Network Working Group Q. Wu Internet-Draft F. Xia Intended status: Standards Track R. Even Expires: September 9, 2010 Huawei March 8, 2010 Proposal for an extension to RTCP Receiver Report for Feedback Storm Suppression draft-wu-avt-retransmission-supression-rtp-01 Abstract This document specifies an extension to the messages defined in the Audio-Visual Profile with Feedback (AVPF) designed to allow intermediate node to suppress the feedback implosion from the receivers. One of examples for feedback implosion is utilizing RTCP NACK to request retransmission of the missing packets which may result in NACK storm targeting to the same media sender. This issue can be addressed to define one new RTCP message, which is referred to as the Feedback Storm Suppression receiver report and carries the information regarding feedback suppression early indication events to the receiver before the receiver detects an original packet loss and all the packet loss repair methods are applied. By using feedback Suppression message together with RTCP based feedback message, the delay for the receiver to recover from the packet loss can be reduced and the risk of increasing network congestion can be mitigated or diminished. This document also registers a new RTCP receiver report for Feedback Storm Suppression. Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. Wu, et al. Expires September 9, 2010 [Page 1] Internet-Draft Feedback Storm Suppression March 2010 The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on September 9, 2010. Copyright Notice Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the BSD License. This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English. Wu, et al. Expires September 9, 2010 [Page 2] Internet-Draft Feedback Storm Suppression March 2010 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Basic Operation . . . . . . . . . . . . . . . . . . . . . . . 5 4. Message Format . . . . . . . . . . . . . . . . . . . . . . . . 5 5. SDP Signaling . . . . . . . . . . . . . . . . . . . . . . . . 5 6. IANA Consideration . . . . . . . . . . . . . . . . . . . . . . 5 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6 7.1. Normative References . . . . . . . . . . . . . . . . . . . 6 7.2. Informative References . . . . . . . . . . . . . . . . . . 7 Appendix A. Example scenarios for Feedback Storm Suppression . . 7 A.1. Scenario 1: One media Sender, one Distribution Source . . 7 A.2. Scenario 2: One Media Sender, more distribution sources . 8 Appendix B. Applicability of Feedback Storm Suppression . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11 Wu, et al. Expires September 9, 2010 [Page 3] Internet-Draft Feedback Storm Suppression March 2010 1. Introduction RTP retransmission is an effective packet loss recovery technique for real-time applications with relaxed delay bounds [RFC4588],e.g., streaming media. The conventional RTCP feedback (NACK) message which conveys the RTP sequence number of the lost packets can be used to request the sender to compensate the missing RTP packets based on the RTP sequence number of these packets[RFC4585]. However, in lots of multicast environments, packet loss occurs in the upstream link or downstream aggregate link of the intermediate network element (e.g., Retransmission server, Distribution Source) due to oversaturated network link, faulty networking hardware or corrupted packets rejected in-transit. It may result in NACK implosion targeting at the same sender, i.e., massive NACK request to the same multicast sender for retransmission of the same RTP packets which is also known as "NACK storm" described in [DVB-IPTV]. To increase the robustness to the loss of a NACK or of a retransmission packet, a receiver may also send multiple NACKs for the same packet. Another use case is Fast Update request storm occurs in the conversational multimedia scenarios. In this case, packet loss may happen in the upstream link or downstream aggregate link of intermediate network element like Multipoint Control Unit(MCU) which results in massive fast update request(i.e., Full Intra Request(FIR) described in [RFC5104]) from receivers to the same media sender. As these feedback storms progress (e.g., NACK implosion or Fast update implosion), the network is overwhelmed with constant feedback traffic, in the worsening case, RTCP feedback storm poses a risk of increasing network congestion, with excessive traffic and degrading network performance, this can eventually lead to a complete loss of network connectivity as such feedback packets proliferate, the network may become unusable. In order to solve this, the current text in [I-D.ietf-avt-rtcpssm] allows the distribution source to filter out the NACK messages while this document propose an option to let the receivers know that Feedback for packet loss is not needed in the specified cases. i.e., generating one new generic RTCP receiver report message, which reflects the packet receipt/loss events and feedback suppression early indication events before the receiver detects an original packet loss and all the packet loss repair methods are applied. This new RTCP receiver report, which we refer to as Feedback Storm Suppression, indicates suppressing feedback request for the packet loss(e.g., request retransmission of lost packets or request decoder refresh point) before the receiver sends a request to the media sender for the missing packet. In order to detect the original Wu, et al. Expires September 9, 2010 [Page 4] Internet-Draft Feedback Storm Suppression March 2010 packet loss in the upstream direction before the receivers perceive it, the intermediate node located between the media sender and receiver may monitor a certain packet loss by reserving space to replicate one copy of multicast data and checking the sequence number consistency of the original multicast packets or configuring upstream RTP client or a small subset of RTP receivers to act as immediate reporters described in [DVB-IPTV]. Also this intermediate node should take into account such factors as the tolerable application delay, the network environment, and the media type. Upon the packet loss is detected and initial latency is tolerable, in the upstream direction towards the sender, the intermediate node may ask for retransmission of the lost packet from the sender or re-asking for the correct decoder refresh point, in the meanwhile, in the downstream direction from the sender, the intermediate node may convey Feedback Suppression Indication to all the receivers concerned to indicate the receiver not to transmit feedback message. When the sender receives the request from the intermediate node, the sender resends the missing packet to the receiver via RTP using retransmission payload format[RFC4588]. Similar to RTCP NACK, the Feedback Storm Suppression also conveys the packet receipt/loss events at the packet level and considers missing packets as unrepaired. But different from RTCP NACK, the Feedback Storm Suppression is used by the intermediate node to multicast back to the receivers in response to the RTCP feedback issued by the receivers. Note that the feedback storm suppression should collectively work together with feedback to repair the lost source packets. Thus, the delay for the receiver to recover from the packet loss can be reduced and the risk of increasing network congestion can be mitigated or diminished. The receiver may send a Feedback message before receiving the indication but will not need to resend the Feedback message after receiving the indication. Also the idea of Feedback Storm Suppression can be further extended when the distributed content distribution network are considered. That is to say several intermediate node and media senders may constitute hierarchical model. In this distributed content distribution environment, the Feedback Storm Suppression not only can be used to suppress all the receivers behind itself not to send packet loss request but also suppress the neighboring node not to send packet loss request for the missing packets via unicast. How the neighboring node is discovered is beyond scope of this document. This document registers a new RTCP receiver report message for Feedback Storm Suppression. Applications that are employing one or more loss-repair methods MAY use feedback Storm Suppression together with these loss-repair methods for every packet they receive or for a Wu, et al. Expires September 9, 2010 [Page 5] Internet-Draft Feedback Storm Suppression March 2010 set of specific packets they have received. 2. Terminology The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 3. Basic Operation The new RTCP receiver report, i.e., the Feedback Storm suppression will work in Simple Feedback and in Distribution Source Feedback Summary Models defined in [I-D.ietf-avt-rtcpssm]. The intermediate node between media sender and receivers will include the support for retransmission as part of the offered SDP and will expect such support from the Media Sender. The intermediate node may send this new RTCP receiver report FSEI when detecting a loss on its incoming link while sending a packet loss request to the media sender. The intermdidate node may receive packet loss request messages(e.g., RTCP NACK) from the receivers and may filter them out if it already sent a packet loss request for the missing packet to the media source. If the receiver understands this message it will not send packet loss request(e.g., NACK) for the missing packets reported in the message and will accept a retransmission stream. The receiver may send packet loss request(e.g., NACK messages) if it did not understand this new message. 4. Message Format The Feedback Storm Suppression message is an extension to the RTCP receiver report. [[The message format is to be decided based on the AVT discussion.]] 5. SDP Signaling TBD. 6. IANA Consideration New message type and New parameters for RTCP receiver report are Wu, et al. Expires September 9, 2010 [Page 6] Internet-Draft Feedback Storm Suppression March 2010 subject to IANA registration. For general guidelines on IANA considerations for RTCP feedback, refer to [RFC4585] The contact information for the registrations is: Qin Wu sunseawq@huawei.com Site B, Floor 12F,Huihong Mansion, No.91,Baixia Rd. Nanjing, JiangSu 210001 China 7. References 7.1. Normative References [I-D.ietf-avt-rtcpssm] Ott, J., Chesterfield , J., and E. Schooler, "RTCP Extensions for Single- Source Multicast Sessions with Unicast Feedback", September 2009. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey, "Extended RTP Profile for Real-time Transport Control Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585, July 2006. [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", STD 64, RFC 3550, July 2003. [RFC4588] Rey, J., Leon, D., Miyazaki, A., Varsa, V., and R. Hakenberg, "RTP Retransmission Payload Format", RFC 4588, July 2006. [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session Description Protocol", RFC 4566, July 2006. [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, January 2008. [RFC5104] Wenger, S., Chandra, U., Westerlund, M., and B. Burman, "Codec Control Messages in the RTP Audio-Visual Profile with Feedback (AVPF)", RFC 5104, February 2008. Wu, et al. Expires September 9, 2010 [Page 7] Internet-Draft Feedback Storm Suppression March 2010 7.2. Informative References [DVB-IPTV] ETSI Standard, "Digital Video Broadcasting(DVB); Transport of MPEG-2 TS Based DVB Services over IP Based Networks", ETSI TS 102 034, V1.4.1 , August 2009. [I-D.hunt-avt-monarch-01] Hunt, G. and P. Arden, "Monitoring Architectures for RTP", August 2008. [I-D.ietf-pmol-metrics-framework-02] Clark, A., "Framework for Performance Metric Development". Appendix A. Example scenarios for Feedback Storm Suppression A.1. Scenario 1: One media Sender, one Distribution Source The general architecture is displayed below in Figure 1. In this figure, one or more Media Senders send RTP packets to the Distribution Source. The Distribution Source relays the RTP packets to the receivers using a source-specific multicast channel. In the reverse direction, the receivers transmit RTCP packets via unicast to the distribution source. The Distribution Source in turn relays RTCP packets to the media sender and then transmits the RTCP packets back to the receivers, using source-specific multicast. When packet loss happens between Media sender and distribution source, it may result in massive retransmission request for the same RTP packets from all the receivers using RTCP NACK to the same multicast sender. We refer to it as Retransmission Storm. +-------+ |---->|RTP_Rx1| +--------+ | +-------+ | | +--------------+ | | | | | | +-------+ | Media |-------| Distribution |-------|---->|RTP_Rx2| | | | Source | | +-------+ | Sender | | | | . | | +--------------+ | . | | | . +--------+ | +-------+ |---->|RTP_Rxn| +-------+ Figure 1: One media Sender, one Distribution Source Wu, et al. Expires September 9, 2010 [Page 8] Internet-Draft Feedback Storm Suppression March 2010 A.2. Scenario 2: One Media Sender, more distribution sources The hierarchical model is displayed below in Figure 2. In this figure, one media sender and two Distribution source constitute one hierarchical model. In this model, one Media Senders send RTP packets to two Distribution Sources respectively. These Distribution Sources relay the RTP packets respectively to the receivers behind itself using a source-specific multicast channel. In the reverse direction, the receivers transmit RTCP packets via unicast to the distribution source. The Distribution Source in turn relays RTCP packets to the media sender and then transmits the RTCP packets back to the receivers, using source-specific multicast. When packet loss happens between Media sender and distribution source, it may result in massive retransmission request for the same RTP packets from all the receivers using RTCP NACK to the same multicast sender. We refer to it as Retransmission Storm. +--------+ |---->|RTP_Rx11| | +--------+ +--------------+ | | | | +--------+ |--->| Distribution |----|---->|RTP_Rx12| | | Source1 | | +--------+ | | | | . +--------+ | +--------------+ | . | | | | . | | | | +--------+ | Media | | |---->|RTP_Rx1k| | |---| +--------+ | Sender | | +--------+ | | | |---->|RTP_Rx21| | | | | +--------+ +--------+ | +--------------+ | | | | | +--------+ | | Distribution |----|---->|RTP_Rx22| |--->| Source2 | | +--------+ | | | . +--------------+ | . | . | +--------+ |---->|RTP_Rx2j| +--------+ Figure 2: One Media Sender, more distribution sources Wu, et al. Expires September 9, 2010 [Page 9] Internet-Draft Feedback Storm Suppression March 2010 Appendix B. Applicability of Feedback Storm Suppression This document defines new RTCP receiver report which we refer to as Feedback Storm Suppression to deal with Retransmission Storm mentioned above. Here we give two examples to show how this new RTCP receiver report is applied into two scenarios described in section A.1 for Retransmission Storm Suppression. Applicability of Feedback Storm Suppression in Scenario 1 described in Figure 1 is shown in the Figure 3. In this figure, the distribution source detect the packet loss before the receiver perceive it and ask for retransmission of the missing packets from the media sender, in the meanwhile, the distribution source transmits the RTCP Feedback Storm Suppression Indication back to the receivers using source-specific multicast channel. In this way, the delay for the receiver to recover from the packet loss can be reduced and the risk of increasing network congestion can be mitigated. +------+ +--------------+ +--------+ |Media | | Distribution | | | |Sender| | Source | | RTP_Rx | +--+---+ +------+-------+ +---+----+ | | | | | | |------------------->|------RTP Multicast---->| | | | | | | | +--------+----------+ | | |Detect Packet Loss | | | |and Identify the SN| | | |of missing Packets | | | +--------+----------+ | |<-----RTCP NACK-----| | | | | | +--Multicast RTCP FSEI-->| | RTP Retransmission | | |------------------->| | | |------RTP Multicast---->| | | Retransmission | | | | | | | | | | Figure 3: Applicability of Feedback Suppression Early Indication Applicability of Feedback Storm Suppression in Scenario 2 described in Figure 2 is shown in the figure A.2.2. The procedure in the figure A.2.2 is similar to the one in the figure Figure 4. The only Wu, et al. Expires September 9, 2010 [Page 10] Internet-Draft Feedback Storm Suppression March 2010 difference is distribution source should not only notify all the receiver behind itself not to send NACK but also propagate the retransmission suppression indication to the neighboring distribution sources. In this way, all the receivers behind all the neighboring distribution source can avoid sending massive retransmission request to the media sender. +------+ +-------+ +--------+ +-------+ +--------+ |Media | | | | RTP_Rx | | | | RTP_Rx | |Sender| | DS1 | | (DS1) | | DS2 | | (DS2) | +--+---+ +---+---+ +---+----+ +---+---+ +---+----+ | | | | | | |RTP Multicast | | | |----------->|------------->| | | | | | | | | | | |RTP Multicast| |------------------------------------------->|------------>| | | | | | | +--------+------------+ | | | | |Detect Packet Loss | | | | | |and Identify the SN | | | | | |of the missing Packets | | | | +--------+------------+ | | | | | | | | |<-RTCP NACK-| Multicast RTCP RSSI | | | |------------->| | | | | | | | | |-----Unicast RTCP RSSI-------->|Multicast RTCP FSEI | | | |------------>| |RTP Retransmission | | | |----------->| | | | | | | | | | | RTP Retransmission | | |------------+--------------+--------------->| | | | | | | | | RTP Multicast| | RTP Multicast | |Retransmission| |Retransmission | |------------->| |------------>| | | | | | DS1: Distribution Source 1 DS2: Distribution Source 2 Figure 4: Applicability of Retransmission Suppression Early Indication Wu, et al. Expires September 9, 2010 [Page 11] Internet-Draft Feedback Storm Suppression March 2010 Authors' Addresses Qin Wu Huawei Site B,Floor 12F,Huihong Mansion, No.91 Baixia Rd. Nanjing, Jiangsu 21001 China Phone: +86-25-84565892 Email: sunseawq@huawei.com Frank Xia Huawei 1700 Alma Dr. Suite 500 Plano, TX 75075 USA Phone: +1 972-509-5599 Email: xiayangsong@huawei.com Roni Even Huawei 14 David Hamelech Tel Aviv 64953 Israel Email: even.roni@huawei.com Wu, et al. Expires September 9, 2010 [Page 12]