Internet DRAFT - draft-ietf-avtcore-monarch
draft-ietf-avtcore-monarch
Audio/Video Transport Working Group Q. Wu, Ed.
Internet-Draft Huawei
Intended status: Informational G. Hunt
Expires: March 29, 2013 Unaffiliated
P. Arden
BT
September 25, 2012
Guidelines for Use of the RTP Monitoring Framework
draft-ietf-avtcore-monarch-22.txt
Abstract
This memo proposes an extensible Real-Time Protocol (RTP) monitoring
framework for extending 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 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.
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This Internet-Draft will expire on March 29, 2013.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. RTP Monitoring Framework . . . . . . . . . . . . . . . . . . . 7
3.1. Overview of the RTP Monitoring Framework . . . . . . . . . 7
3.2. Location of Monitors . . . . . . . . . . . . . . . . . . . 9
4. Issues With Reporting Metric Block Using RTCP XR Extension . . 10
4.1. Using compound metrics block . . . . . . . . . . . . . . . 10
4.2. Correlating RTCP XR with the non-RTP data . . . . . . . . 10
4.3. Measurement Information duplication . . . . . . . . . . . 10
4.4. Consumption of XR block code points . . . . . . . . . . . 11
5. Guidelines For Reporting Metric Block Using RTCP XR . . . . . 12
5.1. Contain the single metrics in the Metric Block . . . . . . 12
5.2. Include the payload type in the Metric Block . . . . . . . 12
5.3. Use RTCP SDES to correlate XR reports with non-RTP data . 13
5.4. Reduce Measurement information repetition across
metric blocks . . . . . . . . . . . . . . . . . . . . . . 13
6. An Example of a Metric Block . . . . . . . . . . . . . . . . . 15
7. Application To RFC 5117 Topologies . . . . . . . . . . . . . . 16
7.1. Applicability to Translators . . . . . . . . . . . . . . . 16
7.2. Applicability to MCU . . . . . . . . . . . . . . . . . . . 17
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
9. Security Considerations . . . . . . . . . . . . . . . . . . . 19
10. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 20
11. Informative References . . . . . . . . . . . . . . . . . . . . 21
Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 23
A.1. draft-ietf-avtcore-monarch-22 . . . . . . . . . . . . . . 23
A.2. draft-ietf-avtcore-monarch-20 . . . . . . . . . . . . . . 23
A.3. draft-ietf-avtcore-monarch-19 . . . . . . . . . . . . . . 23
A.4. draft-ietf-avtcore-monarch-18 . . . . . . . . . . . . . . 23
A.5. draft-ietf-avtcore-monarch-17 . . . . . . . . . . . . . . 23
A.6. draft-ietf-avtcore-monarch-16 . . . . . . . . . . . . . . 24
A.7. draft-ietf-avtcore-monarch-15 . . . . . . . . . . . . . . 24
A.8. draft-ietf-avtcore-monarch-14 . . . . . . . . . . . . . . 24
A.9. draft-ietf-avtcore-monarch-13 . . . . . . . . . . . . . . 24
A.10. draft-ietf-avtcore-monarch-12 . . . . . . . . . . . . . . 25
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A.11. draft-ietf-avtcore-monarch-11 . . . . . . . . . . . . . . 25
A.12. draft-ietf-avtcore-monarch-10 . . . . . . . . . . . . . . 25
A.13. draft-ietf-avtcore-monarch-09 . . . . . . . . . . . . . . 25
A.14. draft-ietf-avtcore-monarch-08 . . . . . . . . . . . . . . 26
A.15. draft-ietf-avtcore-monarch-07 . . . . . . . . . . . . . . 26
A.16. draft-ietf-avtcore-monarch-06 . . . . . . . . . . . . . . 26
A.17. draft-ietf-avtcore-monarch-05 . . . . . . . . . . . . . . 26
A.18. draft-ietf-avtcore-monarch-04 . . . . . . . . . . . . . . 26
A.19. draft-ietf-avtcore-monarch-03 . . . . . . . . . . . . . . 27
A.20. draft-ietf-avtcore-monarch-02 . . . . . . . . . . . . . . 27
A.21. draft-ietf-avtcore-monarch-01 . . . . . . . . . . . . . . 27
A.22. draft-ietf-avtcore-monarch-00 . . . . . . . . . . . . . . 28
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29
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1. Introduction
Multimedia services using the Real-Time 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] 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 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 re-usable Quality
of Service (QoS) / QoE metrics which facilitate reduced
implementation costs and help maximize inter-operability. The
"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.
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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 which characterise the three transport
impairments of packet loss, packet delay, jitter (also known as
delay variation). These metrics should be usable by any
application which uses RTP transport.
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
specified in QoE metric reporting Block [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 signalled using an RTCP Measurement Information XR Block
[MEASI]. An example interval metric is the count of the number of
RTP packets lost over the course of the last RTCP reporting
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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 signalled using an RTCP Measurement Information XR Block
[MEASI]. 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
continually updated as each RTP data packet arrives, but only
reported based on a snapshot of the value which is sampled at the
instant the reporting interval ends.
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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], 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 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 Metric Block
Monitor is the functional component defined in the Real-time
Transport Protocol [RFC3550]. It acts as a repository of information
gathered for monitoring purposes.
According to the definition of monitor in the RTP Protocol [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, intermediate and the receiver.
The RTP Metric Block (MB) conveys real time Application QoS/QoE
metric information and is used by the monitor to exchange with other
monitors in the appropriate report block format. The 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 or RTCP XR can be extended to
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transport these metrics, e.g., the basic RTCP Reception Report (RR)
[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 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 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 | | |
+---------------+ +-------------+ +-------------+
----> 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
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 the reception quality reporting.
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3.2. Location of Monitors
As shown in Figure 1, there are several possible locations from where
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 sessions 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 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, video conferencing systems, or IPTV set-top boxes.
Alternatively, they can be terminated in devices that gateway between
RTP and other transport protocols. Transport and end system metrics,
application level metrics that don't reflect end to end user
experience may be collected at all types of end system, 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 an Synchronization source (SSRC)
in that session which it can use for its reports. Transport level
metrics may be collected at such 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.
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.
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4. Issues With Reporting Metric Block Using RTCP XR Extension
The following sections discuss four issues that have come up in the
past with reporting metric block using RTCP XR extensions.
4.1. Using 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, the RTCP Extended Reports (XRs) [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 compound metrics block
only for specific applications may increase implementation cost and
minimize interoperability.
4.2. Correlating RTCP XR with the non-RTP data
Canonical End-Point Identifier SDES Item (CNAME), defined in the RTP
Protocol [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. CNAME may be also fixed across multiple RTP sessions
from the same source. However there may be situations where RTCP
reports are sent to other participating endpoints using non-RTP
protocol in a session. For example, as described in the SIP RTCP
Summary Report Protocol [RFC6035], the data contained in RTCP XR VoIP
metrics reports [RFC3611] are forwarded to a central collection
server systems using SIP. In such case, there is a large portfolio
of quality parameters that can be associated with real time
application, e.g., VOIP application, but only a minimal number of
parameters are included on the RTCP-XR reports. With these minimal
number of RTCP statistics parameters mapped to non-RTCP measurements,
it is hard to provide accurate measures of real time application
quality, conduct detailed data analysis and creates alerts timely to
the users. Therefore correlation between RTCP XR and non-RTP data
should be provided.
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
case, the extra measurement information (e.g., extended sequence
number of 1st packet, measurement period) may be expected. However
if we put such extra measurement information into each metric block,
there may be situations where an RTCP XR packet containing multiple
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metric blocks, reports on the same streams from the same source. In
other words, duplicated data for the measurement is provided multiple
times, once in every metric block. Though this design ensures
immunity to packet loss, it may bring more packetization complexity
and the processing overhead is not completely trivial in some cases.
Therefore 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. Anticipating the potential need to extend the block type
space, it is noted that Block Type 255 is reserved for future
extensions in [RFC3611].
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5. Guidelines For Reporting Metric Block Using RTCP XR
5.1. Contain the single metrics in the Metric 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 SDES packets)
are sufficient. For other applications additional metrics may be
required or at least sufficiently useful to justify the overhead,
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 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 Metric 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 (MOS) were the triggering example, but there may be others).
In such cases the correlation of 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
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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
an SDP offer/answer exchange).
5.3. Use RTCP SDES to correlate XR reports 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 their different identities that are corresponding to different
media transport.
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 Source Description (SDES) item, since such correlation
information describes the source, rather than providing a quality
report. An example use case is for a participant endpoint may convey
a call identifier or a global call identifier associated with the
SSRC of measured RTP stream. In such case, the participant endpoint
uses the SSRC to bind the call identifier using SDES item in the SDES
RTCP packet and send such correlation to the network management
system. A flow measurement tool that is configured with the 5-tuple
and not call-aware then forwards the RTCP XR reports 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. 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 metric blocks
When multiple metric 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 metric blocks between metric blocks. "Measurement Identity
and information Reporting using SDES item and XR Block" [MEASI]
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
measurements 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 metric blocks associated with this
measurement information block. New RTCP XR metric blocks that rely
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on the Measurement information block [MEASI] must specify the
response in case the new RTCP XR metric 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 metric blocks, the measurement
information shall be sent before the related metric blocks that are
from the same reporting interval. Note that for packet loss
robustness if the report blocks for the same interval span over more
than one RTCP packet, then each must have the measurement identity
information even though they will be the same.
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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.
The example [PDV] 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 "interarrival
jitter" field. There are other PDV metrics with a certain similarity
in metric structure which 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]. Use
of these metrics is consistent with the principle in Section 5 of
RTCP guideline [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 consideration using the example of [PDV]
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].
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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 the RTP protocol [RFC3550].
For purposes of reporting connection quality to other RTP systems,
RTP mixers and RTP end systems are very similar. Mixers
resynchronize 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) which
originates, terminates or forwards RTCP XR blocks is expected to
handle RTCP, including RTCP XR, according to the RTP protocol
[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. 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 (e.g.,MCUs) do not behave according to
the RTP protocol [RFC3550].
Considering 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 report works
in different RFC5117 topologies.
7.1. Applicability to Translators
Section 7.2 of the RTP protocol [RFC3550] describes processing of
RTCP by translators. RTCP XR is within the scope of the
recommendations of the RTP protocol [RFC3550]. Some RTCP XR metrics
blocks may usefully be measured at, and reported by, translators. As
described in the RTP protocol [RFC3550] this creates a requirement
for the translator to allocate an SSRC for the monitor collocated
with itself so that the monitor may populate the SSRC in the RTCP XR
packet header as packet sender SSRC and send it out(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
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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.
7.2. 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 (i.e.,media
distribution) unimpaired.
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8. IANA Considerations
There is no IANA action in this document.
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9. 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 RTP layer. The
security issues with monitoring needs to be considered.
In RTP sessions, a RTP system may use its own SSRC to send its
monitoring reports towards its next-neighbour RTP system. Other RTP
system in the session may have a choice as to whether they forward
this RTP system's RTCP packets. This present 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 as
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
deploy 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 is allowed to access to the metric) and forward it to
the third party monitor, otherwise, the third party monitor SHOULD
discard the received encrypted monitoring report.
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10. Acknowledgement
The authors would also 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,Stephen Farrell 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.
[MEASI] Wu, Q., "Measurement Identity and information Reporting
using SDES item and XR Block",
ID draft-ietf-xrblock-rtcp-xr-meas-identity-10,
August 2012.
[PDV] Hunt, G., Clark, A., and Q. Wu, "RTCP XR Report Block for
Packet Delay Variation Metric Reporting",
ID draft-ietf-xrblock-rtcp-xr-pdv-05, August 2012.
[QOE_BLOCK]
Hunt, G., Clark, A., Wu, Q., Schott, R., and G. Zorn,
"RTCP XR Blocks for QoE Metric Reporting",
ID draft-ietf-xrblock-rtcp-xr-qoe-02, July 2012.
[RFC1122] Braden, R., "Requirements for Internet Hosts --
Communication Layers", 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., "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.
[RFC3611] Friedman, T., "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. and S. Wenger, "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
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Flow Information", RFC 5101, January 2008.
[RFC5102] Quittek, J., , S., Claise, B., Aitken, P., and J. Meyer,
"Information Model for IP Flow Information Export",
RFC 5102, January 2008.
[RFC5117] Westerlund, M., "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", RFC 6390, October 2011.
[Y1540] ITU-T, "ITU-T Rec. Y.1540, IP packet transfer and
availability performance parameters", November 2007.
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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-22
The following are the major changes compared to 20,21:
o Editorial changes based on Benoit and WG Review.
A.2. draft-ietf-avtcore-monarch-20
The following are the major changes compared to 19:
o Editorial changes based on IESG Review.
o Some new text in the security section to clarify encryption issue
for third party monitoring.
o Some new text in introduction section to clarify the relationship
with RFC5968 and RFC6390.
A.3. draft-ietf-avtcore-monarch-19
The following are the major changes compared to 18:
o Editorial changes based on Meral Shirazipour's second Gen-Art
review.
o Transport level metrics definition simplifying based on Robert's
comment.
A.4. draft-ietf-avtcore-monarch-18
The following are the major changes compared to 17:
o Some Editorial changes based on Gen-Art review and Secdir Review.
A.5. draft-ietf-avtcore-monarch-17
The following are the major changes compared to 16:
o Some Editorial changes.
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A.6. draft-ietf-avtcore-monarch-16
The following are the major changes compared to 15:
o A few modification to the figure 1.
o Change RTCP XR reports into RTCP reports in the section 3.1.
o References Update.
A.7. draft-ietf-avtcore-monarch-15
The following are the major changes compared to 14:
o Add figure 1 in section 3 to describe RTP monitoring framework.
o Change the title as Guidelines for Use of the RTP Monitoring
Framework.
o Other editorial change to get in line with the title change in the
section 3.
A.8. draft-ietf-avtcore-monarch-14
The following are the major changes compared to 13:
o Incorporate the key points in the section 3.2 into overview
section.
o Remove the figure 1 and use the description instead.
o Add description in the section 3.3 to discuss the possible
location of the monitors and the types of metric at that location.
o Add the description to make the definition of Interval metrics/
cumulative metrics/sampled metrics clear.
o Editorial Changes.
A.9. draft-ietf-avtcore-monarch-13
The following are the major changes compared to 12:
o Editorial Changes.
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A.10. draft-ietf-avtcore-monarch-12
The following are the major changes compared to 11:
o Editorial Changes based on Charles' Comments.
o Reference update.
o Add one new section 5.2 to discuss Correlating RTCP XR with RTP
data.
o Add text in section 5.1 to highlight it is more appropriate to
define each block in a separate draft.
A.11. draft-ietf-avtcore-monarch-11
The following are the major changes compared to 10:
o Editorial Changes.
A.12. draft-ietf-avtcore-monarch-10
The following are the major changes compared to 09:
o Discuss what exist already for monitoring in section 3.1.
o Provide benefit using RTCP XR based monitoring in section 3.1.
o add one new paragraph in section 3.1 to describe how monitoring
architecture is applied to ASM/SSM.
o Other Editorial Changes.
A.13. draft-ietf-avtcore-monarch-09
The following are the major changes compared to 07:
o Rephrase application level metric definition.
o Add one new section to clarify where to measure QoE related
parameters.
o Add text in section 5.3 to clarify the failure case when
measurement interval is not sent.
o Add text in section 5.3 to clarify how to deal with multiple
measurements information blocks carried in the same packet.
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A.14. draft-ietf-avtcore-monarch-08
The following are the major changes compared to 07:
o Editorial change to the reference.
A.15. draft-ietf-avtcore-monarch-07
The following are the major changes compared to 06:
o Clarify the XR block code points consumption issue in the section
4 and new section 5.4.
o Other editorial changes.
A.16. draft-ietf-avtcore-monarch-06
The following are the major changes compared to 05:
o Some editorial changes.
A.17. draft-ietf-avtcore-monarch-05
The following are the major changes compared to 04:
o Replace "chunk" with "new SDES item".
o Add texts in security section to discussion potential security
issues.
o Add new sub-section 5.3 to discuss Reducing Measurement
information repetition.
o Other editorial changes.
A.18. draft-ietf-avtcore-monarch-04
The following are the major changes compared to 03:
o Update section 5.2 to clarify using SDES packet to carry
correlation information.
o Remove section 5.3 since additional identity information goes to
SDES packet and using SSRC to identify each block is standard RTP
feature.
o Swap the last two paragraphs in the section 4 since identity
information duplication can not been 100% avoided.
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o Other editorial changes.
A.19. draft-ietf-avtcore-monarch-03
The following are the major changes compared to 02:
o Update bullet 2 in section 4 to explain the ill-effect of Identity
Information duplication.
o Update bullet 3 in section 4 to explain why Correlating RTCP XR
with the non-RTP data is needed.
o Update section 5.2 to focus on how to reduce the identity
information repetition
o Update section 5.3 to explain how to correlate identity
information with the non-RTP data
A.20. 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 Separate 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.
A.21. 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.
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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.
A.22. 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.
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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
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