Network Working Group E. Stephan
Internet-Draft France Telecom
Expires: April 25, 2006 L. Liang
University of Surrey
A. Morton
AT&T Labs
October 22, 2005
IP Performance Metrics (IPPM) for spatial and multicast
draft-stephan-ippm-multimetrics-02.txt
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Copyright (C) The Internet Society (2005).
Abstract
The IETF IP Performance Metrics (IPPM) working group has standardized
metrics for measuring end-to-end performance between 2 points. This
memo defines 2 sets of metrics to extend these end-to-end ones. It
defines spatial metrics for measuring the performance of segments
along a path and metrics for measuring the performance of a group of
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users in multiparty communications.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1 Multiparty metric . . . . . . . . . . . . . . . . . . . . 5
2.2 Spatial metric . . . . . . . . . . . . . . . . . . . . . . 5
2.3 Spatial metric points of interest . . . . . . . . . . . . 5
2.4 One-to-group metric . . . . . . . . . . . . . . . . . . . 5
2.5 One-to-group metric points of interest . . . . . . . . . . 5
2.6 Reference point . . . . . . . . . . . . . . . . . . . . . 5
3. Motivations for spatial and one-to-group metrics . . . . . . . 6
3.1 spatial metrics . . . . . . . . . . . . . . . . . . . . . 6
3.2 one-to-group metrics . . . . . . . . . . . . . . . . . . . 7
3.3 Discussion on Group-to-one and Group-to-group metrics . . 7
4. Spatial metrics definitions . . . . . . . . . . . . . . . . . 8
4.1 A Definition for Spatial One-way Delay Stream . . . . . . 8
4.2 A Definition of a sample of One-way Delay of a sub path . 11
4.3 A Definition for Spatial One-way Packet Loss Stream . . . 14
4.4 A Definition for Spatial One-way Jitter Stream . . . . . . 15
4.5 Discussion on pure passive measurement of spatial
metrics . . . . . . . . . . . . . . . . . . . . . . . . . 17
4.6 Discussion on spatial statistics . . . . . . . . . . . . . 18
5. One-to-group metrics definitions . . . . . . . . . . . . . . . 18
5.1 A Definition for one-to-group One-way Delay Stream . . . . 18
5.2 A Definition for one-to-group One-way Packet Loss
Stream . . . . . . . . . . . . . . . . . . . . . . . . . . 19
5.3 A Definition for one-to-group One-way Jitter Stream . . . 20
5.4 Discussion on one-to-group statistics . . . . . . . . . . 21
6. Open issues . . . . . . . . . . . . . . . . . . . . . . . . . 23
7. Security Considerations . . . . . . . . . . . . . . . . . . . 23
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 24
9.1 Normative References . . . . . . . . . . . . . . . . . . . 24
9.2 Informative References . . . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 25
Intellectual Property and Copyright Statements . . . . . . . . 27
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1. Introduction
The metrics specified in this memo are built on notions introduced
and discussed in the IPPM Framework document, RFC 2330 [RFC2330].
The reader should be familiar with these documents.
This memo makes use of definitions of end-to-end One-way Delay
Metrics defined in the RFC 2679 [RFC2679] to define metrics for
decomposition of end-to-end one-way delays measurements.
This memo makes use of definitions of end-to-end One-way Packet loss
Metrics defined in the RFC 2680 [RFC2680] to define metrics for
decomposition of end-to-end one-way packet loss measurements.
The IPPM WG defined a framework for metric definitions and end-to-end
measurements:
o A general framework for defining performance metrics, described in
the Framework for IP Performance Metrics, RFC 2330 [RFC2330];
o A One-way Active Measurement Protocol Requirements, RFC 3763
[RFC3763];
o A One-way Active Measurement Protocol (OWAMP) [work in progress];
o An IP Performance Metrics Registry , RFC 4148 [RFC4148];
It specified a set of end-to-end metrics, which conform to this
framework:
o The IPPM Metrics for Measuring Connectivity, RFC 2678 [RFC2678];
o The One-way Delay Metric for IPPM, RFC 2679 [RFC2679];
o The One-way Packet Loss Metric for IPPM, RFC 2680 [RFC2680];
o The Round-trip Delay Metric for IPPM, RFC 2681 [RFC2681];
o A Framework for Defining Empirical Bulk Transfer Capacity Metrics
RFC 3148 [RFC3148];
o One-way Loss Pattern Sample Metrics, RFC 3357 [RFC3357];
o IP Packet Delay Variation Metric for IPPM, RFC 3393 [RFC3393];
o Network performance measurement for periodic streams, RFC 3432
[RFC3432];
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o Packet Reordering Metric for IPPM [Work in progress];
Based on these works, this memo defines 2 kinds of multi party
metrics.
Firstly it defines spatial metrics:
o A 'sample', called Type-P-Spatial-One-way-Delay-Stream, will be
introduced to decompose an end-to-end Type-P-One-way-Delay in a
spatial sequence of one-way delays.
o A 'sample', called Type-P-Spatial-One-way-Packet-Loss-Stream, will
be introduced to decompose an end-to-end Type-P-One-way-Packet-
Loss in a spatial sequence of packet loss.
o Using the Type-P-Spatial-One-way-Delay-Stream metric, a 'sample',
called Type-P-Spatial-One-way-Jitter-Stream, will be introduced to
decompose an end-to-end Type-P-One-way-ipdv in a spatial sequence
of jitter.
o Using the Type-P-Spatial-One-way-Delay-Stream metric, a 'sample',
called Type-P-subpath-One-way-Delay-Stream, will be introduced to
define the one-way-delay between any host of the path. This
metrics is designed too for pure passive measurement methodology
introduced by PSAMP WG.
Then it defines one-to-group metrics.
o Using one test packet sent from one sender to a group of
receivers, a 'sample', called Type-P-one-to-group-One-way-Delay-
Stream, will be introduced to define the list of Type-P-one-way-
delay between this sender and the group of receivers.
o Using one test packet sent from one sender to a group of
receivers, a 'sample', called Type-P-one-to-group-One-way-Packet-
Loss-Stream, will be introduced to define the list of Type-P-One-
way-Packet-Loss between this sender and the group of receivers
o Using one test packet sent from one sender to a group of
receivers, a 'sample', called Type-P-one-to-group-One-way-Jitter-
Stream, will be introduced to define the list of Type-P-One-way-
ipdv between this sender and the group of receivers
o Then a discussion section presents the set of statistics that may
be computed on the top of these metrics to present the QoS in a
view of a group of users as well as the requirements of relative
QoS on multiparty communications.
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2. Terminology
2.1 Multiparty metric
A metric is said to be multiparty if the definition involved more
than two sources or destinations in the measurements. All multiparty
metrics define a set of hosts called "points of interest", where one
host is the source and other hosts are the measurement collection
points. For example, if the set of points of interest is < ha, hb,
hc, ..., hn >, where ha is the source and < hb, hc, ..., hn > are the
destinations, then measurements may be conducted between < ha, hb>, <
ha, hc>, ..., <ha, hn >.
2.2 Spatial metric
A metric is said to be spatial if one of the hosts involved is
neither the source nor the destination of the metered packet.
2.3 Spatial metric points of interest
Points of interest of a spatial metric are the routers or sibling in
the path between source and destination (in addition to the source
and the destination themself).
2.4 One-to-group metric
A metric is said to be one-to-group if the measured packet is sent by
one source and (potentially) received by several destinations. Thus,
the topology of the communication group can be viewed as a centre-
distributed or server-client topology with the source as the centre/
server in the topology.
2.5 One-to-group metric points of interest
Points of interest of One-to-group metrics are the set of host
destinations receiving packets from the source (in addition to the
source itself).
2.6 Reference point
The centre/server in the one-to-group measurement that is controlled
by network operators can be a very good reference point where
measurement data can be collected for further processing although the
actual measurements have to be carried out at all points of interest.
I.e., the measurement points will be all clients/receivers while the
reference point acts as source for the one-to-group metric. Thus, we
can define the reference point as the host while the statistic
calculation will be carried out.
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3. Motivations for spatial and one-to-group metrics
All IPPM metrics are defined for end-to-end measurement. These
metrics provide very good guides for measurement in the pair
communications. However, further efforts should be put to define
metrics for multiparty measurements such as one to one trajectory
metrics and one to multipoint metrics.
3.1 spatial metrics
Decomposition of instantaneous end-to-end measures is needed:
o The PCE WG is extending existing protocols to permit remote path
computation and path computation quality, including inter domain.
One may say that in intra domain the decomposing the performance
of a path is not whished. However such decomposition is desirable
in interdomain to qualify each AS computation with the initial
request. So it is necessary to define standard spatial metrics
before going further in the computation of inter domain path with
QoS constraint.
o Traffic engineering and troubleshooting applications require
spatial views of the one-way delay consumption, identification of
the location of the lost of packets and the decomposition of the
jitter over the path.
o Monitoring the QoS of a multicast tree, of MPLS point-to-
multipoint and inter-domain communication require spatial
decomposition of the one-way delay, of the packet loss and of the
jitter.
o Composition of metrics is a need to scale in the measurement
plane. The definition of composition metrics is a work in
progress [I-D.morton-ippm-composition]; . Spatial measure give
typically the individual performance of an intra domain segment.
It is the elementary piece of information to exchange for
measuring interdomain performance based on composition of metrics.
o The PSAMP WG defines capabilities to sample packets in a way to to
support measurement. [I-D.boschi-export-perpktinfo]; defines a
method to collect packets information to measure the instantaneous
spatial performance without injecting test traffic. Consequently
it is urgent to define a set of common spatial metrics for passive
and active techniques which respect the IPPM framework [RFC2330].
This need is emphases by the fact that end-to-end spatial
measurement involves the 2 techniques;
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3.2 one-to-group metrics
To understand the connection situation between one source and any one
receiver in the multiparty communication group, we need the
decomposition of instantaneous end-to-end measures. It will give us
very detailed insight into each branch of the routing tree in terms
of node-to-node absolute QoS. It can provide clear and helpful
information for engineers to identify the connection with problems in
a complex multiparty routing tree.
While the node-to-node based spatial measures can provide very useful
data in the view of each connection, we also need measures to present
the performance of a multiparty communication in the view of a group
with consideration that it involves a group of people rather than
two. As a consequence a simple one-way metric cannot describe the
multi-connection situation. We need some new metrics to collect
performance of all the connections for further statistics analysis.
A group of metrics are proposed in this stage named one-to-group
performance metrics based on the unicast metrics defined in IPPM WG.
One-to-group metrics are trying to composite one-way metrics from one
source to a group of destinations to make up new metrics. The
compositions are necessary for judging the network performance of
multiparty communications and can also be used to describe the
difference of the QoS served among a group of users.
One-to-group performance metrics are needed for several reasons:
o For designing and engineering multicast trees and MPLS point-to-
multipoint LSP;
o For evaluating and controlling of the quality of the multicast
services;
o For controlling the performance of the inter domain multicast
services;
o For presenting and evaluating the relative QoS requirements for
the multiparty communications.
3.3 Discussion on Group-to-one and Group-to-group metrics
We note that points of interest can also be selected to define
measurements on Group-to-one and Group-to-group topologies. These
topologies are currently beyond the scope of this memo, because they
would involve multiple packets launched from different sources.
However, we can give some clues here on these two cases.
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The measurements for group-to-one topology can be easily derived from
the one-to-group measurement. The measurement point is the reference
point that is acting as a receiver while all of clients/receivers
defined for one-to-group measurement act as sources in this case.
For the group-to-group connection topology, we can hardly define the
reference point and, therefore, have difficulty to define the
measurement points. However, we can always avoid this confusion by
treating the connections as one-to-group or group-to-one in our
measurements without consideration on how the real communication will
be carried out. For example, if one group of hosts < ha, hb, hc,
..., hn > are acting as sources to send data to another group of
hosts < Ha, Hb, Hc, ..., Hm >, we can always decompose them into n
one-to-group communications as < ha, Ha, Hb, Hc, ..., Hm >, < hb, Ha,
Hb, Hc, ..., Hm >, <hc, Ha, Hb, Hc, ..., Hm >, ..., < hn, Ha, Hb, Hc,
..., Hm >.
4. Spatial metrics definitions
Spatial decomposition metrics are based on standard end-to-end
metrics.
The definition of a spatial metric is coupled with the corresponding
end-to-end metric. The methodoly is based on the measure of the same
test packet and parameters of the corresponding end-to-end metric.
4.1 A Definition for Spatial One-way Delay Stream
This section is coupled with the definition of Type-P-One-way-Delay.
When a parameter from section 3 of [RFC2679] is first used in this
section, it will be tagged with a trailing asterisk.
Sections 3.5 to 3.8 of [RFC2679] give requirements and applicability
statements for end-to-end one-way-delay measurements. They are
applicable to each point of interest Hi involved in the measure.
Spatial one-way-delay measurement SHOULD be respectful of them,
especially those related to methodology, clock, uncertainities and
reporting.
Following we adapt some of them and introduce points specific to
spatial measurement.
4.1.1 Metric Name
Type-P-Spatial-One-way-Delay-Stream
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4.1.2 Metric Parameters
+ Src*, the IP address of the sender.
+ Dst*, the IP address of the receiver.
+ i, An integer which ordered the hosts in the path.
+ Hi, exchange points of the path digest.
+ T*, a time, the sending (or initial observation) time for
a measured packet.
+ dT* a delay, the one-way delay for a measured packet.
+ dT1,..., dTn a list of delay.
+ P*, the specification of the packet type.
+ <Src, H1, H2,..., Hn, Dst>, a path digest.
4.1.3 Metric Units
A sequence of times.
4.1.4 Definition
Given a Type-P packet sent by the sender Src at wire-time (first bit)
T to the receiver Dst in the path <H1, H2,..., Hn>. Given the
sequence of values <T+dT1,T+dT2,...,T+dTn,T+dT> such that dT is the
Type-P-One-way-Delay from Src to Dst and such that for each Hi of the
path, T+dTi is either a real number corresponding to the wire-time
the packet passes (last bit received) Hi, or undefined if the packet
never passes Hi.
Type-P-Spatial-One-way-Delay-Stream metric is defined for the path
<Src, H1, H2,..., Hn, Dst> as the sequence of values
<T,dT1,dT2,...,dTn,dT>.
4.1.5 Discussion
Following are specific issues which may occur:
o the delay looks to decrease: dTi > DTi+1. this seem typically du
to some clock synchronisation issue. this point is discussed in
the section 3.7.1. "Errors or uncertainties related to Clocks" of
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of [RFC2679];.
o The location of the point of interest in the device influences the
result (see [I-D.quittek-ipfix-middlebox]). If the packet is not
observed on the input interface the delay includes buffering time
and consequently an uncertainty due to the difference between
'wire time' and 'host time';
4.1.6 Interference with other test packet
To avoid packet collision it is preferable to include a sequence
number in the packet.
4.1.7 loss threshold
To determine if a dTi is defined or undefined it is necessary to
define a period of time after which a packet is considered loss.
4.1.8 Methodologies
Section 3.6 of [RFC2679] gives methodologies for end-to-end one-way-
delay measurements. Most of them apply to each points interest Hi
and are relevant to this section.
Generally, for a given Type-P, in a given Hi, the methodology would
proceed as follows:
o At each Hi, prepare to capture the packet sent a time T, take a
timestamp Ti', determine the internal delay correction dTi',
extract the timestamp T from the packet, then compute the one-way-
delay from Src to Hi: dTi = Ti' - dTi' - T. The one-way delay is
undefined (infinite) if the packet is not detected after the 'loss
threshold' duration;
o Gather the set of dTi of each Hi and order them according to the
path to build the Type-P-Spatial-One-way-Delay-Stream metric
<T,dT1,dT2,...,dTn,dT> over the path <H1, H2,..., Hn>.
It is out of the scope of this document to define how each Hi detects
the packet.
4.1.9 Reporting the metric
Section 3.6 of [RFC2679] indicates the items to report.
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4.1.10 Path
It is clear that a end-to-end Type-P-One-way-Delay can't determine
the list of hosts the packet passes throught. Section 3.8.4 of
[RFC2679] says that the path traversed by the packet SHOULD be
reported but is practically impossible to determine.
This part of the job is provide by Type-P-Spatial-One-way-Delay-
Stream metric because each points of interest Hi which capture the
packet is part of the path.
4.2 A Definition of a sample of One-way Delay of a sub path
This metric is similar to the metric Type-P-One-way-Delay-Poisson-
stream defined in [RFC2679] and to the metric Type-P-One-way-Delay-
Periodic-Stream defined in [RFC3432]
Nevertheless its definition differs because it is based of the
decomposition of end-to-end One-way delay using the metric Type-P-
Spatial-One-way-Delay-Stream defined above.
It aims is to define a sample of One-way-Delay between a pair of
hosts of a path usable by active and passive measurements.
Sections 3.5 to 3.8 of [RFC2679] give requirements and applicability
statements for end-to-end one-way-delay measurements. They are
applicable to each point of interest Hi involved in the measure.
Subpath one-way-delay measurement SHOULD be respectful of them,
especially those related to methodology, clock, uncertainities and
reporting.
4.2.1 Metric Name
Type-P-subpath-One-way-Delay-Stream
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4.2.2 Metric Parameters
+ Src*, the IP address of the sender.
+ Dst*, the IP address of the receiver.
+ i, An integer which orders exchange points in the path.
+ k, An integer which orders the packets sent.
+ <Src, H1, H2,..., Hn, Dst>, a path digest.
+ Ha, a host of the path digest different from Dst and Hb;
+ Hb, a host of the path digest different from Src and Ha.
Hb order in the path must greater that Ha;
+ Hi, exchange points of the path digest.
+ dT1,..., dTn a list of delay.
+ P*, the specification of the packet type.
4.2.3 Metric Units
A sequence of pairs <Tk,dt>.
T is one of time of the sequence T1...Tn;
dT is a delay.
4.2.4 Definition
Given 2 hosts Ha and Hb of the path <Src, H1, H2,..., Hn, Dst>, given
a flow of packets of Type-P sent from Src to Dst at the times T1,
T2... Tn. At each of these times, we obtain a Type-P-Spatial-One-
way-Delay-Stream <T1,dT1.1, dT1.2,..., dT1.n,dT1>. We define the
value of the sample Type-P-subpath-One-way-Delay-Stream as the
sequence made up of the couples <Tk,dTk.b - dTk.a>. dTk.a is the
delay between Src and Ha. dTk.b is the delay between Src and Hb.
'dTk.b - dTk.a' is the one-way delay experienced by the packet sent
at the time Tk by Src when going from Ha to Hb.
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4.2.5 Discussion
Following are specific issues which may occur:
o The definition permits the measure of <Tk,dTk.b - dTk.a> when a is
Src.
o The definition permits the measure of <Tk,dTk.b - dTk.a> when b is
Dst.
o the delay looks to decrease: dTi > DTi+1. this seem typically du
to some clock synchronisation issue. this point is discussed in
the section 3.7.1. "Errors or uncertainties related to Clocks" of
of [RFC2679];.
o The location of the point of interest in the device influences the
result (see [I-D.quittek-ipfix-middlebox]). If the packet is not
observed on the input interface the delay includes buffering time
and consequently an uncertainty due to the difference between
'wire time' and 'host time';
o dTk.b may be observed and not dTk.a.
o Tk is unknown if the flow is made of end user packets, that is
pure passive measure. In this case Tk may be forced to Tk+dTk.a.
This motivate separate metrics names for pure passive measurement
or specific reporting information.
o Pure passive measure should consider packets of the same size and
of the same Type-P.
4.2.6 Interference with other packet
4.2.7 loss threshold
To determine if a dTi is defined or undefined it is necessary to
define a period of time after which a packet is considered loss.
4.2.8 Methodologies
Both active and passive method should discussed.
4.2.9 Reporting the metric
Section 3.6 of [RFC2679] indicates the items to report.
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4.2.10 Path
4.3 A Definition for Spatial One-way Packet Loss Stream
This section is coupled with the definition of Type-P-One-way-Packet-
Loss. Then when a parameter from the section 2 of [RFC2680] is first
used in this section, it will be tagged with a trailing asterisk.
Sections 2.5 to 2.8 of [RFC2680] give requirements and applicability
statements for end-to-end one-way-Packet-Loss measurements. They are
applicable to each point of interest Hi involved in the measure.
Spatial packet loss measurement SHOULD be respectful of them,
especially those related to methodology, clock, uncertainities and
reporting.
Following we define the spatial metric, then we adapt some of the
points above and introduce points specific to spatial measurement.
4.3.1 Metric Name
Type-P-Spatial-One-way-Packet-Loss-Stream
4.3.2 Metric Parameters
+ Src*, the IP address of the sender.
+ Dst*, the IP address of the receiver.
+ i, An integer which ordered the hosts in the path.
+ Hi, exchange points of the path digest.
+ T*, a time, the sending (or initial observation) time for
a measured packet.
+ dT1,..., dTn, dT, a list of delay.
+ P*, the specification of the packet type.
+ <Src, H1, H2,..., Hn, Dst>, a path digest.
+ B1, B2, ..., Bi, ..., Bn, a list of boolean values.
4.3.3 Metric Units
A sequence of boolean values.
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4.3.4 Definition
Given a Type-P packet sent by the sender Src at time T to the
receiver Dst in the path <H1, H2, ..., Hn>. Given the sequence of
times <T+dT1,T+dT2,...,T+dTn,T+dT> the packet passes <H1, H2 ..., Hn,
Dst>,
Type-P-One-way-Packet-Lost-Stream metric is defined as the sequence
of values <B1, B2, ..., Bn> such that for each Hi of the path, a
value of Bi of 0 means that dTi is a finite value, and a value of 1
means that dTi is undefined.
4.3.5 Discussion
Following are specific issues wich may occur:
o the result includes the sequence 1,0. This case means that the
packet was seen by a host but not by it successor on the path;
4.3.6 Discussion
The location of the meter in the device influences the result:
o Even if the packet is received by a device, it may be not observed
by a meter located after a buffer;
4.3.7 Sections in progress
4.4 A Definition for Spatial One-way Jitter Stream
This section uses parameters from the definition of Type-P-One-way-
ipdv. When a parameter from section 2 of [RFC3393] is first used in
this section, it will be tagged with a trailing asterisk.
Sections 3.5 to 3.7 of [RFC3393] give requirements and applicability
statements for end-to-end one-way-ipdv measurements. They are
applicable to each point of interest Hi involved in the measure.
Spatial one-way-ipdv measurement SHOULD be respectful of them,
especially those related to methodology, clock, uncertainities and
reporting.
Following we adapt some of them and introduce points specific to
spatial measurement.
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4.4.1 Metric Name
Type-P-Spatial-One-way-Jitter-Stream
4.4.2 Metric Parameters
+ Src*, the IP address of the sender.
+ Dst*, the IP address of the receiver.
+ i, An integer which ordered the hosts in the path.
+ Hi, exchange points of the path digest.
+ T1*, the time the first packet was sent.
+ T2*, the time the second packet was sent.
+ P, the specification of the packet type.
+ P1, the first packet sent at time T1.
+ P2, the second packet sent at time T2.
+ <Src, H1, H2,..., Hn, Dst>, a path digest.
+ <T1,dT1.1, dT1.2,..., dT1.n,dT1>,
the Type-P-Spatial-One-way-Delay-Stream for packet sent at
time T1;
+ <T2,dT2.1, dT2.2,..., dT2.n,dT2>,
the Type-P-Spatial-One-way-Delay-Stream for packet sent at
time T2;
+ L*, a packet length in bits. The packets of a Type P
packet stream from which the
Type-P-Spatial-One-way-Delay-Stream metric is taken MUST
all be of the same length.
4.4.3 Metric Units
A sequence of times.
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4.4.4 Definition
Given the Type-P packet having the size L and sent by the sender Src
at wire-time (first bit) T1 to the receiver Dst in the path <H1,
H2,..., Hn>.
Given the Type-P packet having the size L and sent by the sender Src
at wire-time (first bit) T2 to the receiver Dst in the same path.
Given the Type-P-Spatial-One-way-Delay-Stream <T1,dT1.1, dT1.2,...,
dT1,n,dT1> of the packet P1.
Given the Type-P-Spatial-One-way-Delay-Stream <T2,dT2.1, dT2.2,...,
dT2,n,dT2> of the packet P2.
Type-P-Spatial-One-way-Jitter-Stream metric is defined as the
sequence of values <T2-T1,dT2.1-dT1.1,dT2.2-dT1.2,...,dT2.n-
dT1.n,dT2-dT1> Such that for each Hi of the path <H1, H2,..., Hn>,
dT2.i-dT1.i is either a real number if the packets P1 and P2 passes
Hi at wire-time (last bit) dT1.i, respectively dT2.i, or undefined if
at least one of them never passes Hi. T2-T1 is the inter-packet
emission interval and dT2-dT1 is ddT* the Type-P-One-way-ipdv at
T1,T2*.
4.4.5 Sections in progress
See sections 3.5 to 3.7 of [RFC3393].
4.5 Discussion on pure passive measurement of spatial metrics
Spatial metrics may be measured without injecting test traffic as
described in [I-D.boschi-export-perpktinfo] even if such a technique
have some limitations.
o The packet is not a test packet, so it does not include the time
it was sent. Consequently a point of interest Hi ignores the time
the packet was send. So It is not possible to measure the first
hop delay. The collector ignores the time the packet was
received. So it is not possible to measure the last hop delay.
One might says that most of the operational issues occur in the
last mile and that consequently such measure are not
useful.Nevertheless they are usable for network TE and interdomain
QoS monitoring.
o The collector ignores the time the packet was send. So It is not
possible to determine that it is lost.
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o A point of interest Hi ignores the time the packet is send because
the packet does not carry the time it was injected in the network.
So a probe Hi can not compute dTi.
An alternative to these issues consist in considering that T is the
time when H1 (the first passive probe of the path) observed the
packet.
To avoid misunderstanding and to address specific reporting
constraint a proposal consists in defining distinct metrics for pure
passive measurement based on the definition above. Having distinct
metrics identifiers for spatial metrics and passive spatial metrics
in the [RFC4148] will avoid interoperabily issues. They may be named
o Type-P-Passive-One-way-delay-Stream
o Type-P-Passive-One-way-Packet-Loss-Stream
o Type-P-Passive-One-way-jitter-Stream
4.6 Discussion on spatial statistics
Do we define min, max, avg of spatial metrics ?
having the maximum loss metric value could be interesting. Say,
the segment between router A and B always contributes loss metric
value of "1" means it could be the potential problem segment.
Uploading dTi of each Hi consume a lot of bandwidth. Computing
statistics (min, max and avg) of dTi locally in each Hi reduce the
bandwidth consumption.
5. One-to-group metrics definitions
5.1 A Definition for one-to-group One-way Delay Stream
5.1.1 Metric Name
Type-P-one-to-group-One-way-Delay-Stream
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5.1.2 Metric Parameters
+ Src, the IP address of a host acting as the source.
+ Recv1,..., RecvN, the IP addresses of the N hosts acting as
receivers.
+ T, a time.
+ dT1,...,dTn a list of time.
+ P, the specification of the packet type.
5.1.3 Metric Units
The value of a Type-P-one-to-group-One-way-Delay-Stream is a set of
singletons metrics Type-P-One-way-Delay [RFC2679].
5.1.4 Definition
Given a Type P packet sent by the source Src at Time T, given the N
hosts { Recv1,...,RecvN } which receive the packet at the time {
T+dT1,...,T+dTn }, a Type-P-one-to-group-One-way-Delay-Stream is
defined as the set of the Type-P-One-way-Delay singleton between Src
and each receiver with value of { dT1, dT2,...,dTn }.
5.2 A Definition for one-to-group One-way Packet Loss Stream
5.2.1 Metric Name
Type-P-one-to-group-One-way-Packet-Loss-Stream
5.2.2 Metric Parameters
+ Src, the IP address of a host acting as the source.
+ Recv1,..., RecvN, the IP addresses of the N hosts acting as
receivers.
+ T, a time.
+ T1,...,Tn, a list of time.
+ P, the specification of the packet type.
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5.2.3 Metric Units
The value of a Type-P-one-to-group-One-way-Packet-Loss-Stream is a
set of singletons metrics Type-P-One-way-Packet-Loss [RFC2680].
5.2.4 Definition
Given a Type P packet sent by the source Src at T and the N hosts,
Recv1,...,RecvN, which should receive the packet at T1,...,Tn, a
Type-P-one-to-group-One-way-Packet-Loss-Stream is defined as a set of
the Type-P-One-way-Packet-Loss singleton between Src and each of the
receivers {<T1,0|1>,<T2,0|1>,..., <Tn,0|1>}.
5.3 A Definition for one-to-group One-way Jitter Stream
5.3.1 Metric Name
Type-P-one-to-group-One-way-Jitter-Stream
5.3.2 Metric Parameters
+ Src, the IP address of a host acting as the source.
+ Recv1,..., RecvN, the IP addresses of the N hosts acting as
receivers.
+ T1, a time.
+ T2, a time.
+ ddT1,...,ddTn, a list of time.
+ P, the specification of the packet type.
+ F, a selection function defining unambiguously the two
packets from the stream selected for the metric.
5.3.3 Metric Units
The value of a Type-P-one-to-group-One-way-Jitter-Stream is a set of
singletons metrics Type-P-One-way-ipdv [RFC3393].
5.3.4 Definition
Given a Type P packet stream, Type-P-one-to-group-One-way- Jitter-
Stream is defined for two packets from the source Src to the N hosts
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{Recv1,...,RecvN },which are selected by the selection function F, as
the difference between the value of the Type-P-one-to-group-One-way-
Delay-Stream from Src to { Recv1,..., RecvN } at time T1 and the
value of the Type-P-one-to-group- One-way-Delay-Stream from Src to {
Recv1,...,RecvN } at time T2. T1 is the wire-time at which Scr sent
the first bit of the first packet, and T2 is the wire-time at which
Src sent the first bit of the second packet. This metric is derived
from the Type-P-one-to- group-One-way-Delay-Stream metric.
Therefore, for a set of real number {ddT1,...,ddTn},Type-P-one- to-
group-One-way-Jitter-Stream from Src to { Recv1,...,RecvN } at T1, T2
is {ddT1,...,ddTn} means that Src sent two packets, the first at
wire-time T1 (first bit), and the second at wire-time T2 (first bit)
and the packets were received by { Recv1,...,RecvN } at wire-time
{dT1+T1,...,dTn+T1}(last bit of the first packet), and at wire-time
{dT'1+T2,...,dT'n+T2} (last bit of the second packet), and that
{dT'1-dT1,...,dT'n-dTn} ={ddT1,...,ddTn}.
5.4 Discussion on one-to-group statistics
The defined one-to-group metrics above can all be directly achieved
from the relevant unicast one-way metrics. They managed to collect
all unicast measurement results of one-way metrics together in one
profile and sort them by receivers and packets in a multicast group.
They can provide sufficient information regarding the network
performance in terms of each receiver and guide engineers to identify
potential problem happened on each branch of a multicast routing
tree. However, these metrics can not be directly used to
conveniently present the performance in terms of a group and neither
to identify the relative QoS situation.
One may say that no matter how many people join the communication,
the connections can still be treated as a set of one-to-one
connection. However, we might not describe a multiparty
communication by a set of one-way measurement metrics because of the
difficulty for understanding and the lack of convenience. For
instance, an engineer might not describe the connections of a
multiparty online conference in terms of one-to-group one-way delay
for user A and B, B and C, and C and A because people might be
confused. If there are more users in the same communication, the
description might be very long. And he might use the one-way metrics
with worst and the best value to give users an idea of the QoS range
of the service they are providing. But it is not clear enough and
might not be accurate in a large multiparty communication scenario.
From the QoS point of view, the multiparty communication services not
only require the absolute QoS support but also the relative QoS. The
relative QoS means the difference between absolute QoS of all users.
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Directly using the one-way metrics cannot present the relative QoS
situation. However, if we use the variations of all users one-way
parameters, we can have new metrics to measure the difference of the
absolute QoS and hence provide the threshold value of relative QoS
that a multiparty service might demand. A very good example of the
high relative QoS requirement is the online gaming. A very light
worse delay will result in failure in the game. We have to use the
new statistic metrics to define exactly how small the relative delay
the online gaming requires. There are many other services, e.g.
online biding, online stock market, etc., need a rule to judge the
relative QoS requirement. Therefore, we can see the importance of
new statistic metrics to feed this need.
We might use some one-to-group statistic conceptions to present the
group performance and relative QoS. In this stage, we define one-to-
group mean stream and one-to-group variation stream. These
statistics are offered mostly to be illustrative of what could be
done.
One-to-group mean streams are trying to measure the overall QoS for a
multicast group associated to one source. It is a reflection of the
absolute QoS of a multiparty communication service when we treat all
receivers as one customer. It can also present the trend of the
absolute QoS of all receivers, i.e., it shows that most of the
receivers in the multiparty communication service trend to receive an
absolute QoS close to the mean.
One-to-group variation streams are trying to measure how the QoS
varies among all of the users in a multicast group associated to one
source. The word "variation" in this memo is the population standard
deviation. It reflects the relative QoS situation in a multiparty
communication service, i.e., the level of the difference between the
absolute QoS of each receivers.
Using the one-to-group mean and one-to-group variation concepts, we
can have a much clear understand on the QoS of a multiparty
communication service in terms of its trend and range. There can be
mean and variation stream definitions for each of the three one-to-
group metrics defined above. We only present the definition of Type-
P-one-to-group-One-way- Delay-Mean-Stream and Type-P-one-to-group-
One-way-Delay-Variation-Stream as examples in this memo.
5.4.1 Type-P-one-to-group-One-way-Delay-Mean-Stream
Given a Type-P-one-to-group-One-way-Delay-Stream, the mean stream of
all { dT1, dT2,...,dTn } for the packet from Src at time T to {
Recv1,...,RecvN }.
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For example, suppose we take a sample and the results are:
Delay_Stream = <
{T1,...,Tn}
{T'1,...,T'n}
{T''1,...T''n}
>
Then the mean stream would be:
Delay_Mean_Stream = <
DM1
DM2
DM3
>
= <
sum{T1,...,Tn}/n
sum{T'1,...,T'n}/n
sum{T''1,...T''n}/n
>
5.4.2 Type-P-one-to-group-One-way-Delay-Variation-Stream
Given a Type-P-one-to-group-One-way-Delay-Stream, the variation
stream of all { dT1, dT2,...,dTn } for the packet from Src at time T
to { Recv1,...,RecvN }.
We still take the above Delay_Stream as a sample and the variation
stream would be:
Delay_Variation_Stream = <
DV1
DV2
DV3
>
=<
(SUM{(T1-DM1)^2,...,(Tn-DM1)^2)}/n)^(1/2)
(SUM{(T'1-DM2)^2,...,(T'n-DM2)^2)}/n)^(1/2)
(SUM{(T''1-DM3)^2,...,(T''n-DM3)^2)}/n)^(1/2)
>
6. Open issues
7. Security Considerations
Active measumrement: see security section in owd pl, jitter rfcs
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(editor notes: add references).
passive measurement: The rate of packet sampling is controled by hash
funcion. The analysis of such a function to generate packets that
match the hash funcion may lead to a DoS attack toward the collector.
The generation of packets with spoofing adresses may corrupt the
results without any possibility to detect the spoofing.
TODO: one-to-group metrics defined here are not intrusive: they rely
on measures of owd... nevertheless they require collection of
singletons which may overload the network the measurement controller
is attach to.
The one-to-group metrics are derived from one-way metrics and
therefore, they have very close relationship.
8. IANA Considerations
Metrics defined in this memo will be registered in the IANA IPPM
METRICS REGISTRY as described in initial version of the registry
[RFC4148].
9. References
9.1 Normative References
[RFC2330] Paxson, V., Almes, G., Mahdavi, J., and M. Mathis,
"Framework for IP Performance Metrics", RFC 2330,
May 1998.
[RFC2679] Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
Delay Metric for IPPM", RFC 2679, September 1999.
[RFC2680] Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
Packet Loss Metric for IPPM", RFC 2680, September 1999.
[RFC3393] Demichelis, C. and P. Chimento, "IP Packet Delay Variation
Metric for IP Performance Metrics (IPPM)", RFC 3393,
November 2002.
[RFC4148] Stephan, E., "IP Performance Metrics (IPPM) Metrics
Registry", BCP 108, RFC 4148, August 2005.
9.2 Informative References
[I-D.boschi-export-perpktinfo]
Boschi, E. and L. Mark, "Use of IPFIX for Export of Per-
Packet Information", draft-boschi-export-perpktinfo-00
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(work in progress), June 2005.
[I-D.morton-ippm-composition]
Morton, A., "Composition of Metrics",
draft-morton-ippm-composition-00 (work in progress),
July 2005.
[I-D.quittek-ipfix-middlebox]
Quittek, J., "Guidelines for IPFIX Implementations on
Middleboxes", draft-quittek-ipfix-middlebox-00 (work in
progress), February 2004.
[RFC2678] Mahdavi, J. and V. Paxson, "IPPM Metrics for Measuring
Connectivity", RFC 2678, September 1999.
[RFC2681] Almes, G., Kalidindi, S., and M. Zekauskas, "A Round-trip
Delay Metric for IPPM", RFC 2681, September 1999.
[RFC3148] Mathis, M. and M. Allman, "A Framework for Defining
Empirical Bulk Transfer Capacity Metrics", RFC 3148,
July 2001.
[RFC3357] Koodli, R. and R. Ravikanth, "One-way Loss Pattern Sample
Metrics", RFC 3357, August 2002.
[RFC3432] Raisanen, V., Grotefeld, G., and A. Morton, "Network
performance measurement with periodic streams", RFC 3432,
November 2002.
[RFC3763] Shalunov, S. and B. Teitelbaum, "One-way Active
Measurement Protocol (OWAMP) Requirements", RFC 3763,
April 2004.
Authors' Addresses
Stephan Emile
France Telecom Division R&D
2 avenue Pierre Marzin
Lannion, F-22307
Fax: +33 2 96 05 18 52
Email: emile.stephan@francetelecom.com
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Lei Liang
CCSR, University of Surrey
Guildford
Surrey, GU2 7XH
Fax: +44 1483 683641
Email: L.Liang@surrey.ac.uk
Al Morton
200 Laurel Ave. South
Middletown, NJ 07748
USA
Phone: +1 732 420 1571
Email: acmorton@att.com
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