draft-ietf-issll-atm-imp-req-00.txt   draft-ietf-issll-atm-imp-req-01.txt 
Internet Draft L. Berger Internet Draft L. Berger
Expires: January 1998 FORE Systems Expires: May 1998 FORE Systems
File: draft-ietf-issll-atm-imp-req-00.txt File: draft-ietf-issll-atm-imp-req-01.txt
RSVP over ATM Implementation Requirements RSVP over ATM Implementation Requirements
July 11, 1997 November 18, 1997
Status of Memo Status of Memo
This document is an Internet-Draft. Internet-Drafts are working This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas, documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute and its working groups. Note that other groups may also distribute
working documents as Internet-Drafts. working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
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Directories on ds.internic.net (US East Coast), nic.nordu.net Directories on ds.internic.net (US East Coast), nic.nordu.net
(Europe), ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific (Europe), ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific
Rim). Rim).
Abstract Abstract
This note presents specific implementation requirements for running This note presents specific implementation requirements for running
RSVP over ATM switched virtual circuits (SVCs). It presents RSVP over ATM switched virtual circuits (SVCs). It presents
requirements that ensure interoperability between multiple requirements that ensure interoperability between multiple
implementations and conformance to the RSVP and Integrated Services implementations and conformance to the RSVP and Integrated Services
specifications. A separate document [6] provides specific guidelines specifications. A separate document [5] provides specific guidelines
for running over today's ATM networks. The general problem is for running over today's ATM networks. The general problem is
discussed in [11]. Integrated Services to ATM service mappings are discussed in [8]. Integrated Services to ATM service mappings are
covered in [9]. The full set of documents present the background and covered in [6]. The full set of documents present the background and
information needed to implement Integrated Services and RSVP over information needed to implement Integrated Services and RSVP over
ATM. ATM.
Table of Contents Table of Contents
1. Introduction ........................................................3 1. Introduction ........................................................3
1.1 Terms ...........................................................3 1.1 Terms ...........................................................3
1.2 Assumptions .....................................................4 1.2 Assumptions .....................................................4
2. General RSVP Session Support ........................................4 2. General RSVP Session Support ........................................4
2.1 VC Usage ........................................................4 2.1 RSVP Message VC Usage ...........................................4
2.2 VC Initiation ...................................................5 2.2 VC Initiation ...................................................5
2.3 VC Teardown .....................................................5 2.3 VC Teardown .....................................................6
2.4 Dynamic QoS .....................................................6 2.4 Dynamic QoS .....................................................7
2.5 Encapsulation ...................................................7 2.5 Encapsulation ...................................................7
3. Multicast RSVP Session Support ......................................7 3. Multicast RSVP Session Support ......................................8
3.1 Data VC Management for Heterogeneous Sessions ...................7 3.1 Data VC Management for Heterogeneous Sessions ...................8
3.2 Multicast End-Point Identification ..............................9 3.2 Multicast End-Point Identification ..............................9
3.3 Multicast Data Distribution .....................................10 3.3 Multicast Data Distribution .....................................10
3.4 Receiver Transitions ............................................11 3.4 Receiver Transitions ............................................11
4. Security ............................................................12 4. Security ............................................................12
5. Acknowledgments .....................................................12 5. Acknowledgments .....................................................12
6. Author's Address ....................................................12 6. Author's Address ....................................................12
1. Introduction 1. Introduction
This note discusses running IP over ATM in an environment where SVCs This note discusses running IP over ATM in an environment where SVCs
are used to support QoS flows and RSVP is used as the internet level are used to support QoS flows and RSVP is used as the internet level
QoS signaling protocol. It applies when using CLIP/ION, LANE2.0 and QoS signaling protocol. It applies when using CLIP/ION, LANE2.0 and
MPOA[4] methods for supporting IP over ATM. The general issues MPOA[4] methods for supporting IP over ATM. The general issues
related to running RSVP[10] over ATM have been covered in several related to running RSVP[7] over ATM have been covered in several
papers including [11,7,5,8]. This document is intended as a papers including [8] and other superseded internet drafts. This
companion to [11,6]. The reader should be familiar with both document is intended as a companion to [8,5]. The reader should be
documents. familiar with both documents.
This document will define specific requirements for implementations This document will define specific requirements for implementations
using ATM UNI3.x and 4.0. These requirements must be adhered to by using ATM UNI3.x and 4.0. These requirements must be adhered to by
all RSVP over ATM implementations to ensure interoperability. all RSVP over ATM implementations to ensure interoperability.
Further recommendations to guide implementers of RSVP over ATM are Further recommendations to guide implementers of RSVP over ATM are
provided in [6]. provided in [5].
The rest of this section will define terms and assumptions. Section 2 The rest of this section will define terms and assumptions. Section 2
will cover implementation guidelines common to all RSVP session. will cover implementation guidelines common to all RSVP session.
Section 3 will cover implementation guidelines specific to multicast Section 3 will cover implementation guidelines specific to multicast
sessions. sessions.
1.1 Terms 1.1 Terms
The terms "reservation" and "flow" are used in many contexts, The terms "reservation" and "flow" are used in many contexts,
often with different meaning. These terms are used in this often with different meaning. These terms are used in this
document with the following meaning: document with the following meaning:
o Reservation is used in this document to refer to an RSVP o Reservation is used in this document to refer to an RSVP
initiated request for resources. RSVP initiates requests for initiated request for resources. RSVP initiates requests for
resources based on RESV message processing. RESV messages resources based on RESV message processing. RESV messages
that simply refresh state do not trigger resource requests. that simply refresh state do not trigger resource requests.
Resource requests may be made based on RSVP sessions and RSVP Resource requests may be made based on RSVP sessions and RSVP
reservation styles. RSVP styles dictate whether the reserved reservation styles. RSVP styles dictate whether the reserved
resources are used by one sender or shared by multiple resources are used by one sender or shared by multiple
senders. See [10] for details of each. Each new request is senders. See [7] for details of each. Each new request is
referred to in this document as an RSVP reservation, or referred to in this document as an RSVP reservation, or
simply reservation. simply reservation.
o Flow is used to refer to the data traffic associated with a o Flow is used to refer to the data traffic associated with a
particular reservation. The specific meaning of flow is RSVP particular reservation. The specific meaning of flow is RSVP
style dependent. For shared style reservations, there is one style dependent. For shared style reservations, there is one
flow per session. For distinct style reservations, there is flow per session. For distinct style reservations, there is
one flow per sender (per session). one flow per sender (per session).
1.2 Assumptions 1.2 Assumptions
The following assumptions are made: The following assumptions are made:
o RSVP We assume RSVP as the internet signalling protocol which o RSVP
is described in [10]. The reader is assumed to be familiar
with [10].
o IPv4 and IPv6 RSVP support has been defined for both IPv4 and We assume RSVP as the internet signalling protocol which is
IPv6. The guidelines in this document are intended to be described in [7]. The reader is assumed to be familiar with
used to support RSVP with either IPv4 or IPv6. This document [7].
does not require one version over the other.
o Best effort service model The current Internet only supports o IPv4 and IPv6
best effort service. We assume that as additional components
of the Integrated Services model that best effort service
will continue to be a supported.
o ATM UNI 3.x and 4.0 We assume ATM service as defined by UNI RSVP support has been defined for both IPv4 and IPv6. The
3.x and 4.0. ATM provides both point-to-point and point-to- guidelines in this document are intended to be used to
multipoint Virtual Circuits (VCs) with a specified Quality of support RSVP with either IPv4 or IPv6. This document does
Service (QoS). ATM provides both Permanent Virtual Circuits not require one version over the other.
(PVCs) and Switched Virtual Circuits (SVCs). In the
Permanent Virtual Circuit (PVC) environment, PVCs are o Best effort service model
typically used as point-to-point link replacements. So the
support issues are similar to point-to-point links. This The current Internet only supports best effort service. We
draft assumes that SVCs are used to support RSVP over ATM. assume that as additional components of the Integrated
Services model that best effort service must continue to be a
supported.
o ATM UNI 3.x and 4.0
We assume ATM service as defined by UNI 3.x and 4.0. ATM
provides both point-to-point and point-to-multipoint Virtual
Circuits (VCs) with a specified Quality of Service (QoS).
ATM provides both Permanent Virtual Circuits (PVCs) and
Switched Virtual Circuits (SVCs). In the Permanent Virtual
Circuit (PVC) environment, PVCs are typically used as point-
to-point link replacements. So the support issues are
similar to point-to-point links. This draft assumes that
SVCs are used to support RSVP over ATM.
2. General RSVP Session Support 2. General RSVP Session Support
This section provides implementation requirements that are common for This section provides implementation requirements that are common for
all (both unicast and multicast) RSVP sessions. The section covers all (both unicast and multicast) RSVP sessions. The section covers
VC usage, QoS VC initiation, VC teardown, handling requested changes VC usage, QoS VC initiation, VC teardown, handling requested changes
in QoS, and encapsulation. in QoS, and encapsulation.
2.1 VC Usage 2.1 RSVP Message VC Usage
There are several options open to implementations on which VC to There are several RSVP Message VC Usage options available to
use for RSVP messages and how to aggregate RSVP sessions over QoS implementers. Implementers must select which VC to use for RSVP
VCs. These options have been covered in [11] and some specific messages and how to aggregate RSVP sessions over QoS VCs. These
implementation guidelines are stated in [6]. In order to ensure options have been covered in [8] and some specific implementation
interoperability between implementations that follow different guidelines are stated in [5]. In order to ensure interoperability
options, RSVP over ATM implementations MUST be able to receive between implementations that follow different options, RSVP over
RSVP (control) messages on both QoS and best-effort VCs, and MUST ATM implementations MUST NOT send RSVP (control) messages on the
be able to receive multiple RSVP sessions per QoS VC. same QoS VC as RSVP associated data packets. RSVP over ATM
implementations MAY send RSVP messages on either the best effort
data path or on a separate control VC.
Since RSVP (control) messages and RSVP associated data packets are
not sent on the same VCs, it is possible for a VC supporting one
type of traffic to fail while the other remains in place. When
the VC associated with data packets fails and cannot be
reestablished, RSVP should treat this as an allocation failure.
When the VC used to forward RSVP control messages is abnormally
released and cannot be reestablished, the RSVP associated QoS VCs
MUST also be released. The release of the associated data VCs is
required to maintain the synchronization between forwarding and
reservation states for the associated data flows.
2.2 VC Initiation 2.2 VC Initiation
There is an apparent mismatch between RSVP and ATM. Specifically, There is an apparent mismatch between RSVP and ATM. Specifically,
RSVP control is receiver oriented and ATM control is sender RSVP control is receiver oriented and ATM control is sender
oriented. This initially may seem like a major issue but really oriented. This initially may seem like a major issue but really
is not. While RSVP reservation (RESV) requests are generated at is not. While RSVP reservation (RESV) requests are generated at
the receiver, actual allocation of resources takes place at the the receiver, actual allocation of resources takes place at the
sub-net sender. sub-net sender.
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Initiator Initiator
Figure 1: Data Flow VC Initiation Figure 1: Data Flow VC Initiation
RSVP over ATM implementations MAY send data in the backwards RSVP over ATM implementations MAY send data in the backwards
direction on a RSVP initiated QoS point-to-point VC. When sending direction on a RSVP initiated QoS point-to-point VC. When sending
in the backwards data path, the sender MUST ensure that the data in the backwards data path, the sender MUST ensure that the data
conforms to the backwards direction traffic parameters. Since the conforms to the backwards direction traffic parameters. Since the
traffic parameters are set by the VC initiator, it is quite likely traffic parameters are set by the VC initiator, it is quite likely
that no resources will be requested for traffic originating at the that no resources will be requested for traffic originating at the
called party. Of course, the backwards data path is not available called party. It should be noted that the backwards data path is
with point-to-multipoint VCs. not available with point-to-multipoint VCs.
2.3 VC Teardown 2.3 VC Teardown
VCs supporting IP over ATM data are typically torndown based on VCs supporting IP over ATM data are typically torndown based on
inactivity timers. This mechanism is used since IP is inactivity timers. This mechanism is used since IP is
connectionless and there is therefore no way to know when a VC is connectionless and there is therefore no way to know when a VC is
no longer needed. Since RSVP provides explicit mechanisms no longer needed. Since RSVP provides explicit mechanisms
(messages and timeouts) to determine when an associated data VC is (messages and timeouts) to determine when an associated data VC is
no longer needed, the traditional VC timeout mechanisms is not no longer needed, the traditional VC timeout mechanisms is not
needed. Data VCs set up to support RSVP controlled flows should needed. Additionally, under normal operations RSVP implementations
expect to be able to allocate resources and have those resource
remain allocated until released at the direction of RSVP.
Therefore, data VCs set up to support RSVP controlled flows should
only be released at the direction of RSVP. Such VCs must not be only be released at the direction of RSVP. Such VCs must not be
timed out due to inactivity by either the VC initiator or the VC timed out due to inactivity by either the VC initiator or the VC
receiver. This conflicts with VCs timing out as described in RFC receiver. This conflicts with VCs timing out as described in RFC
1755[14], section 3.4 on VC Teardown. RFC 1755 recommends tearing 1755[10], section 3.4 on VC Teardown. RFC 1755 recommends tearing
down a VC that is inactive for a certain length of time. Twenty down a VC that is inactive for a certain length of time. Twenty
minutes is recommended. This timeout is typically implemented at minutes is recommended. This timeout is typically implemented at
both the VC initiator and the VC receiver. Although, section 3.1 both the VC initiator and the VC receiver. Although, section 3.1
of the update to RFC 1755[15] states that inactivity timers must of the update to RFC 1755[11] states that inactivity timers must
not be used at the VC receiver. not be used at the VC receiver.
In RSVP over ATM implementations, the configurable inactivity In RSVP over ATM implementations, the configurable inactivity
timer mentioned in [14] MUST be set to "infinite" for VCs timer mentioned in [10] MUST be set to "infinite" for VCs
initiated at the request of RSVP. Setting the inactivity timer initiated at the request of RSVP. Setting the inactivity timer
value at the VC initiator should not be problematic since the value at the VC initiator should not be problematic since the
proper value can be relayed internally at the originator. Setting proper value can be relayed internally at the originator. Setting
the inactivity timer at the VC receiver is more difficult, and the inactivity timer at the VC receiver is more difficult, and
would require some mechanism to signal that an incoming VC was would require some mechanism to signal that an incoming VC was
RSVP initiated. To avoid this complexity and to conform to [15], RSVP initiated. To avoid this complexity and to conform to [11],
RSVP over ATM implementations MUST not use an inactivity timer to RSVP over ATM implementations MUST not use an inactivity timer to
clear any received connection. clear any received connections.
2.4 Dynamic QoS 2.4 Dynamic QoS
As stated in [11], there is a mismatch in the service provided by As stated in [8], there is a mismatch in the service provided by
RSVP and that provided by ATM UNI3.x and 4.0. RSVP allows RSVP and that provided by ATM UNI3.x and 4.0. RSVP allows
modifications to QoS parameters at any time, while ATM does not modifications to QoS parameters at any time while ATM does not
support any modifications to QoS parameters after VC setup. See support any modifications to QoS parameters post VC setup. See
[11] for more detail. [8] for more detail.
The method for supporting changes in RSVP reservations is to The method for supporting changes in RSVP reservations is to
attempt to replace an existing VC with a new appropriately sized attempt to replace an existing VC with a new appropriately sized
VC. During setup of the replacement VC, the old VC MUST be left in VC. During setup of the replacement VC, the old VC MUST be left in
place unmodified. The old VC is left unmodified to minimize place unmodified. The old VC is left unmodified to minimize
interruption of QoS data delivery. Once the replacement VC is interruption of QoS data delivery. Once the replacement VC is
established, data transmission is shifted to the new VC, and only established, data transmission is shifted to the new VC, and only
then is the old VC closed. then is the old VC closed.
If setup of the replacement VC fails, then the old QoS VC MUST If setup of the replacement VC fails, then the old QoS VC MUST
continue to be used. When the new reservation is greater than the continue to be used. When the new reservation is greater than the
old reservation, the reservation request MUST be answered with an old reservation, the reservation request MUST be answered with an
error. When the new reservation is less than the old reservation, error. When the new reservation is less than the old reservation,
the request MUST be treated as if the modification was successful. the request MUST be treated as if the modification was successful.
While leaving the larger allocation in place is suboptimal, it While leaving the larger allocation in place is suboptimal, it
maximizes delivery of service to the user. The behavior is also maximizes delivery of service to the user. The behavior is also
required in order to conform to RSVP error handling as defined in required in order to conform to RSVP error handling as defined in
sections 2.5, 3.1.8 and 3.11.2 of [10]. Implementations SHOULD sections 2.5, 3.1.8 and 3.11.2 of [7]. Implementations SHOULD
retry replacing the too large VC after some appropriate elapsed retry replacing a too large VC after some appropriate elapsed
time. time.
One additional issue is that only one QoS change can be processed One additional issue is that only one QoS change can be processed
at one time per reservation. If the (RSVP) requested QoS is at one time per reservation. If the (RSVP) requested QoS is
changed while the first replacement VC is still being setup, then changed while the first replacement VC is still being setup, then
the replacement VC is released and the whole VC replacement the replacement VC SHOULD BE released and the whole VC replacement
process is restarted. Implementations MAY also limit number of process is restarted. Implementations MAY also limit number of
changes processed in a time period per [11]. changes processed in a time period per [8].
2.5 Encapsulation 2.5 Encapsulation
There are multiple encapsulation options for data sent over RSVP There are multiple encapsulation options for data sent over RSVP
triggered QoS VCs. All RSVP over ATM implementations MUST be able triggered QoS VCs. All RSVP over ATM implementations MUST be able
to support LLC encapsulation per RFC 1483[12] on such QoS VCs. to support LLC encapsulation per RFC 1483[9] on such QoS VCs.
Implementations MAY negotiate alternative encapsulations using the Implementations MAY negotiate alternative encapsulations using the
B-LLI negotiation procedures defined in ATM Signalling, see [14] B-LLI negotiation procedures defined in ATM Signalling, see [10]
for details. When a QoS VC is only being used to carry IP for details. When a QoS VC is only being used to carry IP
packets, implementations SHOULD negotiate VC based multiplexing to packets, implementations SHOULD negotiate VC based multiplexing to
avoid incurring the overhead of the LLC header. avoid incurring the overhead of the LLC header.
3. Multicast RSVP Session Support 3. Multicast RSVP Session Support
There are several aspects to running RSVP over ATM that are There are several aspects to running RSVP over ATM that are unique to
particular to multicast sessions. These issues result from the multicast sessions. This section addresses multicast end-point
nature of ATM point-to-multipoint connections. This section identification, multicast data distribution, multicast receiver
addresses multicast end-point identification, multicast data transitions and next-hops requesting different QoS values
distribution, multicast receiver transitions and next-hops requesting (heterogeneity) which includes the handling of multicast best effort
different QoS values (heterogeneity) which includes the handling of receivers. Handling of best effort receivers is not strictly an RSVP
multicast best-effort receivers. Handling of best-effort receivers issues, but needs to be addressed by any RSVP over ATM implementation
is not strictly an RSVP issues, but needs to be addressed in any RSVP in order to maintain expected best effort Internet service.
over ATM implementation in order to maintain expected Internet
service.
3.1 Data VC Management for Heterogeneous Sessions 3.1 Data VC Management for Heterogeneous Sessions
The issues relating to data VC management of heterogeneous The issues relating to data VC management of heterogeneous
sessions are covered in detail in [11] and not repeated. In sessions are covered in detail in [8]. In summary, heterogeneity
summary, heterogeneity occurs when receivers request different occurs when receivers request different levels of QoS within a
levels of QoS within a single session, and also when some single session, and also when some receivers do not request any
receivers do not request any QoS. Both types of heterogeneity are QoS. Both types of heterogeneity are shown in figure 2.
shown in figure 2.
+----+ +----+
+------> | R1 | +------> | R1 |
| +----+ | +----+
| |
| +----+ | +----+
+-----+ -----+ +--> | R2 | +-----+ -----+ +--> | R2 |
| | ---------+ +----+ Receiver Request Types: | | ---------+ +----+ Receiver Request Types:
| Src | ----> QoS 1 and QoS 2 | Src | ----> QoS 1 and QoS 2
| | .........+ +----+ ....> Best-Effort | | .........+ +----+ ....> Best-Effort
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: +----+ : +----+
/\ : /\ :
|| : +----+ || : +----+
|| +......> | R4 | || +......> | R4 |
|| +----+ || +----+
Single Single
IP Mulicast IP Mulicast
Group Group
Figure 2: Types of Multicast Receivers Figure 2: Types of Multicast Receivers
[8] provides four models for dealing with heterogeneity: full
[11] provides four models for dealing with heterogeneity: full
heterogeneity, limited heterogeneity, homogeneous, and modified heterogeneity, limited heterogeneity, homogeneous, and modified
homogeneous models. No matter which model or combination of homogeneous models. No matter which model or combination of
models is used by an implementation, implementations MUST NOT models is used by an implementation, implementations MUST NOT
normally send more than one copy of a particular data packet to a normally send more than one copy of a particular data packet to a
particular next-hop (ATM end-point). Some transient over particular next-hop (ATM end-point). Some transient duplicate
transmission is acceptable, but only during VC setup and transmission is acceptable, but only during VC setup and
transition. transition.
Implementations MUST also ensure that data traffic is sent to Implementations MUST also ensure that data traffic is sent to best
best-effort receivers. Data traffic MAY be sent to best-effort effort receivers. Data traffic MAY be sent to best effort
receivers via best-effort or QoS VCs as is appropriate for the receivers via best effort or QoS VCs as is appropriate for the
implemented model. In all cases, implementations MUST NOT create implemented model. In all cases, implementations MUST NOT create
VCs in such a way that data cannot be sent to best-effort VCs in such a way that data cannot be sent to best effort
receivers. This includes the case of not being able to add a receivers. This includes the case of not being able to add a best
best-effort receiver to a QoS VC, but does not include the case effort receiver to a QoS VC, but does not include the case where
where best-effort VCs cannot be setup. The failure to establish best effort VCs cannot be setup. The failure to establish best
best-effort VCs is considered to be a general IP over ATM failure effort VCs is considered to be a general IP over ATM failure and
and is therefore beyond the scope of this document. is therefore beyond the scope of this document.
There is an interesting interaction between dynamic QoS and There is an interesting interaction between dynamic QoS and
heterogeneous requests when using the limited heterogeneity, heterogeneous requests when using the limited heterogeneity,
homogeneous, or modified homogeneous models. In the case where a homogeneous, or modified homogeneous models. In the case where a
RESV message is received from a new next-hop and the requested RESV message is received from a new next-hop and the requested
resources are larger than any existing reservation, both dynamic resources are larger than any existing reservation, both dynamic
QoS and heterogeneity need to be addressed. A key issue is QoS and heterogeneity need to be addressed. A key issue is
whether to first add the new next-hop or to change to the new QoS. whether to first add the new next-hop or to change to the new QoS.
This is a fairly straight forward special case. Since the older, This is a fairly straight forward special case. Since the older,
smaller reservation does not support the new next-hop, the dynamic smaller reservation does not support the new next-hop, the dynamic
QoS process SHOULD be initiated first. Since the new QoS is only QoS process SHOULD be initiated first. Since the new QoS is only
needed by the new next-hop, it SHOULD be the first end-point of needed by the new next-hop, it SHOULD be the first end-point of
the new VC. This way signalling is minimized when the setup to the new VC. This way signalling is minimized when the setup to
the new next-hop fails. the new next-hop fails.
3.2 Multicast End-Point Identification 3.2 Multicast End-Point Identification
Implementations must be able to identify ATM end-points Implementations must be able to identify ATM end-points
participating in an IP multicast group. The ATM end-points will participating in an IP multicast group. The ATM end-points will
be IP multicast receivers and/or next-hops. Both QoS and best- be IP multicast receivers and/or next-hops. Both QoS and best
effort end-points must be identified. RSVP next-hop information effort end-points must be identified. RSVP next-hop information
will usually provide QoS end-points, but not best-effort end- will usually provide QoS end-points, but not best effort end-
points. points.
There is a special case where RSVP next-hop information will not There is a special case where RSVP next-hop information will not
provide the appropriate end-point. This occurs when the next-hop provide the appropriate end-points. This occurs when a next-hop
is not RSVP capable, and RSVP is being automatically tunneled. In is not RSVP capable and RSVP is being automatically tunneled. In
this case a PATH message travels through a non-RSVP egress router this case a PATH message travels through a non-RSVP egress router
on the way to the next hop RSVP node. When the next hop RSVP node on the way to the next-hop RSVP node. When the next-hop RSVP node
sends a RESV message it may arrive at the source over a different sends a RESV message it may arrive at the source via a different
route than what the data is using. The source will get the RESV route than used by the PATH message. The source will get the RESV
message, but will not know which egress router needs the QoS. For message, but will not know which ATM end-point should be
unicast sessions, there is no problem since the ATM end-point will associated with the reservation. For unicast sessions, there is no
be the IP next-hop router. Unfortunately, multicast routing may problem since the ATM end-point will be the IP next-hop router.
not be able to uniquely identify the IP next-hop router. It is There is a problem with multicast, since multicast routing may not
therefore possible that a multicast end-point can not be properly be able to uniquely identify the IP next-hop router. It is
therefore possible for a multicast end-point to not be properly
identified. identified.
In the host case, some multicast over ATM control mechanisms, such In certain cases it is also possible to identify the list of all
as MARS, can be used to identify all end-points of a multicast best effort end-points. Some multicast over ATM control
group. In the router to router case, a multicast routing protocol mechanisms, such as MARS in mesh mode, can be used to identify all
may provide all next-hops for a particular multicast group. In end-points of a multicast group. Also, some multicast routing
either case, RSVP over ATM implementations must obtain a full list protocols can provide all next-hops for a particular multicast
of end-points, both QoS and non-QoS, using the appropriate group. In both cases, RSVP over ATM implementations can obtain a
mechanisms. The full list can be compared against the RSVP full list of end-points, both QoS and non-QoS, using the
identified end-points to determine the list of best-effort appropriate mechanisms. The full list can then be compared
receivers. against the RSVP identified end-points to determine the list of
best effort receivers.
There is no straightforward solution to uniquely identifying end- While there are cases where QoS and best effort end-points can be
points of multicast traffic handled by non-RSVP next hops. The identified, there is no straightforward solution to uniquely
preferred solution is to use multicast routing protocols that identifying end-points of multicast traffic handled by non-RSVP
support unique end-point identification. In cases where such next-hops. The preferred solution is to use multicast control
routing protocols are unavailable, all IP routers that will be mechanisms and routing protocols that support unique end-point
used to support RSVP over ATM should support RSVP. To ensure identification. In cases where such mechanisms and routing
proper behavior, baseline RSVP over ATM implementations MUST only protocols are unavailable, all IP routers that will be used to
support RSVP over ATM should support RSVP. To ensure proper
behavior, baseline RSVP over ATM implementations MUST only
establish RSVP-initiated VCs to RSVP capable end-points. It is establish RSVP-initiated VCs to RSVP capable end-points. It is
permissible to allow a user to override this behavior. permissible to allow a user to override this behavior.
3.3 Multicast Data Distribution 3.3 Multicast Data Distribution
Two models are planned for IP multicast data distribution over Two basic models exist for IP multicast data distribution over
ATM. In one model, senders establish point-to-multipoint VCs to ATM. In one model, senders establish point-to-multipoint VCs to
all ATM attached destinations, and data is then sent over these all ATM attached destinations, and data is then sent over these
VCs. This model is often called "multicast mesh" or "VC mesh" VCs. This model is often called "multicast mesh" or "VC mesh"
mode distribution. In the second model, senders send data over mode distribution. In the second model, senders send data over
point-to-point VCs to a central point and the central point relays point-to-point VCs to a central point and the central point relays
the data onto point-to-multipoint VCs that have been established the data onto point-to-multipoint VCs that have been established
to all receivers of the IP multicast group. This model is often to all receivers of the IP multicast group. This model is often
referred to as "multicast server" mode distribution. Figure 3 referred to as "multicast server" mode distribution. Figure 3
shows data flow for both modes of IP multicast data distribution. shows data flow for both modes of IP multicast data distribution.
The goal of RSVP over ATM solutions is to ensure that IP multicast
data is distributed with appropriate QoS.
_________ _________
/ \ / \
/ Multicast \ / Multicast \
\ Server / \ Server /
\_________/ \_________/
^ | | ^ | |
| | +--------+ | | +--------+
+-----+ | | | +-----+ | | |
| | -------+ | | Data Flow: | | -------+ | | Data Flow:
skipping to change at page 10, line 42 skipping to change at page 11, line 25
| | : | : +----+ ....> Mesh | | : | : +----+ ....> Mesh
+-----+ : | +...>| R1 | +-----+ : | +...>| R1 |
: | +----+ : | +----+
: V : V
: +----+ : +----+
+..> | R2 | +..> | R2 |
+----+ +----+
Figure 3: IP Multicast Data Distribution Over ATM Figure 3: IP Multicast Data Distribution Over ATM
Current multicast servers [1,2] do not support any mechanisms for The goal of RSVP over ATM solutions is to ensure that IP multicast
communicating QoS requirements to a multicast server. For this data is distributed with appropriate QoS. Current multicast
reason, RSVP over ATM implementations SHOULD support "mesh-mode" servers [1,2] do not support any mechanisms for communicating QoS
distribution for RSVP controlled multicast flows. When using requirements to a multicast server. For this reason, RSVP over
multicast servers that do not support QoS requests, a sender MUST ATM implementations SHOULD support "mesh-mode" distribution for
set the service, not global, break bit(s). Use of the service- RSVP controlled multicast flows. When using multicast servers
specific break bit tells the receiver(s) that RSVP and Integrated that do not support QoS requests, a sender MUST set the service,
Services are supported by the router but that the service cannot not global, break bit(s). Use of the service-specific break bit
be delivered over the ATM network for the specific request. tells the receiver(s) that RSVP and Integrated Services are
supported by the router but that the service cannot be delivered
over the ATM network for the specific request.
In the case of MARS[1], the selection of distribution modes is In the case of MARS[1], the selection of distribution modes is
administratively controlled. Therefore network administrators administratively controlled. Therefore network administrators
that desire proper RSVP over ATM operation MUST appropriately that desire proper RSVP over ATM operation MUST appropriately
configure their network to support mesh mode distribution for configure their network to support mesh mode distribution for
multicast groups that will be used in RSVP sessions. For LANE1.0 multicast groups that will be used in RSVP sessions. For LANE1.0
networks the only multicast distribution option is over the BUS, networks the only multicast distribution option is over the BUS,
which means that the break bit MUST always be set. For LANE2.0 which means that the break bit MUST always be set. For LANE2.0
[3] there are provisions that allow for non-BUS solutions with [3] there are provisions that allow for non-BUS solutions with
which it may be possible to ensure proper QoS delivery. which it may be possible to ensure proper QoS delivery.
3.4 Receiver Transitions 3.4 Receiver Transitions
When setting up a point-to-multipoint VCs there will be a time When setting up a point-to-multipoint VCs there will be a time
when some receivers have been added to a QoS VC and some have not. when some receivers have been added to a QoS VC and some have not.
During such transition times it is possible to start sending data During such transition times it is possible to start sending data
on the newly established VC. The issue is when to start send data on the newly established VC. If data is sent both on the new VC
on the new VC. If data is sent both on the new VC and the old VC, and the old VC, then data will be delivered with proper QoS to
then data will be delivered with proper QoS to some receivers and some receivers and with the old QoS to all receivers.
with the old QoS to all receivers. This means the QoS receivers Additionally, the QoS receivers would get duplicate data. If data
would get duplicate data. If data is sent just on the new QoS VC, is sent just on the new QoS VC, the receivers that have not yet
the receivers that have not yet been added will lose information. been added will miss data. So, the issue comes down to whether to
So, the issue comes down to whether to send to both the old and send to both the old and new VCs, or to just send to one of the
new VCs, or to send to just one of the VCs. In one case duplicate VCs. In one case duplicate data will be received, in the other
information will be received, in the other some information may some data may not be received. This issue needs to be considered
not be received. This issue needs to be considered for three for three cases: when establishing the first QoS VC, when
cases: when establishing the first QoS VC, when establishing a VC establishing a VC to support a QoS change, and when adding a new
to support a QoS change, and when adding a new end-point to an end-point to an already established QoS VC.
already established QoS VC.
The first two cases are essentially the same. In both, it is The first two cases are essentially the same. In both, it is
possible to send data on the partially completed new VC, and the possible to send data on the partially completed new VC. In both,
issue of duplicate versus lost information is similar. The last there is the option of duplicate or lost data. In order to ensure
case occurs when an end-point must be added to an existing QoS VC. predictable behavior and to conform to the requirement to deliver
In this case the end-point must be both added to the QoS VC and data to all receivers, data MUST NOT be sent on new VCs until all
dropped from a best-effort VC. The issue is which to do first. parties have been added. This will ensure that all data is only
If the add is first requested, then the end-point may get delivered once to all receivers.
duplicate information. If the drop is requested first, then the
end-point may loose information.
In order to ensure predictable behavior and to conform to the The last case differs from the others and occurs when an end-point
requirement to deliver data to all receivers, data MUST NOT be must be added to an existing QoS VC. In this case the end-point
sent on new VCs until all parties have been added. This will must be both added to the QoS VC and dropped from a best effort
ensure that all data is only delivered once to all receivers. VC. The issue is which to do first. If the add is first
This approach does not quite apply for the last case. In the last requested, then the end-point may get duplicate data. If the drop
case, the add MUST be completed first, then the drop. This last is requested first, then the end-point may miss data. In order to
behavior requires receivers to be prepared to receive some avoid loss of data, the add MUST be completed first and then
duplicate packets at times of QoS setup. followed by the drop. This behavior requires receivers to be
prepared to receive some duplicate packets at times of QoS setup.
4. Security 4. Security
The same considerations stated in [10] and [14] apply to this The same considerations stated in [7] and [10] apply to this
document. There are no additional security issues raised in this document. There are no additional security issues raised in this
document. document.
5. Acknowledgments 5. Acknowledgments
This work is based on earlier drafts [5,7] and comments from the This work is based on earlier drafts and comments from the ISSLL
ISSLL working group. The author would like to acknowledge their working group. The author would like to acknowledge their
contribution, most notably Steve Berson who coauthored [7]. contribution, most notably Steve Berson who coauthored one of the
drafts.
6. Author's Address 6. Author's Address
Lou Berger Lou Berger
FORE Systems FORE Systems
6905 Rockledge Drive 6905 Rockledge Drive
Suite 800 Suite 800
Bethesda, MD 20817 Bethesda, MD 20817
Phone: +1 301 571 2534 Phone: +1 301 571 2534
EMail: lberger@fore.com EMail: lberger@fore.com
REFERENCES REFERENCES
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[1] Armitage, G., "Support for Multicast over UNI 3.0/3.1 based ATM [1] Armitage, G., "Support for Multicast over UNI 3.0/3.1 based ATM
Networks," RFC 2022, November 1996. Networks," RFC 2022, November 1996.
[2] The ATM Forum, "LAN Emulation Over ATM Specification", Version 1.0. [2] The ATM Forum, "LAN Emulation Over ATM Specification", Version 1.0.
[3] The ATM Forum, "LAN Emulation over ATM Version 2 - LUNI [3] The ATM Forum, "LAN Emulation over ATM Version 2 - LUNI
Specification ", April 1997. Specification ", April 1997.
[4] The ATM Forum, "MPOA Baseline Version 1", May 1997. [4] The ATM Forum, "MPOA Baseline Version 1", May 1997.
[5] Berger, L., "RSVP over ATM: Framework and UNI3.0/3.1 Method", [5] Berger, L., "RSVP over ATM Implementation Guidelines", Internet
Internet Draft, June 1996. Draft, November 1997.
[6] Berger, L., "RSVP over ATM Implementation Guidelines", Internet
Draft, July 1997.
[7] Berson, S., Berger, L., "IP Integrated Services with RSVP over ATM,"
Internet Draft, draft-ietf-issll-atm-support-02.txt, November 1996.
[8] Borden, M., Crawley, E., Krawczyk, J, Baker, F., and Berson, S.,
"Issues for RSVP and Integrated Services over ATM," Internet Draft,
February 1996.
[9] Borden, M., and Garrett, M., "Interoperation of Controlled-Load and [6] Borden, M., and Garrett, M., "Interoperation of Controlled-Load and
Guaranteed-Service with ATM," Internet Draft, March 1997. Guaranteed-Service with ATM," Internet Draft, July 1997.
[10] Braden, R., Zhang, L., Berson, S., Herzog, S., and Jamin, S., [7] Braden, R., Zhang, L., Berson, S., Herzog, S., and Jamin, S.,
"Resource ReSerVation Protocol (RSVP) -- Version 1 Functional "Resource ReSerVation Protocol (RSVP) -- Version 1 Functional
Specification," Internet Draft, June 1997. Specification," RFC 2205, September 1997.
[11] Crawley, E., Berger, L., Berson, S., Baker, F., Borden, M., and [8] Crawley, E., Berger, L., Berson, S., Baker, F., Borden, M., and
Krawczyk, J, "Issues for Integrated Services and RSVP over ATM," Krawczyk, J, "Issues for Integrated Services and RSVP over ATM,"
Internet Draft, July 1997. Internet Draft, July 1997.
[12] Heinanen, J., "Multiprotocol Encapsulation over ATM Adaptation [9] Heinanen, J., "Multiprotocol Encapsulation over ATM Adaptation Layer
Layer 5," RFC 1483. 5," RFC 1483.
[13] Onvural, R., Srinivasan, V., "A Framework for Supporting RSVP Flows
Over ATM Networks," Internet Draft, March 1996.
[14] Perez, M., Liaw, F., Grossman, D., Mankin, A., Hoffman, E., and [10] Perez, M., Liaw, F., Grossman, D., Mankin, A., Hoffman, E., and
Malis, A., "ATM Signalling Support for IP over ATM," RFC 1755. Malis, A., "ATM Signalling Support for IP over ATM," RFC 1755.
[15] Maher, M., "ATM Signalling Support for IP over ATM - UNI 4.0 [11] Maher, M., "ATM Signalling Support for IP over ATM - UNI 4.0
Update" Internet Draft, May 1997. Update" Internet Draft, May 1997.
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