GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc5560

Network Working Group H. Uijterwaal Request for Comments: 5560 RIPE NCC Category: Standards Track May 2009

                A One-Way Packet Duplication Metric

Status of This Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (c) 2009 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
 Provisions Relating to IETF Documents in effect on the date of
 publication of this document (http://trustee.ietf.org/license-info).
 Please review these documents carefully, as they describe your rights
 and restrictions with respect to this document.

Abstract

 When a packet is sent from one host to the other, one normally
 expects that exactly one copy of the packet that was sent arrives at
 the destination.  It is, however, possible that a packet is either
 lost or that multiple copies arrive.
 In earlier work, a metric for packet loss was defined.  This metric
 quantifies the case where a packet that is sent does not arrive at
 its destination within a reasonable time.  In this memo, a metric for
 another case is defined: a packet is sent, but multiple copies
 arrive.  The document also discusses streams and methods to summarize
 the results of streams.

Uijterwaal Standards Track [Page 1] RFC 5560 Packet Duplication Metric May 2009

Table of Contents

 1. Introduction ....................................................3
    1.1. Requirements Notation ......................................3
    1.2. Motivation .................................................4
 2. A Singleton Definition for One-Way Packet Arrival Count .........4
    2.1. Metric Name ................................................4
    2.2. Metrics Parameters .........................................4
    2.3. Metric Units ...............................................4
    2.4. Definition .................................................4
    2.5. Discussion .................................................5
    2.6. Methodology ................................................6
    2.7. Errors and Uncertainties ...................................6
    2.8. Reporting the Metric .......................................6
 3. A Singleton Definition for One-Way Packet Duplication ...........6
    3.1. Metric Name ................................................6
    3.2. Metrics Parameters .........................................7
    3.3. Metric Units ...............................................7
    3.4. Definition .................................................7
    3.5. Discussion .................................................7
 4. Definition for Samples for One-Way Packet Duplication ...........7
    4.1. Poisson Streams ............................................7
         4.1.1. Metric Name .........................................7
         4.1.2. Metric Parameters ...................................8
         4.1.3. Metric Units ........................................8
         4.1.4. Definition ..........................................8
         4.1.5. Methodology .........................................8
         4.1.6. Errors and Uncertainties ............................8
         4.1.7. Reporting the Metric ................................8
    4.2. Periodic Streams ...........................................9
         4.2.1. Metric Name .........................................9
         4.2.2. Metric Parameters ...................................9
         4.2.3. Metric Units ........................................9
         4.2.4. Definition ..........................................9
         4.2.5. Methodology .........................................9
         4.2.6. Errors and uncertainties ............................9
         4.2.7. Reporting the metric ...............................10
 5. Some Statistics Definitions for One-Way Duplication ............10
    5.1. Type-P-one-way-packet-duplication-fraction ................10
    5.2. Type-P-one-way-replicated-packet-rate .....................10
    5.3. Examples ..................................................11
 6. Security Considerations ........................................12
 7. IANA Considerations ............................................12
 8. Acknowledgements ...............................................13
 9. References .....................................................13
    9.1. Normative References ......................................13
    9.2. Informative References ....................................13

Uijterwaal Standards Track [Page 2] RFC 5560 Packet Duplication Metric May 2009

1. Introduction

 This document defines a metric for one-way packet duplication across
 Internet paths.  It builds on the IP Performance Metrics (IPPM)
 Framework document [RFC2330]; the reader is assumed to be familiar
 with that document.
 This document follows the same structure as the document for one-way
 packet loss [RFC2680]; the reader is assumed to be familiar with that
 document as well.
 The structure of this memo is as follows:
 o  First, a singleton metric, called Type-P-one-way-packet-arrival-
    count, is introduced to measure the number of arriving packets for
    each packet sent.
 o  Then, a singleton metric, called Type-P-one-way-packet-
    duplication, is defined to describe a single instance of packet
    duplication.
 o  Next, this singleton metric is used to define samples, Type-P-one-
    way-Packet-Duplication-Poisson-Stream and Type-P-one-way-Packet-
    Duplication-Periodic-Stream.  These are introduced to measure
    duplication in a series of packets sent with either Poisson-
    distributed [RFC2680] or periodic [RFC3432] intervals between the
    packets.
 o  Finally, statistics that summarize the properties of these samples
    are introduced.

1.1. Requirements Notation

 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 RFC 2119 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.

Uijterwaal Standards Track [Page 3] RFC 5560 Packet Duplication Metric May 2009

1.2. Motivation

 When a packet is sent from one host to the other, one normally
 expects that exactly one copy of the packet that was sent arrives at
 the destination.  It is, however, possible that a packet is either
 lost or that multiple copies arrive.
 In earlier work, a metric for packet loss was defined [RFC2680].
 This metric distinguishes between cases where the packet arrives and
 where the packet does not arrive within a reasonable time.  In this
 memo, a metric for a third outcome is defined: a single packet is
 sent, but multiple copies arrive.
 As this document describes a case similar to the one discussed in
 [RFC2680], all considerations from that document on timing and
 accuracy apply.

2. A Singleton Definition for One-Way Packet Arrival Count

2.1. Metric Name

 Type-P-one-way-packet-arrival-count

2.2. Metrics Parameters

 o  src, the IP address of a host
 o  dst, the IP address of a host
 o  T, the wire time of a packet at the source
 o  T0, the maximum waiting time for a packet to arrive at the
    destination.

2.3. Metric Units

 An integer number.

2.4. Definition

 Two packets are considered identical if and only if:
 o  Both contain identical information fields (see Section 2.5).  The
    recipient thus could take either packet and use the data in an
    application.  The other packet does not contain any additional
    information.

Uijterwaal Standards Track [Page 4] RFC 5560 Packet Duplication Metric May 2009

 o  Both packets appear to have been sent by one and the same host, to
    one and the same destination.  Hosts are identified by their IP
    addresses.
 The value of a Type-P-one-way-packet-arrival-count is a positive
 integer number indicating the number of (uncorrupted and identical)
 copies received by dst in the interval [T, T+T0] for a packet sent by
 src at time T.
 If a packet is sent, but it is lost or does not arrive in the
 interval [T, T+T0], then the metric is undefined.  Applications MAY
 report an "impossible" value (for example, -1) to indicate this
 condition instead of undefined.
 If a packet is fragmented during transport and if, for whatever
 reason, reassembly does not occur, then the packet will be deemed
 lost.  It is thus not included in the Type-P-one-way-packet-arrival-
 count.

2.5. Discussion

 This metric counts the number of packets arriving for each packet
 sent.  The time-out value T0 SHOULD be set to a value when the
 application could potentially still use the packet and would not
 discard it automatically.
 If this metric is used in parallel with the Packet Loss Metric
 [RFC2680], the value of T0 MUST be the same for both cases in order
 to keep the results comparable.
 The metric only counts packets that are not corrupted during
 transmission and may have been resent automatically by lower layers
 or intermediate devices.  Packets that were corrupted during
 transmission but, nevertheless, still arrived at dst are not counted.
 Clocks do have to be synchronized between src and dst such that it is
 possible to uniquely and accurately determine the interval [T, T+T0]
 at both sides.
 If this metric is used in an active measurement system, the system
 MUST NOT send multiple packets with identical information fields in
 order to avoid that all packets will be declared duplicates.  This
 metric can be used inside a passive measurement system as well, using
 packets generated by another source.  However, if the source can send
 two identical packets within the interval [T, T+T0], this will be
 incorrectly labeled as a duplicate, resulting in a false positive.
 It is up to the implementor to estimate if this scenario is likely to
 happen and the rate of false positives that is acceptable.

Uijterwaal Standards Track [Page 5] RFC 5560 Packet Duplication Metric May 2009

 The definition of identical information fields is such that two
 packets are considered to be identical if they are sent from the same
 source and contain the same information.  This does not necessarily
 mean that all bits in the packet are the same.  For example, when a
 packet is replicated and the copies are transferred along different
 paths, the Time to Live (TTL) may be different.  The implementation
 MUST specify which fields are compared when deciding whether or not
 two packets are identical.
 In the case of IPv4, these will usually be: version, ihl,
 identification, src, dst, protocol, some or all upper-layer protocol
 data.
 In IPv6, these will usually be: version, next header, source,
 destination, some or all upper-layer protocol data
 Note that the use of the identification field is not present in non-
 fragmented IPv6 packets and may not be sufficient to distinguish
 packets from each even in IPv4, particularly at higher transmission
 speeds

2.6. Methodology

 The basic technique to measure this metric follows the methodology
 described in Section 2.6 of [RFC2680] with one exception.
 [RFC2680] does not specify that the receiving host should be able to
 receive multiple copies of a single packet, as it only needs one copy
 to determine the metrics.  Implementations for this metric should
 obviously be capable of receiving multiple copies.

2.7. Errors and Uncertainties

 Refer to Section 2.7 of [RFC2680].

2.8. Reporting the Metric

 Refer to Section 2.8 of [RFC2680].

3. A Singleton Definition for One-Way Packet Duplication

3.1. Metric Name

 Type-P-one-way-packet-duplication

Uijterwaal Standards Track [Page 6] RFC 5560 Packet Duplication Metric May 2009

3.2. Metrics Parameters

 o  src, the IP address of a host
 o  dst, the IP address of a host
 o  T, the wire time of a packet at the source
 o  T0, the maximum waiting time for a packet to arrive at the
    destination.

3.3. Metric Units

 An integer number.

3.4. Definition

 The value of a Type-P-one-way-packet-duplication is a positive
 integer number indicating the number of (uncorrupted and identical)
 additional copies of an individual packet received by dst in the
 interval [T, T+T0] as sent by src at time T.
 If a packet is sent and only one copy arrives in the interval [T,
 T+T0], then the metric is 0.  If no copy arrives in this interval,
 then the metric is undefined.  Applications MAY report an
 "impossible" value (for example, -1) to indicate this condition.

3.5. Discussion

 This metric is equal to:
      Type-P-one-way-packet-arrival-count - 1
 This metric is expected to be used for applications that need to know
 duplication for an individual packet.  All considerations regarding
 methodology, errors, and reporting from the previous section apply.

4. Definition for Samples for One-Way Packet Duplication

4.1. Poisson Streams

4.1.1. Metric Name

 Type-P-one-way-Packet-Duplication-Poisson-Stream

Uijterwaal Standards Track [Page 7] RFC 5560 Packet Duplication Metric May 2009

4.1.2. Metric Parameters

 o  src, the IP address of a host.
 o  dst, the IP address of a host.
 o  Ts, a time.
 o  Tf, a time.  Ts and Tf specify the time interval when packets can
    be sent for this stream.
 o  T0, the maximum waiting time for a packet to arrive at the
    destination.
 o  lambda, a rate in reciprocal seconds.

4.1.3. Metric Units

 A sequence of pairs; the elements of each pair are:
 o  T, a time
 o  Type-P-one-way-packet-arrival-count for the packet sent at T.

4.1.4. Definition

 Given Ts, Tf, and lambda, we compute a pseudo-random Poisson process
 beginning at or before Ts, with average-rate lambda, and ending at or
 after Tf.  Those time values greater than or equal to Ts, 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-arrival-count.
 The value of the sample is the sequence made up of the resulting
 {time, duplication} pairs.  If there are no such pairs, the sequence
 is of length zero, and the sample is said to be empty.

4.1.5. Methodology

 Refer to Section 3.6 of [RFC2680].

4.1.6. Errors and Uncertainties

 Refer to Section 3.7 of [RFC2680].

4.1.7. Reporting the Metric

 Refer to Section 3.8 of [RFC2680].

Uijterwaal Standards Track [Page 8] RFC 5560 Packet Duplication Metric May 2009

4.2. Periodic Streams

4.2.1. Metric Name

 Type-P-one-way-Packet-Duplication-Periodic-Stream

4.2.2. Metric Parameters

 o  src, the IP address of a host.
 o  dst, the IP address of a host.
 o  Ts, a time.
 o  Tf, a time.  Ts and Tf specify the time interval when packets can
    be sent for this stream.
 o  T0, the maximum waiting time for a packet to arrive at the
    destination.
 o  lambda, a rate in reciprocal seconds.

4.2.3. Metric Units

 A sequence of pairs; the elements of each pair are:
 o  T, a time
 o  Type-P-one-way-packet-arrival-count for the packet sent at T.

4.2.4. Definition

 At time Ts, we start sending packets with a constant-rate lambda,
 until time Tf.  For each packet sent, we obtain the value of Type-P-
 one-way-packet-arrival-count.  The value of the sample is the
 sequence made up of the resulting {time, duplication} pairs.  If
 there are no such pairs, the sequence is of length zero and the
 sample is said to be empty.

4.2.5. Methodology

 Refer to Section 4.5 of [RFC3432].

4.2.6. Errors and uncertainties

 Refer to Section 4.6 of [RFC3432].

Uijterwaal Standards Track [Page 9] RFC 5560 Packet Duplication Metric May 2009

4.2.7. Reporting the metric

 Refer to Section 4.7 of [RFC3432].

5. Some Statistics Definitions for One-Way Duplication

 Note: the statistics described in this section can be used for both
 Type-P-one-way-Packet-Duplication-Poisson-Stream and Type-P-one-way-
 Packet-Duplication-Periodic-Stream.  The application SHOULD report
 which sample was used as input.

5.1. Type-P-one-way-packet-duplication-fraction

 This statistic gives the fraction of additional packets that arrived
 in a stream.
 Given a Type-P-one-way-Packet-Duplication-Poisson-Stream, one first
 removes all values of Type-P-one-way-Packet-Duplication that are
 undefined.  For the remaining pairs in the stream, one calculates:
 (Sum Type-P-one-way-packet-arrival-count/Number of pairs left) - 1
 (In other words, (number of packets received)/(number of packets sent
 and not lost).)
 The number can be expressed as a percentage.
 Note: this statistic is the equivalent to the Y.1540 IPDR [Y1540].

5.2. Type-P-one-way-replicated-packet-rate

 This statistic gives the fraction of packets that was duplicated (one
 or more times) in a stream.
 Given a Type-P-one-way-Packet-Duplication-Poisson-Stream, one first
 removes all values of Type-P-one-way-packet-arrival-count that are
 undefined.  For the remaining pairs in the stream, one counts the
 number of pairs with Type-P-one-way-packet-arrival-count greater than
 1.  Then, one calculates the fraction of packets that meet this
 criterion as a fraction of the total.  (In other words: (number of
 duplicated packets)/(number of packets sent and not lost).)
 The number can be expressed as a percentage.
 Note: this statistic is the equivalent of the Y.1540 RIPR [Y1540].

Uijterwaal Standards Track [Page 10] RFC 5560 Packet Duplication Metric May 2009

5.3. Examples

 Consider a stream of 4 packets, sent as:
      (1, 2, 3, 4)
 and arriving as:
 o  Case 1: (1, 2, 3, 4)
 o  Case 2: (1, 1, 2, 2, 3, 3, 4, 4)
 o  Case 3: (1, 1, 1, 2, 2, 2, 3, 3, 3, 4, 4, 4)
 o  Case 4: (1, 1, 1, 2, 3, 3, 3, 4)
 Case 1: No packets are duplicated in a stream, and both the Type-P-
 one-way-packet-duplication-fraction and the Type-P-one-way-packet-
 replicated-packet-rate are 0.
 Case 2: Every packet is duplicated once, and the Type-P-one-way-
 packet-duplication-fraction is 100%.  The Type-P-one-way-replicated-
 packet-rate is 100%, too.
 Case 3: Every packet is duplicated twice, so the Type-P-one-way-
 packet-duplication-fraction is 200%.  The Type-P-one-way-replicated-
 packet-rate is still 100%.
 Case 4: Half the packets are duplicated twice and the other half are
 not duplicated.  The Type-P-one-way-packet-duplication-fraction is
 again 100%, and this number does not show the difference with case 2.
 However, the Type-P-one-way-packet-replicated-packet-rate is 50% in
 this case and 100% in case 2.
 However, the Type-P-one-way-packet-duplication-rate will not show the
 difference between cases 2 and 3.  For this, one has to look at the
 Type-P-one-way-packet-duplication-fraction.
 Finally, note that the order in which the packets arrived does not
 affect the results.  For example, these variations of case 2:
 o  Case 2a: (1, 1, 2, 2, 3, 3, 4, 4)
 o  Case 2b: (1, 2, 3, 4, 1, 2, 3, 4)
 o  Case 2c: (1, 2, 3, 4, 4, 3, 2, 1)

Uijterwaal Standards Track [Page 11] RFC 5560 Packet Duplication Metric May 2009

 (as well as any other permutation) all yield the same results for
 Type-P-one-way-packet-duplication-fraction and the Type-P-one-way-
 replicated-packet-rate.

6. 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 that 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 they
 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 that 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.

7. IANA Considerations

 IANA has registered the metrics defined in this document in the IP
 Performance Metrics (IPPM) Metrics Registry, see [RFC4148].

Uijterwaal Standards Track [Page 12] RFC 5560 Packet Duplication Metric May 2009

8. Acknowledgements

 The idea to write this document came up in a meeting with Al Morton,
 Stanislav Shalunov, Emile Stephan, and the author on the IPPM
 reporting document.
 This document relies heavily on [RFC2680], and the author would like
 to thank the authors of that document for writing it.
 Finally, thanks are due to Lars Eggert, Al Morton, Martin Swany, and
 Matt Zekauskas for their comments.

9. References

9.1. Normative References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [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.

9.2. Informative References

 [RFC2330]  Paxson, V., Almes, G., Mahdavi, J., and M. Mathis,
            "Framework for IP Performance Metrics", RFC 2330,
            May 1998.
 [RFC4148]  Stephan, E., "IP Performance Metrics (IPPM) Metrics
            Registry", BCP 108, RFC 4148, August 2005.
 [Y1540]    "Y.1540 ITU-T Recommendation Y.1540 (2007), Internet
            protocol data communication service IP packet transfer and
            availability performance parameters.", 2007.

Uijterwaal Standards Track [Page 13] RFC 5560 Packet Duplication Metric May 2009

Author's Address

 Henk Uijterwaal
 RIPE NCC
 Singel 258
 1016 AB Amsterdam
 The Netherlands
 Phone: +31 20 535 4444
 EMail: henk@ripe.net

Uijterwaal Standards Track [Page 14]

/data/webs/external/dokuwiki/data/pages/rfc/rfc5560.txt · Last modified: 2009/05/29 16:39 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki