Network Working Group Q. Wu Internet-Draft F. Xia Intended status: Standards Track R. Even Expires: December 12, 2010 Huawei June 10, 2010 Proposal for an extension to RTCP Receiver Report for Feedback Storm Suppression draft-wu-avt-retransmission-supression-rtp-02 Abstract This document specifies an extension to the RTCP messages defined in the Audio-Visual Profile with Feedback (AVPF) designed to allow intermediate node of the network side to suppress the feedback implosion from the receivers. An example of feedback implosion is NACK storm, i.e., a large number of RTCP NACK messages used to request retransmission of the missing packets going to the same media sender. The Feedback Storm Suppression receiver report is used to carry 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 and filtering of unnecessary feedback messages when the receivers have already send out packet loss requests. By using feedback Suppression message together with filter mechanism, the delay for the receiver to recover from the packet loss can be reduced and the risk of increasing network congestion can be mitigated. This document also registers two new RTCP receiver reports for Feedback Storm Suppression. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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." This Internet-Draft will expire on December 12, 2010. Copyright Notice Wu, et al. Expires December 12, 2010 [Page 1] Internet-Draft Feedback Storm Suppression June 2010 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. 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Expires December 12, 2010 [Page 2] Internet-Draft Feedback Storm Suppression June 2010 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6 3. Basic Operation . . . . . . . . . . . . . . . . . . . . . . . 7 4. Simple Feedback Model . . . . . . . . . . . . . . . . . . . . 9 5. Distribution Source Feedback Summary Model . . . . . . . . . . 10 6. RTCP Receiver Feedback Report Extension . . . . . . . . . . . 11 6.1. Transport Layer Feedback Message . . . . . . . . . . . . . 11 6.1.1. NACK implosion Suppression Summary report . . . . . . 11 6.2. Payload Specific Feedback Message . . . . . . . . . . . . 12 6.2.1. FIR implosion Suppression Summary report . . . . . . . 12 7. SDP Signaling . . . . . . . . . . . . . . . . . . . . . . . . 13 8. IANA Consideration . . . . . . . . . . . . . . . . . . . . . . 14 9. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 15 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15 10.1. Normative References . . . . . . . . . . . . . . . . . . . 15 10.2. Informative References . . . . . . . . . . . . . . . . . . 16 Appendix A. Example scenarios for Retransmission Storm Suppression . . . . . . . . . . . . . . . . . . . . . 16 A.1. Scenario 1: One or more media sender,One distribution source . . . . . . . . . . . . . . . . . . . . . . . . . . 16 A.2. Scenario 2:One media sender, Two distribution sources in cascade . . . . . . . . . . . . . . . . . . . . . . . . 17 A.3. Scenario 3:One media sender, Two distribution sources in parallel . . . . . . . . . . . . . . . . . . . . . . . 17 Appendix B. Applicability of Feedback Storm Suppression . . . . . 18 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20 Wu, et al. Expires December 12, 2010 [Page 3] Internet-Draft Feedback Storm Suppression June 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 which may aggravate the NACK implosion. A similar use case is video Fast Update request storm occurs in the conversational multimedia scenarios. In this case, packet loss may happen in the upstream 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 may be 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 [RFC5760] 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 Wu, et al. Expires December 12, 2010 [Page 4] Internet-Draft Feedback Storm Suppression June 2010 refresh point) before the receiver sends a request to the media sender for the missing packet. In order to detect the original packet loss in the upstream direction before the receivers perceive it, the intermediate node of network side located between the media sender and receiver may monitor a certain packet loss by 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. When 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 ask for the correct decoder refresh point, meanwhile, in the downstream direction from the sender, the intermediate node may convey Feedback Suppression Indication to all the receivers concerned to indicate that the receiver should not to transmit feedback messages. When the sender receives the request from the intermediate node, the sender resends the missing packets to the receiver via RTP using retransmission payload format [RFC4588]or a new refresh point for FIR Initiator [RFC5104] 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 can only be forwarded by the intermediate node to the receivers impacted by packet loss or generated directly at the intermediate node and sent to the corresponding 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 a distributed content distribution network (CDN) 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 two new RTCP receiver report messages for Feedback Storm Suppression. Applications that are employing one or Wu, et al. Expires December 12, 2010 [Page 5] Internet-Draft Feedback Storm Suppression June 2010 more loss-repair methods MAY use feedback Storm Suppression together with these loss-repair methods for every packet they receive or for a set of specific packets they have received. Note: The draft focus on the SSM case. The video MCU has similar issue with packet loss since the MCU need to multi-unicast the stream from the source to all participants and may have the same problem when packets are lost between the source and the MCU. If the consensus is that the only relevant use case is the NACK implosion we can look at adding semantics to NACK for this case. Otherwise we can expand the text on the video packet loss case. 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]. Upstream RTP Client: The RTP Client located in the upstream from the distribution source as described in [DVB-IPTV]. This Client is able to detect upstream packet loss impacting all the RTP receivers serviced by the distribution source and receiving SSM service. Immediate reporting RTP Client: The RTP Client located in the downstream aggregate link from the distribution source as described in [DVB-IPTV]. This Client is able to detect downstream packet loss in the aggregate link impacting all the RTP receivers serviced by the distribution source and receiving SSM service. Loss Reporter: The Loss Reporter is one logical function which is used to detect the packet loss at the RTP layer and report it to the distribution source. The function of the loss reporter may be collocated or integrated in the same entity. In this case, for a session defined as having a Distribution Source A, on ports n for the RTP channel and k for the RTCP channel, the unicast RTCP Feedback Target is identified by an IP address of Distribution Source A on port k. The loss reporter MAY also be implemented in one or more entities different from the Distribution Source. In this case, the loss reporter may be an upstream RTP client or immediate reporting RTP client located in the downstream aggregate link of distribution source. Wu, et al. Expires December 12, 2010 [Page 6] Internet-Draft Feedback Storm Suppression June 2010 3. Basic Operation As described in [RFC5760], 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 arrangement. In case of upstream packet loss or downstream aggregate link packet loss, the Loss reporter located in the upstream link or downstream aggregate link may send extended receiver report described in section 6 indicating the packet loss to the distribution source. And then the distribution source creates packet loss suppression report and transmits it to all the RTP receivers, using source- specific multicast. The distribution source can ask for retransmission of the lost packets from the media sender on behalf of all the RTP receivers. Upon receiving the lost packet, the distribution source forwards them to all the receivers which are impacted by packet loss. When the loss reporter(s) are collocated with distribution source, redistribution of packet loss report is trivial. In such case, loss reporter should detect contiguous packet loss coming from upstream link by checking sequence number of RTP packets. Also the loss reporter may detect contiguous packet loss occurring in the collocated distribution source using the similar method mentioned above. When the loss reporter(s) are physically and(or) topologically distinct from distribution source, each loss reporter MUST create packet loss report at the RTP layer and send it to the distribution source. The loss reporters may be upstream client or downstream immediate reporter who is dedicated to detect and report packet loss. The Distribution Source MUST be able to communicate with all group members in order for either mechanism to work. The general architecture is displayed below in Figure 1 Wu, et al. Expires December 12, 2010 [Page 7] Internet-Draft Feedback Storm Suppression June 2010 +--------+ +------------+ Source-specific |Media | | | Multicast |Sender 1|<------->| | +----------------> R(1) +--------+ | | | | | +--+ +--------+ |DISTRIBUTION| | | |Media |<------->| SOURCE | | +-----------> R(2) |Sender 2| | |->+ +---- : +--------+ | | | +------> R(n-1) : | | | | : | +--------+ | +--+--> R(n) | |Feedback| | +--------+ +---->| Target | | |Media | | | +--------+ | |Sender M|<----+-->| | +--------+ | +------------+ | | |Unicast+--------+ +-------+ Loss | |Reporter| +--------+ Transport from the Loss Reporter to the Distribution Source is via unicast feedback if they are not co-located. Figure 1: System Architecture In this figure, we assume the distribution source is separated from a particular media sender and the Feedback Target is collocated with Distribution source. The communication between the Media sender and the distribution source is compliant with the ways described in [RFC5760]. Also besides following the configuration information described in [RFC5760], the additional configuration information should be supplied as follows: o The Loss Reporters know the addresses of their respectively responsible Feedback Targets. As outlined in the [RFC5760], there are two Unicast Feedback models that are used for reporting, i.e., Simple Feedback model and Distribution Source Feedback Summary Model. The RTCP receiver report extension specified in the section 6 of this document will work in both two Feedback models. Wu, et al. Expires December 12, 2010 [Page 8] Internet-Draft Feedback Storm Suppression June 2010 4. Simple Feedback Model In the simple Feedback Model, the Loss reporter(s) are disjoint from distribution source. In this case, the upstream client or immediate reporting receiver may be chosen as the loss reporter. Also in this model, the distribution source will include the support for retransmission as part of the offered SDP and will expect such support from the Media Sender As one dedicated receiver for packet loss reporting, the Loss reporter MUST listen on the RTP channel for data. When the Loss reporter observes RTP packets from a Media Sender are not consecutive by checking the sequence number of packets, the Loss reporter MUST use the same packet types as traditional RTCP feedback described in [RFC3550]and generate Receiver Feedback Report with information on the RTP sequence number of the lost packets and suppression early indication event. When a receiver is eligible to transmit, it MUST send this Report packet to the distribution source via unicast feedback. The Distribution Source (unicast Feedback Target) MUST listen for unicast RTCP data sent to the RTCP port. Upon receiving the unicast Receiver Feedback Report packet from the loss reporter, the Distribution Source MUST forward it to the group on the multicast RTCP channel. Every RTCP packet from each Loss reporter MUST be reflected individually. If the loss reporter is part of group, the Distribution source Must filter this packet out and not forward it back to this loss reporter. If there are a couple of loss reporters looking at the same RTP stream, then the loss may be identified by all and they will all send requests for the same packet loss. In this case, the distribution source MUST filter the duplicated packet loss request out and only forward one copy of the receiver Feedback report packet from the first loss reporter to the group impacted by packet loss. Because this unicast Receiver Feedback Report is used to let the receivers/hosts know that Feedback for packet loss is not needed and should not be sent to the media sender(s). If the Media Sender(s) are part of the SSM group for RTCP packet reflection, the Distribution Source MUST filter this packet out. If the Media Sender(s) are not part of the SSM group for RTCP packet, the Distribution Source MUST not forward this RTCP packets received from the receivers to the Media Sender(s). When the host receives the RTCP packet, if the host 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 Wu, et al. Expires December 12, 2010 [Page 9] Internet-Draft Feedback Storm Suppression June 2010 retransmission stream transmitted from the Distribution Source. If it did not understand this new message, the host may send packet loss request(e.g., NACK messages) to the specified media sender. When the distribution source receives the packet loss request from the hosts, the distribution source MUST filter it out until the Retransmission stream is ready in the Distribution Source. 5. Distribution Source Feedback Summary Model In the distribution source feedback summary model, the distribution source will include the support for retransmission as part of the offered SDP and will expect such support from the Media Sender, also the Loss reporter instance may be integrated in the distribution source or may be separated from the distribution source. In some cases, several loss reporter instances for the same session can exist at the same time, e.g., one loss reporter instance (loss reporter A) is implemented in the upstream client A, one loss reporter instance (loss reporter B) is implemented in the upstream client B, another loss reporter instance for the same session (loss reporter C) is integrated in the distribution source. In this section, we focus on this generic case to discuss the distribution Source Feedback Summary Model. The Loss reporter A and the Loss reporter B MUST listen on the RTP channel for data. When the Loss reporter observes RTP packets from a Media Sender are not consecutive by checking the sequence number of packets, the loss reporter generates NACK message described in [RFC4585] or generates the new Receiver Feedback Report packet described in the section 6, and then send either of them to the distribution source via unicast feedback. The Distribution Source (unicast Feedback Target) MUST listen for unicast RTCP data sent to the RTCP port. Upon receiving the unicast Receiver Feedback Report packet from the loss reporter, the distribution source needs to filter them out, i.e., identify these unicast RTCP packets coming from the Dedicated receivers (i.e.,Loss Reporter A and Loss Reporter B)based on the IP address of loss reporters or dedicated RTCP port for loss report, then summarize the information received from all the Receiver Feedback Reports generated by the Dedicated receivers together with the information generated by the loss reporter integrated in the distribution source and then create the summary report to include these information. In order to reduce the processing load at the distribution source, the individual instance of Loss Reporter may provide preliminary summarization report. In some case, the distribution source may receive RTCP NACK messages Wu, et al. Expires December 12, 2010 [Page 10] Internet-Draft Feedback Storm Suppression June 2010 from the receivers behind the Distribution Source before the distribution source detects the packet loss which may cause potential Feedback implosion. In such case, the distribution source may filter them out if it already sent a packet loss request for the missing packet to the media sender. When the distribution source confirms packet loss reported by the receiver, the distribution source generates the summary report to include the packet loss information from the corresponding receiver (e.g., upstream client or loss reporter). The distribution source may send this new RTCP summary report described in the section 6 to the group on the multicast RTCP channel and in the meanwhile sending a packet loss request to the media sender. If the loss reporter is part of group, the Distribution source MUST not send the summary report back to this loss reporter. If there are a couple of loss reporters looking at the same RTP stream, then the loss may be identified by all and they will all send requests for the same packet loss. In this case, the distribution source MUST filter out the duplicated information from various loss reporters and only append one copy of such information to the summary report. When the host receives the RTCP packet, if the host 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 transmitted from the Distribution Source. If it did not understand this new message, the host may send packet loss request(e.g., NACK messages) to the specified media sender. When the distribution source receives the packet loss request from the hosts, the distribution source MUST filter it out until the Retransmission stream is ready in the Distribution Source. 6. RTCP Receiver Feedback Report Extension 6.1. Transport Layer Feedback Message 6.1.1. NACK implosion Suppression Summary report The NACK implosion Suppression message is an extension to the RTCP receiver feedback report and identified by RTCP packet type value PT=RTPFB and FMT=TBD. The FCI field MUST contain one or more NACK Suppression Early Indication (NSEI) entries. Each entry applies to a different media Wu, et al. Expires December 12, 2010 [Page 11] Internet-Draft Feedback Storm Suppression June 2010 sender, identified by its SSRC. The Feedback Control Information (FCI) for NSEI uses the similar format of message Types defined in the section 4.3.1.1 of [RFC5104]. The format is shown in Figure 2. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SSRC | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SLSN | LLSN | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: Message Format for the NSEI report SSRC (32 bits): The SSRC value of the media sender that is requested to send the lost packet. Starting Sequence Number (SSN):16bits The SSN field is used to specify the contiguous packet loss. The SSN field refers to the RTP sequence number of the first lost packet. Last Sequence Number (LSN): 16 bits The LSN field is used to specify the contiguous packet loss. The LSN refers to the RTP sequence number of the last lost packet. 6.2. Payload Specific Feedback Message 6.2.1. FIR implosion Suppression Summary report The FIR implosion Suppression message is an extension to the RTCP receiver feedback report and identified by RTCP packet type value PT=PSFB and FMT=TBD. The FCI field MUST contain one or more FIR suppression Early Indication (FSEI) entries. Each entry applies to a different media sender, identified by its SSRC. The Feedback Control Information (FCI) for FSEI uses the similar format of message Types defined in the section 4.3.1.1 of [RFC5104]. The format is shown in Figure 3. Wu, et al. Expires December 12, 2010 [Page 12] Internet-Draft Feedback Storm Suppression June 2010 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SSRC | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Seq nr. | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 3: Message Format for the FSEI report SSRC (32 bits): The SSRC value of the media sender that is requested to send a decoder refresh point. Seq nr:8bits Command sequence number. The sequence number space is unique for each pairing of the SSRC of command source and the SSRC of the command target. The sequence number SHALL be increased by 1 modulo 256 for each new command. Reserved: 24 bits All bits SHALL be set to 0 by the sender and SHALL be ignored on reception. 7. SDP Signaling A new feedback value "fss" needs to be defined for the Feedback Storm Suppression message to be used with Session Description Protocol (SDP) [RFC4566] using the Augmented Backus-Naur Form (ABNF) [RFC4585]. The "fss" feedback value SHOULD be used with parameters that indicate the feedback suppression supported. In this document, we define two such parameters, namely: o "fsei" denotes support of fir suppression early indication (fsei). o "nsei" denotes support of NACK suppression early indication In the ABNF for rtcp-fb-val defined in [RFC4585], there is a placeholder called rtcp-fb-id to define new feedback types. "fss" is defined as a new feedback type in this document, and the ABNF for the parameters for fss is defined here (please refer to section 4.2 of [RFC4585] for complete ABNF syntax). Wu, et al. Expires December 12, 2010 [Page 13] Internet-Draft Feedback Storm Suppression June 2010 rtcp-fb-val =/ "fss" rtcp-fb-fss-param rtcp-fb-fss-param = SP "nsei";nack suppression early indication / SP "fsei";fir suppression early indication / SP token [SP byte-string] ; for future commands/indications byte-string = Refer to Section 4.2 of [RFC4585] for a detailed description and the full syntax of the "rtcp-fb" attribute. 8. IANA Consideration New feedback type and New parameters for RTCP FSS receiver feedback report are subject to IANA registration. For general guidelines on IANA considerations for RTCP feedback, refer to [RFC4585]. This document assigns one new feedback type value x in the RTCP receiver feedback report registry to "Feedback Storm Suppression" with the following registrations format: Name: FSS Long Name: Feedback Storm Suppression Value: TBD Reference: This document. This document also assigns the parameter value y in the RTCP FSS receiver feedback report Registry to "NACK Suppression Early Indication ", with the following registrations format: Name: NSEI Long name: NACK Suppression Early Indication Value: TBD Reference: this document. This document also assigns the parameter value z in the RTCP FSS receiver feedback report Registry to "FIR Suppression Early Indication ", with the following registrations format: Name: FSEI Long name: FIR Suppression Early Indication Value: TBD Reference: this document. The contact information for the registrations is: Wu, et al. Expires December 12, 2010 [Page 14] Internet-Draft Feedback Storm Suppression June 2010 Qin Wu sunseawq@huawei.com Site B, Floor 12F,Huihong Mansion, No.91,Baixia Rd. Nanjing, JiangSu 210001 China 9. Acknowledgement The authors would like to thank Tom David R Oran,Tom VAN CAENEGEM for their valuable comments and suggestions on this document. 10. References 10.1. Normative References [RFC5760] Ott, J., Chesterfield, J., and E. Schooler, "RTP Control Protocol (RTCP) Extensions for Single-Source Multicast Sessions with Unicast Feedback", RFC 5760, February 2010. [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 December 12, 2010 [Page 15] Internet-Draft Feedback Storm Suppression June 2010 10.2. 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 Retransmission Storm Suppression A.1. Scenario 1: One or more media sender,One distribution source The general architecture for scenario 1 is displayed below in Figure 4. In this architecture, one or more Media Senders send RTP packets to the RTP Receivers through the same 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 in the upstream link or downstream aggregate link of 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 4: One media Sender, one Distribution Source Wu, et al. Expires December 12, 2010 [Page 16] Internet-Draft Feedback Storm Suppression June 2010 A.2. Scenario 2:One media sender, Two distribution sources in cascade +-------+ |---->|RTP_Rx1| | +-------+ +------+ | | | +------------+ +------------+ | +-------+ |Media |-+Distribution+--|Distribution+--|---->|RTP_Rx2| |Sender| | Source1 | | Source2 | | +-------+ | | +------------+ +------------+ | . +------+ | . | . | +-------+ |---->|RTP_Rxn| +-------+ Figure 5: One media sender, Two distribution sources in cascade The general architecture for scenario 2 is displayed below in Figure 5. In this architecture, One media sender passes through two distribution source in cascading and sends RTP packets to all the RTP receivers. When packet loss happens in the upstream link or downstream aggregate link of distribution source1, 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. In this case, the distribution source 2 can be taken as one special RTP receiver located in the downstream direction of distribution source 1. A.3. Scenario 3:One media sender, Two distribution sources in parallel The general architecture for scenario 3 is displayed below in Figure 6. In this architecture, one media sender and two Distribution source constitute one hierarchical tree model. In this model, one Media Senders send RTP packets to all the RTP receivers through two different path respectively. When packet loss happens in the upstream link or downstream aggregate link of 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. Wu, et al. Expires December 12, 2010 [Page 17] Internet-Draft Feedback Storm Suppression June 2010 +--------+ |---->|RTP_Rx11| | +--------+ +--------------+ | | | | +--------+ |--->| Distribution |----|---->|RTP_Rx12| | | Source1 | | +--------+ | | | | . +--------+ | +--------------+ | . | | | | . | | | | +--------+ | Media | | |---->|RTP_Rx1k| | |---| +--------+ | Sender | | +--------+ | | | |---->|RTP_Rx21| | | | | +--------+ +--------+ | +--------------+ | | | | | +--------+ | | Distribution |----|---->|RTP_Rx22| |--->| Source2 | | +--------+ | | | . +--------------+ | . | . | +--------+ |---->|RTP_Rx2j| +--------+ Figure 6: One Media Sender, more distribution sources Appendix B. Applicability of Feedback Storm Suppression This document defines new RTCP Receiver feedback 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 feedback report is applied into three scenarios described in Appendix A for Retransmission Storm Suppression. Applicability of Retransmission Storm Suppression in Scenario 1 described in Figure 4 is shown in the Figure 7. 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 Retransmission 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. Wu, et al. Expires December 12, 2010 [Page 18] Internet-Draft Feedback Storm Suppression June 2010 +------+ +--------------+ +--------+ |Media | | Distribution | | | |Sender| | Source | | RTP_Rx | +--+---+ +------+-------+ +---+----+ | | | | | | |------------------->|------RTP Multicast---->| | | | | | | | +--------+----------+ | | |Detect Packet Loss | | | |and Identify the SN| | | |of missing Packets | | | +--------+----------+ | |<-----RTCP NACK-----| | | | | | +--Multicast RTCP FSS--->| | RTP Retransmission | | |------------------->| | | |------RTP Multicast---->| | | Retransmission | | | | | | | | | | Figure 7: Applicability of Feedback Suppression Early Indication Applicability of Feedback Storm Suppression in Scenario 2 or 3 described in Figure 5 and Figure 6 is shown in the Figure 8. The procedure in the Figure 8 is similar to the one in the figure Figure 7. The only 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. Wu, et al. Expires December 12, 2010 [Page 19] Internet-Draft Feedback Storm Suppression June 2010 +------+ +-------+ +--------+ +-------+ +--------+ |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 FSS | | | |------------>| |RTP Retransmission | | | |----------->| | | | | | | | | | | RTP Retransmission | | |------------+--------------+--------------->| | | | | | | | | RTP Multicast| | RTP Multicast | |Retransmission| |Retransmission | |------------->| |------------>| | | | | | DS1: Distribution Source 1 DS2: Distribution Source 2 Figure 8: Applicability of Retransmission Suppression Early Indication Wu, et al. Expires December 12, 2010 [Page 20] Internet-Draft Feedback Storm Suppression June 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 December 12, 2010 [Page 21]