Network Working Group A.Morton,Editor Internet Draft AT&T Labs Document: <draft-morton-ippm-composition-00.txt> Category: Individual Composition of Metrics Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. This document is an Internet-Draft and is subject to all provisions of section 3 of BCP 78. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Copyright Notice Copyright (C) The Internet Society (2005). Abstract This memo intends to define metrics that are applicable to both complete paths and sub-paths, where a corresponding relationship can be specified to compose the complete path metric from the sub-path metrics with sufficient accuracy. The current memo gives some background and proposes wording for a Scope and Application section to define this new work. The description of an example metric and statistic follows. Morton, et al. Individual exp. January 2006 Page 1 Composition of Metrics July 2005 Contents Status of this Memo................................................1 Copyright Notice...................................................1 Abstract...........................................................1 Authors/Contributors...............................................2 1. Conventions used in this document...............................3 2. Introduction....................................................3 3. Proposed Scope and Application..................................4 3.1 Scope of Work.................................................4 3.2 Application...................................................4 3.3 Measurement Points............................................5 4. One-way Delay Composition Metrics and Statistics................5 4.1 Name: Type-P-Finite-One-way-Delay-Poisson/Periodic-Stream......5 4.1.1 Metric Parameters:...........................................5 4.1.2 Definition:..................................................5 4.1.3 Discussion and other details.................................6 4.1.4 Mean Statistic...............................................6 4.1.5 Composition Relationship: Sum of Mean Delays.................6 4.1.6 Statement of Conjecture......................................6 4.1.7 Justification for the composite relationship.................6 4.1.8 Sources of Error.............................................6 4.1.9 Specific cases where the conjecture might fail...............7 4.1.10 Application of Measurement Methodology......................7 5. Loss Metrics/Statistics.........................................7 6. Delay Variation Metrics/Statistics..............................7 7. Other Metrics/Statistics........................................7 8. Security Considerations.........................................7 8.1 Denial of Service Attacks......................................7 8.2 User data confidentiality......................................8 8.3 Interference with the metric...................................8 9. IANA Considerations.............................................8 10. Normative References...........................................8 11. Informative References.........................................9 12. Acknowledgments................................................9 13. Author's Addresses.............................................9 Full Copyright Statement..........................................10 Intellectual Property.............................................10 Acknowledgement...................................................10 Authors/Contributors Thus far, the following people have contributed useful ideas or suggestions that have been incorporated into this memo: - Phil Chimento <vze275m9@verizon.net> - Reza Fardid <RFardid@Covad.COM> - Roman Krzanowski <roman.krzanowski@verizon.com> - Maurizio Molina <maurizio.molina@dante.org.uk> - Emile Stephan <emile.stephan@francetelecom.com> Morton, et al. Individual exp. January 2006 Page 2 Composition of Metrics July 2005 1. Conventions used in this 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 RFC 2119 [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. In this memo, the characters "<=" should be read as "less than or equal to" and ">=" as "greater than or equal to". 2. Introduction The IPPM framework RFC 2330 [RFC2330] describes two forms of metric composition, spatial and temporal. Spatial composition encompasses the definitions of performance metrics that are applicable to the complete path, and to various sub-paths. Also, the text suggests that the concepts of the analytical framework (or A-frame) would help to define useful relationships between the complete path metrics and the sub-path metrics. The effectiveness of such metrics is dependent on their usefulness in analysis and applicability with practical measurement methods. The relationships may involve conjecture, and [RFC2330] lists four points that the metric definitions should include: + the specific conjecture applied to the metric, + a justification of the practical utility of the composition in terms of making accurate measurements of the metric on the path, + a justification of the usefulness of the composition in terms of making analysis of the path using A-frame concepts more effective, and + an analysis of how the conjecture could be incorrect. RFC 2330 also gives an example where a conjecture that the delay of a path is very nearly the sum of the delays of the exchanges and clouds of the corresponding path digest. This example is particularly relevant to those who wish to assess the performance of an Inter-domain path without direct measurement, and the performance estimate of the complete path is related to the measured results for various sub-paths instead. Approximate relationships between the sub-path and complete path metrics are useful, with knowledge of the circumstances where the relationships are/are not applicable. For example, we would not expect that delay singletons from each sub-path would sum to produce an accurate estimate of a delay singleton for the complete path Morton, et al. Individual exp. January 2006 Page 3 Composition of Metrics July 2005 (unless all the delays were essentially constant - very unlikely). However, other delay statistics (based on a reasonable sample size) may have a sufficiently large set of circumstances where they are applicable. 3. Proposed Scope and Application 3.1 Scope of Work For the primary IPPM metrics (currently Loss, Delay, and Delay Variation), this memo gives a set of complete path metrics that can be composed from the same or similar sub-path metrics. This means that the complete path metric may be composed from: + the same metric for each sub-path + multiple metrics for each sub-path (possibly one that is the same as the complete path metric) + a single sub-path metrics that is different from the complete path metric Each metric will clearly state: - the definition (and statistic, where appropriate) - the composition relationship - the specific conjecture on which the relationship is based - a justification of practical utility or usefulness for analysis using the A-frame concepts - one or more examples of how the conjecture could be incorrect and lead to inaccuracy 3.2 Application For each metric, the applicable circumstances are defined, in terms of whether the composition: Requires the same test packets to traverse all sub-paths, or may use similar packets sent and collected separately in each sub-path. Requires homogeneity of measurement methodologies, or can allow a degree of flexibility (e.g., active or passive methods produce the "same" metric). Needs information or access that will only be available within an operator's domain, or is applicable to Inter-domain composition. Morton, et al. Individual exp. January 2006 Page 4 Composition of Metrics July 2005 Requires synchronized measurement time intervals in all sub-paths, or largely overlapping, or no timing requirements. Requires assumption of sub-path independence w.r.t. the metric being defined/composed, or other assumptions. Has known sources of inaccuracy/error, and identifies the sources. 3.3 Measurement Points This section will define the terminology applicable to both complete path and sub-path metrics. 4. One-way Delay Composition Metrics and Statistics 4.1 Name: Type-P-Finite-One-way-Delay-Poisson/Periodic-Stream 4.1.1 Metric Parameters: + Src, the IP address of a host + Dst, the IP address of a host + T, a time (start of test interval) + Tf, a time (end of test interval) + lambda, a rate in reciprocal seconds (for Poisson Streams) + incT, the nominal duration of inter-packet interval, first bit to first bit (for Periodic Streams) + T0, a time that MUST be selected at random from the interval [T, T+dT] to start generating packets and taking measurements (for Periodic Streams) + TstampSrc, the wire time of the packet as measured at MP(Src) + TstampDst, the wire time of the packet as measured at MP(Dst), assigned to packets that arrive within a "reasonable" time. 4.1.2 Definition: Using the parameters above, we obtain the value of Type-P-One-way- Delay singleton as per RFC 2679 [RFC2679]. For each packet [i] that has a finite One-way Delay (in other words, excluding packets which have undefined, or infinite one-way delay): Type-P-Finite-One-way-Delay-Poisson/Periodic-Stream[i] = FiniteDelay[i] = TstampDst - TstampSrc Morton, et al. Individual exp. January 2006 Page 5 Composition of Metrics July 2005 4.1.3 Discussion and other details... 4.1.4 Mean Statistic + L, the total number of packets received at Dst (sent between T0 and Tf) The Type-P-Finite-One-way-Delay-Mean = MeanDelay = (1/L)Sum(from i=1 to L, FiniteDelay[i]) where all packets i= 1 through L have finite singleton delays. 4.1.5 Composition Relationship: Sum of Mean Delays The Type-P-Finite-One-way-Delay-Mean, or MeanDelay for the complete Source to Destination path can be calculated from sum of the Mean Delays of all its constituent sub-paths. 4.1.6 Statement of Conjecture The mean of a sufficiently large stream of packets measured on each sub-path during the interval [T, Tf] will be representative of the true mean of the delay distribution (and the distributions themselves are sufficiently independent), such that the means may be added to produce an estimate of the complete path mean delay. 4.1.7 Justification for the composite relationship It is sometimes impractical to conduct active measurements between every Src-Dst pair. For example, it may not be possible to collect the desired sample size in each test interval when access link speed is limited, because of the potential for measurement traffic to degrade the user traffic performance. The conditions on a low-speed access link may be understood well-enough to permit use of a small sample size/rate, while a larger sample size/rate may be used on other sub-paths. Also, since measurement operations have a real monetary cost, there is value in re-using measurements where they are applicable, rather than launching new measurements for every possible source- destination pair. 4.1.8 Sources of Error The measurement packets, each having source and destination addresses intended for collection at edges of the sub-path, may take a different specific path through the network equipment and parallel exchanges than packets with the source and destination addresses of Morton, et al. Individual exp. January 2006 Page 6 Composition of Metrics July 2005 the complete path. Therefore, the sub-path measurements may differ from the performance experienced by packets on the complete path. Measurements employing sufficient sub-path address pairs might produce bounds on the extent of this error. others... 4.1.9 Specific cases where the conjecture might fail If any of the sub-path distributions are bimodal, then the measured means may not be stable, and in this case the mean will not be a particularly useful statistic when describing the delay distribution of the complete path. The mean may not be sufficiently robust statistic to produce a reliable estimate, or to be useful even if it can be measured. others... 4.1.10 Application of Measurement Methodology SHOULD use similar packets sent and collected separately in each sub-path. Allows a degree of flexibility (e.g., active or passive methods can produce the "same" metric, but timing and correlation of passive measurements is much more challenging). Applicable to both Inter-domain and Intra-domain composition. SHOULD have synchronized measurement time intervals in all sub- paths, but largely overlapping intervals MAY suffice. REQUIRES assumption of sub-path independence w.r.t. the metric being defined/composed. 5. Loss Metrics/Statistics 6. Delay Variation Metrics/Statistics 7. Other Metrics/Statistics 8. Security Considerations 8.1 Denial of Service Attacks This metric requires a stream of packets sent from one host (source) to another host (destination) through intervening networks. This method could be abused for denial of service attacks directed at destination and/or the intervening network(s). Morton, et al. Individual exp. January 2006 Page 7 Composition of Metrics July 2005 Administrators of source, destination, and the intervening network(s) should establish bilateral or multi-lateral agreements regarding the timing, size, and frequency of collection of sample metrics. Use of this method in excess of the terms agreed between the participants may be cause for immediate rejection or discard of packets or other escalation procedures defined between the affected parties. 8.2 User data confidentiality Active use of this method generates packets for a sample, rather than taking samples based on user data, and does not threaten user data confidentiality. Passive measurement must restrict attention to the headers of interest. Since user payloads may be temporarily stored for length analysis, suitable precautions MUST be taken to keep this information safe and confidential. In most cases, a hashing function will produce a value suitable for payload comparisons. 8.3 Interference with the metric 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 and/or the intervening networks, it is possible to change the processing of the packets (e.g. increasing or decreasing delay) that may distort the measured performance. It may also be possible to generate additional packets that appear to be part of the sample metric. These additional packets are likely to perturb the results of the sample measurement. To discourage the kind of interference mentioned above, packet interference checks, such as cryptographic hash, may be used. 9. IANA Considerations Since this metric does not define a protocol or well-known values, there are no IANA considerations in this memo. 10. Normative References [RFC791] Postel, J., "Internet Protocol", STD 5, RFC 791, September 1981. Obtain via: http://www.rfc-editor.org/rfc/rfc791.txt [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, March 1997. Obtain via: http://www.rfc-editor.org/rfc/rfc2119.txt [RFC2330] Paxson, V., Almes, G., Mahdavi, J., and Mathis, M., "Framework for IP Performance Metrics", RFC 2330, May 1998. Obtain via: http://www.rfc-editor.org/rfc/rfc2330.txt Morton, et al. Individual exp. January 2006 Page 8 Composition of Metrics July 2005 [RFC2679] Almes, G., Kalidindi, S. and M. Zekauskas, "A one-way delay metric for IPPM", RFC 2679, September 1999. Obtain via: http://www.rfc-editor.org/rfc/rfc2679.txt [RFC3148] Mathis, M. and Allman, M., "A Framework for Defining Empirical Bulk Transfer Capacity Metrics", RFC 3148, July 2001. Obtain via: http://www.rfc-editor.org/rfc/rfc3148.txt [RFC3432] Raisanen, V., Grotefeld, G., and Morton, A., "Network performance measurement with periodic streams", RFC 3432, November 2002. 11. Informative References [I.356] ITU-T Recommendation I.356, "B-ISDN ATM layer cell transfer performance", March 2000. [Pax98] V.Paxson, "Measurements and Analysis of End-to-End Internet Dynamics," Ph.D. dissertation, U.C. Berkeley, 1997, ftp://ftp.ee.lbl.gov/papers/vp-thesis/dis.ps.gz. [RFC3393] Demichelis, C., and Chimento, P., "IP Packet Delay Variation Metric for IP Performance Metrics (IPPM)", RFC 3393, November 2002. [Y.1540] ITU-T Recommendation Y.1540, "Internet protocol data communication service - IP packet transfer and availability performance parameters", December 2002. 12. Acknowledgments The authors would like to acknowledge many helpful discussions with . . . (lots of people, eventually). 13. Author's Addresses Al Morton AT&T Labs Room D3 - 3C06 200 Laurel Ave. South Middletown, NJ 07748 USA Phone +1 732 420 1571 EMail: <acmorton@att.com> Morton, et al. Individual exp. January 2006 Page 9 Composition of Metrics July 2005 Need addresses for: - Phil Chimento <vze275m9@verizon.net> - Reza Fardid <RFardid@Covad.COM> - Roman Krzanowski <roman.krzanowski@verizon.com> - Maurizio Molina <maurizio.molina@dante.org.uk> - Emile Stephan <emile.stephan@francetelecom.com> Full Copyright Statement Copyright (C) The Internet Society (2005). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Intellectual Property The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf- ipr@ietf.org. Acknowledgement Morton, et al. Individual exp. January 2006 Page 10 Composition of Metrics July 2005 Funding for the RFC Editor function is currently provided by the Internet Society. Morton, et al. Individual exp. January 2006 Page 11