Audio/Video Transport Working Group G. Hunt
Internet-Draft Unaffiliated
Intended status: Standards Track A. Clark
Expires: June 9, 2012 Telchemy
Q. Wu
Huawei
December 7, 2011
RTCP XR Report Block for Packet Delay Variation Metric Reporting
draft-ietf-xrblock-rtcp-xr-pdv-02.txt
Abstract
This document defines an RTCP XR Report Block that allows the
reporting of Packet Delay Variation metrics for a range of RTP
applications.
Status of this Memo
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This Internet-Draft will expire on June 9, 2012.
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Packet Delay Variation Metrics Block . . . . . . . . . . . 3
1.2. RTCP and RTCP XR Reports . . . . . . . . . . . . . . . . . 3
1.3. Performance Metrics Framework . . . . . . . . . . . . . . 3
1.4. Applicability . . . . . . . . . . . . . . . . . . . . . . 3
2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Packet Delay Variation Metrics Block . . . . . . . . . . . . . 5
3.1. Report Block Structure . . . . . . . . . . . . . . . . . . 5
3.2. Definition of Fields in PDV Metrics Block . . . . . . . . 5
3.3. Guidance on use of PDV metrics . . . . . . . . . . . . . . 9
3.4. Examples of use . . . . . . . . . . . . . . . . . . . . . 9
4. SDP Signaling . . . . . . . . . . . . . . . . . . . . . . . . 11
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
5.1. New RTCP XR Block Type value . . . . . . . . . . . . . . . 12
5.2. New RTCP XR SDP Parameter . . . . . . . . . . . . . . . . 12
5.3. Contact information for registrations . . . . . . . . . . 12
5.4. New registry of PDV types . . . . . . . . . . . . . . . . 12
6. Security Considerations . . . . . . . . . . . . . . . . . . . 14
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
7.1. Normative References . . . . . . . . . . . . . . . . . . . 15
7.2. Informative References . . . . . . . . . . . . . . . . . . 15
Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 16
A.1. draft-ietf-avt-rtcp-xr-pdv-03 . . . . . . . . . . . . . . 16
A.2. draft-ietf-xrblock-rtcp-xr-pdv-00 . . . . . . . . . . . . 16
A.3. draft-ietf-xrblock-rtcp-xr-pdv-01 . . . . . . . . . . . . 16
A.4. draft-ietf-xrblock-rtcp-xr-pdv-02 . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17
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1. Introduction
1.1. Packet Delay Variation Metrics Block
This draft defines a new block type to augment those defined in
[RFC3611], for use in a range of RTP applications.
The new block type provides information on Packet Delay Variation
using one of several standard metrics.
The metrics belong to the class of transport metrics defined in
[MONARCH] (work in progress).
1.2. RTCP and RTCP XR Reports
The use of RTCP for reporting is defined in [RFC3550]. [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 in accordance with [RFC3550] and [RFC3611].
1.3. Performance Metrics Framework
The Performance Metrics Framework [RFC6390] 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
[RFC6390].
1.4. Applicability
These metrics are applicable to a range of RTP applications.
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2. Definitions
This report block makes use of binary fractions. The terminology
used is
Numeric formats S X:Y
where S indicates a two's complement signed representation, X
the number of bits prior to the decimal place and Y the number
of bits after the decimal place.
Hence 8:8 represents an unsigned number in the range 0.0 to
255.996 with a granularity of 0.0039. S7:8 would represent the
range -127.996 to +127.996. 0:16 represents a proper binary
fraction with range
0.0 to 1 - 1/65536 = 0.9999847
though note that use of flag values at the top of the numeric
range slightly reduces this upper limit. For example, if the
16- bit values 0xfffe and 0xffff are used as flags for "over-
range" and "unavailable" conditions, a 0:16 quantity has range
0.0 to 1 - 3/65536 = 0.9999542
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3. Packet Delay Variation Metrics Block
Metrics in this block report on packet delay variation in the stream
arriving at the RTP system. Instances of this Metrics Block refer by
SSRC to the separate auxiliary Measurement Information block [MEASI]
which contains measurement intervals. This metric block relies on
the measurement interval in the Measurement Information block
indicating the span of the report. If the measurement interval is
not received for this metric block, this metric block should be
discarded.
3.1. Report Block Structure
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 |pdvtyp |Rsv| block length=3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SSRC of Source |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Pos PDV Threshold/Peak | Pos PDV Percentile |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Neg PDV Threshold/Peak | Neg PDV Percentile |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mean PDV | unused |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Report Block Structure
3.2. Definition of Fields in PDV Metrics Block
Block type (BT): 8 bits
A Packet Delay Variation Metrics Report Block is identified by the
constant NPDV.
[Note to RFC Editor: please replace NPDV with the IANA provided
RTCP XR block type for this block.]
Interval Metric flag (I): 2 bit
This field is used to indicate whether the Basic Loss/Discard
metrics are Sampled, Interval or Cumulative metrics, that is,
whether the reported values applies to the most recent measurement
interval duration between successive metrics reports (I=10) (the
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Interval Duration) or to the accumulation period characteristic of
cumulative measurements (I=11) (the Cumulative Duration) or to the
value of a continuously measured or calculated that has been
sampled at end of the interval (I=01) (Sampled Value).
Packet Delay Variation Metric Type (pdvtyp): 4 bits
This field is used to identify the Packet Delay Variation Metric
Type used in this report block, according to the following code:
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].
Rsv.: 2 bits
This field is reserved for future definition. In the absence of
such a definition, the bits in this field MUST be set to zero and
MUST be ignored by the receiver.
Block Length: 16 bits
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.
SSRC of source: 32 bits
As defined in Section 4.1 of [RFC3611].
Positive PDV Threshold/Peak: 16 bits
This field is associated with the Positive PDV percentile and
expressed in Milliseconds with numeric format S11:4. The term
Positive represents that the packets are arriving later than the
expected time.
If the measured value is more negative than -2047.9375 (the value
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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.
Positive PDV Percentile: 16 bits
The percentages of packets in the RTP stream for which individual
packet delays were less than the Positive PDV Threshold. It is
expressed in numeric format 8:8 with values from 0 to 100th
percentile.
If the measurement is unavailable, the value 0xFFFF SHOULD be
reported.
Negative PDV Threshold/Peak: 16 bits
This field is associated with the Negative PDV percentile and
expressed in Milliseconds with numeric format S11:4. The term
Negative represents that the packets are arriving earlier than the
expected time.
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.
Negative PDV Percentile: 16 bits
The percentages of packets in the RTP stream for which individual
packet delays were more than the Negative PDV Threshold. It is
expressed in numeric format 8:8 with values from 0 to 100th
percentile.
If the measurement is unavailable, the value 0xFFFF SHOULD be
reported.
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
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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.
Mean PDV: 16 bits
The mean PDV value of data packets is expressed in milliseconds
with Numeric format S11:4 format.
For MAPDV2 this value is generated according to Clause 6.2.3.2 of
[G.1020]. For interval reports the MAPDV2 value is reset at the
start of the interval.
For interarrival jitter, the value reported is the value of J(i)
calculated according to [RFC3550] at the time the report is
generated.
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.
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.
Unused: 16 bits
These bits are unused. They SHOULD be set to zero by the sender
and MUST be ignored by the receiver.
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3.3. Guidance on use of PDV metrics
This subsection provides informative guidance on when it might be
appropriate to use each of the PDV metric types.
Interarrival jitter (Section 6.4.1 of [RFC3550]) allows comparison of
results with those from RTP end systems which support only RTCP as
defined in [RFC3550].
MAPDV2 (Clause 6.2.3.2 of [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 adaptive de-jitter buffer have
similar averaging behaviour as the MAPDV2 algorithm.
2-point PDV (Clause 6.2.4 of [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
[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 [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.
3.4. Examples of use
(a) To report interarrival jitter [RFC3550]:
PDV Threshold = FFFF (Undefined); PDV Percentile = FFFF
(Undefined); PDV type = 0 (interarrival jitter)
causes interarrival jitter to be reported in the Mean PDV
field.
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(b) To report MAPDV2 [G.1020]:
Pos PDV Threshold = 50.0; Pos PDV Percentile = 95.3; Neg PDV
Threshold = 50.0 (note this implies -50ms); Neg PDV Percentile
= 98.4; PDV type = 1 (MAPDV2)
causes average MAPDV2 to be reported in the Mean PDV field.
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).
2-point PDV, according to [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.
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4. SDP Signaling
[RFC3611] defines the use of SDP (Session Description Protocol)
[RFC4566] for signaling the use of XR blocks. XR blocks MAY be used
without prior signaling.
This section augments the SDP [RFC4566] attribute "rtcp-xr" defined
in [RFC3611] by providing an additional value of "xr-format" to
signal the use of the report block defined in this document.
rtcp-xr-attrib = "a=" "rtcp-xr" ":" [xr-format *(SP xr-format)] CRLF
(defined in [RFC3611])
xr-format =/ xr-pdv-block
xr-pdv-block = "pkt-dly-var" [ "," pdvtype ] [ "," nspec "," pspec ]
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 PDV threshold (ms)
/ "npc=" fixpoint ; negative PDV percentile
pspec = "pthr=" fixpoint ; positive PDV threshold (ms)
/ "ppc=" fixpoint ; positive PDV percentile
fixpoint = 1*DIGIT "." 1*DIGIT ; fixed point decimal
DIGIT = %x30-39
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 metric block with the flag value indicating that the metric
is unavailable.
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5. IANA Considerations
New block types for RTCP XR are subject to IANA registration. For
general guidelines on IANA considerations for RTCP XR, refer to
[RFC3611].
5.1. New RTCP XR Block Type value
This document assigns the block type value NPDV in the IANA "RTCP XR
Block Type Registry" to the "Packet Delay Variation Metrics Block".
[Note to RFC Editor: please replace NPDV with the IANA provided RTCP
XR block type for this block.]
5.2. New RTCP XR SDP Parameter
This document also registers a new parameter "pkt-dly-var" in the
"RTCP XR SDP Parameters Registry".
5.3. Contact information for registrations
The contact information for the registrations is:
Qin Wu (sunseawq@huawei.com)
101 Software Avenue, Yuhua District
Nanjing, Jiangsu 210012
China
5.4. New registry of PDV types
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:
o 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 PDV
Threshold/Peak", "Neg PDV Threshold/Peak" and "Mean PDV" within
the report block, and how the metric uses the two 16-bit fields
"Pos PDV Percentile" and "Neg PDV Percentile".
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o The review process for the registry is "Specification Required" as
described in Section 4.1 of [RFC5226].
o 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.
o Initial assignments are as follows:
1. interarrival jitter, Section 6.4.1 of [RFC3550],
2. MAPDV2, Clause 6.2.3.2 of [G.1020],
3. 2-point PDV, Clause 6.2.4 of [Y.1540]
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6. Security Considerations
It is believed that this proposed RTCP XR report block introduces no
new security considerations beyond those described in [RFC3611].
This block does not provide per-packet statistics so the risk to
confidentiality documented in Section 7, paragraph 3 of [RFC3611]
does not apply.
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7. References
7.1. Normative References
[G.1020] ITU-T, "ITU-T Rec. G.1020, Performance parameter
definitions for quality of speech and other voiceband
applications utilizing IP networks", July 2006.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", March 1997.
[RFC3550] Schulzrinne, H., "RTP: A Transport Protocol for Real-Time
Applications", RFC 3550, July 2003.
[RFC3611] Friedman, T., Caceres, R., and A. Clark, "RTP Control
Protocol Extended Reports (RTCP XR)", November 2003.
[RFC4040] Kreuter, R., "RTP Payload Format for a 64 kbit/s
Transparent Call", April 2005.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", July 2006.
[RFC5226] Narten, T., "Guidelines for Writing an IANA Considerations
Section in RFCs", May 2008.
BCP 26
[Y.1540] ITU-T, "ITU-T Rec. Y.1540, IP packet transfer and
availability performance parameters", November 2007.
7.2. Informative References
[MEASI] Hunt, G., "Measurement Identity and information Reporting
using SDES item and XR Block",
ID draft-ietf-xrblock-rtcp-xr-measu-identity-01,
October 2011.
[MONARCH] Hunt, G., "Monitoring Architectures for RTP",
ID draft-ietf-avtcore-monarch-04, August 2011.
[RFC6390] Clark, A. and B. Claise, "Framework for Performance Metric
Development", RFC 6390, October 2011.
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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-avt-rtcp-xr-pdv-03
The following are the major changes to previous version :
o Changed BNF for SDP following Christian Groves' and Tom Taylor's
comments (4th and 5th May 2009).
o Updated references.
A.2. draft-ietf-xrblock-rtcp-xr-pdv-00
The following are the major changes to previous version
draft-ietf-avt-rtcp-xr-pdv-03 :
o Updated references.
A.3. draft-ietf-xrblock-rtcp-xr-pdv-01
The following are the major changes to previous version
draft-ietf-xrblock-rtcp-xr-pdv-00 :
o Fix typos or nits in the definition of Negative PDV Threshold/
Peak.
o Fix nits in Numeric format S7:8.
o remove the text that is relevant to tag field.
o Add text in SDP signaling section to clarify indicationof metric
unavailable.
A.4. draft-ietf-xrblock-rtcp-xr-pdv-02
The following are the major changes to previous version
draft-ietf-xrblock-rtcp-xr-pdv-00 :
o Updated references.
o Allocate one more bit for Interval metric flag to indicate sampled
metric can be used.
o Add a few clarification text for failure mode.
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Authors' Addresses
Geoff Hunt
Unaffiliated
Email: r.geoff.hunt@gmail.com
Alan Clark
Telchemy Incorporated
2905 Premiere Parkway, Suite 280
Duluth, GA 30097
USA
Email: alan.d.clark@telchemy.com
Qin Wu
Huawei
101 Software Avenue, Yuhua District
Nanjing, Jiangsu 210012
China
Email: sunseawq@huawei.com
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