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The IETF has standardized IP Performance Metrics (IPPM) for measuring endtoend 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 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 (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.) [RFC2119].
1.
Introduction and Scope
2.
Terminology
3.
Brief Metric Descriptions
4.
Motivations
5.
Spatial vector metrics definitions
6.
Spatial Segment Metrics Definitions
7.
Onetogroup metrics definitions
8.
Onetogroup Sample Statistics
9.
Measurement Methods: Scalability and Reporting
10.
Manageability Considerations
11.
Security Considerations
12.
Acknowledgments
13.
IANA Considerations
14.
References
14.1.
Normative References
14.2.
Informative References
§
Authors' Addresses
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IETF has standardized IP Performance Metrics (IPPM) for measuring endtoend 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 measure the performance of each segment along a path. Onetogroup metrics measure the performance for a group of users. These metrics are derived from oneway endtoend metrics, all of which follow the IPPM framework [RFC2330] (Paxson, V., Almes, G., Mahdavi, J., and M. Mathis, “Framework for IP Performance Metrics,” May 1998.).
This memo is organized as follows: Section 2 introduces new terms that extend the original IPPM framework [RFC2330] (Paxson, V., Almes, G., Mahdavi, J., and M. Mathis, “Framework for IP Performance Metrics,” May 1998.). Section 3 motivates each metric category and briefly introduces the new metrics. Sections 4 through 7 develop each category of metrics with definitions and statistics. Then the memo discusses the impact of the measurement methods on the scalability and proposes an information model for reporting the measurements. Finally, the memo discusses security aspects related to measurement and registers the metrics in the IANA IP Performance Metrics Registry [RFC4148] (Stephan, E., “IP Performance Metrics (IPPM) Metrics Registry,” August 2005.).
The scope of this memo is limited to metrics using a single source packet or stream, and observations of corresponding packets along the path (spatial), at one or more destinations (onetogroup), or both. Note that all the metrics defined herein are based on observations of packets dedicated to testing, a process which is called active measurement. Passive measurement (for example, a spatial metric based on the observation of user traffic) is beyond the scope of this memo.
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The names of the metrics, including capitalization letters, are as close as possible of the names of the oneway endtoend metrics they are derived from.
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host: section 5 of RFC 2330
loss threshold: section 2.8.2 of RFC 2680
path: section 5 of RFC 2330
path digest: section 5 of RFC 2330
sample: section 11 of RFC 2330
singleton: section 11 of RFC 2330
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The list of the hosts on a path from the source to the destination, also referred to as the host path digest.
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A metric is said to be multiparty if the topology involves more than one measurement collection point. All multiparty metrics designate a set of hosts as "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 >.
For the purposes of this memo (reflecting the scope of a single source), the only multiparty metrics are onetogroup metrics.
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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(s). Such measurement hosts will usually be members of the path digest.
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A metric is said to be onetogroup if the measured packet is sent by one source and (potentially) received by more than one destination. Thus, the topology of the communication group can be viewed as a centerdistributed or serverclient topology with the source as the center/server in the topology.
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Points of interest are the hosts (as per the RFC 2330 definition, "hosts" include routing nodes) that are measurement collection points, a subset of the set of hosts involved in the delivery of the packets (in addition to the source itself).
For spatial metrics, points of interest are a (possibly arbitrary) subset of all the hosts involved in the path.
Points of interest of onetogroup metrics are the intended destination hosts for packets from the source (in addition to the source itself).
Src Dst `. ,. `. ,' `...... 1 `. ; : `. ; : ; :... 2   : ; : ;.... 3 : ; `. ,' `'....... I
Figure 1: Onetogroup 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 source to destination.
Src . Hosts \ `X ... 1 \ x / .X .... 2 / x \ `X .... 3 \ \ \ X .... J \ \ \ ` Dst Note: 'x' are nodes which are not points of interest
Figure 2: Spatial points of interest 
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A reference point is defined as the server where the statistical calculations will be carried out. It is usually a centralized server in the measurement architecture that is controlled by a network operator, where measurement data can be collected for further processing. The reference point is distinctly different from hosts at measurement collection points, where the actual measurements are carried out (e.g., points of interest).
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A vector is a set of singletons (single atomic results) comprised of observations corresponding to a single source packet at different hosts in a network. For instance, if the oneway delay singletons observed at N receivers for Packet P sent by the source Src are dT1, dT2,..., dTN, then a vector V with N elements can be organized as {dT1, dT2,…, dTN}. The element dT1 is distinct from all others as the singleton at receiver 1 in response to a packet sent from the source at a specific time. The complete vector gives information over the dimension of space; a set of N receivers in this example.
The singleton elements of any vector are distinctly different from each other in terms of their measurement collection point. Different vectors for common measurement points of interest are distinguished by the source packet sending time.
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Several vectors form a matrix, which contains results observed over a sampling interval at different places in a network at different times. For example, the Oneway delay vectors V1={dT11, dT12,..., dT1N}, V2={dT21, dT22,…, dT2N},…, Vm={dTm1, dTm2,…, dTmN} for Packet P1, P2,…,Pm, form a Oneway delay Matrix {V1, V2,…,Vm}. The matrix organizes the vector information to present network performance in both space and time.
A onedimensional matrix (row) corresponds to a sample in simple pointtopoint measurement.
The relationship among singleton, sample, vector and matrix is illustrated in the following Figure 3 (Relationship between singletons, samples, vectors and matrix).
points of singleton interest / samples(time) ,. ^ / / 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 and space)
Figure 3: Relationship between singletons, samples, vectors and matrix 
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The metrics for spatial and onetogroup measurement are based on the sourcetodestination, or endtoend metrics defined by IETF in [[RFC2679] (Almes, G., Kalidindi, S., and M. Zekauskas, “A Oneway Delay Metric for IPPM,” September 1999.), [RFC2680] (Almes, G., Kalidindi, S., and M. Zekauskas, “A Oneway Packet Loss Metric for IPPM,” September 1999.), [RFC3393] (Demichelis, C. and P. Chimento, “IP Packet Delay Variation Metric for IP Performance Metrics (IPPM),” November 2002.), [RFC3432] (Raisanen, V., Grotefeld, G., and A. Morton, “Network performance measurement with periodic streams,” November 2002.).
This memo defines seven new spatial metrics using the [RFC2330] (Paxson, V., Almes, G., Mahdavi, J., and M. Mathis, “Framework for IP Performance Metrics,” May 1998.) framework of parameters, units of measure, and measurement methodologies. Each definition includes a section that describes measurements constraints and issues, and provides guidance to increase the accuracy of the results.
The spatial metrics are:
The memo also defines three onetogroup metrics to measure the oneway performance between a source and a group of receivers. They are:
Finally, based on the onetogroup vector metrics listed above, statistics are defined to capture single receiver performance, group performance and the relative performance for a multiparty communication:
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All existing IPPM metrics are defined for endtoend (source to destination) measurement of pointtopoint paths. It is logical to extend them to multiparty situations such as one to one trajectory metrics and one to multipoint metrics.
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Spatial metrics are needed for:
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While the nodetonode 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 pointtopoint metric cannot completely describe the multiparty situation. New onetogroup metrics assess performance of the multiple paths for further statistical analysis. The new metrics are named onetogroup performance metrics, and they are based on the unicast metrics defined in IPPM RFCs. Onetogroup metrics are oneway metrics from one source to a group of destinations, or receivers. The metrics are helpful for judging the overall performance of a multiparty communications network, and for describing the performance variation across a group of destinations.
Onetogroup performance metrics are needed for:
To understand the packet transfer performance between one source and any one receiver in the multiparty communication group, we need to collect instantaneous endtoend metrics, or singletons. This gives a very detailed view into the performance of each branch of the multicast tree, and can provide clear and helpful information for engineers to identify the branch with problems in a complex multiparty routing tree.
The onetogroup metrics described in this memo introduce the multiparty topology into the IPPM framework, and describe the performance delivered to a group receiving packets from the same source. The concept extends the "path" of the pointtopoint measurement to "path tree" to cover onetomany topologies. If applied to onetoone topology, the onetogroup metrics provide exactly the same results as the corresponding onetoone metrics.
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We note that points of interest can also be selected to define measurements on grouptoone and grouptogroup topologies. These topologies are beyond the scope of this memo, because they would involve multiple packets launched from different sources. However, this section gives some insights on these two cases.
The measurements for grouptoone topology can be easily derived from the onetogroup measurement. The measurement point is the host that is acting as a receiver while all other hosts act as sources in this case.
The grouptogroup communication topology has no obvious focal point: the sources and the measurement collection points can be anywhere. However, it is possible to organize the problem by applying measurements in onetogroup or grouptoone topologies for each host in a uniform way (without taking account of how the real communication might be carried out). For example, one group of hosts < ha, hb, hc, ..., hn > might act as sources to send data to another group of hosts < Ha, Hb, Hc, ..., Hm >, and they can be organized into n sets of points of interest for onetogroup communications:
< ha, Ha, Hb, Hc, ..., Hm >, < hb, Ha, Hb, Hc, ..., Hm >, <hc, Ha, Hb, Hc, ..., Hm >, ..., < hn, Ha, Hb, Hc, ..., Hm >.
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This section defines vectors for the spatial decomposition of endtoend singleton metrics over a path.
Spatial vector metrics are based on the decomposition of standard endtoend metrics defined by the IPPM WG in [RFC2679] (Almes, G., Kalidindi, S., and M. Zekauskas, “A Oneway Delay Metric for IPPM,” September 1999.), [RFC2680] (Almes, G., Kalidindi, S., and M. Zekauskas, “A Oneway Packet Loss Metric for IPPM,” September 1999.), [RFC3393] (Demichelis, C. and P. Chimento, “IP Packet Delay Variation Metric for IP Performance Metrics (IPPM),” November 2002.) and [RFC3432] (Raisanen, V., Grotefeld, G., and A. Morton, “Network performance measurement with periodic streams,” November 2002.).
The spatial vector definitions are coupled with the corresponding endtoend metrics. Measurement methodology aspects are common to all the vectors defined and are consequently discussed in a common section.
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This section is coupled with the definition of TypePOnewayDelay of the section 3 of [RFC2679] (Almes, G., Kalidindi, S., and M. Zekauskas, “A Oneway Delay Metric for IPPM,” September 1999.). When a parameter from the definition in [RFC2679] (Almes, G., Kalidindi, S., and M. Zekauskas, “A Oneway Delay Metric for IPPM,” September 1999.) is reused in this section, the first instance will be tagged with a trailing asterisk.
Sections 3.5 to 3.8 of [RFC2679] (Almes, G., Kalidindi, S., and M. Zekauskas, “A Oneway Delay Metric for IPPM,” September 1999.) give requirements and applicability statements for endtoend onewaydelay measurements. They are applicable to each point of interest, Hi, involved in the measure. Spatial onewaydelay measurement MUST respect them, especially those related to methodology, clock, uncertainties and reporting.
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TypePSpatialOnewayDelayVector
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The value of TypePSpatialOnewayDelayVector is a sequence of times (a real number in the dimension of seconds with sufficient resolution to convey the results).
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Given a TypeP packet sent by the Src at wiretime (first bit) T to the receiver Dst on the path <H1, H2,..., Hn>. There is a sequence of values <T+dT1,T+dT2,...,T+dTn,T+dT> such that dT is the TypePOnewayDelay from Src to Dst, and for each Hi of the path, T+dTi is either a real number corresponding to the wiretime the packet passes (last bit received) Hi, or undefined if the packet does not pass Hi within a specified loss threshold* time.
TypePSpatialOnewayDelayVector metric is defined for the path <Src, H1, H2,..., Hn, Dst> as the sequence of values <T,dT1,dT2,...,dTn,dT>.
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Some specific issues that may occur are as follows:
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This section is coupled with the definition of TypePOnewayPacketLoss. When a parameter from the section 2 of [RFC2680] (Almes, G., Kalidindi, S., and M. Zekauskas, “A Oneway Packet Loss Metric for IPPM,” September 1999.) is used in this section, the first instance will be tagged with a trailing asterisk.
Sections 2.5 to 2.8 of [RFC2680] (Almes, G., Kalidindi, S., and M. Zekauskas, “A Oneway Packet Loss Metric for IPPM,” September 1999.) give requirements and applicability statements for endtoend oneway packet loss measurements. They are applicable to each point of interest, Hi, involved in the measure. Spatial packet loss measurement MUST respect them, especially those related to methodology, clock, uncertainties and reporting.
The following sections define the spatial loss vector, adapt some of the points above, and introduce points specific to spatial loss measurement.
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TypePSpatialPacketLossVector
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The value of TypePSpatialPacketLossVector is a sequence of Boolean values.
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Given a TypeP packet sent by the Src at time T to the receiver Dst on the path <H1, H2, ..., Hn>. For the sequence of times <T+dT1,T+dT2,..., T+dTi, ...,T+dTn> the packet passes in <H1, H2, ..., Hi, ..., Hn>, define the TypePPacketLossVector metric as the sequence of values <T, 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.
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Some specific issues that may occur are as follows:
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When a parameter from section 2 of [RFC3393] (Demichelis, C. and P. Chimento, “IP Packet Delay Variation Metric for IP Performance Metrics (IPPM),” November 2002.) (the definition of TypePOnewayipdv) is used in this section, the first instance will be tagged with a trailing asterisk.
The following sections define the spatial ipdv vector, adapt some of the points above, and introduce points specific to spatial ipdv measurement.
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TypePSpatialOnewayipdvVector
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The value of TypePSpatialOnewayipdvVector is a sequence of times (a real number in the dimension of seconds with sufficient resolution to convey the results).
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Given P1 the TypeP packet sent by the sender Src at wiretime (first bit) T1 to the receiver Dst and <T1, dT1.1, dT1.2,..., dT1.n, dT1> its TypePSpatialOnewayDelayVector over the path <H1, H2,..., Hn>.
Given P2 the TypeP packet sent by the sender Src at wiretime (first bit) T2 to the receiver Dst and <T2, dT2.1, dT2.2,..., dT2.n, dT2> its TypePSpatialOnewayDelayVector over the same path.
TypePSpatialOnewayipdvVector metric is defined as the sequence of values <T1, T2, dT2.1dT1.1, dT2.2dT1.2 ,..., dT2.ndT1.n, dT2dT1> such that for each Hi of the path <H1, H2,..., Hn>, dT2.idT1.i is either a real number if the packets P1 and P2 pass Hi at wiretime (last bit) dT1.i and dT2.i respectively, or undefined if at least one of them never passes Hi (and the respective oneway delay is undefined). The T1,T2* pair indicates the interpacket emission interval and dT2dT1 is ddT* the TypePOnewayipdv.
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The methodology, reporting specifications, and uncertainties specified in section 3 of [RFC2679] (Almes, G., Kalidindi, S., and M. Zekauskas, “A Oneway Delay Metric for IPPM,” September 1999.) apply to each point of interest (or measurement collection point), Hi, measuring an element of a spatial delay vector.
Likewise, the methodology, reporting specifications, and uncertainties specified in section 2 of [RFC2680] (Almes, G., Kalidindi, S., and M. Zekauskas, “A Oneway Packet Loss Metric for IPPM,” September 1999.) apply to each point of interest, Hi, measuring an element of a spatial packet loss vector.
Sections 3.5 to 3.7 of [RFC3393] (Demichelis, C. and P. Chimento, “IP Packet Delay Variation Metric for IP Performance Metrics (IPPM),” November 2002.) give requirements and applicability statements for endtoend Oneway ipdv measurements. They are applicable to each point of interest, Hi, involved in the measure. Spatial Oneway ipdv measurement MUST respect the methodology, clock, uncertainties and reporting aspects given there.
Generally, for a given TypeP packet of length L at a specific Hi, the methodology for spatial vector metrics may proceed as follows:
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In a pure endtoend measurement, packet losses are detected by the receiver only. A packet is lost when TypePOnewayDelay is undefined or very large (See section 2.4 ans 2.5 of [RFC2680] (Almes, G., Kalidindi, S., and M. Zekauskas, “A Oneway Packet Loss Metric for IPPM,” September 1999.) and section 3.5 of [RFC2680] (Almes, G., Kalidindi, S., and M. Zekauskas, “A Oneway Packet Loss Metric for IPPM,” September 1999.)). A packet is deemed lost by the receiver after a duration which starts at the time the packet is sent. This timeout value is chosen by a measurement process. It determines the threshold between recording a long packet transfer time as a finite value or an undefined value.
In a spatial measurement, packet losses may be detected at several measurement collection points. Depending on the consistency of the packet loss detections among the points of interest, a packet may be considered as lost at one point despite having a finite delay at another one, or may be observed by the last measurement collection point of the path but considered lost by Dst.
There is a risk of misinterpreting such results: Has the path changed? Did the packet arrive at the destination or was it lost on the very last link?
The same concern applies to onewaydelay measures: a delay measured may be computed as infinite by one observation point but as a real value by another one, or may be measured as a real value by the last observation point of the path but designated as undefined by Dst.
The observation/measurement collection points and the destination SHOULD use consistent methods to detect packets losses. The methods and parameters must be systematically reported to permit careful comparison and to avoid introducing any confounding factors in the analysis.
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The methodology given above relies on knowing the order of the hosts/measurement collection points on the path [RFC2330] (Paxson, V., Almes, G., Mahdavi, J., and M. Mathis, “Framework for IP Performance Metrics,” May 1998.).
Path instability might cause a test packet to be observed more than once by the same host, resulting in the repetition of one or more hosts in the Path Digest.
For example, repeated observations may occur 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 was from Ha to Hb and that the new path is from Hb to Ha.
Consequently, duplication of hosts in the path digest of a vector MUST be identified before computation of statistics to avoid producing corrupted information.
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This section defines samples to measure the performance of a segment of a path over time. The definitions rely on the matrix of the spatial vector metrics defined above.
Firstly this section defines a sample of oneway delay, TypePSegmentOnewayDelayStream, and a sample of packet loss, TypePsegmentPacketLossStream.
Then it defines 2 different samples of ipdv: TypePSegmentipdvprevStream uses the current and previous packets as the selection function, and TypePSegmentipdvminStream, uses the minimum delay as one of the selected packets in every pair.
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This metric defines a sample of Oneway delays over time between a pair of hosts on a path. Since it is very close semantically to the metric TypePOnewayDelayPoissonStream defined in section 4 of [RFC2679] (Almes, G., Kalidindi, S., and M. Zekauskas, “A Oneway Delay Metric for IPPM,” September 1999.), sections 4.5 to 4.8 of [RFC2679] (Almes, G., Kalidindi, S., and M. Zekauskas, “A Oneway Delay Metric for IPPM,” September 1999.) are integral parts of the definition text below.
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TypePSegmentOnewayDelayStream
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The value of a TypePSegmentOnewayDelayStream is a pair of:
A list of times <T1, T2, ..., Tm>;
A sequence of delays.
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Given 2 hosts, Ha and Hb, of the path <H1, H2,..., Ha, ..., Hb, ..., Hn>, and the matrix of TypePSpatialOnewayDelayVector for the packets sent from Src to Dst at times <T1, T2, ..., Tm1, 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 TypePsegmentOnewayDelayStream 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 sent at time Tk passes Ha and Hb or undefined if this packet never passes Ha or (inclusive) never passes Hb.
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Some specific issues that may occur are as follows:
The metric SHALL be invalid for times < T1 , T2, ..., Tm1, Tm> if the following conditions occur:
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This metric defines a sample of packet loss over time between a pair of hosts of a path. Since it is very close semantically to the metric TypePPacketlossStream defined in section 3 of [RFC2680] (Almes, G., Kalidindi, S., and M. Zekauskas, “A Oneway Packet Loss Metric for IPPM,” September 1999.), sections 3.5 to 3.8 of [RFC2680] (Almes, G., Kalidindi, S., and M. Zekauskas, “A Oneway Packet Loss Metric for IPPM,” September 1999.) are integral parts of the definition text below.
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TypePsegmentPacketLossStream
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The value of a TypePsegmentPacketLossStream is a pair of:
A The list of times <T1, T2, ..., Tm>;
A sequence of Boolean values.
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Given two hosts, Ha and Hb, of the path <H1, H2,..., Ha, ..., Hb, ..., Hn>, and the matrix of TypePSpatialPacketLossVector for the packets sent from Src to Dst at times <T1, T2, ..., Tm1, Tm> :
<T1, L1.1, L1.2,..., L1.a, ..., L1.b, ..., L1.n, L>,
<T2, L2.1, L2.2,..., L2.a, ..., L2.b, ..., L2.n, L>,
...,
<Tm, Lm.1, Lm.2,..., Lma, ..., Lm.b, ..., Lm.n, L>.
We define the value of the sample TypePsegmentPacketLostStream from Ha to Hb as the sequence of Booleans <L1.ab, L2.ab,..., Lk.ab, ..., Lm.ab> such that for each Tk:
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Unlike TypePPacketlossStream, TypePSegmentPacketLossStream relies on the stability of the host path digest. The metric SHALL be invalid for times < T1 , T2, ..., Tm1, Tm> if the following conditions occur:
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This metric defines a sample of ipdv [RFC3393] (Demichelis, C. and P. Chimento, “IP Packet Delay Variation Metric for IP Performance Metrics (IPPM),” November 2002.) over time between a pair of hosts using the previous packet as the selection function.
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TypePSegmentipdvprevStream
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The value of a TypePSegmentipdvprevStream is a pair of:
The list of <T1, T2, ..., Tm1, Tm>;
A list of pairs of interval of times and delays;
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Given two hosts, Ha and Hb, of the path <H1, H2,..., Ha, ..., Hb, ..., Hn>, and the matrix of TypePSpatialOnewayDelayVector for the packets sent from Src to Dst at times <T1, T2, ..., Tm1, 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 TypePSegmentipdvprevStream as the sequence of packet time pairs and delay variations
<(T1, T2 , dT2.ab  dT1.ab) ,...,
(Tk1, Tk, dTk.ab  dTk1.ab), ...,
(Tm1, Tm, dTm.ab  dTm1.ab)>
For any pair, Tk, Tk1 in k=1 through m, the difference dTk.ab  dTk1.ab is undefined if:
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This metric belongs to the family of inter packet delay variation metrics (IPDV in upper case) whose results are extremely sensitive to the interpacket interval in practice.
The interpacket interval of an endtoend IPDV metric is under the control of the source (ingress point of interest). In contrast, the interpacket interval of a segment IPDV metric is not under the control the ingress point of interest of the measure, Ha. The interval will certainly vary if there is delay variation between the Source and Ha. Therefore, the ingress interpacket interval must be known at Ha in order to fully comprehend the delay variation between Ha and Hb.
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This metric defines a sample of ipdv [RFC3393] (Demichelis, C. and P. Chimento, “IP Packet Delay Variation Metric for IP Performance Metrics (IPPM),” November 2002.) over time between a pair of hosts on a path using the minimum delay as one of the selected packets in every pair.
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TypePSegmentOnewayipdvminStream
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The value of a TypePSegmentOnewayipdvminStream is a pair of:
The list of <T1, T2, ..., Tm1, Tm>;
A list of times.
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Given two hosts, Ha and Hb, of the path <H1, H2,..., Ha, ..., Hb, ..., Hn>, and the matrix of TypePSpatialOnewayDelayVector for the packets sent from Src to Dst at times <T1, T2, ..., Tm1, 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 TypePSegmentOnewayipdvminStream as the sequence of times <dT1.ab  min(dTi.ab) ,..., dTk.ab  min(dTi.ab), ..., dTm.ab  min(dTi.ab)> where:
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This metric belongs to the family of packet delay variation metrics (PDV). PDV distributions have less sensitivity to interpacket interval variations than IPDV values, as discussed above.
In principle, the PDV distribution reflects the variation over many different interpacket intervals, from the smallest interpacket 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, because a wide range of spacings are reflected in any PDV distribution.
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This section defines performance metrics between a source and a group of receivers.
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This section defines a metric for oneway delay between a source and a group of receivers.
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TypePOnetogroupDelayVector
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The value of a TypePOnetogroupDelayVector is a set of TypePOnewayDelay singletons [RFC2679] (Almes, G., Kalidindi, S., and M. Zekauskas, “A Oneway Delay Metric for IPPM,” September 1999.), which is a sequence of times (a real number in the dimension of seconds with sufficient resolution to convey the results).
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Given a TypeP packet sent by the source Src at time T, and the N hosts { Recv1,...,RecvN } which receive the packet at the time { T+dT1,...,T+dTn }, or the packet does not pass a receiver within a specified loss threshold time, then the TypePOnetogroupDelayVector is defined as the set of the TypePOnewayDelay singletons between Src and each receiver with value of { dT1, dT2,...,dTn }, where any of the singletons may be undefined if the packet did not pass the corresponding receiver within a specified loss threshold time.
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TypePOnetogroupPacketLossVector
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The value of a TypePOnetogroupPacketLossVector is a set of TypePOnewayPacketLoss singletons [RFC2680] (Almes, G., Kalidindi, S., and M. Zekauskas, “A Oneway Packet Loss Metric for IPPM,” September 1999.).
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Given a Type P packet sent by the source Src at T and the N hosts, Recv1,...,RecvN, the TypePOnetogroupPacketLossVector is defined as a set of the TypePOnewayPacketLoss singletons between Src and each of the receivers
{T, <L1=01>,<L2=01>,..., <LN=01>},
where the boolean value 01 depends on receiving the packet at a particular receiver within a loss threshold time.
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TypePOnetogroupipdvVector
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The value of a TypePOnetogroupipdvVector is a set of TypePOnewayipdv singletons [RFC3393] (Demichelis, C. and P. Chimento, “IP Packet Delay Variation Metric for IP Performance Metrics (IPPM),” November 2002.).
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Given a TypeP packet stream, TypePOnetogroupipdvVector is defined for two packets transferred 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 TypePOnetogroupDelayVector from Src to { Recv1,..., RecvN } at time T1 and the value of the TypePOnetogroupDelayVector from Src to { Recv1,...,RecvN } at time T2. T1 is the wiretime at which Src sent the first bit of the first packet, and T2 is the wiretime at which Src sent the first bit of the second packet. This metric is derived from the TypePOnetogroupDelayVector metric.
For a set of real numbers {ddT1,...,ddTn}, the TypePOnetogroupipdvVector from Src to { Recv1,...,RecvN } at T1, T2 is {ddT1,...,ddTn} means that Src sent two packets, the first at wiretime T1 (first bit), and the second at wiretime T2 (first bit) and the packets were received by { Recv1,...,RecvN } at wiretime {dT1+T1,...,dTn+T1}(last bit of the first packet), and at wiretime {dT'1+T2,...,dT'n+T2} (last bit of the second packet), and that {dT'1dT1,...,dT'ndTn} ={ddT1,...,ddTn}.
For any pair of selected packets, the difference dT'ndTn is undefined if:
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The onetogroup metrics defined above are directly achieved by collecting relevant unicast oneway metrics measurements results and by gathering them per group of receivers. They produce network performance information which guides engineers toward potential problems which may have happened on any branch of a multicast routing tree.
The results of these metrics are not directly usable to present the performance of a group because each result is made of a huge number of singletons which are difficult to read and analyze. As an example, delays are not comparable because the distance between receiver and sender differs. Furthermore they don't capture relative performance situation a multiparty communication.
From the performance point of view, the multiparty communication services not only require the support of absolute performance information but also information on "relative performance". The relative performance means the difference between absolute performance of all users. Directly using the oneway metrics cannot present the relative performance situation. However, if we use the variations of all users oneway 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 online gaming. A very small difference in delay might result in failure in the game. We have to use multicast specific statistic metrics to define the relative delay required by online gaming. 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 onetogroup 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 Oneway delay in [RFC2679]. However, there is a dramatic difference between the statistics for onetoone communications and for onetomany 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 illustrated in Figure 4 (Matrix M (n*m)). For a Matrix M each row is a set of Oneway singletons spreading over the time dimension and each column is another set of Oneway 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 oneway delay singleton. Each column is a delay vector contains the Oneway 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 Oneway 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 predefined time interval to the reference point rather than sending every oneway 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 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 these statistics are distributed over the space dimension. For instance, a TV broadcast service provider had the performance Matrix M and calculated the Oneway 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 requires twice as much calculation to have this statistic over both time and space dimensions. This kind of statistics is referred to as 2level statistics to distinguish them from 1level statistics calculated over either space or time dimension. It can be easily proven that no matter over which dimension a 2level statistic is calculated first, the results are the same. I.e. one can calculate the 2level delay mean using the Matrix M by having the 1level delay mean over the time dimension first and then calculate the mean of the obtained vector to find out the 2level delay mean. Or, he can do the 1level statistic calculation over the space dimension first and then have the 2level delay mean. Both two results will be exactly the same. Therefore, when defining a 2level statistic there is no need to specify the order in which the calculation is executed.
Many statistics can be defined for the proposed onetogroup 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 onetoone communication. New statistic definitions are presented, which summarize the onetoone statistics over all the Receivers in the Group.
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The packet loss does have effects on oneway metrics and their statistics. For example, a lost packet can result in an infinite oneway 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 such a strong impact on the statistics calculation for the onetogroup metrics that it can not be solved by the same method used for oneway metrics. This is due to the complexity 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 oneway 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. The extreme situation being the case when no packets arrive at any user. 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 … R1dTK1 UNDEF R1dTK+1… R1DM } where “UNDEF” is an undefined value, the reference point can replace it by R1dTK = {(R1dTK1)+( 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 TypePFiniteOnewayDelayMean R1DM as shown in Figure. 8 without any packet loss and User2 calculates the R2DM with N2 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.
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This section defines the overall oneway 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 R1MD \  2 R2dT1 R2dT2 R2dT3 ... R2dTk R2MD   3 R3dT1 R3dT2 R3dT3 ... R3dTk R3MD > Group delay .  .  .  n RndT1 RndT2 RndT3 ... RndTk RnMD / Receivern delay
Figure 5: Onetogroup Mean Delay 
Statistics are computed on the finite Oneway delays of the matrix above.
All Onetogroup delay statistics are expressed in seconds with sufficient resolution to convey 3 significant digits.
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This section defines TypePOnetogroupReceivernMeanDelay the Delay Mean at each Receiver N, also named RnDM.
We obtain the value of TypePOnewayDelay singleton for all packets sent during the test interval at each Receiver (Destination), as per [RFC2679] (Almes, G., Kalidindi, S., and M. Zekauskas, “A Oneway Delay Metric for IPPM,” September 1999.). For each packet that arrives within Tmax of its sending time, TstampSrc, the oneway 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 \ RnMD =  * > TstampRecv[i]  TstampSrc[i] J[n] /  i = 1
Figure 6: TypePOnetogroupReceiverNMeanDelay 
where all packets i= 1 through J[n] have finite singleton delays.
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This section defines TypePOnetogroupMeanDelay, the Mean Oneway delay calculated over the entire Group, also named GMD.
N  1 \ GMD =  * > RnDM N /  n = 1
Figure 7: TypePOnetogroupMeanDelay 
Note that the Group Mean Delay can also be calculated by summing the Finite oneway Delay singletons in the Matrix, and dividing by the number of Finite Oneway Delay singletons.
TOC 
This section defines a metric for the range of mean delays over all N receivers in the group (R1DM, R2DM,...RnDM).
TypePOnetogroupRangeMeanDelay = GRMD = max(RnDM)  min(RnDM)
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This section defines a metric for the maximum of mean delays over all N receivers in the group (R1DM, R2DM,...RnDM).
TypePOnetogroupMaxMeanDelay = GMMD = max(RnDM)
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This section defines the overall oneway 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 / Receivern Loss Ratio
Figure 8: Onetogroup Loss Ratio 
Statistics are computed on the sample of TypePOnewayPacketLoss [RFC2680] (Almes, G., Kalidindi, S., and M. Zekauskas, “A Oneway Packet Loss Metric for IPPM,” September 1999.) of the matrix above.
All loss ratios are expressed in units of packets lost to total packets sent.
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Given a Matrix of loss singletons as illustrated above, determine
the TypePOnewayPacketLossAverage for the sample at each
receiver, according to the definitions and method of [RFC2680] (Almes, G., Kalidindi, S., and M. Zekauskas, “A Oneway Packet Loss Metric for IPPM,” September 1999.). The TypePOnewayPacketLossAverage and
the TypePOnetogroupReceivernLossRatio, 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: TypePOnetogroupReceivernLossRatio 
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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: TypePOnetogroupReceivernCompLossRatio 
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TypePOnetogroupLossRatio, the overall Group loss ratio, also named GLR, is defined as
K,N  1 \ GLR =  * > L(k,n) K*N /  k,n = 1
Figure 11: TypePOnetogroupLossRatio 
TOC 
The Onetogroup Loss Ratio Range is defined as:
TypePOnetogroupRangeLossRatio = 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.
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This section defines oneway 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: Onetogroup Delay Variation Matrix (DVMa) 
Statistics are computed on the sample of TypePOnewayDelayVariation singletons of the group delay variation matrix above where RnddTk is the TypePOnewayDelayVariation singleton evaluated at Receiver n for the packet k and where RnDV is the pointtopoint oneway packet delay variation for Receiver n.
All Onetogroup delay variation statistics are expressed in seconds with sufficient resolution to convey 3 significant digits.
TOC 
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 pointtopoint metric). For each receiver, the DV is usually expressed as the 110^(3) quantile of oneway delay minus the minimum oneway delay.
TypePOnetogroupRangeDelayVariation = GRDV =
= max(RnDV) – min(RnDV) for all n receivers
This range is determined from the minimum and maximum values of the pointtopoint oneway 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 110^3 quantile of oneway delay minus the minimum oneway delay. If a more demanding service is considered, one alternative is to use the 110^5 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.
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Virtually all the guidance on measurement processes supplied by the earlier IPPM RFCs (such as [RFC2679] (Almes, G., Kalidindi, S., and M. Zekauskas, “A Oneway Delay Metric for IPPM,” September 1999.) and [RFC2680] (Almes, G., Kalidindi, S., and M. Zekauskas, “A Oneway Packet Loss Metric for IPPM,” September 1999.)) for onetoone 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.
In recognition of the likely need to minimize the form of the results for storage and communication, the Group metrics above have been constructed to allow some computations on a perReceiver 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).
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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 a very large number of the points of interest. It can lead to a scalability issue at the reference point by overloading the network resources.
The distributed calculation method can save much more bandwidth and mitigate issues arising from scalability at the reference point side.
However, it may result in a lost of information. As all measured singletons are not available for building up the group matrix, the real performance over time can be hidden from the result. For example, the loss pattern can be missed by simply accepting the loss ratio. This tradeoff between bandwidth consumption and information acquisition has to be taken into account when designing the measurement approach.
One possible solution could be to transit the statistic parameters to the reference point first to obtain the general information of the group performance. If detailed 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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To prevent any bias in the result, the configuration of a onetomany measure must take in consideration that intrically more packets will to be routed than sent (copies of a packet sent are expected to arrive at many destination points) and selects a test packets rate that will not impact the network performance.
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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 not colocated and that results are gathered in a point of reference for further usages.
Multimetrics samples are represented in 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 
Two methods are available to compute statistics on a matrix:
These 2 methods differ only by the order of the aggregation. The order does not impact the computation resources required. It does not change the value of the result. However, it impacts severely the minimal volume of data to report:
Method 2 has severe drawbacks in terms of security and dimensioning:
The computation period over time period (commonly named aggregation period) provides the reporting side with a control of various collecting aspects such as bandwidth, computation and storage capacities. So this draft defines metrics based on method 1.
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Two methods are available to compute spatial statistics:
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Two methods are available to compute group statistics:
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Usually IPPM WG documents defines each metric reporting within its 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 onetogroup 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.
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The reporting of spatial metrics shares a lot of aspects with RFC267980. 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.
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Endtoend metrics can't determine the path of the measure despite IPPM RFCs recommend it to be reported (See Section 3.8.4 of [RFC2679] (Almes, G., Kalidindi, S., and M. Zekauskas, “A Oneway Delay Metric for IPPM,” September 1999.)). 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.
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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.
TOC 
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 timestamping compared to wire time.
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The reporting includes information to report for onewaydelay as the Section 3.6 of [RFC2679] (Almes, G., Kalidindi, S., and M. Zekauskas, “A Oneway Delay Metric for IPPM,” September 1999.). The same apply for packet loss and ipdv.
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All reporting rules described in [RFC2679] (Almes, G., Kalidindi, S., and M. Zekauskas, “A Oneway Delay Metric for IPPM,” September 1999.) and [RFC2680] (Almes, G., Kalidindi, S., and M. Zekauskas, “A Oneway Packet Loss Metric for IPPM,” September 1999.) apply to the corresponding Onetogroup metrics. Following are specific parameters that should be reported.
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As suggested by the [RFC2679] (Almes, G., Kalidindi, S., and M. Zekauskas, “A Oneway Delay Metric for IPPM,” September 1999.) and [RFC2680] (Almes, G., Kalidindi, S., and M. Zekauskas, “A Oneway Packet Loss Metric for IPPM,” September 1999.), the path traversed by the packet SHOULD be reported, if possible. For Onetogroup metrics, the path tree between the source and the destinations or the set of paths between the source and each destination SHOULD be reported.
Path tree might not be as valuable as individual paths because an incomplete path might be difficult to identify in the path tree. For example, how many points of interest are reached by a packet travelling along an incomplete path?
TOC 
The group size should be reported as one of the critical management parameters. Onetogroup metrics, unlike spatial metrics, don't require the ordering of the points of interests because group members receive the packets in parallel.
TOC 
It is the same as described in section 10.1.3.
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It is the same as described in section 10.1.4.
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As explained in section 9, the measurement method will have impact on the analysis of the measurement result. Therefore, it should be reported.
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IANA assigns each metric defined by the IPPM WG with a unique identifier as per [RFC4148] (Stephan, E., “IP Performance Metrics (IPPM) Metrics Registry,” August 2005.) in the IANAIPPMMETRICSREGISTRYMIB.
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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 built with pieces of information introduced and explained in oneway delay definitions [RFC2679] (Almes, G., Kalidindi, S., and M. Zekauskas, “A Oneway Delay Metric for IPPM,” September 1999.), in packet loss definitions [RFC2680] (Almes, G., Kalidindi, S., and M. Zekauskas, “A Oneway Packet Loss Metric for IPPM,” September 1999.) and in IPDV definitions of [RFC3393] (Demichelis, C. and P. Chimento, “IP Packet Delay Variation Metric for IP Performance Metrics (IPPM),” November 2002.) and [RFC3432] (Raisanen, V., Grotefeld, G., and A. Morton, “Network performance measurement with periodic streams,” November 2002.). It includes not only information given by "Reporting the metric" sections but by sections "Methodology" and "Errors and Uncertainties".
Following are the elements of information taken from endtoend metrics definitions referred in this memo and from spatial and multicast metrics it defines:
Following is the information of each vector that should be available to compute samples:
A spatial or a onetogroup 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:
Following is the information of each statistic that should be reported:
TOC 
Spatial and onetogroup metrics are defined on the top of endtoend metrics. Security considerations discussed in Oneway delay metrics definitions of [RFC2679] (Almes, G., Kalidindi, S., and M. Zekauskas, “A Oneway Delay Metric for IPPM,” September 1999.) , in packet loss metrics definitions of [RFC2680] (Almes, G., Kalidindi, S., and M. Zekauskas, “A Oneway Packet Loss Metric for IPPM,” September 1999.) and in IPDV metrics definitions of[RFC3393] (Demichelis, C. and P. Chimento, “IP Packet Delay Variation Metric for IP Performance Metrics (IPPM),” November 2002.) and [RFC3432] (Raisanen, V., Grotefeld, G., and A. Morton, “Network performance measurement with periodic streams,” November 2002.) apply to metrics defined in this memo.
TOC 
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.
TOC 
Reporting of measurement results from a huge number of probes may overload reference point resources (network, network interfaces, computation capacities ...).
The configuration of a measurement must take in consideration that implicitly more packets will be routed than sent 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.
Onetogroup 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.
TOC 
Lei would like to acknowledge Prof. Zhili Sun from CCSR, University of Surrey, for his instruction and helpful comments on this work.
TOC 
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] (Stephan, E., “IP Performance Metrics (IPPM) Metrics Registry,” August 2005.) :
IANA is asked to register the following metrics in the IANAIPPMMETRICSREGISTRYMIB :
ietfSpatialOneWayDelayVector OBJECTIDENTITY
STATUS current
DESCRIPTION
"TypePSpatialOnewayDelayVector"
REFERENCE
:= { ianaIppmMetrics nn }  IANA assigns nn"Reference "RFCyyyy, section 5.1."
 RFC Ed.: replace yyyy with actual RFC number & remove this note
ietfSpatialPacketLossVector OBJECTIDENTITY
STATUS current
DESCRIPTION
"TypePSpatialPacketLossVector"
REFERENCE
:= { ianaIppmMetrics nn }  IANA assigns nn"Reference "RFCyyyy, section 5.2."
 RFC Ed.: replace yyyy with actual RFC number & remove this note
ietfSpatialOneWayIpdvVector OBJECTIDENTITY
STATUS current
DESCRIPTION
"TypePSpatialOnewayipdvVector"
REFERENCE
:= { ianaIppmMetrics nn }  IANA assigns nn"Reference "RFCyyyy, section 5.3."
 RFC Ed.: replace yyyy with actual RFC number & remove this note
ietfSegmentOneWayDelayStream OBJECTIDENTITY
STATUS current
DESCRIPTION
"TypePSegmentOnewayDelayStream"
REFERENCE
:= { ianaIppmMetrics nn }  IANA assigns nn"Reference "RFCyyyy, section 6.1."
 RFC Ed.: replace yyyy with actual RFC number & remove this note
ietfSegmentPacketLossStream OBJECTIDENTITY
STATUS current
DESCRIPTION
"TypePSegmentPacketLossStream"
REFERENCE
:= { ianaIppmMetrics nn }  IANA assigns nn"Reference "RFCyyyy, section 6.2."
 RFC Ed.: replace yyyy with actual RFC number & remove this note
ietfSegmentIpdvPrevStream OBJECTIDENTITY
STATUS current
DESCRIPTION
"TypePSegmentipdvprevStream"
REFERENCE
:= { ianaIppmMetrics nn }  IANA assigns nn"Reference "RFCyyyy, section 6.3."
 RFC Ed.: replace yyyy with actual RFC number & remove this note
ietfSegmentIpdvMinStream OBJECTIDENTITY
STATUS current
DESCRIPTION
"TypePSegmentipdvminStream"
REFERENCE
:= { ianaIppmMetrics nn }  IANA assigns nn"Reference "RFCyyyy, section 6.4."
 RFC Ed.: replace yyyy with actual RFC number & remove this note
 Onetogroup metrics
ietfOneToGroupDelayVector OBJECTIDENTITY
STATUS current
DESCRIPTION
"TypePOnetogroupDelayVector"
REFERENCE
:= { ianaIppmMetrics nn }  IANA assigns nn"Reference "RFCyyyy, section 7.1."
 RFC Ed.: replace yyyy with actual RFC number & remove this note
ietfOneToGroupPacketLossVector OBJECTIDENTITY
STATUS current
DESCRIPTION
"TypePOnetogroupPacketLossVector"
REFERENCE
:= { ianaIppmMetrics nn }  IANA assigns nn"Reference "RFCyyyy, section 7.2."
 RFC Ed.: replace yyyy with actual RFC number & remove this note
ietfOneToGroupIpdvVector OBJECTIDENTITY
STATUS current
DESCRIPTION
"TypePOnetogroupipdvVector"
REFERENCE
:= { ianaIppmMetrics nn }  IANA assigns nn"Reference "RFCyyyy, section 7.3."
 RFC Ed.: replace yyyy with actual RFC number & remove this note
 One to group statistics

ietfOnetoGroupReceiverNMeanDelay OBJECTIDENTITY
STATUS current
DESCRIPTION
"TypePOnetogroupReceivernMeanDelay"
REFERENCE
:= { ianaIppmMetrics nn }  IANA assigns nn"Reference "RFCyyyy, section 8.3.1."
 RFC Ed.: replace yyyy with actual RFC number & remove this note
ietfOneToGroupMeanDelay OBJECTIDENTITY
STATUS current
DESCRIPTION
"TypePOnetogroupMeanDelay"
REFERENCE
:= { ianaIppmMetrics nn }  IANA assigns nn"Reference "RFCyyyy, section 8.3.2."
 RFC Ed.: replace yyyy with actual RFC number & remove this note
ietfOneToGroupRangeMeanDelay OBJECTIDENTITY
STATUS current
DESCRIPTION
"TypePOnetogroupRangeMeanDelay"
REFERENCE
:= { ianaIppmMetrics nn }  IANA assigns nn"Reference "RFCyyyy, section 8.3.3."
 RFC Ed.: replace yyyy with actual RFC number & remove this note
ietfOneToGroupMaxMeanDelay OBJECTIDENTITY
STATUS current
DESCRIPTION
"TypePOnetogroupMaxMeanDelay"
REFERENCE
:= { ianaIppmMetrics nn }  IANA assigns nn"Reference "RFCyyyy, section 8.3.4."
 RFC Ed.: replace yyyy with actual RFC number & remove this note
ietfOneToGroupReceiverNLossRatio OBJECTIDENTITY
STATUS current
DESCRIPTION
"TypePOnetogroupReceivernLossRatio"
REFERENCE
:= { ianaIppmMetrics nn }  IANA assigns nn"Reference "RFCyyyy, section 8.4.1."
 RFC Ed.: replace yyyy with actual RFC number & remove this note

ietfOneToGroupReceiverNCompLossRatio OBJECTIDENTITY
STATUS current
DESCRIPTION
"TypePOnetogroupReceivernCompLossRatio"
REFERENCE
:= { ianaIppmMetrics nn }  IANA assigns nn"Reference "RFCyyyy, section 8.4.2."
 RFC Ed.: replace yyyy with actual RFC number & remove this note
ietfOneToGroupLossRatio OBJECTIDENTITY
STATUS current
DESCRIPTION
"TypePOnetogroupLossRatio"
REFERENCE
:= { ianaIppmMetrics nn }  IANA assigns nn"Reference "RFCyyyy, section 8.4.3."
 RFC Ed.: replace yyyy with actual RFC number & remove this note

ietfOneToGroupRangeLossRatio OBJECTIDENTITY
STATUS current
DESCRIPTION
"TypePOnetogroupRangeLossRatio"
REFERENCE
:= { ianaIppmMetrics nn }  IANA assigns nn"Reference "RFCyyyy, section 8.4.4."
 RFC Ed.: replace yyyy with actual RFC number & remove this note
ietfOneToGroupRangeDelayVariation OBJECTIDENTITY
STATUS current
DESCRIPTION
"TypePOnetogroupRangeDelayVariation"
REFERENCE
:= { ianaIppmMetrics nn }  IANA assigns nn"Reference "RFCyyyy, section 8.5.1."
 RFC Ed.: replace yyyy with actual RFC number & remove this note

TOC 
TOC 
[RFC2119]  Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” BCP 14, RFC 2119, March 1997 (TXT, HTML, XML). 
[RFC2679]  Almes, G., Kalidindi, S., and M. Zekauskas, “A Oneway Delay Metric for IPPM,” RFC 2679, September 1999 (TXT). 
[RFC2680]  Almes, G., Kalidindi, S., and M. Zekauskas, “A Oneway Packet Loss Metric for IPPM,” RFC 2680, September 1999 (TXT). 
[RFC3393]  Demichelis, C. and P. Chimento, “IP Packet Delay Variation Metric for IP Performance Metrics (IPPM),” RFC 3393, November 2002 (TXT). 
[RFC4148]  Stephan, E., “IP Performance Metrics (IPPM) Metrics Registry,” BCP 108, RFC 4148, August 2005 (TXT). 
TOC 
[ID.ietfippmspatialcomposition]  Morton, A. and E. Stephan, “Spatial Composition of Metrics,” draftietfippmspatialcomposition11 (work in progress), April 2010 (TXT). 
[RFC2330]  Paxson, V., Almes, G., Mahdavi, J., and M. Mathis, “Framework for IP Performance Metrics,” RFC 2330, May 1998 (TXT, HTML, XML). 
[RFC3432]  Raisanen, V., Grotefeld, G., and A. Morton, “Network performance measurement with periodic streams,” RFC 3432, November 2002 (TXT). 
TOC 
Stephan Emile  
France Telecom Division R&D  
2 avenue Pierre Marzin  
Lannion, F22307  
Fax:  +33 2 96 05 18 52 
Email:  emile.stephan@orangeftgroup.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 