Discard bit 1
skipping to change at page 23, line 10 skipping to change at page 29, line 49
Note 1: See discussion Section 2.5.1. Note 1: See discussion Section 2.5.1.
Note 2: Value 3 (BCOB-C) can also be used. Note 2: Value 3 (BCOB-C) can also be used.
Note 3: The ATC value 19 is not used. The value 19 implies CLR Note 3: The ATC value 19 is not used. The value 19 implies CLR
objective applies to the aggregate CLP=0+1 stream and objective applies to the aggregate CLP=0+1 stream and
that does not give desirable treatment of excess that does not give desirable treatment of excess
traffic in the case of IP. traffic in the case of IP.
Note 4: For QoS VCs supporting GS or CLS, the layer 3 protocol should Note 4: For QoS VCs supporting GS or CLS, the layer 3 protocol should
be specified. For BE VCs, it can be left unspecified, allowing be specified. For BE VCs, it can be left unspecified, allowing
the VC to be shared by multiple protocols, following RFC 1755. the VC to be shared by multiple protocols, following RFC 1755.
Note 5: Cf ITU I.365 (Oct 1996) for new definition. Note 5: Cf ITU I.365 (Oct 1996) for new QoS Class definitions.
Note 6: See section 2.6 for the values to be used The cumulative CDV Note 6: See Section 2.6 for the values to be used.
is also provided, but it depends on local implementation, and
not on values mapped from IP level service parameters.
5.2 Encoding GS Using CBR (ATM Forum TM/UNI 4.0) 5.2 Encoding GS Using CBR (ATM Forum TM/UNI 4.0)
It is also possible to support GS using a CBR ``pipe.'' The It is also possible to support GS using a CBR "pipe." The advantage
advantage of this is that CBR is probably supported; the disadvantage of this is that CBR is probably supported; the disadvantage is that
is that data flows may not fill the pipe (utilization loss) and there data flows may not fill the pipe (utilization loss) and there is no
is no tagging option available. tagging option available.
AAL AAL
Type 5 Type 5
Forward CPCS-SDU Size parameter M of TSpec Forward CPCS-SDU Size parameter M of receiver TSpec
Backward CPCS-SDU Size parameter M of TSpec Backward CPCS-SDU Size parameter M of receiver TSpec
SSCS Type 0 (Null SSCS) SSCS Type 0 (Null SSCS)
Traffic Descriptor Traffic Descriptor
Forward PCR 0 Note 1 Forward PCR CLP=0+1 Note 1
Backward PCR 0 Backward PCR CLP=0+1 0
Forward PCR 0+1 Note 1
Backward PCR 0+1 0
BE indicator NOT included BE indicator NOT included
Forward Frame Discard bit 1 Forward Frame Discard bit 1
Backward Frame Discard bit 1 Backward Frame Discard bit 1
Tagging Forward bit 1 (Tagging requested) Tagging Forward bit 0 (Tagging not requested)
Tagging Backward bit 1 (Tagging requested) Tagging Backward bit 0 (Tagging not requested)
Broadband Bearer Capability Broadband Bearer Capability
Bearer Class 16 (BCOB-X) Note 2 Bearer Class 16 (BCOB-X) Note 2
ATM Transfer Capability 5 (CBR) Note 3, 4 ATM Transfer Capability 5 (CBR) Note 3, 4
Susceptible to Clipping 00 (bit encoding for Not Susceptible to Clipping 00 (bit encoding for Not
susceptible) susceptible)
User Plane Configuration 01 (bit encoding for pt-to-mpt) User Plane Configuration 01 (bit encoding for pt-to-mpt)
Broadband Low Layer Information Broadband Low Layer Information
User Information Layer 2 User Information Layer 2
skipping to change at page 24, line 29 skipping to change at page 31, line 16
Note 1: See discussion Section 2.5.1. Note 1: See discussion Section 2.5.1.
Note 2: Value 1 (BCOB-A) can also be used. Note 2: Value 1 (BCOB-A) can also be used.
Note 3: If bearer class A is chosen the ATC field must be absent. Note 3: If bearer class A is chosen the ATC field must be absent.
Note 4: The ATC value 7 is not used. The value 7 implies CLR Note 4: The ATC value 7 is not used. The value 7 implies CLR
objective applies to the aggregate CLP=0+1 stream and objective applies to the aggregate CLP=0+1 stream and
that does not give desirable treatment of excess that does not give desirable treatment of excess
traffic in the case of IP. traffic in the case of IP.
Note 5: For QoS VCs supporting GS or CLS, the layer 3 protocol should Note 5: For QoS VCs supporting GS or CLS, the layer 3 protocol should
be specified. For BE VCs, it can be left unspecified, allowing be specified. For BE VCs, it can be left unspecified, allowing
the VC to be shared by multiple protocols, following RFC 1755. the VC to be shared by multiple protocols, following RFC 1755.
Note 6: Cf ITU I.365 (Oct 1996) for new definition. Note 6: Cf ITU I.365 (Oct 1996) for new QoS Class definitions.
Note 7: See section 2.6 for the values to be used The cumulative CDV Note 7: See Section 2.6 for the values to be used.
is also provided, but it depends on local implementation, and
not on values mapped from IP level service parameters.
5.3 Encoding GS Using Non-Real-Time VBR (ATM Forum TM/UNI 4.0) 5.3 Encoding GS Using Non-Real-Time VBR (ATM Forum TM/UNI 4.0)
The remaining ATM service categories, including nrtVBR, do not The remaining ATM service categories, including nrtVBR, do not
provide delay guarantees and cannot be recommended as the best fits. provide delay guarantees and cannot be recommended as the best fits.
However in some circumstances, the best fits may not be available. However in some circumstances, the best fits may not be available.
If nrtVBR is used, no hard delay can be given. However by using a If nrtVBR is used, no hard delay can be given. However by using a
variable rate service with low utilization, delay may be variable rate service with low utilization, delay may be
`reasonable', but not controlled. The encoding of GS as nrtVBR is `reasonable', but not controlled. The encoding of GS as nrtVBR is
the same as that for CLS using nrtVBR, except that the Forward PCR the same as that for CLS using nrtVBR, except that the Forward PCR
would be derived from the Tspec peak rate. See Section 6.2 below. would be derived from the TSpec peak rate. See Section 6.2 below.
5.4 Encoding GS Using ABR (ATM Forum TM/UNI 4.0) 5.4 Encoding GS Using ABR (ATM Forum TM/UNI 4.0)
This is a very unlikely combination. The objective of the ABR GS using ABR is a very unlikely combination. The objective of the
service is to provide `low' loss rates which, via flow control, can ABR service is to provide "low" loss rates. The delay objectives for
result in delays. The introduction of delays is contrary to the ABR should be expected to be very loose. If ABR were used for GS,
design objectives of GS. If ABR were used for GS, the VC parameters the VC parameters would follow as for CLS over ABR. See Section 6.1.
would follow as for CLS over ABR. See Section 6.1.
5.5 Encoding GS Using UBR (ATM Forum TM/UNI 4.0) 5.5 Encoding GS Using UBR (ATM Forum TM/UNI 4.0)
The UBR service is the default lowest common denominator of the The UBR service is the default lowest common denominator of the
services. It cannot provide delay or loss guarantees. However if it services. It cannot provide delay or loss guarantees. However if it
is used for GS, it will be encoded in the same way as Best Effort is used for GS, it will be encoded in the same way as Best Effort
over UBR, with the exception that the PCR would be determined from over UBR, with the exception that the PCR would be determined from
the peak rate of the Tspec. See Section 5.1. the peak rate of the receiver TSpec. See Section 7.1.
5.6 Encoding GS Using ATM Forum UNI 3.0/3.1 Specifications 5.6 Encoding GS Using ATM Forum UNI 3.0/3.1 Specifications
It is not recommended to support GS using VBR for the following It is not recommended to support GS using UNI 3.x VBR mode for the
reasons. The Class C bearer class does not represent real-time following reasons. The Class C bearer class does not represent
behavior. Appendix F of UNI 3.1 specification precludes the real-time behavior. Appendix F of UNI 3.1 specification precludes
specification of traffic type "VBR" with the timing requirement "End the specification of traffic type "VBR" with the timing requirement
to End timing Required" in conjunction with bearer class X. "End to End timing Required" in conjunction with bearer class X.
It is possible to support GS using a CBR ``pipe.'' The following It is possible to support GS using a CBR "pipe." The following
table specifies the support of GS using CBR. table specifies the support of GS using CBR.
AAL AAL
Type 5 Type 5
Forward CPCS-SDU Size parameter M of TSpec Forward CPCS-SDU Size parameter M of receiver TSpec
Backward CPCS-SDU Size parameter M of TSpec Backward CPCS-SDU Size parameter M of receiver TSpec
Mode 1 (Message mode) Note 1 Mode 1 (Message mode) Note 1
SSCS Type 0 (Null SSCS) SSCS Type 0 (Null SSCS)
Traffic Descriptor Traffic Descriptor
Forward PCR 0 Note 2 Forward PCR CLP=0 Note 2
Backward PCR 0 Backward PCR CLP=0 0
Forward PCR 0+1 Note 2 Forward PCR CLP=0+1 Note 2
Backward PCR 0+1 0 Backward PCR CLP=0+1 0
BE indicator NOT included BE indicator NOT included
Tagging Forward bit 1 (Tagging requested) Tagging Forward bit 1 (Tagging requested)
Tagging Backward bit 1 (Tagging requested) Tagging Backward bit 1 (Tagging requested)
Broadband Bearer Capability Broadband Bearer Capability
Bearer Class 16 (BCOB-X) Note 3 Bearer Class 16 (BCOB-X) Note 3
Traffic Type 001 (bit encoding for Constant Bit Traffic Type 001 (bit encoding for Constant Bit
Rate) Rate)
Timing Requirements 01 (bit encoding for Timing Timing Requirements 01 (bit encoding for Timing
Required) Required)
skipping to change at page 26, line 36 skipping to change at page 33, line 19
ISO/IEC TR 9577 IPI 204 ISO/IEC TR 9577 IPI 204
QoS Class QoS Class
QoS Class Forward 1 QoS Class Forward 1
QoS Class Backward 1 QoS Class Backward 1
QoS Parameters QoS Parameters
Parameters are implied by the QOS Class Parameters are implied by the QOS Class
Note 1: Only included for UNI 3.0. Note 1: Only included for UNI 3.0.
Note 2: See discussion, Section 2.5.1. Note 2: See discussion, Section 2.5.1. PCR CLP=0 should be set identical
to PCR CLP=0+1. Although this culd potentially allow a CBR VC
to carry excess traffic as tagged cells, it is not recommended
since it is not supported in UNI 4.0
Note 3: Value 1 (BCOB-A) can also be used. If BCOB-A is used Traffic Note 3: Value 1 (BCOB-A) can also be used. If BCOB-A is used Traffic
Type and Timing Requirements fields are not included. Type and Timing Requirements fields are not included.
Note 4: For QoS VCs supporting GS or CLS, the layer 3 protocol should Note 4: For QoS VCs supporting GS or CLS, the layer 3 protocol should
be specified. For BE VCs, it can be left unspecified, allowing be specified. For BE VCs, it can be left unspecified, allowing
the VC to be shared by multiple protocols, following RFC 1755. the VC to be shared by multiple protocols, following RFC 1755.
6.0 Summary of ATM VC Setup Parameters for Controlled Load Service 6.0 Summary of ATM VC Setup Parameters for Controlled Load Service
This section describes how to create ATM VCs appropriately matched This section describes how to create ATM VCs appropriately matched
for Controlled Load. CLS traffic is partly delay tolerant and of for Controlled Load. CLS traffic is partly delay tolerant and of
variable rate. NrtVBR and ABR (for TM/UNI 4.0 only) are the possible variable rate. NrtVBR and ABR (for TM/UNI 4.0 only) are the best
choices in supporting CLS. choices in supporting CLS.
Generally we prefer to use point-to-multipoint connections. However Note, these encodings assume point to multipoint connections, where
this is not yet available in ABR. Other than in ABR, the encodings the backward channel is not used. If the IP session is unicast only,
assume a point-to-multipoint connection. For a unicast connection, then a point-to-point VC may be used and the IWF may make use of the
the backward parameters would be equal to the forward parameters. backward channel, provided that the QoS parameters are mapped
consistently for the service provided.
6.1 Encoding CLS Using ABR (ATM Forum TM/UNI 4.0) 6.1 Encoding CLS Using ABR (ATM Forum TM/UNI 4.0)
AAL AAL
Type 5 Type 5
Forward CPCS-SDU Size parameter M of TSpec Forward CPCS-SDU Size parameter M of receiver TSpec
Backward CPCS-SDU Size parameter M of TSpec Backward CPCS-SDU Size parameter M of receiver TSpec
SSCS Type 0 (Null SSCS) SSCS Type 0 (Null SSCS)
Traffic Descriptor Traffic Descriptor
Forward PCR CLP=0+1 From line rate Forward PCR CLP=0+1 Note 1
Backward PCR CLP=0+1 From line rate Backward PCR CLP=0+1 0
Forward MCR CLP 0+1 From TSpec token bucket rate Forward MCR CLP=0+1 Note 1
Backward MCR CLP 0+1 From TSpec token bucket rate Backward MCR CLP=0+1 0
BE indicator NOT included BE indicator NOT included
Forward Frame Discard bit 1 Forward Frame Discard bit 1
Backward Frame Discard bit 1 Backward Frame Discard bit 1
Tagging Forward bit 0 (Tagging not requested) Tagging Forward bit 0 (Tagging not requested)
Tagging Backward bit 0 (Tagging not requested) Tagging Backward bit 0 (Tagging not requested)
Broadband Bearer Capability Broadband Bearer Capability
Bearer Class 16 (BCOB-X) Note 1 Bearer Class 16 (BCOB-X) Note 2
ATM Transfer Capability 12 (ABR) ATM Transfer Capability 12 (ABR)
Traffic Type 010 (Variable Bit Rate) Traffic Type 010 (Variable Bit Rate)
Timing Requirements 10 (Timing Not Required) Timing Requirements 10 (Timing Not Required)
Susceptible to Clipping 00 (Not susceptible) Susceptible to Clipping 00 (Not susceptible)
User Plane Configuration 00 (For pt-to-pt) User Plane Configuration 00 (For pt-to-pt)
Broadband Low Layer Information Broadband Low Layer Information
User Information Layer 2 User Information Layer 2
Protocol 12 (ISO 8802/2) Protocol 12 (ISO 8802/2)
User Information Layer 3 User Information Layer 3
Protocol 11 (ISO/IEC TR 9577) Note 2 Protocol 11 (ISO/IEC TR 9577) Note 3
ISO/IEC TR 9577 IPI 204 ISO/IEC TR 9577 IPI 204
QoS Class QoS Class
QoS Class Forward 3 Note 3 QoS Class Forward 0 Note 4
QoS Class Backward 3 Note 3 QoS Class Backward 0 Note 4
QoS Parameters Note 4
QoS Parameters Note 5
Acceptable Forward CDV Acceptable Forward CDV
Acceptable Forward CLR Acceptable Forward CLR
Forward Max CTD Forward Max CTD
ABR Setup Parameters Note 5 ABR ABR Setup Parameters Note 6
Additional Parameters Note 5 ABR Additional Parameters Note 6
Note 1: Value 3 (BCOB-C) can also be used. Note 1: See discussion, Section 2.5.2.
Note 2: For QoS VCs supporting GS or CLS, the layer 3 protocol should Note 2: Value 3 (BCOB-C) can also be used.
Note 3: For QoS VCs supporting GS or CLS, the layer 3 protocol should
be specified. For BE VCs, it can be left unspecified, allowing be specified. For BE VCs, it can be left unspecified, allowing
the VC to be shared by multiple protocols, following RFC 1755. the VC to be shared by multiple protocols, following RFC 1755.
Note 3: Cf ITU I.365 (Oct 1996) for new definition. Note 4: Cf ITU I.365 (Oct 1996) for new QoS Class definitions.
Note 4: See section 2.6 for the values to be used. The cumulative CDV Note 5: See Section 2.6 for the values to be used.
is also provided, but it depends on local implementation, and Note 6: Discussion of ABR-specific parameters is beyond the scope of
not on values mapped from IP level service parameters. this document. These generally depend on local implementation and
Note 5: Discussion of these parameters is beyond the scope of this draft. not on values mapped from IP level service parameters (with the
exception of MCR).
6.2 Encoding CLS Using Non-Real-Time VBR (ATM Forum TM/UNI 4.0) 6.2 Encoding CLS Using Non-Real-Time VBR (ATM Forum TM/UNI 4.0)
AAL AAL
Type 5 Type 5
Forward CPCS-SDU Size parameter M of TSpec Forward CPCS-SDU Size parameter M of receiver TSpec
Backward CPCS-SDU Size 0 Backward CPCS-SDU Size parameter M of receiver TSpec
SSCS Type 0 (Null SSCS) SSCS Type 0 (Null SSCS)
Traffic Descriptor Traffic Descriptor
Forward PCR CLP=0+1 From line rate Forward PCR CLP=0+1 Note 1
Backward PCR CLP=0+1 0 Backward PCR CLP=0+1 0
Forward SCR CLP=0 From TSpec token bucket rate Forward SCR CLP=0 Note 1
Backward SCR CLP=0 0 Backward SCR CLP=0 0
Forward MBS (CLP=0) From TSpec bucket size param Forward MBS (CLP=0) Note 1
Backward MBS (CLP=0) 0 Backward MBS (CLP=0) 0
BE indicator NOT included BE indicator NOT included
Forward Frame Discard bit 1 Forward Frame Discard bit 1
Backward Frame Discard bit 1 Backward Frame Discard bit 1
Tagging Forward bit 1 (Tagging requested) Tagging Forward bit 1 (Tagging requested)
Tagging Backward bit 1 (Tagging requested) Tagging Backward bit 1 (Tagging requested)
Broadband Bearer Capability Broadband Bearer Capability
Bearer Class 16 (BCOB-X) Note 1 Bearer Class 16 (BCOB-X) Note 2
ATM Transfer Capability 10 (Non-real time VBR) Note 2, 3 ATM Transfer Capability 10 (Non-real time VBR) Note 3, 4
Susceptible to Clipping 00 (bit encoding Not susceptible) Susceptible to Clipping 00 (bit encoding Not susceptible)
User Plane Configuration 01 (bit encoding pt-to-mpt) User Plane Configuration 01 (bit encoding pt-to-mpt)
Broadband Low Layer Information Broadband Low Layer Information
User Information Layer 2 User Information Layer 2
Protocol 12 (ISO 8802/2) Protocol 12 (ISO 8802/2)
User Information Layer 3 User Information Layer 3
Protocol 11 (ISO/IEC TR 9577) Note 4 Protocol 11 (ISO/IEC TR 9577) Note 5
ISO/IEC TR 9577 IPI 204 ISO/IEC TR 9577 IPI 204
QoS Class QoS Class
QoS Class Forward 3 Note 5 QoS Class Forward 3 Note 6
QoS Class Backward 3 Note 5 QoS Class Backward 3 Note 6
QoS Parameters Note 6 QoS Parameters Note 7
Acceptable Forward CDV Acceptable Forward CDV
Acceptable Forward CLR Acceptable Forward CLR
Forward Max CTD Forward Max CTD
Note 1: Value 3 (BCOB-C) can also be used. Note 1: See discussion, Section 2.5.2.
Note 2: If bearer class C is used, the ATC field must be absent Note 2: Value 3 (BCOB-C) can also be used.
Note 3: The ATC value 11 is not used. The value 11 implies CLR Note 3: If bearer class C is used, the ATC field must be absent
Note 4: The ATC value 11 is not used. The value 11 implies CLR
objective applies to the aggregate CLP=0+1 stream and objective applies to the aggregate CLP=0+1 stream and
that does not give desirable treatment of excess that does not give desirable treatment of excess
traffic in the case of IP. traffic in the case of IP.
Note 4: For QoS VCs supporting GS or CLS, the layer 3 protocol should Note 5: For QoS VCs supporting GS or CLS, the layer 3 protocol should
be specified. For BE VCs, it can be left unspecified, allowing be specified. For BE VCs, it can be left unspecified, allowing
the VC to be shared by multiple protocols, following RFC 1755. the VC to be shared by multiple protocols, following RFC 1755.
Note 5: Cf ITU I.365 (Oct 1996) for new definition. Note 6: Cf ITU I.365 (Oct 1996) for new QoS Class definitions.
Note 6: See section 2.6 for the values to be used. The cumulative CDV Note 7: See Section 2.6 for the values to be used.
is also provided, but it depends on local implementation, and
not on values mapped from IP level service parameters.
6.3 Encoding CLS Using Real-Time VBR (ATM Forum TM/UNI 4.0) 6.3 Encoding CLS Using Real-Time VBR (ATM Forum TM/UNI 4.0)
The encoding of CLS using rtVBR imposes a hard limit on the delay, The encoding of CLS using rtVBR imposes a hard limit on the delay,
which is specified as an end-to-end delay in the ATM network. This which is specified as an end-to-end delay in the ATM network. This
is more stringent than the CLS service specifies and may result in is more stringent than the CLS service requires.
less utilization of the network.
If rtVBR is used to encode CLS, then the encoding is essentially the If rtVBR is used to encode CLS, then the encoding is essentially the
same as that for GS. The exceptions are that the Forward PCR is same as that for GS. See Section 5.1 and discussion in Section
derived from the line rate and probably a different value of the 2.5.2.
transit delay and CDV will be specified. See Section 3.1.
6.4 Encoding CLS Using CBR (ATM Forum TM/UNI 4.0) 6.4 Encoding CLS Using CBR (ATM Forum TM/UNI 4.0)
The encoding of CLS using CBR is more stringent than using rtVBR Although CBR does not explicitly take into account the variable rate
since it does not take into account the variable rate of the data. of source data, it may be convenient to use ATM connectivity between
Consequently there may be even lower utilization of the network. edge routers to provide a simple "pipe" service, as a leased line
replacement.
To use CBR for CLS, the same encoding as in Section 3.2 would be To use CBR for CLS, the same encoding for GS over CBR (Section 5.2
used. However a different set of values of the QoS parameters will would be used. See Section 2.5.2.
likely be used.
6.5 Encoding CLS Using UBR (ATM Forum TM/UNI 4.0) 6.5 Encoding CLS Using UBR (ATM Forum TM/UNI 4.0)
This encoding gives no QoS guarantees and would be done in the same This encoding gives no QoS guarantees. If used, it is coded in the
way as for BE traffic. See Section 5.1. same way as for BE over UBR, except that the PCR would be determined
from the peak rate of the receiver TSpec. See Section 7.1.
6.6 Encoding CLS Using Non-Real-Time VBR as in UNI 3.0/3.1 6.6 Encoding CLS Using ATM Forum UNI 3.0/3.1 Specifications
Specifications
This encoding is equivalent to the nrtVBR service category.
AAL AAL
Type 5 Type 5
Forward CPCS-SDU Size parameter M of TSpec Forward CPCS-SDU Size parameter M of receiver TSpec
Backward CPCS-SDU Size 0 Backward CPCS-SDU Size 0
Mode 1 (Message mode) Note 1 Mode 1 (Message mode) Note 1
SSCS Type 0 (Null SSCS) SSCS Type 0 (Null SSCS)
Traffic Descriptor Traffic Descriptor
Forward PCR CLP=0+1 From line rate Forward PCR CLP=0+1 Note 2
Backward PCR CLP=0+1 0 Backward PCR CLP=0+1 0
Forward SCR CLP=0 From TSpec token bucket rate Forward SCR CLP=0 Note 2
Backward SCR CLP=0 0 Backward SCR CLP=0 0
Forward MBS (CLP=0) From TSpec bucket size param Forward MBS (CLP=0) Note 2
Backward MBS (CLP=0) 0 Backward MBS (CLP=0) 0
BE indicator NOT included BE indicator NOT included
Tagging Forward bit 1 (Tagging requested) Tagging Forward bit 1 (Tagging requested)
Tagging Backward bit 1 (Tagging requested) Tagging Backward bit 1 (Tagging requested)
Broadband Bearer Capability Broadband Bearer Capability
Bearer Class 16 (BCOB-X) Note 2 Bearer Class 16 (BCOB-X) Note 3
Traffic Type 010 (bit encoding for Variable Bit Traffic Type 010 (bit encoding for Variable Bit
Rate) Rate)
Timing Requirements 00 (bit encoding for No Indication) Timing Requirements 00 (bit encoding for No Indication)
Susceptible to Clipping 00 (bit encoding for Not Susceptible to Clipping 00 (bit encoding for Not
susceptible) susceptible)
User Plane Configuration 01 (bit encoding for For pt-to-mpt) User Plane Configuration 01 (bit encoding for For pt-to-mpt)
Broadband Low Layer Information Broadband Low Layer Information
User Information Layer 2 User Information Layer 2
Protocol 12 (ISO 8802/2) Protocol 12 (ISO 8802/2)
User Information Layer 3 User Information Layer 3
Protocol 11 (ISO/IEC TR 9577) Note 3 Protocol 11 (ISO/IEC TR 9577) Note 4
ISO/IEC TR 9577 IPI 204 ISO/IEC TR 9577 IPI 204
QoS Class QoS Class
QoS Class Forward 3 QoS Class Forward 3
QoS Class Backward 3 QoS Class Backward 3
QoS Parameters QoS Parameters
Parameters are implied by the QOS Class Parameters are implied by the QOS Class
Note 1: Only included for UNI 3.0. Note 1: Only included for UNI 3.0.
Note 2: Value 3 (BCOB-C) can also be used. If BCOB-C is used Traffic Note 2: See discussion, Section 2.5.2.
Note 3: Value 3 (BCOB-C) can also be used. If BCOB-C is used Traffic
Type and Timing Requirements fields are not included. Type and Timing Requirements fields are not included.
Note 3: For QoS VCs supporting GS or CLS, the layer 3 protocol should Note 4: For QoS VCs supporting GS or CLS, the layer 3 protocol should
be specified. For BE VCs, it can be left unspecified, allowing be specified. For BE VCs, it can be left unspecified, allowing
the VC to be shared by multiple protocols, following RFC 1755. the VC to be shared by multiple protocols, following RFC 1755.
7.0 Summary of ATM VC Setup Parameters for Best Effort Service 7.0 Summary of ATM VC Setup Parameters for Best Effort Service
This section describes how to create ATM VCs appropriately matched for This section should be considered informational only. RFC 1755 [10] and
Best Effort. The BE service does not need a reservation of resources. the IETF ION working group draft on ATM signalling support for IP over
ATM using UNI 4.0 [11] provide more definitive specification of Best
The following subsections are for information only. See the IETF ION Effort IP service over ATM.
working group draft on ATM signalling support for IP over ATM using UNI
4.0 [11] for recommendations.
7.1 Encoding Best Effort Service Using UBR (ATM Forum TM/UNI 4.0) The best-matched ATM service category to IP Best Effort is UBR. We
provide the setup details for this case below. The BE service does not
require reservation of resources.
This section is for information only. For recommendation, see the Note, VCs supporting best effort service are usually point to point,
IETF ION working group draft on ATM signalling support for IP over rather than point to multipoint, and the backward channels of VCs are
ATM using UNI 4.0 [11]. used. In specific cases where VCs are set up to support best effort
multicast sessions, multipoint VCs can be used and the backward channels
would be not have resources reserved. Related situations include
transport of excess traffic on IP-multicast QoS sessions, or to support
the subset of multicast end systems that have not made rsvp
reservations.
7.1 Encoding Best Effort Service Using UBR (ATM Forum TM/UNI 4.0)
AAL AAL
Type 5 Type 5
Forward CPCS-SDU Size MTU of link Forward CPCS-SDU Size 9180 (default MTU for AAL5)
Backward CPCS-SDU Size MTU of link Backward CPCS-SDU Size 9180 (default MTU for AAL5)
SSCS Type 0 (Null SSCS) SSCS Type 0 (Null SSCS)
Traffic Descriptor Traffic Descriptor
Forward PCR CLP=0+1 From line rate Forward PCR CLP=0+1 Note 1
Backward PCR CLP=0+1 0 Backward PCR CLP=0+1 0
BE indicator included BE indicator included
Forward Frame Discard bit 1 Forward Frame Discard bit 1
Backward Frame Discard bit 1 Backward Frame Discard bit 1
Tagging Forward bit 1 (Tagging requested) Tagging Forward bit 1 (Tagging requested)
Tagging Backward bit 1 (Tagging requested) Tagging Backward bit 1 (Tagging requested)
Broadband Bearer Capability Broadband Bearer Capability
Bearer Class 16 (BCOB-X) Note 1 Bearer Class 16 (BCOB-X) Note 2
ATM Transfer Capability 10 (Non-real time VBR) Note 2 ATM Transfer Capability 10 (Non-real time VBR) Note 3
Susceptible to Clipping 00 (bit encoding for Not susceptible) Susceptible to Clipping 00 (bit encoding for Not susceptible)
User Plane Configuration 01 (bit encoding for pt-to-mpt) User Plane Configuration 01 (bit encoding for pt-to-mpt)
Broadband Low Layer Information Broadband Low Layer Information
User Information Layer 2 User Information Layer 2
Protocol 12 (ISO 8802/2) Protocol 12 (ISO 8802/2)
User Information Layer 3 User Information Layer 3
Protocol 11 (ISO/IEC TR 9577) Note 3 Protocol 11 (ISO/IEC TR 9577) Note 4
ISO/IEC TR 9577 IPI 204 ISO/IEC TR 9577 IPI 204
QoS Class QoS Class
QoS Class Forward 0 QoS Class Forward 0
QoS Class Backward 0 QoS Class Backward 0
Note 1: Value 3 (BCOB-C) can also be used. Note 1: See discussion, Section 2.5.3.
Note 2: If bearer class C is used, the ATC field must be absent Note 2: Value 3 (BCOB-C) can also be used.
Note 3: For QoS VCs supporting GS or CLS, the layer 3 protocol should Note 3: If bearer class C is used, the ATC field must be absent
Note 4: For QoS VCs supporting GS or CLS, the layer 3 protocol should
be specified. For BE VCs, it can be left unspecified, allowing be specified. For BE VCs, it can be left unspecified, allowing
the VC to be shared by multiple protocols, following RFC 1755. the VC to be shared by multiple protocols, following RFC 1755.
.fi
7.2 Encoding Best Effort Service Using Other ATM Service Categories
See the IETF ION working group draft on ATM signalling support for IP
over ATM using UNI 4.0 [11].
8.0 Security 8.0 Security
Some security issues are raised in the rsvp specification [2], which Some security issues are raised in the rsvp specification [2], which
would apply here as well. There are no additional security would apply here as well. There are no additional security
considerations raised in this document. considerations raised in this document.
9.0 Acknowledgements 9.0 Acknowledgements
The authors would like to thank the members of the ISSLL working The authors would like to thank the members of the ISSLL working
group for their input. In particular, thanks to Jon Bennett of Fore group for their input. In particular, thanks to Drew Perkins and Jon
Systems, Roch Guerin of IBM and Susan Thomson of Bellcore. Bennett of Fore Systems, Roch Guerin of IBM, Susan Thomson and Sudha
Ramesh of Bellcore.
Appendix 1 Abbreviations Appendix 1 Abbreviations
AAL ATM Adaptation Layer AAL ATM Adaptation Layer
ABR Available Bit Rate ABR Available Bit Rate
APB Available Path Bandwidth (int-serv GCP)
ATM Asynchronous Transfer Mode ATM Asynchronous Transfer Mode
B-LLI Broadband Low Layer Information B-LLI Broadband Low Layer Information
BCOB Broadband Connection-Oriented Bearer Capability BCOB Broadband Connection-Oriented Bearer Capability
BCOB-{A,C,X} Bearer Class A, C, or X BCOB-{A,C,X} Bearer Class A, C, or X
BE Best Effort BE Best Effort
BT Burst Tolerance BT Burst Tolerance
CBR Constant Bit Rate CBR Constant Bit Rate
CDV Cell Delay Variation CDV Cell Delay Variation
CDVT Cell Delay Variation Tolerance CDVT Cell Delay Variation Tolerance
CLP Cell Loss Priority (bit) CLP Cell Loss Priority (bit)
CLR Cell Loss Ratio CLR Cell Loss Ratio
CLS Controlled Load Service CLS Controlled Load Service
CPCS Common Part Convergence Sublayer CPCS Common Part Convergence Sublayer
CTD Cell Transfer Delay CTD Cell Transfer Delay
EOM End of Message EOM End of Message
FFS For Further Study FFS For Further Study
GCP General Characterization Parameter
GCRA Generic Cell Rate Algorithm GCRA Generic Cell Rate Algorithm
GS Guaranteed Service GS Guaranteed Service
IE Information Element IE Information Element
IETF Internet Engineering Task Force IETF Internet Engineering Task Force
IP Internet Protocol IP Internet Protocol
IPI Initial Protocol Identifier
IS Integrated Services IS Integrated Services
ISSLL Integrated Services over Specific Link Layers ISSLL Integrated Services over Specific Link Layers
ITU International Telecommunication Union ITU International Telecommunication Union
IWF Interworking Function IWF Interworking Function
LIJ Leaf Initiated Join LIJ Leaf Initiated Join
LLC Logical Link Control LLC Logical Link Control
MBS Maximum Burst Size MBS Maximum Burst Size
MCR Minimum Cell Rate MCR Minimum Cell Rate
MPL Minimum Path Latency MPL Minimum Path Latency
MTU Maximum Transfer Unit MTU Maximum Transfer Unit
nrtVBR Non-real-time VBR nrtVBR Non-real-time VBR
PCR Peak Cell Rate PCR Peak Cell Rate
PDU Protocol Data Unit PDU Protocol Data Unit
PVC Permanent Virtual Connection
QoS Quality of Service QoS Quality of Service
RESV Reservation Message (of rsvp protocol) RESV Reservation Message (of rsvp protocol)
RFC Request for Comment RFC Request for Comment
RSVP Resource Reservation Protocol RSVP Resource Reservation Protocol
Rspec Reservation Specification Rspec Reservation Specification
rtVBR Real-time VBR rtVBR Real-time VBR
SCR Sustained Cell Rate SCR Sustained Cell Rate
SDU Service Data Unit SDU Service Data Unit
SIG ATM Signaling (ATM Forum document)
SNAP Subnetwork Attachment Point SNAP Subnetwork Attachment Point
SSCS Service-Specific Convergence Sub-layer SSCS Service-Specific Convergence Sub-layer
SVC Switched Virtual Connection
Sw Switch Sw Switch
TCP Transport Control Protocol TCP Transport Control Protocol
TM Traffic Management TM Traffic Management
TSpec Traffic Specification TSpec Traffic Specification
UBR Unspecified Bit Rate UBR Unspecified Bit Rate
UNI User-Network Interface UNI User-Network Interface
UPC Usage Parameter Control (ATM traffic policing function) UPC Usage Parameter Control (ATM traffic policing function)
VBR Variable Bit Rate VBR Variable Bit Rate
VC (ATM) Virtual Connection VC (ATM) Virtual Connection
REFERENCES References
[1] R. Braden, D. Clark and S. Shenker, "Integrated Services in the [1] R. Braden, D. Clark and S. Shenker, "Integrated Services in the
Internet Architecture: an Overview", RFC 1633, June 1994. Internet Architecture: an Overview", RFC 1633, June 1994.
[2] R. Braden, L. Zhang, S. Berson, S. Herzog and S. Jamin, [2] R. Braden, L. Zhang, S. Berson, S. Herzog and S. Jamin,
"Resource ReSerVation Protocol (RSVP) - Version 1 Functional "Resource ReSerVation Protocol (RSVP) - Version 1 Functional
Specification", Internet Draft, May 1996, <draft-ietf-rsvp- Specification", Internet Draft, May 1996, <draft-ietf-rsvp-
spec-12.txt> spec-12.txt>
[3] The ATM Forum, "ATM User-Network Interface Specification, Ver- [3] The ATM Forum, "ATM User-Network Interface Specification, Ver-
sion 3.0", Prentice Hall, Englewood Cliffs NJ, 1993. sion 3.0", Prentice Hall, Englewood Cliffs NJ, 1993.
[4] The ATM Forum, "ATM User-Network Interface Specification, Ver- [4] The ATM Forum, "ATM User-Network Interface Specification, Ver-
sion 3.1", Prentice Hall, Upper Saddle River NJ, 1995. sion 3.1", Prentice Hall, Upper Saddle River NJ, 1995.
[5] The ATM Forum, "ATM User-Network Interface (UNI) Signalling [5] The ATM Forum, "ATM User-Network Interface (UNI) Signalling
Specification, Version 4.0", Prentice Hall, Upper Saddle River Specification, Version 4.0", Prentice Hall, Upper Saddle River
NJ, specification finalized July 1996; expected publication, NJ, specification finalized July 1996; expected publication,
late 1996; available at ftp://ftp.atmforum.com/pub. late 1996; available at ftp://ftp.atmforum.com/pub/approved-
specs/af-sig-0061.000.ps.
[6] The ATM Forum, "ATM Traffic Management Specification, Version [6] The ATM Forum, "ATM Traffic Management Specification, Version
4.0", Prentice Hall, Upper Saddle River NJ; specification final- 4.0", Prentice Hall, Upper Saddle River NJ; specification final-
ized April 1996; expected publication, late 1996; available at ized April 1996; expected publication, late 1996; available at
ftp://ftp.atmforum.com/pub. ftp://ftp.atmforum.com/pub/approved-specs/af-tm-0056.000.ps.
[7] M. W. Garrett, "A Service Architecture for ATM: From Applica- [7] M. W. Garrett, "A Service Architecture for ATM: From Applica-
tions to Scheduling", IEEE Network Mag., Vol. 10, No. 3, pp. 6- tions to Scheduling", IEEE Network Mag., Vol. 10, No. 3, pp. 6-
14, May 1996. 14, May 1996.
[8] S. Shenker, C. Partridge and R. Guerin, "Specification of [8] S. Shenker, C. Partridge and R. Guerin, "Specification of
Guaranteed Quality of Service", Internet Draft, August 1996, Guaranteed Quality of Service", Internet Draft, July 1997,
<draft-ietf-intserv-guaranteed-svc-06.txt> <draft-ietf-intserv-guaranteed-svc-08.txt>
[9] J. Wroclawski, "Specification of the Controlled-Load Network [9] J. Wroclawski, "Specification of the Controlled-Load Network
Element Service", Internet Draft, August 1996, draft-ietf- Element Service", Internet Draft, November 1996, <draft-ietf-
intserv-ctrl-load-svc-03.txt intserv-ctrl-load-svc-04.txt>
[10] M. Perez, F. Liaw, A. Mankin, E. Hoffman, D. Grossman and A. [10] M. Perez, F. Liaw, A. Mankin, E. Hoffman, D. Grossman and A.
Malis, "ATM Signaling Support for IP over ATM", RFC 1755, Febru- Malis, "ATM Signaling Support for IP over ATM", RFC 1755, Febru-
ary 1995. ary 1995.
[11] M. Perez and A. Mankin, "ATM Signalling Support for IP over ATM [11] M. Perez and A. Mankin, "ATM Signaling Support for IP over ATM -
- UNI 4.0 Update", Internet Draft, November 1996, <draft-ietf- UNI 4.0 Update", Internet Draft, May 1997, <draft-ietf-ion-sig-
ion-sig-uni4.0-01.txt> uni4.0-04.txt>
[12] S. Berson, L. Berger, "IP Integrated Services with RSVP over [12] S. Berson, L. Berger, "IP Integrated Services with RSVP over
ATM", Internet Draft, September 1996, <draft-ietf-issll-atm- ATM", Internet Draft, September 1996, <draft-ietf-issll-atm-
support-01.txt> support-01.txt>
[13] S. Shenker and J. Wroclawski, "Network Element Service Specifi- [13] S. Shenker and J. Wroclawski, "Network Element Service Specifi-
cation Template", Internet Draft, November 1995, <draft-ietf- cation Template", Internet Draft, November 1995, <draft-ietf-
intserv-svc-template-02.txt> intserv-svc-template-02.txt>
[14] J. Wroclawski, "The Use of RSVP with IETF Integrated Services", [14] J. Wroclawski, "The Use of RSVP with IETF Integrated Services",
Internet Draft, August 1996, <draft-ietf-intserv-use-00.txt> Internet Draft, August 1996, <draft-ietf-intserv-use-00.txt>
[15] M. Borden, E. Crawley, B. Davie and S. Batsell, "Integration of [15] M. Borden, E. Crawley, B. Davie and S. Batsell, "Integration of
Real-time Services in an IP-ATM Network Architecture", "IP Real-time Services in an IP-ATM Network Architecture", "IP
Authentication Header", RFC 1821, August 1995. Authentication Header", RFC 1821, August 1995.
[16] J. Heinanen, "Multiprotocol Encapsulation over ATM Adaptation [16] J. Heinanen, "Multiprotocol Encapsulation over ATM Adaptation
Layer 5", RFC 1483, July 1993. Layer 5", RFC 1483, July 1993.
AUTHORS' ADDRESSES [17] M. Laubach, "Classical IP and ARP over ATM", RFC 1577, January
1994.
[18] L. Berger, "RSVP over ATM Implementation Requirements", Internet
Draft, July 1997, <draft-ietf-issll-atm-imp-req-00.txt>
[19] L. Berger, "RSVP over ATM Implementation Guidelines", Internet
Draft, July 1997, <draft-ietf-issll-imp-guide-01.txt>
[20] A. Romanow, S. Floyd, "Dynamics of TCP Traffic over ATM Net-
works", IEEE J. Sel. Areas in Commun., Vol. 13, No. 4, pp. 633-
-41, May 1995,
[21] S. Floyd, V. Jacobson, "Link-sharing and Resource Management
Models for Packet Networks", IEEE/ACM Trans. Networking, Vol. 3,
No. 4, August 1995.
[22] S. Shenker and J. Wroclawski, "General Characterization Parame-
ters for Integrated Service Network Elements", Internet Draft,
July 1997, <draft-ietf-intserv-charac-03.txt>
Authors' Addresses
Mark W. Garrett Marty Borden Mark W. Garrett Marty Borden
Bellcore New Oak Communications, Inc. Bellcore New Oak Communications, Inc.
445 South Street 42 Nanog Park 445 South Street 42 Nagog Park
Morristown, NJ 07960 Acton MA, 01720 Morristown, NJ 07960 Acton MA, 01720
USA USA USA USA
phone: +1 201 829-4439 phone: +1 508 266-1011 phone: +1 201 829-4439 phone: +1 508 266-1011
email: mwg@bellcore.com email: mborden@newoak.com email: mwg@bellcore.com email: mborden@newoak.com
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