draft-morton-ippm-2680-bis-03.txt   draft-morton-ippm-2680-bis-04.txt 
Network Working Group G. Almes Network Working Group G. Almes
Internet-Draft Texas A&M Internet-Draft Texas A&M
Obsoletes: 2680 (if approved) S. Kalidindi Obsoletes: 2680 (if approved) S. Kalidindi
Intended status: Standards Track Ixia Intended status: Standards Track Ixia
Expires: January 5, 2015 M. Zekauskas Expires: April 9, 2015 M. Zekauskas
Internet2 Internet2
A. Morton, Ed. A. Morton, Ed.
AT&T Labs AT&T Labs
July 4, 2014 October 6, 2014
A One-Way Loss Metric for IPPM A One-Way Loss Metric for IPPM
draft-morton-ippm-2680-bis-03 draft-morton-ippm-2680-bis-04
Abstract Abstract
This memo (RFC 2680 bis) defines a metric for one-way loss of packets This memo (RFC 2680 bis) defines a metric for one-way loss of packets
across Internet paths. It builds on notions introduced and discussed across Internet paths. It builds on notions introduced and discussed
in the IPPM Framework document, RFC 2330; the reader is assumed to be in the IPPM Framework document, RFC 2330; the reader is assumed to be
familiar with that document. familiar with that document.
Requirements Language Requirements Language
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 5, 2015. This Internet-Draft will expire on April 9, 2015.
Copyright Notice Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. General Issues Regarding Time . . . . . . . . . . . . . . 5 1.2. General Issues Regarding Time . . . . . . . . . . . . . . 5
2. A Singleton Definition for One-way Packet Loss . . . . . . . 6 2. A Singleton Definition for One-way Packet Loss . . . . . . . 6
2.1. Metric Name: . . . . . . . . . . . . . . . . . . . . . . 6 2.1. Metric Name: . . . . . . . . . . . . . . . . . . . . . . 6
2.2. Metric Parameters: . . . . . . . . . . . . . . . . . . . 6 2.2. Metric Parameters: . . . . . . . . . . . . . . . . . . . 6
2.3. Metric Units: . . . . . . . . . . . . . . . . . . . . . . 6 2.3. Metric Units: . . . . . . . . . . . . . . . . . . . . . . 6
2.4. Definition: . . . . . . . . . . . . . . . . . . . . . . . 6 2.4. Definition: . . . . . . . . . . . . . . . . . . . . . . . 6
2.5. Discussion: . . . . . . . . . . . . . . . . . . . . . . . 6 2.5. Discussion: . . . . . . . . . . . . . . . . . . . . . . . 6
2.6. Methodologies: . . . . . . . . . . . . . . . . . . . . . 7 2.6. Methodologies: . . . . . . . . . . . . . . . . . . . . . 7
2.7. Errors and Uncertainties: . . . . . . . . . . . . . . . . 8 2.7. Errors and Uncertainties: . . . . . . . . . . . . . . . . 9
2.8. Reporting the metric: . . . . . . . . . . . . . . . . . . 9 2.8. Reporting the metric: . . . . . . . . . . . . . . . . . . 10
2.8.1. Type-P . . . . . . . . . . . . . . . . . . . . . . . 10 2.8.1. Type-P . . . . . . . . . . . . . . . . . . . . . . . 10
2.8.2. Loss Threshold . . . . . . . . . . . . . . . . . . . 10 2.8.2. Loss Threshold . . . . . . . . . . . . . . . . . . . 10
2.8.3. Calibration Results . . . . . . . . . . . . . . . . . 10 2.8.3. Calibration Results . . . . . . . . . . . . . . . . . 10
2.8.4. Path . . . . . . . . . . . . . . . . . . . . . . . . 10 2.8.4. Path . . . . . . . . . . . . . . . . . . . . . . . . 10
3. A Definition for Samples of One-way Packet Loss . . . . . . . 10 3. A Definition for Samples of One-way Packet Loss . . . . . . . 11
3.1. Metric Name: . . . . . . . . . . . . . . . . . . . . . . 11 3.1. Metric Name: . . . . . . . . . . . . . . . . . . . . . . 11
3.2. Metric Parameters: . . . . . . . . . . . . . . . . . . . 11 3.2. Metric Parameters: . . . . . . . . . . . . . . . . . . . 11
3.3. Metric Units: . . . . . . . . . . . . . . . . . . . . . . 11 3.3. Metric Units: . . . . . . . . . . . . . . . . . . . . . . 12
3.4. Definition: . . . . . . . . . . . . . . . . . . . . . . . 12 3.4. Definition: . . . . . . . . . . . . . . . . . . . . . . . 12
3.5. Discussion: . . . . . . . . . . . . . . . . . . . . . . . 12 3.5. Discussion: . . . . . . . . . . . . . . . . . . . . . . . 12
3.6. Methodologies: . . . . . . . . . . . . . . . . . . . . . 13 3.6. Methodologies: . . . . . . . . . . . . . . . . . . . . . 13
3.7. Errors and Uncertainties: . . . . . . . . . . . . . . . . 13 3.7. Errors and Uncertainties: . . . . . . . . . . . . . . . . 13
3.8. Reporting the metric: . . . . . . . . . . . . . . . . . . 13 3.8. Reporting the metric: . . . . . . . . . . . . . . . . . . 14
4. Some Statistics Definitions for One-way Packet Loss . . . . . 14 4. Some Statistics Definitions for One-way Packet Loss . . . . . 14
4.1. Type-P-One-way-Packet Loss-Average . . . . . . . . . . . 14 4.1. Type-P-One-way-Packet Loss-Average . . . . . . . . . . . 14
5. Security Considerations . . . . . . . . . . . . . . . . . . . 15 5. Security Considerations . . . . . . . . . . . . . . . . . . . 15
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15
7. RFC 2680 bis . . . . . . . . . . . . . . . . . . . . . . . . 16 7. RFC 2680 bis . . . . . . . . . . . . . . . . . . . . . . . . 16
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 17 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 17
10. References (temporary) . . . . . . . . . . . . . . . . . . . 17 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 17 10.1. Normative References . . . . . . . . . . . . . . . . . . 18
11.1. Normative References . . . . . . . . . . . . . . . . . . 17 10.2. Informative References . . . . . . . . . . . . . . . . . 19
11.2. Informative References . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
1. 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, [RFC2330]; the reader is assumed to be familiar
familiar with that document. 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 ("A One-way Delay Metric for IPPM") [2]; document for One-way Delay ("A One-way Delay Metric for IPPM")
the reader is assumed to be familiar with that document. [RFC2679]; the reader is assumed to 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[RFC2119]. Although
Although RFC 2119 was written with protocols in mind, the key words [RFC2119] was written with protocols in mind, the key words are used
are used in this document for similar reasons. They are used to in this document for similar reasons. They are used to ensure the
ensure the results of measurements from two different implementations results of measurements from two different implementations are
are comparable, and to note instances when an implementation could comparable, and to note instances when an implementation could
perturb the network. perturb the network.
The structure of the memo is as follows: The structure of the memo is as follows:
+ A 'singleton' analytic metric, called Type-P-One-way-Packet-Loss, + A 'singleton' analytic metric, called Type-P-One-way-Packet-Loss,
is introduced to measure a single observation of packet transmission is introduced to measure a single observation of packet transmission
or loss. or loss.
+ Using this singleton metric, a 'sample', called Type-P-One-way- + Using this singleton metric, a 'sample', called Type-P-One-way-
Packet-Loss-Poisson-Stream, is introduced to measure a sequence of Packet-Loss-Poisson-Stream, is introduced to measure a sequence of
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+ In today's Internet, the path from a source to a destination may be + In today's Internet, the path from a source to a destination may be
different than the path from the destination back to the source different than the path from the destination back to the source
("asymmetric paths"), such that different sequences of routers are ("asymmetric paths"), such that different sequences of routers are
used for the forward and reverse paths. Therefore round-trip used for the forward and reverse paths. Therefore round-trip
measurements actually measure the performance of two distinct paths measurements actually measure the performance of two distinct paths
together. Measuring each path independently highlights the together. Measuring each path independently highlights the
performance difference between the two paths which may traverse performance difference between the two paths which may traverse
different Internet service providers, and even radically different different Internet service providers, and even radically different
types of networks (for example, research versus commodity networks, types of networks (for example, research versus commodity networks,
or ATM versus packet-over-SONET). or networks with asymmetric link capacities, or wireless vs. wireline
access).
+ Even when the two paths are symmetric, they may have radically + Even when the two paths are symmetric, they may have radically
different performance characteristics due to asymmetric queueing. different performance characteristics due to asymmetric queueing.
+ Performance of an application may depend mostly on the performance + Performance of an application may depend mostly on the performance
in one direction. For example, a file transfer using TCP may depend in one direction. For example, a TCP-based communication may
more on the performance in the direction that data flows, rather than experience reduced throughput if congestion occurs in one direction
the direction in which acknowledgements travel. of its communication. Trouble shooting may be simplified if the
congested direction of TCP transmission can be identified.
+ 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 reverse direction may be radically different than provisioning in the reverse
direction, and thus the QoS guarantees differ. Measuring the paths direction, and thus the QoS guarantees differ. Measuring the paths
independently allows the verification of both guarantees. independently allows the verification of both 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.
1.2. General Issues Regarding Time 1.2. General Issues Regarding Time
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error".} error".}
accuracy* accuracy*
measures the extent to which a given clock agrees with UTC. For measures the extent to which a given clock agrees with UTC. For
example, the clock on a host might be 27.1 msec behind UTC. {Comment: example, the clock on a host might be 27.1 msec behind UTC. {Comment:
A rough ITU-T equivalent is "time error from UTC".} A rough ITU-T equivalent is "time error from UTC".}
resolution* resolution*
measures the precision of a given clock. For example, the clock on specification of the smallest unit by which the clock's time is
an old Unix host might tick only once every 10 msec, and thus have a updated. It gives a lower bound on the clock's uncertainty. For
resolution of only 10 msec. {Comment: A very rough ITU-T equivalent example, the clock on an old Unix host might tick only once every 10
is "sampling period".} msec, and thus have a resolution of only 10 msec. {Comment: A very
rough ITU-T equivalent is "sampling period".}
skew* skew*
measures the change of accuracy, or of synchronization, with time. measures the change of accuracy, or of synchronization, with time.
For example, the clock on a given host might gain 1.3 msec per hour 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 and only 25.8 msec an 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 clock of the given host hour later. In this case, we say that the clock of the given host
has a skew of 1.3 msec per hour relative to UTC, which threatens has a skew of 1.3 msec per hour relative to UTC, which threatens
accuracy. We might also speak of the skew of one clock relative to accuracy. We might also speak of the skew of one clock relative to
another clock, which threatens synchronization. {Comment: A rough another clock, which threatens synchronization. {Comment: A rough
ITU-T equivalent is "time drift".} ITU-T equivalent is "time drift".}
2. A Singleton Definition for One-way Packet Loss 2. A Singleton Definition for One-way Packet Loss
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2.5. 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 value, and it is 1 exactly when Type-P-One-way- Delay is a finite value, and it is 1 exactly when Type-P-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 noted between a packet loss and a very large (but finite) delay. As noted
by Mahdavi and Paxson [3], simple upper bounds (such as the 255 by Mahdavi and Paxson [RFC2678], simple upper bounds (such as the 255
seconds theoretical upper bound on the lifetimes of IP packets [4]) seconds theoretical upper bound on the lifetimes of IP packets
could be used, but good engineering, including an understanding of [RFC0791]) could be used, but good engineering, including an
packet lifetimes, will be needed in practice. {Comment: Note that, understanding of packet lifetimes, will be needed in practice.
for many applications of these metrics, there may be no harm in {Comment: Note that, for many applications of these metrics, there
treating a large delay as packet loss. An audio playback packet, for may be no harm in treating a large delay as packet loss. An audio
example, that arrives only after the playback point may as well have playback packet, for example, that arrives only after the playback
been lost.} point may as well have been lost. See section 4.1.1 of [RFC6703] for
examination of unusual packet delays and application performance
estimation.}
+ If the packet arrives, but is corrupted, then it is counted as + If the packet arrives, but is corrupted, then it is counted as
lost. {Comment: one is tempted to count the packet as received since lost. {Comment: one is tempted to count the packet as received since
corruption and packet loss are related but distinct phenomena. If corruption and packet loss are related but distinct phenomena. If
the IP header is corrupted, however, one cannot be sure about the the IP header is corrupted, however, one cannot be sure about the
source or destination IP addresses and is thus on shaky grounds about source or destination IP addresses and is thus on shaky grounds about
knowing that the corrupted received packet corresponds to a given knowing that the corrupted received packet corresponds to a given
sent test packet. Similarly, if other parts of the packet needed by sent test packet. Similarly, if other parts of the packet needed by
the methodology to know that the corrupted received packet the methodology to know that the corrupted received packet
corresponds to a given sent test packet, then such a packet would corresponds to a given sent test packet, then such a packet would
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each other. The degree of synchronization is a parameter of the each other. The degree of synchronization is a parameter of the
methodology, and depends on the threshold used to determine loss (see methodology, and depends on the threshold used to determine loss (see
below). below).
+ At the Src host, select Src and Dst IP addresses, and form a test + At the Src host, select Src and Dst IP addresses, and form a test
packet of Type-P with these addresses. packet of Type-P with these addresses.
+ At the Dst host, arrange to receive the packet. + At the Dst host, arrange to receive the packet.
+ At the Src host, place a timestamp in the prepared Type-P packet, + At the Src host, place a timestamp in the prepared Type-P packet,
and send it towards Dst. and send it towards Dst (ideally minimizing time before sending).
+ If the packet arrives within a reasonable period of time, the one- + If the packet arrives within a reasonable period of time, the one-
way packet-loss is taken to be zero. way packet-loss is taken to be zero (and take a timestamp as soon as
possible upon the receipt of the packet).
+ If the packet fails to arrive within a reasonable period of time, + If the packet fails to arrive within a reasonable period of time,
the one-way packet-loss is taken to be one. Note that the threshold Tmax, the one-way packet-loss is taken to be one. Note that the
of "reasonable" here is a parameter of the methodology. threshold of "reasonable" here is a parameter of the metric.
{Comment: The definition of reasonable is intentionally vague, and is {Comment: The definition of reasonable is intentionally vague, and is
intended to indicate a value "Th" so large that any value in the intended to indicate a value "Th" so large that any value in the
closed interval [Th-delta, Th+delta] is an equivalent threshold for closed interval [Th-delta, Th+delta] is an equivalent threshold for
loss. Here, delta encompasses all error in clock synchronization loss. Here, delta encompasses all error in clock synchronization and
along the measured path. If there is a single value after which the timestamp acquisition and assignment along the measured path. If
packet must be counted as lost, then we reintroduce the need for a there is a single value, Tmax, after which the packet must be counted
degree of clock synchronization similar to that needed for one-way as lost, then we reintroduce the need for a degree of clock
delay. Therefore, if a measure of packet loss parameterized by a synchronization similar to that needed for one-way delay, and
virtually all practical measurement systems combine methods for delay
and loss. Therefore, if a measure of packet loss parameterized by a
specific non-huge "reasonable" time-out value is needed, one can specific non-huge "reasonable" time-out value is needed, one can
always measure one-way delay and see what percentage of packets from always measure one-way delay and see what percentage of packets from
a given stream exceed a given time-out value. This point is examined a given stream exceed a given time-out value. This point is examined
in detail in [RFC6703], including analysis preferences to assign in detail in [RFC6703], including analysis preferences to assign
undefined delay to packets that fail to arrive with the difficulties undefined delay to packets that fail to arrive with the difficulties
emerging from the informal "infinite delay" assignment, and an emerging from the informal "infinite delay" assignment, and an
estimation of an upper bound on waiting time for packets in transit. estimation of an upper bound on waiting time for packets in transit.
Further, enforcing a specific constant waiting time on stored Further, enforcing a specific constant waiting time on stored
singletons of one-way delay is compliant with this specification and singletons of one-way delay is compliant with this specification and
may allow the results to serve more than one reporting audience.} may allow the results to serve more than one reporting audience.}
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arrive and the difference between Src timestamp and Dst timestamp is arrive and the difference between Src timestamp and Dst timestamp is
greater than the "reasonable period of time", or loss threshold. If greater than the "reasonable period of time", or loss threshold. If
the clocks are not sufficiently synchronized, the loss threshold may the clocks are not sufficiently synchronized, the loss threshold may
not be "reasonable" - the packet may take much less time to arrive not be "reasonable" - the packet may take much less time to arrive
than its Src timestamp indicates. Similarly, if the loss threshold than its Src timestamp indicates. Similarly, if the loss threshold
is set too low, then many packets may be counted as lost. The loss is set too low, then many packets may be counted as lost. The loss
threshold must be high enough, and the clocks synchronized well threshold must be high enough, and the clocks synchronized well
enough so that a packet that arrives is rarely counted as lost. (See enough so that a packet that arrives is rarely counted as lost. (See
the discussions in the previous two sections.) the discussions in the previous two sections.)
Since the sensitivity of packet loss measurement to lack of clock Since the sensitivity of packet loss measurement alone to lack of
synchronization is less than for delay, we refer the reader to the clock synchronization is less than for delay, we refer the reader to
treatment of synchronization errors in the One-way Delay metric [2] the treatment of synchronization errors in the One-way Delay metric
for more details. [RFC2330] for more details.
The last source of error, resource limits, cause the packet to be The last source of error, resource limits, cause the packet to be
dropped by the measurement instrument, and counted as lost when in dropped by the measurement instrument, and counted as lost when in
fact the network delivered the packet in reasonable time. fact the network delivered the packet in reasonable time.
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
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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 (see [RFC6703] applications of the metrics should also be reported (see [RFC6703]
for extensive discussion of reporting considerations for different for extensive discussion of reporting considerations for different
audiences). audiences).
2.8.1. 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 [RFC2330], the value of the metric
depend on the type of IP packets used to make the measurement, or may 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.
2.8.2. Loss Threshold 2.8.2. Loss Threshold
The threshold, Tmax, (or methodology to distinguish) between a large The threshold, Tmax, (or methodology to distinguish) between a large
finite delay and loss MUST be reported. finite delay and loss MUST be reported.
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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 1/ The time interval between successive values of T will then average 1/
lambda. lambda.
{Comment: Note that Poisson sampling is only one way of defining a Note that Poisson sampling is only one way of defining a sample.
sample. Poisson has the advantage of limiting bias, but other Poisson has the advantage of limiting bias, but other methods of
methods of sampling might be appropriate for different situations. sampling will be appropriate for different situations. For example,
We encourage others who find such appropriate cases to use this a truncated Poisson distribution may be needed to avoid reactive
general framework and submit their sampling method for network state changes during intervals of inactivity, see section 4.6
standardization.} of [RFC7321]. Sometimes, the goal is sampling with a known bias, and
[RFC3432] describes a method for periodic sampling with random start
>>> Editor proposal: Add ref to RFC 3432 Periodic sampling above. times.
3.1. Metric Name: 3.1. Metric Name:
Type-P-One-way-Packet-Loss-Poisson-Stream Type-P-One-way-Packet-Loss-Poisson-Stream
3.2. 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
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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.
3.5. 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 [RFC2330], which includes methods
compute and verify the pseudo-random Poisson process. to 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
suggestions for, lambda elsewhere, culminating in a "best current suggestions for, lambda elsewhere, culminating in a "best current
practices" document.} practices" document.}
Since a pseudo-random number sequence is employed, the sequence of Since a pseudo-random number sequence is employed, the sequence of
times, and hence the value of the sample, is not fully specified. times, and hence the value of the sample, is not fully specified.
Pseudo-random number generators of good quality will be needed to Pseudo-random number generators of good quality will be needed to
achieve the desired qualities. achieve the desired qualities.
The sample is defined in terms of a Poisson process both to avoid the The sample is defined in terms of a Poisson process both to avoid the
effects of self-synchronization and also capture a sample that is effects of self-synchronization and also capture a sample that is
statistically as unbiased as possible. The Poisson process is used statistically as unbiased as possible. The Poisson process is used
to schedule the delay measurements. The test packets will generally to schedule the loss measurements. The test packets will generally
not arrive at Dst according to a Poisson distribution, since they are not arrive at Dst according to a Poisson distribution, since they are
influenced by the network. influenced by the network. Time-slotted links described in [RFC7321]
can greatly modify the sample characteristics.
{Comment: there is, of course, no claim that real Internet traffic {Comment: there is, of course, no claim that real Internet traffic
arrives according to a Poisson arrival process. arrives according to a Poisson arrival process.
It is important to note that, in contrast to this metric, loss rates It is important to note that, in contrast to this metric, loss rates
observed by transport connections do not reflect unbiased samples. observed by transport connections do not reflect unbiased samples.
For example, TCP transmissions both (1) occur in bursts, which can For example, TCP transmissions both (1) occur in bursts, which can
induce loss due to the burst volume that would not otherwise have induce loss due to the burst volume that would not otherwise have
been observed, and (2) adapt their transmission rate in an attempt to been observed, and (2) adapt their transmission rate in an attempt to
minimize the loss rate observed by the connection.} minimize the loss rate observed by the connection.}
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+ 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]. Metrics for reordering may be found in
[RFC4737].
>>> Editor proposal: Add ref to RFC 4737 Reordering metric above.
3.7. 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
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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.
7. RFC 2680 bis 7. RFC 2680 bis
The text above constitutes RFC 2680 bis proposed for advancement on The text above constitutes RFC 2680 bis proposed for advancement on
the IETF Standards Track. the IETF Standards Track.
[I-D.ietf-ippm-testplan-rfc2680] provides the test plan and results [RFC7290] provides the test plan and results supporting [RFC2680]
supporting [RFC2680] advancement along the standards track, according advancement along the standards track, according to the process in
to the process in [RFC6576]. The conclusions of [RFC6576]. The conclusions of [RFC7290] list four minor
[I-D.ietf-ippm-testplan-rfc2680] list four minor modifications for modifications for inclusion:
inclusion:
1. Section 6.2.3 of [I-D.ietf-ippm-testplan-rfc2680] asserts that 1. Section 6.2.3 of [RFC7290] asserts that the assumption of post-
the assumption of post-processing to enforce a constant waiting processing to enforce a constant waiting time threshold is
time threshold is compliant, and that the text of the RFC should compliant, and that the text of the RFC should be revised
be revised slightly to include this point (see the last list item slightly to include this point (see the last list item of section
of section 2.6, above). 2.6, above).
2. Section 6.5 of [I-D.ietf-ippm-testplan-rfc2680] indicates that 2. Section 6.5 of [RFC7290] indicates that Type-P-One-way-Packet-
Type-P-One-way-Packet-Loss-Average statistic is more commonly Loss-Average statistic is more commonly called Packet Loss Ratio,
called Packet Loss Ratio, so it is re-named in RFC2680bis (this so it is re-named in RFC2680bis (this small discrepancy does not
small discrepancy does not affect candidacy for advancement) (see affect candidacy for advancement) (see section 4.1, above).
section 4.1, above).
3. The IETF has reached consensus on guidance for reporting metrics 3. The IETF has reached consensus on guidance for reporting metrics
in [RFC6703], and this memo should be referenced in RFC2680bis to in [RFC6703], and this memo should be referenced in RFC2680bis to
incorporate recent experience where appropriate (see the last incorporate recent experience where appropriate (see the last
list item of section 2.6, section 2.8, and section 4 above). list item of section 2.6, section 2.8, and section 4 above).
4. There are currently two errata with status "Verified" and "Held 4. There are currently two errata with status "Verified" and "Held
for document update" for [RFC2680], and it appears these minor for document update" for [RFC2680], and it appears these minor
revisions should be incorporated in RFC2680bis (see section 1 and revisions should be incorporated in RFC2680bis (see section 1 and
section 2.7). section 2.7).
A small number of updates to the [RFC2680] text have been proposed A number of updates to the [RFC2680] text have been implemented in
(by the current Editor) in the text, principally to reference key the text, to reference key IPPM RFCs that were approved after
IPPM RFCs that were approved after [RFC2680] (see sections 3 and 3.6, [RFC2680] (see sections 3 and 3.6, above), and to address comments on
above). the IPPM mailing list describing current conditions and experience.
1. Near the end of section 1.1, update of a network example using
ATM and clarification of TCP's affect on queue occupation and
importance of one-way delay measurement.
2. Clarification of the definition of "resolution" in section 1.2.
3. Explicit inclusion of the maximum waiting time input parameter in
sections 2.2, 2.4, and 3.2, reflecting recognition of this
parameter in more recent RFCs and ITU-T Recommendation Y.1540.
4. Addition of reference to RFC6703 in the discussion of packet life
time and application timeouts in section 2.5.
5. Added parenthetical guidance on minimizing interval between
timestamp placement to send time or reception time in section
2.6. Also, the text now recognizes the timestamp acquisition
process and that practical systems measure both delay and loss
(thus require the max waiting time parameter).
6. Added reference to RFC 3432 Periodic sampling alongside Poisson
sampling in section 3, and also noting that a truncated Poisson
distribution may be needed with modern networks as described in
the IPPM Framework update, RFC7312.
7. Recognition that Time-slotted links described in [RFC7321] can
greatly modify the sample characteristics, in section 3.5.
8. Add reference to RFC 4737 Reordering metric in the related
discussion of section 3.6, Methodologies.
9.
Section 5.4.4 of [RFC6390] suggests a common template for performance Section 5.4.4 of [RFC6390] suggests a common template for performance
metrics partially derived from previous IPPM and BMWG RFCs, but also metrics partially derived from previous IPPM and BMWG RFCs, but also
some new items. All of the RFC 6390 Normative points are covered, contains some new items. All of the [RFC6390] Normative points are
but not quite in the same section names or orientation. Several of covered, but not quite in the same section names or orientation.
the Informative points are covered. It is proposed to "grandfather- Several of the Informative points are covered. Maintaining the
in" bis RFCs w.r.t. RFC 6390 (keeping the familiar outline and familiar outline of IPPM literature has both value and minimizes
minimizing unnecessary differences), and consider applying the unnecessary differences between this revised RFC and current/future
template with new metric memos instead. IPPM RFCs.
8. IANA Considerations 8. IANA Considerations
This memo makes no requests of IANA. This memo makes no requests of IANA.
9. Acknowledgements 9. Acknowledgements
Special thanks are due to Vern Paxson of Lawrence Berkeley Labs for Special thanks are due to Vern Paxson of Lawrence Berkeley Labs for
his helpful comments on issues of clock uncertainty and statistics. his helpful comments on issues of clock uncertainty and statistics.
Thanks also to Garry Couch, Will Leland, Andy Scherrer, Sean Shapira, Thanks also to Garry Couch, Will Leland, Andy Scherrer, Sean Shapira,
and Roland Wittig for several useful suggestions. and Roland Wittig for several useful suggestions.
10. References (temporary) 10. References
[1] Paxson, V., Almes,G., Mahdavi, J. and M. Mathis, "Framework for
IP Performance Metrics", RFC 2330, May 1998.
[2] Almes, G., Kalidindi, S. and M. Zekauskas, "A One-way Delay
Metric for IPPM", RFC 2679, September 1999.
[3] Mahdavi, J. and V. Paxson, "IPPM Metrics for Measuring
Connectivity", RFC 2678, September 1999.
[4] Postel, J., "Internet Protocol", STD 5, RFC 791, September 1981.
[5] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[6] Bradner, S., "The Internet Standards Process -- Revision 3", BCP
9, RFC 2026, October 1996.
11. References 10.1. Normative References
11.1. Normative References [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, September
1981.
[RFC2026] Bradner, S., "The Internet Standards Process -- Revision [RFC2026] Bradner, S., "The Internet Standards Process -- Revision
3", BCP 9, RFC 2026, October 1996. 3", BCP 9, RFC 2026, October 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2330] Paxson, V., Almes, G., Mahdavi, J., and M. Mathis, [RFC2330] Paxson, V., Almes, G., Mahdavi, J., and M. Mathis,
"Framework for IP Performance Metrics", RFC 2330, May "Framework for IP Performance Metrics", RFC 2330, May
1998. 1998.
[RFC2678] Mahdavi, J. and V. Paxson, "IPPM Metrics for Measuring
Connectivity", RFC 2678, September 1999.
[RFC2679] Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way [RFC2679] Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
Delay Metric for IPPM", RFC 2679, September 1999. Delay Metric for IPPM", RFC 2679, September 1999.
[RFC2680] Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way [RFC2680] Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
Packet Loss Metric for IPPM", RFC 2680, September 1999. Packet Loss Metric for IPPM", RFC 2680, September 1999.
[RFC3432] Raisanen, V., Grotefeld, G., and A. Morton, "Network [RFC3432] Raisanen, V., Grotefeld, G., and A. Morton, "Network
performance measurement with periodic streams", RFC 3432, performance measurement with periodic streams", RFC 3432,
November 2002. November 2002.
skipping to change at page 18, line 38 skipping to change at page 19, line 13
Metrics", RFC 6049, January 2011. Metrics", RFC 6049, January 2011.
[RFC6576] Geib, R., Morton, A., Fardid, R., and A. Steinmitz, "IP [RFC6576] Geib, R., Morton, A., Fardid, R., and A. Steinmitz, "IP
Performance Metrics (IPPM) Standard Advancement Testing", Performance Metrics (IPPM) Standard Advancement Testing",
BCP 176, RFC 6576, March 2012. BCP 176, RFC 6576, March 2012.
[RFC6703] Morton, A., Ramachandran, G., and G. Maguluri, "Reporting [RFC6703] Morton, A., Ramachandran, G., and G. Maguluri, "Reporting
IP Network Performance Metrics: Different Points of View", IP Network Performance Metrics: Different Points of View",
RFC 6703, August 2012. RFC 6703, August 2012.
11.2. Informative References [RFC7321] McGrew, D. and P. Hoffman, "Cryptographic Algorithm
Implementation Requirements and Usage Guidance for
Encapsulating Security Payload (ESP) and Authentication
Header (AH)", RFC 7321, August 2014.
10.2. Informative References
[ADK] Scholz, F. and M. Stephens, "K-sample Anderson-Darling [ADK] Scholz, F. and M. Stephens, "K-sample Anderson-Darling
Tests of fit, for continuous and discrete cases", Tests of fit, for continuous and discrete cases",
University of Washington, Technical Report No. 81, May University of Washington, Technical Report No. 81, May
1986. 1986.
[I-D.ietf-ippm-testplan-rfc2680] [I-D.ietf-ippm-testplan-rfc2680]
Ciavattone, L., Geib, R., Morton, A., and M. Wieser, "Test Ciavattone, L., Geib, R., Morton, A., and M. Wieser, "Test
Plan and Results for Advancing RFC 2680 on the Standards Plan and Results for Advancing RFC 2680 on the Standards
Track", draft-ietf-ippm-testplan-rfc2680-05 (work in Track", draft-ietf-ippm-testplan-rfc2680-05 (work in
progress), April 2014. progress), April 2014.
[RFC3931] Lau, J., Townsley, M., and I. Goyret, "Layer Two Tunneling [RFC3931] Lau, J., Townsley, M., and I. Goyret, "Layer Two Tunneling
Protocol - Version 3 (L2TPv3)", RFC 3931, March 2005. Protocol - Version 3 (L2TPv3)", RFC 3931, March 2005.
[RFC4737] Morton, A., Ciavattone, L., Ramachandran, G., Shalunov,
S., and J. Perser, "Packet Reordering Metrics", RFC 4737,
November 2006.
[RFC6390] Clark, A. and B. Claise, "Guidelines for Considering New [RFC6390] Clark, A. and B. Claise, "Guidelines for Considering New
Performance Metric Development", BCP 170, RFC 6390, Performance Metric Development", BCP 170, RFC 6390,
October 2011. October 2011.
[RFC7290] Ciavattone, L., Geib, R., Morton, A., and M. Wieser, "Test
Plan and Results for Advancing RFC 2680 on the Standards
Track", RFC 7290, July 2014.
Authors' Addresses Authors' Addresses
Guy Almes Guy Almes
Texas A&M Texas A&M
Email: galmes@tamu.edu
Sunil Kalidindi Sunil Kalidindi
Ixia Ixia
Email: skalidindi@ixiacom.com
Matt Zekauskas Matt Zekauskas
Internet2 Internet2
Email: matt@internet2.edu Email: matt@internet2.edu
Al Morton (editor) Al Morton (editor)
AT&T Labs AT&T Labs
200 Laurel Avenue South 200 Laurel Avenue South
Middletown, NJ 07748 Middletown, NJ 07748
USA USA
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