Delay Variation Applicability Statement

draft-morton-ippm-delay-var-as-02

March 21, 2007

Al Morton

Benoit Claise

“

Page 2

Recap of activity since IETF-67

Benoit Claise read the draft (through the early comparison section) and shared comments with Al off-list.

Al summarized those comments on list, and produced the -01.txt version (Nov 27, 2006).

Benoit completed his review and summarized all his comments on the list (Dec 1, 2006).

Al and Benoit discussed these comments over the next few months.

-02.txt version March 4, 2007 with Benoit as co-author. much new material and questions for IPPM WG discussion

Page 3

Applicability Problem:“How will the results be used?”

Krzanowski introduced the Delay Variation Problem at IETF-64 “How” Question asked at IETF-65, no suggestions yet RFC 3393 lists two key uses for the Delay Variation Metric Memo Considers these 2 Tasks and 2 Special Circumstances

SRC DST

NetworkCharacterization:Inferring Queue Occupation on a Path

Application Performance Estimation:Sizing of De-Jitter Buffers

What about Spatial

Composition ?

What if circumstance

s are challenging?

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Modified Outline of the Draft

1.  Introduction    1.1.  Background Literature in IPPM and Elsewhere    1.2.  Organization of the Memo

2.  Purpose and Scope

3.  Brief Descriptions of Delay Variation Uses (four) 4.  Formulations of IPDV & PDV

5.  Earlier Comparisons

6.  Additional Properties and Comparisons    6.1.  Packet Loss    6.2.  Path Changes        6.2.1.  Lossless Path Change        6.2.2.  Path Change with Loss    6.3.  Clock Stability and Error    6.4.  Spatial Composition    6.5.  Reporting a Single Number    6.6.  Jitter in RTCP Reports    6.7.  MAPDV2    6.8.  Load Balancing

7.  Applicability of the Delay Variation Forms and Rec    7.1.  Uses            7.2.  Challenging Circumstances        7.2.1.  Clock Issues        7.2.2.  Frequent Path Changes        7.2.3.  Frequent Loss        7.2.4.  Load Balancing

8.  Measurement Considerations for Vendors, Testers, and Users    8.1.  Measurement Stream Characteristics    8.2.  Measurement Units    8.3.  Test Duration    8.4.  Clock Sync Options    8.5.  Distinguishing Long Delay from Loss    8.6.  Accounting for Packet Reordering    8.7.  Results Representation and Reporting…

12.  Appendix on Reducing Delay Variation in Networks

13.  Appendix on Calculating the D(min) in PDV

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Inter-Packet Delay Var. (selection f = previous packet)

Src Dst

T1

R1

T2

R2

T3

R3

T4

R4T5

R5

IPDV(2) = (R2-R1) – (T2-T1)

(5)(2) (4)

IPDV(4) = (R4-R3) – (T4-T3)

(3)

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Packet Delay Variation(selection f = minimum delay pkt in stream)

Src Dst

T1

R1

T2

R2 (minimum)

T3

R3

T4

R4T5

R5

PDV(3) = (R3-T3) – (R2-T2)

(2) (4)

PDV(4) = (R4-T4) – (R2-T2)

(1,3,5)

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Summary of Comparisons

Challenging Circumstances for measurement: IPDV form offers advantages when

Path changes are Frequent Meas. System Clocks exhibit significant Skew

PDV form is less sensitive to Packet LossSpatial Composition of DV metric:

All known methods use PDV, IPDV sensitivity to sequence is an issue

Estimate of Queuing Time & Variation: PDV estimates this, especially when sample min = true min

Determine De-jitter Buffer Size Required PDV “pseudo-range” reveals this property by anchoring the

distribution at the minimum delay

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Examples from IPPM List Discussion (2000)

-20

0

20

40

60

80

100

120

140

160

1 2 3 4 5 6 7 8 9 10 11

Delay IPDV PDV

-40

-20

0

20

40

60

80

100

120

140

160

1 2 3 4 5 6 7 8 9 10 11

Delay IPDV PDV

Ex. A – Smooth TrendIPDV Range = (-10, 10)PDV Range = ( 0, 50 )

Ex. B – Faster Var with lossIPDV Range = (-20, 40)PDV Range = ( 0, 50 )

How can the detailed information IPDV provides be used?(to complete some task)

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What if there is load-balancing in the network?

Load- balancing is based on the IGP metrics, while the delay depends on the path. So, we could have a multi-modal distribution, if we send test packets with different characteristics such as IP addresses/ports.

Should the delay singletons using multiple addresses/ports be combined in the same sample?

The PDV form makes the identification of multiple modes possible.

Should we characterize each mode separately? This question also applies to the Path Change case.

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New Sections

Section 8: Measurement Considerations for Vendors, Testers, and Users This section provides guidance in many areas – Useful? Do we want to recommend measuring BOTH IPDV and

PDV? Do we want to reconstruct the IPDV and DV later on, with a

different interval?Appendix: Guidance for reducing DV in networks

Useful?Appendix: Calculation of the Minimum Delay, D(min)

how is this D(min) calculated? Is it DV(99%) as mentioned by Roman in http://www3.ietf.org/proceedings/05nov/slides/ippm-3.pdf?

do we need to keep all the values from the interval, then take the minimum?

Or do we keep the minimum from previous intervals?

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Summary

IPDV and PDV each have their Strengths and Weaknesses

Suggestions for additional Tasks & CircumstancesNeed Feedback on newly proposed sections and

questions raised in the text of the draft.