draft-ietf-rmcat-coupled-cc-05.txt   draft-ietf-rmcat-coupled-cc-06.txt 
RTP Media Congestion Avoidance S. Islam RTP Media Congestion Avoidance Techniques (rmcat) S. Islam
Techniques (rmcat) M. Welzl Internet-Draft M. Welzl
Internet-Draft S. Gjessing Intended status: Experimental S. Gjessing
Intended status: Experimental University of Oslo Expires: September 29, 2017 University of Oslo
Expires: June 10, 2017 December 7, 2016 March 28, 2017
Coupled congestion control for RTP media Coupled congestion control for RTP media
draft-ietf-rmcat-coupled-cc-05 draft-ietf-rmcat-coupled-cc-06
Abstract Abstract
When multiple congestion controlled RTP sessions traverse the same When multiple congestion controlled RTP sessions traverse the same
network bottleneck, combining their controls can improve the total network bottleneck, combining their controls can improve the total
on-the-wire behavior in terms of delay, loss and fairness. This on-the-wire behavior in terms of delay, loss and fairness. This
document describes such a method for flows that have the same sender, document describes such a method for flows that have the same sender,
in a way that is as flexible and simple as possible while minimizing in a way that is as flexible and simple as possible while minimizing
the amount of changes needed to existing RTP applications. It the amount of changes needed to existing RTP applications. It
specifies how to apply the method for the NADA congestion control specifies how to apply the method for the NADA congestion control
algorithm, and provides suggestions on how to apply it to other algorithm, and provides suggestions on how to apply it to other
congestion control algorithms. congestion control algorithms.
Status of this Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
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
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 10, 2017. This Internet-Draft will expire on September 29, 2017.
Copyright Notice Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Limitations . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Limitations . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Architectural overview . . . . . . . . . . . . . . . . . . . . 4 4. Architectural overview . . . . . . . . . . . . . . . . . . . 5
5. Roles . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5. Roles . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1. SBD . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5.1. SBD . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.2. FSE . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 5.2. FSE . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5.3. Flows . . . . . . . . . . . . . . . . . . . . . . . . . . 8 5.3. Flows . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5.3.1. Example algorithm 1 - Active FSE . . . . . . . . . . . 8 5.3.1. Example algorithm 1 - Active FSE . . . . . . . . . . 9
5.3.2. Example algorithm 2 - Conservative Active FSE . . . . 9 5.3.2. Example algorithm 2 - Conservative Active FSE . . . . 10
6. Application . . . . . . . . . . . . . . . . . . . . . . . . . 10 6. Application . . . . . . . . . . . . . . . . . . . . . . . . . 11
6.1. NADA . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 6.1. NADA . . . . . . . . . . . . . . . . . . . . . . . . . . 11
6.2. General recommendations . . . . . . . . . . . . . . . . . 11 6.2. General recommendations . . . . . . . . . . . . . . . . . 11
7. Expected feedback from experiments . . . . . . . . . . . . . . 12 7. Expected feedback from experiments . . . . . . . . . . . . . 12
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
10. Security Considerations . . . . . . . . . . . . . . . . . . . 12 10. Security Considerations . . . . . . . . . . . . . . . . . . . 13
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
11.1. Normative References . . . . . . . . . . . . . . . . . . . 13 11.1. Normative References . . . . . . . . . . . . . . . . . . 13
11.2. Informative References . . . . . . . . . . . . . . . . . . 13 11.2. Informative References . . . . . . . . . . . . . . . . . 14
Appendix A. Application to GCC . . . . . . . . . . . . . . . . . 15 Appendix A. Application to GCC . . . . . . . . . . . . . . . . . 15
Appendix B. Scheduling . . . . . . . . . . . . . . . . . . . . . 15 Appendix B. Scheduling . . . . . . . . . . . . . . . . . . . . . 16
Appendix C. Example algorithm - Passive FSE . . . . . . . . . . . 15 Appendix C. Example algorithm - Passive FSE . . . . . . . . . . 16
C.1. Example operation (passive) . . . . . . . . . . . . . . . 18 C.1. Example operation (passive) . . . . . . . . . . . . . . . 19
Appendix D. Change log . . . . . . . . . . . . . . . . . . . . . 22 Appendix D. Change log . . . . . . . . . . . . . . . . . . . . . 23
D.1. draft-welzl-rmcat-coupled-cc . . . . . . . . . . . . . . . 22 D.1. draft-welzl-rmcat-coupled-cc . . . . . . . . . . . . . . 23
D.1.1. Changes from -00 to -01 . . . . . . . . . . . . . . . 22 D.1.1. Changes from -00 to -01 . . . . . . . . . . . . . . . 23
D.1.2. Changes from -01 to -02 . . . . . . . . . . . . . . . 22 D.1.2. Changes from -01 to -02 . . . . . . . . . . . . . . . 23
D.1.3. Changes from -02 to -03 . . . . . . . . . . . . . . . 23 D.1.3. Changes from -02 to -03 . . . . . . . . . . . . . . . 23
D.1.4. Changes from -03 to -04 . . . . . . . . . . . . . . . 23 D.1.4. Changes from -03 to -04 . . . . . . . . . . . . . . . 24
D.1.5. Changes from -04 to -05 . . . . . . . . . . . . . . . 23 D.1.5. Changes from -04 to -05 . . . . . . . . . . . . . . . 24
D.2. draft-ietf-rmcat-coupled-cc . . . . . . . . . . . . . . . 23 D.2. draft-ietf-rmcat-coupled-cc . . . . . . . . . . . . . . . 24
D.2.1. Changes from draft-welzl-rmcat-coupled-cc-05 . . . . . 23 D.2.1. Changes from draft-welzl-rmcat-coupled-cc-05 . . . . 24
D.2.2. Changes from -00 to -01 . . . . . . . . . . . . . . . 23 D.2.2. Changes from -00 to -01 . . . . . . . . . . . . . . . 24
D.2.3. Changes from -01 to -02 . . . . . . . . . . . . . . . 23 D.2.3. Changes from -01 to -02 . . . . . . . . . . . . . . . 24
D.2.4. Changes from -02 to -03 . . . . . . . . . . . . . . . 24 D.2.4. Changes from -02 to -03 . . . . . . . . . . . . . . . 24
D.2.5. Changes from -03 to -04 . . . . . . . . . . . . . . . 24 D.2.5. Changes from -03 to -04 . . . . . . . . . . . . . . . 24
D.2.6. Changes from -04 to -05 . . . . . . . . . . . . . . . 24 D.2.6. Changes from -04 to -05 . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 24 D.2.7. Changes from -05 to -06 . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25
1. Introduction 1. Introduction
When there is enough data to send, a congestion controller must When there is enough data to send, a congestion controller must
increase its sending rate until the path's capacity has been reached; increase its sending rate until the path's capacity has been reached;
depending on the controller, sometimes the rate is increased further, depending on the controller, sometimes the rate is increased further,
until packets are ECN-marked or dropped. This process inevitably until packets are ECN-marked or dropped. This process inevitably
creates undesirable queuing delay when multiple congestion controlled creates undesirable queuing delay when multiple congestion controlled
connections traverse the same network bottleneck. connections traverse the same network bottleneck.
skipping to change at page 3, line 27 skipping to change at page 3, line 27
connection congestion control functionality, which is quite a connection congestion control functionality, which is quite a
significant change to existing RTP based applications. This document significant change to existing RTP based applications. This document
presents a method to combine the behavior of congestion control presents a method to combine the behavior of congestion control
mechanisms that is easier to implement than the Congestion Manager mechanisms that is easier to implement than the Congestion Manager
[RFC3124] and also requires less significant changes to existing RTP [RFC3124] and also requires less significant changes to existing RTP
based applications. It attempts to roughly approximate the CM based applications. It attempts to roughly approximate the CM
behavior by sharing information between existing congestion behavior by sharing information between existing congestion
controllers. It is able to honor user-specified priorities, which is controllers. It is able to honor user-specified priorities, which is
required by rtcweb [RFC7478]. required by rtcweb [RFC7478].
The described mechanisms are believed safe to use, but are
experimental and are presented for wider review and operational
evaluation.
2. Definitions 2. Definitions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
Available Bandwidth: Available Bandwidth:
The available bandwidth is the nominal link capacity minus the The available bandwidth is the nominal link capacity minus the
amount of traffic that traversed the link during a certain time amount of traffic that traversed the link during a certain time
interval, divided by that time interval. interval, divided by that time interval.
Bottleneck: Bottleneck:
The first link with the smallest available bandwidth along the The first link with the smallest available bandwidth along the
path between a sender and receiver. path between a sender and receiver.
Flow: Flow:
A flow is the entity that congestion control is operating on. A flow is the entity that congestion control is operating on.
It could, for example, be a transport layer connection, an RTP It could, for example, be a transport layer connection, an RTP
session, or a subsession that is multiplexed onto a single RTP stream [RFC7656], whether or not this RTP stream is multiplexed
session together with other subsessions. onto an RTP session with other RTP streams.
Flow Group Identifier (FGI): Flow Group Identifier (FGI):
A unique identifier for each subset of flows that is limited by A unique identifier for each subset of flows that is limited by
a common bottleneck. a common bottleneck.
Flow State Exchange (FSE): Flow State Exchange (FSE):
The entity that maintains information that is exchanged between The entity that maintains information that is exchanged between
flows. flows.
Flow Group (FG): Flow Group (FG):
A group of flows having the same FGI. A group of flows having the same FGI.
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instead updates information in the FSE and performs a query on the instead updates information in the FSE and performs a query on the
FSE, leading to a sending rate that can be different from what the FSE, leading to a sending rate that can be different from what the
congestion controller originally determined. Using information congestion controller originally determined. Using information
about/from the currently active flows, SBD updates the FSE with the about/from the currently active flows, SBD updates the FSE with the
correct Flow State Identifiers (FSIs). This document describes both correct Flow State Identifiers (FSIs). This document describes both
active and passive versions, however the passive version is put into active and passive versions, however the passive version is put into
the appendix as it is extremely experimental. Figure 2 shows the the appendix as it is extremely experimental. Figure 2 shows the
interaction between flows and the FSE, using the variable names interaction between flows and the FSE, using the variable names
defined in Section 5.2. defined in Section 5.2.
------- <--- Flow 1 ------- <--- Flow 1
| FSE | <--- Flow 2 .. | FSE | <--- Flow 2 ..
------- <--- .. Flow N ------- <--- .. Flow N
^ ^
| | | |
------- | ------- |
| SBD | <-------| | SBD | <-------|
------- -------
Figure 1: Coupled congestion control architecture Figure 1: Coupled congestion control architecture
Flow#1(cc) FSE Flow#2(cc) Flow#1(cc) FSE Flow#2(cc)
---------- --- ---------- ---------- --- ----------
#1 JOIN ----register--> REGISTER #1 JOIN ----register--> REGISTER
REGISTER <--register-- JOIN #1 REGISTER <--register-- JOIN #1
#2 CC_R ----UPDATE----> UPDATE (in) #2 CC_R(1) ----UPDATE----> UPDATE (in)
#3 NEW RATE <---FSE_R------ UPDATE (out) --FSE_R----> #3 NEW RATE #3 NEW RATE <---FSE_R(1)-- UPDATE (out) --FSE_R(2)-> #3 NEW RATE
Figure 2: Flow-FSE interaction Figure 2: Flow-FSE interaction
Since everything shown in Figure 1 is assumed to operate on a single Since everything shown in Figure 1 is assumed to operate on a single
host (the sender) only, this document only describes aspects that host (the sender) only, this document only describes aspects that
have an influence on the resulting on-the-wire behavior. It does, have an influence on the resulting on-the-wire behavior. It does,
for instance, not define how many bits must be used to represent for instance, not define how many bits must be used to represent
FSIs, or in which way the entities communicate. Implementations can FSIs, or in which way the entities communicate. Implementations can
take various forms: for instance, all the elements in the figure take various forms: for instance, all the elements in the figure
could be implemented within a single application, thereby operating could be implemented within a single application, thereby operating
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5.1. SBD 5.1. SBD
SBD uses knowledge about the flows to determine which flows belong in SBD uses knowledge about the flows to determine which flows belong in
the same Flow Group (FG), and assigns FGIs accordingly. This the same Flow Group (FG), and assigns FGIs accordingly. This
knowledge can be derived in three basic ways: knowledge can be derived in three basic ways:
1. From multiplexing: it can be based on the simple assumption that 1. From multiplexing: it can be based on the simple assumption that
packets sharing the same five-tuple (IP source and destination packets sharing the same five-tuple (IP source and destination
address, protocol, and transport layer port number pair) and address, protocol, and transport layer port number pair) and
having the same Differentiated Services Code Point (DSCP) in the having the same values for the Differentiated Services Code Point
IP header are typically treated in the same way along the path. (DSCP) and the ECN field in the IP header are typically treated
The latter method is the only one specified in this document: SBD in the same way along the path. The latter method is the only
MAY consider all flows that use the same five-tuple and DSCP to one specified in this document: SBD MAY consider all flows that
belong to the same FG. This classification applies to certain use the same five-tuple, DSCP and ECN field value to belong to
tunnels, or RTP flows that are multiplexed over one transport the same FG. This classification applies to certain tunnels, or
(cf. [transport-multiplex]). Such multiplexing is also a RTP flows that are multiplexed over one transport (cf.
recommended usage of RTP in rtcweb [rtcweb-rtp-usage]. [transport-multiplex]). Such multiplexing is also a recommended
usage of RTP in rtcweb [rtcweb-rtp-usage].
2. Via configuration: e.g. by assuming that a common wireless uplink 2. Via configuration: e.g. by assuming that a common wireless uplink
is also a shared bottleneck. is also a shared bottleneck.
3. From measurements: e.g. by considering correlations among 3. From measurements: e.g. by considering correlations among
measured delay and loss as an indication of a shared bottleneck. measured delay and loss as an indication of a shared bottleneck.
The methods above have some essential trade-offs: e.g., multiplexing The methods above have some essential trade-offs: e.g., multiplexing
is a completely reliable measure, however it is limited in scope to is a completely reliable measure, however it is limited in scope to
two end points (i.e., it cannot be applied to couple congestion two end points (i.e., it cannot be applied to couple congestion
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[I-D.ietf-rmcat-sbd] for details). Using system configuration to [I-D.ietf-rmcat-sbd] for details). Using system configuration to
decide about shared bottlenecks can be more efficient (faster to decide about shared bottlenecks can be more efficient (faster to
obtain) than using measurements, but it relies on assumptions about obtain) than using measurements, but it relies on assumptions about
the network environment. the network environment.
5.2. FSE 5.2. FSE
The FSE contains a list of all flows that have registered with it. The FSE contains a list of all flows that have registered with it.
For each flow, it stores the following: For each flow, it stores the following:
o a unique flow number to identify the flow o a unique flow number f to identify the flow.
o the FGI of the FG that it belongs to (based on the definitions in o the FGI of the FG that it belongs to (based on the definitions in
this document, a flow has only one bottleneck, and can therefore this document, a flow has only one bottleneck, and can therefore
be in only one FG) be in only one FG).
o a priority P, which here is assumed to be represented as a o a priority P(f), which is a positive number, greater than zero.
floating point number in the range from 0.1 (unimportant) to 1
(very important).
o The rate used by the flow in bits per second, FSE_R. o The rate used by the flow in bits per second, FSE_R(f).
Note that the priority does not need to be a floating point value and Note that the absolute range of priorities does not matter: the
its value range does not matter for this algorithm: the algorithm algorithm works with a flow's priority portion of the sum of all
works with a flow's priority portion of the sum of all priority priority values. For example, if there are two flows, flow 1 with
values. Priorities can therefore be mapped to the "very-low", "low", priority 1 and flow 2 with priority 2, the sum of the priorities is
"medium" or "high" priority levels described in 3. Then, flow 1 will be assigned 1/3 of the aggregate sending rate
[I-D.ietf-rtcweb-transports] using the values 1, 2, 4 and 8, and flow 2 will be assigned 2/3 of the aggregate sending rate.
respectively.
Priorities can be mapped to the "very-low", "low", "medium" or "high"
priority levels described in [I-D.ietf-rtcweb-transports] by simply
using the values 1, 2, 4 and 8, respectively.
In the FSE, each FG contains one static variable S_CR which is the In the FSE, each FG contains one static variable S_CR which is the
sum of the calculated rates of all flows in the same FG. This value sum of the calculated rates of all flows in the same FG. This value
is used to calculate the sending rate. is used to calculate the sending rate.
The information listed here is enough to implement the sample flow The information listed here is enough to implement the sample flow
algorithm given below. FSE implementations could easily be extended algorithm given below. FSE implementations could easily be extended
to store, e.g., a flow's current sending rate for statistics to store, e.g., a flow's current sending rate for statistics
gathering or future potential optimizations. gathering or future potential optimizations.
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sending rate. Via UPDATE, they provide the newly calculated rate and sending rate. Via UPDATE, they provide the newly calculated rate and
optionally (if the algorithm supports it) the desired rate. The optionally (if the algorithm supports it) the desired rate. The
desired rate is less than the calculated rate in case of application- desired rate is less than the calculated rate in case of application-
limited flows; otherwise, it is the same as the calculated rate. limited flows; otherwise, it is the same as the calculated rate.
Below, two example algorithms are described. While other algorithms Below, two example algorithms are described. While other algorithms
could be used instead, the same algorithm must be applied to all could be used instead, the same algorithm must be applied to all
flows. Names of variables used in the algorithms are explained flows. Names of variables used in the algorithms are explained
below. below.
o CC_R - The rate received from a flow's congestion controller when o CC_R(f) - The rate received from the congestion controller of flow
it calls UPDATE. f when it calls UPDATE.
o FSE_R - The rate calculated by the FSE for a flow. o FSE_R(f) - The rate calculated by the FSE for flow f.
o S_CR - The sum of the calculated rates of all flows in the same o S_CR - The sum of the calculated rates of all flows in the same
FG; this value is used to calculate the sending rate. FG; this value is used to calculate the sending rate.
o FG - A group of flows having the same FGI, and hence sharing the o FG - A group of flows having the same FGI, and hence sharing the
same bottleneck. same bottleneck.
o P - The priority of a flow which is received from the flow's o P(f) - The priority of flow f which is received from the flow's
congestion controller; the FSE uses this variable for calculating congestion controller; the FSE uses this variable for calculating
FSE R. FSE_R(f).
o S_P - The sum of all the priorities. o S_P - The sum of all the priorities.
5.3.1. Example algorithm 1 - Active FSE 5.3.1. Example algorithm 1 - Active FSE
This algorithm was designed to be the simplest possible method to This algorithm was designed to be the simplest possible method to
assign rates according to the priorities of flows. Simulations assign rates according to the priorities of flows. Simulations
results in [fse] indicate that it does however not significantly results in [fse] indicate that it does however not significantly
reduce queuing delay and packet loss. reduce queuing delay and packet loss.
(1) When a flow f starts, it registers itself with SBD and the FSE. (1) When a flow f starts, it registers itself with SBD and the FSE.
FSE_R is initialized with the congestion controller's initial FSE_R(f) is initialized with the congestion controller's initial
rate. SBD will assign the correct FGI. When a flow is assigned rate. SBD will assign the correct FGI. When a flow is assigned
an FGI, it adds its FSE_R to S_CR. an FGI, it adds its FSE_R(f) to S_CR.
(2) When a flow f stops or pauses, its entry is removed from the (2) When a flow f stops or pauses, its entry is removed from the
list. list.
(3) Every time the congestion controller of the flow f determines a (3) Every time the congestion controller of the flow f determines a
new sending rate CC_R, the flow calls UPDATE, which carries out new sending rate CC_R(f), the flow calls UPDATE, which carries
the tasks listed below to derive the new sending rates for all out the tasks listed below to derive the new sending rates for
the flows in the FG. A flow's UPDATE function uses a local all the flows in the FG. A flow's UPDATE function uses a local
(i.e. per-flow) temporary variable S_P, which is the sum of all (i.e. per-flow) temporary variable S_P, which is the sum of all
the priorities. the priorities.
(a) It updates S_CR. (a) It updates S_CR.
S_CR = S_CR + CC_R - FSE_R(f) S_CR = S_CR + CC_R(f) - FSE_R(f)
(b) It calculates the sum of all the priorities, S_P. (b) It calculates the sum of all the priorities, S_P.
S_P = 0 S_P = 0
for all flows i in FG do for all flows i in FG do
S_P = S_P + P(i) S_P = S_P + P(i)
end for end for
(c) It calculates the sending rates for all the flows in an FG (c) It calculates the sending rates for all the flows in an FG
and distributes them. and distributes them.
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end for end for
5.3.2. Example algorithm 2 - Conservative Active FSE 5.3.2. Example algorithm 2 - Conservative Active FSE
This algorithm extends algorithm 1 to conservatively emulate the This algorithm extends algorithm 1 to conservatively emulate the
behavior of a single flow by proportionally reducing the aggregate behavior of a single flow by proportionally reducing the aggregate
rate on congestion. Simulations results in [fse] indicate that it rate on congestion. Simulations results in [fse] indicate that it
can significantly reduce queuing delay and packet loss. can significantly reduce queuing delay and packet loss.
(1) When a flow f starts, it registers itself with SBD and the FSE. (1) When a flow f starts, it registers itself with SBD and the FSE.
FSE_R is initialized with the congestion controller's initial FSE_R(f) is initialized with the congestion controller's initial
rate. SBD will assign the correct FGI. When a flow is assigned rate. SBD will assign the correct FGI. When a flow is assigned
an FGI, it adds its FSE_R to S_CR. an FGI, it adds its FSE_R(f) to S_CR.
(2) When a flow f stops or pauses, its entry is removed from the (2) When a flow f stops or pauses, its entry is removed from the
list. list.
(3) Every time the congestion controller of the flow f determines a (3) Every time the congestion controller of the flow f determines a
new sending rate CC_R, the flow calls UPDATE, which carries out new sending rate CC_R(f), the flow calls UPDATE, which carries
the tasks listed below to derive the new sending rates for all out the tasks listed below to derive the new sending rates for
the flows in the FG. A flow's UPDATE function uses a local all the flows in the FG. A flow's UPDATE function uses a local
(i.e. per-flow) temporary variable S_P, which is the sum of all (i.e. per-flow) temporary variable S_P, which is the sum of all
the priorities, and a local variable DELTA, which is used to the priorities, and a local variable DELTA, which is used to
calculate the difference between CC_R and the previously stored calculate the difference between CC_R(f) and the previously
FSE_R. To prevent flows from either ignoring congestion or stored FSE_R(f). To prevent flows from either ignoring
overreacting, a timer keeps them from changing their rates congestion or overreacting, a timer keeps them from changing
immediately after the common rate reduction that follows a their rates immediately after the common rate reduction that
congestion event. This timer is set to 2 RTTs of the flow that follows a congestion event. This timer is set to 2 RTTs of the
experienced congestion because it is assumed that a congestion flow that experienced congestion because it is assumed that a
event can persist for up to one RTT of that flow, with another congestion event can persist for up to one RTT of that flow,
RTT added to compensate for fluctuations in the measured RTT with another RTT added to compensate for fluctuations in the
value. measured RTT value.
(a) It updates S_CR based on DELTA. (a) It updates S_CR based on DELTA.
if Timer has expired or not set then if Timer has expired or not set then
DELTA = CC_R - FSE_R(f) DELTA = CC_R(f) - FSE_R(f)
if DELTA < 0 then // Reduce S_CR proportionally if DELTA < 0 then // Reduce S_CR proportionally
S_CR = S_CR * CC_R / FSE_R(f) S_CR = S_CR * CC_R(f) / FSE_R(f)
Set Timer for 2 RTTs Set Timer for 2 RTTs
else else
S_CR = S_CR + DELTA S_CR = S_CR + DELTA
end if end if
end if end if
(b) It calculates the sum of all the priorities, S_P. (b) It calculates the sum of all the priorities, S_P.
S_P = 0 S_P = 0
for all flows i in FG do for all flows i in FG do
skipping to change at page 12, line 17 skipping to change at page 12, line 33
The algorithm described in this memo has so far been evaluated using The algorithm described in this memo has so far been evaluated using
simulations covering all the tests for more than one flow from simulations covering all the tests for more than one flow from
[I-D.ietf-rmcat-eval-test] (see [IETF-93], [IETF-94]). Experiments [I-D.ietf-rmcat-eval-test] (see [IETF-93], [IETF-94]). Experiments
should confirm these results using at least the NADA congestion should confirm these results using at least the NADA congestion
control algorithm with real-life code (e.g., browsers communicating control algorithm with real-life code (e.g., browsers communicating
over an emulated network covering the conditions in over an emulated network covering the conditions in
[I-D.ietf-rmcat-eval-test]. The tests with real-life code should be [I-D.ietf-rmcat-eval-test]. The tests with real-life code should be
repeated afterwards in real network environments and monitored. repeated afterwards in real network environments and monitored.
Experiments should investigate cases where the media coder's output Experiments should investigate cases where the media coder's output
rate is below the rate that is calculated by the coupling algorithm rate is below the rate that is calculated by the coupling algorithm
(FSE_R in algorithms 1 and 2, section 5.3). Implementers and testers (FSE_R(i) in algorithms 1 and 2, section 5.3). Implementers and
are invited to document their findings in an Internet draft. testers are invited to document their findings in an Internet draft.
8. Acknowledgements 8. Acknowledgements
This document has benefitted from discussions with and feedback from This document has benefitted from discussions with and feedback from
Andreas Petlund, Anna Brunstrom, David Hayes, David Ros (who also Andreas Petlund, Anna Brunstrom, Colin Perkins, David Hayes, David
gave the FSE its name), Ingemar Johansson, Karen Nielsen, Kristian Ros (who also gave the FSE its name), Ingemar Johansson, Karen
Hiorth, Mirja Kuehlewind, Martin Stiemerling, Varun Singh, Xiaoqing Nielsen, Kristian Hiorth, Mirja Kuehlewind, Martin Stiemerling, Varun
Zhu, and Zaheduzzaman Sarker. The authors would like to especially Singh, Xiaoqing Zhu, and Zaheduzzaman Sarker. The authors would like
thank Xiaoqing Zhu and Stefan Holmer for helping with NADA and GCC. to especially thank Xiaoqing Zhu and Stefan Holmer for helping with
NADA and GCC.
This work was partially funded by the European Community under its This work was partially funded by the European Community under its
Seventh Framework Programme through the Reducing Internet Transport Seventh Framework Programme through the Reducing Internet Transport
Latency (RITE) project (ICT-317700). Latency (RITE) project (ICT-317700).
9. IANA Considerations 9. IANA Considerations
This memo includes no request to IANA. This memo includes no request to IANA.
10. Security Considerations 10. Security Considerations
skipping to change at page 13, line 22 skipping to change at page 13, line 39
a fair allocation in which the priority mechanism is implicitly a fair allocation in which the priority mechanism is implicitly
eliminated, and no major harm is done. eliminated, and no major harm is done.
11. References 11. References
11.1. Normative References 11.1. Normative References
[I-D.ietf-rmcat-nada] [I-D.ietf-rmcat-nada]
Zhu, X., Pan, R., Ramalho, M., Cruz, S., Jones, P., Fu, Zhu, X., Pan, R., Ramalho, M., Cruz, S., Jones, P., Fu,
J., D'Aronco, S., and C. Ganzhorn, "NADA: A Unified J., D'Aronco, S., and C. Ganzhorn, "NADA: A Unified
Congestion Control Scheme for Real-Time Media", Congestion Control Scheme for Real-Time Media", draft-
draft-ietf-rmcat-nada-03 (work in progress), ietf-rmcat-nada-03 (work in progress), September 2016.
September 2016.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/ Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
RFC2119, March 1997, RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
[RFC3124] Balakrishnan, H. and S. Seshan, "The Congestion Manager", [RFC3124] Balakrishnan, H. and S. Seshan, "The Congestion Manager",
RFC 3124, DOI 10.17487/RFC3124, June 2001, RFC 3124, DOI 10.17487/RFC3124, June 2001,
<http://www.rfc-editor.org/info/rfc3124>. <http://www.rfc-editor.org/info/rfc3124>.
[RFC5348] Floyd, S., Handley, M., Padhye, J., and J. Widmer, "TCP [RFC5348] Floyd, S., Handley, M., Padhye, J., and J. Widmer, "TCP
Friendly Rate Control (TFRC): Protocol Specification", Friendly Rate Control (TFRC): Protocol Specification", RFC
RFC 5348, DOI 10.17487/RFC5348, September 2008, 5348, DOI 10.17487/RFC5348, September 2008,
<http://www.rfc-editor.org/info/rfc5348>. <http://www.rfc-editor.org/info/rfc5348>.
11.2. Informative References 11.2. Informative References
[anrw2016]
Islam, S. and M. Welzl, "Start Me Up:Determining and
Sharing TCP's Initial Congestion Window", ACM, IRTF, ISOC
Applied Networking Research Workshop 2016 (ANRW 2016) ,
2016.
[fse] Islam, S., Welzl, M., Gjessing, S., and N. Khademi,
"Coupled Congestion Control for RTP Media", ACM SIGCOMM
Capacity Sharing Workshop (CSWS 2014) and ACM SIGCOMM CCR
44(4) 2014; extended version available as a technical
report from
http://safiquli.at.ifi.uio.no/paper/fse-tech-report.pdf ,
2014.
[fse-noms]
Islam, S., Welzl, M., Hayes, D., and S. Gjessing,
"Managing Real-Time Media Flows through a Flow State
Exchange", IEEE NOMS 2016, Istanbul, Turkey , 2016.
[I-D.ietf-rmcat-eval-test] [I-D.ietf-rmcat-eval-test]
Sarker, Z., Singh, V., Zhu, X., and M. Ramalho, "Test Sarker, Z., Singh, V., Zhu, X., and M. Ramalho, "Test
Cases for Evaluating RMCAT Proposals", Cases for Evaluating RMCAT Proposals", draft-ietf-rmcat-
draft-ietf-rmcat-eval-test-04 (work in progress), eval-test-04 (work in progress), October 2016.
October 2016.
[I-D.ietf-rmcat-gcc] [I-D.ietf-rmcat-gcc]
Holmer, S., Lundin, H., Carlucci, G., Cicco, L., and S. Holmer, S., Lundin, H., Carlucci, G., Cicco, L., and S.
Mascolo, "A Google Congestion Control Algorithm for Real- Mascolo, "A Google Congestion Control Algorithm for Real-
Time Communication", draft-ietf-rmcat-gcc-02 (work in Time Communication", draft-ietf-rmcat-gcc-02 (work in
progress), July 2016. progress), July 2016.
[I-D.ietf-rmcat-sbd] [I-D.ietf-rmcat-sbd]
Hayes, D., Ferlin, S., Welzl, M., and K. Hiorth, "Shared Hayes, D., Ferlin, S., Welzl, M., and K. Hiorth, "Shared
Bottleneck Detection for Coupled Congestion Control for Bottleneck Detection for Coupled Congestion Control for
RTP Media.", draft-ietf-rmcat-sbd-04 (work in progress), RTP Media.", draft-ietf-rmcat-sbd-04 (work in progress),
March 2016. March 2016.
[I-D.ietf-rtcweb-transports] [I-D.ietf-rtcweb-transports]
Alvestrand, H., "Transports for WebRTC", Alvestrand, H., "Transports for WebRTC", Internet-draft
draft-ietf-rtcweb-transports-11.txt (work in progress), draft-ietf-rtcweb-transports-17.txt, October 2016.
January 2016.
[IETF-93] Islam, S., Welzl, M., and S. Gjessing, "Updates on Coupled [IETF-93] Islam, S., Welzl, M., and S. Gjessing, "Updates on Coupled
Congestion Control for RTP Media", July 2015, Congestion Control for RTP Media", July 2015,
<https://www.ietf.org/proceedings/93/rmcat.html>. <https://www.ietf.org/proceedings/93/rmcat.html>.
[IETF-94] Islam, S., Welzl, M., and S. Gjessing, "Updates on Coupled [IETF-94] Islam, S., Welzl, M., and S. Gjessing, "Updates on Coupled
Congestion Control for RTP Media", November 2015, Congestion Control for RTP Media", November 2015,
<https://www.ietf.org/proceedings/94/rmcat.html>. <https://www.ietf.org/proceedings/94/rmcat.html>.
[RFC7478] Holmberg, C., Hakansson, S., and G. Eriksson, "Web Real- [RFC7478] Holmberg, C., Hakansson, S., and G. Eriksson, "Web Real-
Time Communication Use Cases and Requirements", RFC 7478, Time Communication Use Cases and Requirements", RFC 7478,
DOI 10.17487/RFC7478, March 2015, DOI 10.17487/RFC7478, March 2015,
<http://www.rfc-editor.org/info/rfc7478>. <http://www.rfc-editor.org/info/rfc7478>.
[anrw2016] [RFC7656] Lennox, J., Gross, K., Nandakumar, S., Salgueiro, G., and
Islam, S. and M. Welzl, "Start Me Up:Determining and B. Burman, Ed., "A Taxonomy of Semantics and Mechanisms
Sharing TCP's Initial Congestion Window", ACM, IRTF, ISOC for Real-Time Transport Protocol (RTP) Sources", RFC 7656,
Applied Networking Research Workshop 2016 (ANRW 2016) , DOI 10.17487/RFC7656, November 2015,
2016. <http://www.rfc-editor.org/info/rfc7656>.
[fse] Islam, S., Welzl, M., Gjessing, S., and N. Khademi,
"Coupled Congestion Control for RTP Media", ACM SIGCOMM
Capacity Sharing Workshop (CSWS 2014) and ACM SIGCOMM CCR
44(4) 2014; extended version available as a technical
report from
http://safiquli.at.ifi.uio.no/paper/fse-tech-report.pdf ,
2014.
[fse-noms]
Islam, S., Welzl, M., Hayes, D., and S. Gjessing,
"Managing Real-Time Media Flows through a Flow State
Exchange", IEEE NOMS 2016, Istanbul, Turkey , 2016.
[rtcweb-rtp-usage] [rtcweb-rtp-usage]
Perkins, C., Westerlund, M., and J. Ott, "Web Real-Time Perkins, C., Westerlund, M., and J. Ott, "Web Real-Time
Communication (WebRTC): Media Transport and Use of RTP", Communication (WebRTC): Media Transport and Use of RTP",
draft-ietf-rtcweb-rtp-usage-26.txt (work in progress), Internet-draft draft-ietf-rtcweb-rtp-usage-26.txt, March
March 2016. 2016.
[transport-multiplex] [transport-multiplex]
Westerlund, M. and C. Perkins, "Multiple RTP Sessions on a Westerlund, M. and C. Perkins, "Multiple RTP Sessions on a
Single Lower-Layer Transport", Single Lower-Layer Transport", Internet-draft draft-
draft-westerlund-avtcore-transport-multiplexing-07.txt westerlund-avtcore-transport-multiplexing-07.txt, October
(work in progress), October 2013. 2013.
Appendix A. Application to GCC Appendix A. Application to GCC
Google Congestion Control (GCC) [I-D.ietf-rmcat-gcc] is another Google Congestion Control (GCC) [I-D.ietf-rmcat-gcc] is another
congestion control scheme for RTP flows that is under development. congestion control scheme for RTP flows that is under development.
GCC is not yet finalised, but at the time of this writing, the rate GCC is not yet finalised, but at the time of this writing, the rate
control of GCC employs two parts: controlling the bandwidth estimate control of GCC employs two parts: controlling the bandwidth estimate
based on delay, and controlling the bandwidth estimate based on loss. based on delay, and controlling the bandwidth estimate based on loss.
Both are designed to estimate the available bandwidth, A_hat. Both are designed to estimate the available bandwidth, A_hat.
skipping to change at page 16, line 8 skipping to change at page 16, line 29
rate that should be used instead of the rate that the congestion rate that should be used instead of the rate that the congestion
controller has determined. This can make a passive algorithm easier controller has determined. This can make a passive algorithm easier
to implement; however, when round-trip times of flows are unequal, to implement; however, when round-trip times of flows are unequal,
shorter-RTT flows may (depending on the congestion control algorithm) shorter-RTT flows may (depending on the congestion control algorithm)
update and react to the overall FSE state more often than longer-RTT update and react to the overall FSE state more often than longer-RTT
flows, which can produce unwanted side effects. This problem is more flows, which can produce unwanted side effects. This problem is more
significant when the congestion control convergence depends on the significant when the congestion control convergence depends on the
RTT. While the passive algorithm works better for congestion RTT. While the passive algorithm works better for congestion
controls with RTT-independent convergence, it can still produce controls with RTT-independent convergence, it can still produce
oscillations on short time scales. The algorithm described below is oscillations on short time scales. The algorithm described below is
therefore considered as highly experimental. Results of a simplified therefore considered as highly experimental and not safe to deploy
passive FSE algorithm with both NADA and GCC can be found in outside of testbed environments. Results of a simplified passive FSE
[fse-noms]. algorithm with both NADA and GCC can be found in [fse-noms].
This passive version of the FSE stores the following information in This passive version of the FSE stores the following information in
addition to the variables described in Section 5.2: addition to the variables described in Section 5.2:
o The desired rate DR. This can be smaller than the calculated rate o The desired rate DR(f) of flow f. This can be smaller than the
if the application feeding into the flow has less data to send calculated rate if the application feeding into the flow has less
than the congestion controller would allow. In case of a bulk data to send than the congestion controller would allow. In case
transfer, DR must be set to CC_R received from the flow's of a bulk transfer, DR(f) must be set to CC_R(f) received from the
congestion module. congestion module of flow f.
The passive version of the FSE contains one static variable per FG The passive version of the FSE contains one static variable per FG
called TLO (Total Leftover Rate -- used to let a flow 'take' called TLO (Total Leftover Rate -- used to let a flow 'take'
bandwidth from application-limited or terminated flows) which is bandwidth from application-limited or terminated flows) which is
initialized to 0. For the passive version, S_CR is limited to initialized to 0. For the passive version, S_CR is limited to
increase or decrease as conservatively as a flow's congestion increase or decrease as conservatively as a flow's congestion
controller decides in order to prohibit sudden rate jumps. controller decides in order to prohibit sudden rate jumps.
(1) When a flow f starts, it registers itself with SBD and the FSE. (1) When a flow f starts, it registers itself with SBD and the FSE.
FSE_R and DR are initialized with the congestion controller's FSE_R(f) and DR(f) are initialized with the congestion
initial rate. SBD will assign the correct FGI. When a flow is controller's initial rate. SBD will assign the correct FGI.
assigned an FGI, it adds its FSE_R to S_CR. When a flow is assigned an FGI, it adds its FSE_R(f) to S_CR.
(2) When a flow f stops or pauses, it sets its DR to 0 and sets P to (2) When a flow f stops or pauses, it sets its DR(f) to 0 and sets
-1. P(f) to -1.
(3) Every time the congestion controller of the flow f determines a (3) Every time the congestion controller of the flow f determines a
new sending rate CC_R, assuming the flow's new desired rate new sending rate CC_R(f), assuming the flow's new desired rate
new_DR to be "infinity" in case of a bulk data transfer with an new_DR(f) to be "infinity" in case of a bulk data transfer with
unknown maximum rate, the flow calls UPDATE, which carries out an unknown maximum rate, the flow calls UPDATE, which carries
the tasks listed below to derive the flow's new sending rate, out the tasks listed below to derive the flow's new sending
Rate. A flow's UPDATE function uses a few local (i.e. per-flow) rate, Rate(f). A flow's UPDATE function uses a few local (i.e.
temporary variables, which are all initialized to 0: DELTA, per-flow) temporary variables, which are all initialized to 0:
new_S_CR and S_P. DELTA, new_S_CR and S_P.
(a) For all the flows in its FG (including itself), it (a) For all the flows in its FG (including itself), it
calculates the sum of all the calculated rates, new_S_CR. calculates the sum of all the calculated rates, new_S_CR.
Then it calculates the difference between FSE_R(f) and Then it calculates DELTA: the difference between FSE_R(f)
CC_R, DELTA. and CC_R(f).
for all flows i in FG do for all flows i in FG do
new_S_CR = new_S_CR + FSE_R(i) new_S_CR = new_S_CR + FSE_R(i)
end for end for
DELTA = CC_R - FSE_R(f) DELTA = CC_R(f) - FSE_R(f)
(b) It updates S_CR, FSE_R(f) and DR(f). (b) It updates S_CR, FSE_R(f) and DR(f).
FSE_R(f) = CC_R FSE_R(f) = CC_R(f)
if DELTA > 0 then // the flow's rate has increased if DELTA > 0 then // the flow's rate has increased
S_CR = S_CR + DELTA S_CR = S_CR + DELTA
else if DELTA < 0 then else if DELTA < 0 then
S_CR = new_S_CR + DELTA S_CR = new_S_CR + DELTA
end if end if
DR(f) = min(new_DR,FSE_R(f)) DR(f) = min(new_DR(f),FSE_R(f))
(c) It calculates the leftover rate TLO, removes the terminated (c) It calculates the leftover rate TLO, removes the terminated
flows from the FSE and calculates the sum of all the flows from the FSE and calculates the sum of all the
priorities, S_P. priorities, S_P.
for all flows i in FG do for all flows i in FG do
if P(i)<0 then if P(i)<0 then
delete flow delete flow
else else
S_P = S_P + P(i) S_P = S_P + P(i)
end if end if
end for end for
if DR(f) < FSE_R(f) then if DR(f) < FSE_R(f) then
TLO = TLO + (P(f)/S_P) * S_CR - DR(f)) TLO = TLO + (P(f)/S_P) * S_CR - DR(f))
end if end if
(d) It calculates the sending rate, Rate. (d) It calculates the sending rate, Rate(f).
Rate = min(new_DR, (P(f)*S_CR)/S_P + TLO) Rate(f) = min(new_DR(f), (P(f)*S_CR)/S_P + TLO)
if Rate != new_DR and TLO > 0 then if Rate(f) != new_DR(f) and TLO > 0 then
TLO = 0 // f has 'taken' TLO TLO = 0 // f has 'taken' TLO
end if end if
(e) It updates DR(f) and FSE_R(f) with Rate. (e) It updates DR(f) and FSE_R(f) with Rate(f).
if Rate > DR(f) then if Rate(f) > DR(f) then
DR(f) = Rate DR(f) = Rate(f)
end if end if
FSE_R(f) = Rate FSE_R(f) = Rate(f)
The goals of the flow algorithm are to achieve prioritization, The goals of the flow algorithm are to achieve prioritization,
improve network utilization in the face of application-limited flows, improve network utilization in the face of application-limited flows,
and impose limits on the increase behavior such that the negative and impose limits on the increase behavior such that the negative
impact of multiple flows trying to increase their rate together is impact of multiple flows trying to increase their rate together is
minimized. It does that by assigning a flow a sending rate that may minimized. It does that by assigning a flow a sending rate that may
not be what the flow's congestion controller expected. It therefore not be what the flow's congestion controller expected. It therefore
builds on the assumption that no significant inefficiencies arise builds on the assumption that no significant inefficiencies arise
from temporary application-limited behavior or from quickly jumping from temporary application-limited behavior or from quickly jumping
to a rate that is higher than the congestion controller intended. to a rate that is higher than the congestion controller intended.
skipping to change at page 19, line 29 skipping to change at page 20, line 17
| | | | | | | | | | | | | |
| 1 | 1 | 1 | 10 | 10 | 10 | | 1 | 1 | 1 | 10 | 10 | 10 |
| 2 | 1 | 0.5 | 1 | 1 | 1 | | 2 | 1 | 0.5 | 1 | 1 | 1 |
------------------------------------------ ------------------------------------------
S_CR = 11, TLO = 0 S_CR = 11, TLO = 0
Now assume that the first flow updates its rate to 8, because the Now assume that the first flow updates its rate to 8, because the
total sending rate of 11 exceeds the total capacity. Let us take a total sending rate of 11 exceeds the total capacity. Let us take a
closer look at what happens in step 3 of the flow algorithm. closer look at what happens in step 3 of the flow algorithm.
CC_R = 8. new_DR = infinity. CC_R(1) = 8. new_DR(1) = infinity.
3 a) new_S_CR = 11; DELTA = 8 - 10 = -2. 3 a) new_S_CR = 11; DELTA = 8 - 10 = -2.
3 b) FSE_Rf) = 8. DELTA is negative, hence S_CR = 9; 3 b) FSE_R(1) = 8. DELTA is negative, hence S_CR = 9;
DR(f) = 8. DR(1) = 8.
3 c) S_P = 1.5. 3 c) S_P = 1.5.
3 d) new sending rate = min(infinity, 1/1.5 * 9 + 0) = 6. 3 d) new sending rate Rate(1) = min(infinity, 1/1.5 * 9 + 0) = 6.
3 e) FSE_R(f) = 6. 3 e) FSE_R(1) = 6.
The resulting FSE looks as follows: The resulting FSE looks as follows:
------------------------------------------- -------------------------------------------
| # | FGI | P | FSE_R | DR | Rate | | # | FGI | P | FSE_R | DR | Rate |
| | | | | | | | | | | | | |
| 1 | 1 | 1 | 6 | 8 | 6 | | 1 | 1 | 1 | 6 | 8 | 6 |
| 2 | 1 | 0.5 | 1 | 1 | 1 | | 2 | 1 | 0.5 | 1 | 1 | 1 |
------------------------------------------- -------------------------------------------
S_CR = 9, TLO = 0 S_CR = 9, TLO = 0
The effect is that flow #1 is sending with 6 Mbit/s instead of the 8 The effect is that flow #1 is sending with 6 Mbit/s instead of the 8
Mbit/s that the congestion controller derived. Let us now assume Mbit/s that the congestion controller derived. Let us now assume
that flow #2 updates its rate. Its congestion controller detects that flow #2 updates its rate. Its congestion controller detects
that the network is not fully saturated (the actual total sending that the network is not fully saturated (the actual total sending
rate is 6+1=7) and increases its rate. rate is 6+1=7) and increases its rate.
CC_R=2. new_DR = infinity. CC_R(2) = 2. new_DR(2) = infinity.
3 a) new_S_CR = 7; DELTA = 2 - 1 = 1. 3 a) new_S_CR = 7; DELTA = 2 - 1 = 1.
3 b) FSE_R(f) = 2. DELTA is positive, hence S_CR = 9 + 1 = 10; 3 b) FSE_R(2) = 2. DELTA is positive, hence S_CR = 9 + 1 = 10;
DR(f) = 2. DR(2) = 2.
3 c) S_P = 1.5. 3 c) S_P = 1.5.
3 d) new sending rate = min(infinity, 0.5/1.5 * 10 + 0) = 3.33. 3 d) Rate(2) = min(infinity, 0.5/1.5 * 10 + 0) = 3.33.
3 e) DR(f) = FSE_R(f) = 3.33. 3 e) DR(2) = FSE_R(2) = 3.33.
The resulting FSE looks as follows: The resulting FSE looks as follows:
------------------------------------------- -------------------------------------------
| # | FGI | P | FSE_R | DR | Rate | | # | FGI | P | FSE_R | DR | Rate |
| | | | | | | | | | | | | |
| 1 | 1 | 1 | 6 | 8 | 6 | | 1 | 1 | 1 | 6 | 8 | 6 |
| 2 | 1 | 0.5 | 3.33 | 3.33 | 3.33 | | 2 | 1 | 0.5 | 3.33 | 3.33 | 3.33 |
------------------------------------------- -------------------------------------------
S_CR = 10, TLO = 0 S_CR = 10, TLO = 0
The effect is that flow #2 is now sending with 3.33 Mbit/s, which is The effect is that flow #2 is now sending with 3.33 Mbit/s, which is
close to half of the rate of flow #1 and leads to a total utilization close to half of the rate of flow #1 and leads to a total utilization
of 6(#1) + 3.33(#2) = 9.33 Mbit/s. Flow #2's congestion controller of 6(#1) + 3.33(#2) = 9.33 Mbit/s. Flow #2's congestion controller
has increased its rate faster than the controller actually expected. has increased its rate faster than the controller actually expected.
Now, flow #1 updates its rate. Its congestion controller detects Now, flow #1 updates its rate. Its congestion controller detects
that the network is not fully saturated and increases its rate. that the network is not fully saturated and increases its rate.
Additionally, the application feeding into flow #1 limits the flow's Additionally, the application feeding into flow #1 limits the flow's
sending rate to at most 2 Mbit/s. sending rate to at most 2 Mbit/s.
CC_R=7. new_DR=2. CC_R(1) = 7. new_DR(1) = 2.
3 a) new_S_CR = 9.33; DELTA = 1. 3 a) new_S_CR = 9.33; DELTA = 1.
3 b) FSE_R(f) = 7, DELTA is positive, hence S_CR = 10 + 1 = 11; 3 b) FSE_R(1) = 7, DELTA is positive, hence S_CR = 10 + 1 = 11;
DR = min(2, 7) = 2. DR(1) = min(2, 7) = 2.
3 c) S_P = 1.5; DR(f) < FSE_R(f), hence TLO = 1/1.5 * 11 - 2 = 5.33. 3 c) S_P = 1.5; DR(1) < FSE_R(1), hence TLO = 1/1.5 * 11 - 2 = 5.33.
3 d) new sending rate = min(2, 1/1.5 * 11 + 5.33) = 2. 3 d) Rate(1) = min(2, 1/1.5 * 11 + 5.33) = 2.
3 e) FSE_R(f) = 2. 3 e) FSE_R(1) = 2.
The resulting FSE looks as follows: The resulting FSE looks as follows:
------------------------------------------- -------------------------------------------
| # | FGI | P | FSE_R | DR | Rate | | # | FGI | P | FSE_R | DR | Rate |
| | | | | | | | | | | | | |
| 1 | 1 | 1 | 2 | 2 | 2 | | 1 | 1 | 1 | 2 | 2 | 2 |
| 2 | 1 | 0.5 | 3.33 | 3.33 | 3.33 | | 2 | 1 | 0.5 | 3.33 | 3.33 | 3.33 |
------------------------------------------- -------------------------------------------
S_CR = 11, TLO = 5.33 S_CR = 11, TLO = 5.33
Now, the total rate of the two flows is 2 + 3.33 = 5.33 Mbit/s, i.e. Now, the total rate of the two flows is 2 + 3.33 = 5.33 Mbit/s, i.e.
the network is significantly underutilized due to the limitation of the network is significantly underutilized due to the limitation of
flow #1. Flow #2 updates its rate. Its congestion controller flow #1. Flow #2 updates its rate. Its congestion controller
detects that the network is not fully saturated and increases its detects that the network is not fully saturated and increases its
rate. rate.
CC_R=4.33. new_DR = infinity. CC_R(2) = 4.33. new_DR(2) = infinity.
3 a) new_S_CR = 5.33; DELTA = 1. 3 a) new_S_CR = 5.33; DELTA = 1.
3 b) FSE_R(f) = 4.33. DELTA is positive, hence S_CR = 12; 3 b) FSE_R(2) = 4.33. DELTA is positive, hence S_CR = 12;
DR(f) = 4.33. DR(2) = 4.33.
3 c) S_P = 1.5. 3 c) S_P = 1.5.
3 d) new sending rate: min(infinity, 0.5/1.5 * 12 + 5.33 ) = 9.33. 3 d) Rate(2) = min(infinity, 0.5/1.5 * 12 + 5.33 ) = 9.33.
3 e) FSE_R(f) = 9.33, DR(f) = 9.33. 3 e) FSE_R(2) = 9.33, DR(2) = 9.33.
The resulting FSE looks as follows: The resulting FSE looks as follows:
------------------------------------------- -------------------------------------------
| # | FGI | P | FSE_R | DR | Rate | | # | FGI | P | FSE_R | DR | Rate |
| | | | | | | | | | | | | |
| 1 | 1 | 1 | 2 | 2 | 2 | | 1 | 1 | 1 | 2 | 2 | 2 |
| 2 | 1 | 0.5 | 9.33 | 9.33 | 9.33 | | 2 | 1 | 0.5 | 9.33 | 9.33 | 9.33 |
------------------------------------------- -------------------------------------------
S_CR = 12, TLO = 0 S_CR = 12, TLO = 0
Now, the total rate of the two flows is 2 + 9.33 = 11.33 Mbit/s. Now, the total rate of the two flows is 2 + 9.33 = 11.33 Mbit/s.
Finally, flow #1 terminates. It sets P to -1 and DR to 0. Let us Finally, flow #1 terminates. It sets P(1) to -1 and DR(1) to 0. Let
assume that it terminated late enough for flow #2 to still experience us assume that it terminated late enough for flow #2 to still
the network in a congested state, i.e. flow #2 decreases its rate in experience the network in a congested state, i.e. flow #2 decreases
the next iteration. its rate in the next iteration.
CC_R = 7.33. new_DR = infinity. CC_R(2) = 7.33. new_DR(2) = infinity.
3 a) new_S_CR = 11.33; DELTA = -2. 3 a) new_S_CR = 11.33; DELTA = -2.
3 b) FSE_R(f) = 7.33. DELTA is negative, hence S_CR = 9.33; 3 b) FSE_R(2) = 7.33. DELTA is negative, hence S_CR = 9.33;
DR(f) = 7.33. DR(2) = 7.33.
3 c) Flow 1 has P = -1, hence it is deleted from the FSE. 3 c) Flow 1 has P(1) = -1, hence it is deleted from the FSE.
S_P = 0.5. S_P = 0.5.
3 d) new sending rate: min(infinity, 0.5/0.5*9.33 + 0) = 9.33. 3 d) Rate(2) = min(infinity, 0.5/0.5*9.33 + 0) = 9.33.
3 e) FSE_R(f) = DR(f) = 9.33. 3 e) FSE_R(2) = DR(2) = 9.33.
The resulting FSE looks as follows: The resulting FSE looks as follows:
------------------------------------------- -------------------------------------------
| # | FGI | P | FSE_R | DR | Rate | | # | FGI | P | FSE_R | DR | Rate |
| | | | | | | | | | | | | |
| 2 | 1 | 0.5 | 9.33 | 9.33 | 9.33 | | 2 | 1 | 0.5 | 9.33 | 9.33 | 9.33 |
------------------------------------------- -------------------------------------------
S_CR = 9.33, TLO = 0 S_CR = 9.33, TLO = 0
Appendix D. Change log Appendix D. Change log
skipping to change at page 24, line 34 skipping to change at page 25, line 21
o Changed several occurrences of "NADA and GCC" to "NADA", including o Changed several occurrences of "NADA and GCC" to "NADA", including
the abstract. the abstract.
o Moved the application to GCC to an appendix, and made the GCC o Moved the application to GCC to an appendix, and made the GCC
reference informative. reference informative.
o Provided a few more general recommendations on applying the o Provided a few more general recommendations on applying the
coupling algorithm. coupling algorithm.
D.2.7. Changes from -05 to -06
o Incorporated comments by Colin Perkins.
Authors' Addresses Authors' Addresses
Safiqul Islam Safiqul Islam
University of Oslo University of Oslo
PO Box 1080 Blindern PO Box 1080 Blindern
Oslo, N-0316 Oslo N-0316
Norway Norway
Phone: +47 22 84 08 37 Phone: +47 22 84 08 37
Email: safiquli@ifi.uio.no Email: safiquli@ifi.uio.no
Michael Welzl Michael Welzl
University of Oslo University of Oslo
PO Box 1080 Blindern PO Box 1080 Blindern
Oslo, N-0316 Oslo N-0316
Norway Norway
Phone: +47 22 85 24 20 Phone: +47 22 85 24 20
Email: michawe@ifi.uio.no Email: michawe@ifi.uio.no
Stein Gjessing Stein Gjessing
University of Oslo University of Oslo
PO Box 1080 Blindern PO Box 1080 Blindern
Oslo, N-0316 Oslo N-0316
Norway Norway
Phone: +47 22 85 24 44 Phone: +47 22 85 24 44
Email: steing@ifi.uio.no Email: steing@ifi.uio.no
 End of changes. 80 change blocks. 
217 lines changed or deleted 233 lines changed or added

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