GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc6792

Internet Engineering Task Force (IETF) Q. Wu, Ed. Request for Comments: 6792 Huawei Category: Informational G. Hunt ISSN: 2070-1721 Unaffiliated

                                                              P. Arden
                                                                    BT
                                                         November 2012
         Guidelines for Use of the RTP Monitoring Framework

Abstract

 This memo proposes an extensible Real-time Transport Protocol (RTP)
 monitoring framework for extending the RTP Control Protocol (RTCP)
 with a new RTCP Extended Reports (XR) block type to report new
 metrics regarding media transmission or reception quality.  In this
 framework, a new XR 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 that 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 that cover their set of concerns.  Where
 possible, a specific block should be designed to be reusable across
 more than one application, for example, for all of voice, streaming
 audio, and video.

Status of This Memo

 This document is not an Internet Standards Track specification; it is
 published for informational purposes.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Not all documents
 approved by the IESG are a candidate for any level of Internet
 Standard; see Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc6792.

Wu, et al. Informational [Page 1] RFC 6792 RTP Monitoring Framework November 2012

Copyright Notice

 Copyright (c) 2012 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. Terminology .....................................................3
 3. RTP Monitoring Framework ........................................5
    3.1. Overview of the RTP Monitoring Framework ...................5
    3.2. Location of Monitors .......................................7
 4. Issues with Reporting Metrics Blocks Using RTCP XR Extensions ...8
    4.1. Using a Compound Metrics Block .............................8
    4.2. Correlating RTCP XR with Non-RTP Data ......................8
    4.3. Measurement Information Duplication ........................9
    4.4. Consumption of XR Block Code Points ........................9
 5. Guidelines for Reporting Metrics Blocks Using RTCP XR ...........9
    5.1. Use a Single Metric in the Metrics Block ...................9
    5.2. Include the Payload Type in the Metrics Block .............10
    5.3. Use RTCP SDES to Correlate XRs with Non-RTP Data ..........10
    5.4. Reduce Measurement Information Repetition across
         Metrics Blocks ............................................11
 6. An Example of a Metrics Block ..................................11
 7. Application to RFC 5117 Topologies .............................12
    7.1. Applicability to Translators ..............................13
    7.2. Applicability to MCUs .....................................13
 8. Security Considerations ........................................14
 9. Acknowledgements ...............................................14
 10. Informative References ........................................15

Wu, et al. Informational [Page 2] RFC 6792 RTP Monitoring Framework November 2012

1. Introduction

 Multimedia services using the Real-time Transport Protocol (RTP) are
 seeing increased use.  Standard methods for gathering RTP performance
 metrics from these applications are needed to manage uncertainties in
 the behavior and availability of their services.  Standards such as
 "RTP Control Protocol Extended Reports (RTCP XR)" [RFC3611] as well
 as other RTCP extensions to sender reports (SRs) and receiver reports
 (RRs) [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 Quality of Experience (QoE) [RFC6390].
 However, the proliferation of RTP-/RTCP-specific metrics for
 transport and application quality monitoring has been identified as a
 potential problem for interoperability when using RTP/RTCP to
 communicate all the parameters of concern to a specific application.
 Given that different applications layered on RTP may have some
 monitoring requirements in common, these metrics should be satisfied
 by a common design.
 The objective of this document is to describe an extensible RTP
 monitoring framework to provide a small number of reusable Quality of
 Service (QoS) / QoE metrics that facilitate reduced implementation
 costs and help maximize interoperability.  "Guidelines for Extending
 the RTP Control Protocol (RTCP)" [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 all the guidelines from RFC 5968 must apply on top of the
 guidelines in this document.  Guidelines for developing new
 performance metrics are specified in [RFC6390].  New RTCP XR report
 block definitions should not define new performance metrics but
 should rather refer to metrics defined elsewhere.

2. Terminology

 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 that characterize the three transport impairments
    of packet loss, packet delay, and jitter (also known as delay
    variation).  These metrics should be usable by any application
    that uses RTP transport.

Wu, et al. Informational [Page 3] RFC 6792 RTP Monitoring Framework November 2012

 Application-level metrics
    Metrics relating to application-specific parameters or QoE-related
    parameters.  Application-specific parameters are measured at the
    application level and focus on quality of content rather than
    network performance.  QoE-related parameters reflect the end-to-
    end performance at the services level and are usually measured at
    the user endpoint.  One example of such metrics is the QoE metric
    as specified in the QoE Metrics Report Block; see [QOE_BLOCK].
 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.
 Direct metrics
    Metrics that can be directly measured or calculated and are not
    dependent on other metrics.
 Interval metrics
    Metrics measured over the course of a single reporting interval
    between two successive report blocks.  This may be the most recent
    RTCP reporting interval ([RFC3550], Section 6.2) or some other
    interval signaled using an RTCP Measurement Information XR Block
    [RFC6776].  An example interval metric is the count of the number
    of RTP packets lost over the course of the last RTCP reporting
    interval.
 Cumulative metrics
    Metrics measured over several reporting intervals for accumulating
    statistics.  The time period over which measurements are
    accumulated can be the complete RTP session, or some other
    interval signaled using an RTCP Measurement Information XR Block
    [RFC6776].  An example cumulative metric is the total number of
    RTP packets lost since the start of the RTP session.
 Sampled metrics
    Metrics measured at a particular time instant and sampled from the
    values of a continuously measured or calculated metric within a
    reporting interval (generally, the value of some measurement as
    taken at the end of the reporting interval).  An example is the
    inter-arrival jitter reported in RTCP SR and RR packets, which is

Wu, et al. Informational [Page 4] RFC 6792 RTP Monitoring Framework November 2012

    continually updated as each RTP data packet arrives but is only
    reported based on a snapshot of the value that is sampled at the
    instant the reporting interval ends.

3. RTP Monitoring Framework

 There are many ways in which the performance of an RTP session can be
 monitored.  These include RTP-based mechanisms such as the RTP MIB
 module [RFC2959]; or the Session Initiation Protocol (SIP) event
 package for RTCP summary reports [RFC6035]; or non-RTP mechanisms
 such as generic MIBs, NetFlow [RFC3954], IP Flow Information Export
 (IPFIX) [RFC5101] [RFC5102], and so on.  Together, these provide
 useful mechanisms for exporting data on the performance of an RTP
 session to non-RTP network management systems.  It is desirable to
 also perform in-session monitoring of RTP performance.  RTCP provides
 the means to do this.  In the following, we review the RTP Monitoring
 Framework, and give guidance for using and extending RTCP for
 monitoring RTP sessions.  One major benefit of such a framework is
 ease of integration with other RTP/RTCP mechanisms.

3.1. Overview of the RTP Monitoring Framework

 The RTP monitoring Framework comprises the following two key
 functional components described below:
 o  Monitor
 o  RTP Metrics Block
 "Monitor" is the functional component defined in the RTP
 specification [RFC3550].  It acts as a repository of information
 gathered for monitoring purposes.
 According to the definition of "monitor" in [RFC3550], the end system
 that runs an application program that sends or receives RTP data
 packets, an intermediate system that forwards RTP packets to end
 devices, or a third party that observes the RTP and RTCP traffic but
 does not make itself visible to the RTP Session participants can play
 the role of the monitor within the RTP monitoring framework.  As
 shown in Figure 1, the third-party monitor can be a passive monitor
 that sees the RTP/RTCP stream pass it, or a system that gets sent
 RTCP reports but not RTP and uses that to collect information.  The
 third-party monitor should be placed on the RTP/RTCP path between the
 sender, the intermediate system, and the receiver.
 The RTP Metrics Block (MB) conveys real-time application QoS/QoE
 metric information and is used by the monitor to exchange information
 with other monitors in the appropriate report block format.  The

Wu, et al. Informational [Page 5] RFC 6792 RTP Monitoring Framework November 2012

 information contained in the RTP MBs is collected by monitors and can
 be formulated as various types of metrics, e.g., direct metrics/
 composed performance metrics [RFC6390] or interval metrics/cumulative
 metrics/sampled metrics, etc.  Both the RTCP and RTCP XR can be
 extended to transport these metrics, e.g., the basic RTCP reception
 report [RFC3550] that conveys reception statistics (i.e., transport-
 level statistics) for multiple RTP media streams, the RTCP XRs
 [RFC3611] that supplement the existing RTCP packets and provide more
 detailed feedback on reception quality, and an RTCP NACK [RFC4585]
 that provides feedback on the RTP sequence numbers for a subset of
 the lost packets or all the currently lost packets.  Ultimately, the
 metric information collected by monitors within the RTP monitoring
 framework may go to the network management tools beyond the RTP
 monitoring framework; e.g., as shown in Figure 1, the monitors may
 export the metric information derived from the RTP monitoring
 framework to the management system using non-RTP means.
                +-----------+                  +----------+
                |Third-Party|                  |Management|
                |  Monitor  |          >>>>>>>>|  System  |<<<<<
                +-----------+          ^       +----------+    ^
                    :   ^              ^                       ^
                    :   |              ^                       ^
 +---------------+  :   |       +-------------+        +-------------+
 | +-----------+ |  :   |       |+-----------+|        |+-----------+|
 | |  Monitor  | |..:...|.......||  Monitor  ||........||  Monitor  ||
 | +-----------+ |      |       |+-----------+|        |+-----------+|
 |               |------+------>|             |------->|             |
 | RTP Sender    |              |RTP Mixer or |        |RTP Receiver |
 |               |              |Translator   |        |             |
 +---------------+              +-------------+        +-------------+
  1. —> RTP media traffic

….. RTCP control channel

 >>>>> Non-RTP/RTCP management flows
               Figure 1: Example Showing the Components
                    of the RTP Monitoring Framework
 RTP may be used with multicast groups: both Any-Source Multicast
 (ASM) and Source-Specific Multicast (SSM).  These groups can be
 monitored using RTCP.  In the ASM case, the monitor is a member of
 the multicast group and listens to RTCP reports from all members of
 the ASM group.  In the SSM case, there is a unicast feedback target
 that receives RTCP feedback from receivers and distributes it to
 other members of the SSM group (see Figure 1 of [RFC5760]).  The
 monitor will need to be co-located with the feedback target to

Wu, et al. Informational [Page 6] RFC 6792 RTP Monitoring Framework November 2012

 receive all feedback from the receivers (this may also be an
 intermediate system).  In both ASM and SSM scenarios, receivers can
 send RTCP reports to enhance reception-quality reporting.

3.2. Location of Monitors

 As shown in Figure 1, there are several possible locations from which
 RTP sessions can be monitored.  These include end systems that
 terminate RTP sessions, intermediate systems that are an active part
 of an RTP session, and third-party devices that passively monitor an
 RTP session.  Not every RTP session will include monitoring, and
 those sessions that are monitored will not all include each type of
 monitor.  The performance metrics collected by monitors can be
 divided into end-system metrics, application-level metrics, and
 transport-level metrics.  Some of these metrics may be specific to
 the measurement point of the monitor or may depend on where the
 monitors are located in the network, while others are more general
 and can be collected in any monitoring location.
 End-system monitoring is monitoring that is deployed on devices that
 terminate RTP flows.  Flows can be terminated in user equipment, such
 as phones, videoconferencing systems, or IPTV set-top boxes.
 Alternatively, they can be terminated in devices that gateway between
 RTP and other transport protocols.  Transport-level metrics, end-
 system metrics, and application-level metrics that don't reflect the
 end-to-end user experience may be collected at all types of end
 systems, but some application-level metrics (i.e., quality of
 experience (QoE) metrics) may only be applicable for user-facing end
 systems.
 RTP sessions can include intermediate systems that are an active part
 of the system.  These intermediate systems include RTP mixers and
 translators, Multipoint Control Units (MCUs), retransmission servers,
 etc.  If the intermediate system establishes separate RTP sessions to
 the other participants, then it must act as an end system in each of
 those separate RTP sessions for the purposes of monitoring.  If a
 single RTP session traverses the intermediate system, then the
 intermediate system can be assigned a synchronization source (SSRC)
 in that session, which it can use for its reports.  Transport-level
 metrics may be collected at such an intermediate system.
 Third-party monitors may be deployed that passively monitor RTP
 sessions for network management purposes.  Third-party monitors often
 do not send reports into the RTP session being monitored but instead
 collect transport-level metrics, end-system metrics, and application-
 level metrics.  In some cases, however, third-party monitors can send
 reports to some or all participants in the session being monitored.

Wu, et al. Informational [Page 7] RFC 6792 RTP Monitoring Framework November 2012

 For example, in a media streaming scenario, third-party monitors may
 be deployed that passively monitor the session and send reception-
 quality reports to the media source but not to the receivers.

4. Issues with Reporting Metrics Blocks Using RTCP XR Extensions

 The following sections discuss four issues that have come up in the
 past with reporting metrics blocks using RTCP XR extensions.

4.1. Using a Compound Metrics Block

 A compound metrics block is designed to contain a large number of
 parameters from different classes for a specific application in a
 single block.  For example, "RTP Control Protocol Extended Reports
 (RTCP XR)" [RFC3611] defines seven report block formats for network
 management and quality monitoring.  Some of these block types defined
 in the RTCP XRs [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 different monitoring requirements.  Designing
 a compound metrics block only for specific applications may increase
 implementation costs and minimize interoperability.

4.2. Correlating RTCP XR with Non-RTP Data

 The Canonical End-Point Identifier SDES Item (CNAME), as defined in
 RTP [RFC3550], is an example of an existing tool that allows binding
 an SSRC that may change to a name that is fixed within one RTP
 session.  The CNAME may also be fixed across multiple RTP sessions
 from the same source.  However, there may be situations where RTCP
 reports are sent to other participating endpoints using a non-RTP
 protocol in a session.  For example, as described in [RFC6035] in
 relation to summary reports, the data contained in RTCP XR VoIP
 metrics reports [RFC3611] is forwarded to a central collection server
 system using SIP.  In such a case, there is a large portfolio of
 quality parameters that can be associated with real-time
 applications, e.g., VOIP applications, but only a minimal number of
 parameters are included in the RTCP XRs.  With this minimal number of
 RTCP statistical parameters mapped to non-RTCP measurements, it is
 hard to provide accurate measurements of real-time application
 quality, conduct detailed data analysis, and create timely alerts for
 users.  Therefore, a correlation between RTCP XRs and non-RTP data
 should be provided.

Wu, et al. Informational [Page 8] RFC 6792 RTP Monitoring Framework November 2012

4.3. Measurement Information Duplication

 We may set a measurement interval for the session and monitor RTP
 packets within one or several consecutive report intervals.  In such
 a case, extra measurement information (e.g., extended sequence number
 of the first packet, measurement period) may be expected.  However,
 if we put such extra measurement information into each metrics block,
 there may be situations where an RTCP XR packet that contains
 multiple metrics blocks will report on the same streams from the same
 source.  In other words, duplicated data for the measurement is
 provided multiple times, once in every metrics block.  Though this
 design ensures immunity to packet loss, it may result in more
 packetization complexity, and this processing overhead is not
 completely trivial in some cases.  Therefore, a compromise between
 processing overhead and reliability should be taken into account.

4.4. Consumption of XR Block Code Points

 The RTCP XR block namespace is limited by the 8-bit block type field
 in the RTCP XR header.  Space exhaustion may be a concern in the
 future.  In anticipation of the potential need to extend the block
 type space, it is noted that Block Type 255 is reserved for future
 extensions in [RFC3611].

5. Guidelines for Reporting Metrics Blocks Using RTCP XR

5.1. Use a Single Metric in the Metrics Block

 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 Source
 Description (SDES) packets) are sufficient.  For other applications,
 additional metrics may be required or at least may be sufficiently
 useful to justify the overhead, in terms of both 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 optimize 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

Wu, et al. Informational [Page 9] RFC 6792 RTP Monitoring Framework November 2012

 larger blocks are defined containing multiple metrics to address the
 needs of each application, it becomes likely that many such different
 larger blocks are defined, which poses a danger to interoperability.
 To avoid this pitfall, this memo recommends the definition of metrics
 blocks 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 "IP Packet Delay Variation (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.  Further, it is appropriate to not only define
 report blocks separately but also to do so in separate documents
 where possible.  This makes it easier to evolve the reports (i.e., to
 update each type of report block separately) and also makes it easier
 to require compliance with a particular report block.

5.2. Include the Payload Type in the Metrics Block

 There are some classes of metrics that can only be interpreted with
 knowledge of the media codec that is being used (audio mean opinion
 scores (MOSs) were the triggering example, but there may be others).
 In such cases, the correlation of an RTCP XR with RTP data is needed.
 Report blocks that require such correlation need to include the
 payload type of the reported media.  In addition, it is necessary to
 signal the details and parameters of the payload format to which that
 payload type is bound using some out-of-band means (e.g., as part of
 a Session Description Protocol (SDP) offer/answer exchange).

5.3. Use RTCP SDES to Correlate XRs with Non-RTP Data

 There may be situations where more than one media transport protocol
 is used by one application to interconnect to the same session in the
 gateway.  For example, one RTCP XR packet is sent to the
 participating endpoints using non-RTP-based media transport (e.g.,
 using SIP) in a VoIP session.  One crucial factor lies in how to
 handle the different identities that correspond to these different
 media transport protocols.
 This memo recommends an approach to facilitate the correlation of the
 RTCP session with other session-related non-RTP data.  That is to
 say, if there is a need to correlate RTP sessions with non-RTP
 sessions, then the correlation information needed should be conveyed
 in a new RTCP SDES item, since such correlation information describes
 the source rather than providing a quality report.  An example use
 case is where a participant endpoint may convey a call identifier or
 a global call identifier associated with the SSRC of a measured RTP

Wu, et al. Informational [Page 10] RFC 6792 RTP Monitoring Framework November 2012

 stream.  In such a case, the participant endpoint uses the SSRC to
 bind the call identifier using the SDES item in the SDES RTCP packet
 and sends this correlation to the network management system.  A flow
 measurement tool that is configured with the 5-tuple and is not call-
 aware then forwards the RTCP XRs along with the SSRC of the measured
 RTP stream, which is included in the XR Block header and 5-tuple to
 the network management system.  The network management system can
 then correlate this report using SSRC with other diagnostic
 information, such as call detail records.

5.4. Reduce Measurement Information Repetition across Metrics Blocks

 When multiple metrics blocks are carried in one RTCP XR packet,
 reporting on the same stream from the same source for the same time
 period, RTCP should use the SSRC to identify and correlate the
 multiple metrics blocks placed between Measurement Information
 Blocks; see "Measurement Identity and Information Reporting Using a
 Source Description (SDES) Item and an RTCP Extended Report (XR)
 Block" [RFC6776].  [RFC6776] enables an RTCP sender to convey the
 common time period and the number of packets sent during this period.
 If the measurement interval for a metric is different from the RTCP
 reporting interval, then this measurement duration in the Measurement
 Information Block should be used to specify the interval.  When there
 may be multiple Measurement Information Blocks with the same SSRC in
 one RTCP XR compound packet, the Measurement Information Block should
 be put in order and followed by all the metrics blocks associated
 with this Measurement Information Block.  New RTCP XR metrics blocks
 that rely on the Measurement Information Block must specify the
 response in case the new RTCP XR metrics block is received without an
 associated Measurement Information Block.  In most cases, it is
 expected that the correct response is to discard the received metric.
 In order to reduce measurement information repetition in one RTCP XR
 compound packet containing multiple metrics blocks, the measurement
 information shall be sent before the related metrics blocks that are
 from the same reporting interval.  Note that for packet loss
 robustness, if the report blocks for the same interval span more than
 one RTCP packet, then each block must have the measurement identity
 information sent together with itself in the same RTCP compound
 packet, even though the information will be the same.

6. An Example of a Metrics Block

 This section uses the example of an existing proposed metrics block
 to illustrate the application of the principles set out in Section 5.
 The example [RFC6798] 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

Wu, et al. Informational [Page 11] RFC 6792 RTP Monitoring Framework November 2012

 simple metric of PDV is available in the RTCP RR packet as the
 "inter-arrival jitter" field.  There are other PDV metrics with a
 certain similarity in metric structure that may be more useful to
 certain applications.  Two such metrics are the IPDV metric ([Y1540]
 [RFC3393]) and the mean absolute packet delay variation 2 (MAPDV2)
 metric [G1020].  The use of these metrics is consistent with the
 principle in Section 5 of the RTCP guidelines document [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 architectural
 considerations, using the example of [RFC6798], 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 that contains all three metrics.
 o  Provide a single RTCP block to convey any one of the three
    metrics, together with an 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 the 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 and so could be rejected on that
 basis, but in any case a single application is quite unlikely to
 require the 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 that may be transported by
 this block, as discussed further in [RFC6798].

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 as well as combinations
 of the two), and Topo-Mixer.  These topologies use RTP end systems,
 RTP mixers, and RTP translators as defined in [RFC3550].  For the
 purposes of reporting connection quality to other RTP systems, RTP
 mixers and RTP end systems are very similar.  Mixers resynchronize

Wu, et al. Informational [Page 12] RFC 6792 RTP Monitoring Framework November 2012

 packets and do not relay 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) that originates,
 terminates, or forwards RTCP XR blocks is expected to handle RTCP,
 including RTCP XR, according to RTP [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) that does not use RTCP XR.  The second category relates
 to deployed system models used in many H.323 [H323] videoconferences.
 The topologies in this category are Topo-Video-switch-MCU and
 Topo-RTCP-terminating-MCU.  Such topologies based on systems (e.g.,
 MCUs) do not behave according to RTP [RFC3550].
 Considering that the translator and MCU are two typical intermediate
 systems in these two categories mentioned above, this document will
 take them as two typical examples to explain how RTCP XR works in
 different [RFC5117] topologies.

7.1. Applicability to Translators

 Section 7.2 of the RTP specification [RFC3550] describes the
 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 co-located with itself so that the
 monitor may populate the SSRC in the RTCP XR packet header as the
 packet sender SSRC and send it out (although the translator is not a
 synchronization 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-neighbor 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 behavior based on local policy, which might differ between
 different interfaces of the same translator.

7.2. Applicability to MCUs

 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

Wu, et al. Informational [Page 13] RFC 6792 RTP Monitoring Framework November 2012

 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 speaking,
 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 (i.e.,
 media distribution) unimpaired.

8. Security Considerations

 This document focuses on the RTCP reporting extension using RTCP XR
 and should not give rise to any new security vulnerabilities beyond
 those described in RTCP XRs [RFC3611].  However, it also describes
 the architectural framework to be used for monitoring at the RTP
 layer.  The security issues with monitoring need to be considered.
 In RTP sessions, an RTP system may use its own SSRC to send its
 monitoring reports towards its next-neighbor RTP system.  Other RTP
 systems in the session may have a choice as to whether they forward
 this RTP system's RTCP packets.  This presents a security issue,
 since the information in the report may be exposed by the other RTP
 system to any malicious node.  Therefore, if the information is
 considered sensitive, the monitoring reports should be secured to the
 same extent as the RTP flows that they measure.  If encryption is
 used and the encrypted monitoring report is received by the RTP
 system that deploys the third-party monitor, the RTP system may
 decrypt the monitor report for the third-party monitor based on local
 policy (e.g., third-party monitors are allowed access to the metric)
 and forward it to the third-party monitor; otherwise, the third-party
 monitor should discard the received encrypted monitoring report.

9. Acknowledgements

 The authors would like to thank Colin Perkins, Charles Eckel, Robert
 Sparks, Salvatore Loreto, Graeme Gibbs, Debbie Greenstreet, Keith
 Drage, Dan Romascanu, Ali C. Begen, Roni Even, Magnus Westerlund,
 Meral Shirazipour, Tina Tsou, Barry Leiba, Benoit Claise, Russ
 Housley, and Stephen Farrell for their valuable comments and
 suggestions on early versions of this document.

Wu, et al. Informational [Page 14] RFC 6792 RTP Monitoring Framework November 2012

10. Informative References

 [G1020]      ITU-T, "Performance parameter definitions for quality of
              speech and other voiceband applications utilizing IP
              networks", ITU-T Rec. G.1020, July 2006.
 [H323]       ITU-T, "Packet-based multimedia communications systems",
              ITU-T Rec. H.323, December 2009.
 [QOE_BLOCK]  Clark, A., Wu, Q., Schott, R., and G. Zorn, "RTP Control
              Protocol (RTCP) Extended Report (XR) Blocks for QoE
              Metric Reporting", Work in Progress, October 2012.
 [RFC1122]    Braden, R., "Requirements for Internet Hosts -
              Communication Layers", STD 3, RFC 1122, October 1989.
 [RFC2959]    Baugher, M., Strahm, B., and I. Suconick, "Real-Time
              Transport Protocol Management Information Base",
              RFC 2959, October 2000.
 [RFC3393]    Demichelis, C. and P. Chimento, "IP Packet Delay
              Variation Metric for IP Performance Metrics (IPPM)",
              RFC 3393, November 2002.
 [RFC3550]    Schulzrinne, H., Casner, S., Frederick, R., and V.
              Jacobson, "RTP: A Transport Protocol for Real-Time
              Applications", STD 64, RFC 3550, July 2003.
 [RFC3611]    Friedman, T., Caceres, R., and A. Clark, "RTP Control
              Protocol Extended Reports (RTCP XR)", RFC 3611,
              November 2003.
 [RFC3954]    Claise, B., "Cisco Systems NetFlow Services Export
              Version 9", RFC 3954, October 2004.
 [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.
 [RFC5101]    Claise, B., "Specification of the IP Flow Information
              Export (IPFIX) Protocol for the Exchange of IP Traffic
              Flow Information", RFC 5101, January 2008.
 [RFC5102]    Quittek, J., Bryant, S., Claise, B., Aitken, P., and J.
              Meyer, "Information Model for IP Flow Information
              Export", RFC 5102, January 2008.

Wu, et al. Informational [Page 15] RFC 6792 RTP Monitoring Framework November 2012

 [RFC5117]    Westerlund, M. and S. Wenger, "RTP Topologies",
              RFC 5117, January 2008.
 [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.
 [RFC5968]    Ott, J. and C. Perkins, "Guidelines for Extending the
              RTP Control Protocol (RTCP)", RFC 5968, September 2010.
 [RFC6035]    Pendleton, A., Clark, A., Johnston, A., and H.
              Sinnreich, "Session Initiation Protocol Event Package
              for Voice Quality Reporting", RFC 6035, November 2010.
 [RFC6390]    Clark, A. and B. Claise, "Guidelines for Considering New
              Performance Metric Development", BCP 170, RFC 6390,
              October 2011.
 [RFC6776]    Clark, A. and Q. Wu, "Measurement Identity and
              Information Reporting Using a Source Description (SDES)
              Item and an RTCP Extended Report (XR) Block", RFC 6776,
              October 2012.
 [RFC6798]    Clark, A. and Q. Wu, "RTP Control Protocol (RTCP)
              Extended Report (XR) Block for Packet Delay Variation
              Metric Reporting", RFC 6798, November 2012.
 [Y1540]      ITU-T, "IP packet transfer and availability performance
              parameters", ITU-T Rec. Y.1540, March 2011.

Wu, et al. Informational [Page 16] RFC 6792 RTP Monitoring Framework November 2012

Authors' Addresses

 Qin Wu (editor)
 Huawei
 101 Software Avenue, Yuhua District
 Nanjing, Jiangsu  210012
 China
 EMail: sunseawq@huawei.com
 Geoff Hunt
 Unaffiliated
 EMail: r.geoff.hunt@gmail.com
 Philip Arden
 BT
 Orion 3/7 PP4
 Adastral Park
 Martlesham Heath
 Ipswich, Suffolk  IP5 3RE
 United Kingdom
 Phone: +44 1473 644192
 EMail: philip.arden@bt.com

Wu, et al. Informational [Page 17]

/data/webs/external/dokuwiki/data/pages/rfc/rfc6792.txt · Last modified: 2012/11/23 17:34 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki