draft-ietf-ippm-delay-var-as-00.txt   draft-ietf-ippm-delay-var-as-01.txt 
Network Working Group A. Morton Network Working Group A. Morton
Internet-Draft AT&T Labs Internet-Draft AT&T Labs
Intended status: Informational B. Claise Intended status: Informational B. Claise
Expires: August 20, 2008 Cisco Systems, Inc. Expires: January 14, 2009 Cisco Systems, Inc.
February 17, 2008 July 13, 2008
Packet Delay Variation Applicability Statement Packet Delay Variation Applicability Statement
draft-ietf-ippm-delay-var-as-00 draft-ietf-ippm-delay-var-as-01
Status of this Memo Status of this Memo
By submitting this Internet-Draft, each author represents that any By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79. aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
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This Internet-Draft will expire on August 20, 2008. This Internet-Draft will expire on January 14, 2009.
Copyright Notice
Copyright (C) The IETF Trust (2008).
Abstract Abstract
Packet delay variation metrics appear in many different standards Packet delay variation metrics appear in many different standards
documents. The metric definition in RFC 3393 has considerable documents. The metric definition in RFC 3393 has considerable
flexibility, and it allows multiple formulations of delay variation flexibility, and it allows multiple formulations of delay variation
through the specification of different packet selection functions. through the specification of different packet selection functions.
Although flexibility provides wide coverage and room for new ideas, Although flexibility provides wide coverage and room for new ideas,
it can make comparisons of independent implementations more it can make comparisons of independent implementations more
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document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Background Literature in IPPM and Elsewhere . . . . . . . 5 1.1. Background Literature in IPPM and Elsewhere . . . . . . . 5
1.2. Organization of the Memo . . . . . . . . . . . . . . . . . 6 1.2. Organization of the Memo . . . . . . . . . . . . . . . . . 6
2. Purpose and Scope . . . . . . . . . . . . . . . . . . . . . . 6 2. Purpose and Scope . . . . . . . . . . . . . . . . . . . . . . 6
3. Brief Descriptions of Delay Variation Uses . . . . . . . . . . 7 3. Brief Descriptions of Delay Variation Uses . . . . . . . . . . 7
3.1. Inferring Queue Occupation on a Path . . . . . . . . . . . 7 3.1. Inferring Queue Occupation on a Path . . . . . . . . . . . 7
3.2. Determining De-jitter Buffer Size . . . . . . . . . . . . 7 3.2. Determining De-jitter Buffer Size . . . . . . . . . . . . 8
3.3. Spatial Composition . . . . . . . . . . . . . . . . . . . 9 3.3. Spatial Composition . . . . . . . . . . . . . . . . . . . 9
3.4. Service Level Comparison . . . . . . . . . . . . . . . . . 9 3.4. Service Level Comparison . . . . . . . . . . . . . . . . . 9
3.5. <your favorite here> . . . . . . . . . . . . . . . . . . . 10 3.5. Application-Layer FEC Design . . . . . . . . . . . . . . . 10
4. Formulations of IPDV and PDV . . . . . . . . . . . . . . . . . 10 4. Formulations of IPDV and PDV . . . . . . . . . . . . . . . . . 10
4.1. IPDV: Inter-Packet Delay Variation . . . . . . . . . . . . 10 4.1. IPDV: Inter-Packet Delay Variation . . . . . . . . . . . . 10
4.2. PDV: Packet Delay Variation . . . . . . . . . . . . . . . 11 4.2. PDV: Packet Delay Variation . . . . . . . . . . . . . . . 11
4.3. A "Point" about Measurement Points . . . . . . . . . . . . 11 4.3. A "Point" about Measurement Points . . . . . . . . . . . . 11
4.4. Examples and Initial Comparisons . . . . . . . . . . . . . 11 4.4. Examples and Initial Comparisons . . . . . . . . . . . . . 12
5. Survey of Earlier Comparisons . . . . . . . . . . . . . . . . 12 5. Survey of Earlier Comparisons . . . . . . . . . . . . . . . . 13
5.1. Demichelis' Comparison . . . . . . . . . . . . . . . . . . 13 5.1. Demichelis' Comparison . . . . . . . . . . . . . . . . . . 13
5.2. Ciavattone et al. . . . . . . . . . . . . . . . . . . . . 14 5.2. Ciavattone et al. . . . . . . . . . . . . . . . . . . . . 14
5.3. IPPM List Discussion from 2000 . . . . . . . . . . . . . . 15 5.3. IPPM List Discussion from 2000 . . . . . . . . . . . . . . 15
5.4. Y.1540 Appendix II . . . . . . . . . . . . . . . . . . . . 17 5.4. Y.1540 Appendix II . . . . . . . . . . . . . . . . . . . . 17
5.5. Clark's ITU-T SG 12 Contribution . . . . . . . . . . . . . 17 5.5. Clark's ITU-T SG 12 Contribution . . . . . . . . . . . . . 17
6. Additional Properties and Comparisons . . . . . . . . . . . . 17 6. Additional Properties and Comparisons . . . . . . . . . . . . 17
6.1. Packet Loss . . . . . . . . . . . . . . . . . . . . . . . 17 6.1. Packet Loss . . . . . . . . . . . . . . . . . . . . . . . 17
6.2. Path Changes . . . . . . . . . . . . . . . . . . . . . . . 18 6.2. Path Changes . . . . . . . . . . . . . . . . . . . . . . . 18
6.2.1. Lossless Path Change . . . . . . . . . . . . . . . . . 19 6.2.1. Lossless Path Change . . . . . . . . . . . . . . . . . 19
6.2.2. Path Change with Loss . . . . . . . . . . . . . . . . 20 6.2.2. Path Change with Loss . . . . . . . . . . . . . . . . 20
6.3. Clock Stability and Error . . . . . . . . . . . . . . . . 21 6.3. Clock Stability and Error . . . . . . . . . . . . . . . . 21
6.4. Spatial Composition . . . . . . . . . . . . . . . . . . . 23 6.4. Spatial Composition . . . . . . . . . . . . . . . . . . . 23
6.5. Reporting a Single Number (SLA) . . . . . . . . . . . . . 23 6.5. Reporting a Single Number (SLA) . . . . . . . . . . . . . 23
6.6. Jitter in RTCP Reports . . . . . . . . . . . . . . . . . . 24 6.6. Jitter in RTCP Reports . . . . . . . . . . . . . . . . . . 24
6.7. MAPDV2 . . . . . . . . . . . . . . . . . . . . . . . . . . 24 6.7. MAPDV2 . . . . . . . . . . . . . . . . . . . . . . . . . . 24
6.8. Load Balancing . . . . . . . . . . . . . . . . . . . . . . 25 6.8. Load Balancing . . . . . . . . . . . . . . . . . . . . . . 25
7. Applicability of the Delay Variation Forms and 7. Applicability of the Delay Variation Forms and
Recommendations . . . . . . . . . . . . . . . . . . . . . . . 26 Recommendations . . . . . . . . . . . . . . . . . . . . . . . 26
7.1. Uses . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 7.1. Uses . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
7.1.1. Inferring Queue Occupancy . . . . . . . . . . . . . . 26 7.1.1. Inferring Queue Occupancy . . . . . . . . . . . . . . 26
7.1.2. Determining De-jitter Buffer Size . . . . . . . . . . 26 7.1.2. Determining De-jitter Buffer Size (and FEC Design) . . 26
7.1.3. Spatial Composition . . . . . . . . . . . . . . . . . 27 7.1.3. Spatial Composition . . . . . . . . . . . . . . . . . 27
7.1.4. Service Level Specification: Reporting a Single 7.1.4. Service Level Specification: Reporting a Single
Number . . . . . . . . . . . . . . . . . . . . . . . . 27 Number . . . . . . . . . . . . . . . . . . . . . . . . 27
7.2. Challenging Circumstances . . . . . . . . . . . . . . . . 27 7.2. Challenging Circumstances . . . . . . . . . . . . . . . . 27
7.2.1. Clock and Storage Issues . . . . . . . . . . . . . . . 27 7.2.1. Clock and Storage Issues . . . . . . . . . . . . . . . 27
7.2.2. Frequent Path Changes . . . . . . . . . . . . . . . . 27 7.2.2. Frequent Path Changes . . . . . . . . . . . . . . . . 28
7.2.3. Frequent Loss . . . . . . . . . . . . . . . . . . . . 28 7.2.3. Frequent Loss . . . . . . . . . . . . . . . . . . . . 28
7.2.4. Load Balancing . . . . . . . . . . . . . . . . . . . . 28 7.2.4. Load Balancing . . . . . . . . . . . . . . . . . . . . 28
7.3. Summary . . . . . . . . . . . . . . . . . . . . . . . . . 28 7.3. Summary . . . . . . . . . . . . . . . . . . . . . . . . . 28
8. Measurement Considerations . . . . . . . . . . . . . . . . . . 29 8. Measurement Considerations . . . . . . . . . . . . . . . . . . 29
8.1. Measurement Stream Characteristics . . . . . . . . . . . . 29 8.1. Measurement Stream Characteristics . . . . . . . . . . . . 30
8.2. Measurement Devices . . . . . . . . . . . . . . . . . . . 31 8.2. Measurement Devices . . . . . . . . . . . . . . . . . . . 31
8.3. Units of Measurement . . . . . . . . . . . . . . . . . . . 31 8.3. Units of Measurement . . . . . . . . . . . . . . . . . . . 31
8.4. Test Duration . . . . . . . . . . . . . . . . . . . . . . 31 8.4. Test Duration . . . . . . . . . . . . . . . . . . . . . . 32
8.5. Clock Sync Options . . . . . . . . . . . . . . . . . . . . 32 8.5. Clock Sync Options . . . . . . . . . . . . . . . . . . . . 32
8.6. Distinguishing Long Delay from Loss . . . . . . . . . . . 32 8.6. Distinguishing Long Delay from Loss . . . . . . . . . . . 32
8.7. Accounting for Packet Reordering . . . . . . . . . . . . . 32 8.7. Accounting for Packet Reordering . . . . . . . . . . . . . 33
8.8. Results Representation and Reporting . . . . . . . . . . . 33 8.8. Results Representation and Reporting . . . . . . . . . . . 33
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 33 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 34
10. Security Considerations . . . . . . . . . . . . . . . . . . . 33 10. Security Considerations . . . . . . . . . . . . . . . . . . . 34
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 33 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 34
12. Appendix on Reducing Delay Variation in Networks . . . . . . . 34 12. Appendix on Calculating the D(min) in PDV . . . . . . . . . . 34
13. Appendix on Calculating the D(min) in PDV . . . . . . . . . . 34 13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 35
14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 35 13.1. Normative References . . . . . . . . . . . . . . . . . . . 35
14.1. Normative References . . . . . . . . . . . . . . . . . . . 35 13.2. Informative References . . . . . . . . . . . . . . . . . . 36
14.2. Informative References . . . . . . . . . . . . . . . . . . 36
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 37 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 37
Intellectual Property and Copyright Statements . . . . . . . . . . 39 Intellectual Property and Copyright Statements . . . . . . . . . . 39
1. Introduction 1. Introduction
There are many ways to formulate packet delay variation metrics for There are many ways to formulate packet delay variation metrics for
the Internet and other packet-based networks. The IETF itself has the Internet and other packet-based networks. The IETF itself has
several specifications for delay variation [RFC3393], sometimes several specifications for delay variation [RFC3393], sometimes
called jitter [RFC3550] or even inter-arrival jitter [RFC3550], and called jitter [RFC3550] or even inter-arrival jitter [RFC3550], and
these have achieved wide adoption. The International these have achieved wide adoption. The International
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1.2. Organization of the Memo 1.2. Organization of the Memo
The Purpose and Scope follows in Section 2. We then give a summary The Purpose and Scope follows in Section 2. We then give a summary
of the main tasks for delay variation metrics in section 3. Section of the main tasks for delay variation metrics in section 3. Section
4 defines the two primary forms of delay variation, and section 5 4 defines the two primary forms of delay variation, and section 5
presents summaries of four earlier comparisons. Section 6 adds new presents summaries of four earlier comparisons. Section 6 adds new
comparisons to the analysis, and section 7 reviews the applicability comparisons to the analysis, and section 7 reviews the applicability
and recommendations for each form of delay variation. Section 8 then and recommendations for each form of delay variation. Section 8 then
looks at many important delay variation measurement considerations. looks at many important delay variation measurement considerations.
Following the IANA and Security Considerations, there are two Following the IANA and Security Considerations, there is an Appendix
Appendices. One presents guidance on reducing delay variation in on the calculation of the minimum delay for the PDV form.
networks, and the other calculation of the minimum delay for the PDV
form.
2. Purpose and Scope 2. Purpose and Scope
The IPDV and PDV formulations have certain features that make them The IPDV and PDV formulations have certain features that make them
more suitable for one circumstance and less so for another. The more suitable for one circumstance and less so for another. The
purpose of this memo is to compare two forms of delay variation, so purpose of this memo is to compare two forms of delay variation, so
that it will be evident which of the two is better suited for each of that it will be evident which of the two is better suited for each of
many possible uses and their related circumstances. many possible uses and their related circumstances.
The scope of this memo is limited to the two forms of delay variation The scope of this memo is limited to the two forms of delay variation
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queues. Some types of the delay sources along the path are constant, queues. Some types of the delay sources along the path are constant,
such as links between two locations. But the latency encountered in such as links between two locations. But the latency encountered in
each queue varies, depending on the number of packets in the queue each queue varies, depending on the number of packets in the queue
when a particular packet arrives. If one assumes that at least one when a particular packet arrives. If one assumes that at least one
of the packets in a test stream encounters virtually empty queues all of the packets in a test stream encounters virtually empty queues all
along the path (and the path is stable), then the additional delay along the path (and the path is stable), then the additional delay
observed on other packets can be attributed to the time spent in one observed on other packets can be attributed to the time spent in one
or more queues. Otherwise, the delay variation observed is the or more queues. Otherwise, the delay variation observed is the
variation in queue time experienced by the test stream. variation in queue time experienced by the test stream.
It is worth noting that delay variation can occur beyond IP router
queues, in other communication components. Examples include media
contention: DOCSIS, IEEE 802.11 and some mobile radio technologies.
However, delay variation from all sources at the IP layer and below
will be quantified using the two formulations discussed here.
3.2. Determining De-jitter Buffer Size 3.2. Determining De-jitter Buffer Size
Note - while this memo and other IPPM literature prefer the term Note - while this memo and other IPPM literature prefer the term
delay variation, the terms "jitter buffer" and the more accurate "de- delay variation, the terms "jitter buffer" and the more accurate "de-
jitter buffer" are widely adopted names for a component of packet jitter buffer" are widely adopted names for a component of packet
communication systems, and they will be used here to designate that communication systems, and they will be used here to designate that
system component. system component.
Most Isochronous applications (a.k.a. real-time applications) employ Most Isochronous applications (a.k.a. real-time applications) employ
a buffer to smooth out delay variation encountered on the path from a buffer to smooth out delay variation encountered on the path from
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customers. The measurement results must compare favorably with the customers. The measurement results must compare favorably with the
performance levels specified in the agreement. performance levels specified in the agreement.
Packet delay variation is usually one of the metrics specified in Packet delay variation is usually one of the metrics specified in
these agreements. In principle, any formulation could be specified these agreements. In principle, any formulation could be specified
in the Service Level Agreement (SLA). However, the SLA is most in the Service Level Agreement (SLA). However, the SLA is most
useful when the measured quantities can be related to ways in which useful when the measured quantities can be related to ways in which
the communication service will be utilized by the customer, and this the communication service will be utilized by the customer, and this
can usually be derived from one of the tasks described above. can usually be derived from one of the tasks described above.
3.5. <your favorite here> 3.5. Application-Layer FEC Design
Note: At the IETF-68 IPPM session, Alan Clark suggested another The design of application-layer Forward Error Correction (FEC)
possible task for DV measurements, that of detecting and somehow components is closely related to the design of a de-jitter buffer in
removing the delay variation associated with a smoothing buffer used several ways. The FEC designer must choose a protection interval
with a video codec. Further work is needed to define the problem and (time to send/receive a block of packets in a constant packet rate
to investigate the applicability of IPDV and PDV. system) consistent with the packet loss characteristics, but also
mindful of the extent of delay variation expected. Further, the
system designer must decide how long to wait for "late" packets to
arrive. Again, the range of delay variation is the relevant
expression delay variation for these tasks.
4. Formulations of IPDV and PDV 4. Formulations of IPDV and PDV
This section presents the formulations of IPDV and PDV, and provides This section presents the formulations of IPDV and PDV, and provides
some illustrative examples. We use the basic singleton definition in some illustrative examples. We use the basic singleton definition in
[RFC3393] (which itself is based on [RFC2679]): [RFC3393] (which itself is based on [RFC2679]):
"Type-P-One-way-ipdv is defined for two packets from Src to Dst "Type-P-One-way-ipdv is defined for two packets from Src to Dst
selected by the selection function F, as the difference between the selected by the selection function F, as the difference between the
value of the Type-P-One-way-delay from Src to Dst at T2 and the value value of the Type-P-One-way-delay from Src to Dst at T2 and the value
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change could be kept separated, presenting two different change could be kept separated, presenting two different
distributions. This avoids the difficult task of determining the distributions. This avoids the difficult task of determining the
different modes of a multi-modal distribution. different modes of a multi-modal distribution.
6.2.2. Path Change with Loss 6.2.2. Path Change with Loss
If the path change is accompanied by loss, such that the are no If the path change is accompanied by loss, such that the are no
consecutive packet pairs that span the change, then no IPDV consecutive packet pairs that span the change, then no IPDV
singletons will reflect the change. This may or may not be singletons will reflect the change. This may or may not be
desirable, depending on the ultimate use of the delay variation desirable, depending on the ultimate use of the delay variation
measurement. The Figure 6, in which L means Lost and U means measurement. Figure 6, in which L means Lost and U means undefined,
undefined, illustrates this case. illustrates this case.
Packet # 1 2 3 4 5 6 7 8 9 Packet # 1 2 3 4 5 6 7 8 9
Lost L L Lost L L
------------------------------------ ------------------------------------
Delay, ms 3 4 3 3 U U 8 9 8 Delay, ms 3 4 3 3 U U 8 9 8
IPDV U 1 -1 0 U U U 1 -1 IPDV U 1 -1 0 U U U 1 -1
PDV 0 1 0 0 U U 5 6 5 PDV 0 1 0 0 U U 5 6 5
Figure 6: Path Change with Loss Figure 6: Path Change with Loss
PDV will again produce a bimodal distribution. But here, the PDV will again produce a bimodal distribution. But here, the
decision process to define sub-intervals associated with each path is decision process to define sub-intervals associated with each path is
further assisted by the presence of loss, in addition to TTL, further assisted by the presence of loss, in addition to TTL,
reordering information, and use of short measurement intervals reordering information, and use of short measurement intervals
consistent with the duration of user sessions. It is reasonable to consistent with the duration of user sessions. It is reasonable to
assume that at least loss and delay will be measured simultaneously assume that at least loss and delay will be measured simultaneously
with PDV and/or IPDV. with PDV and/or IPDV.
IPDV does not help to detect path changes when accompanied by loss,
and this is a disadvantage for those who rely solely on IPDV
measurements.
6.3. Clock Stability and Error 6.3. Clock Stability and Error
Low cost or low complexity measurement systems may be embedded in Low cost or low complexity measurement systems may be embedded in
communication devices that do not have access to high stability communication devices that do not have access to high stability
clocks, and time errors will almost certainly be present. However, clocks, and time errors will almost certainly be present. However,
larger time-related errors (~1ms) may offer an acceptable trade-off larger time-related errors (~1ms) may offer an acceptable trade-off
for monitoring performance over a large population (the accuracy for monitoring performance over a large population (the accuracy
needed to detect problems may be much less than required for a needed to detect problems may be much less than required for a
scientific study, ~0.01ms for example). scientific study, ~0.01ms for example).
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0.05ms. 0.05ms.
o If PDV measurements are made on the same packets over a 60 second o If PDV measurements are made on the same packets over a 60 second
measurement interval, then the delay variation due to the max measurement interval, then the delay variation due to the max
free-running clock error will be 60 x 5 x 10-5 seconds, or 3ms free-running clock error will be 60 x 5 x 10-5 seconds, or 3ms
delay variation error from the first packet to the last. delay variation error from the first packet to the last.
Therefore, the additional accuracy required for equivalent PDV error Therefore, the additional accuracy required for equivalent PDV error
under these conditions is a factor of 60 more than for IPDV. This is under these conditions is a factor of 60 more than for IPDV. This is
a rather extreme scenario, because time-of-day error of 1 second a rather extreme scenario, because time-of-day error of 1 second
would accumulate in ~5.5 hours, potentially causing the measurment would accumulate in ~5.5 hours, potentially causing the measurement
interval alignment issue described above. interval alignment issue described above.
If skew is present in a sample of one-way-delays, its symptom is If skew is present in a sample of one-way-delays, its symptom is
typically a nearly linear growth or decline over all the one-way- typically a nearly linear growth or decline over all the one-way-
delay values. As a practical matter, if the same slope appears delay values. As a practical matter, if the same slope appears
consistently in the measurements, then it may be possible to fit the consistently in the measurements, then it may be possible to fit the
slope and compensate for the skew in the one-way-delay measurements, slope and compensate for the skew in the one-way-delay measurements,
thereby avoiding the issue in the PDV calculations that follow. See thereby avoiding the issue in the PDV calculations that follow. See
[RFC3393] for additional information on compensating for skew. [RFC3393] for additional information on compensating for skew.
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6.4. Spatial Composition 6.4. Spatial Composition
ITU-T Recommendation [Y.1541] gives a provisional method to compose a ITU-T Recommendation [Y.1541] gives a provisional method to compose a
PDV metric using PDV measurement results from two or more sub-paths. PDV metric using PDV measurement results from two or more sub-paths.
Additional methods are considered in Additional methods are considered in
[I-D.ietf-ippm-spatial-composition]. [I-D.ietf-ippm-spatial-composition].
PDV has a clear advantage at this time, since there is no validated PDV has a clear advantage at this time, since there is no validated
method to compose an IPDV metric. In addition, IPDV results depend method to compose an IPDV metric. In addition, IPDV results depend
greatly on the exact sequence of packets and may not lend themselves greatly on the exact sequence of packets and may not lend themselves
easily to the composition problem. easily to the composition problem, where segments must be assumed to
have independent delay distributions.
6.5. Reporting a Single Number (SLA) 6.5. Reporting a Single Number (SLA)
Despite the risk of over-summarization, measurements must often be Despite the risk of over-summarization, measurements must often be
displayed for easy consumption. If the right summary report is displayed for easy consumption. If the right summary report is
prepared, then the "dashboard" view correctly indicates whether there prepared, then the "dashboard" view correctly indicates whether there
is something different and worth investigating further, or that the is something different and worth investigating further, or that the
status has not changed. The dashboard model restricts every status has not changed. The dashboard model restricts every
instrument display to a single number. The packet network dashboard instrument display to a single number. The packet network dashboard
could have different instruments for loss, delay, delay variation, could have different instruments for loss, delay, delay variation,
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was avoided for several reasons, including stability of the maximum was avoided for several reasons, including stability of the maximum
delay. The 99.9%-ile of PDV is helpful to performance planners delay. The 99.9%-ile of PDV is helpful to performance planners
(seeking to meet some user-to-user objective for delay) and in design (seeking to meet some user-to-user objective for delay) and in design
of de-jitter buffer sizes, even those with adaptive capabilities. of de-jitter buffer sizes, even those with adaptive capabilities.
IPDV does not lend itself to summarization so easily. The mean IPDV IPDV does not lend itself to summarization so easily. The mean IPDV
is typically zero. As the IPDV distribution will have two tails is typically zero. As the IPDV distribution will have two tails
(positive and negative) the range or pseudo-range would not match the (positive and negative) the range or pseudo-range would not match the
needed de-jitter buffer size. Additional complexity may be needed de-jitter buffer size. Additional complexity may be
introduced when the variation exceeds the inter-packet sending introduced when the variation exceeds the inter-packet sending
interval, as discussed above. Should the Inter-Quartile Range be interval, as discussed above (in sections 5.2 and 6.2.1). Should the
used? Should the singletons beyond some threshold be counted (e.g., Inter-Quartile Range be used? Should the singletons beyond some
mean +/- 50ms)? A strong rationale for one of these summary threshold be counted (e.g., mean +/- 50ms)? A strong rationale for
statistics has yet to emerge. one of these summary statistics has yet to emerge.
When summarizing IPDV, some prefer the simplicity of the single-sided When summarizing IPDV, some prefer the simplicity of the single-sided
distribution created by taking the absolute value of each singleton distribution created by taking the absolute value of each singleton
result, abs(D(i)-D(i-1)). This approach sacrifices the two-sided result, abs(D(i)-D(i-1)). This approach sacrifices the two-sided
inter-arrival spread information in the distribution. It also makes inter-arrival spread information in the distribution. It also makes
the evaluation using percentiles more confusing, because a single the evaluation using percentiles more confusing, because a single
late packet that exceeds the variation threshold will cause two late packet that exceeds the variation threshold will cause two pairs
singleton measurement pairs to fail the criteria (one positive, the of singletons to fail the criteria (one positive, the other negative
other negative converted to positive). The single-sided PDV converted to positive). The single-sided PDV distribution is an
distribution is an advantage in this category. advantage in this category.
6.6. Jitter in RTCP Reports 6.6. Jitter in RTCP Reports
[RFC3550] gives the calculation of the inter-arrival Jitter field for [RFC3550] gives the calculation of the inter-arrival Jitter field for
the RTCP report, with a sample implementation in an Appendix. the RTCP report, with a sample implementation in an Appendix.
The RTCP Jitter value can be calculated using IPDV singletons. If The RTCP Jitter value can be calculated using IPDV singletons. If
there is packet reordering, as defined in [RFC4737], then estimates there is packet reordering, as defined in [RFC4737], then estimates
of Jitter based on IPDV may vary slightly, because [RFC3550] of Jitter based on IPDV may vary slightly, because [RFC3550]
specifies the use of receive packet order. specifies the use of receive packet order.
skipping to change at page 26, line 30 skipping to change at page 26, line 34
stream. If the minimum delay is not the true minimum, then the PDV stream. If the minimum delay is not the true minimum, then the PDV
distribution captures the variation in queuing time and some distribution captures the variation in queuing time and some
additional amount of queuing time is experienced, but unknown. One additional amount of queuing time is experienced, but unknown. One
can summarize the PDV distribution with the mean, median, and other can summarize the PDV distribution with the mean, median, and other
statistics. statistics.
IPDV can capture the difference in queuing time from one packet to IPDV can capture the difference in queuing time from one packet to
the next, but this is a different distribution from the queue the next, but this is a different distribution from the queue
occupancy revealed by PDV. occupancy revealed by PDV.
7.1.2. Determining De-jitter Buffer Size 7.1.2. Determining De-jitter Buffer Size (and FEC Design)
This task is complimentary to the problem of inferring queue This task is complimentary to the problem of inferring queue
occupancy through measurement. Again, use of the sample minimum as occupancy through measurement. Again, use of the sample minimum as
the reference delay for PDV yields a distribution that is very the reference delay for PDV yields a distribution that is very
relevant to de-jitter buffer size. This is because the minimum delay relevant to de-jitter buffer size. This is because the minimum delay
is an alignment point for the smoothing operation of de-jitter is an alignment point for the smoothing operation of de-jitter
buffers. A de-jitter buffer that is ideally aligned with the delay buffers. A de-jitter buffer that is ideally aligned with the delay
variation adds zero buffer time to packets with the longest variation adds zero buffer time to packets with the longest
accommodated network delay (any packets with longer delays are accommodated network delay (any packets with longer delays are
discarded). Thus, a packet experiencing minimum network delay should discarded). Thus, a packet experiencing minimum network delay should
be aligned to wait the maximum length of the de-jitter buffer. With be aligned to wait the maximum length of the de-jitter buffer. With
this alignment, the stream is smoothed with no unnecessary delay this alignment, the stream is smoothed with no unnecessary delay
added. [G.1020] illustrates the ideal relationship between network added. [G.1020] illustrates the ideal relationship between network
delay variation and buffer time. delay variation and buffer time.
The PDV distribution is also useful for this task, but different The PDV distribution is also useful for this task, but different
statistics are preferred. The range (max-min) or the 99.9%-ile of statistics are preferred. The range (max-min) or the 99.9%-ile of
PDV (pseudo-range) are closely related to the buffer size needed to PDV (pseudo-range) are closely related to the buffer size needed to
accommodate the observed network delay variation. accommodate the observed network delay variation.
The PDV distribution directly addresses the FEC waiting time
question. When the PDV distribution has a 99th percentile of 10ms,
then waiting 10ms longer than the FEC protection interval will allow
99% of late packets to arrive and be used in the FEC block.
In some cases, the positive excursions (or series of positive In some cases, the positive excursions (or series of positive
excursions) of IPDV may help to approximate the de-jitter buffer excursions) of IPDV may help to approximate the de-jitter buffer
size, but there is no guarantee that a good buffer estimate will size, but there is no guarantee that a good buffer estimate will
emerge, especially when the delay varies as a positive trend over emerge, especially when the delay varies as a positive trend over
several test packets. several test packets.
7.1.3. Spatial Composition 7.1.3. Spatial Composition
PDV has a clear advantage at this time, since there is no validated PDV has a clear advantage at this time, since there is no validated
method to compose an IPDV metric. method to compose an IPDV metric.
skipping to change at page 28, line 33 skipping to change at page 29, line 4
7.2.4. Load Balancing 7.2.4. Load Balancing
PDV distributions offer the most straightforward way to identify that PDV distributions offer the most straightforward way to identify that
a sample of packets have traversed multiple paths. The tasks of de- a sample of packets have traversed multiple paths. The tasks of de-
jitter buffer sizing or assessing queue occupation with PDV should be jitter buffer sizing or assessing queue occupation with PDV should be
use a sample with a single flow because flows will experience only use a sample with a single flow because flows will experience only
one mode on a stable path, and it simplifies the analysis. one mode on a stable path, and it simplifies the analysis.
7.3. Summary 7.3. Summary
+---------------+----------------------+----------------------------+
+---------------+-----------------------+---------------------------+
| Comparison | PDV | IPDV | | Comparison | PDV | IPDV |
| Area | | | | Area | | |
+---------------+-----------------------+---------------------------+ +---------------+----------------------+----------------------------+
| Challenging | Less sensitive to | Preferred when path | | Challenging | Less sensitive to | Preferred when path |
| Circumstances | packet loss, and | changes are frequent or | | Circumstances | packet loss, and | changes are frequent or |
| | simplifies analysis | when measurement clocks | | | simplifies analysis | when measurement clocks |
| | when Load balancing | exhibit some skew | | | when load balancing | exhibit some skew |
| | or multiple paths are | | | | or multiple paths | |
| | present | | | | are present | |
| Spatial | All validated methods | Has sensitivity to | | Spatial | All validated | Has sensitivity to |
| Composition | use this form | sequence and spacing | | Composition | methods use this | sequence and spacing |
| of DV metric | | changes, which tend to | | of DV metric | form | changes, which tends to |
| | | break the segment IID | | | | break the requirement for |
| | | requirement | | | | independent distributions |
| | | between path segments |
| Determine | "Pseudo-range" | No reliable relationship, | | Determine | "Pseudo-range" | No reliable relationship, |
| De-Jitter | reveals this property | but some heuristics | | De-Jitter | reveals this | but some heuristics |
| Buffer Size | by anchoring the | | | Buffer Size | property by | |
| Required | distribution at the | | | Required | anchoring the | |
| | distribution at the | |
| | minimum delay | | | | minimum delay | |
| Estimate of | Distribution has | No reliable relationship | | Estimate of | Distribution has | No reliable relationship |
| Queuing Time | one-to-one | | | Queuing Time | one-to-one | |
| and Variation | relationship on a | | | and Variation | relationship on a | |
| | stable path, | | | | stable path, | |
| | especially when | | | | especially when | |
| | sample min = true min | | | | sample min = true | |
| Specification | One constraint needed | Distribution is | | | min | |
| Simplicity: | for single-sided | two-sided, usually has | | Specification | One constraint | Distribution is two-sided, |
| Single Number | distribution, and | zero mean, and no | | Simplicity: | needed for | usually has zero mean, and |
| SLS | easily related to | universal summary | | Single Number | single-sided | no universal summary |
| | quantities above | statistic that relates to | | SLS | distribution, and | statistic that relates to |
| | | a physical quantity | | | easily related to | a physical quantity |
+---------------+-----------------------+---------------------------+ | | quantities above | |
+---------------+----------------------+----------------------------+
Summary of Comparisons Summary of Comparisons
8. Measurement Considerations 8. Measurement Considerations
TO DO: Add info comparing methodological approximations for each This section discusses the practical aspects of delay variation
form, including on-the-fly statistics, memory requirements, measurement, with special attention to the two formulations compared
implications on the reference value (D(min)), quantiles not available in this memo.
as a running measure, (possibly in a new subsection)
8.1. Measurement Stream Characteristics 8.1. Measurement Stream Characteristics
As stated in the background section, there is a strong dependency As stated in the background section, there is a strong dependency
between the active measurement stream characteristics and the between the active measurement stream characteristics and the
results. The IPPM literature includes two primary methods for results. The IPPM literature includes two primary methods for
collecting samples: Poisson sampling described in [RFC2330], and collecting samples: Poisson sampling described in [RFC2330], and
Periodic sampling in[RFC3432]. The Poisson method was intended to Periodic sampling in[RFC3432]. The Poisson method was intended to
collect an unbiased sample of performance, while the Periodic method collect an unbiased sample of performance, while the Periodic method
addresses a "known bias of interest". Periodic streams are required addresses a "known bias of interest". Periodic streams are required
skipping to change at page 31, line 8 skipping to change at page 31, line 25
times, avoid synchronization with periodic events that are present in times, avoid synchronization with periodic events that are present in
networks, and avoid inducing synchronization with congestion-aware networks, and avoid inducing synchronization with congestion-aware
senders. When a Poisson stream is used with IPDV, the distribution senders. When a Poisson stream is used with IPDV, the distribution
will reflect inter-packet delay variation on many different time will reflect inter-packet delay variation on many different time
scales (or packet spacings). The unbiased Poisson sampling brings a scales (or packet spacings). The unbiased Poisson sampling brings a
new layer of complexity in the analysis of IPDV distributions. new layer of complexity in the analysis of IPDV distributions.
8.2. Measurement Devices 8.2. Measurement Devices
One key aspect of measurement devices is their ability to store One key aspect of measurement devices is their ability to store
singleton measurements. This feature usually is closely related to singletons (or individual measurements). This feature usually is
local calculation capabilities. For example, an embedded measurement closely related to local calculation capabilities. For example, an
device with limited storage will like provide only a few statistics embedded measurement device with limited storage will like provide
on the delay variation distribution, while dedicated measurement only a few statistics on the delay variation distribution, while
systems store all the singletons and allow detailed analysis (later dedicated measurement systems store all the singletons and allow
calculation of either form of delay variation is possible with the detailed analysis (later calculation of either form of delay
original singletons). variation is possible with the original singletons).
Therefore, systems with limited storage must choose their metrics and Therefore, systems with limited storage must choose their metrics and
summary statistics in advance. If both IPDV and PDV statistics are summary statistics in advance. If both IPDV and PDV statistics are
desired, the supporting information must be collected as packets desired, the supporting information must be collected as packets
arrive. For example, the PDV range and high percentiles can be arrive. For example, the PDV range and high percentiles can be
determined later if the minimum and several of the largest delays are determined later if the minimum and several of the largest delays are
stored while the measurement is in-progress. stored while the measurement is in-progress.
8.3. Units of Measurement 8.3. Units of Measurement
skipping to change at page 32, line 22 skipping to change at page 32, line 40
1. Global Positioning System receivers 1. Global Positioning System receivers
2. In some parts of the world, Cellular Code Division Multiple 2. In some parts of the world, Cellular Code Division Multiple
Access (CDMA) systems distribute timing signals that are derived Access (CDMA) systems distribute timing signals that are derived
from GPS and traceable to UTC. from GPS and traceable to UTC.
3. Network Time Protocol [RFC1305] is a convenient choice in many 3. Network Time Protocol [RFC1305] is a convenient choice in many
cases, but usually offers lower accuracy than the options above. cases, but usually offers lower accuracy than the options above.
When clock synchronization is inconvenient or subject to appreciable
errors, then round-trip measurements may give a cumulative indication
of the delay variation present on both directions of the path.
However, delay distributions are rarely symmetrical, so it is
difficult to infer much about the one-way delay variation from round-
trip measurements. Also, measurements on asymmetrical paths add
complications for the one-way delay metric.
8.6. Distinguishing Long Delay from Loss 8.6. Distinguishing Long Delay from Loss
Lost and delayed packets are separated by a waiting time threshold. Lost and delayed packets are separated by a waiting time threshold.
Packets that arrive at the measurement destination within their Packets that arrive at the measurement destination within their
waiting time have finite delay and are not lost. Otherwise, packets waiting time have finite delay and are not lost. Otherwise, packets
are designated lost and their delay is undefined. Guidance on are designated lost and their delay is undefined. Guidance on
setting the waiting time threshold may be found in [RFC2680] and setting the waiting time threshold may be found in [RFC2680] and
[I-D.morton-ippm-reporting-metrics]. [I-D.morton-ippm-reporting-metrics].
In essence, [I-D.morton-ippm-reporting-metrics] suggests to use a In essence, [I-D.morton-ippm-reporting-metrics] suggests to use a
skipping to change at page 33, line 8 skipping to change at page 33, line 30
variation. variation.
IPDV results will change if reordering is present because they are IPDV results will change if reordering is present because they are
sensitive to the sequence of delays of arriving packets. The main sensitive to the sequence of delays of arriving packets. The main
example of this sensitivity is in the truncation of the negative tail example of this sensitivity is in the truncation of the negative tail
of the distribution. of the distribution.
o When there is no reordering, the negative tail is limited by the o When there is no reordering, the negative tail is limited by the
sending time spacing between packets. sending time spacing between packets.
o If reordering occurs, the negative tail can take on any value (in o If reordering occurs (and the reordered packets are not
discarded), the negative tail can take on any value (in
principal). principal).
In general, measurement systems should have the capability to detect In general, measurement systems should have the capability to detect
when sequence has changed. If IPDV measurements are made without when sequence has changed. If IPDV measurements are made without
regard to packet arrival order, the IPDV will be under-reported when regard to packet arrival order, the IPDV will be under-reported when
reordering occurs. reordering occurs.
8.8. Results Representation and Reporting 8.8. Results Representation and Reporting
All of the references that discuss or define delay variation suggest All of the references that discuss or define delay variation suggest
skipping to change at page 33, line 45 skipping to change at page 34, line 22
10. Security Considerations 10. Security Considerations
The security considerations that apply to any active measurement of The security considerations that apply to any active measurement of
live networks are relevant here as well. See [RFC4656] live networks are relevant here as well. See [RFC4656]
11. Acknowledgements 11. Acknowledgements
The authors would like to thank Phil Chimento for his suggestion to The authors would like to thank Phil Chimento for his suggestion to
employ the convention of conditional distributions for Delay to deal employ the convention of conditional distributions for Delay to deal
with packet loss, and his encouragement to "write the memo" after with packet loss, and his encouragement to "write the memo" after
hearing the talk on this topic at IETF-65. We also acknowledge hearing "the talk" on this topic at IETF-65. We also acknowledge
constructive comments from Alan Clark, Loki Jorgenson, Carsten constructive comments from Alan Clark, Loki Jorgenson, Carsten
Schmoll, and Robert Holley. Schmoll, and Robert Holley.
12. Appendix on Reducing Delay Variation in Networks 12. Appendix on Calculating the D(min) in PDV
>>> The Authors plan to Delete this section, unless someone raises a
strong rationale to keep it.
This text is both preliminary and generic but we want to explain the
basic troubleshooting.
If there is a DV problem, it may be because:
1. there is congestion. Find where the bottleneck is, and increase
the buffer Alternatively, increase the bandwidth Alternatively,
remove some applications from that class of service
2. there is a variability of the traffic Discover that traffic, then
change/apply QoS (for example, rate-limiting)
13. Appendix on Calculating the D(min) in PDV
Practitioners have raised questions several questions that this Practitioners have raised questions several questions that this
section intends to answer: section intends to answer:
- how is this D_min calculated? Is it DV(99%) as mentioned in - how is this D_min calculated? Is it DV(99%) as mentioned in
[Krzanowski]? [Krzanowski]?
- do we need to keep all the values from the interval, then take the - do we need to keep all the values from the interval, then take the
minimum? Or do we keep the minimum from previous intervals? minimum? Or do we keep the minimum from previous intervals?
skipping to change at page 35, line 13 skipping to change at page 35, line 18
soon after collection. soon after collection.
It is not necessary to store all delay values in a sample when It is not necessary to store all delay values in a sample when
storage is a major concern. D_min can be found by comparing each new storage is a major concern. D_min can be found by comparing each new
singleton value with the current value and replacing it when singleton value with the current value and replacing it when
required. In a sample with 5000 packets, evaluation of the 99.9%-ile required. In a sample with 5000 packets, evaluation of the 99.9%-ile
can also be achieved with limited storage. One method calls for can also be achieved with limited storage. One method calls for
storing the top 50 delay singletons and revising the top value list storing the top 50 delay singletons and revising the top value list
each time 50 more packets arrive. each time 50 more packets arrive.
14. References 13. References
14.1. Normative References 13.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2330] Paxson, V., Almes, G., Mahdavi, J., and M. Mathis, [RFC2330] Paxson, V., Almes, G., Mahdavi, J., and M. Mathis,
"Framework for IP Performance Metrics", RFC 2330, "Framework for IP Performance Metrics", RFC 2330,
May 1998. May 1998.
[RFC2679] Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way [RFC2679] Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
Delay Metric for IPPM", RFC 2679, September 1999. Delay Metric for IPPM", RFC 2679, September 1999.
skipping to change at page 35, line 38 skipping to change at page 35, line 43
Packet Loss Metric for IPPM", RFC 2680, September 1999. Packet Loss Metric for IPPM", RFC 2680, September 1999.
[RFC3393] Demichelis, C. and P. Chimento, "IP Packet Delay Variation [RFC3393] Demichelis, C. and P. Chimento, "IP Packet Delay Variation
Metric for IP Performance Metrics (IPPM)", RFC 3393, Metric for IP Performance Metrics (IPPM)", RFC 3393,
November 2002. November 2002.
[RFC3432] Raisanen, V., Grotefeld, G., and A. Morton, "Network [RFC3432] Raisanen, V., Grotefeld, G., and A. Morton, "Network
performance measurement with periodic streams", RFC 3432, performance measurement with periodic streams", RFC 3432,
November 2002. November 2002.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003.
[RFC4090] Pan, P., Swallow, G., and A. Atlas, "Fast Reroute [RFC4090] Pan, P., Swallow, G., and A. Atlas, "Fast Reroute
Extensions to RSVP-TE for LSP Tunnels", RFC 4090, Extensions to RSVP-TE for LSP Tunnels", RFC 4090,
May 2005. May 2005.
[RFC4656] Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M. [RFC4656] Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M.
Zekauskas, "A One-way Active Measurement Protocol Zekauskas, "A One-way Active Measurement Protocol
(OWAMP)", RFC 4656, September 2006. (OWAMP)", RFC 4656, September 2006.
[RFC4737] Morton, A., Ciavattone, L., Ramachandran, G., Shalunov, [RFC4737] Morton, A., Ciavattone, L., Ramachandran, G., Shalunov,
S., and J. Perser, "Packet Reordering Metrics", RFC 4737, S., and J. Perser, "Packet Reordering Metrics", RFC 4737,
November 2006. November 2006.
14.2. Informative References 13.2. Informative References
[COM12.D98] [COM12.D98]
Clark, Alan., "ITU-T Delayed Contribution COM 12 - D98, Clark, Alan., "ITU-T Delayed Contribution COM 12 - D98,
"Analysis, measurement and modelling of Jitter"", "Analysis, measurement and modelling of Jitter"",
January 2003. January 2003.
[Casner] "A Fine-Grained View of High Performance Networking, NANOG [Casner] "A Fine-Grained View of High Performance Networking, NANOG
22 Conf.; http://www.nanog.org/mtg-0105/agenda.html", May 22 Conf.; http://www.nanog.org/mtg-0105/agenda.html", May
20-22 2001. 20-22 2001.
skipping to change at page 36, line 40 skipping to change at page 36, line 43
evaluating multimedia transmission performance over evaluating multimedia transmission performance over
Internet Protocol"", November 2005. Internet Protocol"", November 2005.
[I-D.ietf-ippm-framework-compagg] [I-D.ietf-ippm-framework-compagg]
Morton, A., "Framework for Metric Composition", Morton, A., "Framework for Metric Composition",
draft-ietf-ippm-framework-compagg-06 (work in progress), draft-ietf-ippm-framework-compagg-06 (work in progress),
February 2008. February 2008.
[I-D.ietf-ippm-spatial-composition] [I-D.ietf-ippm-spatial-composition]
Morton, A. and E. Stephan, "Spatial Composition of Morton, A. and E. Stephan, "Spatial Composition of
Metrics", draft-ietf-ippm-spatial-composition-05 (work in Metrics", draft-ietf-ippm-spatial-composition-06 (work in
progress), November 2007. progress), February 2008.
[I-D.morton-ippm-reporting-metrics] [I-D.morton-ippm-reporting-metrics]
Morton, A., Ramachandran, G., and G. Maguluri, "Reporting Morton, A., Ramachandran, G., and G. Maguluri, "Reporting
Metrics: Different Points of View", Metrics: Different Points of View",
draft-morton-ippm-reporting-metrics-04 (work in progress), draft-morton-ippm-reporting-metrics-05 (work in progress),
November 2007. May 2008.
[Krzanowski] [Krzanowski]
Presentation at IPPM, IETF-64, "Jitter Definitions: What Presentation at IPPM, IETF-64, "Jitter Definitions: What
is What?", November 2005. is What?", November 2005.
[Li.Mills] [Li.Mills]
Li, Quong. and David. Mills, ""The Implications of Short- Li, Quong. and David. Mills, ""The Implications of Short-
Range Dependency on Delay Variation Measurement", Second Range Dependency on Delay Variation Measurement", Second
IEEE Symposium on Network Computing and Applications", IEEE Symposium on Network Computing and Applications",
2003. 2003.
skipping to change at page 37, line 22 skipping to change at page 37, line 24
Morton, A., ""A Brief Jitter Metrics Comparison, and not Morton, A., ""A Brief Jitter Metrics Comparison, and not
the last word, by any means...", Slide Presentation at the last word, by any means...", Slide Presentation at
IETF-65, IPPM Session,", March 2006. IETF-65, IPPM Session,", March 2006.
[RFC1305] Mills, D., "Network Time Protocol (Version 3) [RFC1305] Mills, D., "Network Time Protocol (Version 3)
Specification, Implementation", RFC 1305, March 1992. Specification, Implementation", RFC 1305, March 1992.
[RFC3357] Koodli, R. and R. Ravikanth, "One-way Loss Pattern Sample [RFC3357] Koodli, R. and R. Ravikanth, "One-way Loss Pattern Sample
Metrics", RFC 3357, August 2002. Metrics", RFC 3357, August 2002.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003.
[Y.1540] ITU-T Recommendation Y.1540, "Internet protocol data [Y.1540] ITU-T Recommendation Y.1540, "Internet protocol data
communication service - IP packet transfer and communication service - IP packet transfer and
availability performance parameters", December 2002. availability performance parameters", December 2002.
[Y.1541] ITU-T Recommendation Y.1540, "Network Performance [Y.1541] ITU-T Recommendation Y.1540, "Network Performance
Objectives for IP-Based Services", February 2006. Objectives for IP-Based Services", February 2006.
[Zhang.Duff] [Zhang.Duff]
Zhang, Yin., Duffield, Nick., Paxson, Vern., and Scott. Zhang, Yin., Duffield, Nick., Paxson, Vern., and Scott.
Shenker, ""On the Constancy of Internet Path Properties", Shenker, ""On the Constancy of Internet Path Properties",
skipping to change at page 39, line 44 skipping to change at line 1745
attempt made to obtain a general license or permission for the use of attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr. http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at this standard. Please address the information to the IETF at
ietf-ipr@ietf.org. ietf-ipr@ietf.org.
Acknowledgment
Funding for the RFC Editor function is provided by the IETF
Administrative Support Activity (IASA).
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