Network Working Group E. Stephan
Internet-Draft France Telecom
Intended status: Standards Track L. Liang
Expires: December 28, 2008 University of Surrey
A. Morton
AT&T Labs
June 26, 2008
IP Performance Metrics (IPPM) for spatial and multicast
draft-ietf-ippm-multimetrics-07
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Abstract
The IETF IP Performance Metrics (IPPM) working group has standardized
metrics for measuring end-to-end performance between two points.
This memo defines two new categories of metrics that extend the
coverage to multiple measurement points. It defines spatial metrics
for measuring the performance of segments of a source to destination
path, and metrics for measuring the performance between a source and
many destinations in multiparty communications (e.g., a multicast
tree).
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Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1. Path Digest Hosts . . . . . . . . . . . . . . . . . . . . 6
2.2. Multiparty metric . . . . . . . . . . . . . . . . . . . . 6
2.3. Spatial metric . . . . . . . . . . . . . . . . . . . . . . 7
2.4. One-to-group metric . . . . . . . . . . . . . . . . . . . 7
2.5. Points of interest . . . . . . . . . . . . . . . . . . . . 7
2.6. Reference point . . . . . . . . . . . . . . . . . . . . . 8
2.7. Vector . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.8. Matrix . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3. Motivations . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.1. Motivations for spatial metrics . . . . . . . . . . . . . 9
3.2. Motivations for One-to-group metrics . . . . . . . . . . . 10
3.3. Discussion on Group-to-one and Group-to-group metrics . . 11
4. Spatial vectors metrics definitions . . . . . . . . . . . . . 11
4.1. A Definition for Spatial One-way Delay Vector . . . . . . 12
4.2. A Definition for Spatial One-way Packet Loss Vector . . . 13
4.3. A Definition for Spatial One-way Ipdv Vector . . . . . . . 14
4.4. Spatial Methodology . . . . . . . . . . . . . . . . . . . 16
5. Spatial Segments metrics definitions . . . . . . . . . . . . . 17
5.1. A Definition of a sample of One-way Delay of a segment
of the path . . . . . . . . . . . . . . . . . . . . . . . 18
5.2. A Definition of a sample of Packet Loss of a segment
of the path . . . . . . . . . . . . . . . . . . . . . . . 19
5.3. A Definition of a sample of ipdv of a segment using
the previous packet selection function . . . . . . . . . . 20
5.4. A Definition of a sample of ipdv of a segment using
the minimum delay selection function . . . . . . . . . . . 22
6. One-to-group metrics definitions . . . . . . . . . . . . . . . 23
6.1. A Definition for One-to-group One-way Delay . . . . . . . 23
6.2. A Definition for One-to-group One-way Packet Loss . . . . 24
6.3. A Definition for One-to-group One-way Ipdv . . . . . . . . 25
7. One-to-Group Sample Statistics . . . . . . . . . . . . . . . . 26
7.1. Discussion on the Impact of packet loss on statistics . . 28
7.2. General Metric Parameters . . . . . . . . . . . . . . . . 29
7.3. One-to-Group one-way Delay Statistics . . . . . . . . . . 30
7.4. One-to-Group one-way Loss Statistics . . . . . . . . . . . 32
7.5. One-to-Group one-way Delay Variation Statistics . . . . . 34
8. Measurement Methods: Scalability and Reporting . . . . . . . . 35
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8.1. Computation methods . . . . . . . . . . . . . . . . . . . 36
8.2. Measurement . . . . . . . . . . . . . . . . . . . . . . . 37
8.3. Effect of Time and Space Aggregation Order on Stats . . . 37
9. Manageability Considerations . . . . . . . . . . . . . . . . . 38
9.1. Reporting spatial metric . . . . . . . . . . . . . . . . . 39
9.2. Reporting One-to-group metric . . . . . . . . . . . . . . 40
9.3. Metric identification . . . . . . . . . . . . . . . . . . 40
9.4. Information model . . . . . . . . . . . . . . . . . . . . 41
10. Security Considerations . . . . . . . . . . . . . . . . . . . 43
10.1. Spatial metrics . . . . . . . . . . . . . . . . . . . . . 43
10.2. one-to-group metric . . . . . . . . . . . . . . . . . . . 43
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 44
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 44
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 48
13.1. Normative References . . . . . . . . . . . . . . . . . . . 48
13.2. Informative References . . . . . . . . . . . . . . . . . . 49
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 49
Intellectual Property and Copyright Statements . . . . . . . . . . 50
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1. Introduction
The IETF IP Performance Metrics (IPPM) working group has standardized
metrics for measuring end-to-end performance between two points.
This memo defines two new categories of metrics that extend the
coverage to multiple measurement points. It defines spatial metrics
for measuring the performance of segments of a source to destination
path, and metrics for measuring the performance between a source and
many destinations in multiparty communications (e.g., a multicast
tree).
The purpose of the memo is to define metrics to fulfill the new
requirements of measurement involving multiple measurement points.
Spatial metrics are defined to measure the performance of each
segments along a path while the one-to-group metrics are aiming to
provide a ruler to measure the performance of a group of users.
These metrics are derived from one-way end-to-end metrics defined by
IETF and follow the criteria described in the IPPM framework
[RFC2330].
New terms are introduced to extend the terminology of the IPPM
framework to spatial metrics and one-to-group metrics. Then a
section motivates the need of defining each category of metrics.
After, each category is defined in a separate section. Then the memo
discusses the impact of the measurement methods on the scalability
and proposes an information model for reporting the measurements.
Finally the document discusses security aspects related to
measurement and registers the metrics in the IANA IP Performance
Metrics Registry [RFC4148].
Note that all these metrics are based on observations of packets
dedicated to testing, a process which is called Active measurement.
Purely passive spatial measurement (for example, a spatial metric
based on the observation of user traffic) is beyond the scope of this
memo.
Following is a summary of the metrics defined.
This memo firstly defines metrics for spatial measurement based on
the decomposition of standard end-to-end metrics defined by IETF in
[[RFC2679], [RFC2680], [RFC3393], [RFC3432]. Seven metrics are
defined including their names, parameters, units and measurement
methodologies. Each definion includes a specific section discussing
measurements constraints and issues, and proposing guidance to
increase results accucacy. These spatial metrics are:
o A 'Vector', called Type-P-Spatial-One-way-Delay-Vector, will be
introduced to divide an end-to-end Type-P-One-way-Delay [RFC2679]
into a spatial sequence of one-way delay metrics.
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o A 'Vector', called Type-P-Spatial-One-way-Packet-Loss-Vector, will
be introduced to divide an end-to-end Type-P-One-way-Packet-Loss
[RFC2680] in a spatial sequence of packet loss metrics.
o Using the Type-P-Spatial-One-way-Delay-Vector metric, a 'vector',
called Type-P-Spatial-One-way-ipdv-Vector, will be introduced to
divide an end-to-end Type-P-One-way-ipdv in a spatial sequence of
ipdv metrics.
o Using the Type-P-Spatial-One-way-Delay-Vector metric, a 'sample',
called Type-P-Segment-One-way-Delay-Stream, will be introduced to
collect one-way delay metrics over time between two points of
interest of the path;
o Using the Type-P-Spatial-Packet-Loss-Vector metric, a 'sample',
called Type-P-Segment-Packet-Loss-Stream, will be introduced to
collect packet loss metrics over time between two points of
interest of the path;
o Using the Type-P-Spatial-One-way-Delay-Vector metric, a 'sample',
called Type-P-Segment-ipdv-prev-Stream, will be introduced to
compute ipdv metrics over time between two points of interest of
the path using the previous packet selection function;
o Using the Type-P-Spatial-One-way-Delay-Vector metric, a 'sample',
called Type-P-Segment-ipdv-min-Stream, will be introduced to
compute ipdv metrics over time between two points of interest of
the path using the shortest delay selection function;
Then the memo defines one-to-group metrics and one-to-group
statistics.
Three one-to-group metrics are defined to measure the one-way
performance between a source and a group of receivers. Definitions
derive from one-way metrics definitions of RFCs in [RFC2679],
[RFC2680], [RFC3393], [RFC3432]:
o A 'Vector', called Type-P-One-to-Group-One-way-Delay-Vector, will
be introduced to collect the set of Type-P-one-way-delay
singletons between one sender and N receivers;
o A 'Vector', called Type-P-One-to-Group-One-way-Packet-Loss-Vector,
will be introduced to collect the set of Type-P-One-way-Packet-
Loss singletons between one sender and N receivers;
o A 'Vector', called Type-P-One-to-Group-One-way-ipdv-Vector, will
be introduced to collect the set of Type-P-One-way-ipdv singletons
between one sender and N receivers.
Then, based on the One-to-group vector metrics listed above,
statistics are defined to capture single receiver performance, group
performance and relative performance situation inside a multiparty
communication for each packet sent during the test interval between
one sender and N receivers:
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o Using the Type-P-One-to-Group-One-way-Delay-Vector, a metric
called Type-P-One-to-Group-Receiver-n-Mean-Delay will be
introduced to present the mean of delays between one sender and a
receiver 'n'. Then, based on this definition, 3 metrics will be
defined to characterize the mean delay over the entire group
during this interval:
* a metric called Type-P-One-to-Group-Mean-Delay, will be
introduced to present the mean of delays;
* a metric called Type-P-One-to-Group-Range-Mean-Delay will be
introduced to present the range of mean delays;
* a metric called Type-P-One-to-Group-Max-Mean-Delay will be
introduced to present the maximum of mean delays;
o Using the Type-P-one-to-group-One-way-Packet-Loss-Vector, a metric
called Type-P-One-to-Group-Receiver-n-Loss-Ratio will be
introduced to capture packet loss ratio between one sender and a
receiver 'n'. Then based on this definition, 2 metrics will be
defined to characterize packet loss over the entire group during
this interval:
* a metric called Type-P-One-to-Group-Loss-Ratio will be
introduced to capture packet loss ratio overall over the entire
group or all receivers;
* a metric called Type-P-One-to-Group-Range-Loss-Ratio will be
introduced to present comparative packet loss ratio for each
packet during the test interval between one sender and N
Receivers.
o Using Type-P-one-to-group-One-way-ipdv-Vector, a metric called
Type-P-One-to-Group-Range-Delay-Variation will be introduced to
present the range of delay variation between one sender and a
group of receivers.
2. Terminology
2.1. Path Digest Hosts
The list of the hosts on a path from the source to the destination.
2.2. Multiparty metric
A metric is said to be multiparty if the topology involves more than
one measurement collection point. 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 >.
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For the purposes of this memo (reflecting the scope of a single
source), the only multiparty metrics are one-to-group metrics.
2.3. Spatial metric
A metric is said to be spatial if one of the hosts (measurement
collection points) involved is neither the source nor a destination
of the measured packet.
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. Points of interest
Points of interest are the hosts* (as per RFC2330 definition, that
includes routing nodes) that are measurement collection points, a
sub-set of the set of hosts involved in the delivery of the packets
(in addition to the source itself). Note that the points of interest
are a possibly arbitrary sub-set of all the hosts involved in the
path.
Points of interest of one-to-group metrics are the intended
destination hosts for packets from the source (in addition to the
source itself).
Src Recv
`. ,-.
`. ,' `...... 1
`. ; :
`. ; :
; :... 2
| |
: ;
: ;.... 3
: ;
`. ,'
`-'....... N
Figure 1: One-to-group points of interest
A candidate point of interest for spatial metrics is a host from the
set of hosts involved in the delivery of the packets from the source.
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Src ------. Hosts
\
`---X ... 1
\
x
/
.---------X .... 2
/
x
\
`---X .... 3
\
\
\
X .... N
\
\
\
`---- Dst
Note: 'x' are nodes which are not points of interest
Figure 2: Spatial points of interest
2.6. Reference point
A reference point is defined as the server where the statistical
calculations will be carried out. A centre/server in the
multimetrics measurement that is controlled by a network operator is
a good example of a reference point, where measurement data can be
collected for further processing. However, the actual measurements
have to be carried out at all points of interest.
2.7. Vector
A Vector is a set of singletons, which are a set of results of the
observation of the behaviour of the same packet at different places
of a network at different times. For instance, if one-way delay
singletons observed at N receivers for Packet P sent by the source
Src are dT1, dT2,..., dTN, it can be say that a vector V with N
elements can be organized as {dT1, dT2,..., dTN}. The elements in
one vector are singletons distinct with each other in terms of both
measurement point and sending time. Given the vector V as an
example, the element dT1 is distinct from all others as the singleton
at receiver 1 in response to a packet sent from the source at time
T1. The complete Vector gives information over the dimension of
space.
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2.8. Matrix
Several vectors form a Matrix, which contains results observed in a
sampling interval at different places in a network at different
times. For instance, given One-way delay vectors V1={dT11, dT12,...,
dT1N}, V2={dT21, dT22,..., dT2N},..., Vm={dTm1, dTm2,..., dTmN} for
Packet P1, P2,...,Pm, we can have a One-way delay Matrix {V1,
V2,...,Vm}. Additional to the information given by a Vector, a
Matrix is more powerful to present network performance in both space
and time dimensions. It normally corresponds to a sample in simple
point-to-point measurement.
The relation among Singleton, Vector and Matrix can be shown in the
following Figure 3.
Point of Singleton
interest / Samples
,----. ^ /
/ R1.....| / R1dT1 R1dT2 R1dT3 ... R3dTk \
/ \ | | |
; R2........| | R2dT1 R2dT2 R2dT3 ... R3dTk |
Src | || | |
| R3....| | R3dT1 R3dT2 R3dT3 ... R3dTk |
| || | |
: ;| | |
\ / | | |
\ Rn......| \ RndT1 RndT2 RndT3 ... RndTk /
`-----' +-------------------------------------> time
Vector Matrix
(space) (time)
Figure 3: Relation beween Singletons, vectors and matrix
3. Motivations
All IPPM metrics are defined for end-to-end (source to destination)
measurement of point-to-point paths. It is a logical extension to
define metrics for multiparty measurements such as one to one
trajectory metrics and one to multipoint metrics.
3.1. Motivations for spatial metrics
Decomposition of instantaneous end-to-end measures is needed:
o Decomposing the performance of interdomain path is desirable to
quantify the per-AS contribution to the performance. It is
valuable to define standard spatial metrics before pursuing inter-
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domain path performance specifications.
o Traffic engineering and troubleshooting applications benefit from
spatial views of one-way delay and ipdv consumption, and
identification of the location of the lost of packets.
o Monitoring the performance of a multicast tree composed of MPLS
point-to-multipoint and inter-domain communication require spatial
decomposition of the one-way delay, ipdv, and packet loss.
o Composition of metrics is needed to help measurement systems reach
large scale coverage. Spatial measures typically give the
individual performance of an intra domain segment and provide an
elementary piece of information needed to estimate interdomain
performance based on composition of metrics.
3.2. Motivations for One-to-group metrics
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 topology. A simple
one-way metric cannot completely describe the multiparty situation.
New one-to-group metrics assess performance of all the paths for
further statistical analysis. The new metrics proposed in this stage
are named one-to-group performance metrics, and they are based on the
unicast metrics defined in IPPM WG. One-to-group metrics are one-way
metrics from one source to a group of destinations. The metrics are
helpful for judging the network performance of multiparty
communications and can also be used to describe the variation of
performance delivered to a group of destination hosts and their
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 performance requirements for
multiparty communications and overlay multicast.
To understand the packet transfer performance between one source and
any one receiver in the multiparty communication group, we need to
collect instantaneous end-to-end metrics, or singletons. It will
give a very detailed insight into each branch of the multicast tree
in terms of end-to-end absolute performance. This detail can provide
clear and helpful information for engineers to identify the sub-path
with problems in a complex multiparty routing tree.
The one-to-group metrics described in this memo introduce the
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multiparty topology to the IPPM working group; the goal is to measure
the performance delivered to a group of users who are receiving
packets from the same source. The concept extends the "path" in the
one-way measurement to "path tree" to cover both one-to-one and one-
to-many communications. If applied to one-to-one communications, the
one-to-group metrics provide exactly the same results as the
corresponding one-to-one metrics.
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.
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, it is difficult to define
the reference point and therefore it is difficult 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 vectors metrics definitions
This section defines vectors for the decomposition of end-to-end
singleton metrics over a path.
Spatial vectors metrics are based on the decomposition of standard
end-to-end metrics defined by the IPPM WG in [RFC2679], [RFC2680],
[RFC3393] and [RFC3432].
Definitions are coupled with the corresponding end-to-end metrics.
Methodology specificities are common to all the vectors defined and
are consequently discussed in a common section.
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4.1. A Definition for Spatial One-way Delay Vector
This section is coupled with the definition of Type-P-One-way-Delay
of the section 3 of [RFC2679]. When a parameter of this definition
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, uncertainties and
reporting.
4.1.1. Metric Name
Type-P-Spatial-One-way-Delay-Vector
4.1.2. Metric Parameters
o Src*, the IP address of the sender.
o Dst*, the IP address of the receiver.
o i, An integer in the ordered list <1,2,...,n> of hosts in the
path.
o Hi, A host* of the path digest.
o T*, a time, the sending (or initial observation) time for a
measured packet.
o dT*, a delay, the one-way delay for a measured packet.
o <dT1,..., dTn> a list of delay.
o P*, the specification of the packet type.
o <H1, H2,..., Hn>, hosts path digest.
4.1.3. Metric Units
The value of Type-P-Spatial-One-way-Delay-Vector is 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-Vector metric is defined for the path
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<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 may occur despite
it does not make sense per definition:
* This is frequently due to some clock synchronization issue.
This point is discussed in the section 3.7.1. "Errors or
uncertainties related to Clocks" of [RFC2679]. Consequently,
times of a measure at different hosts do not guaranty the
ordering of the hosts on the path of a measure.
* During some change of routes the order of 2 hosts may change on
the main path;
* The location of the point of interest in the device influences
the result. If the packet is not observed directly on the
input interface the delay includes buffering time and
consequently an uncertainty due to the difference between 'wire
time' and 'host time'
4.2. A Definition for Spatial One-way Packet Loss Vector
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, uncertainties and
reporting.
Following we define the spatial metric, then we adapt some of the
points above and introduce points specific to spatial measurement.
4.2.1. Metric Name
Type-P-Spatial-One-way-Packet-Loss-Vector
4.2.2. Metric Parameters
o Src*, the IP address of the sender.
o Dst*, the IP address of the receiver.
o i, an integer which ordered the hosts in the path.
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o Hi, points of interests of the path digest.
o T*, a time, the sending time for a measured packet.
o <dT1,..., dTn, dT>, a list of delay.
o P*, the specification of the packet type.
o <H1, H2,..., Hn>, hosts path digest.
o <L1, L2, ...,Ln>, a list of Boolean values.
4.2.3. Metric Units
The value of Type-P-Spatial-One-way-Packet-Loss-Vector is a sequence
of Boolean values.
4.2.4. 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> the packet passes in <H1, H2 ..., Hn>,
we define Type-P-One-way-Packet-Lost-Vector metric as the sequence of
values <L1, L2, ..., Ln> such that for each Hi of the path, a value
of 0 for Li means that dTi is a finite value, and a value of 1 means
that dTi is undefined.
4.2.5. Discussion
Following are specific issues which may occur:
o The result includes the sequence 1,0. This may occur under
specific situations:
* During some change of routes a packet may be seen by a host but
not by it successor on the main path;
* A packet may not be observed in a host due to some buffer or
CPU overflow in the point of interest;
4.3. A Definition for Spatial One-way Ipdv Vector
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.
In the following we adapt some of them and introduce points specific
to spatial measurement.
4.3.1. Metric Name
Type-P-Spatial-One-way-ipdv-Vector
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4.3.2. Metric Parameters
o Src*, the IP address of the sender.
o Dst*, the IP address of the receiver.
o i, An integer in the ordered list <1,2,...,n> of hosts in the
path.
o Hi, A host* of the path digest.
o T1*, a time, the sending time for a first measured packet.
o T2*, a time, the sending time for a second measured packet.
o dT*, a delay, the one-way delay for a measured packet.
o P*, the specification of the packets type.
o P1, the first packet sent at time T1.
o P2, the second packet sent at time T2.
o <H1, H2,..., Hn>, hosts path digest.
o <T1,dT1.1, dT1.2,..., dT1.n,dT1>, the Type-P-Spatial-One-way-
Delay-Vector for packet sent at time T1.
o <T2,dT2.1, dT2.2,..., dT2.n,dT2>, the Type-P-Spatial-One-way-
Delay-Vector for packet sent at time T2.
o L*, a packet length in bits. The packets of a Type P packet
stream from which the Type-P-Spatial-One-way-Delay-Vector metric
is taken MUST all be of the same length.
4.3.3. Metric Units
The value of Type-P-Spatial-One-way-ipdv-Vector is a sequence of
times.
4.3.4. Definition
Given P1 the Type-P packet sent by the sender Src at wire-time (first
bit) T1 to the receiver Dst and <T1, dT1.1, dT1.2,..., dT1.n, dT1>
its Type-P-Spatial-One-way-Delay-Vector over the path <H1, H2,...,
Hn>.
Given P2 the Type-P packet sent by the sender Src at wire-time (first
bit) T2 to the receiver Dst and <T2, dT2.1, dT2.2,..., dT2.n, dT2>
its Type-P-Spatial-One-way-Delay-Vector over the same path.
Type-P-Spatial-One-way-ipdv-Vector 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 passe 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*.
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4.4. Spatial Methodology
Methodology, reporting and uncertainties points specified in section
3 of [RFC2679] applies to each point of interest Hi measuring a
element of a spatial delay vector.
Methodology, reporting and uncertainties points specified in section
2 of [RFC2680] applies to each point of interest Hi measuring a
element of a spatial packet loss vector.
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 methodology,
clock, uncertainties and reporting aspects given in this section.
Generally, for a given Type-P of length L, in a given Hi, the
methodology for spatial vector metrics may proceed as follows:
o At each Hi, points of interest prepare to capture the packet sent
a time T, take a timestamp Ti', determine the internal delay
correction dTi' (See section 3.7.1. "Errors or uncertainties
related to Clocks" of [RFC2679]),
o Each Hi extracts the path ordering information from the packet
(e.g. time-to-live);
o Each Hi compute the wiretime from Src to Hi: Ti = Ti' - dTi'.
This arrival time is undefined (infinite) if the packet is not
detected after the 'loss threshold' duration;
o Each Hi extracts the timestamp T from the packet;
o Each Hi computes the one-way-delay from Src to Hi: dTi = Ti - T;
o The reference point gathers the result of each Hi and order them
according to the path ordering information received to build the
type-P spatial one-way vector (e.g. Type-P-Spatial-One-way-Delay-
Vector metric <T, dT1, dT2,..., dTn, dT> ) over the path <Src, H1,
H2,..., Hn, Dst> at time T.
4.4.1. Loss threshold
Loss threshold is the centrality of any methodology because it
determines the presence the packet in the measurement process of the
point of interest and consequently determines any ground truth metric
result. It determines the presence of an effective delay, and bias
the measure of ipdv, of packet loss and of the statistics.
This is consistent for end-to-end but impacts spatial measure:
depending on the consistency of the loss threshold among the points
of interest, a packet may be considered loss a one host but present
in another one, or may be observed by the last host (last hop) of the
path but considered lost by Dst. The analysis of such results is not
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deterministic: Has the path change? Does the packet arrive at
destination or was it lost during the last mile? The same applies,
of course, for one-way-delay measures: a delay measured may be
infinite at one host but a real value in another one, or may be
measured as a real value by the last host of the path but observed as
infinite by Dst. The loss threshold should be set up with the same
value in each host of the path and in the destination. The loss
threshold must be systematically reported to permit careful
introspection and to avoid the introduction of any contradiction in
the statistic computation process.
4.4.2. Host Path Digest
The methodology given above relies on the order of the points of
interest over the path to [RFC2679] one's.
A test packets may cross several times the same host resulting in the
repetition of one or several hosts in the Path Digest.
As an example. This occurs typically during rerouting phases which
introduce temporary micro loops. During such an event the host path
digest for a packet crossing Ha and Hb may include the pattern <Hb,
Ha, Hb, Ha, Hb> meaning that Ha ended the computation of the new path
before Hb and that the initial path wath from Ha to Hb and that the
new path is from Hb to Ha.
Consequently, duplication of hosts in the Path Digest of a vectors
MUST be identified before statistics computation to avoid corrupted
results' production.
5. Spatial Segments metrics definitions
This section defines samples to measure the performance of a segment
of a path over time. Definitions rely on matrix of the spatial
vector metrics defined above.
Firstly it defines a sample of one-way delay, Type-P-Segment-One-way-
Delay-Stream, and a sample of packet loss, Type-P-segment-Packet-
loss-Stream.
Then it defines 2 different samples of ipdv. The first metric, Type-
P-Segment-One-way-ipdv-prev-Stream, uses the previous packet as the
selection function. The second metric, Type-P-Segment-One-way-ipdv-
min-Stream, uses the minimum delay as the selection.
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5.1. A Definition of a sample of One-way Delay of a segment of the path
This metric defines a sample of One-way delays over time between a
pair of hosts of a path.
As its semantic is very close to the metric Type-P-Packet-loss-Stream
defined in section 4 of [RFC2679], sections 4.5 to 4.8 of [RFC2679]
are part of the current definition.
5.1.1. Metric Name
Type-P-Segment-One-way-Delay-Stream
5.1.2. Metric Parameters
o Src*, the IP address of the sender.
o Dst*, the IP address of the receiver.
o P*, the specification of the packet type.
o i, an integer in the ordered list <1,2,...,n> of hosts in the
path.
o k, an integer which orders the packets sent.
o a and b, 2 integers where b > a.
o Hi, a host* of the path digest.
o <H1,..., Ha, ..., Hb, ...., Hn>, hosts path digest.
o <T1, T2, ..., Tm>, a list of times.
5.1.3. Metric Units
The value of a Type-P-Segment-One-way-Delay-Stream is a pair of
list of times <T1, T2, ..., Tm>;
sequence of delays.
5.1.4. Definition
Given 2 hosts, Ha and Hb, of the path <H1, H2,..., Ha, ..., Hb, ...,
Hn>, given the matrix of Type-P-Spatial-One-way-Delay-Vector for the
packets sent from Src to Dst at times <T1, T2, ..., Tm-1, Tm> :
<T1, dT1.1, dT1.2, ..., dT1.a, ..., dT1.b,..., dT1.n, dT1>;
<T2, dT2.1, dT2.2, ..., dT2.a, ..., dT2.b,..., dT2.n, dT2>;
...
<Tm, dTm.1, dTm.2, ..., dTm.a, ..., dTm.b,..., dTm.n, dTm>.
We define the sample Type-P-segment-One-way-Delay-Stream as the
sequence <dT1.ab, dT2.ab, ..., dTk.ab, ..., dTm.ab> such that for
each time Tk, 'dTk.ab' is either the real number 'dTk.b - dTk.a' if
the packet send a time Tk passes Ha and Hb or undefined if this
packet never passes Ha or (inclusive) never passes Hb.
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5.1.5. Discussion
Following are specific issues which may occur:
o the delay looks to decrease: dTi > DTi+1:
* This is typically due to clock synchronization issue. this
point is discussed in the section 3.7.1. "Errors or
uncertainties related to Clocks" of of [RFC2679];
* This may occurs too when the clock resolution of one probe is
bigger than the minimum delay of a path. As an example this
happen when measuring the delay of a path which is 500 km long
with one probe synchronized using NTP having a clock resolution
of 8ms.
The metric can not be performed on < T1 , T2, ..., Tm-1, Tm> in the
following cases:
o Ha or Hb disappears from the path due to some change of routes;
o The order of Ha and Hb changes in the path;
5.2. A Definition of a sample of Packet Loss of a segment of the path
This metric defines a sample of packet lost over time between a pair
of hosts of a path. As its semantic is very close to the metric
Type-P-Packet-loss-Stream defined in section 3 of [RFC2680], sections
3.5 to 3.8 of [RFC2680] are part of the current definition.
5.2.1. Metric Name
Type-P-segment-Packet-loss-Stream
5.2.2. Metric Parameters
o Src*, the IP address of the sender.
o Dst*, the IP address of the receiver.
o P*, the specification of the packet type.
o k, an integer which orders the packets sent.
o n, an integer which orders the hosts on the path.
o a and b, 2 integers where b > a.
o <H1, H2, ..., Ha, ..., Hb, ...,Hn>, hosts path digest.
o Hi, exchange points of the path digest.
o <T1, T2, ..., Tm>, a list of times.
o <L1, L2, ..., Ln> a list of boolean values.
5.2.3. Metric Units
The value of a Type-P-segment-Packet-loss-Stream is a pair of
The list of times <T1, T2, ..., Tm>;
a sequence of booleans.
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5.2.4. Definition
Given 2 hosts, Ha and Hb, of the path <H1, H2,..., Ha, ..., Hb, ...,
Hn>, given the matrix of Type-P-Spatial-Packet-loss-Vector for the
packets sent from Src to Dst at times <T1, T2, ..., Tm-1, Tm> :
<L1.1, L1.2,..., L1.a, ..., L1.b, ..., L1.n, L>,
<L2.1, L2.2,..., L2.a, ..., L2.b, ..., L2.n, L>,
...,
<Lm.1, Lm.2,..., Lma, ..., Lm.b, ..., Lm.n, L>.
We define the value of the sample Type-P-segment-Packet-Lost-Stream
from Ha to Hb as the sequence of booleans <L1.ab, L2.ab,..., Lk.ab,
..., Lm.ab> such that for each Tk:
o A value of Lk of 0 means that Ha and Hb observed the packet sent
at time Tk (Lk.a and Lk.b have a value of 0);
o A value of Lk of 1 means that Ha observed the packet sent at time
Tk (Lk.a has a value of 0) and that Hb did not observed the packet
sent at time Tk (Lk.b have a value of 1);
o The value of Lk is undefined when Neither Ha or Hb observe the
packet;
5.2.5. Discussion
Unlike Type-P-Packet-loss-Stream, Type-P-Segment-Packet-loss-Stream
relies on the stability of the host path digest. The metric can not
be performed on < T1 , T2, ..., Tm-1, Tm> in the following cases:
o Ha or Hb disappears from the path due to some change of routes;
o the order of Ha and Hb changes in the path;
o Lk.a or Lk.b is undefined;
o Lk.a has the value 1 (not observed) and Lk.b has the value 0
(observed);
o L has the value 0 (the packet was received by Dst) and Lk.ab has
the value 1 (the packet was lost between Ha and Hb).
5.3. A Definition of a sample of ipdv of a segment using the previous
packet selection function
This metric defines a sample of ipdv [RFC3393] over time between a
pair of hosts using the previous packet as the selection function.
5.3.1. Metric Name
Type-P-Segment-One-way-ipdv-prev-Stream
5.3.2. Metric Parameters
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o Src*, the IP address of the sender.
o Dst*, the IP address of the receiver.
o P*, the specification of the packet type.
o k, an integer which orders the packets sent.
o n, an integer which orders the hosts on the path.
o a and b, 2 integers where b > a.
o <H1, H2, ..., Ha, ..., Hb, ...,Hn>, the hosts path digest.
o <T1, T2, ..., Tm-1, Tm>, a list of times.
o <Tk, dTk.1, dTk.2, ..., dTk.a, ..., dTk.b,..., dTk.n, dTk>, a
Type-P-Spatial-One-way-Delay-Vector.
5.3.3. Metric Units
The value of a Type-P-Segment-One-way-ipdv-prev-Stream is a pair of:
The list of <T1, T2, ..., Tm-1, Tm>;
A list of pairs of interval of times and delays;
5.3.4. Definition
Given 2 hosts, Ha and Hb, of the path <H1, H2,..., Ha, ..., Hb, ...,
Hn>, given the matrix of Type-P-Spatial-One-way-Delay-Vector for the
packets sent from Src to Dst at times <T1, T2, ..., Tm-1, Tm> :
<T1, dT1.1, dT1.2, ..., dT1.a, ..., dT1.b,..., dT1.n, dT1>,
<T2, dT2.1, dT2.2, ..., dT2.a, ..., dT2.b,..., dT2.n, dT2>,
...
<Tm, dTm.1, dTm.2, ..., dTm.a, ..., dTm.b,..., dTm.n, dTm>.
We define the Type-P-Segment-One-way-ipdv-prev-Stream as the sequence
of pair of packet intervals and delay variations <(dT2_1.a , dT2.ab -
dT1.ab) ,..., (dTk_k-1.a, dTk.ab - dTk-1.ab), ..., (dTm_m-1.a, dTm.ab
- dTm-1.ab)> such that for each Tk:
o dTk_k-1.a is either undefined if the delay dTk.a or the delay
dTk-1.a is undefined, or the interval of time, 'dTk.a - dTk-1.a',
between the 2 packets at Ha;
o dTk_k-1.ab, is either undefined if one of the delays dTk.b, dTk.a,
dTk-1.b or dTk-1.a is undefined, or , (dTk.b - dTk.a) - (dTk-1.b -
dTk-1.a), the delay variation from Ha to Hb between the 2 packets
sent at time Tk and Tk-1.
5.3.5. Discussion
This metric belongs to the family of inter packet delay variation
metrics (IPDV in upper case) which results can be extremely sensitive
to the inter-packet interval.
The inter-packet interval of a end-to-end IPDV metric is under the
control of the ingress point of interest which corresponds exactly to
the Source of the packet. Unlikely, the inter-packet interval of a
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segment IPDV metric is not under the control the ingress point of
interest of the measure, Ha. However, the interval will vary if
there is delay variation between the Source and Ha. Therefore, the
actual inter-packet interval must be known at Ha in order to fully
comprehend the delay variation between Ha and Hb.
5.4. A Definition of a sample of ipdv of a segment using the minimum
delay selection function
This metric defines a sample of ipdv [RFC3393] over time between a
pair of hosts of a path using the shortest delay as the selection
function.
5.4.1. Metric Name
Type-P-Segment-One-way-ipdv-min-Stream
5.4.2. Metric Parameters
o Src*, the IP address of the sender.
o Dst*, the IP address of the receiver.
o P*, the specification of the packet type.
o k, an integer which orders the packets sent.
o i, an integer which identifies a packet sent.
o n, an integer which orders the hosts on the path.
o a and b, 2 integers where b > a.
o <H1, H2, ..., Ha, ..., Hb, ...,Hn>, the hosts path digest.
o <T1, T2, ..., Tm-1, Tm>, a list of times.
o <Tk, dTk.1, dTk.2, ..., dTk.a, ..., dTk.b,..., dTk.n, dTk>, a
Type-P-Spatial-One-way-Delay-Vector.
5.4.3. Metric Units
The value of a Type-P-Segment-One-way-ipdv-min-Stream is a pair of:
The list of <T1, T2, ..., Tm-1, Tm>;
A list of times;
5.4.4. Definition
Given 2 hosts, Ha and Hb, of the path <H1, H2,..., Ha, ..., Hb, ...,
Hn>, given the matrix of Type-P-Spatial-One-way-Delay-Vector for the
packets sent from Src to Dst at times <T1, T2, ..., Tm-1, Tm> :
<T1, dT1.1, dT1.2, ..., dT1.a, ..., dT1.b,..., dT1.n, dT1>,
<T2, dT2.1, dT2.2, ..., dT2.a, ..., dT2.b,..., dT2.n, dT2>,
...
<Tm, dTm.1, dTm.2, ..., dTm.a, ..., dTm.b,..., dTm.n, dTm>.
We define the Type-P-Segment-One-way-ipdv-min-Stream as the sequence
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of times <dT1.ab - min(dTi.ab) ,..., dTk.ab - min(dTi.ab), ...,
dTm.ab - min(dTi.ab)> such that:
min(dTi.ab) is the minimum value of the tuples (dTk.b - dTk.a);
for each time Tk, dTk.ab is undefined if dTk.a or (inclusive)
dTk.b is undefined, or the real number (dTk.b - dTk.a).
5.4.5. Discussion
This metric belongs to the family of packet delay variation metrics
(PDV). PDV distributions are less sensitive to inter-packet interval
variations than IPDV results.
In principle, the PDV distribution reflects the variation over many
different inter-packet intervals, from the smallest inter-packet
interval, up to the length of the evaluation interval, Tm - T1.
Therefore, when delay variation occurs and disturbs the packet
spacing observed at Ha, the PDV results will likely compare favorably
to a PDV measurement where the source is Ha and the destination is
Hb.
6. One-to-group metrics definitions
This metric defines metrics to measure the performance between a
source and a group of receivers.
6.1. A Definition for One-to-group One-way Delay
This metric defines a metric to measure one-way delay between a
source and a group of receivers.
6.1.1. Metric Name
Type-P-One-to-group-One-way-Delay-Vector
6.1.2. Metric Parameters
o Src, the IP address of a host acting as the source.
o Recv1,..., RecvN, the IP addresses of the N hosts acting as
receivers.
o T, a time.
o dT1,...,dTn a list of time.
o P, the specification of the packet type.
o Gr, the receiving group identifier. The parameter Gr is the
multicast group address if the measured packets are transmitted
over IP multicast. This parameter is to differentiate the
measured traffic from other unicast and multicast traffic. It is
optional in the metric to avoid losing any generality, i.e. to
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make the metric also applicable to unicast measurement where there
is only one receiver.
6.1.3. Metric Units
The value of a Type-P-One-to-group-One-way-Delay-Vector is a set of
Type-P-One-way-Delay singletons [RFC2679].
6.1.4. 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-Vector is
defined as the set of the Type-P-One-way-Delay singleton between Src
and each receiver with value of { dT1, dT2,...,dTn }.
6.2. A Definition for One-to-group One-way Packet Loss
6.2.1. Metric Name
Type-P-One-to-group-One-way-Packet-Loss-Vector
6.2.2. Metric Parameters
o Src, the IP address of a host acting as the source.
o Recv1,..., RecvN, the IP addresses of the N hosts acting as
receivers.
o T, a time.
o T1,...,Tn a list of time.
o P, the specification of the packet type.
o Gr, the receiving group identifier.
6.2.3. Metric Units
The value of a Type-P-One-to-group-One-way-Packet-Loss-Vector is a
set of Type-P-One-way-Packet-Loss singletons [RFC2680].
6.2.4. 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-Vector 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>}.
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6.3. A Definition for One-to-group One-way Ipdv
6.3.1. Metric Name
Type-P-One-to-group-One-way-ipdv-Vector
6.3.2. Metric Parameters
o Src, the IP address of a host acting as the source.
o Recv1,..., RecvN, the IP addresses of the N hosts acting as
receivers.
o T1, a time.
o T2, a time.
o ddT1, ...,ddTn, a list of time.
o P, the specification of the packet type.
o F, a selection function defining unambiguously the two packets
from the stream selected for the metric.
o Gr, the receiving group identifier. The parameter Gr is the
multicast group address if the measured packets are transmitted
over IP multicast. This parameter is to differentiate the
measured traffic from other unicast and multicast traffic. It is
optional in the metric to avoid losing any generality, i.e. to
make the metric also applicable to unicast measurement where there
is only one receiver.
6.3.3. Metric Units
The value of a Type-P-One-to-group-One-way-ipdv-Vector is a set of
Type-P-One-way-ipdv singletons [RFC3393].
6.3.4. Definition
Given a Type P packet stream, Type-P-One-to-group-One-way-ipdv-Vector
is defined for two packets from the source Src to the N hosts
{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-Vector from Src to { Recv1,..., RecvN } at time T1 and the
value of the Type-P-One-to-group-One-way-Delay-Vector from Src to {
Recv1,...,RecvN } at time T2. T1 is the wire-time at which Src 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-Vector metric.
Therefore, for a set of real number {ddT1,...,ddTn},Type-P-One-to-
group-One-way-ipdv-Vector 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
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{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}.
7. One-to-Group Sample Statistics
The defined one-to-group metrics above can all be directly achieved
from the relevant unicast one-way metrics. They collect all unicast
measurement results of one-way metrics together in one profile and
sort them by receivers and packets in a receiving group. They
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 cannot be directly used to conveniently
present the performance in terms of a group and neither to identify
the relative performance situation.
From the performance point of view, the multiparty communication
services not only require the absolute performance support but also
the relative performance. The relative performance means the
difference between absolute performance of all users. Directly using
the one-way metrics cannot present the relative performance
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 performance and hence provide the threshold value of
relative performance that a multiparty service might demand. A very
good example of the high relative performance requirement is the
online gaming. A very light difference in delay might result in
failure in the game. We have to use multicast specific 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., that require multicast metrics in order to
evaluate the network against their requirements. Therefore, we can
see the importance of new, multicast specific, statistic metrics to
feed this need.
We might also use some one-to-group statistic conceptions to present
and report the group performance and relative performance to save the
report transmission bandwidth. Statistics have been defined for One-
way metrics in corresponding RFCs. They provide the foundation of
definition for performance statistics. For instance, there are
definitions for minimum and maximum One-way delay in [RFC2679].
However, there is a dramatic difference between the statistics for
one-to-one communications and for one-to-many communications. The
former one only has statistics over the time dimension while the
later one can have statistics over both time and space dimensions.
This space dimension is introduced by the Matrix concept as
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illustrated in Figure 4. For a Matrix M each row is a set of One-way
singletons spreading over the time dimension and each column is
another set of One-way singletons spreading over the space dimension.
Receivers
Space
^
1 | / R1dT1 R1dT2 R1dT3 ... R3dTk \
| | |
2 | | R2dT1 R2dT2 R2dT3 ... R3dTk |
| | |
3 | | R3dT1 R3dT2 R3dT3 ... R3dTk |
. | | |
. | | |
. | | |
n | \ RndT1 RndT2 RndT3 ... RndTk /
+--------------------------------------------> time
T0
Figure 4: Matrix M (n*m)
In Matrix M, each element is a one-way delay singleton. Each column
is a delay vector contains the One-way delays of the same packet
observed at M points of interest. It implies the geographical factor
of the performance within a group. Each row is a set of One-way
delays observed during a sampling interval at one of the points of
interest. It presents the delay performance at a receiver over the
time dimension.
Therefore, one can either calculate statistics by rows over the space
dimension or by columns over the time dimension. It's up to the
operators or service provides which dimension they are interested in.
For example, a TV broadcast service provider might want to know the
statistical performance of each user in a long term run to make sure
their services are acceptable and stable. While for an online gaming
service provider, he might be more interested to know if all users
are served fairly by calculating the statistics over the space
dimension. This memo does not intend to recommend which of the
statistics are better than the other.
To save the report transmission bandwidth, each point of interest can
send statistics in a pre-defined time interval to the reference point
rather than sending every one-way singleton it observed. As long as
an appropriate time interval is decided, appropriate statistics can
represent the performance in a certain accurate scale. How to decide
the time interval and how to bootstrap all points of interest and the
reference point depend on applications. For instance, applications
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with lower transmission rate can have the time interval longer and
ones with higher transmission rate can have the time interval
shorter. However, this is out of the scope of this memo.
Moreover, after knowing the statistics over the time dimension, one
might want to know how this statistics distributed over the space
dimension. For instance, a TV broadcast service provider had the
performance Matrix M and calculated the One-way delay mean over the
time dimension to obtain a delay Vector as {V1,V2,..., VN}. He then
calculated the mean of all the elements in the Vector to see what
level of delay he has served to all N users. This new delay mean
gives information on how good the service has been delivered to a
group of users during a sampling interval in terms of delay. It
needs twice calculation to have this statistic over both time and
space dimensions. We name this kind of statistics 2-level statistics
to distinct with those 1-level statistics calculated over either
space or time dimension. It can be easily prove that no matter over
which dimension a 2-level statistic is calculated first, the results
are the same. I.e. one can calculate the 2-level delay mean using
the Matrix M by having the 1-level delay mean over the time dimension
first and then calculate the mean of the obtained vector to find out
the 2-level delay mean. Or, he can do the 1-level statistic
calculation over the space dimension first and then have the 2-level
delay mean. Both two results will be exactly the same. Therefore,
when define a 2-level statistic, there is no need to specify in which
procedure the calculation should follow.
Comment: The above statement depends on whether the order of
operations has any affect on the outcome.
Many statistics can be defined for the proposed one-to-group metrics
over either the space dimension or the time dimension or both. This
memo treats the case where a stream of packets from the Source
results in a sample at each of the Receivers in the Group, and these
samples are each summarized with the usual statistics employed in
one-to-one communication. New statistic definitions are presented,
which summarize the one-to-one statistics over all the Receivers in
the Group.
7.1. Discussion on the Impact of packet loss on statistics
The packet loss does have effects on one-way metrics and their
statistics. For example, the lost packet can result an infinite one-
way delay. It is easy to handle the problem by simply ignoring the
infinite value in the metrics and in the calculation of the
corresponding statistics. However, the packet loss has so strong
impact on the statistics calculation for the one-to-group metrics
that it can not be solved by the same method used for one-way
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metrics. This is due to the complex of building a Matrix, which is
needed for calculation of the statistics proposed in this memo.
The situation is that measurement results obtained by different end
users might have different packet loss pattern. For example, for
User1, packet A was observed lost. And for User2, packet A was
successfully received but packet B was lost. If the method to
overcome the packet loss for one-way metrics is applied, the two
singleton sets reported by User1 and User2 will be different in terms
of the transmitted packets. Moreover, if User1 and User2 have
different number of lost packets, the size of the results will be
different. Therefore, for the centralized calculation, the reference
point will not be able to use these two results to build up the group
Matrix and can not calculate the statistics. In an extreme
situation, no single packet arrives all users in the measurement and
the Matrix will be empty. One of the possible solutions is to
replace the infinite/undefined delay value by the average of the two
adjacent values. For example, if the result reported by user1 is {
R1dT1 R1dT2 R1dT3 ... R1dTK-1 UNDEF R1dTK+1... R1DM } where "UNDEF"
is an undefined value, the reference point can replace it by R1dTK =
{(R1dTK-1)+( R1dTK+1)}/2. Therefore, this result can be used to
build up the group Matrix with an estimated value R1dTK. There are
other possible solutions such as using the overall mean of the whole
result to replace the infinite/undefined value, and so on. However
this is out of the scope of this memo.
For the distributed calculation, the reported statistics might have
different "weight" to present the group performance, which is
especially true for delay and ipdv relevant metrics. For example,
User1 calculates the Type-P-Finite-One-way-Delay-Mean R1DM as shown
in Figure. 8 without any packet loss and User2 calculates the R2DM
with N-2 packet loss. The R1DM and R2DM should not be treated with
equal weight because R2DM was calculated only based on 2 delay values
in the whole sample interval. One possible solution is to use a
weight factor to mark every statistic value sent by users and use
this factor for further statistic calculation.
7.2. General Metric Parameters
o Src, the IP address of a host;
o G, the receiving group identifier;
o N, the number of Receivers (Recv1, Recv2, ... RecvN);
o T, a time (start of test interval);
o Tf, a time (end of test interval);
o K, the number of packets sent from the source during the test
interval;
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o J[n], the number of packets received at a particular Receiver, n,
where 1<=n<=N;
o lambda, a rate in reciprocal seconds (for Poisson Streams);
o incT, the nominal duration of inter-packet interval, first bit to
first bit (for Periodic Streams);
o T0, a time that MUST be selected at random from the interval [T,
T+I] to start generating packets and taking measurements (for
Periodic Streams);
o TstampSrc, the wire time of the packet as measured at MP(Src) (the
Source Measurement Point);
o TstampRecv, the wire time of the packet as measured at MP(Recv),
assigned to packets that arrive within a "reasonable" time;
o Tmax, a maximum waiting time for packets at the destination, set
sufficiently long to disambiguate packets with long delays from
packets that are discarded (lost), thus the distribution of delay
is not truncated;
o dT, shorthand notation for a one-way delay singleton value;
o L, shorthand notation for a one-way loss singleton value, either
zero or one, where L=1 indicates loss and L=0 indicates arrival at
the destination within TstampSrc + Tmax, may be indexed over n
Receivers;
o DV, shorthand notation for a one-way delay variation singleton
value;
7.3. One-to-Group one-way Delay Statistics
This section defines the overall one-way delay statistics for a
receiver and for an entire group as illustrated by the matrix below.
Recv /----------- Sample -------------\ Stats Group Stat
1 R1dT1 R1dT2 R1dT3 ... R1dTk R1DM \
|
2 R2dT1 R2dT2 R2dT3 ... R2dTk R2DM |
|
3 R3dT1 R3dT2 R3dT3 ... R3dTk R2DM > Group delay
. |
. |
. |
n RndT1 RndT2 RndT3 ... RndTk RnDM /
Receiver-n
delay
Figure 5: One-to-Group Mean Delay
Statistics are computed on the finite One-way delays of the matrix
above.
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All One-to-group delay statistics are expressed in seconds with
sufficient resolution to convey 3 significant digits.
7.3.1. Type-P-One-to-Group-Receiver-n-Mean-Delay
This section defines Type-P-One-to-Group-Receiver-n-Mean-Delay the
Delay Mean at each Receiver N, also named RnDM.
We obtain the value of Type-P-One-way-Delay singleton for all packets
sent during the test interval at each Receiver (Destination), as per
[RFC2679]. For each packet that arrives within Tmax of its sending
time, TstampSrc, the one-way delay singleton (dT) will be the finite
value TstampRecv[i] - TstampSrc[i] in units of seconds. Otherwise,
the value of the singleton is Undefined.
J[n]
---
1 \
RnDM = --- * > TstampRecv[i] - TstampSrc[i]
J[n] /
---
i = 1
Figure 6: Type-P-One-to-Group-Receiver-Mean-Delay
where all packets i= 1 through J[n] have finite singleton delays.
7.3.2. Type-P-One-to-Group-Mean-Delay
This section defines Type-P-One-to-Group-Mean-Delay, the Mean One-way
delay calculated over the entire Group, also named GMD.
N
---
1 \
GMD = - * > RnDM
N /
---
n = 1
Figure 7: Type-P-One-to-Group-Mean-Delay
Note that the Group Mean Delay can also be calculated by summing the
Finite one-way Delay singletons in the Matrix, and dividing by the
number of Finite One-way Delay singletons.
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7.3.3. Type-P-One-to-Group-Range-Mean-Delay
This section defines a metric for the range of mean delays over all N
receivers in the Group, (R1DM, R2DM,...RnDM).
Type-P-One-to-Group-Range-Mean-Delay = GRMD = max(RnDM) - min(RnDM)
7.3.4. Type-P-One-to-Group-Max-Mean-Delay
This section defines a metric for the maximum of mean delays over all
N receivers in the Group, (R1DM, R2DM,...RnDM).
Type-P-One-to-Group-Max-Mean-Delay = GMMD = max(RnDM)
7.4. One-to-Group one-way Loss Statistics
This section defines the overall one-way loss statistics for a
receiver and for an entire group as illustrated by the matrix below.
Recv /----------- Sample ----------\ Stats Group Stat
1 R1L1 R1L2 R1L3 ... R1Lk R1LR \
|
2 R2L1 R2L2 R2L3 ... R2Lk R2LR |
|
3 R3L1 R3L2 R3L3 ... R3Lk R3LR > Group Loss Ratio
. |
. |
. |
n RnL1 RnL2 RnL3 ... RnLk RnLR /
Receiver-n
Loss Ratio
Figure 8: One-to-Group Loss Ratio
Statistics are computed on the sample of Type-P-One-way-Packet-Loss
[RFC2680] of the matrix above.
All loss ratios are expressed in units of packets lost to total
packets sent.
7.4.1. Type-P-One-to-Group-Receiver-n-Loss-Ratio
Given a Matrix of loss singletons as illustrated above, determine the
Type-P-One-way-Packet-Loss-Average for the sample at each receiver,
according to the definitions and method of [RFC2680]. The Type-P-
One-way-Packet-Loss-Average and the Type-P-One-to-Group-Receiver-n-
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Loss-Ratio, also named RnLR, are equivalent metrics. In terms of the
parameters used here, these metrics definitions can be expressed as
K
---
1 \
RnLR = - * > RnLk
K /
---
k = 1
Figure 9: Type-P-One-to-Group-Receiver-n-Loss-Ratio
7.4.2. Type-P-One-to-Group-Receiver-n-Comp-Loss-Ratio
Usually, the number of packets sent is used in the denominator of
packet loss ratio metrics. For the comparative metrics defined here,
the denominator is the maximum number of packets received at any
receiver for the sample and test interval of interest.
The Comparative Loss Ratio, also named, RnCLR, is defined as
K
---
\
> Ln(k)
/
---
k=1
RnCLR = -----------------------------
/ K \
| --- |
| \ |
K - Min | > Ln(k) |
| / |
| --- |
\ k=1 / N
Figure 10: Type-P-One-to-Group-Receiver-n-Comp-Loss-Ratio
7.4.3. Type-P-One-to-Group-Loss-Ratio
Type-P-One-to-Group-Loss-Ratio, the overall Group loss ratio, also
named GLR, is defined as
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K,N
---
1 \
GLR = --- * > L(k,n)
K*N /
---
k,n = 1
Figure 11: Type-P-One-to-Group-Loss-Ratio
7.4.4. Type-P-One-to-Group-Range-Loss-Ratio
The One-to-Group Loss Ratio Range is defined as:
Type-P-One-to-Group-Range-Loss-Ratio = max(RnLR) - min(RnLR)
It is most effective to indicate the range by giving both the max and
minimum loss ratios for the Group, rather than only reporting the
difference between them.
7.5. One-to-Group one-way Delay Variation Statistics
This section defines one-way delay variation (DV) statistics for an
entire group as illustrated by the matrix below.
Recv /------------- Sample --------------\ Stats
1 R1ddT1 R1ddT2 R1ddT3 ... R1ddTk R1DV \
|
2 R2ddT1 R2ddT2 R2ddT3 ... R2ddTk R2DV |
|
3 R3ddT1 R3ddT2 R3ddT3 ... R3ddTk R3DV > Group Stat
. |
. |
. |
n RnddT1 RnddT2 RnddT3 ... RnddTk RnDV /
Figure 12: One-to-Group Delay Variation Matrix (DVMa)
Statistics are computed on the sample of Type-P-One-way-Delay-
Variation singletons of the group delay variation matrix above where
RnddTk is the Type-P-One-way-Delay-Variation singleton evaluated at
Receiver n for the packet k and where RnDV is the point-to-point one-
way packet delay variation for Receiver n.
All One-to-group delay variation statistics are expressed in seconds
with sufficient resolution to convey 3 significant digits.
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7.5.1. Type-P-One-to-Group-Delay-Variation-Range
This section defines a metric for the range of delays variation over
all N receivers in the Group.
Maximum DV and minimum DV over all receivers summarize the
performance over the Group (where DV is a point-to-point metric).
For each receiver, the DV is usually expressed as the 1-10^(-3)
quantile of one-way delay minus the minimum one-way delay.
Type-P-One-to-Group-Delay-Variation-Range = GDVR =
= max(RnDV) - min(RnDV) for all n receivers
This range is determined from the minimum and maximum values of the
point-to-point one-way IP Packet Delay Variation for the set of
Destinations in the group and a population of interest, using the
Packet Delay Variation expressed as the 1-10^-3 quantile of one-way
delay minus the minimum one-way delay. If a more demanding service
is considered, one alternative is to use the 1-10^-5 quantile, and in
either case the quantile used should be recorded with the results.
Both the minimum and the maximum delay variation are recorded, and
both values are given to indicate the location of the range.
8. Measurement Methods: Scalability and Reporting
Virtually all the guidance on measurement processes supplied by the
earlier IPPM RFCs (such as [RFC2679] and [RFC2680]) for one-to-one
scenarios is applicable here in the spatial and multiparty
measurement scenario. The main difference is that the spatial and
multiparty configurations require multiple points of interest where a
stream of singletons will be collected. The amount of information
requiring storage grows with both the number of metrics and the
points of interest, so the scale of the measurement architecture
multiplies the number of singleton results that must be collected and
processed.
It is possible that the architecture for results collection involves
a single reference point with connectivity to all the points of
interest. In this case, the number of points of interest determines
both storage capacity and packet transfer capacity of the host acting
as the reference point. However, both the storage and transfer
capacity can be reduced if the points of interest are capable of
computing the summary statistics that describe each measurement
interval. This is consistent with many operational monitoring
architectures today, where even the individual singletons may not be
stored at each point of interest.
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In recognition of the likely need to minimize form of the results for
storage and communication, the Group metrics above have been
constructed to allow some computations on a per-Receiver basis. This
means that each Receiver's statistics would normally have an equal
weight with all other Receivers in the Group (regardless of the
number of packets received).
8.1. Computation methods
The scalability issue can be raised when there are thousands of
points of interest in a group who are trying to send back the
measurement results to the reference point for further processing and
analysis. The points of interest can send either the whole measured
sample or only the calculated statistics. The former one is a
centralized statistic calculation method and the latter one is a
distributed statistic calculation method. The sample should include
all metrics parameters, the values and the corresponding sequence
numbers. The transmission of the whole sample can cost much more
bandwidth than the transmission of the statistics that should include
all statistic parameters specified by policies and the additional
information about the whole sample, such as the size of the sample,
the group address, the address of the point of interest, the ID of
the sample session, and so on. Apparently, the centralized
calculation method can require much more bandwidth than the
distributed calculation method when the sample size is big. This is
especially true when the measurement has huge number of the points of
interest. It can lead to a scalability issue at the reference point
by over load the network resources. The distributed calculation
method can save much more bandwidth and release the pressure of the
scalability issue at the reference point side. However, it can
result in the lack of information because not all measured singletons
are obtained for building up the group matrix. The performance over
time can be hidden from the analysis. For example, the loss pattern
can be missed by simply accepting the loss ratio as well as the delay
pattern. This tradeoff between the bandwidth consuming and the
information acquiring has to be taken into account when design the
measurement campaign to optimize the measurement results delivery.
The possible solution could be to transit the statistic parameters to
the reference point first to obtain the general information of the
group performance. If the detail results are required, the reference
point should send the requests to the points of interest, which could
be particular ones or the whole group. This procedure can happen in
the off peak time and can be well scheduled to avoid delivery of too
many points of interest at the same time. Compression techniques can
also be used to minimize the bandwidth required by the transmission.
This could be a measurement protocol to report the measurement
results. However, this is out of the scope of this memo.
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8.2. Measurement
To prevent any bias in the result, the configuration of a one-to-many
measure must take in consideration that implicitly more packets will
to be routed than send and selects a test packets rate that will not
impact the network performance.
8.3. Effect of Time and Space Aggregation Order on Stats
This section presents the impact of the aggregation order on the
scalability of the reporting and of the computation. It makes the
hypothesis that receivers are managed remotely and not co-located.
multimetrics samples represented a matrix as illustrated below
Point of
interest
1 R1S1 R1S1 R1S1 ... R1Sk \
|
2 R2S1 R2S2 R2S3 ... R2Sk |
|
3 R3S1 R3S2 R3S3 ... R3Sk > sample over space
. |
. |
. |
n RnS1 RnS2 RnS3 ... RnSk /
S1M S2M S3M ... SnM Stats over space
\------------- ------------/
\/
Stat over space and time
Figure 13: Impact of space aggregation on multimetrics Stat
2 methods are available to compute statistics on the resulting
matrix:
o metric is computed over time and then over space;
o metric is computed over space and then over time.
They differ only by the order of the time and of the space
aggregation. View as a matrix this order is neutral as does not
impact the result, but the impact on a measurement deployment is
critical.
In both cases the volume of data to report is proportional to the
number of probes. But there is a major difference between these 2
methods:
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method2: In space and time aggregation mode the volume of data to
collect is proportional to the number of test packets received;
Each received packet RiSi triggers out a block of data that must
be reported to a common place for computing the stat over space;
method1: In time and space aggregation mode the volume of data to
collect is proportional to the period of aggregation, so it does
not depend on the number of packet received;
Method 2 property has severe drawbacks in terms of security and
dimensioning:
The increasing of the rate of the test packets may result in a
sort of DoS toward the computation points;
The dimensioning of a measurement system is quite impossible to
validate.
The time aggregation interval provides the reporting side with a
control of various collecting aspects such as bandwidth and
computation and storage capacities. So this draft defines metrics
based on method 1.
Note: In some specific cases one may need sample of singletons over
space. To address this need it is suggested firstly to limit the
number of test and the number of test packets per seconds. Then
reducing the size of the sample over time to one packet give sample
of singleton over space..
8.3.1. Impact on spatial statistics
2 methods are available to compute spatial statistics:
o method 1: spatial segment metrics and statistics are preferably
computed over time by each points of interest;
o method 2: Vectors metrics are intrinsically instantaneous space
metrics which must be reported using method2 whenever
instantaneous metrics information is needed.
8.3.2. Impact on one-to-group statistics
2 methods are available to compute group statistics:
o method1: Figure 5 andFigure 8 illustrate the method chosen: the
one-to-one statistic is computed per interval of time before the
computation of the mean over the group of receivers;
o method2: Figure 13 presents the second one, metric is computed
over space and then over time.
9. Manageability Considerations
Usually IPPM WG documents defines each metric reporting within its
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definition. This document defines the reporting of all the metrics
introduced in a single section to provide consistent information, to
avoid repetitions and to conform to IESG recommendation of gathering
manageability considerations in a dedicated section.
Information models of spatial metrics and of one-to-group metrics are
similar excepted that points of interests of spatial vectors must be
ordered.
The complexity of the reporting relies on the number of points of
interests.
9.1. Reporting spatial metric
The reporting of spatial metrics shares a lot of aspects with
RFC2679-80. New ones are common to all the definitions and are
mostly related to the reporting of the path and of methodology
parameters that may bias raw results analysis. This section presents
these specific parameters and then lists exhaustively the parameters
that shall be reported.
9.1.1. Path
End-to-end metrics can't determine the path of the measure despite
IPPM RFCs recommend it to be reported (See Section 3.8.4 of
[RFC2679]). Spatial metrics vectors provide this path. The report
of a spatial vector must include the points of interests involved:
the sub set of the hosts of the path participating to the
instantaneous measure.
9.1.2. Host order
A spatial vector must order the points of interest according to their
order in the path. It is highly suggested to use the TTL in IPv4,
the Hop Limit in IPv6 or the corresponding information in MPLS.
The report of a spatial vector must include the ordered list of the
hosts involved in the instantaneous measure.
9.1.3. Timestamping bias
The location of the point of interest inside a node influences the
timestamping skew and accuracy. As an example, consider that some
internal machinery delays the timestamping up to 3 milliseconds then
the minimal uncertainty reported be 3 ms if the internal delay is
unknown at the time of the timestamping.
The report of a spatial vector must include the uncertainty of the
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timestamping compared to wire time.
9.1.4. Reporting spatial One-way Delay
The reporting includes information to report for one-way-delay as the
Section 3.6 of [RFC2679]. The same apply for packet loss and ipdv.
9.2. Reporting One-to-group metric
All reporting rules described in RFC2679-80 apply to the
corresponding One-to-group metrics. Following are specific
parameters that should be reported.
9.2.1. Path
As suggested by the RFC2679-80, the path traversed by the packet
SHOULD be reported, if possible. For One-to-group metrics, there is
a path tree SHOULD be reported rather than A path. This is even more
impractical. If, by anyway, partial information is available to
report, it might not be as valuable as it is in the one-to-one case
because the incomplete path might be difficult to identify its
position in the path tree. For example, how many points of interest
are reached by the packet traveled through this incomplete path?
9.2.2. Group size
The group size should be reported as one of the critical management
parameters. Unlike the spatial metrics, there is no need of order of
points of interests.
9.2.3. Timestamping bias
It is the same as described in section 9.1.3.
9.2.4. Reporting One-to-group One-way Delay
It is the same as described in section 9.1.4.
9.2.5. Measurement method
As explained in section 8, the measurement method will have impact on
the analysis of the measurement result. Therefore, it should be
reported.
9.3. Metric identification
IANA assigns each metric defined by the IPPM WG with a unique
identifier as per [RFC4148] in the IANA-IPPM-METRICS-REGISTRY-MIB.
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9.4. Information model
This section presents the elements of information and the usage of
the information reported for network performance analysis. It is out
of the scope of this section to define how the information is
reported.
The information model is build with pieces of information introduced
and explained in one-way delay definitions [RFC2679], in packet loss
definitions [RFC2680] and in IPDV definitions of [RFC3393] and
[RFC3432]. It includes not only information given by "Reporting the
metric" sections but by sections "Methodology" and "Errors and
Uncertainties" sections.
Following are the elements of information taken from end-to-end
definitions referred in this memo and from spatial and multicast
metrics it defines:
o Packet_type, The Type-P of test packets (Type-P);
o Packet_length, a packet length in bits (L);
o Src_host, the IP address of the sender;
o Dst_host, the IP address of the receiver;
o Hosts_serie: <H1, H2,..., Hn>, a list of points of interest;
o Loss_threshold: The threshold of infinite delay;
o Systematic_error: constant delay between wire time and
timestamping;
o Calibration_error: maximal uncertainty;
o Src_time, the sending time for a measured packet;
o Dst_time, the receiving time for a measured packet;
o Result_status : an indicator of usability of a result 'Resource
exhaustion' 'infinite', 'lost';
o Delays_serie: <dT1,..., dTn> a list of delays;
o Losses_serie: <B1, B2, ..., Bi, ..., Bn>, a list of Boolean values
(spatial) or a set of Boolean values (one-to-group);
o Result_status_serie: a list of results status;
o dT: a delay;
o Singleton_number: a number of singletons;
o Observation_duration: An observation duration;
o metric_identifier.
Following is the information of each vector that should be available
to compute samples:
o Packet_type;
o Packet_length;
o Src_host, the sender of the packet;
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o Dst_host, the receiver of the packet, apply only for spatial
vectors;
o Hosts_serie: not ordered for one-to-group;
o Src_time, the sending time for the measured packet;
o dT, the end-to-end one-way delay for the measured packet, apply
only for spatial vectors;
o Delays_serie: apply only for delays and ipdv vector, not ordered
for one-to-group;
o Losses_serie: apply only for packets loss vector, not ordered for
one-to-group;
o Result_status_serie;
o Observation_duration: the difference between the time of the last
singleton and the time of the first singleton.
o Following is the context information (measure, points of
interests) that should be available to compute samples :
* Loss threshold;
* Systematic error: constant delay between wire time and
timestamping;
* Calibration error: maximal uncertainty;
A spatial or a one-to-group sample is a collection of singletons
giving the performance from the sender to a single point of interest.
Following is the information that should be available for each sample
to compute statistics:
o Packet_type;
o Packet_length;
o Src_host, the sender of the packet;
o Dst_host, the receiver of the packet;
o Start_time, the sending time of the first packet;
o Delays_serie: apply only for delays and ipdv samples;
o Losses_serie: apply only for packets loss samples;
o Result_status_serie;
o Observation_duration: the difference between the time of the last
singleton of the last sample and the time of the first singleton
of the first sample.
o Following is the context information (measure, points of
interests) that should be available to compute statistics :
* Loss threshold;
* Systematic error: constant delay between wire time and
timestamping;
* Calibration error: maximal uncertainty;
Following is the information of each statistic that should be
reported:
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o Result;
o Start_time;
o Duration;
o Result_status;
o Singleton_number, the number of singletons the statistic is
computed on;
10. Security Considerations
Spatial and one-to-group metrics are defined on the top of end-to-end
metrics. Security considerations discussed in One-way delay metrics
definitions of [RFC2679] , in packet loss metrics definitions of
[RFC2680] and in IPDV metrics definitions of[RFC3393] and [RFC3432]
apply to metrics defined in this memo.
10.1. Spatial metrics
Malicious generation of packets with spoofing addresses may corrupt
the results without any possibility to detect the spoofing.
Malicious generation of packets which match systematically the hash
function used to detect the packets may lead to a DoS attack toward
the point of reference.
10.2. one-to-group metric
Reporting of measurement results from a huge number of probes may
overload reference point ressources (network, network interfaces,
computation capacities ...).
The configuration of a measurement must take in consideration that
implicitly more packets will to be routed than send and selects a
test packets rate accordingly. Collecting statistics from a huge
number of probes may overload any combination of the network where
the measurement controller is attached to, measurement controller
network interfaces and measurement controller computation capacities.
One-to-group metrics measurement should consider using source
authentication protocols, standardized in the MSEC group, to avoid
fraud packet in the sampling interval. The test packet rate could be
negotiated before any measurement session to avoid deny of service
attacks.
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11. Acknowledgments
Lei would like to acknowledge Prof. Zhili Sun from CCSR, University
of Surrey, for his instruction and helpful comments on this work.
12. IANA Considerations
Metrics defined in this memo Metrics defined in this memo are
designed to be registered in the IANA IPPM METRICS REGISTRY as
described in initial version of the registry [RFC4148] :
IANA is asked to register the following metrics in the IANA-IPPM-
METRICS-REGISTRY-MIB :
ietfSpatialOneWayDelayVector OBJECT-IDENTITY
STATUS current
DESCRIPTION
"Type-P-Spatial-One-way-Delay-Vector"
REFERENCE
"Reference "RFCyyyy, section 4.1."
-- RFC Ed.: replace yyyy with actual RFC number & remove this
note
:= { ianaIppmMetrics nn } -- IANA assigns nn
ietfSpatialPacketLossVector OBJECT-IDENTITY
STATUS current
DESCRIPTION
"Type-P-Spatial-Packet-Loss-Vector"
REFERENCE
"Reference "RFCyyyy, section 4.2."
-- RFC Ed.: replace yyyy with actual RFC number & remove this
note
:= { ianaIppmMetrics nn } -- IANA assigns nn
ietfSpatialOneWayIpdvVector OBJECT-IDENTITY
STATUS current
DESCRIPTION
"Type-P-Spatial-One-way-ipdv-Vector"
REFERENCE
"Reference "RFCyyyy, section 4.3."
-- RFC Ed.: replace yyyy with actual RFC number & remove this
note
:= { ianaIppmMetrics nn } -- IANA assigns nn
ietfSegmentOneWayDelayStream OBJECT-IDENTITY
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STATUS current
DESCRIPTION
"Type-P-Segment-One-way-Delay-Stream"
REFERENCE
"Reference "RFCyyyy, section 5.1."
-- RFC Ed.: replace yyyy with actual RFC number & remove this
note
:= { ianaIppmMetrics nn } -- IANA assigns nn
ietfSegmentPacketLossStream OBJECT-IDENTITY
STATUS current
DESCRIPTION
"Type-P-Segment-Packet-Loss-Stream"
REFERENCE
"Reference "RFCyyyy, section 5.2."
-- RFC Ed.: replace yyyy with actual RFC number & remove this
note
:= { ianaIppmMetrics nn } -- IANA assigns nn
ietfSegmentOneWayIpdvPrevStream OBJECT-IDENTITY
STATUS current
DESCRIPTION
"Type-P-Segment-One-way-ipdv-prev-Stream"
REFERENCE
"Reference "RFCyyyy, section 5.3."
-- RFC Ed.: replace yyyy with actual RFC number & remove this
note
:= { ianaIppmMetrics nn } -- IANA assigns nn
ietfSegmentOneWayIpdvMinStream OBJECT-IDENTITY
STATUS current
DESCRIPTION
"Type-P-Segment-One-way-ipdv-min-Stream"
REFERENCE
"Reference "RFCyyyy, section 5.4."
-- RFC Ed.: replace yyyy with actual RFC number & remove this
note
:= { ianaIppmMetrics nn } -- IANA assigns nn
-- One-to-group metrics
ietfOneToGroupOneWayDelayVector OBJECT-IDENTITY
STATUS current
DESCRIPTION
"Type-P-One-to-group-One-way-Delay-Vector"
REFERENCE
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"Reference "RFCyyyy, section 6.1."
-- RFC Ed.: replace yyyy with actual RFC number & remove this
note
:= { ianaIppmMetrics nn } -- IANA assigns nn
ietfOneToGroupOneWayPktLossVector OBJECT-IDENTITY
STATUS current
DESCRIPTION
"Type-P-One-to-Group-One-way-Packet-Loss-Vector"
REFERENCE
"Reference "RFCyyyy, section 6.2."
-- RFC Ed.: replace yyyy with actual RFC number & remove this
note
:= { ianaIppmMetrics nn } -- IANA assigns nn
ietfOneToGroupOneWayIpdvVector OBJECT-IDENTITY
STATUS current
DESCRIPTION
"Type-P-One-to-Group-One-way-ipdv-Vector"
REFERENCE
"Reference "RFCyyyy, section 6.3."
-- RFC Ed.: replace yyyy with actual RFC number & remove this
note
:= { ianaIppmMetrics nn } -- IANA assigns nn
-- One to group statistics
--
ietfOnetoGroupReceiverNMeanDelay OBJECT-IDENTITY
STATUS current
DESCRIPTION
"Type-P-One-to-Group-Receiver-n-Mean-Delay"
REFERENCE
"Reference "RFCyyyy, section 7.3.1."
-- RFC Ed.: replace yyyy with actual RFC number & remove this
note
:= { ianaIppmMetrics nn } -- IANA assigns nn
ietfOneToGroupMeanDelay OBJECT-IDENTITY
STATUS current
DESCRIPTION
"Type-P-One-to-Group-Mean-Delay"
REFERENCE
"Reference "RFCyyyy, section 7.3.2."
-- RFC Ed.: replace yyyy with actual RFC number & remove this
note
:= { ianaIppmMetrics nn } -- IANA assigns nn
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ietfOneToGroupRangeMeanDelay OBJECT-IDENTITY
STATUS current
DESCRIPTION
"Type-P-One-to-Group-Range-Mean-Delay"
REFERENCE
"Reference "RFCyyyy, section 7.3.3."
-- RFC Ed.: replace yyyy with actual RFC number & remove this
note
:= { ianaIppmMetrics nn } -- IANA assigns nn
ietfOneToGroupMaxMeanDelay OBJECT-IDENTITY
STATUS current
DESCRIPTION
"Type-P-One-to-Group-Max-Mean-Delay"
REFERENCE
"Reference "RFCyyyy, section 7.3.4."
-- RFC Ed.: replace yyyy with actual RFC number & remove this
note
:= { ianaIppmMetrics nn } -- IANA assigns nn
ietfOneToGroupReceiverNLossRatio OBJECT-IDENTITY
STATUS current
DESCRIPTION
"Type-P-One-to-Group-Receiver-n-Loss-Ratio"
REFERENCE
"Reference "RFCyyyy, section 7.4.1."
-- RFC Ed.: replace yyyy with actual RFC number & remove this
note
:= { ianaIppmMetrics nn } -- IANA assigns nn
--
ietfOneToGroupReceiverNCompLossRatio OBJECT-IDENTITY
STATUS current
DESCRIPTION
"Type-P-One-to-Group-Receiver-n-Comp-Loss-Ratio"
REFERENCE
"Reference "RFCyyyy, section 7.4.2."
-- RFC Ed.: replace yyyy with actual RFC number & remove this
note
:= { ianaIppmMetrics nn } -- IANA assigns nn
ietfOneToGroupLossRatio OBJECT-IDENTITY
STATUS current
DESCRIPTION
"Type-P-One-to-Group-Loss-Ratio"
REFERENCE
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"Reference "RFCyyyy, section 7.4.3."
-- RFC Ed.: replace yyyy with actual RFC number & remove this
note
:= { ianaIppmMetrics nn } -- IANA assigns nn
--
ietfOneToGroupRangeLossRatio OBJECT-IDENTITY
STATUS current
DESCRIPTION
"Type-P-One-to-Group-Range-Loss-Ratio"
REFERENCE
"Reference "RFCyyyy, section 7.4.4."
-- RFC Ed.: replace yyyy with actual RFC number & remove this
note
:= { ianaIppmMetrics nn } -- IANA assigns nn
ietfOneToGroupRangeDelayVariation OBJECT-IDENTITY
STATUS current
DESCRIPTION
"Type-P-One-to-Group-Range-Delay-Variation"
REFERENCE
"Reference "RFCyyyy, section 7.5.1."
-- RFC Ed.: replace yyyy with actual RFC number & remove this
note
:= { ianaIppmMetrics nn } -- IANA assigns nn
--
13. References
13.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[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.
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13.2. Informative References
[RFC2330] Paxson, V., Almes, G., Mahdavi, J., and M. Mathis,
"Framework for IP Performance Metrics", RFC 2330,
May 1998.
[RFC3432] Raisanen, V., Grotefeld, G., and A. Morton, "Network
performance measurement with periodic streams", RFC 3432,
November 2002.
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@orange-ftgroup.com
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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