draft-ietf-ippm-loss-06.txt   rfc2680.txt 
Network Working Group G. Almes Network Working Group G. Almes
INTERNET-DRAFT S. Kalidindi Request for Comments: 2680 S. Kalidindi
Expiration Date: August 1999 M. Zekauskas Category: Standards Track M. Zekauskas
Advanced Network & Services Advanced Network & Services
February 1999 September 1999
A One-way Packet Loss Metric for IPPM A One-way Packet Loss Metric for IPPM
<draft-ietf-ippm-loss-06.txt>
1. Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months Status of this Memo
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at This document specifies an Internet standards track protocol for the
http://www.ietf.org/ietf/1id-abstracts.txt Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
The list of Internet-Draft shadow directories can be accessed at Copyright Notice
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This memo provides information for the Internet community. This memo Copyright (C) The Internet Society (1999). All Rights Reserved.
does not specify an Internet standard of any kind. Distribution of
this memo is unlimited.
2. Introduction 1. Introduction
This memo defines a metric for one-way packet loss across Internet This memo defines a metric for one-way packet loss across Internet
paths. It builds on notions introduced and discussed in the IPPM paths. It builds on notions introduced and discussed in the IPPM
Framework document, RFC 2330 [1]; the reader is assumed to be Framework document, RFC 2330 [1]; the reader is assumed to be
familiar with that document. familiar with that document.
This memo is intended to be parallel in structure to a companion This memo is intended to be parallel in structure to a companion
document for One-way Delay (currently "A One-way Delay Metric for document for One-way Delay ("A One-way Delay Metric for IPPM") [2];
IPPM" <draft-ietf-ippm-delay-06.txt>) [2]; the reader is assumed to the reader is assumed to be familiar with that document.
be familiar with that document.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [5]. document are to be interpreted as described in RFC 2119 [5].
Although RFC 2119 was written with protocols in mind, the key words Although RFC 2119 was written with protocols in mind, the key words
are used in this document for similar reasons. They are used to are used in this document for similar reasons. They are used to
ensure the results of measurements from two different implementations ensure the results of measurements from two different implementations
are comparable, and to note instances when an implementation could are comparable, and to note instances when an implementation could
perturb the network. perturb the network.
skipping to change at page 2, line 36 skipping to change at page 2, line 20
+ Using this sample, several 'statistics' of the sample are defined + Using this sample, several 'statistics' of the sample are defined
and discussed. and discussed.
This progression from singleton to sample to statistics, with clear This progression from singleton to sample to statistics, with clear
separation among them, is important. separation among them, is important.
Whenever a technical term from the IPPM Framework document is first Whenever a technical term from the IPPM Framework document is first
used in this memo, it will be tagged with a trailing asterisk. For used in this memo, it will be tagged with a trailing asterisk. For
example, "term*" indicates that "term" is defined in the Framework. example, "term*" indicates that "term" is defined in the Framework.
2.1. Motivation: 1.1. Motivation:
Understanding one-way packet loss of Type-P* packets from a source Understanding one-way packet loss of Type-P* packets from a source
host* to a destination host is useful for several reasons: host* to a destination host is useful for several reasons:
+ Some applications do not perform well (or at all) if end-to-end + Some applications do not perform well (or at all) if end-to-end
loss between hosts is large relative to some threshold value. loss between hosts is large relative to some threshold value.
+ Excessive packet loss may make it difficult to support certain + Excessive packet loss may make it difficult to support certain
real-time applications (where the precise threshold of "excessive" real-time applications (where the precise threshold of "excessive"
depends on the application). depends on the application).
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+ In quality-of-service (QoS) enabled networks, provisioning in one + In quality-of-service (QoS) enabled networks, provisioning in one
direction may be radically different than provisioning in the direction may be radically different than provisioning in the
reverse direction, and thus the QoS guarantees differ. Measuring reverse direction, and thus the QoS guarantees differ. Measuring
the paths independently allows the verification of both the paths independently allows the verification of both
guarantees. guarantees.
It is outside the scope of this document to say precisely how loss It is outside the scope of this document to say precisely how loss
metrics would be applied to specific problems. metrics would be applied to specific problems.
2.2. General Issues Regarding Time 1.2. General Issues Regarding Time
{Comment: the terminology below differs from that defined by ITU-T {Comment: the terminology below differs from that defined by ITU-T
documents (e.g., G.810, "Definitions and terminology for documents (e.g., G.810, "Definitions and terminology for
synchronization networks" and I.356, "B-ISDN ATM layer cell transfer synchronization networks" and I.356, "B-ISDN ATM layer cell transfer
performance"), but is consistent with the IPPM Framework document. performance"), but is consistent with the IPPM Framework document.
In general, these differences derive from the different backgrounds; In general, these differences derive from the different backgrounds;
the ITU-T documents historically have a telephony origin, while the the ITU-T documents historically have a telephony origin, while the
authors of this document (and the Framework) have a computer systems authors of this document (and the Framework) have a computer systems
background. Although the terms defined below have no direct background. Although the terms defined below have no direct
equivalent in the ITU-T definitions, after our definitions we will equivalent in the ITU-T definitions, after our definitions we will
skipping to change at page 5, line 5 skipping to change at page 4, line 31
Skew measures the change of accuracy, or of synchronization, Skew measures the change of accuracy, or of synchronization,
with time. For example, the clock on a given host might gain with time. For example, the clock on a given host might gain
1.3 msec per hour and thus be 27.1 msec behind UTC at one time 1.3 msec per hour and thus be 27.1 msec behind UTC at one time
and only 25.8 msec an hour later. In this case, we say that the and only 25.8 msec an hour later. In this case, we say that the
clock of the given host has a skew of 1.3 msec per hour relative clock of the given host has a skew of 1.3 msec per hour relative
to UTC, which threatens accuracy. We might also speak of the to UTC, which threatens accuracy. We might also speak of the
skew of one clock relative to another clock, which threatens skew of one clock relative to another clock, which threatens
synchronization. {Comment: A rough ITU-T equivalent is "time synchronization. {Comment: A rough ITU-T equivalent is "time
drift".} drift".}
3. A Singleton Definition for One-way Packet Loss 2. A Singleton Definition for One-way Packet Loss
3.1. Metric Name: 2.1. Metric Name:
Type-P-One-way-Packet-Loss Type-P-One-way-Packet-Loss
3.2. Metric Parameters: 2.2. Metric Parameters:
+ Src, the IP address of a host + Src, the IP address of a host
+ Dst, the IP address of a host + Dst, the IP address of a host
+ T, a time + T, a time
3.3. Metric Units: 2.3. Metric Units:
The value of a Type-P-One-way-Packet-Loss is either a zero The value of a Type-P-One-way-Packet-Loss is either a zero
(signifying successful transmission of the packet) or a one (signifying successful transmission of the packet) or a one
(signifying loss). (signifying loss).
3.4. Definition: 2.4. Definition:
>>The *Type-P-One-way-Packet-Loss* from Src to Dst at T is 0<< means >>The *Type-P-One-way-Packet-Loss* from Src to Dst at T is 0<< means
that Src sent the first bit of a Type-P packet to Dst at wire-time* T that Src sent the first bit of a Type-P packet to Dst at wire-time* T
and that Dst received that packet. and that Dst received that packet.
>>The *Type-P-One-way-Packet-Loss* from Src to Dst at T is 1<< means >>The *Type-P-One-way-Packet-Loss* from Src to Dst at T is 1<< means
that Src sent the first bit of a type-P packet to Dst at wire-time T that Src sent the first bit of a type-P packet to Dst at wire-time T
and that Dst did not receive that packet. and that Dst did not receive that packet.
3.5. Discussion: 2.5. Discussion:
Thus, Type-P-One-way-Packet-Loss is 0 exactly when Type-P-One-way- Thus, Type-P-One-way-Packet-Loss is 0 exactly when Type-P-One-way-
Delay is a finite positive value, and it is 1 exactly when Type-P- Delay is a finite value, and it is 1 exactly when Type-P-One-way-
One-way-Delay is undefined. Delay is undefined.
The following issues are likely to come up in practice: The following issues are likely to come up in practice:
+ A given methodology will have to include a way to distinguish + A given methodology will have to include a way to distinguish
between a packet loss and a very large (but finite) delay. As between a packet loss and a very large (but finite) delay. As
noted by Mahdavi and Paxson [3], simple upper bounds (such as the noted by Mahdavi and Paxson [3], simple upper bounds (such as the
255 seconds theoretical upper bound on the lifetimes of IP 255 seconds theoretical upper bound on the lifetimes of IP
packets [4]) could be used, but good engineering, including an packets [4]) could be used, but good engineering, including an
understanding of packet lifetimes, will be needed in practice. understanding of packet lifetimes, will be needed in practice.
{Comment: Note that, for many applications of these metrics, there {Comment: Note that, for many applications of these metrics, there
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these packets as lost but packet with corruption in other parts of these packets as lost but packet with corruption in other parts of
the packet as not lost would be inconsistent.} the packet as not lost would be inconsistent.}
+ If the packet is duplicated along the path (or paths) so that + If the packet is duplicated along the path (or paths) so that
multiple non-corrupt copies arrive at the destination, then the multiple non-corrupt copies arrive at the destination, then the
packet is counted as received. packet is counted as received.
+ If the packet is fragmented and if, for whatever reason, + If the packet is fragmented and if, for whatever reason,
reassembly does not occur, then the packet will be deemed lost. reassembly does not occur, then the packet will be deemed lost.
3.6. Methodologies: 2.6. Methodologies:
As with other Type-P-* metrics, the detailed methodology will depend As with other Type-P-* metrics, the detailed methodology will depend
on the Type-P (e.g., protocol number, UDP/TCP port number, size, on the Type-P (e.g., protocol number, UDP/TCP port number, size,
precedence). precedence).
Generally, for a given Type-P, one possible methodology would proceed Generally, for a given Type-P, one possible methodology would proceed
as follows: as follows:
+ Arrange that Src and Dst have clocks that are synchronized with + Arrange that Src and Dst have clocks that are synchronized with
each other. The degree of synchronization is a parameter of the each other. The degree of synchronization is a parameter of the
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see what percentage of packets from a given stream exceed a given see what percentage of packets from a given stream exceed a given
time-out value.} time-out value.}
Issues such as the packet format, the means by which Dst knows when Issues such as the packet format, the means by which Dst knows when
to expect the test packet, and the means by which Src and Dst are to expect the test packet, and the means by which Src and Dst are
synchronized are outside the scope of this document. {Comment: We synchronized are outside the scope of this document. {Comment: We
plan to document elsewhere our own work in describing such more plan to document elsewhere our own work in describing such more
detailed implementation techniques and we encourage others to as detailed implementation techniques and we encourage others to as
well.} well.}
3.7. Errors and Uncertainties: 2.7. Errors and Uncertainties:
The description of any specific measurement method should include an The description of any specific measurement method should include an
accounting and analysis of various sources of error or uncertainty. accounting and analysis of various sources of error or uncertainty.
The Framework document provides general guidance on this point. The Framework document provides general guidance on this point.
For loss, there are three sources of error: For loss, there are three sources of error:
+ Synchronization between clocks on Src and Dst. + Synchronization between clocks on Src and Dst.
+ The packet-loss threshold (which is related to the synchronization + The packet-loss threshold (which is related to the synchronization
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The measurement instruments should be calibrated such that the loss The measurement instruments should be calibrated such that the loss
threshold is reasonable for application of the metrics and the clocks threshold is reasonable for application of the metrics and the clocks
are synchronized enough so the loss threshold remains reasonable. are synchronized enough so the loss threshold remains reasonable.
In addition, the instruments should be checked to ensure the that the In addition, the instruments should be checked to ensure the that the
possibility a packet arrives at the network interface, but is lost possibility a packet arrives at the network interface, but is lost
due to congestion on the interface or to other resource exhaustion due to congestion on the interface or to other resource exhaustion
(e.g., buffers) on the instrument is low. (e.g., buffers) on the instrument is low.
3.8. Reporting the metric: 2.8. Reporting the metric:
The calibration and context in which the metric is measured MUST be The calibration and context in which the metric is measured MUST be
carefully considered, and SHOULD always be reported along with metric carefully considered, and SHOULD always be reported along with metric
results. We now present four items to consider: Type-P of the test results. We now present four items to consider: Type-P of the test
packets, the loss threshold, instrument calibration, and the path packets, the loss threshold, instrument calibration, and the path
traversed by the test packets. This list is not exhaustive; any traversed by the test packets. This list is not exhaustive; any
additional information that could be useful in interpreting additional information that could be useful in interpreting
applications of the metrics should also be reported. applications of the metrics should also be reported.
3.8.1. Type-P 2.8.1. Type-P
As noted in the Framework document [1], the value of the metric may As noted in the Framework document [1], the value of the metric may
depend on the type of IP packets used to make the measurement, or depend on the type of IP packets used to make the measurement, or
"Type-P". The value of Type-P-One-way-Delay could change if the "Type-P". The value of Type-P-One-way-Delay could change if the
protocol (UDP or TCP), port number, size, or arrangement for special protocol (UDP or TCP), port number, size, or arrangement for special
treatment (e.g., IP precedence or RSVP) changes. The exact Type-P treatment (e.g., IP precedence or RSVP) changes. The exact Type-P
used to make the measurements MUST be accurately reported. used to make the measurements MUST be accurately reported.
3.8.2. Loss threshold 2.8.2. Loss threshold
The threshold (or methodology to distinguish) between a large finite The threshold (or methodology to distinguish) between a large finite
delay and loss MUST be reported. delay and loss MUST be reported.
3.8.3. Calibration results 2.8.3. Calibration results
The degree of synchronization between the Src and Dst clocks MUST be The degree of synchronization between the Src and Dst clocks MUST be
reported. If possible, possibility that a test packet that arrives reported. If possible, possibility that a test packet that arrives
at the Dst network interface is reported as lost due to resource at the Dst network interface is reported as lost due to resource
exhaustion on Dst SHOULD be reported. exhaustion on Dst SHOULD be reported.
3.8.4. Path 2.8.4. Path
Finally, the path traversed by the packet SHOULD be reported, if Finally, the path traversed by the packet SHOULD be reported, if
possible. In general it is impractical to know the precise path a possible. In general it is impractical to know the precise path a
given packet takes through the network. The precise path may be given packet takes through the network. The precise path may be
known for certain Type-P on short or stable paths. If Type-P known for certain Type-P on short or stable paths. If Type-P
includes the record route (or loose-source route) option in the IP includes the record route (or loose-source route) option in the IP
header, and the path is short enough, and all routers* on the path header, and the path is short enough, and all routers* on the path
support record (or loose-source) route, then the path will be support record (or loose-source) route, then the path will be
precisely recorded. This is impractical because the route must be precisely recorded. This is impractical because the route must be
short enough, many routers do not support (or are not configured for) short enough, many routers do not support (or are not configured for)
record route, and use of this feature would often artificially worsen record route, and use of this feature would often artificially worsen
the performance observed by removing the packet from common-case the performance observed by removing the packet from common-case
processing. However, partial information is still valuable context. processing. However, partial information is still valuable context.
For example, if a host can choose between two links* (and hence two For example, if a host can choose between two links* (and hence two
separate routes from Src to Dst), then the initial link used is separate routes from Src to Dst), then the initial link used is
valuable context. {Comment: For example, with Merit's NetNow setup, valuable context. {Comment: For example, with Merit's NetNow setup,
a Src on one NAP can reach a Dst on another NAP by either of several a Src on one NAP can reach a Dst on another NAP by either of several
different backbone networks.} different backbone networks.}
4. A Definition for Samples of One-way Packet Loss 3. A Definition for Samples of One-way Packet Loss
Given the singleton metric Type-P-One-way-Packet-Loss, we now define Given the singleton metric Type-P-One-way-Packet-Loss, we now define
one particular sample of such singletons. The idea of the sample is one particular sample of such singletons. The idea of the sample is
to select a particular binding of the parameters Src, Dst, and Type- to select a particular binding of the parameters Src, Dst, and Type-
P, then define a sample of values of parameter T. The means for P, then define a sample of values of parameter T. The means for
defining the values of T is to select a beginning time T0, a final defining the values of T is to select a beginning time T0, a final
time Tf, and an average rate lambda, then define a pseudo-random time Tf, and an average rate lambda, then define a pseudo-random
Poisson process of rate lambda, whose values fall between T0 and Tf. Poisson process of rate lambda, whose values fall between T0 and Tf.
The time interval between successive values of T will then average The time interval between successive values of T will then average
1/lambda. 1/lambda.
{Comment: Note that Poisson sampling is only one way of defining a {Comment: Note that Poisson sampling is only one way of defining a
sample. Poisson has the advantage of limiting bias, but other sample. Poisson has the advantage of limiting bias, but other
methods of sampling might be appropriate for different situations. methods of sampling might be appropriate for different situations.
We encourage others who find such appropriate cases to use this We encourage others who find such appropriate cases to use this
general framework and submit their sampling method for general framework and submit their sampling method for
standardization.} standardization.}
4.1. Metric Name: 3.1. Metric Name:
Type-P-One-way-Packet-Loss-Poisson-Stream Type-P-One-way-Packet-Loss-Poisson-Stream
4.2. Metric Parameters: 3.2. Metric Parameters:
+ Src, the IP address of a host + Src, the IP address of a host
+ Dst, the IP address of a host + Dst, the IP address of a host
+ T0, a time + T0, a time
+ Tf, a time + Tf, a time
+ lambda, a rate in reciprocal seconds + lambda, a rate in reciprocal seconds
4.3. Metric Units: 3.3. Metric Units:
A sequence of pairs; the elements of each pair are: A sequence of pairs; the elements of each pair are:
+ T, a time, and + T, a time, and
+ L, either a zero or a one + L, either a zero or a one
The values of T in the sequence are monotonic increasing. Note that The values of T in the sequence are monotonic increasing. Note that
T would be a valid parameter to Type-P-One-way-Packet-Loss, and that T would be a valid parameter to Type-P-One-way-Packet-Loss, and that
L would be a valid value of Type-P-One-way-Packet-Loss. L would be a valid value of Type-P-One-way-Packet-Loss.
4.4. Definition: 3.4. Definition:
Given T0, Tf, and lambda, we compute a pseudo-random Poisson process Given T0, Tf, and lambda, we compute a pseudo-random Poisson process
beginning at or before T0, with average arrival rate lambda, and beginning at or before T0, with average arrival rate lambda, and
ending at or after Tf. Those time values greater than or equal to T0 ending at or after Tf. Those time values greater than or equal to T0
and less than or equal to Tf are then selected. At each of the times and less than or equal to Tf are then selected. At each of the times
in this process, we obtain the value of Type-P-One-way-Packet-Loss at in this process, we obtain the value of Type-P-One-way-Packet-Loss at
this time. The value of the sample is the sequence made up of the this time. The value of the sample is the sequence made up of the
resulting <time, loss> pairs. If there are no such pairs, the resulting <time, loss> pairs. If there are no such pairs, the
sequence is of length zero and the sample is said to be empty. sequence is of length zero and the sample is said to be empty.
4.5. Discussion: 3.5. Discussion:
The reader should be familiar with the in-depth discussion of Poisson The reader should be familiar with the in-depth discussion of Poisson
sampling in the Framework document [1], which includes methods to sampling in the Framework document [1], which includes methods to
compute and verify the pseudo-random Poisson process. compute and verify the pseudo-random Poisson process.
We specifically do not constrain the value of lambda, except to note We specifically do not constrain the value of lambda, except to note
the extremes. If the rate is too large, then the measurement traffic the extremes. If the rate is too large, then the measurement traffic
will perturb the network, and itself cause congestion. If the rate will perturb the network, and itself cause congestion. If the rate
is too small, then you might not capture interesting network is too small, then you might not capture interesting network
behavior. {Comment: We expect to document our experiences with, and behavior. {Comment: We expect to document our experiences with, and
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All the singleton Type-P-One-way-Packet-Loss metrics in the sequence All the singleton Type-P-One-way-Packet-Loss metrics in the sequence
will have the same values of Src, Dst, and Type-P. will have the same values of Src, Dst, and Type-P.
Note also that, given one sample that runs from T0 to Tf, and given Note also that, given one sample that runs from T0 to Tf, and given
new time values T0' and Tf' such that T0 <= T0' <= Tf' <= Tf, the new time values T0' and Tf' such that T0 <= T0' <= Tf' <= Tf, the
subsequence of the given sample whose time values fall between T0' subsequence of the given sample whose time values fall between T0'
and Tf' are also a valid Type-P-One-way-Packet-Loss-Poisson-Stream and Tf' are also a valid Type-P-One-way-Packet-Loss-Poisson-Stream
sample. sample.
4.6. Methodologies: 3.6. Methodologies:
The methodologies follow directly from: The methodologies follow directly from:
+ the selection of specific times, using the specified Poisson + the selection of specific times, using the specified Poisson
arrival process, and arrival process, and
+ the methodologies discussion already given for the singleton Type- + the methodologies discussion already given for the singleton Type-
P-One-way-Packet-Loss metric. P-One-way-Packet-Loss metric.
Care must be given to correctly handle out-of-order arrival of test Care must be given to correctly handle out-of-order arrival of test
packets; it is possible that the Src could send one test packet at packets; it is possible that the Src could send one test packet at
TS[i], then send a second one (later) at TS[i+1], while the Dst could TS[i], then send a second one (later) at TS[i+1], while the Dst could
receive the second test packet at TR[i+1], and then receive the first receive the second test packet at TR[i+1], and then receive the first
one (later) at TR[i]. one (later) at TR[i].
4.7. Errors and Uncertainties: 3.7. Errors and Uncertainties:
In addition to sources of errors and uncertainties associated with In addition to sources of errors and uncertainties associated with
methods employed to measure the singleton values that make up the methods employed to measure the singleton values that make up the
sample, care must be given to analyze the accuracy of the Poisson sample, care must be given to analyze the accuracy of the Poisson
arrival process of the wire-times of the sending of the test packets. arrival process of the wire-times of the sending of the test packets.
Problems with this process could be caused by several things, Problems with this process could be caused by several things,
including problems with the pseudo-random number techniques used to including problems with the pseudo-random number techniques used to
generate the Poisson arrival process. The Framework document shows generate the Poisson arrival process. The Framework document shows
how to use the Anderson-Darling test verify the accuracy of the how to use the Anderson-Darling test verify the accuracy of the
Poisson process over small time frames. {Comment: The goal is to Poisson process over small time frames. {Comment: The goal is to
ensure that the test packets are sent "close enough" to a Poisson ensure that the test packets are sent "close enough" to a Poisson
schedule, and avoid periodic behavior.} schedule, and avoid periodic behavior.}
4.8. Reporting the metric: 3.8. Reporting the metric:
The calibration and context for the underlying singletons MUST be The calibration and context for the underlying singletons MUST be
reported along with the stream. (See "Reporting the metric" for reported along with the stream. (See "Reporting the metric" for
Type-P-One-way-Packet-Loss.) Type-P-One-way-Packet-Loss.)
5. Some Statistics Definitions for One-way Packet Loss 4. Some Statistics Definitions for One-way Packet Loss
Given the sample metric Type-P-One-way-Packet-Loss-Poisson-Stream, we Given the sample metric Type-P-One-way-Packet-Loss-Poisson-Stream, we
now offer several statistics of that sample. These statistics are now offer several statistics of that sample. These statistics are
offered mostly to be illustrative of what could be done. offered mostly to be illustrative of what could be done.
5.1. Type-P-One-way-Packet-Loss-Average 4.1. Type-P-One-way-Packet-Loss-Average
Given a Type-P-One-way-Packet-Loss-Poisson-Stream, the average of all Given a Type-P-One-way-Packet-Loss-Poisson-Stream, the average of all
the L values in the Stream. In addition, the Type-P-One-way-Packet- the L values in the Stream. In addition, the Type-P-One-way-Packet-
Loss-Average is undefined if the sample is empty. Loss-Average is undefined if the sample is empty.
Example: suppose we take a sample and the results are: Example: suppose we take a sample and the results are:
Stream1 = < Stream1 = <
<T1, 0> <T1, 0>
<T2, 0> <T2, 0>
<T3, 1> <T3, 1>
<T4, 0> <T4, 0>
<T5, 0> <T5, 0>
> >
Then the average would be 0.2. Then the average would be 0.2.
Note that, since healthy Internet paths should be operating at loss Note that, since healthy Internet paths should be operating at loss
rates below 1% (particularly if high delay-bandwidth products are to rates below 1% (particularly if high delay-bandwidth products are to
be sustained), the sample sizes needed might be larger than one would be sustained), the sample sizes needed might be larger than one would
like. Thus, for example, if one wants to discriminate between like. Thus, for example, if one wants to discriminate between
various fractions of 1% over one-minute periods, then several hundred various fractions of 1% over one-minute periods, then several hundred
samples per minute might be needed. This would result in larger samples per minute might be needed. This would result in larger
values of lambda than one would ordinarily want. values of lambda than one would ordinarily want.
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various fractions of 1% over one-minute periods, then several hundred various fractions of 1% over one-minute periods, then several hundred
samples per minute might be needed. This would result in larger samples per minute might be needed. This would result in larger
values of lambda than one would ordinarily want. values of lambda than one would ordinarily want.
Note that although the loss threshold should be set such that any Note that although the loss threshold should be set such that any
errors in loss are not significant, if the possibility that a packet errors in loss are not significant, if the possibility that a packet
which arrived is counted as lost due to resource exhaustion is which arrived is counted as lost due to resource exhaustion is
significant compared to the loss rate of interest, Type-P-One-way- significant compared to the loss rate of interest, Type-P-One-way-
Packet-Loss-Average will be meaningless. Packet-Loss-Average will be meaningless.
6. Security Considerations 5. Security Considerations
Conducting Internet measurements raises both security and privacy Conducting Internet measurements raises both security and privacy
concerns. This memo does not specify an implementation of the concerns. This memo does not specify an implementation of the
metrics, so it does not directly affect the security of the Internet metrics, so it does not directly affect the security of the Internet
nor of applications which run on the Internet. However, nor of applications which run on the Internet. However,
implementations of these metrics must be mindful of security and implementations of these metrics must be mindful of security and
privacy concerns. privacy concerns.
There are two types of security concerns: potential harm caused by There are two types of security concerns: potential harm caused by
the measurements, and potential harm to the measurements. The the measurements, and potential harm to the measurements. The
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rate will be artificially lowered. Therefore, the measurement rate will be artificially lowered. Therefore, the measurement
methodologies SHOULD include appropriate techniques to reduce the methodologies SHOULD include appropriate techniques to reduce the
probability measurement traffic can be distinguished from "normal" probability measurement traffic can be distinguished from "normal"
traffic. Authentication techniques, such as digital signatures, may traffic. Authentication techniques, such as digital signatures, may
be used where appropriate to guard against injected traffic attacks. be used where appropriate to guard against injected traffic attacks.
The privacy concerns of network measurement are limited by the active The privacy concerns of network measurement are limited by the active
measurements described in this memo. Unlike passive measurements, measurements described in this memo. Unlike passive measurements,
there can be no release of existing user data. there can be no release of existing user data.
7. Acknowledgements 6. Acknowledgements
Thanks are due to Matt Mathis for encouraging this work and for Thanks are due to Matt Mathis for encouraging this work and for
calling attention on so many occasions to the significance of packet calling attention on so many occasions to the significance of packet
loss. loss.
Thanks are due also to Vern Paxson for his valuable comments on early Thanks are due also to Vern Paxson for his valuable comments on early
drafts, and to Garry Couch and Will Leland for several useful drafts, and to Garry Couch and Will Leland for several useful
suggestions. suggestions.
8. References 7. References
[1] V. Paxson, G. Almes, J. Mahdavi, and M. Mathis, "Framework for [1] Paxson, V., Almes,G., Mahdavi, J. and M. Mathis, "Framework for
IP Performance Metrics", RFC 2330, May 1998. IP Performance Metrics", RFC 2330, May 1998.
[2] G. Almes, S. Kalidindi, and M. Zekauskas, "A One-way Delay [2] Almes, G., Kalidindi, S. and M. Zekauskas, "A One-way Delay
Metric for IPPM", Internet-Draft <draft-ietf-ippm-delay-06.txt>, Metric for IPPM", RFC 2679, September 1999.
February, 1999.
[3] J. Mahdavi and V. Paxson, "IPPM Metrics for Measuring [3] Mahdavi, J. and V. Paxson, "IPPM Metrics for Measuring
Connectivity", RFC 2498, January 1999. Connectivity", RFC 2678, September 1999.
[4] J. Postel, "Internet Protocol", RFC 791, September 1981. [4] Postel, J., "Internet Protocol", STD 5, RFC 791, September 1981.
[5] S. Bradner, "Key words for use in RFCs to Indicate Requirement [5] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, March 1997. Levels", BCP 14, RFC 2119, March 1997.
[7] S. Bradner, "The Internet Standards Process -- Revision 3", RFC [6] Bradner, S., "The Internet Standards Process -- Revision 3", BCP
2026, October 1996. 9, RFC 2026, October 1996.
9. Authors' Addresses 8. Authors' Addresses
Guy Almes Guy Almes
Advanced Network & Services, Inc. Advanced Network & Services, Inc.
200 Business Park Drive 200 Business Park Drive
Armonk, NY 10504 Armonk, NY 10504
USA USA
Phone: +1 914 765 1120 Phone: +1 914 765 1120
EMail: almes@advanced.org EMail: almes@advanced.org
skipping to change at page 16, line 4 skipping to change at page 14, line 32
EMail: almes@advanced.org EMail: almes@advanced.org
Sunil Kalidindi Sunil Kalidindi
Advanced Network & Services, Inc. Advanced Network & Services, Inc.
200 Business Park Drive 200 Business Park Drive
Armonk, NY 10504 Armonk, NY 10504
USA USA
Phone: +1 914 765 1128 Phone: +1 914 765 1128
EMail: kalidindi@advanced.org EMail: kalidindi@advanced.org
Matthew J. Zekauskas Matthew J. Zekauskas
Advanced Network & Services, Inc. Advanced Network & Services, Inc.
200 Buisiness Park Drive 200 Business Park Drive
Armonk, NY 10504 Armonk, NY 10504
USA USA
Phone: +1 914 765 1112 Phone: +1 914 765 1112
EMail: matt@advanced.org EMail: matt@advanced.org
Expiration date: August, 1999 9. Full Copyright Statement
Copyright (C) The Internet Society (1999). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
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