One document matched: draft-ietf-avt-rtcp-xr-pdv-03.xml
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<rfc category="std" ipr="trust200811" docName="draft-ietf-avt-rtcp-xr-pdv-03.txt">
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<front>
<title abbrev='RTCP XR Packet Delay Variation'>RTCP XR Report Block for Packet Delay Variation Metric Reporting</title>
<author initials='G.' surname='Hunt' fullname='Geoff Hunt'>
<organization abbrev='BT'>BT</organization>
<address>
<postal>
<street>Orion 2 PP3</street>
<street>Adastral Park</street>
<street>Martlesham Heath</street>
<city>Ipswich</city> <region>Suffolk</region>
<code>IP5 3RE</code>
<country>United Kingdom</country>
</postal>
<phone>+44 1473 651704</phone>
<email>geoff.hunt@bt.com</email>
</address>
</author>
<author initials='A.' surname='Clark' fullname='Alan Clark'>
<organization abbrev='Telchemy'>Telchemy Incorporated</organization>
<address>
<postal>
<street>2905 Premiere Parkway, Suite 280</street>
<city>Duluth</city> <region>GA</region>
<code>30097</code>
<country>USA</country>
</postal>
<email>alan.d.clark@telchemy.com</email>
</address>
</author>
<date month='May' year='2009' />
<area>Real-time Applications and Infrastructure Area</area>
<workgroup>Audio/Video Transport Working Group</workgroup>
<keyword>RFC</keyword>
<keyword>Request for Comments</keyword>
<keyword>I-D</keyword>
<keyword>Internet-Draft</keyword>
<keyword>Real Time Control Protocol</keyword>
<abstract>
<t>
This document defines an RTCP XR Report Block that allows the
reporting of Packet Delay Variation metrics for a range of RTP applications.
</t>
</abstract>
</front>
<middle>
<section anchor='intro' title="Introduction">
<section anchor='intro1' title="Packet Delay Variation Metrics Block">
<t>
This draft defines a new block type to augment those defined
in <xref target='RFC3611'/>, for use in a range of RTP applications.
</t><t>
The new block type provides information on Packet Delay Variation using one of several standard metrics.
</t>
<t>
The metrics belong to the class of transport metrics defined in [MONARCH] (work in progress).
</t>
<t>
Instances of this Metrics Block refer by tag to the separate auxiliary Measurement Identity block
<xref target='MEASIDENT'/> which contains information
such as the SSRC of the measured stream, and RTP sequence numbers and time intervals indicating the span of the report.
</t>
</section>
<section anchor='intro2' title="RTCP and RTCP XR Reports">
<t>
The use of RTCP for reporting is defined in <xref target='RFC3550'/>.
<xref target='RFC3611'/> defined an extensible structure for reporting using
an RTCP Extended Report (XR). This draft defines
a new Extended Report block that MUST be used as defined in
<xref target='RFC3550'/> and <xref target='RFC3611'/>.
</t>
</section>
<section anchor='intro3' title="Performance Metrics Framework">
<t>
The Performance Metrics Framework <xref target='PMOLFRAME'/> provides guidance on the
definition and specification of performance metrics. Metrics
described in this draft either reference external definitions
or define metrics generally in accordance with the guidelines
in <xref target='PMOLFRAME'/>.
</t>
</section>
<section anchor='intro4' title="Applicability">
<t>
These metrics are applicable to a range of RTP applications.
</t>
</section>
</section>
<section anchor='blockdef' title="Packet Delay Variation Metrics Block">
<t>
Metrics in this block report on packet delay variation in the stream arriving at the RTP system.
</t>
<section anchor='blockdef1' title="Report Block Structure">
<figure anchor='blockdata' title="Report Block Structure">
<artwork>
PDV metrics block
0 1 2 3
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BT=NPDV |I| tag |pdvtyp | block length=3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Pos Threshold/Peak PDV | Pos PDV Percentile |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Neg Threshold/Peak PDV | Neg PDV Percentile |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mean PDV | unused |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
</section>
<section anchor='blockdef2' title="Definition of Fields in PDV Metrics Block">
<t>
block type (BT): 8 bits
</t>
<t>
<list style='empty'>
<t>
A Packet Delay Variation Metrics Report Block is identified by the constant
NPDV.
</t>
</list>
</t>
<t>
[Note to RFC Editor: please replace NPDV with the
IANA provided RTCP XR block type for this block.]
</t>
<t>
Interval Metric flag (I): 1 bit
</t>
<t>
<list style='empty'>
<t>
This field is used to indicate whether the Packet Delay Variation metrics block is an Interval or a Cumulative report,
that is, whether the reported values apply to the most
recent measurement interval duration between successive metrics reports (I=1) (the Interval Duration) or to the accumulation period
characteristic of cumulative
measurements (I=0) (the Cumulative Duration). Numerical values for both these intervals are provided in the Measurement Identifier block
referenced by the tag field below.
</t>
</list>
</t>
<t>
Measurement Identifier association (tag): 3 bits
</t>
<t>
<list style='empty'>
<t>
This field is used to identify the Measurement Identifier block <xref target='MEASIDENT'/> which describes this measurement. The relevant
Measurement Identifier block has the same tag value as the Packet Delay Variation Metrics block. Note that there may be
more than one Measurement Identifier block per RTCP packet.
</t>
</list>
</t>
<t>
Packet Delay Variation Metric Type (pdvtyp): 4 bits
</t>
<t>
<list style='empty'>
<t>
This field is used to identify the Packet Delay Variation Metric Type used in this report block, according
to the following code:
</t>
</list>
</t>
<figure>
<artwork>
bits 014-017
0: interarrival jitter, Section 6.4.1 of [RFC3550],
1: MAPDV2, Clause 6.2.3.2 of [G.1020],
2: 2-point PDV, Clause 6.2.4 of [Y.1540]
</artwork>
</figure>
<t>
<list style='empty'>
<t>
Other values as registered by IANA in new registry "RTCP XR PDV block - PDV type", see <xref target='ianareg'/>.
</t>
</list>
</t>
<t>
block length: 16 bits
</t>
<t>
<list style='empty'>
<t>
The length of this report block in 32-bit words, minus one. For the Packet Delay Variation Metrics block, the
block length is equal to 3.
</t>
</list>
</t>
<t>
Positive Threshold/Peak PDV: 16 bit, S11:4 format
</t>
<t>
<list style='empty'>
<t>
The PDV associated with the Positive PDV percentile expressed in milliseconds.
The term Positive is associated
with packets arriving later than the expected time.
</t><t>
If the measured value is more negative than -2047.9375 (the value
which would be coded as 0x8001), the value 0x8000 SHOULD be reported
to indicate an over-range negative measurement. If the measured
value is more positive than +2047.8125 (the value which would be
coded as 0x7FFD), the value 0x7FFE SHOULD be reported to indicate an
over-range positive measurement. If the measurement is unavailable,
the value 0x7FFF SHOULD be reported.
</t>
</list>
</t>
<t>
Positive PDV Percentile: 16 bit, 8:8 format
</t>
<t>
<list style='empty'>
<t>
The percentage of packets on the call for which individual packet
delays were less than the Positive Threshold PDV.
</t><t>
If the measurement is unavailable, the value 0xFFFF SHOULD be
reported.
</t>
</list>
</t>
<t>
Negative Threshold/Peak PDV: 16 bit, S11:4 format
</t>
<t>
<list style='empty'>
<t>
The PDV associated with the Negative PDV percentile expressed in milliseconds.
The term Negative is associated
with packets arriving earlier than the expected time.
</t><t>
If the measured value is more negative than -2047.9375 (the value
which would be coded as 0x8001), the value 0x8000 SHOULD be reported
to indicate an over-range negative measurement. If the measured
value is more positive than +2047.8125 (the value which would be
coded as 0x7FFD), the value 0x7FFE SHOULD be reported to indicate an
over-range positive measurement. If the measurement is unavailable,
the value 0x7FFF SHOULD be reported.
</t>
</list>
</t>
<t>
Negative PDV Percentile: 16 bit, 8:8 format
</t>
<t>
<list style='empty'>
<t>
The percentage of packets on the call for which individual packet
delays were more than the Negative Threshold PDV.
</t><t>
If the measurement is unavailable, the value 0xFFFF SHOULD be
reported.
</t>
</list>
</t>
<t>
If the PDV Type indicated is 2-point PDV and the Positive and Negative PDV
Percentiles are set to 100.0 then the Positive and Negative
Threshold/Peak PDV values are the peak values measured during the
reporting interval (which may be from the start of the call for
cumulative reports). In this case, the difference between the
Positive and Negative Threshold/Peak values defines the range of
2-point PDV.
</t>
<t>
Mean PDV: (16 bit, S11:4 format) expressed in milliseconds
</t>
<t>
<list style='empty'>
<t>
For MAPDV2 this value is generated according to Clause 6.2.3.2 of <xref target='G.1020'/>. For
interval reports the MAPDV2 value is reset at the start of the
interval.
</t><t>
For interarrival jitter, the value reported is the value of J(i) calculated according
to <xref target='RFC3550'/> at the time the report is generated.
</t><t>
For 2-point PDV, the value reported is the mean of per-packet 2-point PDV values. This metric
indicates the arrival time of the first media packet of the session with respect to the
mean of the arrival times of every packet of the session. A single value of the metric (for a
single session) may not be
useful by itself, but its average over a number of sessions may be useful in diagnosing media
delay at session startup. For example, this might occur if media packets are often delayed behind
signalling packets due to head-of-line blocking.
</t><t>
If the measured value is more negative than -2047.9375 (the value
which would be coded as 0x8001), the value 0x8000 SHOULD be reported
to indicate an over-range negative measurement. If the measured
value is more positive than +2047.8125 (the value which would be
coded as 0x7FFD), the value 0x7FFE SHOULD be reported to indicate an
over-range positive measurement. If the measurement is unavailable,
the value 0x7FFF SHOULD be reported.
</t>
</list>
</t>
<t>
unused: 16 bits
</t>
<t>
<list style='empty'>
<t>
These bits are unused. They SHOULD be set to zero by the sender and MUST be ignored by the receiver.
</t>
</list>
</t>
</section>
<section anchor='guide' title="Guidance on use of PDV metrics">
<t>
This subsection provides informative guidance on when it might be appropriate to use each of the
PDV metric types.
</t>
<t>
Interarrival jitter (Section 6.4.1 of <xref target='RFC3550'/>) allows comparison of results with those from RTP
end systems which support only RTCP as defined in <xref target='RFC3550'/>.
</t>
<t>
MAPDV2 (Clause 6.2.3.2 of <xref target='G.1020'/>) compares instantaneous (per-packet) delay variation against a moving average delay
variation. This metric could be useful in determining residual impairment when an RTP end system uses an adaptive de-jitter
buffer which tracks the average delay variation, provided the MAPDV2 algorithm and the adaptive de-jitter buffer have similar
averaging behaviour.
</t>
<t>
2-point PDV (Clause 6.2.4 of <xref target='Y.1540'/>) reports absolute packet delay variation with respect to the time of arrival of the
first packet of the connection. In an RTP context, the two "points" are at the sender (the synchronization source which applies RTP timestamps)
and at the receiver.
The value of this metric for the packet with index j is identical to the quantity D(i,j) defined in Section 6.4.1 of <xref target='RFC3550'/>
if the packet index i is set equal to 1, that is, the reference packet for the metric is the first packet of the connection. The metric includes
the effect of the frequency offsets of clocks in both the
sender and receiver end systems, so it is useful mainly in network where synchronisation is distributed. As well as
measuring packet delay variation in such networks, it may be used to ensure that synchronisation is effective, for
example where the network carries ISDN data traffic over RTP <xref target='RFC4040'/>. The metric is likely to be useful in networks
which use fixed de-jitter buffering, because it may be used to determine the length of the required de-jitter buffer, or to determine
if network performance has deteriorated such that existing de-jitter buffers are too small to accommodate the observed delay variation.
</t>
</section>
<section anchor='examples' title="Examples of use">
<t>
(a) To report interarrival jitter <xref target='RFC3550'/>:
</t><t>
Threshold PDV = FFFF (Undefined); PDV Percentile = FFFF (Undefined);
PDV type = 0 (interarrival jitter)
</t><t>
causes interarrival jitter to be reported in the Mean PDV field.
</t><t>
(b) To report MAPDV2 <xref target='G.1020'/>:
</t><t>
Pos Threshold PDV = 50.0; Pos PDV Percentile = 95.3; Neg Threshold
PDV = 50.0 (note this implies -50ms); Neg PDV Percentile = 98.4; PDV
type = 1 (MAPDV2)
</t><t>
causes average MAPDV2 to be reported in the Mean PDV field.
</t><t>
Note that implementations may either fix the reported percentile and
calculate the associated PDV level OR may fix a threshold PDV level
and calculate the associated percentile. From a practical
implementation perspective it is simpler to use the second of these
approaches (except of course in the extreme case of a 100%
percentile).
</t><t>
2-point PDV, according to <xref target='Y.1540'/> is the difference in delay between the current
packet and the first packet of the stream. If the sending and
receiving clocks are not synchronized, this metric includes the
effect of relative timing drift.
</t>
</section>
</section>
<section anchor='sdp' title="SDP Signaling">
<t>
<xref target='RFC3611'/> defines the use of SDP (Session Description Protocol)
<xref target='RFC4566'/> for signaling the use of XR blocks. XR blocks MAY be used without
prior signaling.
</t>
<t>
This section augments the SDP <xref target='RFC4566'/> attribute "rtcp-xr" defined in
<xref target='RFC3611'/> by providing an additional value of "xr-format" to signal the use of the report
block defined in this document.
</t><t>
rtcp-xr-attrib = "a=" "rtcp-xr" ":" [xr-format *(SP xr-format)] CRLF
</t><t>
(defined in <xref target='RFC3611'/>)
</t><t>
xr-format =/ xr-pdv-block
</t>
<figure>
<artwork>
xr-pdv-block = "pkt-dly-var" [ "," pdvtype ] [ "," nspec "," pspec ]
</artwork>
</figure>
<figure>
<artwork>
pdvtype = "pdv=" 0 ; interarrival jitter RFC 3550
/ 1 ; MAPDV2 ITU-T G.1020
/ 2 ; 2-point PDV ITU-T Y.1540
nspec = "nthr=" fixpoint ; negative threshold PDV (ms)
/ "npc=" fixpoint ; negative PDV percentile
pspec = "pthr=" fixpoint ; positive threshold PDV (ms)
/ "ppc=" fixpoint ; positive PDV percentile
</artwork>
</figure>
<figure>
<artwork>
fixpoint = 1*DIGIT "." 1*DIGIT ; fixed point decimal
DIGIT = %x30-39
</artwork>
</figure>
<t>
When SDP is used in offer-answer, a system sending SDP may request a specific type of PDV measurement. In addition, they
may state a specific percentile or threshold value, and expect to receive the corresponding threshold or
percentile metric, respectively. The system receiving the SDP SHOULD send the PDV metrics requested, but
if the metric is not available, the system receiving the SDP SHOULD send the flag value indicating that the
metric is unavailable.
</t>
</section>
<section title="IANA Considerations">
<t>
New block types for RTCP XR are subject to IANA registration. For
general guidelines on IANA considerations for RTCP XR, refer to
[RFC3611].
</t>
<section title="New RTCP XR Block Type value">
<t>
This document assigns the block type value NPDV in the IANA "RTCP XR Block
Type Registry" to the "Packet Delay Variation Metrics Block".
</t>
<t>
[Note to RFC Editor: please replace NPDV with the
IANA provided RTCP XR block type for this block.]
</t>
</section>
<section title="New RTCP XR SDP Parameter">
<t>
This document also registers a new
parameter "pkt-dly-var" in the "RTCP XR SDP Parameters Registry".
</t>
</section>
<section title="Contact information for registrations">
<t>
The contact information for the registrations is:
</t>
<t>
Geoff Hunt (geoff.hunt@bt.com)
</t>
<t>
Orion 2 PP3, Adastral Park, Martlesham Heath, Ipswich IP5 3RE, United Kingdom
</t>
</section>
<section anchor='ianareg' title="New registry of PDV types">
<t>
This document creates a new registry to be called "RTCP XR PDV block - PDV type" as a sub-registry of
the "RTP Control Protocol Extended Reports (RTCP XR) Block Type Registry". Policies for this new
registry are as follows:
</t>
<t>
<list style='symbols'>
<t>
The information required to support an assignment is an unambiguous definition of the new metric, covering the base measurements
and how they are processed to generate the reported metric. This should include the units of measurement, how values of the metric
are reported in the three 16-bit fields "Pos Threshold/Peak PDV", "Neg Threshold/Peak PDV" and "Mean PDV" within the report block,
and how the metric uses the two 16-bit fields "Pos PDV Percentile" and "Neg PDV Percentile".
</t>
<t>
The review process for the registry is "Specification Required" as described in Section 4.1 of <xref target='RFC5226'/>.
</t>
<t>
Entries in the registry are integers. The valid range is 0 to 15 corresponding to the 4-bit field "pdvtyp" in the block.
Values are to be recorded in decimal.
</t>
<t>
Initial assignments are as follows:
</t>
</list>
</t>
<t>
<figure>
<artwork>
0: interarrival jitter, Section 6.4.1 of [RFC3550],
1: MAPDV2, Clause 6.2.3.2 of [G.1020],
2: 2-point PDV, Clause 6.2.4 of [Y.1540]
</artwork>
</figure>
</t>
</section>
</section>
<section title="Security Considerations">
<t>
It is believed that this proposed RTCP XR report block introduces no
new security considerations beyond those described in <xref target='RFC3611'/>. This block does not provide
per-packet statistics so the risk
to confidentiality documented in Section 7, paragraph 3 of <xref target='RFC3611'/> does
not apply.
</t>
</section>
<section title="Changes from previous version">
<t>
Changed BNF for SDP following Christian Groves' and Tom Taylor's comments (4th and 5th May 2009), now aligned with RFC 5234 section 3.3
"Incremental Alternatives".
</t>
<t>
Updated references.
</t>
</section>
</middle>
<back>
<references title='Normative References'>
<reference anchor='MEASIDENT'>
<front>
<title>RTCP XR Measurement Identifier Block</title>
<author initials='G.' surname='Hunt' fullname='Geoff Hunt'>
<organization>BT</organization>
</author>
<date month='May' year='2009' />
</front>
<seriesInfo name='ID' value='draft-ietf-avt-rtcp-xr-meas-identity-02' />
<format type='TXT' />
</reference>
<reference anchor='RFC3550'>
<front>
<title>RTP: A Transport Protocol for Real-Time Applications</title>
<author initials='H.' surname='Schulzrinne' fullname='Henning Schulzrinne'>
<organization>Columbia University</organization>
</author>
<date month='July' year='2003' />
</front>
<seriesInfo name='RFC' value='3550' />
<format type='TXT' />
</reference>
<reference anchor='RFC3611'>
<front>
<title>RTP Control Protocol Extended Reports (RTCP XR)</title>
<author initials='T. (Ed)' surname='Friedman' fullname='Timur Friedman'>
<organization> Paris 6 </organization>
</author>
<date month='November' year='2003' />
</front>
<seriesInfo name='RFC' value='3611' />
<format type='TXT' />
</reference>
<reference anchor='RFC4040'>
<front>
<title>RTP Payload Format for a 64 kbit/s Transparent Call</title>
<author initials='R.' surname='Kreuter' fullname='Ruediger Kreuter'>
<organization>Siemens AG</organization>
</author>
<date month='April' year='2005' />
</front>
<seriesInfo name='RFC' value='4040' />
<format type='TXT' />
</reference>
<reference anchor='RFC2119'>
<front>
<title>Key words for use in RFCs to Indicate Requirement Levels</title>
<author initials='S.' surname='Bradner' fullname='Scott Bradner'>
<organization>Harvard University</organization>
</author>
<date month='March' year='1997' />
</front>
<seriesInfo name='RFC' value='2119' />
<seriesInfo name='BCP' value='14' />
<format type='TXT' />
</reference>
<reference anchor='RFC4566'>
<front>
<title>SDP: Session Description Protocol</title>
<author initials='M.' surname='Handley' fullname='Mark Handley'>
<organization>UCL</organization>
</author>
<date month='July' year='2006' />
</front>
<seriesInfo name='RFC' value='4566'/>
<format type='TXT' />
</reference>
<reference anchor='RFC5226'>
<front>
<title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
<author initials='T.' surname='Narten' fullname='Thomas Narten'>
<organization>IBM</organization>
</author>
<date month='May' year='2008' />
</front>
<seriesInfo name='RFC' value='5226'/>
<seriesInfo name='BCP' value='26'/>
<format type='TXT' />
</reference>
<reference anchor='G.1020'>
<front>
<title>ITU-T Rec. G.1020, Performance parameter definitions for quality of speech and
other voiceband applications utilizing IP networks</title>
<author initials='' surname='' fullname=''>
<organization>ITU-T</organization>
</author>
<date month='July' year='2006' />
</front>
<format type='TXT' />
</reference>
<reference anchor='Y.1540'>
<front>
<title>ITU-T Rec. Y.1540, IP packet transfer and availability performance parameters</title>
<author initials='' surname='' fullname=''>
<organization>ITU-T</organization>
</author>
<date month='November' year='2007' />
</front>
<format type='TXT' />
</reference>
</references>
<references title='Informative References'>
<reference anchor='PMOLFRAME'>
<front>
<title>Framework for Performance Metric Development</title>
<author initials='A.' surname='Clark' fullname='Alan Clark'>
<organization>Telchemy Incorporated</organization>
</author>
<date month='March' year='2009' />
</front>
<seriesInfo name='ID' value='draft-ietf-pmol-metrics-framework-02' />
<format type='TXT' />
</reference>
<reference anchor='MONARCH'>
<front>
<title>Monitoring Architectures for RTP</title>
<author initials='G.' surname='Hunt' fullname='Geoff Hunt'>
<organization>BT</organization>
</author>
<date month='August' year='2008' />
</front>
<seriesInfo name='ID' value='draft-hunt-avt-monarch-01' />
<format type='TXT' />
</reference>
</references>
</back>
</rfc>
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