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Network Working Group                                      H. UijterwaalRequest for Comments: 5560                                      RIPE NCCCategory: Standards Track                                       May 2009A One-Way Packet Duplication MetricStatus 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 toBCP 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 2009Table of Contents1. Introduction ....................................................31.1. Requirements Notation ......................................31.2. Motivation .................................................42. A Singleton Definition for One-Way Packet Arrival Count .........42.1. Metric Name ................................................42.2. Metrics Parameters .........................................42.3. Metric Units ...............................................42.4. Definition .................................................42.5. Discussion .................................................52.6. Methodology ................................................62.7. Errors and Uncertainties ...................................62.8. Reporting the Metric .......................................63. A Singleton Definition for One-Way Packet Duplication ...........63.1. Metric Name ................................................63.2. Metrics Parameters .........................................73.3. Metric Units ...............................................73.4. Definition .................................................73.5. Discussion .................................................74. Definition for Samples for One-Way Packet Duplication ...........74.1. Poisson Streams ............................................74.1.1. Metric Name .........................................74.1.2. Metric Parameters ...................................84.1.3. Metric Units ........................................84.1.4. Definition ..........................................84.1.5. Methodology .........................................84.1.6. Errors and Uncertainties ............................84.1.7. Reporting the Metric ................................84.2. Periodic Streams ...........................................94.2.1. Metric Name .........................................94.2.2. Metric Parameters ...................................94.2.3. Metric Units ........................................94.2.4. Definition ..........................................94.2.5. Methodology .........................................94.2.6. Errors and uncertainties ............................94.2.7. Reporting the metric ...............................105. Some Statistics Definitions for One-Way Duplication ............105.1. Type-P-one-way-packet-duplication-fraction ................105.2. Type-P-one-way-replicated-packet-rate .....................105.3. Examples ..................................................116. Security Considerations ........................................127. IANA Considerations ............................................128. Acknowledgements ...............................................139. References .....................................................139.1. Normative References ......................................139.2. Informative References ....................................13Uijterwaal                  Standards Track                     [Page 2]

RFC 5560               Packet Duplication Metric                May 20091.  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].   AlthoughRFC 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 20091.2.  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 Count2.1.  Metric Name   Type-P-one-way-packet-arrival-count2.2.  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 (seeSection 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   speeds2.6.  Methodology   The basic technique to measure this metric follows the methodology   described inSection 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 toSection 2.7 of [RFC2680].2.8.  Reporting the Metric   Refer toSection 2.8 of [RFC2680].3.  A Singleton Definition for One-Way Packet Duplication3.1.  Metric Name   Type-P-one-way-packet-duplicationUijterwaal                  Standards Track                     [Page 6]

RFC 5560               Packet Duplication Metric                May 20093.2.  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 Duplication4.1.  Poisson Streams4.1.1.  Metric Name   Type-P-one-way-Packet-Duplication-Poisson-StreamUijterwaal                  Standards Track                     [Page 7]

RFC 5560               Packet Duplication Metric                May 20094.1.2.  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 toSection 3.6 of [RFC2680].4.1.6.  Errors and Uncertainties   Refer toSection 3.7 of [RFC2680].4.1.7.  Reporting the Metric   Refer toSection 3.8 of [RFC2680].Uijterwaal                  Standards Track                     [Page 8]

RFC 5560               Packet Duplication Metric                May 20094.2.  Periodic Streams4.2.1.  Metric Name   Type-P-one-way-Packet-Duplication-Periodic-Stream4.2.2.  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 toSection 4.5 of [RFC3432].4.2.6.  Errors and uncertainties   Refer toSection 4.6 of [RFC3432].Uijterwaal                  Standards Track                     [Page 9]

RFC 5560               Packet Duplication Metric                May 20094.2.7.  Reporting the metric   Refer toSection 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 20095.3.  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 20098.  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.  References9.1.  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 2009Author's Address   Henk Uijterwaal   RIPE NCC   Singel 258   1016 AB Amsterdam   The Netherlands   Phone: +31 20 535 4444   EMail: henk@ripe.netUijterwaal                  Standards Track                    [Page 14]