draft-ietf-rmcat-coupled-cc-06.txt   draft-ietf-rmcat-coupled-cc-07.txt 
RTP Media Congestion Avoidance Techniques (rmcat) S. Islam RTP Media Congestion Avoidance Techniques (rmcat) S. Islam
Internet-Draft M. Welzl Internet-Draft M. Welzl
Intended status: Experimental S. Gjessing Intended status: Experimental S. Gjessing
Expires: September 29, 2017 University of Oslo Expires: March 19, 2018 University of Oslo
March 28, 2017 September 15, 2017
Coupled congestion control for RTP media Coupled congestion control for RTP media
draft-ietf-rmcat-coupled-cc-06 draft-ietf-rmcat-coupled-cc-07
Abstract Abstract
When multiple congestion controlled RTP sessions traverse the same When multiple congestion controlled Real-time Transport Protocol
network bottleneck, combining their controls can improve the total (RTP) sessions traverse the same network bottleneck, combining their
on-the-wire behavior in terms of delay, loss and fairness. This controls can improve the total on-the-wire behavior in terms of
document describes such a method for flows that have the same sender, delay, loss and fairness. This document describes such a method for
in a way that is as flexible and simple as possible while minimizing flows that have the same sender, in a way that is as flexible and
the amount of changes needed to existing RTP applications. It simple as possible while minimizing the amount of changes needed to
specifies how to apply the method for the NADA congestion control existing RTP applications. It specifies how to apply the method for
the Network-Assisted Dynamic Adaptation (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 September 29, 2017. This Internet-Draft will expire on March 19, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2017 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.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
skipping to change at page 2, line 51 skipping to change at page 3, line 4
D.1.4. Changes from -03 to -04 . . . . . . . . . . . . . . . 24 D.1.4. Changes from -03 to -04 . . . . . . . . . . . . . . . 24
D.1.5. Changes from -04 to -05 . . . . . . . . . . . . . . . 24 D.1.5. Changes from -04 to -05 . . . . . . . . . . . . . . . 24
D.2. draft-ietf-rmcat-coupled-cc . . . . . . . . . . . . . . . 24 D.2. draft-ietf-rmcat-coupled-cc . . . . . . . . . . . . . . . 24
D.2.1. Changes from draft-welzl-rmcat-coupled-cc-05 . . . . 24 D.2.1. Changes from draft-welzl-rmcat-coupled-cc-05 . . . . 24
D.2.2. Changes from -00 to -01 . . . . . . . . . . . . . . . 24 D.2.2. Changes from -00 to -01 . . . . . . . . . . . . . . . 24
D.2.3. Changes from -01 to -02 . . . . . . . . . . . . . . . 24 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 . . . . . . . . . . . . . . . 25 D.2.6. Changes from -04 to -05 . . . . . . . . . . . . . . . 25
D.2.7. Changes from -05 to -06 . . . . . . . . . . . . . . . 25 D.2.7. Changes from -05 to -06 . . . . . . . . . . . . . . . 25
D.2.8. Changes from -06 to -07 . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 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 attempts
increase its sending rate until the path's capacity has been reached; to increase its sending rate until the path's capacity has been
depending on the controller, sometimes the rate is increased further, reached. Some controllers detect path capacity by increasing the
until packets are ECN-marked or dropped. This process inevitably sending rate further, until packets are ECN-marked [RFC8087] or
creates undesirable queuing delay when multiple congestion controlled dropped, and then decreasing the sending rate until that stops
connections traverse the same network bottleneck. happening. This process inevitably creates undesirable queuing delay
when multiple congestion-controlled connections traverse the same
network bottleneck, and each connection overshoots the path capacity
as it determines its sending rate.
The Congestion Manager (CM) [RFC3124] couples flows by providing a The Congestion Manager (CM) [RFC3124] couples flows by providing a
single congestion controller. It is hard to implement because it single congestion controller. It is hard to implement because it
requires an additional congestion controller and removes all per- requires an additional congestion controller and removes all per-
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 [I-D.ietf-rtcweb-overview] [RFC7478].
The described mechanisms are believed safe to use, but are The described mechanisms are believed safe to use, but are
experimental and are presented for wider review and operational experimental and are presented for wider review and operational
evaluation. 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].
skipping to change at page 3, line 47 skipping to change at page 4, line 4
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, or an
stream [RFC7656], whether or not this RTP stream is multiplexed RTP stream [RFC7656], whether or not this RTP stream is
onto an RTP session with other RTP streams. multiplexed 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.
skipping to change at page 4, line 22 skipping to change at page 4, line 28
Flow Group (FG): Flow Group (FG):
A group of flows having the same FGI. A group of flows having the same FGI.
Shared Bottleneck Detection (SBD): Shared Bottleneck Detection (SBD):
The entity that determines which flows traverse the same The entity that determines which flows traverse the same
bottleneck in the network, or the process of doing so. bottleneck in the network, or the process of doing so.
3. Limitations 3. Limitations
Sender-side only: Sender-side only:
Coupled congestion control as described here only operates Shared bottlenecks can exist when multiple flows originate from
inside a single host on the sender side. This is because, the same sender, or when flows from different senders reach the
irrespective of where the major decisions for congestion same receiver (see [I-D.ietf-rmcat-sbd], section 3). Coupled
control are taken, the sender of a flow needs to eventually congestion control as described here only supports the former
decide on the transmission rate. Additionally, the necessary case, not the latter, as it operates inside a single host on
information about how much data an application can currently the sender side.
send on a flow is often only available at the sender side,
making the sender an obvious choice for placement of the
elements and mechanisms described here.
Shared bottlenecks do not change quickly: Shared bottlenecks do not change quickly:
As per the definition above, a bottleneck depends on cross As per the definition above, a bottleneck depends on cross
traffic, and since such traffic can heavily fluctuate, traffic, and since such traffic can heavily fluctuate,
bottlenecks can change at a high frequency (e.g., there can be bottlenecks can change at a high frequency (e.g., there can be
oscillation between two or more links). This means that, when oscillation between two or more links). This means that, when
flows are partially routed along different paths, they may flows are partially routed along different paths, they may
quickly change between sharing and not sharing a bottleneck. quickly change between sharing and not sharing a bottleneck.
For simplicity, here it is assumed that a shared bottleneck is For simplicity, here it is assumed that a shared bottleneck is
valid for a time interval that is significantly longer than the valid for a time interval that is significantly longer than the
skipping to change at page 5, line 21 skipping to change at page 5, line 21
it initiates communication with flows and SBD. However, in the it initiates communication with flows and SBD. However, in the
passive version, it does not actively initiate communication with passive version, it does not actively initiate communication with
flows and SBD; its only active role is internal state maintenance flows and SBD; its only active role is internal state maintenance
(e.g., an implementation could use soft state to remove a flow's data (e.g., an implementation could use soft state to remove a flow's data
after long periods of inactivity). Every time a flow's congestion after long periods of inactivity). Every time a flow's congestion
control mechanism would normally update its sending rate, the flow control mechanism would normally update its sending rate, the flow
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 Group Identifiers (FGIs).
active and passive versions, however the passive version is put into
the appendix as it is extremely experimental. Figure 2 shows the This document describes both active and passive versions. While the
interaction between flows and the FSE, using the variable names passive algorithm works better for congestion controls with RTT-
defined in Section 5.2. independent convergence, it can still produce oscillations on short
time scales. The passive algorithm, described in Appendix C, is
therefore considered as highly experimental and not safe to deploy
outside of testbed environments. Figure 2 shows the interaction
between flows and the FSE, using the variable names defined in
Section 5.2.
------- <--- Flow 1 ------- <--- Flow 1
| FSE | <--- Flow 2 .. | FSE | <--- Flow 2 ..
------- <--- .. Flow N ------- <--- .. Flow N
^ ^
| | | |
------- | ------- |
| SBD | <-------| | SBD | <-------|
------- -------
skipping to change at page 6, line 19 skipping to change at page 6, line 19
REGISTER <--register-- JOIN #1 REGISTER <--register-- JOIN #1
#2 CC_R(1) ----UPDATE----> UPDATE (in) #2 CC_R(1) ----UPDATE----> UPDATE (in)
#3 NEW RATE <---FSE_R(1)-- UPDATE (out) --FSE_R(2)-> #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 not, for instance, define how many bits must be used to represent
FSIs, or in which way the entities communicate. Implementations can FGIs, or in which way the entities communicate.
take various forms: for instance, all the elements in the figure
could be implemented within a single application, thereby operating Implementations can take various forms: for instance, all the
on flows generated by that application only. Another alternative elements in the figure could be implemented within a single
could be to implement both the FSE and SBD together in a separate application, thereby operating on flows generated by that application
process which different applications communicate with via some form only. Another alternative could be to implement both the FSE and SBD
of Inter-Process Communication (IPC). Such an implementation would together in a separate process which different applications
extend the scope to flows generated by multiple applications. The communicate with via some form of Inter-Process Communication (IPC).
FSE and SBD could also be included in the Operating System kernel. Such an implementation would extend the scope to flows generated by
multiple applications. The FSE and SBD could also be included in the
Operating System kernel. However, only one type of coupling
algorithm should be used for all flows. Combinations of multiple
algorithms at different aggregation levels (e.g., the Operating
System coupling application aggregates with one algorithm, and
applications coupling their flows with another) have not been tested
and are therefore not recommended.
5. Roles 5. Roles
This section gives an overview of the roles of the elements of This section gives an overview of the roles of the elements of
coupled congestion control, and provides an example of how coupled coupled congestion control, and provides an example of how coupled
congestion control can operate. congestion control can operate.
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 values for the Differentiated Services Code Point having the same values for the Differentiated Services Code Point
(DSCP) and the ECN field in the IP header are typically treated (DSCP) and the ECN field in the IP header are typically treated
in the same way along the path. The latter method is the only in the same way along the path. This method is the only one
one specified in this document: SBD MAY consider all flows that specified in this document: SBD MAY consider all flows that use
use the same five-tuple, DSCP and ECN field value to belong to the same five-tuple, DSCP and ECN field value to belong to the
the same FG. This classification applies to certain tunnels, or same FG. This classification applies to certain tunnels, or RTP
RTP flows that are multiplexed over one transport (cf. flows that are multiplexed over one transport (cf.
[transport-multiplex]). Such multiplexing is also a recommended [transport-multiplex]). Such multiplexing is also a recommended
usage of RTP in rtcweb [rtcweb-rtp-usage]. 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
skipping to change at page 12, line 41 skipping to change at page 12, line 41
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(i) in algorithms 1 and 2, section 5.3). Implementers and (FSE_R(i) in algorithms 1 and 2, section 5.3). Implementers and
testers 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, Colin Perkins, David Hayes, David Andreas Petlund, Anna Brunstrom, Colin Perkins, David Hayes, David
Ros (who also gave the FSE its name), Ingemar Johansson, Karen Ros (who also gave the FSE its name), Ingemar Johansson, Karen
Nielsen, Kristian Hiorth, Mirja Kuehlewind, Martin Stiemerling, Varun Nielsen, Kristian Hiorth, Mirja Kuehlewind, Martin Stiemerling,
Singh, Xiaoqing Zhu, and Zaheduzzaman Sarker. The authors would like Spencer Dawkins, Varun Singh, Xiaoqing Zhu, and Zaheduzzaman Sarker.
to especially thank Xiaoqing Zhu and Stefan Holmer for helping with The authors would like to especially thank Xiaoqing Zhu and Stefan
NADA and GCC. 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 32 skipping to change at page 13, line 32
In the case of a single-user system, it should also be in the In the case of a single-user system, it should also be in the
interest of any application programmer to give the user the best interest of any application programmer to give the user the best
possible experience by using reasonable flow priorities or even possible experience by using reasonable flow priorities or even
letting the user choose them. In a multi-user system, this interest letting the user choose them. In a multi-user system, this interest
may not be given, and one could imagine the worst case of an "arms may not be given, and one could imagine the worst case of an "arms
race" situation, where applications end up setting their priorities race" situation, where applications end up setting their priorities
to the maximum value. If all applications do this, the end result is to the maximum value. If all applications do this, the end result is
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.
Implementers should also be aware of the Security Considerations
sections of [RFC3124], [RFC5348], and [RFC7478].
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., and S. D'Aronco, "NADA: A Unified Congestion Control
Congestion Control Scheme for Real-Time Media", draft- Scheme for Real-Time Media", draft-ietf-rmcat-nada-04
ietf-rmcat-nada-03 (work in progress), September 2016. (work in progress), March 2017.
[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, <https://www.rfc-editor.org/info/
<http://www.rfc-editor.org/info/rfc2119>. 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>. <https://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", RFC Friendly Rate Control (TFRC): Protocol Specification", RFC
5348, DOI 10.17487/RFC5348, September 2008, 5348, DOI 10.17487/RFC5348, September 2008,
<http://www.rfc-editor.org/info/rfc5348>. <https://www.rfc-editor.org/info/rfc5348>.
11.2. Informative References 11.2. Informative References
[anrw2016] [anrw2016]
Islam, S. and M. Welzl, "Start Me Up:Determining and Islam, S. and M. Welzl, "Start Me Up:Determining and
Sharing TCP's Initial Congestion Window", ACM, IRTF, ISOC Sharing TCP's Initial Congestion Window", ACM, IRTF, ISOC
Applied Networking Research Workshop 2016 (ANRW 2016) , Applied Networking Research Workshop 2016 (ANRW 2016) ,
2016. 2016.
[fse] Islam, S., Welzl, M., Gjessing, S., and N. Khademi, [fse] Islam, S., Welzl, M., Gjessing, S., and N. Khademi,
skipping to change at page 14, line 34 skipping to change at page 14, line 34
2014. 2014.
[fse-noms] [fse-noms]
Islam, S., Welzl, M., Hayes, D., and S. Gjessing, Islam, S., Welzl, M., Hayes, D., and S. Gjessing,
"Managing Real-Time Media Flows through a Flow State "Managing Real-Time Media Flows through a Flow State
Exchange", IEEE NOMS 2016, Istanbul, Turkey , 2016. 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", draft-ietf-rmcat- Cases for Evaluating RMCAT Proposals", draft-ietf-rmcat-
eval-test-04 (work in progress), October 2016. eval-test-05 (work in progress), April 2017.
[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-08 (work in progress),
March 2016. July 2017.
[I-D.ietf-rtcweb-overview]
Alvestrand, H., "Overview: Real Time Protocols for
Browser-based Applications", draft-ietf-rtcweb-overview-18
(work in progress), March 2017.
[I-D.ietf-rtcweb-transports] [I-D.ietf-rtcweb-transports]
Alvestrand, H., "Transports for WebRTC", Internet-draft Alvestrand, H., "Transports for WebRTC", Internet-draft
draft-ietf-rtcweb-transports-17.txt, October 2016. draft-ietf-rtcweb-transports-17.txt, October 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, <https://www.rfc-
<http://www.rfc-editor.org/info/rfc7478>. editor.org/info/rfc7478>.
[RFC7656] Lennox, J., Gross, K., Nandakumar, S., Salgueiro, G., and [RFC7656] Lennox, J., Gross, K., Nandakumar, S., Salgueiro, G., and
B. Burman, Ed., "A Taxonomy of Semantics and Mechanisms B. Burman, Ed., "A Taxonomy of Semantics and Mechanisms
for Real-Time Transport Protocol (RTP) Sources", RFC 7656, for Real-Time Transport Protocol (RTP) Sources", RFC 7656,
DOI 10.17487/RFC7656, November 2015, DOI 10.17487/RFC7656, November 2015, <https://www.rfc-
<http://www.rfc-editor.org/info/rfc7656>. editor.org/info/rfc7656>.
[RFC8087] Fairhurst, G. and M. Welzl, "The Benefits of Using
Explicit Congestion Notification (ECN)", RFC 8087, DOI
10.17487/RFC8087, March 2017, <https://www.rfc-
editor.org/info/rfc8087>.
[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",
Internet-draft draft-ietf-rtcweb-rtp-usage-26.txt, March Internet-draft draft-ietf-rtcweb-rtp-usage-26.txt, 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", Internet-draft draft- Single Lower-Layer Transport", Internet-draft draft-
skipping to change at page 16, line 7 skipping to change at page 16, line 14
When applying the FSE to GCC, the UPDATE function call described in When applying the FSE to GCC, the UPDATE function call described in
Section 5.3 gives the FSE GCC's estimate of available bandwidth Section 5.3 gives the FSE GCC's estimate of available bandwidth
A_hat. The recommended algorithm for GCC is the Active FSE in A_hat. The recommended algorithm for GCC is the Active FSE in
Section 5.3.1. In step 3 (c), when the FSE_R(i) is "sent" to the Section 5.3.1. In step 3 (c), when the FSE_R(i) is "sent" to the
flow i, this means updating A_hat of flow i with the value of flow i, this means updating A_hat of flow i with the value of
FSE_R(i). FSE_R(i).
Appendix B. Scheduling Appendix B. Scheduling
When connections originate from the same host, it would be possible When flows originate from the same host, it would be possible to use
to use only one single sender-side congestion controller which only one single sender-side congestion controller which determines
determines the overall allowed sending rate, and then use a local the overall allowed sending rate, and then use a local scheduler to
scheduler to assign a proportion of this rate to each RTP session. assign a proportion of this rate to each RTP session. This way,
This way, priorities could also be implemented as a function of the priorities could also be implemented as a function of the scheduler.
scheduler. The Congestion Manager (CM) [RFC3124] also uses such a The Congestion Manager (CM) [RFC3124] also uses such a scheduling
scheduling function. function.
Appendix C. Example algorithm - Passive FSE Appendix C. Example algorithm - Passive FSE
Active algorithms calculate the rates for all the flows in the FG and Active algorithms calculate the rates for all the flows in the FG and
actively distribute them. In a passive algorithm, UPDATE returns a actively distribute them. In a passive algorithm, UPDATE returns a
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
skipping to change at page 25, line 25 skipping to change at page 25, line 25
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 D.2.7. Changes from -05 to -06
o Incorporated comments by Colin Perkins. o Incorporated comments by Colin Perkins.
D.2.8. Changes from -06 to -07
o Addressed OPSDIR, SECDIR, GENART, AD and IESG comments.
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
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