Audio/Video Transport Working Group Q. Wu
Internet-Draft Huawei
Intended status: Informational May 5, 2011
Expires: November 6, 2011
Monitoring Architectures for RTP
draft-ietf-avtcore-monarch-01.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
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Internet-Drafts are draft documents valid for a maximum of six months
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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, 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
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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 block . . . . . . . . . . . . . . . . 10
6. An example of a metric block . . . . . . . . . . . . . . . . . 15
7. Application to RFC 5117 topologies . . . . . . . . . . . . . . 16
7.1. Applicability to MCU . . . . . . . . . . . . . . . . . . . 16
7.2. Applicability to Translators . . . . . . . . . . . . . . . 16
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
9. Security Considerations . . . . . . . . . . . . . . . . . . . 19
10. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 20
11. Informative References . . . . . . . . . . . . . . . . . . . . 21
Appendix A. Appendix A. Change Log . . . . . . . . . . . . . . . 22
A.1. draft-ietf-avtcore-monarch-00 . . . . . . . . . . . . . . 22
A.2. draft-ietf-avtcore-monarch-01 . . . . . . . . . . . . . . 22
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 23
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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.
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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.
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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 3.2.
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|---------------+
| 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
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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
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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.
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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 same RTCP XR packet contain measurement data for the same
stream and period, it bring inefficiency to Repeat the information
in a number of metrics blocks within the same RTCP packet.
o Metric Blocks association. When an RTCP XR packet containing four
metrics blocks, reporting on streams from two sources, 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 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.
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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 block
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:
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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] .
The approach is to define a stand-alone block containing only
identification information, and to tag this identification block with
a number which is unique 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
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which all of the contained metrics were measured, hence this SSRC
need not be repeated in the stand-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.
There will be zero or more metrics blocks dependent on each
identification block. The dependence of an instance of a metrics
block on an identification block is 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 example an RTCP
XR packet containing four metrics blocks, reporting on streams from
two sources. The measurement identity 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.
Each of these two identity blocks will specify the SSRC of one of the
monitored streams, as well as information about the span of the
measurement. There are two metrics blocks with tag=0 indicating
their association with the measurement identity block which also has
tag=0. These are the two blocks following the identity block with
tag=0, though this positioning is not mandatory. There are also two
metrics blocks 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:
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o multiple instances of the same metrics block may occur within a
containing RTCP XR packet, associated with different
identification information, and
o differing measurements may be made, and reported, for the
different streams arriving at an 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 only a
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single metrics block is sent in an RTCP packet, but becomes
beneficial as soon as more than one metrics block shares common
identification.
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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
architecure 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).
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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
relates to deployed system models used in many H.323 [H323] video
conferences. The topologies in this category are Topo-Video-Switch-
MCU and Topo-RTCP-terminating-MCU. Such topologies based on systems
do not behave according to [RFC3550]. As for the first 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 typical topologies in thetwo categories mentioned
above, this document will take them as two typical examples to
explain how RTCP XR report works in different RFC5117 topologies.
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.
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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 send XR to
have a way to declare itself explicitly.
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8. IANA Considerations
None.
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9. Security Considerations
This document itself contains no normative text and hence should not
give rise to any new security considerations, to be confirmed.
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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.
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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.
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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.
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Author's Address
Qin Wu
Huawei
101 Software Avenue, Yuhua District
Nanjing, Jiangsu 210012
China
Email: sunseawq@huawei.com
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