Internet DRAFT - draft-morton-ippm-2680-bis
draft-morton-ippm-2680-bis
Network Working Group G. Almes
Internet-Draft Texas A&M
Obsoletes: 2680 (if approved) S. Kalidindi
Intended status: Standards Track Ixia
Expires: April 9, 2015 M. Zekauskas
Internet2
A. Morton, Ed.
AT&T Labs
October 6, 2014
A One-Way Loss Metric for IPPM
draft-morton-ippm-2680-bis-04
Abstract
This memo (RFC 2680 bis) defines a metric for one-way loss of packets
across Internet paths. It builds on notions introduced and discussed
in the IPPM Framework document, RFC 2330; the reader is assumed to be
familiar with that document.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
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."
This Internet-Draft will expire on April 9, 2015.
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Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. General Issues Regarding Time . . . . . . . . . . . . . . 5
2. A Singleton Definition for One-way Packet Loss . . . . . . . 6
2.1. Metric Name: . . . . . . . . . . . . . . . . . . . . . . 6
2.2. Metric Parameters: . . . . . . . . . . . . . . . . . . . 6
2.3. Metric Units: . . . . . . . . . . . . . . . . . . . . . . 6
2.4. Definition: . . . . . . . . . . . . . . . . . . . . . . . 6
2.5. Discussion: . . . . . . . . . . . . . . . . . . . . . . . 6
2.6. Methodologies: . . . . . . . . . . . . . . . . . . . . . 7
2.7. Errors and Uncertainties: . . . . . . . . . . . . . . . . 9
2.8. Reporting the metric: . . . . . . . . . . . . . . . . . . 10
2.8.1. Type-P . . . . . . . . . . . . . . . . . . . . . . . 10
2.8.2. Loss Threshold . . . . . . . . . . . . . . . . . . . 10
2.8.3. Calibration Results . . . . . . . . . . . . . . . . . 10
2.8.4. Path . . . . . . . . . . . . . . . . . . . . . . . . 10
3. A Definition for Samples of One-way Packet Loss . . . . . . . 11
3.1. Metric Name: . . . . . . . . . . . . . . . . . . . . . . 11
3.2. Metric Parameters: . . . . . . . . . . . . . . . . . . . 11
3.3. Metric Units: . . . . . . . . . . . . . . . . . . . . . . 12
3.4. Definition: . . . . . . . . . . . . . . . . . . . . . . . 12
3.5. Discussion: . . . . . . . . . . . . . . . . . . . . . . . 12
3.6. Methodologies: . . . . . . . . . . . . . . . . . . . . . 13
3.7. Errors and Uncertainties: . . . . . . . . . . . . . . . . 13
3.8. Reporting the metric: . . . . . . . . . . . . . . . . . . 14
4. Some Statistics Definitions for One-way Packet Loss . . . . . 14
4.1. Type-P-One-way-Packet Loss-Average . . . . . . . . . . . 14
5. Security Considerations . . . . . . . . . . . . . . . . . . . 15
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15
7. RFC 2680 bis . . . . . . . . . . . . . . . . . . . . . . . . 16
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
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9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 17
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
10.1. Normative References . . . . . . . . . . . . . . . . . . 18
10.2. Informative References . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
1. Introduction
This memo defines a metric for one-way packet loss across Internet
paths. It builds on notions introduced and discussed in the IPPM
Framework document, [RFC2330]; the reader is assumed to be familiar
with that document.
This memo is intended to be parallel in structure to a companion
document for One-way Delay ("A One-way Delay Metric for IPPM")
[RFC2679]; the reader is assumed to be familiar with that document.
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[RFC2119]. Although
[RFC2119] was written with protocols in mind, the key words are used
in this document for similar reasons. They are used to ensure the
results of measurements from two different implementations are
comparable, and to note instances when an implementation could
perturb the network.
The structure of the memo is as follows:
+ A 'singleton' analytic metric, called Type-P-One-way-Packet-Loss,
is introduced to measure a single observation of packet transmission
or loss.
+ Using this singleton metric, a 'sample', called Type-P-One-way-
Packet-Loss-Poisson-Stream, is introduced to measure a sequence of
singleton transmissions and/or losses measured at times taken from a
Poisson process.
+ Using this sample, several 'statistics' of the sample are defined
and discussed.
This progression from singleton to sample to statistics, with clear
separation among them, is important.
Whenever a technical term from the IPPM Framework document is first
used in this memo, it will be tagged with a trailing asterisk. For
example, "term*" indicates that "term" is defined in the Framework.
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1.1. Motivation
Understanding one-way packet loss of Type-P* packets from a source
host* to a destination host is useful for several reasons:
+ Some applications do not perform well (or at all) if end-to-end
loss between hosts is large relative to some threshold value.
+ Excessive packet loss may make it difficult to support certain
real-time applications (where the precise threshold of "excessive"
depends on the application).
+ The larger the value of packet loss, the more difficult it is for
transport-layer protocols to sustain high bandwidths.
+ The sensitivity of real-time applications and of transport-layer
protocols to loss become especially important when very large delay-
bandwidth products must be supported.
The measurement of one-way loss instead of round-trip loss is
motivated by the following factors:
+ 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
("asymmetric paths"), such that different sequences of routers are
used for the forward and reverse paths. Therefore round-trip
measurements actually measure the performance of two distinct paths
together. Measuring each path independently highlights the
performance difference between the two paths which may traverse
different Internet service providers, and even radically different
types of networks (for example, research versus commodity networks,
or networks with asymmetric link capacities, or wireless vs. wireline
access).
+ Even when the two paths are symmetric, they may have radically
different performance characteristics due to asymmetric queueing.
+ Performance of an application may depend mostly on the performance
in one direction. For example, a TCP-based communication may
experience reduced throughput if congestion occurs in one direction
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
direction may be radically different than provisioning in the reverse
direction, and thus the QoS guarantees differ. Measuring the paths
independently allows the verification of both guarantees.
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It is outside the scope of this document to say precisely how loss
metrics would be applied to specific problems.
1.2. General Issues Regarding Time
{Comment: the terminology below differs from that defined by ITU-T
documents (e.g., G.810, "Definitions and terminology for
synchronization networks" and I.356, "B-ISDN ATM layer cell transfer
performance"), but is consistent with the IPPM Framework document.
In general, these differences derive from the different backgrounds;
the ITU-T documents historically have a telephony origin, while the
authors of this document (and the Framework) have a computer systems
background. Although the terms defined below have no direct
equivalent in the ITU-T definitions, after our definitions we will
provide a rough mapping. However, note one potential confusion: our
definition of "clock" is the computer operating systems definition
denoting a time-of-day clock, while the ITU-T definition of clock
denotes a frequency reference.}
Whenever a time (i.e., a moment in history) is mentioned here, it is
understood to be measured in seconds (and fractions) relative to UTC.
As described more fully in the Framework document, there are four
distinct, but related notions of clock uncertainty:
synchronization*
measures the extent to which two clocks agree on what time it is.
For example, the clock on one host might be 5.4 msec ahead of the
clock on a second host. {Comment: A rough ITU-T equivalent is "time
error".}
accuracy*
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:
A rough ITU-T equivalent is "time error from UTC".}
resolution*
specification of the smallest unit by which the clock's time is
updated. It gives a lower bound on the clock's uncertainty. For
example, the clock on an old Unix host might tick only once every 10
msec, and thus have a resolution of only 10 msec. {Comment: A very
rough ITU-T equivalent is "sampling period".}
skew*
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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
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
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
another clock, which threatens synchronization. {Comment: A rough
ITU-T equivalent is "time drift".}
2. A Singleton Definition for One-way Packet Loss
2.1. Metric Name:
Type-P-One-way-Packet-Loss
2.2. Metric Parameters:
+ Src, the IP address of a host
+ Dst, the IP address of a host
+ T, a time
+ Tmax, a loss threshold waiting time
2.3. Metric Units:
The value of a Type-P-One-way-Packet-Loss is either a zero
(signifying successful transmission of the packet) or a one
(signifying loss).
2.4. Definition:
>>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
and that Dst received that packet.
>>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
and that Dst did not receive that packet (within the loss threshold
waiting time, Tmax).
2.5. Discussion:
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 undefined.
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The following issues are likely to come up in practice:
+ A given methodology will have to include a way to distinguish
between a packet loss and a very large (but finite) delay. As noted
by Mahdavi and Paxson [RFC2678], simple upper bounds (such as the 255
seconds theoretical upper bound on the lifetimes of IP packets
[RFC0791]) could be used, but good engineering, including an
understanding of packet lifetimes, will be needed in practice.
{Comment: Note that, for many applications of these metrics, there
may be no harm in treating a large delay as packet loss. An audio
playback packet, for example, that arrives only after the playback
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
lost. {Comment: one is tempted to count the packet as received since
corruption and packet loss are related but distinct phenomena. If
the IP header is corrupted, however, one cannot be sure about the
source or destination IP addresses and is thus on shaky grounds about
knowing that the corrupted received packet corresponds to a given
sent test packet. Similarly, if other parts of the packet needed by
the methodology to know that the corrupted received packet
corresponds to a given sent test packet, then such a packet would
have to be counted as lost. Counting these packets as lost but
packet with corruption in other parts of the packet as not lost would
be inconsistent.}
+ If the packet is duplicated along the path (or paths) so that
multiple non-corrupt copies arrive at the destination, then the
packet is counted as received.
+ If the packet is fragmented and if, for whatever reason, reassembly
does not occur, then the packet will be deemed lost.
2.6. Methodologies:
As with other Type-P-* metrics, the detailed methodology will depend
on the Type-P (e.g., protocol number, UDP/TCP port number, size,
precedence).
Generally, for a given Type-P, one possible methodology would proceed
as follows:
+ Arrange that Src and Dst have clocks that are synchronized with
each other. The degree of synchronization is a parameter of the
methodology, and depends on the threshold used to determine loss (see
below).
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+ At the Src host, select Src and Dst IP addresses, and form a test
packet of Type-P with these addresses.
+ At the Dst host, arrange to receive the packet.
+ At the Src host, place a timestamp in the prepared Type-P packet,
and send it towards Dst (ideally minimizing time before sending).
+ If the packet arrives within a reasonable period of time, the one-
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,
Tmax, the one-way packet-loss is taken to be one. Note that the
threshold of "reasonable" here is a parameter of the metric.
{Comment: The definition of reasonable is intentionally vague, and is
intended to indicate a value "Th" so large that any value in the
closed interval [Th-delta, Th+delta] is an equivalent threshold for
loss. Here, delta encompasses all error in clock synchronization and
timestamp acquisition and assignment along the measured path. If
there is a single value, Tmax, after which the packet must be counted
as lost, then we reintroduce the need for a degree of clock
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
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
in detail in [RFC6703], including analysis preferences to assign
undefined delay to packets that fail to arrive with the difficulties
emerging from the informal "infinite delay" assignment, and an
estimation of an upper bound on waiting time for packets in transit.
Further, enforcing a specific constant waiting time on stored
singletons of one-way delay is compliant with this specification and
may allow the results to serve more than one reporting audience.}
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
synchronized are outside the scope of this document. {Comment: We
plan to document elsewhere our own work in describing such more
detailed implementation techniques and we encourage others to as
well.}
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2.7. Errors and Uncertainties:
The description of any specific measurement method should include an
accounting and analysis of various sources of error or uncertainty.
The Framework document provides general guidance on this point.
For loss, there are three sources of error:
+ Synchronization between clocks on Src and Dst.
+ The packet-loss threshold (which is related to the synchronization
between clocks).
+ Resource limits in the network interface or software on the
receiving instrument.
The first two sources are interrelated and could result in a test
packet with finite delay being reported as lost. Type-P-One-way-
Packet-Loss is 1 if the test packet does not arrive, or if it does
arrive and the difference between Src timestamp and Dst timestamp is
greater than the "reasonable period of time", or loss threshold. If
the clocks are not sufficiently synchronized, the loss threshold may
not be "reasonable" - the packet may take much less time to arrive
than its Src timestamp indicates. Similarly, if the loss threshold
is set too low, then many packets may be counted as lost. The loss
threshold must be high enough, and the clocks synchronized well
enough so that a packet that arrives is rarely counted as lost. (See
the discussions in the previous two sections.)
Since the sensitivity of packet loss measurement alone to lack of
clock synchronization is less than for delay, we refer the reader to
the treatment of synchronization errors in the One-way Delay metric
[RFC2330] for more details.
The last source of error, resource limits, cause the packet to be
dropped by the measurement instrument, and counted as lost when in
fact the network delivered the packet in reasonable time.
The measurement instruments should be calibrated such that the loss
threshold is reasonable for application of the metrics and the clocks
are synchronized enough so the loss threshold remains reasonable.
In addition, the instruments should be checked to ensure the that the
possibility a packet arrives at the network interface, but is lost
due to congestion on the interface or to other resource exhaustion
(e.g., buffers) on the instrument is low.
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2.8. Reporting the metric:
The calibration and context in which the metric is measured MUST be
carefully considered, and SHOULD always be reported along with metric
results. We now present four items to consider: Type-P of the test
packets, the loss threshold, instrument calibration, and the path
traversed by the test packets. This list is not exhaustive; any
additional information that could be useful in interpreting
applications of the metrics should also be reported (see [RFC6703]
for extensive discussion of reporting considerations for different
audiences).
2.8.1. Type-P
As noted in the Framework document [RFC2330], the value of the metric
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
protocol (UDP or TCP), port number, size, or arrangement for special
treatment (e.g., IP precedence or RSVP) changes. The exact Type-P
used to make the measurements MUST be accurately reported.
2.8.2. Loss Threshold
The threshold, Tmax, (or methodology to distinguish) between a large
finite delay and loss MUST be reported.
2.8.3. Calibration Results
The degree of synchronization between the Src and Dst clocks MUST be
reported. If possible, possibility that a test packet that arrives
at the Dst network interface is reported as lost due to resource
exhaustion on Dst SHOULD be reported.
2.8.4. Path
Finally, the path traversed by the packet SHOULD be reported, if
possible. In general it is impractical to know the precise path a
given packet takes through the network. The precise path may be
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
header, and the path is short enough, and all routers* on the path
support record (or loose-source) route, then the path will be
precisely recorded. This is impractical because the route must be
short enough, many routers do not support (or are not configured for)
record route, and use of this feature would often artificially worsen
the performance observed by removing the packet from common-case
processing. However, partial information is still valuable context.
For example, if a host can choose between two links* (and hence two
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separate routes from Src to Dst), then the initial link used is
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
different backbone networks.}
3. A Definition for Samples of One-way Packet Loss
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
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
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
Poisson process of rate lambda, whose values fall between T0 and Tf.
The time interval between successive values of T will then average 1/
lambda.
Note that Poisson sampling is only one way of defining a sample.
Poisson has the advantage of limiting bias, but other methods of
sampling will be appropriate for different situations. For example,
a truncated Poisson distribution may be needed to avoid reactive
network state changes during intervals of inactivity, see section 4.6
of [RFC7321]. Sometimes, the goal is sampling with a known bias, and
[RFC3432] describes a method for periodic sampling with random start
times.
3.1. Metric Name:
Type-P-One-way-Packet-Loss-Poisson-Stream
3.2. Metric Parameters:
+ Src, the IP address of a host
+ Dst, the IP address of a host
+ T0, a time
+ Tf, a time
+ Tmax, a loss threshold waiting time
+ lambda, a rate in reciprocal seconds
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3.3. Metric Units:
A sequence of pairs; the elements of each pair are:
+ T, a time, and
+ L, either a zero or a one
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
L would be a valid value of Type-P-One-way-Packet-Loss.
3.4. Definition:
Given T0, Tf, and lambda, we compute a pseudo-random Poisson process
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
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
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
sequence is of length zero and the sample is said to be empty.
3.5. Discussion:
The reader should be familiar with the in-depth discussion of Poisson
sampling in the Framework document [RFC2330], which includes methods
to compute and verify the pseudo-random Poisson process.
We specifically do not constrain the value of lambda, except to note
the extremes. If the rate is too large, then the measurement traffic
will perturb the network, and itself cause congestion. If the rate
is too small, then you might not capture interesting network
behavior. {Comment: We expect to document our experiences with, and
suggestions for, lambda elsewhere, culminating in a "best current
practices" document.}
Since a pseudo-random number sequence is employed, the sequence of
times, and hence the value of the sample, is not fully specified.
Pseudo-random number generators of good quality will be needed to
achieve the desired qualities.
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
statistically as unbiased as possible. The Poisson process is used
to schedule the loss measurements. The test packets will generally
not arrive at Dst according to a Poisson distribution, since they are
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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
arrives according to a Poisson arrival process.
It is important to note that, in contrast to this metric, loss rates
observed by transport connections do not reflect unbiased samples.
For example, TCP transmissions both (1) occur in bursts, which can
induce loss due to the burst volume that would not otherwise have
been observed, and (2) adapt their transmission rate in an attempt to
minimize the loss rate observed by the connection.}
All the singleton Type-P-One-way-Packet-Loss metrics in the sequence
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
new time values T0' and Tf' such that T0 <= T0' <= Tf' <= Tf, the
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
sample.
3.6. Methodologies:
The methodologies follow directly from:
+ the selection of specific times, using the specified Poisson
arrival process, and
+ the methodologies discussion already given for the singleton Type-
P-One-way-Packet-Loss metric.
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
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
one (later) at TR[i]. Metrics for reordering may be found in
[RFC4737].
3.7. Errors and Uncertainties:
In addition to sources of errors and uncertainties associated with
methods employed to measure the singleton values that make up the
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.
Problems with this process could be caused by several things,
including problems with the pseudo-random number techniques used to
generate the Poisson arrival process. The Framework document shows
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how to use the Anderson-Darling test verify the accuracy of the
Poisson process over small time frames. {Comment: The goal is to
ensure that the test packets are sent "close enough" to a Poisson
schedule, and avoid periodic behavior.}
3.8. Reporting the metric:
The calibration and context for the underlying singletons MUST be
reported along with the stream. (See "Reporting the metric" for
Type-P-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
now offer several statistics of that sample. These statistics are
offered mostly to be illustrative of what could be done. See
[RFC6703] for additional discussion of statistics that are relevant
to different audiences.
4.1. Type-P-One-way-Packet Loss-Average
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-
Loss-Average is undefined if the sample is empty.
Example: suppose we take a sample and the results are:
Stream1 = <
<T1, 0>
<T2, 0>
<T3, 1>
<T4, 0>
<T5, 0>
>
Then the average would be 0.2.
Note that, since healthy Internet paths should be operating at loss
rates below 1% (particularly if high delay-bandwidth products are to
be sustained), the sample sizes needed might be larger than one would
like. Thus, for example, if one wants to discriminate between
various fractions of 1% over one-minute periods, then several hundred
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samples per minute might be needed. This would result in larger
values of lambda than one would ordinarily want.
Note that although the loss threshold should be set such that any
errors in loss are not significant, if the possibility that a packet
which arrived is counted as lost due to resource exhaustion is
significant compared to the loss rate of interest, Type-P-One-way-
Packet-Loss-Average will be meaningless.
5. Security Considerations
Conducting Internet measurements raises both security and privacy
concerns. This memo does not specify an implementation of the
metrics, so it does not directly affect the security of the Internet
nor of applications which run on the Internet. However,
implementations of these metrics must be mindful of security and
privacy concerns.
There are two types of security concerns: potential harm caused by
the measurements, and potential harm to the measurements. The
measurements could cause harm because they are active, and inject
packets into the network. The measurement parameters MUST be
carefully selected so that the measurements inject trivial amounts of
additional traffic into the networks they measure. If they inject
"too much" traffic, they can skew the results of the measurement, and
in extreme cases cause congestion and denial of service.
The measurements themselves could be harmed by routers giving
measurement traffic a different priority than "normal" traffic, or by
an attacker injecting artificial measurement traffic. If routers can
recognize measurement traffic and treat it separately, the
measurements will not reflect actual user traffic. If an attacker
injects artificial traffic that is accepted as legitimate, the loss
rate will be artificially lowered. Therefore, the measurement
methodologies SHOULD include appropriate techniques to reduce the
probability measurement traffic can be distinguished from "normal"
traffic. Authentication techniques, such as digital signatures, may
be used where appropriate to guard against injected traffic attacks.
The privacy concerns of network measurement are limited by the active
measurements described in this memo. Unlike passive measurements,
there can be no release of existing user data.
6. Acknowledgements
Thanks are due to Matt Mathis for encouraging this work and for
calling attention on so many occasions to the significance of packet
loss.
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Thanks are due also to Vern Paxson for his valuable comments on early
drafts, and to Garry Couch and Will Leland for several useful
suggestions.
7. RFC 2680 bis
The text above constitutes RFC 2680 bis proposed for advancement on
the IETF Standards Track.
[RFC7290] provides the test plan and results supporting [RFC2680]
advancement along the standards track, according to the process in
[RFC6576]. The conclusions of [RFC7290] list four minor
modifications for inclusion:
1. Section 6.2.3 of [RFC7290] asserts that the assumption of post-
processing to enforce a constant waiting time threshold is
compliant, and that the text of the RFC should be revised
slightly to include this point (see the last list item of section
2.6, above).
2. Section 6.5 of [RFC7290] indicates that Type-P-One-way-Packet-
Loss-Average statistic is more commonly called Packet Loss Ratio,
so it is re-named in RFC2680bis (this small discrepancy does not
affect candidacy for advancement) (see section 4.1, above).
3. The IETF has reached consensus on guidance for reporting metrics
in [RFC6703], and this memo should be referenced in RFC2680bis to
incorporate recent experience where appropriate (see the last
list item of section 2.6, section 2.8, and section 4 above).
4. There are currently two errata with status "Verified" and "Held
for document update" for [RFC2680], and it appears these minor
revisions should be incorporated in RFC2680bis (see section 1 and
section 2.7).
A number of updates to the [RFC2680] text have been implemented in
the text, to reference key IPPM RFCs that were approved after
[RFC2680] (see sections 3 and 3.6, above), and to address comments on
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.
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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
metrics partially derived from previous IPPM and BMWG RFCs, but also
contains some new items. All of the [RFC6390] Normative points are
covered, but not quite in the same section names or orientation.
Several of the Informative points are covered. Maintaining the
familiar outline of IPPM literature has both value and minimizes
unnecessary differences between this revised RFC and current/future
IPPM RFCs.
8. IANA Considerations
This memo makes no requests of IANA.
9. Acknowledgements
Special thanks are due to Vern Paxson of Lawrence Berkeley Labs for
his helpful comments on issues of clock uncertainty and statistics.
Thanks also to Garry Couch, Will Leland, Andy Scherrer, Sean Shapira,
and Roland Wittig for several useful suggestions.
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10. References
10.1. Normative References
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, September
1981.
[RFC2026] Bradner, S., "The Internet Standards Process -- Revision
3", BCP 9, RFC 2026, October 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2330] Paxson, V., Almes, G., Mahdavi, J., and M. Mathis,
"Framework for IP Performance Metrics", RFC 2330, May
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
Delay Metric for IPPM", RFC 2679, September 1999.
[RFC2680] Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
Packet Loss Metric for IPPM", RFC 2680, September 1999.
[RFC3432] Raisanen, V., Grotefeld, G., and A. Morton, "Network
performance measurement with periodic streams", RFC 3432,
November 2002.
[RFC4656] Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M.
Zekauskas, "A One-way Active Measurement Protocol
(OWAMP)", RFC 4656, September 2006.
[RFC5357] Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J.
Babiarz, "A Two-Way Active Measurement Protocol (TWAMP)",
RFC 5357, October 2008.
[RFC5657] Dusseault, L. and R. Sparks, "Guidance on Interoperation
and Implementation Reports for Advancement to Draft
Standard", BCP 9, RFC 5657, September 2009.
[RFC5835] Morton, A. and S. Van den Berghe, "Framework for Metric
Composition", RFC 5835, April 2010.
[RFC6049] Morton, A. and E. Stephan, "Spatial Composition of
Metrics", RFC 6049, January 2011.
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[RFC6576] Geib, R., Morton, A., Fardid, R., and A. Steinmitz, "IP
Performance Metrics (IPPM) Standard Advancement Testing",
BCP 176, RFC 6576, March 2012.
[RFC6703] Morton, A., Ramachandran, G., and G. Maguluri, "Reporting
IP Network Performance Metrics: Different Points of View",
RFC 6703, August 2012.
[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
Tests of fit, for continuous and discrete cases",
University of Washington, Technical Report No. 81, May
1986.
[I-D.ietf-ippm-testplan-rfc2680]
Ciavattone, L., Geib, R., Morton, A., and M. Wieser, "Test
Plan and Results for Advancing RFC 2680 on the Standards
Track", draft-ietf-ippm-testplan-rfc2680-05 (work in
progress), April 2014.
[RFC3931] Lau, J., Townsley, M., and I. Goyret, "Layer Two Tunneling
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
Performance Metric Development", BCP 170, RFC 6390,
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
Guy Almes
Texas A&M
Email: galmes@tamu.edu
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Sunil Kalidindi
Ixia
Email: skalidindi@ixiacom.com
Matt Zekauskas
Internet2
Email: matt@internet2.edu
Al Morton (editor)
AT&T Labs
200 Laurel Avenue South
Middletown, NJ 07748
USA
Phone: +1 732 420 1571
Fax: +1 732 368 1192
Email: acmorton@att.com
URI: http://home.comcast.net/~acmacm/
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