Audio/Video Transport Working Group Q.
WuWu, Ed. Internet-Draft Huawei Intended status: Informational May 5, 2011G. Hunt Expires: November 6,28, 2011 Unaffiliated P. Arden BT May 27, 2011 Monitoring Architectures for RTP draft-ietf-avtcore-monarch-01.txtdraft-ietf-avtcore-monarch-02.txt Abstract This memo proposes an architecture for extending RTCP with a new RTCP XR (RFC3611) block type to report new metrics regarding media transmission or reception quality, as proposed in RFC5968. This memo suggests that a new block should contain a single metric or a small number of metrics relevant to a single parameter of interest or concern, rather than containing a number of metrics which attempt to provide full coverage of all those parameters of concern to a specific application. Applications may then "mix and match" to create a set of blocks which covers their set of concerns. Where possible, a specific block should be designed to be re-usable across more than one application, for example, for all of voice, streaming audio and video. 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 November 6,28, 2011. Copyright Notice Copyright (c) 2011 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 Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Requirements notation . . . . . . . . . . . . . . . . . . . . 4 3. RTP monitoring architecture . . . . . . . . . . . . . . . . . 5 3.1. Interaction with Management Application . . . . . . . . . 7 3.2.RTCP Metric Block Report and associated parameters . . . . 7 4. Issues with reporting metric block using RTCP XR extension . . 9 5. Guideline for reporting block format using RTCP XR . . . . . . 10 5.1. Using small blocks . . . . . . . . . . . . . . . . . . . . 10 5.2. Sharing the identity blockinformation . . . . . . . . . . . . . 10 5.3. Correlating identity information with the data . . . . . 10. 12 6. An example of a metric block . . . . . . . . . . . . . . . . . 1513 7. Application to RFC 5117 topologies . . . . . . . . . . . . . . 1614 7.1. Applicability to MCU . . . . . . . . . . . . . . . . . . . 1614 7.2. Applicability to Translators . . . . . . . . . . . . . . . 1614 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 1816 9. Security Considerations . . . . . . . . . . . . . . . . . . . 1917 10. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 2018 11. Informative References . . . . . . . . . . . . . . . . . . . . 21 Appendix A.19 Appendix A. Change Log . . . . . . . . . . . . . . . 22. . . . . . 20 A.1. draft-ietf-avtcore-monarch-00 . . . . . . . . . . . . . . 2220 A.2. draft-ietf-avtcore-monarch-01 . . . . . . . . . . . . . . 22 Author's Address20 A.3. draft-ietf-avtcore-monarch-02 . . . . . . . . . . . . . . 20 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23. 22 1. Introduction Service providers and network providers today suffer from lack of good service that can monitor the performance at the user's home, handset or remote office. Without service performance metrics, it is difficult for network operators to properly locate the problem and solve service issues before problems impact subscriber/end user. The resolution generally involves deploying costly field network technician to conduct on-site troubleshooting and diagnostics. By reducing the expensive deployments with more automated remote monitoring capabilities, network operators can save significant costs, reduce mean time to repair and provide a better service offering.As more users and subscribers rely on real time application services, uncertainties in the performance and availability of these services are driving the need to support new standard methods for gathering performance metrics from RTP applications. These rapidly emerging standards, such as RTCP XR [RFC3611]and other RTCP extension to Sender Reports(SR), Receiver Reports (RR) [RFC3550]are being developed for the purpose of collecting and reporting performance metrics from endpoint devices that can be used to correlate the metrics, provide end to end service visibility and measure and monitor QoE. However the proliferation of RTP/RTCP specific metrics for transport and application quality monitoring has been identified as a potential problem for RTP/RTCP interoperability, which attempt to provide full coverage of all those parameters of concern to a specific application. Since different applications layered on RTP may have some monitoring requirements in common, therefore these metrics should be satisfied by a common design. The objective of this document is to define an extensible RTP monitoring framework to provide a small number of re-usable QoS/QoE metrics which facilitate reduced implementation costs and help maximize inter-operability. [RFC5968] has stated that, where RTCP is to be extended with a new metric, the preferred mechanism is by the addition of a new RTCP XR [RFC3611] block. This memo assumes that any requirement for a new metric to be transported in RTCP will use a new RTCP XR block. 2. Requirements notation This memo is informative and as such contains no normative requirements. In addition, the following terms are defined: Transport level metrics A set of metrics which characterise the three transport impairments of packet loss, packet delay, and packet delay variation. These metrics should be usable by any application which uses RTP transport. Application level metrics Metrics relating to QoE related parameters. These metrics are measured at the application level and focus on quality of content rather than network parameters. End System metrics Metrics relating to the way a terminal deals with transport impairments affecting the incident RTP stream. These may include de-jitter buffering, packet loss concealment, and the use of redundant streams (if any) for correction of error or loss. 3. RTP monitoring architecture The RTP monitoring architecture comprises the following two key functional components shown below: o Monitor o Metric Block Structure Monitor is a functional component defined in RFC3550 that acts as a source of information gathered for monitoring purposes. It may also collect statistics from multiple source, stores such information reported by RTCP XR or other RTCP extension appropriately as base metric or calculates composite metric. According to the definition of monitor in RFC3550, the end system that source RTP streams, an intermediate-system that forwards RTP packets to End-devices or a third party that does not participate RTP session (i.e., the third party monitor depicted in figure 1) can be envisioned to act as Monitor within the RTP monitoring architecture. The Metric Block exposes real time Application Quality information in the appropriate report block format to monitor within the RTP monitoring architecture. Both the RTCP or RTCP XR can be extended to convey such information. The details on transport protocol for metric block is described in Section 220.127.116.11. |---------------+ | Management | +-------------------+ | System | | RTP Sender | | +----------+ | | +-----------+ | | | | | ---------------->| Monitor |---------5------->| Monitor | | | | | | | | | | | | | +-----------+ | | +----\-----+ | | |+-----------------+| | | | | ||Application || --------|-------+ | ||-Streaming video || | | |---------|-VOIP || 5 | | ||-Video conference|| | | | ||-Telepresence || +---------------+ | | ||-Ad insertion || | Third Party | 5 | |+-----------------+| | Monitor | | | +-------------------+ +---------------+ | 1 | | +Intermediate------------+ |-------------- ---- ----+ | | | RTP System Report Block | RTP Receiver >--4-| | | | | +---------- transported over| +-----------+ | | | | | | RTCP extension | | Monitor |<-- | |------------- Monitor |<--------5------|----| |<------| | | | | Report Block +----/------+ || | | +----------+ transported over | || | | RTCP XR | |2 || | | +-----------------+ | | +-------/---------+ || | | |Application | | | |Application | || | | |-Streaming video | | | |-Streaming video | || | | |-VOIP | | 1 | |-VOIP | 3| ---->-Video conference|--------------->|-Video conference || | |-Telepresence | | | |-Telepresence | || | |-Ad insertion | | | |-Ad insertion | || | +-----------------+ | | +-----------------+ || | +-----------------+ | | +-----------------+ || | |Transport | | | |Transport | || | |-IP/UDP/RTP | | | |-IP/UDP/RTP >---|| | |-IP/TCP/RTP | | | | -IP/TCP/RTP | | | |-IP/TCP/RTSP/RTP | | | |-IP/TCP/RTSP/RTP | | | +-----------------+ | | +-----------------+ | +------------------------+ +------------------------+ Figure 1: RTP Monitoring Architecture 1. RTP communication between real time applications 2. Application level metrics 3. Transport level metrics 4. End System metrics 5. Reporting Session- metrics transmitted over specified interfaces 3.1. Interaction with Management Application The full solution may include Management application which interacts with monitor. The Monitor outputs reports to the management application. The management application collects raw data from monitor, organizes database, conducts data analysis and creates alerts to the users. However Management application interaction with Monitor is out of scope of this document. 3.2.RTCP Metric Block Report and associated parameters The basic RTCP Reception Report (RR) conveys reception statistics in metric block report format for multiple RTP media streams including o transport level statistics o the fraction of packet lost since the last report o the cumulative number of packets lost o the highest sequence number received o an estimate of the inter-arrival jitter o and information to allow senders to calculate the network round trip time. The RTCP XRs [RFC3611] supplement the existing RTCP packets and provide more detailed feedback on reception quality in several categories: o Loss and duplicate RLE reports o Packet-receipt times reports o Round-trip time reports o Statistics Summary Reports There are also various other scenarios in which it is desirable to send RTCP Metric reports more frequently. The Audio/Video Profile with Feedback [RFC4585]extends the standard A/V Profile[RFC3551] to allow RTCP reports to be sent early provided RTCP bandwidth allocation is respected. There are four use cases but are not limited to: o RTCP NACK is used to provide feedback on the RTP sequence number of the lost packets. o RTCP XR is extended to provide feedback on multicast acquisition statistics information and parameters. o RTCP is extended to convey requests for full intra-coded frames or select the reference picture, and signalchanges in the desired temporal/spatial trade-off and maximum media bit rate. o RTCP or RTCP XR is extended to provide feedback on ECN statistics information. 4. Issues with reporting metric block using RTCP XR extension Issues that have come up in the past with reporting metric block using RTCP XR extensions include (but are probably not limited to) the following: o Using large block. A single report block or metric is designed to contain a large number of parameters in different classes for a specific application. For example, RFC 3611 [RFC3611] defines seven report block formats for network management and quality monitoring. However some of these block types defined in [RFC3611] are only specifically designed for conveying multicast inference of network characteristics(MINC) or voice over IP (VoIP) monitoring. However different applications layered on RTP may have some monitoring requirements in common, design large block only for specific applications may increase implementation cost and minimize interoperability. o Identity Information duplication. When multiple small blocks in the sameThere may be situations where an RTCP XR packet containcontaining more than two metrics blocks, reports on the same streams from the same source. In such case, each metric block should have the same measurement identity, if each metric block carry such duplicated data for the same stream and period, it bring inefficiencymeasurement,it leads to Repeat theredundant information in a number of metrics blocks within the same RTCPthis design since equivalent information is provided multiple times, once in *every* identification packet. Though this ensures immunity to packet loss, the design bring more complexity and the overhead is not completely trivial. o Metric Blocks association. WhenThere may be situations where an RTCP XR packet containing four metrics blocks, reportingreports on streams from two sources,sources. In such case, two identity blocks need to be added into the RTCP XR packet to correlate two sources if identity information is allowed separate from each metric block as one independent block. However how to associate identity block with relevant metric block data or other identity data is a problem, e.g., all identity blocks are following all the metric block or vice versa make one receiving RTCP XR packet hard to distinguish from which metric block belong to which source. 5. Guideline for reporting block format using RTCP XR 5.1. Using small blocks Different applications using RTP for media transport certainly have differing requirements for metrics transported in RTCP to support their operation. For many applications, the basic metrics for transport impairments provided in RTCP SR and RR packets [RFC3550] (together with source identification provided in RTCP SDES packets) are sufficient. For other applications additional metrics may be required or at least sufficiently useful to justify the overheads, both of processing in endpoints and of increased session bandwidth. For example an IPTV application using Forward Error Correction (FEC) might use either a metric of post-repair loss or a metric giving detailed information about pre-repair loss bursts to optimise payload bandwidth and the strength of FEC required for changing network conditions. However there are many metrics available. It is likely that different applications or classes of applications will wish to use different metrics. Any one application is likely to require metrics for more than one parameter but if this is the case, different applications will almost certainly require different combinations of metrics. If larger blocks are defined containing multiple metrics to address the needs of each application, it becomes likely that many different such larger blocks are defined, which becomes a danger to interoperability. To avoid this pitfall, this memo proposes the use of small RTCP XR metrics blocks each containing a very small number of individual metrics characterizing only one parameter of interest to an application running over RTP. For example, at the RTP transport layer, the parameter of interest might be packet delay variation, and specifically the metric "IPDV" defined by [Y1540]. See Section 6 for architectural considerations for a metrics block, using as an example a metrics block to report packet delay variation. 5.2. Sharing the identity blockinformation Any measurement must be identified. However if metrics are delivered in small blocks there is a danger of inefficiency arising from repeating this information in a number of metrics blocks within the same RTCP packet, in cases where the same identification information applies to multiple metrics blocks. An instance of a metric must be identified using information which is likely to include most of the following: o the node at which it was measured, o the source of the measured stream (for example, its CNAME), o the SSRC of the measured stream, o the sequence number of the first packet of the RTP session, o the extended sequence numbers of the first packet of the current measurement interval, and the last packet included in the measurement, o the duration of the most recent measurement interval and o the duration of the interval applicable to cumulative measurements (which may be the duration of the RTP session to date). Note that this set of information may overlap with, but is more extensive than, that in the union of similar information in RTCP RR packets. However we can not assume that RR information is always present when XR is sent, since they may have different measurement intervals. Also the reason for the additional information carried in the XR is the perceived difficulty of "locating" the *start* of the RTP session (sequence number of 1st packet, duration of interval applicable to cumulative measurements) using only RR. However when an RTCP XR packet containing more than two metrics blocks, reporting on the same streams from the same source, each metric block should have the same measurement identity, if each metric block carry the duplicated data for the measurement identity ,it leads to redundant information in this design since equivalent information is provided multiple times, once in *every* identification packet. Though this ensures immunity to packet loss, the design bring more complexity and the overhead is not completely trivial. This section proposes an approach to minimise the inefficiency of providing this identification information, assuming that an architecture based on small blocks means that a typical RTCP packet will contain more than one metrics block needing the same identification. The choice of identification information to be provided is discussed in [IDENTITY] .[IDENTITY]. The approach is to define a stand-alone block containing only identification information, and to tag this identification block with a number which is uniqueinformation within the scope of the containing RTCP XR packet. The "containing RTCP XR packet" is defined here as the RTCP XR header with PT=XR=207 defined in Section 2 of [RFC3611] and the associated payload defined by the length field of this RTCP XR header. The RTCP XR header itself includes the SSRC of the node at which all of the contained metrics were measured, hence this SSRC need not be repeated in the stand-alonestand- alone identification block. A single containing RTCP XR packet may contain multiple identification blocks limited by the range of the tag field. Typically there will be one identification block per monitored source SSRC, but the use of more than one identification block for a single monitored source SSRC within a single containing RTCP XR packet is not ruled out. ThereIn order to reduce overhead of the payload, This stand-alone block need only be exchanged occasionally, for example sent once at the start of a session. 5.3. Correlating identity information with the data This section proposes an approach to facilitate the correlation of the metrics report blocks with other session-related data or identity data, i.e., using correlation tag to associate identity information with the data. For example, there will be zero or more metrics blocks dependent on each identification block.the same set of identity information. The dependence of an instance of a metrics block on an identification block issuch identity information can be established by the metrics block's having the same numeric value of the tag field as its identification block (in the same containing RTCP XR packet). Figure 2 below illustrates this principle using as an examplefield. Also there will be an RTCP XR packet containing four metrics blocks, reporting on streams from two sources. The measurementidentity information is provided in two blocks with Block Type NMI, and tag values 0 and 1 respectively. Note: in this example, RTCP XR block type values for four proposed new block types (work in progress) are given as NMI, NPDV, NBGL and NDEL. Eachdata dependent on the same set of these twoidentity blocks will specifyinformation. If the SSRC of oneset of the monitored streams, as well asidentity information aboutis formed as an independent block, then the spandependence of the measurement. There are two metrics blocks with tag=0 indicating their association with the measurementan instance of a identity block which also has tag=0. These areon identity data can be established by the two blocks followingidentity block's having the tag field to indicate the relationship between identity block with tag=0, though this positioning is not mandatory. There are also two metricsblocks with tag=1 indicating their association with the measurement identity block which also has tag=1, and these are the two blocks following the identity block with tag=1. Note that if metrics blocks associated with an identity block must always follow the identity block, we could save the tag field and possibly simplify processing. However depending on ordering of metric block and identity block may bring inefficiency since you do not know which block is the last metric block associated with identity block unless you identify the next identity block. Hence it is more desirable to to do cross-referencing with a numeric tag,i.e., using tag field to associated metric block with identity block. In the example, the block types of the metrics blocks associated with tag=0 are BT=NPDV (a PDV metrics block) and BT=NBGL (a burst and gap loss metrics block). The block types of the metrics blocks associated with tag=1 are BT=NPDV (a second PDV metrics block)and BT=NDEL (a delay metrics block). This illustrates that: o multiple instances of the same metrics block may occur withina containing RTCP XR packet, associated with different identification information, and o differing measurements may be made, and reported,specific application. An example use case is for the different streams arriving atan RTP system. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |V=2|P|reserved | PT=XR=207 | length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SSRC of RTCP XR packet sender | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | BT=NMI |0|tag=0| resv | block length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SSRC of stream source 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . ...measurement identity information, source 1... . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | BT=NPDV |I|tag=0|pdvtyp | block length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . ...PDV information for source 1... . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | BT=NBGL |I|tag=0| resv | block length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . ...burst-gap-loss information for source 1... . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | BT=NMI |0|tag=1| resv | block length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SSRC of stream source 2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . ...measurement identity information, source 2... . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | BT=NPDV |I|tag=1|pdvtyp | block length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . ...PDV information for source 2... . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | BT=NDEL |I|tag=1| resv | block length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . ...delay information for source 2... . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: RTCP XR block with identity blocks This approach of separating the identification information is more costly than providing identification in each metrics block if onlyendpoint may convey a call identifier or a single metrics blockglobal call identifier associated with identity information. A flow measurement tool that is sent in an RTCP packet, but becomes beneficial as soonnot call-aware can then forward the metric reports along with this correlation tag to network management. Network management can then use this tag to correlate this report with other diagnostic information such as more than one metrics block shares common identification.call detail records. 6. An example of a metric block This section uses the example of an existing proposed metrics block to illustrate the application of the principles set out in Section 5.1. The example [PDV] (work in progress) is a block to convey information about packet delay variation (PDV) only, consistent with the principle that a metrics block should address only one parameter of interest. One simple metric of PDV is available in the RTCP RR packet as the "jit" field. There are other PDV metrics which may be more useful to certain applications. Two such metrics are the IPDV metric ([Y1540], [RFC3393]) and the MAPDV2 metric [G1020]. Use of these metrics is consistent with the principle in Section 5 of [RFC5968] that metrics should usually be defined elsewhere, so that RTCP standards define only the transport of the metric rather than its nature. The purpose of this section is to illustrate the architecurearchitecture using the example of [PDV] (work in progress) rather than to document the design of the PDV metrics block or to provide a tutorial on PDV in general. Given the availability of at least three metrics for PDV, there are design options for the allocation of metrics to RTCP XR blocks: o provide an RTCP XR block per metric o provide a single RTCP XR block which contains all three metrics o provide a single RTCP block to convey any one of the three metrics, together with a identifier to inform the receiving RTP system of the specific metric being conveyed In choosing between these options, extensibility is important, because additional metrics of PDV may well be standardized and require inclusion in this framework. The first option is extensible but only by use of additional RTCP XR blocks, which may consume the limited namespace for RTCP XR blocks at an unacceptable rate. The second option is not extensible, so could be rejected on that basis, but in any case a single application is quite unlikely to require transport of more than one metric for PDV. Hence the third option was chosen. This implies the creation of a subsidiary namespace to enumerate the PDV metrics which may be transported by this block, as discussed further in [PDV] (work in progress). 7. Application to RFC 5117 topologies The topologies specified in [RFC5117] fall into two categories. The first category relates to the RTP system model utilizing multicast and/or unicast. The topologies in this category are specifically Topo-Point-to-Point, Topo- Multicast, Topo-Translator (both variants, Topo-Trn-Translator and Topo-Media-Translator, and combinations of the two), and Topo-Mixer. These topologies use RTP end systems, RTP mixers and RTP translators defined in [RFC3550]. The second category relatesFor purposes of reporting connection quality to deployed system models used in many H.323 [H323] video conferences. The topologies in this category are Topo-Video-Switch- MCUother RTP systems, RTP mixers and Topo-RTCP-terminating-MCU. Such topologies based onRTP end systems are very similar. Mixers resynchronize audio packets and do not behave according to [RFC3550]. As for the firstrelay RTCP reports received from one cloud towards other cloud(s). Translators do not resynchronize packets and SHOULD forward certain RTCP reports between clouds. In this category, the RTP system (end system, mixer or translator) which originates, terminates or forwards RTCP XR blocks is expected to handle RTCP, including RTCP XR, according to [RFC3550]. Provided this expectation is met, an RTP system using RTCP XR is architecturally no different from an RTP system of the same class (end system, mixer, or translator) which does not use RTCP XR. Considering the translator and MCU are two typicalThe second category relates to deployed system models used in many H.323 [H323] video conferences. The topologies in thetwo categories mentioned above,this document will take them as two typical examplescategory are Topo-Video-Switch- MCU and Topo-RTCP-terminating-MCU. Such topologies based on systems do not behave according to explain how RTCP XR report works in different RFC5117 topologies.[RFC3550]. 7.1. Applicability to MCU Topo-Video-Switch-MCU and Topo-RTCP-terminating-MCU, suffer from the difficulties described in [RFC5117]. These difficulties apply to systems sending, and expecting to receive, RTCP XR blocks as much as to systems using other RTCP packet types. For example, a participant RTP end system may send media to a video switch MCU. If the media stream is not selected for forwarding by the switch, neither RTCP RR packets nor RTCP XR blocks referring to the end system's generated stream will be received at the RTP end system. Strictly the RTP end system can only conclude that its RTP has been lost in the network, though an RTP end system complying with the robustness principle of [RFC1122] should survive with essential functions unimpaired. 7.2. Applicability to Translators Section 7.2 of [RFC3550] describes processing of RTCP by translators. RTCP XR is within the scope of the recommendations of [RFC3550]. Some RTCP XR metrics blocks may usefully be measured at, and reported by, translators. As described in [RFC3550] this creates a requirement for the translator to allocate an SSRC for the monitor within itself so that it may populate the SSRC in the RTCP XR packet header (although the translator is not a Synchronisation Source in the sense of originating RTP media packets). It must also supply this SSRC and the corresponding CNAME in RTCP SDES packets. In RTP sessions where one or more translators generate any RTCP traffic towards their next-neighbour RTP system, other translators in the session have a choice as to whether they forward a translator's RTCP packets. Forwarding may provide additional information to other RTP systems in the connection but increases RTCP bandwidth and may in some cases present a security risk. RTP translators may have forwarding behaviour based on local policy, which might differ between different interfaces of the same translator. For bidirectional unicast, an RTP system may usually detect RTCP XR from a translator by noting that the sending SSRC is not present in any RTP media packet. However even for bidirectional unicast there is a possibility of a source sending RTCP XR before it has sent any RTP media (leading to transient mis-categorisation of an RTP end system or RTP mixer as a translator), and for multicast sessions - or unidirectional/streaming unicast - there is a possibility of a receive-only end system being permanently mis-categorised as a translator sending XR report, i.e.,monitor collocated with transaltor. Hence it is desirable for a translator that sendsends XR to have a way to declare itself explicitly. 8. IANA Considerations None. 9. Security Considerations This document itself contains no normative text and hence should not give rise to any new security considerations, to be confirmed. 10. Acknowledgement Geoff Hunt and Philip Arden wrote the initial draft for this document and provided useful reviews. Many thanks to them.The authors would also like to thank Colin Perkins, Graeme Gibbs, Debbie Greenstreet, Keith Drage,Dan Romascanu, Ali C. Begen, Roni Even for their valuable comments and suggestions on the early version of this document. 11. Informative References [G1020] ITU-T, "ITU-T Rec. G.1020, Performance parameter definitions for quality of speech and other voiceband applications utilizing IP networks", July 2006. [H323] ITU-T, "ITU-T Rec. H.323, Packet-based multimedia communications systems", June 2006. [IDENTITY] Hunt, G., "RTCP XR Report Block for Measurement Identity", ID draft-ietf-avt-rtcp-xr-meas-identity-02, May 2009. [PDV] Hunt, G., "RTCP XR Report Block for Packet Delay Variation Metric Reporting", ID draft-ietf-avt-rtcp-xr-pdv-03, May 2009. [RFC1122] Braden, R., "Requirements for Internet Hosts -- Communication Layers", RFC 1122, October 1989. [RFC3393] Demichelis, C., "IP Packet Delay Variation Metric for IP Performance Metrics (IPPM)", RFC 3393, November 2002. [RFC3550] Schulzrinne, H., "RTP: A Transport Protocol for Real-Time Applications", RFC 3550, July 2003. [RFC3551] Schulzrinne , H. and S. Casner, "Extended RTP Profile for Real-time Transport Control Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 3551, July 2003. [RFC3611] Friedman, T., "RTP Control Protocol Extended Reports (RTCP XR)", RFC 3611, November 2003. [RFC4585] Ott, J. and S. Wenger, "Extended RTP Profile for Real-time Transport Control Protocol (RTCP)-Based Feedback (RTP/ AVPF)", RFC 4585, July 2006. [RFC5117] Westerlund, M., "RTP Topologies", RFC 5117, January 2008. [RFC5968] Ott, J. and C. Perkins, "Guidelines for Extending the RTP Control Protocol (RTCP)", RFC 5968, September 2010. [Y1540] ITU-T, "ITU-T Rec. Y.1540, IP packet transfer and availability performance parameters", November 2007. Appendix A. Appendix A.Change Log Note to the RFC-Editor: please remove this section prior to publication as an RFC. A.1. draft-ietf-avtcore-monarch-00 The following are the major changes compared to draft-hunt-avtcore-monarch-02: o Move Geoff Hunt and Philip Arden to acknowledgement section. A.2. draft-ietf-avtcore-monarch-01 The following are the major changes compared to 00: o Restructure the document by merging section 4 into section 3. o Remove section 4.1,section 5 that is out of scope of this document. o Remove the last bullet in section 6 and section 7.3 based on conclusion of last meeting. o Update figure 1 and related text in section 3 according to the monitor definition in RFC3550. o Revise section 9 to address monitor declaration issue. o Merge the first two bullet in section 6. o Add one new bullet to discuss metric block association in section 6. Author's AddressA.3. draft-ietf-avtcore-monarch-02 The following are the major changes compared to 01: o Deleting first paragraph of Section 1. o Deleting Section 3.1, since the interaction with the management application is out of scope of this draft. o Separeate identity information correlation from section 5.2 as new section 5.3. o Remove figure 2 and related text from section 5.2. o Editorial changes in the section 4 and the first paragraph of section 7. Authors' Addresses Qin Wu (editor) Huawei 101 Software Avenue, Yuhua District Nanjing, Jiangsu 210012 China Email: email@example.com Geoff Hunt Unaffiliated Email: firstname.lastname@example.org Philip Arden BT Orion 3/7 PP4 Adastral Park Martlesham Heath Ipswich, Suffolk IP5 3RE United Kingdom Phone: +44 1473 644192 Email: email@example.com