draft-ietf-ippm-rt-loss-03.txt   draft-ietf-ippm-rt-loss-04.txt 
Network Working Group A. Morton Network Working Group A. Morton
Internet-Draft AT&T Labs Internet-Draft AT&T Labs
Intended status: Standards Track March 1, 2012 Intended status: Standards Track April 12, 2012
Expires: September 2, 2012 Expires: October 14, 2012
Round-trip Loss Metrics Round-trip Packet Loss Metrics
draft-ietf-ippm-rt-loss-03 draft-ietf-ippm-rt-loss-04
Abstract Abstract
Many user applications (and the transport protocols that make them Many user applications (and the transport protocols that make them
possible) require two-way communications. To assess this capability, possible) require two-way communications. To assess this capability,
and to achieve test system simplicity, round-trip loss measurements and to achieve test system simplicity, round-trip loss measurements
are frequently conducted in practice. The Two-Way Active Measurement are frequently conducted in practice. The Two-Way Active Measurement
Protocol specified in RFC 5357 establishes a round-trip loss Protocol specified in RFC 5357 establishes a round-trip loss
measurement capability for the Internet. However, there is currently measurement capability for the Internet. However, there is currently
no metric specified according to the RFC 2330 framework. no metric specified according to the RFC 2330 framework.
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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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 September 2, 2012. This Internet-Draft will expire on October 14, 2012.
Copyright Notice Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Provisions Relating to IETF Documents Provisions Relating to IETF Documents
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carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
skipping to change at page 2, line 24 skipping to change at page 2, line 24
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Common Specifications for Round-trip Metrics . . . . . . . . . 4 3. Common Specifications for Round-trip Metrics . . . . . . . . . 4
3.1. Name: Type-P-* . . . . . . . . . . . . . . . . . . . . . . 4 3.1. Name: Type-P-* . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Metric Parameters . . . . . . . . . . . . . . . . . . . . 4 3.2. Metric Parameters . . . . . . . . . . . . . . . . . . . . 5
3.3. Metric Definition . . . . . . . . . . . . . . . . . . . . 5 3.3. Metric Definition . . . . . . . . . . . . . . . . . . . . 5
3.4. Metric Units . . . . . . . . . . . . . . . . . . . . . . . 5 3.4. Metric Units . . . . . . . . . . . . . . . . . . . . . . . 5
4. A Singleton Round-trip Loss Metric . . . . . . . . . . . . . . 5 4. A Singleton Round-trip Loss Metric . . . . . . . . . . . . . . 6
4.1. Name: Type-P-Round-trip-Loss . . . . . . . . . . . . . . . 5 4.1. Name: Type-P-Round-trip-Loss . . . . . . . . . . . . . . . 6
4.2. Metric Parameters . . . . . . . . . . . . . . . . . . . . 6 4.2. Metric Parameters . . . . . . . . . . . . . . . . . . . . 6
4.3. Definition and Metric Units . . . . . . . . . . . . . . . 6 4.3. Definition and Metric Units . . . . . . . . . . . . . . . 6
4.4. Discussion and other details . . . . . . . . . . . . . . . 7 4.4. Discussion and other details . . . . . . . . . . . . . . . 7
5. A Sample Round-trip Loss Metric . . . . . . . . . . . . . . . 7 5. A Sample Round-trip Loss Metric . . . . . . . . . . . . . . . 7
5.1. Name: Type-P-Round-trip-Loss-<Sample>-Stream . . . . . . . 7 5.1. Name: Type-P-Round-trip-Loss-<Sample>-Stream . . . . . . . 8
5.2. Metric Parameters . . . . . . . . . . . . . . . . . . . . 7 5.2. Metric Parameters . . . . . . . . . . . . . . . . . . . . 8
5.3. Definition and Metric Units . . . . . . . . . . . . . . . 7 5.3. Definition and Metric Units . . . . . . . . . . . . . . . 8
5.4. Discussion and other details . . . . . . . . . . . . . . . 8 5.4. Discussion and other details . . . . . . . . . . . . . . . 8
6. Round-trip Loss Statistic . . . . . . . . . . . . . . . . . . 9 6. Round-trip Loss Statistic . . . . . . . . . . . . . . . . . . 9
6.1. Type-P-Round-trip-Loss-<Sample>-Ratio . . . . . . . . . . 9 6.1. Type-P-Round-trip-Loss-<Sample>-Ratio . . . . . . . . . . 9
7. Round-trip Testing and One-way Reporting . . . . . . . . . . . 9 7. Round-trip Testing and One-way Reporting . . . . . . . . . . . 9
8. Measurement Considerations and Calibration . . . . . . . . . . 10 8. Measurement Considerations and Calibration . . . . . . . . . . 10
9. Security Considerations . . . . . . . . . . . . . . . . . . . 10 9. Security Considerations . . . . . . . . . . . . . . . . . . . 11
9.1. Denial of Service Attacks . . . . . . . . . . . . . . . . 10 9.1. Denial of Service Attacks . . . . . . . . . . . . . . . . 11
9.2. User Data Confidentiality . . . . . . . . . . . . . . . . 10 9.2. User Data Confidentiality . . . . . . . . . . . . . . . . 11
9.3. Interference with the metrics . . . . . . . . . . . . . . 11 9.3. Interference with the metrics . . . . . . . . . . . . . . 11
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
12.1. Normative References . . . . . . . . . . . . . . . . . . . 11 12.1. Normative References . . . . . . . . . . . . . . . . . . . 12
12.2. Informative References . . . . . . . . . . . . . . . . . . 12 12.2. Informative References . . . . . . . . . . . . . . . . . . 13
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 12 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction 1. Introduction
This memo defines a metric for round-trip loss on Internet paths. It This memo defines a metric to quantify an IP network's ability to
builds on the notions and conventions introduced in the IP transfer packets in both directions from one host to another host.
Two-way communication is almost always needed, thus failure to
transfer a packet in either direction constitutes a round-trip packet
loss.
This memo defines a metric for round-trip packet loss on Internet
paths. It builds on the notions and conventions introduced in the IP
Performance Metrics (IPPM) framework [RFC2330]. Also, the Performance Metrics (IPPM) framework [RFC2330]. Also, the
specifications of the One-way Loss metric [RFC2680] and the Round- specifications of the One-way Packet Loss Metric for IPPM [RFC2680]
trip Delay metric [RFC2681] are frequently referenced and modified to and the Round-trip Delay Metric for IPPM [RFC2681] are frequently
match the round-trip circumstances addressed here. However, this referenced and modified to match the round-trip circumstances
memo assumes that the reader is familiar with the references, and addressed here. However, this memo assumes that the reader is
does not repeat material as was done in [RFC2681]. familiar with the references, and does not repeat material as was
done in [RFC2681].
This memo uses the terms "two-way" and "round-trip" synonymously. This memo uses the terms "two-way" and "round-trip" synonymously.
1.1. Motivation 1.1. Motivation
Many user applications and the transport protocols that make them Many user applications and the transport protocols that make them
possible require two-way communications. For example, the TCP SYN->, possible require two-way communications. For example, the TCP SYN->,
<-SYN-ACK, ACK-> three-way handshake attempted billions of times each <-SYN-ACK, ACK-> three-way handshake attempted billions of times each
day cannot be completed without two-way connectivity in a near- day cannot be completed without two-way connectivity in a near-
simultaneous time interval. Thus, measurements of Internet round- simultaneous time interval. Thus, measurements of Internet round-
trip loss performance provide a basis to infer application trip packet loss performance provide a basis to infer application
performance more easily. performance more easily.
Measurement system designers have also recognized advantages of Measurement system designers have also recognized advantages of
system simplicity when one host simply echoes or reflects test system simplicity when one host simply echoes or reflects test
packets to the sender. Round-trip loss measurements are frequently packets to the sender. Round-trip packet loss measurements are
conducted and reported in practice. The Two-Way Active Measurement frequently conducted and reported in practice. The ubiquitous "ping"
Protocol (TWAMP) specified in [RFC5357] establishes a round-trip loss tools allow the measurement of round-trip packet loss and delay, but
usually require ICMP Echo-Request/Reply support, and ICMP packets may
encounter exceptional treatment on the measurement path (see Section
2.6 of [RFC2681]). The Two-Way Active Measurement Protocol (TWAMP)
specified in [RFC5357] establishes a round-trip packet loss
measurement capability for the Internet. However, there is currently measurement capability for the Internet. However, there is currently
no round-trip loss metric specified according to the [RFC2330] no round-trip packet loss metric specified according to the [RFC2330]
framework. framework.
[RFC2681] indicates that round-trip measurements may sometimes [RFC2681] indicates that round-trip measurements may sometimes
encounter "asymmetric" paths. When loss is observed using a round- encounter "asymmetric" paths. When loss is observed using a round-
trip measurement, there is often a desire to ascertain which of the trip measurement, there is often a desire to ascertain which of the
two directional paths "lost" the packet. Under some circumstances, two directional paths "lost" the packet. Under some circumstances,
it is possible to make this inference. The round-trip measurement it is possible to make this inference. The round-trip measurement
method raises a few complications when interpreting the embedded one- method raises a few complications when interpreting the embedded one-
way results, and the user should be aware of them. way results, and the user should be aware of them.
[RFC2681] also points out that loss measurement conducted [RFC2681] also points out that loss measurement conducted
sequentially in both directions of a path and reported as a round- sequentially in both directions of a path and reported as a round-
trip result may be exactly the desired metric. On the other hand, it trip result may be exactly the desired metric. On the other hand, it
may be difficult to derive the state of round-trip loss from one-way may be difficult to derive the state of round-trip packet loss from
measurements conducted in each direction unless a method to match the one-way measurements conducted in each direction unless a method to
appropriate one-way measurements has been pre-arranged. match the appropriate one-way measurements has been pre-arranged.
Finally, many measurement systems report statistics on a conditional Finally, many measurement systems report statistics on a conditional
delay distribution, where the condition is packet arrival at the delay distribution, where the condition is packet arrival at the
destination. This condition is encouraged in [RFC3393], [RFC5481], destination. This condition is encouraged in [RFC3393], [RFC5481],
and [draft-ietf-ippm-reporting-metrics]. As a result, lost packets and [draft-ietf-ippm-reporting-metrics]. As a result, lost packets
need to be reported separately, according to a standardized metric. need to be reported separately, according to a standardized metric.
This memo defines such a metric. This memo defines such a metric.
See Section 1.1 of[RFC2680] for additional motivation of the packet See Section 1.1 of[RFC2680] for additional motivation of the packet
loss metric. loss metric.
2. Scope 2. Scope
This memo defines a round-trip loss metric using the conventions of This memo defines a round-trip packet loss metric using the
the IPPM framework [RFC2330]. conventions of the IPPM framework [RFC2330].
The memo defines a singleton metric, a sample metric, and a The memo defines a singleton metric, a sample metric, and a
statistic, as per [RFC2330]. statistic, as per [RFC2330]. The [RFC2330] framework is for active
measurement methods. Although this metric MAY be applicable in
passive measurement as well, discussion of additional considerations
for the passive scenario are beyond the normative scope of this memo.
The memo also investigates the topic of one-way loss inference from a The memo also investigates the topic of one-way loss inference from a
two-way measurement, and lists some key considerations. two-way measurement, and lists some key considerations.
3. Common Specifications for Round-trip Metrics 3. Common Specifications for Round-trip Metrics
To reduce the redundant information presented in the detailed metrics To reduce the redundant information presented in the detailed metrics
sections that follow, this section presents the specifications that sections that follow, this section presents the specifications that
are common to two or more metrics. The section is organized using are common to two or more metrics. The section is organized using
the same subsections as the individual metrics, to simplify the same subsections as the individual metrics, to simplify
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first bit (for Periodic Streams) first bit (for Periodic Streams)
o T0, a time that MUST be selected at random from the interval [T, o T0, a time that MUST be selected at random from the interval [T,
T+dT] to start generating packets and taking measurements (for T+dT] to start generating packets and taking measurements (for
Periodic Streams) Periodic Streams)
o TstampSrc, the wire time of the packet as measured at MP(Src) as o TstampSrc, the wire time of the packet as measured at MP(Src) as
it leaves for Dst. it leaves for Dst.
o TstampDst, the wire time of the packet as measured at MP(Dst), o TstampDst, the wire time of the packet as measured at MP(Dst),
assigned to packets that arrive within a "reasonable" time. assigned to packets that arrive within a "reasonable" time (less
than Tmax).
o Tmax, a maximum waiting time for packets to arrive, set o Tmax, a maximum waiting time for packets to arrive at Src, set
sufficiently long to disambiguate packets with long delays from sufficiently long to disambiguate packets with long delays from
packets that are discarded (lost). packets that are discarded (lost).
o M, the total number of packets sent between T0 and Tf o M, the total number of packets sent between T0 and Tf
o N, the total number of packets received at Dst (sent between T0 o N, the total number of packets received at Dst (sent between T0
and Tf) and Tf)
o Type-P, as defined in [RFC2330], which includes any field that may o Type-P, as defined in [RFC2330], which includes any field that may
affect a packet's treatment as it traverses the network affect a packet's treatment as it traverses the network
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Type-P-Round-trip-Loss SHALL be represented by the binary logical Type-P-Round-trip-Loss SHALL be represented by the binary logical
values (or their equivalents) when the following conditions are met: values (or their equivalents) when the following conditions are met:
Type-P-Round-trip-Loss = 0: Type-P-Round-trip-Loss = 0:
o Src sent the first bit of a Type-P packet to Dst at wire-time o Src sent the first bit of a Type-P packet to Dst at wire-time
TstampSrc, TstampSrc,
o that Dst received that packet, o that Dst received that packet,
o the Dst sent a Type-P packet back to the Src as immediately as o the Dst sent a Type-P packet back to the Src as quickly as
possible, and possible (certainly less than Tmax, and fast enough for the
intended purpose), and
o that Src received the last bit of the reflected packet prior to o that Src received the last bit of the reflected packet prior to
wire-time TstampSrc + Tmax. wire-time TstampSrc + Tmax.
Type-P-Round-trip-Loss = 1: Type-P-Round-trip-Loss = 1:
o Src sent the first bit of a Type-P packet to Dst at wire-time o Src sent the first bit of a Type-P packet to Dst at wire-time
TstampSrc, TstampSrc,
o that Src did not receive the last bit of the reflected packet o that Src did not receive the last bit of the reflected packet
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Possible causes for the Loss = 1 outcome are: Possible causes for the Loss = 1 outcome are:
o the Dst did not receive that packet, o the Dst did not receive that packet,
o the Dst did not send a Type-P packet back to the Src, or o the Dst did not send a Type-P packet back to the Src, or
o the Src did not receive a reflected Type-P packet sent from the o the Src did not receive a reflected Type-P packet sent from the
Dst. Dst.
Following the precedent of[RFC2681], we make the simplifying Following the precedent of Section 2.4 of[RFC2681], we make the
assertion: simplifying assertion, that Round-trip loss measured between two
hosts is equal regardless of the host that originates the test:
Type-P-Round-trip-Loss(Src->Dst) = Type-P-Round-trip-Loss(Dst->Src) Type-P-Round-trip-Loss(Src->Dst->Src) = Type-P-Round-trip-
Loss(Dst->Src->Dst)
(and agree with the rationale presented there, that the ambiguity (and agree with the rationale presented there, that the ambiguity
introduced is a small price to pay for measurement efficiency). introduced is a small price to pay for measurement efficiency).
Therefore, each singleton can be represented by pairs of elements as Therefore, each singleton can be represented by pairs of elements as
follows: follows:
o TstampSrc, the wire time of the packet at the Src (beginning the o TstampSrc, the wire time of the packet at the Src (beginning the
round-trip journey). round-trip journey).
o L, either zero or one (or some logical equivalent), where L=1 o L, either zero or one (or some logical equivalent), where L=1
indicates loss and L=0 indicates successful round-trip arrival indicates loss and L=0 indicates successful round-trip arrival
prior to TstampSrc + Tmax. prior to TstampSrc + Tmax.
4.4. Discussion and other details 4.4. Discussion and other details
See [RFC2680] and [RFC2681] for extensive discussion, methods of See [RFC2680] and [RFC2681] for extensive discussion, methods of
measurement, errors and uncertainties, and other fundamental measurement, errors and uncertainties, and other fundamental
considerations that need not be repeated here. considerations that need not be repeated here.
We add the following guidance regarding the responder process to
"send a Type-P packet back to the Src as quickly as possible".
A response that was not generated within Tmax is inadequate for any
realistic test, and the Src will discard such responses. A responder
that serves typical round-trip packet loss testing (which is relevant
to higher-layer application performance) SHOULD produce a response in
1 second or less. A responder that is unable to satisfy this
requirement SHOULD log the fact so that an operator can adjust the
load and priorities as necessary. Analysis of responder time-stamps
[RFC5357] that finds responses are not generated in a timely fashion
SHOULD result in operator notification, and the operator SHOULD
suspend tests to the responder since it may be overloaded.
Additional measurement considerations are described in Section 8,
below.
5. A Sample Round-trip Loss Metric 5. A Sample Round-trip Loss Metric
Given the singleton metric Type-P-Round-trip-Loss, we now define one Given the singleton metric Type-P-Round-trip-Loss, we now define one
particular sample of such singletons. The idea of the sample is to particular sample of such singletons. The idea of the sample is to
select a particular binding of the parameters Src, Dst, and Type-P, select a particular binding of the parameters Src, Dst, and Type-P,
then define a sample of values of parameter TstampSrc. This can be then define a sample of values of parameter TstampSrc. This can be
done in several ways, including: done in several ways, including:
1. Poisson: a pseudo-random Poisson process of rate lambda, whose 1. Poisson: a pseudo-random Poisson process of rate lambda, whose
values fall between T and Tf. The time interval between values fall between T and Tf. The time interval between
successive values of TstampSrc will then average 1/lambda, as per successive values of TstampSrc will then average 1/lambda, as per
[RFC2330]. Section 11.1 of [RFC2330].
2. Periodic: a periodic stream process with pseudo-random start time 2. Periodic: a periodic stream process with pseudo-random start time
T0 between T and dT, and nominal inter-packet interval incT, as T0 between T and dT, and nominal inter-packet interval incT, as
per [RFC3432]. per [RFC3432].
In the metric name, the variable <Sample> SHALL be replaced with the In the metric name, the variable <Sample> SHALL be replaced with the
process used to define the sample, using one of the above processes process used to define the sample, using one of the above processes
(or other process, the details of which MUST be specified if used). (or another sample process meeting the criteria in Section 11.1 of
[RFC2330], the details of which MUST be reported with the results if
used).
5.1. Name: Type-P-Round-trip-Loss-<Sample>-Stream 5.1. Name: Type-P-Round-trip-Loss-<Sample>-Stream
5.2. Metric Parameters 5.2. Metric Parameters
See section 3.2. See section 3.2.
5.3. Definition and Metric Units 5.3. Definition and Metric Units
Given one of the methods for defining the test interval, the sample Given one of the methods for defining the test interval, the sample
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Type-P-Round-trip-Loss-<Sample>-Stream SHALL be a sequence of pairs Type-P-Round-trip-Loss-<Sample>-Stream SHALL be a sequence of pairs
with elements as follows: with elements as follows:
o TstampSrc, as above o TstampSrc, as above
o L, either zero or one (or some logical equivalent), where L=1 o L, either zero or one (or some logical equivalent), where L=1
indicates loss and L=0 indicates successful round-trip arrival indicates loss and L=0 indicates successful round-trip arrival
prior to TstampSrc + Tmax. prior to TstampSrc + Tmax.
where <Sample> SHALL be replaced with "Poisson", "Periodic", or an and where <Sample> SHALL be replaced with "Poisson", "Periodic", or
appropriate term to designate another sample method meeting the an appropriate term to designate another sample method as described
criteria of [RFC2330]. in Section 5 above.
5.4. Discussion and other details 5.4. Discussion and other details
See [RFC2680] and [RFC2681] for extensive discussion, methods of See [RFC2680] and [RFC2681] for extensive discussion, methods of
measurement, errors and uncertainties, and other fundamental measurement, errors and uncertainties, and other fundamental
considerations that need not be repeated here. However, when these considerations that need not be repeated here. However, when these
references were approved, the packet reordering metrics in [RFC4737] references were approved, the packet reordering metrics in [RFC4737]
had not yet been defined, nor had reordering been addressed in IPPM had not yet been defined, nor had reordering been addressed in IPPM
methodologies. methodologies.
[RFC4737] defines packets that arrive "late" with respect to their [RFC4737] defines packets that arrive "late" with respect to their
sending order as reordered. For example, when packets arrive with sending order as reordered. For example, when packets arrive with
sequence numbers 4, 7, 5, 6, then packets 5 and 6 are reordered, and sequence numbers 4, 7, 5, 6, then packets 5 and 6 are reordered, and
they are obviously not lost because they have arrived within some they are obviously not lost because they have arrived within some
reasonable waiting time threshold. The presence of reordering on a reasonable waiting time threshold. The presence of reordering on a
round-trip path has several likely affects on the measurement. round-trip path has several likely effects on the measurement.
1. Methods of measurement should continue to wait the specified time 1. Methods of measurement should continue to wait the specified time
for packets, and avoid prematurely declaring round-trip loss when for packets, and avoid prematurely declaring round-trip packet
a sequence gap or error is observed. loss when a sequence gap or error is observed.
2. The time distribution of the singletons in the sample has been 2. The time distribution of the singletons in the sample has been
significantly changed. significantly changed.
3. Either the original packet stream or the reflected packet stream 3. Either the original packet stream or the reflected packet stream
experienced path instability, and the original conditions may no experienced path instability, and the original conditions may no
longer be present. longer be present.
Measurement implementations MUST address the possibility for packet Measurement implementations MUST address the possibility for packet
reordering and avoid related errors in their processes. reordering and avoid related errors in their processes.
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Further, the sampling times for the reverse path (Dst->Src) are a Further, the sampling times for the reverse path (Dst->Src) are a
random process that depends on the original sample times (TstampSrc), random process that depends on the original sample times (TstampSrc),
the one-way-delay for successful packet arrival at the Dst, and time the one-way-delay for successful packet arrival at the Dst, and time
taken at the Dst to generate the reflected packet. Therefore, the taken at the Dst to generate the reflected packet. Therefore, the
sampling process for the reverse path will be significantly affected sampling process for the reverse path will be significantly affected
when appreciable delay variation occurs on the Src->Dst path, making when appreciable delay variation occurs on the Src->Dst path, making
an attempt to assess the reverse path performance invalid (for loss an attempt to assess the reverse path performance invalid (for loss
or possibly any metric). or possibly any metric).
As discussed above, packet reordering is always a possibility. In As discussed above in Section 5.4, packet reordering is always a
addition to the severe delay variation that usually accompanies it, possibility. In addition to the severe delay variation that usually
reordering on the Src->Dst path will cause a mis-alignment of accompanies it, reordering on the Src->Dst path will cause a mis-
sequence numbers applied at the reflector when compared to the sender alignment of sequence numbers applied at the Dst when compared to the
numbers. Measurement implementations SHOULD address this possible sender numbers. Measurement implementations MUST address this
outcome. possible outcome.
8. Measurement Considerations and Calibration 8. Measurement Considerations and Calibration
Prior to conducting this measurement, the participating hosts MUST be Prior to conducting this measurement, the participating hosts MUST be
configured to send and receive test packets of the chosen Type-P. configured to send and receive test packets of the chosen Type-P.
Standard measurement protocols are capable of this task [RFC5357], Standard measurement protocols are capable of this task [RFC5357],
but any reliable method is sufficient. but any reliable method is sufficient (e.g., if the issues with ICMP
discussed in section 2.6 of[RFC2681] can be alleviated, then ICMP
could be used).
Two key features of the host that receives test packets and returns Two key features of the host that receives test packets and returns
them to the originating host is described in section 4.2 of [RFC5357] them to the originating host are described in section 4.2 of
. Every received test packet MUST result in a responding packet, and [RFC5357] . Every received test packet MUST result in a responding
the response MUST be generated as immediately as possible. This packet, and the response MUST be generated as quickly as possible.
implies that interface buffers will be serviced promptly, and that This implies that interface buffers will be serviced promptly, and
buffer discards will be extremely rare. These features of the that buffer discards will be extremely rare. These features of the
measurement equipment MUST be calibrated according to Section 3.7.3 measurement equipment MUST be calibrated according to Section 3.7.3
of [RFC2679], when operating under a representative measurement load of [RFC2679], when operating under a representative measurement load
(as defined by the user). Both unexpected test packet discards and (as defined by the user). Both unexpected test packet discards, and
the systematic and random errors and uncertainties MUST be recorded. the systematic and random errors and uncertainties, MUST be recorded.
We note that Section 4.2.1 of [RFC5357] specifies a method to collect We note that Section 4.2.1 of [RFC5357] specifies a method to collect
all four significant time-stamps needed to describe a packet's round- all four significant time-stamps needed to describe a packet's round-
trip delay [RFC2681] and remove the processing time incurred at the trip delay [RFC2681] and remove the processing time incurred at the
responding host. This information supports the measurement of the responding host. This information supports the measurement of the
corresponding One-way Delays encountered on the round-trip path, corresponding One-way Delays encountered on the round-trip path,
which can identify path asymmetry or unexpected processing time at which can identify path asymmetry or unexpected processing time at
the responding host. the responding host.
9. Security Considerations 9. Security Considerations
skipping to change at page 11, line 14 skipping to change at page 11, line 40
headers of interest. Since user payloads may be temporarily stored headers of interest. Since user payloads may be temporarily stored
for length analysis, suitable precautions MUST be taken to keep this for length analysis, suitable precautions MUST be taken to keep this
information safe and confidential. In most cases, a hashing function information safe and confidential. In most cases, a hashing function
will produce a value suitable for payload comparisons. will produce a value suitable for payload comparisons.
9.3. Interference with the metrics 9.3. Interference with the metrics
It may be possible to identify that a certain packet or stream of It may be possible to identify that a certain packet or stream of
packets is part of a sample. With that knowledge at the destination packets is part of a sample. With that knowledge at the destination
and/or the intervening networks, it is possible to change the and/or the intervening networks, it is possible to change the
processing of the packets (e.g. increasing or decreasing delay) that processing of the packets (e.g. increasing or decreasing delay) in a
may distort the measured performance. It may also be possible to way that may distort the measured performance. It may also be
generate additional packets that appear to be part of the sample possible to generate additional packets that appear to be part of the
metric. These additional packets are likely to perturb the results sample metric. These additional packets are likely to perturb the
of the sample measurement. results of the sample measurement.
To discourage the kind of interference mentioned above, packet Authentication or encryption techniques, such as digital signatures,
interference checks, such as cryptographic hash, may be used. MAY be used where appropriate to guard against injected traffic
attacks. [RFC5357] includes both authentication and encryption
features.
10. IANA Considerations 10. IANA Considerations
Metrics previously defined in IETF were registered in the IANA IPPM Metrics previously defined in IETF were registered in the IANA IPPM
METRICS REGISTRY, however this process was discontinued when the METRICS REGISTRY, however this process was discontinued when the
registry structure was found to be inadequate, and the registry was registry structure was found to be inadequate, and the registry was
declared Obsolete [RFC6248]. declared Obsolete [RFC6248].
Although the metrics in this draft may be considered for some form of Although the metrics in this draft may be considered for some form of
registration in the future, no IANA Action is requested at this time. registration in the future, no IANA Action is requested at this time.
11. Acknowledgements 11. Acknowledgements
The author thanks Tiziano Ionta for his careful review of this memo, The author thanks Tiziano Ionta for his careful review of this memo,
primarily resulting in the development of measurement considerations primarily resulting in the development of measurement considerations
using TWAMP [RFC5357] as an example method. using TWAMP [RFC5357] as an example method. The reviews of Adrian
Farrel and Benoit Claise also contributed to the clarity of the memo.
12. References 12. References
12.1. Normative References 12.1. Normative References
[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, "Framework for IP Performance Metrics", RFC 2330,
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