Monitoring Architecture for RTP
draft-ietf-avtcore-monarch-12
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 6792.
|
|
|---|---|---|---|
| Authors | Qin Wu , Geoff Hunt , Philip Arden | ||
| Last updated | 2012-04-17 | ||
| Replaces | draft-hunt-avtcore-monarch | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Reviews |
GENART Telechat review
(of
-18)
by Meral Shirazipour
Ready w/nits
SECDIR Last Call review
by Tina Tsou
Ready w/issues
|
||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Consensus: Waiting for Write-Up | |
| Document shepherd | Magnus Westerlund | ||
| IESG | IESG state | Became RFC 6792 (Informational) | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-ietf-avtcore-monarch-12
Audio/Video Transport Working Group Q. Wu, Ed.
Internet-Draft Huawei
Intended status: Informational G. Hunt
Expires: October 20, 2012 Unaffiliated
P. Arden
BT
April 18, 2012
Monitoring Architecture for RTP
draft-ietf-avtcore-monarch-12.txt
Abstract
This memo proposes an architecture for extending RTP Control Protocol
(RTCP) with a new RTCP Extended Reports (XR) (RFC3611) block type to
report new metrics regarding media transmission or reception quality,
following RTCP guideline established in RFC5968. This memo suggests
that a new block should contain a single metric or a small number of
metrics relevant to a single parameter of interest or concern, rather
than containing a number of metrics which attempt to provide full
coverage of all those parameters of concern to a specific
application. Applications may then "mix and match" to create a set
of blocks which covers their set of concerns. Where possible, a
specific block should be designed to be re-usable across more than
one application, for example, for all of voice, streaming audio and
video.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 20, 2012.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
Wu, et al. Expires October 20, 2012 [Page 1]
Internet-Draft RTP Monitoring Architecture April 2012
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.
Wu, et al. Expires October 20, 2012 [Page 2]
Internet-Draft RTP Monitoring Architecture April 2012
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. RTP monitoring architecture . . . . . . . . . . . . . . . . . 7
3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2. RTCP Metric Block Report and associated parameters . . . . 10
3.3. RTP Sender/Receiver entities located in network nodes . . 11
4. Issues with reporting metric block using RTCP XR extension . . 12
5. Guideline for reporting metric block using RTCP XR . . . . . . 14
5.1. Using single metrics blocks . . . . . . . . . . . . . . . 14
5.2. Correlating RTCP XR with RTP data . . . . . . . . . . . . 14
5.3. Correlating RTCP XR with the non-RTP data . . . . . . . . 15
5.4. Reducing Measurement information repetition . . . . . . . 15
5.5. Expanding the RTCP XR block namespace . . . . . . . . . . 16
6. An example of a metric block . . . . . . . . . . . . . . . . . 17
7. Application to RFC 5117 topologies . . . . . . . . . . . . . . 18
7.1. Applicability to MCU . . . . . . . . . . . . . . . . . . . 18
7.2. Applicability to Translators . . . . . . . . . . . . . . . 19
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
9. Security Considerations . . . . . . . . . . . . . . . . . . . 21
10. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 22
11. Informative References . . . . . . . . . . . . . . . . . . . . 23
Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 25
A.1. draft-ietf-avtcore-monarch-12 . . . . . . . . . . . . . . 25
A.2. draft-ietf-avtcore-monarch-11 . . . . . . . . . . . . . . 25
A.3. draft-ietf-avtcore-monarch-10 . . . . . . . . . . . . . . 25
A.4. draft-ietf-avtcore-monarch-09 . . . . . . . . . . . . . . 25
A.5. draft-ietf-avtcore-monarch-08 . . . . . . . . . . . . . . 26
A.6. draft-ietf-avtcore-monarch-07 . . . . . . . . . . . . . . 26
A.7. draft-ietf-avtcore-monarch-06 . . . . . . . . . . . . . . 26
A.8. draft-ietf-avtcore-monarch-05 . . . . . . . . . . . . . . 26
A.9. draft-ietf-avtcore-monarch-04 . . . . . . . . . . . . . . 26
A.10. draft-ietf-avtcore-monarch-03 . . . . . . . . . . . . . . 27
A.11. draft-ietf-avtcore-monarch-02 . . . . . . . . . . . . . . 27
A.12. draft-ietf-avtcore-monarch-01 . . . . . . . . . . . . . . 27
A.13. draft-ietf-avtcore-monarch-00 . . . . . . . . . . . . . . 28
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29
Wu, et al. Expires October 20, 2012 [Page 3]
Internet-Draft RTP Monitoring Architecture April 2012
1. Introduction
As the delivery of multimedia services using the Real-Time Transport
Protocol (RTP) over IP network is gaining an increasing popularity,
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 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 define 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. RTCP Guideline [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.
Wu, et al. Expires October 20, 2012 [Page 4]
Internet-Draft RTP Monitoring Architecture April 2012
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, and packet 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 ususally measured at
the user endpoint. One example of such metrics is the QoE Metric
specified in QoE metric reporting Block [QOE].
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.
Composed metrics
Metrics that are not measured directly but rather are derived from
one or more other metrics. An example is a metric calculated
based on derived metrics that have been measured.
Wu, et al. Expires October 20, 2012 [Page 5]
Internet-Draft RTP Monitoring Architecture April 2012
Interval metrics
It is referred to as the metrics of which the reported values
apply to the most recent measurement interval duration between
successive metrics reports.
Cumulative metrics
It is referred to as the metrics of which the reported values
apply to the accumulation period characteristic of cumulative
measurements.
Sampled metrics
It is referred to as the metrics of which the reported values only
apply to the value of a continuously measured or calculated metric
that has been sampled at any given instance of the interval.
Wu, et al. Expires October 20, 2012 [Page 6]
Internet-Draft RTP Monitoring Architecture April 2012
3. RTP monitoring architecture
There are many ways in which the performance of an RTP session can be
monitored. These include RTP-based mechanisms such as the RTP SNMP
MIB [RFC2959], or the SIP event package for RTCP summary reports
[RFC6035], or non-RTP mechanisms such as generic MIBs, NetFlow,
IPFix, 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 specify an architecture for using and
extending RTCP for monitoring RTP sessions. One major benefit of
such architecture is ease of integration with other RTP/RTCP
mechanisms.
3.1. Overview
The RTP monitoring architecture comprises the following two key
functional components shown below:
o RTP Monitor
o RTP Metric Block Structure
RTP Monitor is the functional component defined in the Real-time
Transport Protocol [RFC3550] that acts as a source of information
gathered for monitoring purposes. It may gather such information
reported by RTCP XR or other RTCP extension and calculate statistics
from multiple source. 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 (i.e., the third party monitor depicted
in figure 1) can be envisioned to act as the monitor within the RTP
monitoring architecture. Note that the third party monitor should be
placed on the RTP/RTCP paths between the sender, intermediate and the
receiver.
The RTP Metric Block exposes real time Application QoS/QoE metric
information in the appropriate report block format to the management
system (i.e., report collector) within the RTP monitoring
architecture. Such information can be formulated as:
o The direct metrics
o or the composed metrics
Wu, et al. Expires October 20, 2012 [Page 7]
Internet-Draft RTP Monitoring Architecture April 2012
or formulated as
o The Interval metrics
o or cumulative metrics
o or sampled metrics
Both the RTCP or RTCP XR can be extended to convey these metrics.
The details on transport protocols for metric blocks are described in
Section 3.2.
Wu, et al. Expires October 20, 2012 [Page 8]
Internet-Draft RTP Monitoring Architecture April 2012
+-------------------+
| RTP Sender | 6 +----------+
| +-----------+ ||------------>|Management|
-------------->| Monitor |----| 6 | System |
| | | | | |----------->| |
| | +-----------+ | | -------->| |
| |+-----------------+| | | +-------/--+
| ||Application || | | -----------| |
| ||-Streaming video || | | | 1 | |6
| |---------|-VOIP || | | | +--------V------+
| | ||-Video conference|| | | --- Third Party |
| | ||-Telepresence || | | | Monitor |
| | ||-Ad insertion || | 6| +---------------+
5 | |+-----------------+| | |
| | +-------------------+ | |
| 1 | |
| | +Intermediate------------+ | | |------------------------+
| | | RTP System | | | | RTP Receiver >--4-| |
| | | +----------- | | | | +-----------+ |
| | | | -----------| -------| | | |
| | | | | | | | Monitor |<-- |
|----------- Monitor |<--------5------|----| |<------|
| | | | Report Block | +----/------+ ||
| | +----------+Transport Over | ||
| | RTCP XR or RTCP | |2 ||
| | +-----------------+ extension | +-------/---------+ ||
| | |Application | | | |Application | ||
| | |-Streaming video | | | |-Streaming video | ||
| | |-VOIP | | 1 | |-VOIP | 3|
---->-Video conference|--------------->|-Video conference ||
| |-Telepresence | | | |-Telepresence | ||
| |-Ad insertion | | | |-Ad insertion | ||
| +-----------------+ | | +-----------------+ ||
| +-----------------+ | | +-----------------+ ||
| |Transport | | | |Transport | ||
| |-IP/UDP/RTP | | | |-IP/UDP/RTP >---||
| |-IP/TCP/RTP | | | |-IP/TCP/RTP | |
| |-IP/TCP/RTSP/RTP | | | |-IP/TCP/RTSP/RTP | |
| +-----------------+ | | +-----------------+ |
+------------------------+ +------------------------+
Figure 1: RTP Monitoring Architecture
1. RTP communication between real time applications.
2. Application level metrics collection.
Wu, et al. Expires October 20, 2012 [Page 9]
Internet-Draft RTP Monitoring Architecture April 2012
3. Transport level metrics collection.
4. End System metrics collection.
5. Metrics Reporting over the RTP/RTCP paths
6. RTCP information Export to the network management system.
RTP may be used to 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 XR 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 XR reports to enhance the reception quality reporting.
3.2. RTCP Metric Block Report and associated parameters
The basic RTCP Reception Report (RR) [RFC3550] conveys reception
statistics (i.e., transport level statistics) in metric block report
format for multiple RTP media streams including
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 Run Length Encoding (RLE) reports
o Packet-receipt times reports
o Round-trip time reports
Wu, et al. Expires October 20, 2012 [Page 10]
Internet-Draft RTP Monitoring Architecture April 2012
o Statistics Summary Reports
There are also various other scenarios in which it is desirable to
send RTCP Metric reports more frequently. For example, the Audio/
Video Profile with Feedback [RFC4585] extends the standard Audio/
Video Profile [RFC3551] to allow RTCP reports to be sent early
provided RTCP bandwidth allocation is respected. The following are
four use cases but are not limited to:
o RTCP NACK is used to provide feedback on the RTP sequence numbers
for a subset of the lost packets or all the currently lost packets
[RFC4585].
o RTCP is extended to convey requests for full intra-coded frames or
select the reference picture, and signal changes in the desired
temporal/spatial trade-off and maximum media bit rate [RFC5104].
o RTCP or RTCP XR is extended to provide feedback on Explicit
Congestion Notification (ECN) statistics information [ECN].
o RTCP XR is extended to provide feedback on multicast acquisition
statistics information and parameters [RFC6332].
3.3. RTP Sender/Receiver entities located in network nodes
The location of the RTP Sender/Receiver entities may impact a set of
meaningful metrics. For instance, application level metrics for QoE
related performance parameters are under most conditions measured at
the user device that receives RTP data packets. However in some
cases, given the factors ( "measurement point location", "measurement
model location", "awareness of content information", etc [P.NAMS])
taken into account, such metrics may be measured in a network node
instead of a user device.
Wu, et al. Expires October 20, 2012 [Page 11]
Internet-Draft RTP Monitoring Architecture April 2012
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 compound metrics block. A single report block
(i.e.,compound metrics block) is designed to contain a large
number of parameters in different classes for a specific
application. 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.
o 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 a
Synchronization source (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. Therefore correlation between RTCP XR and
non-RTP data should be provided if administration or management
systems need to rely on the mapping RTCP statistics to non-RTCP
measurements to conducts data analysis and creates alerts to the
users. Without such correlation, it is hard to provide accurate
measures of real time application quality with a minimal number of
parameters included on the RTCP-XR reports in such case.
o Measurement Information duplication. Measurement information
provides information relevant to a measurement reported in one or
more other block types. For example we may set a metric interval
for the session and monitor RTP packets within one or several
consecutive metric intervals. In such case, the extra measurement
information (e.g., extended sequence number of 1st packet,
Wu, et al. Expires October 20, 2012 [Page 12]
Internet-Draft RTP Monitoring Architecture April 2012
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 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.
o 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. We therefore may
need a way to extend the block type space, so that new
specifications may continue to be developed.
Wu, et al. Expires October 20, 2012 [Page 13]
Internet-Draft RTP Monitoring Architecture April 2012
5. Guideline for reporting metric block using RTCP XR
5.1. Using single metrics 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 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. Correlating RTCP XR with RTP data
There are some classes of metrics that can only be interpreted with
knowledge of the media codec that is being used (audio MOS scores
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, and must signal details and parameters of the payload
Wu, et al. Expires October 20, 2012 [Page 14]
Internet-Draft RTP Monitoring Architecture April 2012
format to which that payload type is bound.
5.3. Correlating RTCP XR with the 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 of source 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 forward 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. Reducing Measurement information repetition
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. This memo proposes to
define a new XR Block that will be used 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 [MI] 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 on the Measurement information block [MI]
must specify the response in case the new RTCP XR metric block is
received without an associated measurement information block. In
Wu, et al. Expires October 20, 2012 [Page 15]
Internet-Draft RTP Monitoring Architecture April 2012
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 if though they will be the
same.
5.5. Expanding the RTCP XR block namespace
The consumption of XR block code points isn't a major issue. However
if XR block codes points is really close to run out of space, it
might be desirable to define new fields in the XR report block or
define one XR block type for vendor-specific extensions, with an
enterprise number included to identify the vendor making the
extension.
Wu, et al. Expires October 20, 2012 [Page 16]
Internet-Draft RTP Monitoring Architecture April 2012
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] 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 architecture 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].
Wu, et al. Expires October 20, 2012 [Page 17]
Internet-Draft RTP Monitoring Architecture April 2012
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 do not behave according to the RTP
protocol [RFC3550].
Considering the MCU and translator are two typical topologies in the
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 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.
Wu, et al. Expires October 20, 2012 [Page 18]
Internet-Draft RTP Monitoring Architecture April 2012
7.2. 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
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.
Wu, et al. Expires October 20, 2012 [Page 19]
Internet-Draft RTP Monitoring Architecture April 2012
8. IANA Considerations
There is no IANA action in this document.
Wu, et al. Expires October 20, 2012 [Page 20]
Internet-Draft RTP Monitoring Architecture April 2012
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 report should be encrypted.
Also note that the third party monitors are not visible at the RTP
layer since they do not send any RTCP packets. In order to prevent
any sensitive information leakage, the monitoring from the third
party monitors should be prohibited unless the security is in place
to authenticate them.
Wu, et al. Expires October 20, 2012 [Page 21]
Internet-Draft RTP Monitoring Architecture April 2012
10. Acknowledgement
The authors would also like to thank Colin Perkins, Charles Eckel,
Graeme Gibbs, Debbie Greenstreet, Keith Drage, Dan Romascanu, Ali C.
Begen, Roni Even, Magnus Westerlund for their valuable comments and
suggestions on the early version of this document.
Wu, et al. Expires October 20, 2012 [Page 22]
Internet-Draft RTP Monitoring Architecture April 2012
11. Informative References
[ECN] Westerlund, M., Johansson, I., Perkins, C., O'Hanlon, P.,
and K. Carlberg, "Explicit Congestion Notification (ECN)
for RTP over UDP", ID draft-ietf-avtcore-ecn-for-rtp-07,
March 2012.
[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.
[MI] Wu, Q., "Measurement Identity and information Reporting
using SDES item and XR Block",
ID draft-ietf-xrblock-rtcp-xr-meas-identity-05,
April 2012.
[P.NAMS] ITU-T, "Non-intrusive parametric model for the Assessment
of performance of Multimedia Streaming", ITU-T
Recommendation P.NAMS, November 2009.
[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-02, December 2011.
[QOE] 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-00, February 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.
[RFC3551] Schulzrinne , H. and S. Casner, "Extended RTP Profile for
Real-time Transport Control Protocol (RTCP)-Based Feedback
(RTP/AVPF)", RFC 3551, July 2003.
Wu, et al. Expires October 20, 2012 [Page 23]
Internet-Draft RTP Monitoring Architecture April 2012
[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.
[RFC5104] Wenger, S., Chandra, U., Westerlund, M., and B. Burman,
"Session Initiation Protocol Event Package for Voice
Quality Reporting", RFC 5104, February 2008.
[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.
[RFC6035] Pendleton, A., Clark, A., Johnston, A., and H. Sinnreich,
"Session Initiation Protocol Event Package for Voice
Quality Reporting", RFC 6035, November 2010.
[RFC6332] Begen, A. and E. Friedrich, "Multicast Acquisition Report
Block Type for RTP Control Protocol (RTCP) Extended
Reports (XRs)", RFC 6332, July 2011.
[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.
Wu, et al. Expires October 20, 2012 [Page 24]
Internet-Draft RTP Monitoring Architecture April 2012
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-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.2. draft-ietf-avtcore-monarch-11
The following are the major changes compared to 10:
o Editorial Changes.
A.3. 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.4. 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.
Wu, et al. Expires October 20, 2012 [Page 25]
Internet-Draft RTP Monitoring Architecture April 2012
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.
A.5. draft-ietf-avtcore-monarch-08
The following are the major changes compared to 07:
o Editorial change to the reference.
A.6. 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.7. draft-ietf-avtcore-monarch-06
The following are the major changes compared to 05:
o Some editorial changes.
A.8. 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.9. 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.
Wu, et al. Expires October 20, 2012 [Page 26]
Internet-Draft RTP Monitoring Architecture April 2012
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.
o Other editorial changes.
A.10. 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.11. 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.12. 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.
Wu, et al. Expires October 20, 2012 [Page 27]
Internet-Draft RTP Monitoring Architecture April 2012
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.
A.13. 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.
Wu, et al. Expires October 20, 2012 [Page 28]
Internet-Draft RTP Monitoring Architecture April 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. Expires October 20, 2012 [Page 29]