draft-ietf-ippm-metrictest-02.txt   draft-ietf-ippm-metrictest-03.txt 
Internet Engineering Task Force R. Geib, Ed. Internet Engineering Task Force R. Geib, Ed.
Internet-Draft Deutsche Telekom Internet-Draft Deutsche Telekom
Intended status: Standards Track A. Morton Intended status: Standards Track A. Morton
Expires: September 15, 2011 AT&T Labs Expires: December 31, 2011 AT&T Labs
R. Fardid R. Fardid
Cariden Technologies Cariden Technologies
A. Steinmitz A. Steinmitz
HS Fulda Deutsche Telekom
March 14, 2011 June 29, 2011
IPPM standard advancement testing IPPM standard advancement testing
draft-ietf-ippm-metrictest-02 draft-ietf-ippm-metrictest-03
Abstract Abstract
This document specifies tests to determine if multiple independent This document specifies tests to determine if multiple independent
instantiations of a performance metric RFC have implemented the instantiations of a performance metric RFC have implemented the
specifications in the same way. This is the performance metric specifications in the same way. This is the performance metric
equivalent of interoperability, required to advance RFCs along the equivalent of interoperability, required to advance RFCs along the
standards track. Results from different implementations of metric standards track. Results from different implementations of metric
RFCs will be collected under the same underlying network conditions RFCs will be collected under the same underlying network conditions
and compared using state of the art statistical methods. The goal is and compared using state of the art statistical methods. The goal is
skipping to change at page 1, line 44 skipping to change at page 1, line 44
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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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 September 15, 2011. This Internet-Draft will expire on December 31, 2011.
Copyright Notice Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 6 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 7
2. Basic idea . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2. Basic idea . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3. Verification of conformance to a metric specification . . . . 8 3. Verification of conformance to a metric specification . . . . 8
3.1. Tests of an individual implementation against a metric 3.1. Tests of an individual implementation against a metric
specification . . . . . . . . . . . . . . . . . . . . . . 9 specification . . . . . . . . . . . . . . . . . . . . . . 9
3.2. Test setup resulting in identical live network testing 3.2. Test setup resulting in identical live network testing
conditions . . . . . . . . . . . . . . . . . . . . . . . . 11 conditions . . . . . . . . . . . . . . . . . . . . . . . . 11
3.3. Tests of two or more different implementations against 3.3. Tests of two or more different implementations against
a metric specification . . . . . . . . . . . . . . . . . . 15 a metric specification . . . . . . . . . . . . . . . . . . 16
3.4. Clock synchronisation . . . . . . . . . . . . . . . . . . 16 3.4. Clock synchronisation . . . . . . . . . . . . . . . . . . 17
3.5. Recommended Metric Verification Measurement Process . . . 17 3.5. Recommended Metric Verification Measurement Process . . . 18
3.6. Miscellaneous . . . . . . . . . . . . . . . . . . . . . . 20 3.6. Proposal to determine an "equivalence" threshold for
3.7. Proposal to determine an "equivalence" threshold for
each metric evaluated . . . . . . . . . . . . . . . . . . 21 each metric evaluated . . . . . . . . . . . . . . . . . . 21
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 22 4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 22
5. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 22 5. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 22
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
7. Security Considerations . . . . . . . . . . . . . . . . . . . 22 7. Security Considerations . . . . . . . . . . . . . . . . . . . 23
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
8.1. Normative References . . . . . . . . . . . . . . . . . . . 23 8.1. Normative References . . . . . . . . . . . . . . . . . . . 23
8.2. Informative References . . . . . . . . . . . . . . . . . . 24 8.2. Informative References . . . . . . . . . . . . . . . . . . 24
Appendix A. An example on a One-way Delay metric validation . . . 25 Appendix A. An example on a One-way Delay metric validation . . . 25
A.1. Compliance to Metric specification requirements . . . . . 25 A.1. Compliance to Metric specification requirements . . . . . 25
A.2. Examples related to statistical tests for One-way Delay . 26 A.2. Examples related to statistical tests for One-way Delay . 27
Appendix B. Anderson-Darling 2 sample C++ code . . . . . . . . . 28 Appendix B. Anderson-Darling 2 sample C++ code . . . . . . . . . 29
Appendix C. A tunneling set up for remote metric Appendix C. Glossary . . . . . . . . . . . . . . . . . . . . . . 37
implementation testing . . . . . . . . . . . . . . . 36
Appendix D. Glossary . . . . . . . . . . . . . . . . . . . . . . 38
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 38 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 38
1. Introduction 1. Introduction
The Internet Standards Process RFC2026 [RFC2026] requires that for a The Internet Standards Process RFC2026 [RFC2026] requires that for a
IETF specification to advance beyond the Proposed Standard level, at IETF specification to advance beyond the Proposed Standard level, at
least two genetically unrelated implementations must be shown to least two genetically unrelated implementations must be shown to
interoperate correctly with all features and options. This interoperate correctly with all features and options. This
requirement can be met by supplying: requirement can be met by supplying:
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The metric RFC advancement process begins with a request for protocol The metric RFC advancement process begins with a request for protocol
action accompanied by a memo that documents the supporting tests and action accompanied by a memo that documents the supporting tests and
results. The procedures of [RFC2026] are expanded in[RFC5657], results. The procedures of [RFC2026] are expanded in[RFC5657],
including sample implementation and interoperability reports. including sample implementation and interoperability reports.
Section 3 of [morton-advance-metrics-01] can serve as a template for Section 3 of [morton-advance-metrics-01] can serve as a template for
a metric RFC report which accompanies the protocol action request to a metric RFC report which accompanies the protocol action request to
the Area Director, including description of the test set-up, the Area Director, including description of the test set-up,
procedures, results for each implementation and conclusions. procedures, results for each implementation and conclusions.
Changes from WG-02 to WG-03:
o Changes stemming from experiments that implemented this plan, in
general.
o Adoption of the VLAN loopback figure in the main body of the memo
(section 3.2).
Changes from WG-01 to WG-02: Changes from WG-01 to WG-02:
o Clarification of the number of test streams recommended in section o Clarification of the number of test streams recommended in section
3.2. 3.2.
o Clarifications on testing details in sections 3.3 and 3.4. o Clarifications on testing details in sections 3.3 and 3.4.
o Spelling corrections throughout. o Spelling corrections throughout.
Changes from WG -00 to WG -01 draft Changes from WG -00 to WG -01 draft
skipping to change at page 7, line 49 skipping to change at page 8, line 13
requires careful test design: requires careful test design:
o The measurement test setup must be self-consistent to the largest o The measurement test setup must be self-consistent to the largest
possible extent. To minimize the influence of the test and possible extent. To minimize the influence of the test and
measurement setup on the result, network conditions and paths MUST measurement setup on the result, network conditions and paths MUST
be identical for the compared implementations to the largest be identical for the compared implementations to the largest
possible degree. This includes both the stability and non- possible degree. This includes both the stability and non-
ambiguity of routes taken by the measurement packets. See RFC ambiguity of routes taken by the measurement packets. See RFC
2330 for a discussion on self-consistency. 2330 for a discussion on self-consistency.
o To minimize the influence of implementation options on the result,
metric implementations SHOULD use identical options and parameters
for the metric under evaluation.
o The error induced by the sample size must be small enough to o The error induced by the sample size must be small enough to
minimize its influence on the test result. This may have to be minimize its influence on the test result. This may have to be
respected, especially if two implementations measure with respected, especially if two implementations measure with
different average probing rates. different average probing rates.
o Every comparison must be repeated several times based on different
measurement data to avoid random indications of compatibility (or
the lack of it).
o To minimize the influence of implementation options on the result,
metric implementations SHOULD use identical options and parameters
for the metric under evaluation.
o The implementation with the lowest probing frequency determines o The implementation with the lowest probing frequency determines
the smallest temporal interval for which samples can be compared. the smallest temporal interval for which samples can be compared.
o Repeat comparisons with several independent metric samples to
avoid random indications of compatibility (or the lack of it).
The metric specifications themselves are the primary focus of The metric specifications themselves are the primary focus of
evaluation, rather than the implementations of metrics. The evaluation, rather than the implementations of metrics. The
documentation produced by the advancement process should identify documentation produced by the advancement process should identify
which metric definitions and supporting material were found to be which metric definitions and supporting material were found to be
clearly worded and unambiguous, OR, it should identify ways in which clearly worded and unambiguous, OR, it should identify ways in which
the metric specification text should be revised to achieve clarity the metric specification text should be revised to achieve clarity
and unified interpretation. and unified interpretation.
The process should also permit identification of options that were The process should also permit identification of options that were
not implemented, so that they can be removed from the advancing not implemented, so that they can be removed from the advancing
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o Use remotely separated test labs to compare the implementations o Use remotely separated test labs to compare the implementations
and measure across the Internet and include a single impairment and measure across the Internet and include a single impairment
generator to impact all measurement flows in non discriminatory generator to impact all measurement flows in non discriminatory
way. way.
The first two approaches work, but cause higher expenses than the The first two approaches work, but cause higher expenses than the
other ones (due to travel and/or shipping+installation). For the other ones (due to travel and/or shipping+installation). For the
third option, ensuring two identically configured impairment third option, ensuring two identically configured impairment
generators requires well defined test cases and possibly identical generators requires well defined test cases and possibly identical
hard- and software. >>>Comment: for some specific tests, impairment hard- and software.
generator accuracy requirements are less-demanding than others, and
in such cases there is more flexibility in impairment generator
configuration. <<<
It is a fair question, whether the last two options can result in any
applicable test set up at all. While an experimental approach is
given in Appendix C, the trade off that measurement packets of
different sites pass the path segments but always in a different
order of segments probably can't be avoided.
The question of which option above results in identical networking As documented in a test report [morton-testplan-rfc2679], the last
conditions and is broadly accepted can't be answered without more option was required to prove compatibility of two delay metric
practical experience in comparing implementations. The last proposal implementations. An impairment generator is probably required when
has the advantage that, while the measurement equipment is remotely testing compatibility of most other metrics and it therefore
distributed, a single network impairment generator and the Internet RECOMMENDED to include an impairment generator in metric test set
can be used in combination to impact all measurement flows. ups.
3.1. Tests of an individual implementation against a metric 3.1. Tests of an individual implementation against a metric
specification specification
A metric implementation MUST support the requirements classified as A metric implementation MUST support the requirements classified as
"MUST" and "REQUIRED" of the related metric specification to be "MUST" and "REQUIRED" of the related metric specification to be
compliant to the latter. compliant to the latter.
Further, supported options of a metric implementation SHOULD be Further, supported options of a metric implementation SHOULD be
documented in sufficient detail. The documentation of chosen options documented in sufficient detail. The documentation of chosen options
skipping to change at page 10, line 43 skipping to change at page 10, line 42
implementations. A single IPPM conformant implementation MUST under implementations. A single IPPM conformant implementation MUST under
otherwise identical network conditions produce precise results for otherwise identical network conditions produce precise results for
repeated measurements of the same metric. repeated measurements of the same metric.
RFC 2330 prefers the "empirical distribution function" EDF to RFC 2330 prefers the "empirical distribution function" EDF to
describe collections of measurements. RFC 2330 determines, that describe collections of measurements. RFC 2330 determines, that
"unless otherwise stated, IPPM goodness-of-fit tests are done using "unless otherwise stated, IPPM goodness-of-fit tests are done using
5% significance." The goodness of fit test determines by which 5% significance." The goodness of fit test determines by which
precision two or more samples of a metric implementation belong to precision two or more samples of a metric implementation belong to
the same underlying distribution (of measured network performance the same underlying distribution (of measured network performance
events). The goodness of fit test to be applied is the Anderson- events). The goodness of fit test suggested for the metric test is
Darling K sample test (ADK sample test, K stands for the number of the Anderson-Darling K sample test (ADK sample test, K stands for the
samples to be compared) [ADK]. Please note that RFC 2330 and RFC number of samples to be compared) [ADK]. Please note that RFC 2330
2679 apply an Anderson Darling goodness of fit test too. and RFC 2679 apply an Anderson Darling goodness of fit test too.
The results of a repeated test with a single implementation MUST pass The results of a repeated test with a single implementation MUST pass
an ADK sample test with confidence level of 95%. The resolution for an ADK sample test with confidence level of 95%. The conditions for
which the ADK test has been passed with the specified confidence which the ADK test has been passed with the specified confidence
level MUST be documented. To formulate this differently: The level MUST be documented. To formulate this differently: The
requirement is to document the smallest resolution, at which the requirement is to document the set of parameters with the smallest
results of the tested metric implementation pass an ADK test with a deviation, at which the results of the tested metric implementation
confidence level of 95%. The minimum resolution available in the pass an ADK test with a confidence level of 95%. The minimum
reported results from each implementation MUST be taken into account resolution available in the reported results from each implementation
in the ADK test. MUST be taken into account in the ADK test.
The test conditions which MUST be documented for a passed metric test
include:
o The metric resolution at which a test was passed (e.g. the
resolution of timestamps)
o The parameters modified by an impairment generator.
o The impairment generator parameter settings.
3.2. Test setup resulting in identical live network testing conditions 3.2. Test setup resulting in identical live network testing conditions
Two major issues complicate tests for metric compliance across live Two major issues complicate tests for metric compliance across live
networks under identical testing conditions. One is the general networks under identical testing conditions. One is the general
point that metric definition implementations cannot be conveniently point that metric definition implementations cannot be conveniently
examined in field measurement scenarios. The other one is more examined in field measurement scenarios. The other one is more
broadly described as "parallelism in devices and networks", including broadly described as "parallelism in devices and networks", including
mechanisms like those that achieve load balancing (see [RFC4928]). mechanisms like those that achieve load balancing (see [RFC4928]).
skipping to change at page 12, line 14 skipping to change at page 12, line 22
o A low operational overhead may enable a broader audience to set up o A low operational overhead may enable a broader audience to set up
a metric test with the desired properties. a metric test with the desired properties.
o The tunneling protocol should be reliable and stable in set up and o The tunneling protocol should be reliable and stable in set up and
operation to avoid disturbances or influence on the test results. operation to avoid disturbances or influence on the test results.
o The tunneling protocol should not incur any extra cost for those o The tunneling protocol should not incur any extra cost for those
interested in setting up a metric test. interested in setting up a metric test.
An illustration of a test setup with two tunnels and two flows An illustration of a test setup with two layer 2 tunnels and two
between two linecards of one implementation is given in Figure 1. flows between two linecards of one implementation is given in
Figure 1.
Implementation ,---. +--------+ Implementation ,---. +--------+
+~~~~~~~~~~~/ \~~~~~~| Remote | +~~~~~~~~~~~/ \~~~~~~| Remote |
+------->-----F2->-| / \ |->---+ | +------->-----F2->-| / \ |->---+ |
| +---------+ | Tunnel 1( ) | | | | +---------+ | Tunnel 1( ) | | |
| | transmit|-F1->-| ( ) |->+ | | | | transmit|-F1->-| ( ) |->+ | |
| | LC1 | +~~~~~~~~~| |~~~~| | | | | | LC1 | +~~~~~~~~~| |~~~~| | | |
| | receive |-<--+ ( ) | F1 F2 | | | receive |-<--+ ( ) | F1 F2 |
| +---------+ | |Internet | | | | | | +---------+ | |Internet | | | | |
*-------<-----+ F2 | | | | | | *-------<-----+ F2 | | | | | |
+---------+ | | +~~~~~~~~~| |~~~~| | | | +---------+ | | +~~~~~~~~~| |~~~~| | | |
| transmit|-* *-| | | |--+<-* | | transmit|-* *-| | | |--+<-* |
| LC2 | | Tunnel 2( ) | | | | LC2 | | Tunnel 2( ) | | |
| receive |-<-F1-| \ / |<-* | | receive |-<-F1-| \ / |<-* |
+---------+ +~~~~~~~~~~~\ /~~~~~~| Router | +---------+ +~~~~~~~~~~~\ /~~~~~~| Router |
`-+-' +--------+ `-+-' +--------+
Illustration of a test setup with two tunnels. For simplicity, only Illustration of a test setup with two layer 2 tunnels. For
two linecards of one implementation and two flows F between them are simplicity, only two linecards of one implementation and two flows F
shown. between them are shown.
Figure 1 Figure 1
Figure 2 shows the network elements required to set up GRE tunnels or Figure 2 shows the network elements required to set up layer 2
as shown by figure 1. tunnels as shown by figure 1.
Implementation Implementation
+-----+ ,---. +-----+ ,---.
| LC1 | / \ | LC1 | / \
+-----+ / \ +------+ +-----+ / \ +------+
| +-------+ ( ) +-------+ |Remote| | +-------+ ( ) +-------+ |Remote|
+--------+ | | | | | | | | +--------+ | | | | | | | |
|Ethernet| | Tunnel| |Internet | | Tunnel| | | |Ethernet| | Tunnel| |Internet | | Tunnel| | |
|Switch |--| Head |--| |--| Head |--| | |Switch |--| Head |--| |--| Head |--| |
+--------+ | Router| | | | Router| | | +--------+ | Router| | | | Router| | |
| | | ( ) | | |Router| | | | ( ) | | |Router|
+-----+ +-------+ \ / +-------+ +------+ +-----+ +-------+ \ / +-------+ +------+
| LC2 | \ / | LC2 | \ /
+-----+ `-+-' +-----+ `-+-'
Illustration of a hardware setup to realise the test setup Illustration of a hardware setup to realise the test setup
illustrated by figure 1 with GRE tunnels or Pseudowires. illustrated by figure 1 with layer 2 tunnels or Pseudowires.
Figure 2 Figure 2
The test set up successfully used during a delay metric test
[morton-testplan-rfc2679] is given as an example in figure 3. Note
that the shown set up allows a metric test between two remote sites.
+----+ +----+ +----+ +----+
|LC10| |LC11| ,---. |LC20| |LC21|
+----+ +----+ / \ +-------+ +----+ +----+
| V10 | V11 / \ | Tunnel| | V20 | V21
| | ( ) | Head | | |
+--------+ +------+ | | | Router|__+----------+
|Ethernet| |Tunnel| |Internet | +---B---+ |Ethernet |
|Switch |--|Head |-| | | |Switch |
+-+--+---+ |Router| | | +---+---+ +--+--+----+
|__| +--A---+ ( )--|Option.| |__|
\ / |Impair.|
Bridge \ / |Gener. | Bridge
V20 to V21 `-+-? +-------+ V10 to V11
Figure 3
In figure 3, LC10 identify measurement clients /line cards. V10 and
the others denote VLANs. All VLANs are using the same tunnel from A
to B and in the reverse direction. The remote site VLANs are
U-bridged at the local site Ethernet switch. The measurement packets
of site 1 travel tunnel A->B first, are U-bridged at site 2 and
travel tunnel B->A second. Measurement packets of site 2 travel
tunnel B->A first, are U-bridged at site 1 and travel tunnel A->B
second. So all measurement packets pass the same tunnel segments,
but in different segment order.
If tunneling is applied, two tunnels MUST carry all test traffic in If tunneling is applied, two tunnels MUST carry all test traffic in
between the test site and the remote site. For example, if 802.1Q between the test site and the remote site. For example, if 802.1Q
Ethernet Virtual LANs (VLAN) are applied and the measurement streams Ethernet Virtual LANs (VLAN) are applied and the measurement streams
are carried in different VLANs, the IP tunnel or Pseudo Wires are carried in different VLANs, the IP tunnel or Pseudo Wires
respectively MUST be set up in physical port mode to avoid set up of respectively MUST be set up in physical port mode to avoid set up of
Pseudo Wires per VLAN (which may see different paths due to ECMP Pseudo Wires per VLAN (which may see different paths due to ECMP
routing), see RFC 4448. The remote router and the Ethernet switch routing), see RFC 4448. The remote router and the Ethernet switch
shown in figure 2 must support 802.1Q in this set up. shown in figure 3 has to support 802.1Q in this set up.
The IP packet size of the metric implementation SHOULD be chosen The IP packet size of the metric implementation SHOULD be chosen
small enough to avoid fragmentation due to the added Ethernet and small enough to avoid fragmentation due to the added Ethernet and
tunnel headers. Otherwise, the impact of tunnel overhead on tunnel headers. Otherwise, the impact of tunnel overhead on
fragmentation and interface MTU size MUST be understood and taken fragmentation and interface MTU size MUST be understood and taken
into account (see [RFC4459]). into account (see [RFC4459]).
An Ethernet port mode IP tunnel carrying several 802.1Q VLANs each An Ethernet port mode IP tunnel carrying several 802.1Q VLANs each
containing measurement traffic of a single measurement system was set containing measurement traffic of a single measurement system was
up as a proof of concept using RFC4719 [RFC4719], Transport of successfully applied when testing compatibility of two metric
Ethernet Frames over L2TPv3. Ethernet over L2TPv3 seems to fulfill implementations [morton-testplan-rfc2679].
most of the desired tunneling protocol criteria mentioned above.
The following headers may have to be accounted for when calculating The following headers may have to be accounted for when calculating
total packet length, if VLANs and Ethernet over L2TPv3 tunnels are total packet length, if VLANs and Ethernet over L2TPv3 tunnels are
applied: applied:
o Ethernet 802.1Q: 22 Byte. o Ethernet 802.1Q: 22 Byte.
o L2TPv3 Header: 4-16 Byte for L2TPv3 data messages over IP; 16-28 o L2TPv3 Header: 4-16 Byte for L2TPv3 data messages over IP; 16-28
Byte for L2TPv3 data messages over UDP. Byte for L2TPv3 data messages over UDP.
skipping to change at page 14, line 26 skipping to change at page 15, line 11
L2TP is a commodity tunneling protocol [RFC2661]. By the time of L2TP is a commodity tunneling protocol [RFC2661]. By the time of
writing, L2TPv3 [RFC3931]is the latest version of L2TP. If L2TPv3 is writing, L2TPv3 [RFC3931]is the latest version of L2TP. If L2TPv3 is
applied, software based implementations of this protocol are not applied, software based implementations of this protocol are not
suitable for the test set up, as such implementations may cause suitable for the test set up, as such implementations may cause
incalculable delay shifts. incalculable delay shifts.
Ethernet Pseudo Wires may also be set up on MPLS networks [RFC4448]. Ethernet Pseudo Wires may also be set up on MPLS networks [RFC4448].
While there's no technical issue with this solution, MPLS interfaces While there's no technical issue with this solution, MPLS interfaces
are mostly found in the network provider domain. Hence not all of are mostly found in the network provider domain. Hence not all of
the above tunneling criteria are met. the above criteria to select a tunneling protocol are met.
Appendix C provides an experimental tunneling set up for metric Note that setting up a metric test environment isn't a plug and play
implementation testing between two (or more) remote sites. issue. Skilled networking engineers should be consulted and
involved, if a set up between remote sites is preferred.
Each test SHOULD be conducted multiple times. Sequential testing is Passing or failing an ADK test with 2 samples could be a random
possible, but may not be a useful metric test option because WAN result (note that [RFC2330] defines a sample as a set of singleton
conditions are likely to change over time. It is RECOMMENDED that metric values produced by a measurement stream, and we continue to
tests be carried out by establishing at least 2 different parallel use this terminology here). The error margin of a statistical test
measurement flows. Two linecards per implementation that send and is higher if the number of samples it is based on is low (the number
receive measurement flows should be sufficient to create 4 parallel of samples taken influences the so called "degree of freedom" of a
measurement flows (when each card sends and receives 2 flows). Other statistical test and a higher degree of freedom produces more
reliable results). To pass ADK with higher probability, the number
of samples collected per implementation under identical networking
conditions SHOULD be greater than 2. Hardware and load constraints
may enforce an upper limit on the number of simultaneous measurement
streams. The ADK test allows one to combine different samples (see
section 9 [ADK]) and then to run a two sample test between combined
samples. At least 4 samples per implementation captured under
identical networking conditions is RECOMMENDED when comparing
different metric implementations by a statistical test.
It is RECOMMENDED that tests be carried out by establishing N
different parallel measurement flows. Two or three linecards per
implementation serving to send or receive measurement flows should be
sufficient to create 4 or more parallel measurement flows. Other
options are to separate flows by DiffServ marks (without deploying options are to separate flows by DiffServ marks (without deploying
any QoS in the inner or outer tunnel) or using a single CBR flow and any QoS in the inner or outer tunnel) or using a single CBR flow and
evaluating every n-th singleton to belong to a specific measurement evaluating every n-th singleton to belong to a specific measurement
flow. flow. Note that a practical test indeed showed that ADK was passed
with 4 samples even if a 2 sample test
failed[morton-testplan-rfc2679].
Some additional rules to calculate and compare samples have to be Some additional guidelines to calculate and compare samples to
respected to perform a metric test: perform a metric test are:
o To compare different probes of a common underlying distribution in o To compare different probes of a common underlying distribution in
terms of metrics characterising a communication network requires terms of metrics characterising a communication network requires
to respect the temporal nature for which the assumption of common to respect the temporal nature for which the assumption of common
underlying distribution may hold. Any singletons or samples to be underlying distribution may hold. Any singletons or samples to be
compared MUST be captured within the same time interval. compared MUST be captured within the same time interval.
o Whenever statistical events like singletons or rates are used to o If statistical events like rates are used to characterise measured
characterise measured metrics of a time-interval, at least 5 metrics of a time-interval, its RECOMMENDED to pick as a minimum 5
singletons of a relevant metric SHOULD be present to ensure a singletons of a relevant metric to ensure a minimum confidence
minimum confidence into the reported value (see Wikipedia on into the reported value. The error margin of the determined rate
confidence [Rule of thumb]). Note that this criterion also is to depends on the number singletons (refer to statistical textbooks
be respected e.g. when comparing packet loss metrics. Any packet on Student's t-test). As an example, any packet loss measurement
loss measurement interval to be compared with the results of interval to be compared with the results of another implementation
another implementation SHOULD contain at least five lost packets contains at least five lost packets to have some confidence that
to have a minimum confidence that the observed loss rate wasn't the observed loss rate wasn't caused by a small number of random
caused by a small number of random packet drops. packet drops.
o The minimum number of singletons or samples to be compared by an o The minimum number of singletons or samples to be compared by an
Anderson-Darling test SHOULD be 100 per tested metric Anderson-Darling test SHOULD be 100 per tested metric
implementation. Note that the Anderson-Darling test detects small implementation. Note that the Anderson-Darling test detects small
differences in distributions fairly well and will fail for high differences in distributions fairly well and will fail for high
number of compared results (RFC2330 mentions an example with 8192 number of compared results (RFC2330 mentions an example with 8192
measurements where an Anderson-Darling test always failed). measurements where an Anderson-Darling test always failed).
o Generally, the Anderson-Darling test is sensitive to differences o Generally, the Anderson-Darling test is sensitive to differences
in the accuracy or bias associated with varying implementations or in the accuracy or bias associated with varying implementations or
test conditions. These dissimilarities may result in differing test conditions. These dissimilarities may result in differing
averages of samples to be compared. An example may be different averages of samples to be compared. An example may be different
packet sizes, resulting in a constant delay difference between packet sizes, resulting in a constant delay difference between
compared samples. Therefore samples to be compared by an compared samples. Therefore samples to be compared by an Anderson
Anderson-Darling test MAY be calibrated by the difference of the Darling test MAY be calibrated by the difference of the average
average values of the samples. Any calibration of this kind MUST values of the samples. Any calibration of this kind MUST be
be documented in the test result. documented in the test result.
3.3. Tests of two or more different implementations against a metric 3.3. Tests of two or more different implementations against a metric
specification specification
RFC2330 expects "a methodology for a given metric [to] exhibit RFC2330 expects "a methodology for a given metric [to] exhibit
continuity if, for small variations in conditions, it results in continuity if, for small variations in conditions, it results in
small variations in the resulting measurements. Slightly more small variations in the resulting measurements. Slightly more
precisely, for every positive epsilon, there exists a positive delta, precisely, for every positive epsilon, there exists a positive delta,
such that if two sets of conditions are within delta of each other, such that if two sets of conditions are within delta of each other,
then the resulting measurements will be within epsilon of each then the resulting measurements will be within epsilon of each
other." A small variation in conditions in the context of the metric other." A small variation in conditions in the context of the metric
test proposed here can be seen as different implementations measuring test proposed here can be seen as different implementations measuring
the same metric along the same path. the same metric along the same path.
IPPM metric specifications however allow for implementor options to IPPM metric specifications however allow for implementor options to
the largest possible degree. It can not be expected that two the largest possible degree. It cannot be expected that two
implementors pick identical value ranges in options for the implementors allow 100% identical options in their implementations.
implementations. Implementors SHOULD to the highest degree possible Testers SHOULD to the highest degree possible pick the same
pick the same configurations for their systems when comparing their configurations for their systems when comparing their implementations
implementations by a metric test. by a metric test.
In some cases, a goodness of fit test may not be possible or show In some cases, a goodness of fit test may not be possible or show
disappointing results. To clarify the difficulties arising from disappointing results. To clarify the difficulties arising from
different implementation options, the individual options picked for different implementation options, the individual options picked for
every compared implementation SHOULD be documented in sufficient every compared implementation SHOULD be documented in sufficient
detail. Based on this documentation, the underlying metric detail. Based on this documentation, the underlying metric
specification should be improved before it is promoted to a standard. specification should be improved before it is promoted to a standard.
The same statistical test as applicable to quantify precision of a The same statistical test as applicable to quantify precision of a
single metric implementation MUST be used to compare metric result single metric implementation MUST be used to compare metric result
skipping to change at page 17, line 12 skipping to change at page 18, line 14
Examination of the second condition requires RTT measurement for Examination of the second condition requires RTT measurement for
reference, e.g., based on TWAMP (RFC5357, RFC 5357 [RFC5357]), in reference, e.g., based on TWAMP (RFC5357, RFC 5357 [RFC5357]), in
conjunction with one-way delay measurement. conjunction with one-way delay measurement.
Specification of X% to strike a balance between identification of Specification of X% to strike a balance between identification of
unreliable one-way delay samples and misidentification of reliable unreliable one-way delay samples and misidentification of reliable
samples under a wide range of Internet path RTTs probably requires samples under a wide range of Internet path RTTs probably requires
further study. further study.
An implementation of an RFC that requires synchronized clocks is An IPPM compliant metric implementation of an RFC that requires
expected to provide precise measurement results in order to claim synchronized clocks is expected to provide precise measurement
that the metric measured is compliant. results.
IF an implementation publishes a specification of its precision, such IF an implementation publishes a specification of its precision, such
as "a precision of 1 ms (+/- 500 us) with a confidence of 95%", then as "a precision of 1 ms (+/- 500 us) with a confidence of 95%", then
the specification SHOULD be met over a useful measurement duration. the specification SHOULD be met over a useful measurement duration.
For example, if the metric is measured along an Internet path which For example, if the metric is measured along an Internet path which
is stable and not congested, then the precision specification SHOULD is stable and not congested, then the precision specification SHOULD
be met over durations of an hour or more. be met over durations of an hour or more.
3.5. Recommended Metric Verification Measurement Process 3.5. Recommended Metric Verification Measurement Process
In order to meet their obligations under the IETF Standards Process In order to meet their obligations under the IETF Standards Process
the IESG must be convinced that each metric specification advanced to the IESG must be convinced that each metric specification advanced to
Draft Standard or Internet Standard status is clearly written, that Draft Standard or Internet Standard status is clearly written, that
there are the a sufficient number of verified equivalent there are a sufficient number of verified equivalent implementations,
implementations, and that all options have been implemented. and that options that have been implemented are documented.
In the context of this document, metrics are designed to measure some In the context of this document, metrics are designed to measure some
characteristic of a data network. An aim of any metric definition characteristic of a data network. An aim of any metric definition
should be that it should be specified in a way that can reliably should be that it should be specified in a way that can reliably
measure the specific characteristic in a repeatable way across measure the specific characteristic in a repeatable way across
multiple independent implementations. multiple independent implementations.
Each metric, statistic or option of those to be validated MUST be Each metric, statistic or option of those to be validated MUST be
compared against a reference measurement or another implementation by compared against a reference measurement or another implementation by
at least 5 different basic data sets, each one with sufficient size as specified by this document.
to reach the specified level of confidence, as specified by this
document.
Finally, the metric definitions, embodied in the text of the RFCs, Finally, the metric definitions, embodied in the text of the RFCs,
are the objects that require evaluation and possible revision in are the objects that require evaluation and possible revision in
order to advance to the next step on the standards track. order to advance to the next step on the standards track.
IF two (or more) implementations do not measure an equivalent metric IF two (or more) implementations do not measure an equivalent metric
as specified by this document, as specified by this document,
AND sources of measurement error do not adequately explain the lack AND sources of measurement error do not adequately explain the lack
of agreement, of agreement,
skipping to change at page 18, line 23 skipping to change at page 19, line 23
consensus and (possible) advancement along the standards track. consensus and (possible) advancement along the standards track.
Finally, all the findings MUST be documented in a report that can Finally, all the findings MUST be documented in a report that can
support advancement on the standards track, similar to those support advancement on the standards track, similar to those
described in [RFC5657]. The list of measurement devices used in described in [RFC5657]. The list of measurement devices used in
testing satisfies the implementation requirement, while the test testing satisfies the implementation requirement, while the test
results provide information on the quality of each specification in results provide information on the quality of each specification in
the metric RFC (the surrogate for feature interoperability). the metric RFC (the surrogate for feature interoperability).
The complete process of advancing a metric specification to a The complete process of advancing a metric specification to a
standard as defined by this document is illustrated in Figure 3. standard as defined by this document is illustrated in Figure 4.
,---. ,---.
/ \ / \
( Start ) ( Start )
\ / Implementations \ / Implementations
`-+-' +-------+ `-+-' +-------+
| /| 1 `. | /| 1 `.
+---+----+ / +-------+ `.-----------+ ,-------. +---+----+ / +-------+ `.-----------+ ,-------.
| RFC | / |Check for | ,' was RFC `. YES | RFC | / |Check for | ,' was RFC `. YES
| | / |Equivalence.... clause x ------+ | | / |Equivalence.... clause x ------+
skipping to change at page 18, line 45 skipping to change at page 19, line 45
| Metric \.....| 2 ....relevant | `---+---' +----+-----+ | Metric \.....| 2 ....relevant | `---+---' +----+-----+
| Metric |\ +-------+ |identical | No | |Report | | Metric |\ +-------+ |identical | No | |Report |
| Metric | \ |network | +--+----+ |results + | | Metric | \ |network | +--+----+ |results + |
| ... | \ |conditions | |Modify | |Advance | | ... | \ |conditions | |Modify | |Advance |
| | \ +-------+ | | |Spec +--+RFC | | | \ +-------+ | | |Spec +--+RFC |
+--------+ \| n |.'+-----------+ +-------+ |request(?)| +--------+ \| n |.'+-----------+ +-------+ |request(?)|
+-------+ +----------+ +-------+ +----------+
Illustration of the metric standardisation process Illustration of the metric standardisation process
Figure 3 Figure 4
Any recommendation for the advancement of a metric specification MUST Any recommendation for the advancement of a metric specification MUST
be accompanied by an implementation report, as is the case with all be accompanied by an implementation report, as is the case with all
requests for the advancement of IETF specifications. The requests for the advancement of IETF specifications. The
implementation report needs to include the tests performed, the implementation report needs to include the tests performed, the
applied test setup, the specific metrics in the RFC and reports of applied test setup, the specific metrics in the RFC and reports of
the tests performed with two or more implementations. The test plan the tests performed with two or more implementations. The test plan
needs to specify the precision reached for each measured metric and needs to specify the precision reached for each measured metric and
thus define the meaning of "statistically equivalent" for the thus define the meaning of "statistically equivalent" for the
specific metrics being tested. specific metrics being tested.
skipping to change at page 20, line 38 skipping to change at page 21, line 38
by using a layer 2 tunnel. by using a layer 2 tunnel.
o Different IP options. o Different IP options.
o Different DSCP. o Different DSCP.
o If the N measurements are captured using sequential measurements o If the N measurements are captured using sequential measurements
instead of simultaneous ones, then the following factors come into instead of simultaneous ones, then the following factors come into
play: Time varying paths and load conditions. play: Time varying paths and load conditions.
3.6. Miscellaneous 3.6. Proposal to determine an "equivalence" threshold for each metric
A minimum amount of singletons per metric is required if results are
to be compared. To avoid accidental singletons from impacting a
metric comparison, a minimum number of 5 singletons per compared
interval was proposed above. Commercial Internet service is not
operated to reliably create enough rare events of singletons to
characterize bad measurement engineering or bad implementations. In
the case that a metric validation requires capturing rare events, an
impairment generator may have to be added to the test set up.
Inclusion of an impairment generator and the parameterisation of the
impairments generated MUST be documented.
A metric characterising a common impairment condition would be one,
which by expectation creates a singleton result for each measured
packet. Delay or Delay Variation are examples of this type, and in
such cases, the Internet may be used to compare metric
implementations.
Rare events are those, where by expectation no or a rather low number
of "event is present" singletons are captured during a measurement
interval. Packet duplications, packet loss rates above one digit
percentages, loss patterns and packet reordering are examples. Note
especially that a packet reordering or loss pattern metric
implementation comparison may require a more sophisticated test set
up than described here. Spatial and temporal effects combine in the
case of packet re-ordering and measurements with different packet
rates may always lead to different results.
As specified above, 5 singletons are the recommended basis to
minimise interference of random events with the statistical test
proposed by this document. In the case of ratio measurements (like
packet loss), the underlying sum of basic events, against the which
the metric's monitored singletons are "rated", determines the
resolution of the test. A packet loss statistic with a resolution of
1% requires one packet loss statistic-data point to consist of 500
delay singletons (of which at least 5 were lost). To compare EDFs on
packet loss requires one hundred such statistics per flow. That
means, all in all at least 50 000 delay singletons are required per
single measurement flow. Live network packet loss is assumed to be
present during main traffic hours only. Let this interval be 5
hours. The required minimum rate of a single measurement flow in
that case is 2.8 packets/sec (assuming a loss of 1% during 5 hours).
If this measurement is too demanding under live network conditions,
an impairment generator should be used.
3.7. Proposal to determine an "equivalence" threshold for each metric
evaluated evaluated
This section describes a proposal for maximum error of "equivalence", This section describes a proposal for maximum error of "equivalence",
based on performance comparison of identical implementations. This based on performance comparison of identical implementations. This
comparison may be useful for both ADK and non-ADK comparisons. comparison may be useful for both ADK and non-ADK comparisons.
Each metric tested by two or more implementations (cross- Each metric tested by two or more implementations (cross-
implementation testing). implementation testing).
Each metric is also tested twice simultaneously by the *same* Each metric is also tested twice simultaneously by the *same*
skipping to change at page 22, line 30 skipping to change at page 22, line 32
and only the systematic error need be decided beforehand. and only the systematic error need be decided beforehand.
In the case of ADK comparison, the largest same-implementation In the case of ADK comparison, the largest same-implementation
resolution of distribution equivalence can be used as a limit on resolution of distribution equivalence can be used as a limit on
cross-implementation resolutions (at the same confidence level). cross-implementation resolutions (at the same confidence level).
4. Acknowledgements 4. Acknowledgements
Gerhard Hasslinger commented a first version of this document, Gerhard Hasslinger commented a first version of this document,
suggested statistical tests and the evaluation of time series suggested statistical tests and the evaluation of time series
information. Henk Uijterwaal and Lars Eggert have encouraged and information. Matthias Wieser's thesis on a metric test resulted in
helped to orgainize this work. Mike Hamilton, Scott Bradner, David new input for this draft. Henk Uijterwaal and Lars Eggert have
Mcdysan and Emile Stephan commented on this draft. Carol Davids encouraged and helped to orgainize this work. Mike Hamilton, Scott
reviewed the 01 version of the ID before it was promoted to WG draft. Bradner, David Mcdysan and Emile Stephan commented on this draft.
Carol Davids reviewed the 01 version of the ID before it was promoted
to WG draft.
5. Contributors 5. Contributors
Scott Bradner, Vern Paxson and Allison Mankin drafted bradner- Scott Bradner, Vern Paxson and Allison Mankin drafted bradner-
metrictest [bradner-metrictest], and major parts of it are included metrictest [bradner-metrictest], and major parts of it are included
in this document. in this document.
6. IANA Considerations 6. IANA Considerations
This memo includes no request to IANA. This memo includes no request to IANA.
skipping to change at page 25, line 5 skipping to change at page 25, line 8
[morton-advance-metrics] [morton-advance-metrics]
Morton, A., "Problems and Possible Solutions for Advancing Morton, A., "Problems and Possible Solutions for Advancing
Metrics on the Standards Track", draft -morton-ippm- Metrics on the Standards Track", draft -morton-ippm-
advance-metrics-00, (work in progress), July 2009. advance-metrics-00, (work in progress), July 2009.
[morton-advance-metrics-01] [morton-advance-metrics-01]
Morton, A., "Lab Test Results for Advancing Metrics on the Morton, A., "Lab Test Results for Advancing Metrics on the
Standards Track", draft -morton-ippm-advance-metrics-01, Standards Track", draft -morton-ippm-advance-metrics-01,
(work in progress), June 2010. (work in progress), June 2010.
[morton-testplan-rfc2679]
Ciavattone, L., Geib, R., Morton, A., and M. Wieser, "Test
Plan and Results for Advancing RFC 2679 on the Standards
Track", draft -morton-ippm-testplan-rfc2679-01, (work in
progress), June 2011.
Appendix A. An example on a One-way Delay metric validation Appendix A. An example on a One-way Delay metric validation
The text of this appendix is not binding. It is an example how parts The text of this appendix is not binding. It is an example how parts
of a One-way Delay metric test could look like. of a One-way Delay metric test could look like.
http://xml.resource.org/public/rfc/bibxml/ http://xml.resource.org/public/rfc/bibxml/
A.1. Compliance to Metric specification requirements A.1. Compliance to Metric specification requirements
One-way Delay, Loss threshold, RFC 2679 One-way Delay, Loss threshold, RFC 2679
skipping to change at page 36, line 41 skipping to change at page 37, line 27
adk_result = (double) (n_total - 1) / (n_total adk_result = (double) (n_total - 1) / (n_total
* n_total * (k - 1)) * n_total * (k - 1))
* (sum_adk_samp1 / n_sample1 * (sum_adk_samp1 / n_sample1
+ sum_adk_samp2 / n_sample2); + sum_adk_samp2 / n_sample2);
/* if(adk_result <= adk_criterium) /* if(adk_result <= adk_criterium)
* adk_2_sample test is passed * adk_2_sample test is passed
*/ */
Figure 4
Appendix C. A tunneling set up for remote metric implementation testing
Parties interested in testing metric compliance is most convenient if
all involved parties can stay in their local test laboratories.
Figure 4 shows a test configuration which may enable remote metric
compliance testing.
+----+ +----+ +----+ +----+
|LC10| |LC11| ,---. |LC20| |LC21|
+----+ +----+ / \ +-------+ +----+ +----+
| V10 | V11 / \ | Tunnel| | V20 | V21
| | ( ) | Head | | |
+--------+ +------+ | | | Router|__+----------+
|Ethernet| |Tunnel| |Internet | +---B---+ |Ethernet |
|Switch |--|Head |-| | | |Switch |
+-+--+---+ |Router| | | +---+---+ +--+--+----+
|__| +--A---+ ( )--|Option.| |__|
\ / |Impair.|
Bridge \ / |Gener. | Bridge
V20 to V21 `-+-? +-------+ V10 to V11
Figure 5 Figure 5
LC10 identify measurement clients /line cards. V10 and the others Appendix C. Glossary
denote VLANs. All VLANs are using the same tunnel from A to B and in
the reverse direction. The remote site VLANs are U-bridged at the
local site Ethernet switch. The measurement packets of site 1 travel
tunnel A->B first, are U-bridged at site 2 and travel tunnel B->A
second. Measurement packets of site 2 travel tunnel B->A first, are
U-bridged at site 1 and travel tunnel A->B second. So all
measurement packets pass the same tunnel segments, but in different
segment order. An experiment to prove or reject the above test set
up shown in figure 4 has been agreed but not yet scheduled between
Deutsche Telekom and RIPE.
Figure 4 includes an optional impairment generator. If this
impairment generator is inserted in the IP path between the tunnel
head end routers, it equally impacts all measurement packets and
flows. Thus trouble with ensuring identical test set up by
configuring two separated impairment generators identically is
avoided (which was another proposal allowing remote metric compliance
testing).
Appendix D. Glossary
+-------------+-----------------------------------------------------+ +-------------+-----------------------------------------------------+
| ADK | Anderson-Darling K-Sample test, a test used to | | ADK | Anderson-Darling K-Sample test, a test used to |
| | check whether two samples have the same statistical | | | check whether two samples have the same statistical |
| | distribution. | | | distribution. |
| ECMP | Equal Cost Multipath, a load balancing mechanism | | ECMP | Equal Cost Multipath, a load balancing mechanism |
| | evaluating MPLS labels stacks, IP addresses and | | | evaluating MPLS labels stacks, IP addresses and |
| | ports. | | | ports. |
| EDF | The "Empirical Distribution Function" of a set of | | EDF | The "Empirical Distribution Function" of a set of |
| | scalar measurements is a function F(x) which for | | | scalar measurements is a function F(x) which for |
skipping to change at page 39, line 13 skipping to change at page 38, line 30
Table 2 Table 2
Authors' Addresses Authors' Addresses
Ruediger Geib (editor) Ruediger Geib (editor)
Deutsche Telekom Deutsche Telekom
Heinrich Hertz Str. 3-7 Heinrich Hertz Str. 3-7
Darmstadt, 64295 Darmstadt, 64295
Germany Germany
Phone: +49 6151 628 2747 Phone: +49 6151 58 12747
Email: Ruediger.Geib@telekom.de Email: Ruediger.Geib@telekom.de
Al Morton Al Morton
AT&T Labs AT&T Labs
200 Laurel Avenue South 200 Laurel Avenue South
Middletown, NJ 07748 Middletown, NJ 07748
USA USA
Phone: +1 732 420 1571 Phone: +1 732 420 1571
Fax: +1 732 368 1192 Fax: +1 732 368 1192
skipping to change at page 39, line 37 skipping to change at page 39, line 14
Reza Fardid Reza Fardid
Cariden Technologies Cariden Technologies
888 Villa Street, Suite 500 888 Villa Street, Suite 500
Mountain View, CA 94041 Mountain View, CA 94041
USA USA
Phone: Phone:
Email: rfardid@cariden.com Email: rfardid@cariden.com
Alexander Steinmitz Alexander Steinmitz
HS Fulda Deutsche Telekom
Marquardstr. 35 Memmelsdorfer Str. 209b
Fulda, 36039 Bamberg, 96052
Germany Germany
Phone: Phone:
Email: steinionline@gmx.de Email: Alexander.Steinmitz@telekom.de
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