draft-ietf-ippm-2330-update-04.txt   draft-ietf-ippm-2330-update-05.txt 
Network Working Group J. Fabini Network Working Group J. Fabini
Internet-Draft Vienna University of Technology Internet-Draft Vienna University of Technology
Updates: 2330 (if approved) A. Morton Updates: 2330 (if approved) A. Morton
Intended status: Informational AT&T Labs Intended status: Informational AT&T Labs
Expires: October 18, 2014 April 16, 2014 Expires: November 29, 2014 May 28, 2014
Advanced Stream and Sampling Framework for IPPM Advanced Stream and Sampling Framework for IPPM
draft-ietf-ippm-2330-update-04 draft-ietf-ippm-2330-update-05
Abstract Abstract
To obtain repeatable results in modern networks, test descriptions To obtain repeatable results in modern networks, test descriptions
need an expanded stream parameter framework that also augments need an expanded stream parameter framework that also augments
aspects specified as Type-P for test packets. This memo updates the aspects specified as Type-P for test packets. This memo updates the
IP Performance Metrics (IPPM) Framework RFC 2330 with advanced IP Performance Metrics (IPPM) Framework RFC 2330 with advanced
considerations for measurement methodology and testing. The existing considerations for measurement methodology and testing. The existing
framework mostly assumes deterministic connectivity, and that a framework mostly assumes deterministic connectivity, and that a
single test stream will represent the characteristics of the path single test stream will represent the characteristics of the path
skipping to change at page 1, line 48 skipping to change at page 1, line 48
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 18, 2014. This Internet-Draft will expire on November 29, 2014.
Copyright Notice Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Definition: Reactive Path Behavior . . . . . . . . . . . 3 1.1. Definition: Reactive Path Behavior . . . . . . . . . . . 4
2. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. New or Revised Stream Parameters . . . . . . . . . . . . . . 5 3. New or Revised Stream Parameters . . . . . . . . . . . . . . 5
3.1. Test Packet Type-P . . . . . . . . . . . . . . . . . . . 6 3.1. Test Packet Type-P . . . . . . . . . . . . . . . . . . . 6
3.1.1. Multiple Test Packet Lengths . . . . . . . . . . . . 6 3.1.1. Multiple Test Packet Lengths . . . . . . . . . . . . 6
3.1.2. Test Packet Payload Content Optimization . . . . . . 7 3.1.2. Test Packet Payload Content Optimization . . . . . . 7
3.2. Packet History . . . . . . . . . . . . . . . . . . . . . 7 3.2. Packet History . . . . . . . . . . . . . . . . . . . . . 8
3.3. Access Technology Change . . . . . . . . . . . . . . . . 8 3.3. Access Technology Change . . . . . . . . . . . . . . . . 8
3.4. Time-Slotted Randomness Cancellation . . . . . . . . . . 8 3.4. Time-Slotted Randomness Cancellation . . . . . . . . . . 8
4. Quality of Metrics and Methodologies . . . . . . . . . . . . 9 4. Quality of Metrics and Methodologies . . . . . . . . . . . . 10
4.1. Repeatability . . . . . . . . . . . . . . . . . . . . . . 10 4.1. Revised Definition of Repeatability . . . . . . . . . . . 10
4.2. Continuity . . . . . . . . . . . . . . . . . . . . . . . 11 4.2. Continuity No Longer an Alternative Repeatability
4.3. Actionable . . . . . . . . . . . . . . . . . . . . . . . 11 Criterion . . . . . . . . . . . . . . . . . . . . . . . . 11
4.4. Conservative . . . . . . . . . . . . . . . . . . . . . . 12 4.3. Metrics Should Be Actionable . . . . . . . . . . . . . . 12
4.5. Spatial and Temporal Composition . . . . . . . . . . . . 12 4.4. It May Not Be Possible To Be Conservative . . . . . . . . 12
4.6. Poisson Sampling . . . . . . . . . . . . . . . . . . . . 13 4.5. Spatial and Temporal Composition Support Unbiased
Sampling . . . . . . . . . . . . . . . . . . . . . . . . 13
4.6. When to Truncate the Poisson Sampling Distribution . . . 13
5. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 13 5. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 13
6. Security Considerations . . . . . . . . . . . . . . . . . . . 13 6. Security Considerations . . . . . . . . . . . . . . . . . . . 14
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
9.1. Normative References . . . . . . . . . . . . . . . . . . 14 9.1. Normative References . . . . . . . . . . . . . . . . . . 14
9.2. Informative References . . . . . . . . . . . . . . . . . 14 9.2. Informative References . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction 1. Introduction
The IETF IP Performance Metrics (IPPM) working group first created a The IETF IP Performance Metrics (IPPM) working group first created a
framework for metric development in [RFC2330]. This framework has framework for metric development in [RFC2330]. This framework has
stood the test of time and enabled development of many fundamental stood the test of time and enabled development of many fundamental
metrics, while only being updated once in a specific area [RFC5835]. metrics, while only being updated once in a specific area [RFC5835].
The IPPM framework [RFC2330] generally relies on several assumptions, The IPPM framework [RFC2330] generally relies on several assumptions,
one of which is not explicitly stated but assumed: lightly loaded one of which is not explicitly stated but assumed: lightly loaded
skipping to change at page 3, line 23 skipping to change at page 3, line 28
driven resource allocation) and links with time-slotted operation. driven resource allocation) and links with time-slotted operation.
Per-flow state can be observed on test packet streams, and such Per-flow state can be observed on test packet streams, and such
treatment will influence network characterization if it is not taken treatment will influence network characterization if it is not taken
into account. Flow history will also affect the performance of into account. Flow history will also affect the performance of
applications and be perceived by their users. applications and be perceived by their users.
Moreover, Sections 4 and 6.2 of [RFC2330] explicitly recommend Moreover, Sections 4 and 6.2 of [RFC2330] explicitly recommend
repeatable measurement metrics and methodologies. Measurements in repeatable measurement metrics and methodologies. Measurements in
today's access networks illustrate that methodological guidelines of today's access networks illustrate that methodological guidelines of
[RFC2330] must be extended to capture the reactive nature of these [RFC2330] must be extended to capture the reactive nature of these
networks. Although the proposed extensions can support methodologies networks. There are proposed extensions to allow methodologies to
to fulfill the continuity requirement stated in section 6.2 of fulfill the continuity requirement stated in section 6.2 of
[RFC2330], there is no guarantee. Practical measurements confirm [RFC2330], but is impossible to guarantee they can do so. Practical
that some link types exhibit distinct responses to repeated measurements confirm that some link types exhibit distinct responses
measurements with identical stimulus, i.e., identical traffic to repeated measurements with identical stimulus, i.e., identical
patterns. If feasible, appropriate fine-tuning of measurement traffic patterns. If feasible, appropriate fine-tuning of
traffic patterns can improve measurement continuity and repeatability measurement traffic patterns can improve measurement continuity and
for these link types as shown in [IBD]. repeatability for these link types as shown in [IBD].
This memo updates the IP Performance Metrics (IPPM) Framework This memo updates the IP Performance Metrics (IPPM) Framework
[RFC2330] with advanced considerations for measurement methodology [RFC2330] with advanced considerations for measurement methodology
and testing. and testing. We note that the scope of IPPM work at the time of
[RFC2330] publication (and more than a decade of work that followed)
was limited to active techniques, or those which generate packet
streams which are dedicated to measurement and do not monitor user
traffic. This memo retains that same scope.
We stress that this update of [RFC2330] does not invalidate or We stress that this update of [RFC2330] does not invalidate or
require changes to the analytic metric definitions prepared in the require changes to the analytic metric definitions prepared in the
IPPM working group to date. Rather, it adds considerations for IPPM working group to date. Rather, it adds considerations for
active measurement methodologies and expands the importance of active measurement methodologies and expands the importance of
existing conventions and notions in [RFC2330], such as "packets of existing conventions and notions in [RFC2330], such as "packets of
Type-P". Type-P".
Among the evolutionary networking changes is a phenomenon we call Among the evolutionary networking changes is a phenomenon we call
"reactive behavior", defined below. "reactive behavior", defined below.
skipping to change at page 5, line 12 skipping to change at page 5, line 21
information in Section 11.1 of [RFC2330] and described in [RFC3432] information in Section 11.1 of [RFC2330] and described in [RFC3432]
for periodic streams. for periodic streams.
The memo also provides new considerations to update the criteria for The memo also provides new considerations to update the criteria for
metrics in section 4 of [RFC2330], the measurement methodology in metrics in section 4 of [RFC2330], the measurement methodology in
section 6.2 of [RFC2330], and other topics related to the quality of section 6.2 of [RFC2330], and other topics related to the quality of
metrics and methods (see section 4). metrics and methods (see section 4).
Other topics in [RFC2330] which might be updated or augmented are Other topics in [RFC2330] which might be updated or augmented are
deferred to future work. This includes the topics of passive and deferred to future work. This includes the topics of passive and
various forms of of hybrid active/passive measurements. various forms of hybrid active/passive measurements.
3. New or Revised Stream Parameters 3. New or Revised Stream Parameters
There are several areas where measurement methodology definition and There are several areas where measurement methodology definition and
test result interpretation will benefit from an increased test result interpretation will benefit from an increased
understanding of the stream characteristics and the (possibly understanding of the stream characteristics and the (possibly
unknown) network condition that influence the measured metrics. unknown) network condition that influence the measured metrics.
1. Network treatment depends on the fullest extent on the "packet of 1. Network treatment depends on the fullest extent on the "packet of
Type-P" definition in [RFC2330], and has for some time. Type-P" definition in [RFC2330], and has for some time.
* State is often maintained on the per-flow basis at various * State is often maintained on the per-flow basis at various
points in the path, where "flows" are determined by IP and points in the path, where "flows" are determined by IP and
other layers. Significant treatment differences occur with other layers. Significant treatment differences occur with
the simplest of Type-P parameters: packet length. Use of the simplest of Type-P parameters: packet length. Use of
multiple lengths is RECOMMENDED. multiple lengths is RECOMMENDED.
* Payload content optimization (compression or format * Payload content optimization (compression or format
conversion) in intermediate segments. This breaks the conversion) in intermediate segments breaks the convention of
convention of payload correspondence when correlating payload correspondence when correlating measurements are made
measurements made at different points in a path. at different points in a path.
2. Packet history (instantaneous or recent test rate or inactivity, 2. Packet history (instantaneous or recent test rate or inactivity,
also for non-test traffic) profoundly influences measured also for non-test traffic) profoundly influences measured
performance, in addition to all the Type-P parameters described performance, in addition to all the Type-P parameters described
in [RFC2330]. in [RFC2330].
3. Access technology may change during testing. A range of transfer 3. Access technology may change during testing. A range of transfer
capacities and access methods may be encountered during a test capacities and access methods may be encountered during a test
session. When different interfaces are used, the host seeking session. When different interfaces are used, the host seeking
access will be aware of the technology change which access will be aware of the technology change which
skipping to change at page 7, line 19 skipping to change at page 7, line 31
3.1.2. Test Packet Payload Content Optimization 3.1.2. Test Packet Payload Content Optimization
The aim for efficient network resource use has resulted in deployment The aim for efficient network resource use has resulted in deployment
of server-only or client-server lossless or lossy payload compression of server-only or client-server lossless or lossy payload compression
techniques on some links or paths. These optimizers attempt to techniques on some links or paths. These optimizers attempt to
compress high-volume traffic in order to reduce network load. Files compress high-volume traffic in order to reduce network load. Files
are analyzed by application-layer parsers, and parts (like comments) are analyzed by application-layer parsers, and parts (like comments)
might be dropped. Although typically acting on HTTP or JPEG files, might be dropped. Although typically acting on HTTP or JPEG files,
compression might affect measurement packets, too. In particular, compression might affect measurement packets, too. In particular,
measurement packets are qualified for efficient compression when they measurement packets are qualified for efficient compression when they
use standard plain-text payload. use standard plain-text payload. We note that use of transport layer
encryption will counteract the deployment of network-based analysis
and may reduce the adoption of payload optimizations, however.
IPPM-conforming measurements should add packet payload content as a IPPM-conforming measurements should add packet payload content as a
Type-P parameter which can help to improve measurement determinism. Type-P parameter which can help to improve measurement determinism.
Some packet payloads are more susceptible to compression than others, Some packet payloads are more susceptible to compression than others,
but optimizers in the measurement path can be out ruled by using but optimizers in the measurement path can be out ruled by using
incompressible packet payload. This payload content could be either incompressible packet payload. This payload content could be
generated by a random device or by using part of a compressed file supplied by a pseudo-random sequence generator or by using part of a
(e.g., a part of a ZIP compressed archive). compressed file (e.g., a part of a ZIP compressed archive).
Optimization can go beyond the scope of one single data- or Optimization can go beyond the scope of one single data- or
measurement stream. Many more client- or network-centric measurement stream. Many more client- or network-centric
optimization technologies have been proposed or standardized so far, optimization technologies have been proposed or standardized so far,
including Robust Header Compression (ROHC) and Voice over IP including Robust Header Compression (ROHC) and Voice over IP
aggregation as presented for instance in [EEAW]. The trend towards aggregation as presented for instance in [EEAW]. Where optimization
optimization being ubiquitous, many more of these technologies will is feasible and valuable, many more of these technologies may follow.
follow. As general observation, the more concurrent flows an As a general observation, the more concurrent flows an intermediate
intermediate host treats and the longer the paths shared by flows host treats and the longer the paths shared by flows are, the higher
are, the higher becomes the incentive of hosts to aggregate flows becomes the incentive of hosts to aggregate flows belonging to
belonging to distinct sources. Measurements should consider this distinct sources. Measurements should consider this potential
potential additional source of uncertainty with respect to additional source of uncertainty with respect to repeatability.
repeatability. Aggregation of flows in networking devices can, for Aggregation of flows in networking devices can, for instance, result
instance, result in reciprocal timing and performance influence of in reciprocal timing and performance influence of these flows which
these flows which may exceed typical reciprocical queueing effects by may exceed typical reciprocal queueing effects by orders of
orders of magnitude. magnitude.
3.2. Packet History 3.2. Packet History
Recent packet history and instantaneous data rate influence Recent packet history and instantaneous data rate influence
measurement results for reactive links supporting on-demand capacity measurement results for reactive links supporting on-demand capacity
allocation. Measurement uncertainty may be reduced by knowledge of allocation. Measurement uncertainty may be reduced by knowledge of
measurement packet history and total host load. Additionally, small measurement packet history and total host load. Additionally, small
changes in history, e.g., because of lost packets along the path, can changes in history, e.g., because of lost packets along the path, can
be the cause of large performance variations. be the cause of large performance variations.
skipping to change at page 10, line 5 skipping to change at page 10, line 19
Depending mainly on the set of controlled measurement parameters, Depending mainly on the set of controlled measurement parameters,
measurements repeated for a specific network path using a specific measurements repeated for a specific network path using a specific
methodology may or may not yield repeatable results. Challenging methodology may or may not yield repeatable results. Challenging
measurement scenarios for adequate parameter control include measurement scenarios for adequate parameter control include
wireless, reactive, or time-slotted networks as discussed earlier in wireless, reactive, or time-slotted networks as discussed earlier in
this document. This section presents an expanded definition of this document. This section presents an expanded definition of
"repeatability" beyond the definition in [RFC2330] and an expanded "repeatability" beyond the definition in [RFC2330] and an expanded
examination of the [RFC2330] concept of "continuity" and its limited examination of the [RFC2330] concept of "continuity" and its limited
applicability. applicability.
4.1. Repeatability 4.1. Revised Definition of Repeatability
[RFC2330] defines repeatability in a general way: [RFC2330] defines repeatability in a general way:
"A methodology for a metric should have the property that it is "A methodology for a metric should have the property that it is
repeatable: if the methodology is used multiple times under identical repeatable: if the methodology is used multiple times under identical
conditions, the same measurements should result in the same conditions, the same measurements should result in the same
measurements." measurements."
The challenge is to develop this definition further, such that it The challenge is to develop this definition further, such that it
becomes an objective measurable criterion (and does not depend on the becomes an objective measurable criterion (and does not depend on the
skipping to change at page 10, line 46 skipping to change at page 11, line 11
Although the [RFC6808] test plan documented numerical criteria for Although the [RFC6808] test plan documented numerical criteria for
equivalence, we cannot specify the exact numerical criteria for equivalence, we cannot specify the exact numerical criteria for
repeatability *in general*. The process in the BCP [RFC6576] and repeatability *in general*. The process in the BCP [RFC6576] and
statistics in [RFC6808] have been used successfully, and the statistics in [RFC6808] have been used successfully, and the
numerical criteria to declare a metric repeatable should be agreed by numerical criteria to declare a metric repeatable should be agreed by
all interested parties prior to measurement. all interested parties prior to measurement.
We revise the definition slightly, as follows: We revise the definition slightly, as follows:
"A methodology for a metric should have the property that it is A methodology for a metric should have the property that it is
repeatable: if the methodology is used multiple times under identical repeatable: if the methodology is used multiple times under
conditions, the methods should produce equivalent measurement identical conditions, the methods should produce equivalent
results." measurement results.
4.2. Continuity 4.2. Continuity No Longer an Alternative Repeatability Criterion
In the original framework [RFC2330], the concept of continuity was In the original framework [RFC2330], the concept of continuity was
introduced to provide a relaxed criteria for judging repeatability, introduced to provide a relaxed criteria for judging repeatability,
and was described in section 6.2 of [RFC2330] as follows: and was described in section 6.2 of [RFC2330] as follows:
"...a methodology for a given metric exhibits continuity if, for "...a methodology for a given metric exhibits continuity if, for
small variations in conditions, it results in small variations in the small variations in conditions, it results in small variations in the
resulting measurements." resulting measurements."
Although there are conditions where metrics may exhibit continuity, Although there are conditions where metrics may exhibit continuity,
skipping to change at page 11, line 33 skipping to change at page 11, line 44
bottom of page 2: bottom of page 2:
"There is also evidence that most TCP implementations exhibit non- "There is also evidence that most TCP implementations exhibit non-
linear performance over some portion of their operating region. It linear performance over some portion of their operating region. It
is possible to construct simple simulation examples where incremental is possible to construct simple simulation examples where incremental
improvements to a path (such as raising the link data rate) results improvements to a path (such as raising the link data rate) results
in lower overall TCP throughput (or BTC) [Mat98]." in lower overall TCP throughput (or BTC) [Mat98]."
Clearly, the time-slotted network elements described in section 3.4 Clearly, the time-slotted network elements described in section 3.4
above also qualifies as a new exception to the ideal of continuity. above also qualifies as a new exception to the ideal of continuity.
Therefore, we deprecate continuity as an alternate criterion on
metrics, and prefer the more exact evaluation of repeatability
instead.
4.3. Actionable Therefore, we deprecate continuity as an alternate criterion on
metrics, and prefer the more exact evaluation of repeatability
instead.
4.3. Metrics Should Be Actionable
The IP Performance Metrics Framework [RFC2330] includes usefulness as The IP Performance Metrics Framework [RFC2330] includes usefulness as
a metric criterion: a metric criterion:
"...The metrics must be useful to users and providers in "...The metrics must be useful to users and providers in
understanding the performance they experience or provide...". understanding the performance they experience or provide...".
When considering measurements as part of a maintenance process, When considering measurements as part of a maintenance process,
evaluation of measurement results for a path under observation can evaluation of measurement results for a path under observation can
draw attention to potential performance problems "somewhere" on the draw attention to potential performance problems "somewhere" on the
path. Anomaly detection is therefore an important phase and first path. Anomaly detection is therefore an important phase and first
step which already satisfies the usefulness criterion for many step which already satisfies the usefulness criterion for many
metrics. metrics.
This concept of usefulness can be extended, becoming a sub-set of This concept of usefulness can be extended, becoming a sub-set of
what we refer to as "actionable" criterion in the following. Central what we refer to as "actionable" criterion in the following. We note
to maintenance is the isolation of the root cause of reported that this is not the term from law.
Central to maintenance is the isolation of the root cause of reported
anomalies down to a specific sub-path, link or host, and metrics anomalies down to a specific sub-path, link or host, and metrics
should support this second step as well. While detection of path should support this second step as well. While detection of path
anomaly may be the result of an on-going monitoring process, the anomaly may be the result of an on-going monitoring process, the
second step of cause isolation consists of specific, directed on- second step of cause isolation consists of specific, directed on-
demand measurements on components and sub-paths. Metrics must demand measurements on components and sub-paths. Metrics must
support users in this directed search, becoming actionable: support users in this directed search, becoming actionable:
Metrics must enable users and operators to understand path Metrics must enable users and operators to understand path
performance and SHOULD help to direct corrective actions when performance and SHOULD help to direct corrective actions when
warranted, based on the measurement results. warranted, based on the measurement results.
Besides characterizing metrics, usefulness and actionable properties Besides characterizing metrics, usefulness and actionable properties
are also applicable to methodologies and measurements. are also applicable to methodologies and measurements.
4.4. Conservative 4.4. It May Not Be Possible To Be Conservative
[RFC2330] adopts the term "conservative" for measurement [RFC2330] adopts the term "conservative" for measurement
methodologies for which: methodologies for which:
"... the act of measurement does not modify, or only slightly "... the act of measurement does not modify, or only slightly
modifies, the value of the performance metric the methodology modifies, the value of the performance metric the methodology
attempts to measure." attempts to measure."
It should be noted that this definition of "conservative" in the It should be noted that this definition of "conservative" in the
sense of [RFC2330] depends to a large extent on the measurement sense of [RFC2330] depends to a large extent on the measurement
path's technology and characteristics. In particular, when deployed path's technology and characteristics. In particular, when deployed
on reactive paths, sub-paths, links or hosts conforming to the on reactive paths, sub-paths, links or hosts conforming to the
definition in Section 1.1 of this document, measurement packets can definition in Section 1.1 of this document, measurement packets can
originate capacity (re)allocations. In addition, small measurement originate capacity (re)allocations. In addition, small measurement
flow variations can result in other users on the same path perceiving flow variations can result in other users on the same path perceiving
significant variations in measurement results. significant variations in measurement results. Therefore:
4.5. Spatial and Temporal Composition It is not always possible for the method to be conservative.
4.5. Spatial and Temporal Composition Support Unbiased Sampling
Concepts related to temporal and spatial composition of metrics in Concepts related to temporal and spatial composition of metrics in
Section 9 of [RFC2330] have been extended in [RFC5835]. [RFC5835] Section 9 of [RFC2330] have been extended in [RFC5835]. [RFC5835]
defines multiple new types of metrics, including Spatial Composition, defines multiple new types of metrics, including Spatial Composition,
Temporal Aggregation, and Spatial Aggregation. So far, only the Temporal Aggregation, and Spatial Aggregation. So far, only the
metrics for Spatial Composition have been standardized [RFC6049], metrics for Spatial Composition have been standardized [RFC6049],
providing the ability to estimate the performance of a complete path providing the ability to estimate the performance of a complete path
from subpath metrics. Spatial Composition aligns with the finding of from subpath metrics. Spatial Composition aligns with the finding of
[TSRC], that unbiased sampling is not possible beyond the first time- [TSRC], that unbiased sampling is not possible beyond the first time-
slotted link within a measurement path. In cases where measurement slotted link within a measurement path.
of subpaths is not feasible, restoring randomness of measurement
samples when necessary is recommended as presented in [TSRC].
4.6. Poisson Sampling In cases where unbiased measurement for all segments of a path is
not feasible due to the presence of a time-slotted link, restoring
randomness of measurement samples when necessary is recommended as
presented in [TSRC], in combination with Spatial Composition
[RFC6049].
4.6. When to Truncate the Poisson Sampling Distribution
Section 11.1.1 of [RFC2330] describes Poisson sampling, where the Section 11.1.1 of [RFC2330] describes Poisson sampling, where the
inter-packet send times have a Poisson distribution. A path element inter-packet send times have a Poisson distribution. A path element
with reactive behavior sensitive to flow inactivity could change with reactive behavior sensitive to flow inactivity could change
state if the random inter-packet time is too long. It is recommended state if the random inter-packet time is too long.
to truncate the tail of Poisson distribution to avoid reactive
element state changes. Truncation has been used without issue to It is recommended to truncate the tail of Poisson distribution
ensure that minimum sample sizes can be attained in a fixed test when needed to avoid reactive element state changes.
interval.
Tail truncation has been used without issue to ensure that minimum
sample sizes can be attained in a fixed test interval.
5. Conclusions 5. Conclusions
Safeguarding repeatability as a key property of measurement Safeguarding repeatability as a key property of measurement
methodologies is highly challenging and sometimes impossible in methodologies is highly challenging and sometimes impossible in
reactive paths. Measurements in paths with demand-driven allocation reactive paths. Measurements in paths with demand-driven allocation
strategies must use a prototypical application packet stream to infer strategies must use a prototypical application packet stream to infer
a specific application's performance. Measurement repetition with a specific application's performance. Measurement repetition with
unbiased network and flow states (e.g., by rebooting measurement unbiased network and flow states (e.g., by rebooting measurement
hosts) can help to avoid interference with periodic network behavior, hosts) can help to avoid interference with periodic network behavior,
randomness being a mandatory feature for avoiding correlation with randomness being a mandatory feature for avoiding correlation with
network timing. Inferring the path performance between one network timing.
measurement session or packet stream and other streams with alternate
Inferring the path performance between one measurement session or
packet stream and other sessions/streams with alternate
characteristics is generally discouraged with reactive paths because characteristics is generally discouraged with reactive paths because
of the huge set of global parameters which have influence on of the huge set of global parameters which have influence on
instantaneous path performance. instantaneous path performance.
6. Security Considerations 6. Security Considerations
The security considerations that apply to any active measurement of The security considerations that apply to any active measurement of
live paths are relevant here as well. See [RFC4656] and [RFC5357]. live paths are relevant here as well. See [RFC4656] and [RFC5357].
When considering privacy of those involved in measurement or those
whose traffic is measured, the sensitive information available to
potential observers is greatly reduced when using active techniques
which are within this scope of work. Passive observations of user
traffic for measurement purposes raise many privacy issues. We refer
the reader to the privacy considerations described in the Large Scale
Measurement of Broadband Performance (LMAP) Framework
[I-D.ietf-lmap-framework], which covers active and passive
techniques.
7. IANA Considerations 7. IANA Considerations
This memo makes no requests of IANA. This memo makes no requests of IANA.
8. Acknowledgements 8. Acknowledgements
The authors thank Rudiger Geib, Matt Mathis and Konstantinos The authors thank Rudiger Geib, Matt Mathis, Konstantinos
Pentikousis for their helpful comments on this memo, and Ann Cerveny Pentikousis, and Robert Sparks for their helpful comments on this
for her editorial review and comments that helped to improve memo, Alissa Cooper and Kathleen Moriarty for suggesting ways to
readability overall. "update the update" for heightened privacy awareness and its
consequences, and Ann Cerveny for her editorial review and comments
that helped to improve readability overall.
9. References 9. References
9.1. Normative References 9.1. 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, May "Framework for IP Performance Metrics", RFC 2330, May
1998. 1998.
[RFC2679] Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way [RFC2679] Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
skipping to change at page 15, line 5 skipping to change at page 15, line 41
9.2. Informative References 9.2. Informative References
[EEAW] Pentikousis, K., Piri, E., Pinola, J., Fitzek, F., [EEAW] Pentikousis, K., Piri, E., Pinola, J., Fitzek, F.,
Nissilae, T., and I. Harjula, "Empirical Evaluation of Nissilae, T., and I. Harjula, "Empirical Evaluation of
VoIP Aggregation over a Fixed WiMAX Testbed", Proceedings VoIP Aggregation over a Fixed WiMAX Testbed", Proceedings
of the 4th International Conference on Testbeds and of the 4th International Conference on Testbeds and
research infrastructures for the development of networks research infrastructures for the development of networks
and communities (TridentCom '08) and communities (TridentCom '08)
http://dl.acm.org/citation.cfm?id=1390599, March 2008. http://dl.acm.org/citation.cfm?id=1390599, March 2008.
[I-D.ietf-lmap-framework]
Eardley, P., Morton, A., Bagnulo, M., Burbridge, T.,
Aitken, P., and A. Akhter, "A framework for large-scale
measurement platforms (LMAP)", draft-ietf-lmap-
framework-05 (work in progress), May 2014.
[IBD] Fabini, J., Karner, W., Wallentin, L., and T. Baumgartner, [IBD] Fabini, J., Karner, W., Wallentin, L., and T. Baumgartner,
"The Illusion of Being Deterministic - Application-Level "The Illusion of Being Deterministic - Application-Level
Considerations on Delay in 3G HSPA Networks", Lecture Considerations on Delay in 3G HSPA Networks", Lecture
Notes in Computer Science, Springer, Volume 5550, 2009, pp Notes in Computer Science, Springer, Volume 5550, 2009, pp
301-312 , May 2009. 301-312 , May 2009.
[IRR] Fabini, J., Wallentin, L., and P. Reichl, "The Importance [IRR] Fabini, J., Wallentin, L., and P. Reichl, "The Importance
of Being Really Random: Methodological Aspects of IP-Layer of Being Really Random: Methodological Aspects of IP-Layer
2G and 3G Network Delay Assessment", ICC'09 Proceedings of 2G and 3G Network Delay Assessment", ICC'09 Proceedings of
the 2009 IEEE International Conference on Communications, the 2009 IEEE International Conference on Communications,
skipping to change at page 15, line 36 skipping to change at page 16, line 30
[RFC6808] Ciavattone, L., Geib, R., Morton, A., and M. Wieser, "Test [RFC6808] Ciavattone, L., Geib, R., Morton, A., and M. Wieser, "Test
Plan and Results Supporting Advancement of RFC 2679 on the Plan and Results Supporting Advancement of RFC 2679 on the
Standards Track", RFC 6808, December 2012. Standards Track", RFC 6808, December 2012.
[RFC6985] Morton, A., "IMIX Genome: Specification of Variable Packet [RFC6985] Morton, A., "IMIX Genome: Specification of Variable Packet
Sizes for Additional Testing", RFC 6985, July 2013. Sizes for Additional Testing", RFC 6985, July 2013.
[RRC] Peraelae, P., Barbuzzi, A., Boggia, G., and K. [RRC] Peraelae, P., Barbuzzi, A., Boggia, G., and K.
Pentikousis, "Theory and Practice of RRC State Transitions Pentikousis, "Theory and Practice of RRC State Transitions
in UMTS Networks", IEEE Globecom 2009 Workshops doi: in UMTS Networks", IEEE Globecom 2009 Workshops doi: 10
10.1109/GLOCOMW.2009.5360763, November 2009. .1109/GLOCOMW.2009.5360763, November 2009.
[TSRC] Fabini, J. and M. Abmayer, "Delay Measurement Methodology [TSRC] Fabini, J. and M. Abmayer, "Delay Measurement Methodology
Revisited: Time-slotted Randomness Cancellation", IEEE Revisited: Time-slotted Randomness Cancellation", IEEE
Transactions on Instrumentation and Measurement Transactions on Instrumentation and Measurement doi:10
doi:10.1109/TIM.2013.2263914, October 2013. .1109/TIM.2013.2263914, October 2013.
Authors' Addresses Authors' Addresses
Joachim Fabini Joachim Fabini
Vienna University of Technology Vienna University of Technology
Gusshausstrasse 25/E389 Gusshausstrasse 25/E389
Vienna 1040 Vienna 1040
Austria Austria
Phone: +43 1 58801 38813 Phone: +43 1 58801 38813
Fax: +43 1 58801 38898 Fax: +43 1 58801 38898
Email: Joachim.Fabini@tuwien.ac.at Email: Joachim.Fabini@tuwien.ac.at
URI: http://www.tc.tuwien.ac.at/about-us/staff/joachim-fabini/ URI: http://www.tc.tuwien.ac.at/about-us/staff/joachim-fabini/
 End of changes. 36 change blocks. 
84 lines changed or deleted 125 lines changed or added

This html diff was produced by rfcdiff 1.41. The latest version is available from http://tools.ietf.org/tools/rfcdiff/