Network Working Group E. Stephan
Internet Draft France Telecom R&D
Document: draft-stephan-ippm-spatial-metrics-00.txt
Category: Informational Sept 12, 2002
IPPM spatial metrics measurement
Status of this Memo
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Abstract
The IETF IP Performance Metrics (IPPM) working group has standardized
metrics for measuring end to end performance. Measurements system
scope is often limited to administrative boundaries. This memo
defines spatial metrics both for measuring end-to-end network
performance using aggregation of sequence of network measures and for
measuring the performance of segment of an IP path trajectory. It
distinguishes clearly the decomposition of one end-to-end measure
result in a sequence of per hop results from the aggregation of a
sequence of per hop measure results in an end-to-end result.
Table of Contents
1. Introduction................................................2
2. Terminology.................................................3
2.1. Spatial metric..............................................3
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2.2. Asynchronous spatial metrics................................3
2.3. Trajectory..................................................3
3. Motivation..................................................3
3.1. Instantaneous end to end measure decomposition..............3
3.2. End-to-end measures aggregation.............................4
4. Metrics for end-to-end measure decomposition................4
4.1. Spatial one way delay.......................................4
4.2. One way delay Trajectory metric.............................5
4.3. Aggregated One way delay metric.............................6
5. Metrics for end-to-end measures aggregation.................7
5.1. Asynchronous One way delay Trajectory metric................7
5.2. Asynchronous Aggregated One way delay metric................7
6. Spatial Packet loss metrics.................................8
7. Spatial ipdv metrics........................................8
8. Security Considerations.....................................8
8.1. Privacy.....................................................8
8.2. Measurement aspects.........................................8
9. Issues......................................................9
10. Acknowledgments.............................................9
11. Author's Addresses..........................................9
1. Introduction
The metrics specified derivate from those standardized by IPPM
Working Group. There are built on notions introduced and discussed
in the IPPM Framework document, RFC 2330 [2]. The reader should be
familiar with these documents.
The IPPM Framework consists in 4 major components:
+ A general framework for defining performance metrics, described in
the Framework for IP Performance Metrics, RFC 2330;
+ A set of standardized metrics, which conform to this framework.
The IPPM Metrics for Measuring Connectivity, RFC 2678 [3]. The One-
way Delay Metric for IPPM, RFC 2679 [4]. The One-way Packet Loss
Metric for IPPM, RFC 2680 [5]. The Round-trip Delay Metric for IPPM,
RFC 2681 [6];
+ Emerging metrics which are being specified in respect of this
framework;
+ A Reporting MIB to exchange the results of the measures. It is an
interface between a system of measure and the administrative
entities interested in these results. This proxy controls the access
to the results. These entities use the results to compute statistics
and aggregated metrics.
The structure of the memo is as follows:
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+ A 'singleton' analytic metric, called Type-P-spatial-one-way-
delay, will be introduced to measure the one-way delay between 2
consecutive hosts of an IP path.
+ Using this singleton metric, a 'sample', called Type-P-one-way-
delay-trajectory, will be introduced to measure the sequence of
Type-P-spatial-one-way-delay of the successive pair of hosts of the
path.
+ Using this sample the end to end metric, called Type-P-
aggregated-one-way-delay, is defined to measure the end to end
delay.
+ Using the Type-P-one-way-delay metric, the Type-P-spatial-one-
way-delay metric, the Type-P-aggregated-one-way-delay metric and the
Type-P-asynchronous-aggregated-one-way-delay metric, a 'sample',
called Type-P-asynchronous-one-way-delay-trajectory, will be
introduced to measure the sequence of delays of a sequence of clouds
of an IP path.
+ Using this sample the end to end metric, called Type-P-
asynchronous-aggregated-one-way-delay, is defined to measure the end
to end delay.
2. Terminology
2.1. Spatial metric
A metric is spatial if one of the hosts involved is neither the
sender nor the destination of the measurement packet.
2.2. Asynchronous spatial metrics
A spatial metric is named asynchronous if its definition involves
different measurement packets.
2.3. Trajectory
A trajectory is a sequence of hosts of an IP path. All the hosts of
the path may not be present in the sequence.
3. Motivation
3.1. Instantaneous end to end measure decomposition
There is a need to standardize spatial metrics to permit the
decomposition of standard end-to-end measures.
+ for locating delay consumption in a IP path;
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+ for locating the loss of packets on an IP path;
+ for trajectory discovery;
+ for troubleshooting the network;
+ for designing and engineering the networks;
+ for measuring the performance of a multicast network;
+ for controlling the performance of the inter domain services.
These metrics have to be standardized to permit their results to be
collected in the IPPM REPORTING MIB.
3.2. End-to-end measures aggregation
The IPPM WG has designed metrics for measuring end-to-end
performance. There is not currently standard IP measurement packets
to perform inter domain end-to-end measures. They may only be
performed using aggregation of sequence of intra domain measure
results. To permit interdomain end-to-end measure results
aggregations there is a need to standardize spatial metrics
+ for delay aggregation;
+ for packet loss aggregation;
+ for jitter aggregation.
These metrics have to be standardized to permit their results to be
collected in the IPPM REPORTING MIB.
4. Metrics for end-to-end measure decomposition
4.1. Spatial one way delay
4.1.1. Metric Name
Type-P-spatial-one-way-delay
4.1.2. Metric Parameters
+ H0, the address of the sender.
+ Hn, the address of the receiver.
+ I, An integer which ordered the hosts in the path.
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+ Hi, exchange points of the path digest.
+ T0, a time.
+ T1,..., Tn a list of time.
+ dT1,..., dTn a list of time.
+ P, the specification of the packet type.
+
a path digest.
4.1.3. Metric Units
The unit is the same as the singleton Type-P-One-way-Delay defined
in [4]. The value of a Type-P-spatial-One-way-Delay is either a real
number, or an undefined (informally, infinite) number of seconds.
4.1.4. Definition
Given a Type P packet sent by the source H0 at T0 to Hn in the path
, given the sequence of time
of arrival of the packets in , a Type-P-spatial-one-way-delay metric is defined for a hop of
the path as following:
For a real number dTi, the Type-P-spatial-one-way-delay from Hi to
Hi+1 at Ti is dTi means that Hi saw the first bit of a Type-P packet
to Hi+1 at wire-time Ti and that Hi+1 saw the last bit of that
packet at wire-time Ti+dTi.
4.2. One way delay Trajectory metric
4.2.1. Metric Name
Type-P-one-way-delay-trajectory
4.2.2. Metric Parameters
+ H0, the address of the sender.
+ Hn, the address of the receiver.
+ I, An integer which ordered the hosts in the path.
+ Hi, exchange points of the path digest.
+ T0, a time.
+ dT1,..., dTn a list of time.
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+ P, the specification of the packet type.
+ a path digest.
4.2.3. Metric Units
A sequence of time.
4.2.4. Definition
Given a Type-P packet sent by the source H0 at T0 to Hn in the path
, given the sequence of time
of arrival of the packet in , a Type-P-one-way-delay-trajectory metric is defined as the
sequence of the Type-P-spatial-one-way-delay values
4.3. Aggregated One way delay metric
4.3.1. Metric Name
Type-P-aggregated-one-way-delay
4.3.2. Metric Parameters
+ H0, the address of the sender.
+ Hn, the address of the receiver.
+ T0, a time.
+ dT1,..., dTn a list of time.
+ P, the specification of the packet type.
+ a trajectory.
4.3.3. Metric Units
A time.
4.3.4. Definition
Given a Type-P-one-way-delay-trajectory metric value
of the trajectory performed using a single
measurement packet of type P sent at the time T0 by H0, a Type-P-
aggregated-one-way-delay metric is defined as the sum of each term
of the Type-P-one-way-delay-trajectory.
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4.3.5. Discussion
A Type-P-aggregated-one-way-delay measure is performed during a Type-
P-one-way-delay measure. As they measure the performance of the same
measurement packet the result of a Type-P-aggregated-one-way-delay
measure should be identical to the result of the Type-P-one-way-delay
measure.
Practically these results will differ.
5. Metrics for end-to-end measures aggregation
5.1. Asynchronous One way delay Trajectory metric
5.1.1. Metric Name
Type-P-asynchronous-one-way-delay-trajectory
5.1.2. Metric Parameters
+ H0...Hn, the addresses of the hosts
+ I, An integer which ordered the hosts in the path.
+ Hi, exchange points of the path digest.
+ P, the specification of the packet type.
5.1.3. Metric Units
A sequence of time.
5.1.4. Definition
Given the hops , ... , given the Type-P-
one-way-delay Ti from Hi to Hi+1 or the Type-P-spatial-one-way-delay
Ti from Hi to Hi+1 or the Type-P-aggregated-one-way-delay Ti from Hi
to Hi+1 or the Type-P-asynchronous-aggregated-one-way-delay Ti from
Hi to Hi+1, a Type-P-asynchronous-one-way-delay-trajectory metric is
defined as the sequence of the values .
5.2. Asynchronous Aggregated One way delay metric
5.2.1. Metric Name
Type-P-asynchronous-aggregated-one-way-delay
5.2.2. Metric Parameters
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+ T1,..., Tn a list of time.
5.2.3. Metric Units
A time.
5.2.4. Definition
Given a Type-P-asynchronous-one-way-delay-trajectory metric
value, a Type-P-asynchronous-aggregated-one-way-delay
metric is defined as the sum of each term of the Type-P-
asynchronous-one-way-delay-trajectory.
6. Spatial Packet loss metrics
TO BE SPECIFIED
7. Spatial ipdv metrics
TO BE SPECIFIED
8. Security Considerations
Since this draft proposes sample metrics based on the One-way Delay
singleton metric defined in RFC2679 and RFC2680 it inherits the
security considerations mentioned in this RFC.
8.1. Privacy
The privacy concerns of network measurement are intrinsically
limited by the active measurements. Unlike passive measurements,
there can be no release of existing user data.
8.2. Measurement aspects
Conducting Internet measurements raises both security and privacy
concerns. This memo does not specify an implementation of the
metrics, so it does not directly affect the security of the Internet
nor of applications which run on the Internet. However,
implementations of these metrics must be mindful of security and
privacy concerns.
There are two types of security concerns: potential harm caused by
the measurements, and potential harm to the measurements. The
measurements could cause harm because they are active, and inject
packets into the network. The measurement parameters MUST be
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carefully selected so that the measurements inject trivial amounts
of additional traffic into the networks they measure. If they inject
"too much" traffic, they can skew the results of the measurement,
and in extreme cases cause congestion and denial of service.
The measurements themselves could be harmed by routers giving
measurement traffic a different priority than "normal" traffic, or
by an attacker injecting artificial measurement traffic. If routers
can recognize measurement traffic and treat it separately, the
measurements will not reflect actual user traffic. If an attacker
injects artificial traffic that is accepted as legitimate, the loss
rate will be artificially lowered. Therefore, the measurement
methodologies SHOULD include appropriate techniques to reduce the
probability measurement traffic can be distinguished from "normal"
traffic.
Authentication techniques, such as digital signatures, may be used
where appropriate to guard against injected traffic attacks.
9. Issues
Complete the terminology section.
Define the trajectory packet loss metrics and corresponding
statistics.
Define the trajectory ipdv metrics.
10. Acknowledgments
11. Author's Addresses
Emile STEPHAN
France Telecom R & D
2 avenue Pierre Marzin
F-22307 Lannion cedex
Phone: (+ 33) 2 96 05 11 11
Email: emile.stephan@francetelecom.com
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