--- 1/draft-morton-ippm-2679-bis-05.txt 2014-10-07 07:15:18.137473086 -0700 +++ 2/draft-morton-ippm-2679-bis-06.txt 2014-10-07 07:15:18.189474329 -0700 @@ -1,23 +1,23 @@ Network Working Group G. Almes Internet-Draft Texas A&M Obsoletes: 2679 (if approved) S. Kalidindi Intended status: Standards Track Ixia -Expires: January 5, 2015 M. Zekauskas +Expires: April 9, 2015 M. Zekauskas Internet2 A. Morton, Ed. AT&T Labs - July 4, 2014 + October 6, 2014 A One-Way Delay Metric for IPPM - draft-morton-ippm-2679-bis-05 + draft-morton-ippm-2679-bis-06 Abstract This memo (RFC 2679 bis) defines a metric for one-way delay of packets across Internet paths. It builds on notions introduced and discussed in the IPPM Framework document, RFC 2330; the reader is assumed to be familiar with that document. Requirements Language @@ -33,160 +33,203 @@ Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." - This Internet-Draft will expire on January 5, 2015. + This Internet-Draft will expire on April 9, 2015. Copyright Notice Copyright (c) 2014 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. RFC 2679 bis . . . . . . . . . . . . . . . . . . . . . . . . 3 - 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 - 2.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 5 - 2.2. General Issues Regarding Time . . . . . . . . . . . . . . 6 - 3. A Singleton Definition for One-way Delay . . . . . . . . . . 7 - 3.1. Metric Name: . . . . . . . . . . . . . . . . . . . . . . 7 - 3.2. Metric Parameters: . . . . . . . . . . . . . . . . . . . 7 - 3.3. Metric Units: . . . . . . . . . . . . . . . . . . . . . . 7 - 3.4. Definition: . . . . . . . . . . . . . . . . . . . . . . . 7 - 3.5. Discussion: . . . . . . . . . . . . . . . . . . . . . . . 8 - 3.6. Methodologies: . . . . . . . . . . . . . . . . . . . . . 9 - 3.7. Errors and Uncertainties: . . . . . . . . . . . . . . . . 10 - 3.7.1. Errors or uncertainties related to Clocks . . . . . . 10 + 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5 + 2.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 6 + 2.2. General Issues Regarding Time . . . . . . . . . . . . . . 7 + 3. A Singleton Definition for One-way Delay . . . . . . . . . . 8 + 3.1. Metric Name: . . . . . . . . . . . . . . . . . . . . . . 8 + 3.2. Metric Parameters: . . . . . . . . . . . . . . . . . . . 8 + 3.3. Metric Units: . . . . . . . . . . . . . . . . . . . . . . 8 + 3.4. Definition: . . . . . . . . . . . . . . . . . . . . . . . 8 + 3.5. Discussion: . . . . . . . . . . . . . . . . . . . . . . . 9 + 3.6. Methodologies: . . . . . . . . . . . . . . . . . . . . . 10 + 3.7. Errors and Uncertainties: . . . . . . . . . . . . . . . . 11 + 3.7.1. Errors or uncertainties related to Clocks . . . . . . 11 3.7.2. Errors or uncertainties related to Wire-time vs Host- - time . . . . . . . . . . . . . . . . . . . . . . . . 11 - 3.7.3. Calibration . . . . . . . . . . . . . . . . . . . . . 12 - 3.8. Reporting the metric: . . . . . . . . . . . . . . . . . . 14 - 3.8.1. Type-P . . . . . . . . . . . . . . . . . . . . . . . 14 - 3.8.2. Loss Threshold . . . . . . . . . . . . . . . . . . . 14 - 3.8.3. Calibration Results . . . . . . . . . . . . . . . . . 15 - 3.8.4. Path . . . . . . . . . . . . . . . . . . . . . . . . 15 - 4. A Definition for Samples of One-way Delay . . . . . . . . . . 15 - 4.1. Metric Name: . . . . . . . . . . . . . . . . . . . . . . 16 - 4.2. Metric Parameters: . . . . . . . . . . . . . . . . . . . 16 - 4.3. Metric Units: . . . . . . . . . . . . . . . . . . . . . . 16 - 4.4. Definition: . . . . . . . . . . . . . . . . . . . . . . . 16 - 4.5. Discussion: . . . . . . . . . . . . . . . . . . . . . . . 17 - 4.6. Methodologies: . . . . . . . . . . . . . . . . . . . . . 17 - 4.7. Errors and Uncertainties: . . . . . . . . . . . . . . . . 18 - 4.8. Reporting the metric: . . . . . . . . . . . . . . . . . . 18 - 5. Some Statistics Definitions for One-way Delay . . . . . . . . 18 - 5.1. Type-P-One-way-Delay-Percentile . . . . . . . . . . . . . 18 - 5.2. Type-P-One-way-Delay-Median . . . . . . . . . . . . . . . 19 - 5.3. Type-P-One-way-Delay-Minimum . . . . . . . . . . . . . . 19 - 5.4. Type-P-One-way-Delay-Inverse-Percentile . . . . . . . . . 20 - 6. Security Considerations . . . . . . . . . . . . . . . . . . . 20 - 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21 - 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 21 - 9. Refetrences (temporary) . . . . . . . . . . . . . . . . . . . 21 - 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 21 - 10.1. Normative References . . . . . . . . . . . . . . . . . . 21 - 10.2. Informative References . . . . . . . . . . . . . . . . . 22 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23 + time . . . . . . . . . . . . . . . . . . . . . . . . 12 + 3.7.3. Calibration . . . . . . . . . . . . . . . . . . . . . 13 + 3.8. Reporting the metric: . . . . . . . . . . . . . . . . . . 15 + 3.8.1. Type-P . . . . . . . . . . . . . . . . . . . . . . . 15 + 3.8.2. Loss Threshold . . . . . . . . . . . . . . . . . . . 16 + 3.8.3. Calibration Results . . . . . . . . . . . . . . . . . 16 + 3.8.4. Path . . . . . . . . . . . . . . . . . . . . . . . . 16 + 4. A Definition for Samples of One-way Delay . . . . . . . . . . 16 + 4.1. Metric Name: . . . . . . . . . . . . . . . . . . . . . . 17 + 4.2. Metric Parameters: . . . . . . . . . . . . . . . . . . . 17 + 4.3. Metric Units: . . . . . . . . . . . . . . . . . . . . . . 17 + 4.4. Definition: . . . . . . . . . . . . . . . . . . . . . . . 17 + 4.5. Discussion: . . . . . . . . . . . . . . . . . . . . . . . 18 + 4.6. Methodologies: . . . . . . . . . . . . . . . . . . . . . 18 + 4.7. Errors and Uncertainties: . . . . . . . . . . . . . . . . 19 + 4.8. Reporting the metric: . . . . . . . . . . . . . . . . . . 19 + 5. Some Statistics Definitions for One-way Delay . . . . . . . . 19 + 5.1. Type-P-One-way-Delay-Percentile . . . . . . . . . . . . . 19 + 5.2. Type-P-One-way-Delay-Median . . . . . . . . . . . . . . . 20 + 5.3. Type-P-One-way-Delay-Minimum . . . . . . . . . . . . . . 21 + 5.4. Type-P-One-way-Delay-Inverse-Percentile . . . . . . . . . 21 + 6. Security Considerations . . . . . . . . . . . . . . . . . . . 21 + 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22 + 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 22 + 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 22 + 9.1. Normative References . . . . . . . . . . . . . . . . . . 22 + 9.2. Informative References . . . . . . . . . . . . . . . . . 23 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24 1. RFC 2679 bis The following text constitutes RFC 2769 bis proposed for advancement - on the IETF Standards Track. + on the IETF Standards Track. This section tracks the changes from + [RFC2679]. - [I-D.ietf-ippm-testplan-rfc2679] (now approved) provides the test - plan and results supporting [RFC2679] advancement along the standards - track, according to the process in [RFC6576]. The conclusions of - [I-D.ietf-ippm-testplan-rfc2679] list four minor modifications for - inclusion: + [RFC6808] provides the test plan and results supporting [RFC2679] + advancement along the standards track, according to the process in + [RFC6576]. The conclusions of [RFC6808] list four minor + modifications: - 1. Section 6.2.3 of [I-D.ietf-ippm-testplan-rfc2679] asserts that - the assumption of post-processing to enforce a constant waiting - time threshold is compliant, and that the text of the RFC should - be revised slightly to include this point (see the last list item - of section 3.6, below). + 1. Section 6.2.3 of [RFC6808] asserts that the assumption of post- + processing to enforce a constant waiting time threshold is + compliant, and that the text of the RFC should be revised + slightly to include this point (see the last list item of section + 3.6, below). - 2. Section 6.5 of [I-D.ietf-ippm-testplan-rfc2679] indicates that - Type-P-One-way-Delay-Inverse-Percentile statistic has been - ignored in both implementations, so it is a candidate for removal - or deprecation in RFC2679bis (this small discrepancy does not - affect candidacy for advancement) (see section 5.4, below). + 2. Section 6.5 of [RFC6808] indicates that Type-P-One-way-Delay- + Inverse-Percentile statistic has been ignored in both + implementations, so it is a candidate for removal or deprecation + in RFC2679bis (this small discrepancy does not affect candidacy + for advancement) (see section 5.4, below). 3. The IETF has reached consensus on guidance for reporting metrics in [RFC6703], and this memo should be referenced in RFC2679bis to incorporate recent experience where appropriate (see the last list item of section 3.6, section 3.8, and section 5 below). 4. There is currently one erratum with status "Held for document update" for [RFC2679], and it appears this minor revision and additional text should be incorporated in RFC2679bis (see section 5.1). - A small number of updates to the [RFC2679] text have been proposed - (by the current Editor) in the text below, principally to reference - key IPPM RFCs that were approved after [RFC2679]. + A number of updates to the [RFC2679] text have been implemented in + the text below, to reference key IPPM RFCs that were approved after - Section 5.4.4 of RFC 6390 suggests a common template for performance + [RFC2679], and to address comments on the IPPM mailing list + describing current conditions and experience. + + 1. Near the end of section 2.1, update of a network example using + ATM and clarification of TCP's affect on queue occupation and + importance of one-way delay measurement. + + 2. Explicit inclusion of the maximum waiting time input parameter + in section 3.2 and 4.2, reflecting recognition of this parameter + in more recent RFCs and ITU-T Recommendation Y.1540. + + 3. Addition of reference to RFC6703 in the discussion of packet + life time and application timeouts in section 3.5. + + 4. Addition of reference to the default requirement (that packets + be standard-formed) from RFC2330 as a new list item in section + 3.5. + + 5. GPS-based NTP experience replaces "to be tested" in section 3.5. + + 6. Added parenthetical guidance on minimizing interval between + timestamp placement to send time in section 3.6. + + 7. Added text recognizing the impending deployment of transport + layer encryption in section 3.6. + + 8. Section 3.7.2 notes that some current systems perform host time + stamping on the network interface hardware. + + 9. "instrument" replaced by the defined term "host" in sections + 3.7.3 and 3.8.3. + + 10. Added reference to RFC 3432 Periodic sampling alongside Poisson + sampling in section 4, and also noting that a truncated Poisson + distribution may be needed with modern networks as described in + the IPPM Framework update, RFC7312. + + 11. Add reference to RFC 4737 Reordering metric in the related + discussion of section 4.6, Methodologies. + + 12. Clarifying the conclusions on two related points on harm to + measurements (recognition of measurement traffic for unexpected + priority treatment and attacker traffic which emulates + measurement) in section 6, Security Considerations. + + Section 5.4.4 of [RFC6390] suggests a common template for performance metrics partially derived from previous IPPM and BMWG RFCs, but also - some new items. All of the RFC 6390 Normative points are covered, - but not quite in the same section names or orientation. Several of - the Informative points are covered. It is proposed to "grandfather- - in" bis RFCs w.r.t. RFC 6390 (keeping the familiar outline and - minimizing unnecessary differences), and focus efforts on applying - the template with new metric memos instead. + contains some new items. All of the [RFC6390] Normative points are + covered, but not quite in the same section names or orientation. + Several of the Informative points are covered. Maintaining the + familiar outline of IPPM literature has both value and minimizes + unnecessary differences between this revised RFC and current/future + IPPM RFCs. - The publication of RFC 6921 suggests an area where this memo might be - updated. Packet transfer on Faster-Than-Light (FTL) networks could - result in negative delays and packet reordering, and both are covered - as possibilities in the current text (we note that this is an April - 1st RFC). + The publication of RFC 6921 suggested an area where this memo might + need updating. Packet transfer on Faster-Than-Light (FTL) networks + could result in negative delays and packet reordering, however both + are covered as possibilities in the current text and no revisions are + deemed necessary (we also note that this is an April 1st RFC). 2. Introduction This memo defines a metric for one-way delay of packets across Internet paths. It builds on notions introduced and discussed in the - IPPM Framework document, RFC 2330 [1]; the reader is assumed to be + IPPM Framework document, [RFC2330]; the reader is assumed to be familiar with that document. This memo is intended to be parallel in structure to a companion document for Packet Loss ("A One-way Packet Loss Metric for IPPM") - [2]. + [RFC2680]. - Although RFC 2119 was written with protocols in mind, the key words + Although [RFC2119] was written with protocols in mind, the key words are used in this document for similar reasons. They are used to ensure the results of measurements from two different implementations are comparable, and to note instances when an implementation could perturb the network. The structure of the memo is as follows: + A 'singleton' analytic metric, called Type-P-One-way-Delay, will be introduced to measure a single observation of one-way delay. + Using this singleton metric, a 'sample', called Type-P-One-way- Delay-Poisson-Stream, will be introduced to measure a sequence of - singleton delays measured at times taken from a Poisson process. + singleton delays sent at times taken from a Poisson process. + Using this sample, several 'statistics' of the sample will be defined and discussed. This progression from singleton to sample to statistics, with clear separation among them, is important. Whenever a technical term from the IPPM Framework document is first used in this memo, it will be tagged with a trailing asterisk. For example, "term*" indicates that "term" is defined in the Framework. 2.1. Motivation @@ -218,31 +261,31 @@ + In today's Internet, the path from a source to a destination may be different than the path from the destination back to the source ("asymmetric paths"), such that different sequences of routers are used for the forward and reverse paths. Therefore round-trip measurements actually measure the performance of two distinct paths together. Measuring each path independently highlights the performance difference between the two paths which may traverse different Internet service providers, and even radically different types of networks (for example, research versus commodity networks, - or ATM versus packet-over-SONET). + or networks with asymmetric link capacities, or wireless vs. wireline + access). + Even when the two paths are symmetric, they may have radically different performance characteristics due to asymmetric queueing. + Performance of an application may depend mostly on the performance - in one direction. For example, a file transfer using TCP may depend - more on the performance in the direction that data flows (queue - occupation tends to grow in this direction, possibly dominating the - round-trip delay), rather than the direction in which - acknowledgements travel. + in one direction. For example, a TCP-based communication may + experience reduced throughput if congestion occurs in one direction + of its communication. Trouble shooting may be simplified if the + congested direction of TCP transmission can be identified. + In quality-of-service (QoS) enabled networks, provisioning in one direction may be radically different than provisioning in the reverse direction, and thus the QoS guarantees differ. Measuring the paths independently allows the verification of both guarantees. It is outside the scope of this document to say precisely how delay metrics would be applied to specific problems. 2.2. General Issues Regarding Time @@ -348,42 +392,50 @@ values. + Since delay values will often be as low as the 100 usec to 10 msec range, it will be important for Src and Dst to synchronize very closely. GPS systems afford one way to achieve synchronization to within several 10s of usec. Ordinary application of NTP may allow synchronization to within several msec, but this depends on the stability and symmetry of delay properties among those NTP agents used, and this delay is what we are trying to measure. A combination of some GPS-based NTP servers and a conservatively designed and - deployed set of other NTP servers should yield good results, but this - is yet to be tested. + deployed set of other NTP servers should yield good results. This + was tested in [RFC6808], where a GPS measurement system's results + compared well with a GPS-based NTP synchronized system for the same + intercontinental path. + A given methodology will have to include a way to determine whether a delay value is infinite or whether it is merely very large (and the - packet is yet to arrive at Dst). As noted by Mahdavi and Paxson [4], - simple upper bounds (such as the 255 seconds theoretical upper bound - on the lifetimes of IP packets [5]) could be used, but good - engineering, including an understanding of packet lifetimes, will be - needed in practice. {Comment: Note that, for many applications of - these metrics, the harm in treating a large delay as infinite might - be zero or very small. A TCP data packet, for example, that arrives - only after several multiples of the RTT may as well have been lost.} + packet is yet to arrive at Dst). As noted by Mahdavi and Paxson + [RFC2678], simple upper bounds (such as the 255 seconds theoretical + upper bound on the lifetimes of IP packets [RFC0791]) could be used, + but good engineering, including an understanding of packet lifetimes, + will be needed in practice. {Comment: Note that, for many + applications of these metrics, the harm in treating a large delay as + infinite might be zero or very small. A TCP data packet, for + example, that arrives only after several multiples of the RTT may as + well have been lost. See section 4.1.1 of [RFC6703] for examination + of unusual packet delays and application performance estimation.} + If the packet is duplicated along the path (or paths) so that multiple non-corrupt copies arrive at the destination, then the packet is counted as received, and the first copy to arrive determines the packet's one-way delay. + If the packet is fragmented and if, for whatever reason, reassembly does not occur, then the packet will be deemed lost. + + The packet is standard-formed, the default criteria for all metric + definitions defined in Section 15 of [RFC2330], otherwise the packet + will be deemed lost. + 3.6. Methodologies: As with other Type-P-* metrics, the detailed methodology will depend on the Type-P (e.g., protocol number, UDP/TCP port number, size, precedence). Generally, for a given Type-P, the methodology would proceed as follows: + Arrange that Src and Dst are synchronized; that is, that they have @@ -396,41 +448,41 @@ filled with randomized bits to avoid a situation in which the measured delay is lower than it would otherwise be due to compression techniques along the path. Note that use of transport layer encryption will counteract the deployment of network-based analysis and may reduce the adoption of payload optimizations like compression. + At the Dst host, arrange to receive the packet. + At the Src host, place a timestamp in the prepared Type-P packet, - and send it towards Dst. + and send it towards Dst (ideally minimizing time before sending). + If the packet arrives within a reasonable period of time, take a timestamp as soon as possible upon the receipt of the packet. By subtracting the two timestamps, an estimate of one-way delay can be computed. Error analysis of a given implementation of the method must take into account the closeness of synchronization between Src and Dst. If the delay between Src's timestamp and the actual sending of the packet is known, then the estimate could be adjusted by subtracting this amount; uncertainty in this value must be taken into account in error analysis. Similarly, if the delay between the actual receipt of the packet and Dst's timestamp is known, then the estimate could be adjusted by subtracting this amount; uncertainty in this value must be taken into account in error analysis. See the next section, "Errors and Uncertainties", for a more detailed discussion. + If the packet fails to arrive within a reasonable period of time, - the one-way delay is taken to be undefined (informally, infinite). - Note that the threshold of 'reasonable' is a parameter of the - methodology. These points are examined in detail in [RFC6703], + Tmax, the one-way delay is taken to be undefined (informally, + infinite). Note that the threshold of 'reasonable' is a parameter of + the metric. These points are examined in detail in [RFC6703], including analysis preferences to assign undefined delay to packets that fail to arrive with the difficulties emerging from the informal "infinite delay" assignment, and an estimation of an upper bound on waiting time for packets in transit. Further, enforcing a specific constant waiting time on stored singletons of one-way delay is compliant with this specification and may allow the results to serve more than one reporting audience. Issues such as the packet format, the means by which Dst knows when to expect the test packet, and the means by which Src and Dst are @@ -548,117 +600,118 @@ If the systematic error (the constant bias in measured values) can be determined, it can be compensated for in the reported results. reported value = measured value - systematic error therefore reported value = true value + random error The goal of calibration is to determine the systematic and random - error generated by the instruments themselves in as much detail as + error generated by the hosts themselves in as much detail as possible. At a minimum, a bound ("e") should be found such that the reported value is in the range (true value - e) to (true value + e) at least 95 percent of the time. We call "e" the calibration error for the measurements. It represents the degree to which the values - produced by the measurement instrument are repeatable; that is, how - closely an actual delay of 30 ms is reported as 30 ms. {Comment: 95 - percent was chosen because (1) some confidence level is desirable to - be able to remove outliers, which will be found in measuring any - physical property; (2) a particular confidence level should be - specified so that the results of independent implementations can be - compared; and (3) even with a prototype user-level implementation, - 95% was loose enough to exclude outliers.} + produced by the measurement host are repeatable; that is, how closely + an actual delay of 30 ms is reported as 30 ms. {Comment: 95 percent + was chosen because (1) some confidence level is desirable to be able + to remove outliers, which will be found in measuring any physical + property; (2) a particular confidence level should be specified so + that the results of independent implementations can be compared; and + (3) even with a prototype user-level implementation, 95% was loose + enough to exclude outliers.} + From the discussion in the previous two sections, the error in measurements could be bounded by determining all the individual uncertainties, and adding them together to form Esynch(t) + Rsource + Rdest + Hsource + Hdest. However, reasonable bounds on both the clock-related uncertainty captured by the first three terms and the host-related uncertainty captured by the last two terms should be possible by careful design - techniques and calibrating the instruments using a known, isolated, - network in a lab. + techniques and calibrating the hosts using a known, isolated, network + in a lab. For example, the clock-related uncertainties are greatly reduced through the use of a GPS time source. The sum of Esynch(t) + Rsource + Rdest is small, and is also bounded for the duration of the measurement because of the global time source. The host-related uncertainties, Hsource + Hdest, could be bounded by - connecting two instruments back-to-back with a high-speed serial link - or isolated LAN segment. In this case, repeated measurements are + connecting two hosts back-to-back with a high-speed serial link or + isolated LAN segment. In this case, repeated measurements are measuring the same one-way delay. If the test packets are small, such a network connection has a minimal delay that may be approximated by zero. The measured delay therefore contains only systematic and random error in the - instrumentation. The "average value" of repeated measurements is the - systematic error, and the variation is the random error. + measurement hosts. The "average value" of repeated measurements is + the systematic error, and the variation is the random error. One way to compute the systematic error, and the random error to a 95% confidence is to repeat the experiment many times - at least hundreds of tests. The systematic error would then be the median. The random error could then be found by removing the systematic error from the measured values. The 95% confidence interval would be the range from the 2.5th percentile to the 97.5th percentile of these deviations from the true value. The calibration error "e" could then be taken to be the largest absolute value of these two numbers, plus the clock-related uncertainty. {Comment: as described, this bound is relatively loose since the uncertainties are added, and the absolute value of the largest deviation is used. As long as the resulting value is not a significant fraction of the measured values, it is a reasonable bound. If the resulting value is a significant fraction of the measured values, then more exact methods will be needed to compute the calibration error.} Note that random error is a function of measurement load. For - example, if many paths will be measured by one instrument, this might + example, if many paths will be measured by one host, this might increase interrupts, process scheduling, and disk I/O (for example, recording the measurements), all of which may increase the random error in measured singletons. Therefore, in addition to minimal load measurements to find the systematic error, calibration measurements - should be performed with the same measurement load that the - instruments will see in the field. + should be performed with the same measurement load that the hosts + will see in the field. We wish to reiterate that this statistical treatment refers to the - calibration of the instrument; it is used to "calibrate the meter - stick" and say how well the meter stick reflects reality. + calibration of the host; it is used to "calibrate the meter stick" + and say how well the meter stick reflects reality. - In addition to calibrating the instruments for finite one-way delay, - two checks should be made to ensure that packets reported as losses - were really lost. First, the threshold for loss should be verified. - In particular, ensure the "reasonable" threshold is reasonable: that - it is very unlikely a packet will arrive after the threshold value, - and therefore the number of packets lost over an interval is not + In addition to calibrating the hosts for finite one-way delay, two + checks should be made to ensure that packets reported as losses were + really lost. First, the threshold for loss should be verified. In + particular, ensure the "reasonable" threshold is reasonable: that it + is very unlikely a packet will arrive after the threshold value, and + therefore the number of packets lost over an interval is not sensitive to the error bound on measurements. Second, consider the possibility that a packet arrives at the network interface, but is lost due to congestion on that interface or to other resource - exhaustion (e.g. buffers) in the instrument. + exhaustion (e.g. buffers) in the host. 3.8. Reporting the metric: The calibration and context in which the metric is measured MUST be carefully considered, and SHOULD always be reported along with metric results. We now present four items to consider: the Type-P of test packets, the threshold of infinite delay (if any), error calibration, and the path traversed by the test packets. This list is not exhaustive; any additional information that could be useful in interpreting applications of the metrics should also be reported (see [RFC6703] for extensive discussion of reporting considerations for different audiences). 3.8.1. Type-P - As noted in the Framework document [1], the value of the metric may - depend on the type of IP packets used to make the measurement, or + As noted in the Framework document [RFC2330], the value of the metric + may depend on the type of IP packets used to make the measurement, or "type-P". The value of Type-P-One-way-Delay could change if the protocol (UDP or TCP), port number, size, or arrangement for special treatment (e.g., IP precedence or RSVP) changes. The exact Type-P used to make the measurements MUST be accurately reported. 3.8.2. Loss Threshold In addition, the threshold (or methodology to distinguish) between a large finite delay and loss MUST be reported. @@ -666,21 +719,21 @@ + If the systematic error can be determined, it SHOULD be removed from the measured values. + You SHOULD also report the calibration error, e, such that the true value is the reported value plus or minus e, with 95% confidence (see the last section.) + If possible, the conditions under which a test packet with finite delay is reported as lost due to resource exhaustion on the - measurement instrument SHOULD be reported. + measurement host SHOULD be reported. 3.8.4. Path Finally, the path traversed by the packet SHOULD be reported, if possible. In general it is impractical to know the precise path a given packet takes through the network. The precise path may be known for certain Type-P on short or stable paths. If Type-P includes the record route (or loose-source route) option in the IP header, and the path is short enough, and all routers* on the path support record (or loose-source) route, then the path will be @@ -697,48 +750,51 @@ 4. A Definition for Samples of One-way Delay Given the singleton metric Type-P-One-way-Delay, we now define one particular sample of such singletons. The idea of the sample is to select a particular binding of the parameters Src, Dst, and Type-P, then define a sample of values of parameter T. The means for defining the values of T is to select a beginning time T0, a final time Tf, and an average rate lambda, then define a pseudo-random Poisson process of rate lambda, whose values fall between T0 and Tf. + The time interval between successive values of T will then average 1/ lambda. - {Comment: Note that Poisson sampling is only one way of defining a - sample. Poisson has the advantage of limiting bias, but other - methods of sampling might be appropriate for different situations. - - We encourage others who find such appropriate cases to use this - general framework and submit their sampling method for - standardization.} - - >>> Editor proposal: Add ref to RFC 3432 Periodic sampling above. + Note that Poisson sampling is only one way of defining a sample. + Poisson has the advantage of limiting bias, but other methods of + sampling will be appropriate for different situations. For example, + a truncated Poisson distribution may be needed to avoid reactive + network state changes during intervals of inactivity, see section 4.6 + of [RFC7321]. Sometimes, the goal is sampling with a known bias, and + [RFC3432] describes a method for periodic sampling with random start + times. 4.1. Metric Name: Type-P-One-way-Delay-Poisson-Stream 4.2. Metric Parameters: + Src, the IP address of a host + Dst, the IP address of a host + T0, a time + Tf, a time - + lambda, a rate in reciprocal seconds + + Tmax, a loss threshold waiting time + + + lambda, a rate in reciprocal seconds (or parameters for another + distribution) 4.3. Metric Units: A sequence of pairs; the elements of each pair are: + T, a time, and + dT, either a real number or an undefined number of seconds. The values of T in the sequence are monotonic increasing. Note that @@ -752,22 +808,22 @@ ending at or after Tf. Those time values greater than or equal to T0 and less than or equal to Tf are then selected. At each of the times in this process, we obtain the value of Type-P-One-way-Delay at this time. The value of the sample is the sequence made up of the resulting pairs. If there are no such pairs, the sequence is of length zero and the sample is said to be empty. 4.5. Discussion: The reader should be familiar with the in-depth discussion of Poisson - sampling in the Framework document [1], which includes methods to - compute and verify the pseudo-random Poisson process. + sampling in the Framework document [RFC2330], which includes methods + to compute and verify the pseudo-random Poisson process. We specifically do not constrain the value of lambda, except to note the extremes. If the rate is too large, then the measurement traffic will perturb the network, and itself cause congestion. If the rate is too small, then you might not capture interesting network behavior. {Comment: We expect to document our experiences with, and suggestions for, lambda elsewhere, culminating in a "best current practices" document.} Since a pseudo-random number sequence is employed, the sequence of @@ -791,31 +847,29 @@ new time values T0' and Tf' such that T0 <= T0' <= Tf' <= Tf, the subsequence of the given sample whose time values fall between T0' and Tf' are also a valid Type-P-One-way-Delay-Poisson-Stream sample. 4.6. Methodologies: The methodologies follow directly from: + the selection of specific times, using the specified Poisson arrival process, and - + the methodologies discussion already given for the singleton Type- P-One-way-Delay metric. Care must, of course, be given to correctly handle out-of-order arrival of test packets; it is possible that the Src could send one test packet at TS[i], then send a second one (later) at TS[i+1], while the Dst could receive the second test packet at TR[i+1], and - then receive the first one (later) at TR[i]. - - >>> Editor proposal: Add ref to RFC 4737 Reordering metric above. + then receive the first one (later) at TR[i]. Metrics for reordering + may be found in [RFC4737]. 4.7. Errors and Uncertainties: In addition to sources of errors and uncertainties associated with methods employed to measure the singleton values that make up the sample, care must be given to analyze the accuracy of the Poisson process with respect to the wire-times of the sending of the test packets. Problems with this process could be caused by several things, including problems with the pseudo-random number techniques used to generate the Poisson arrival process, or with jitter in the @@ -859,21 +914,21 @@ > Then the 50th percentile would be 110 msec, since 90 msec and 100 msec are smaller and 500 msec and 'undefined' are larger. See - Section 11.3 of [1] for computing percentiles. + Section 11.3 of [RFC2330] for computing percentiles. Note that if the possibility that a packet with finite delay is reported as lost is significant, then a high percentile (90th or 95th) might be reported as infinite instead of finite. 5.2. Type-P-One-way-Delay-Median Given a Type-P-One-way-Delay-Poisson-Stream, the median of all the dT values in the Stream. In computing the median, undefined values are treated as infinitely large. As with Type-P-One-way-Delay- @@ -932,78 +987,66 @@ packets into the network. The measurement parameters MUST be carefully selected so that the measurements inject trivial amounts of additional traffic into the networks they measure. If they inject "too much" traffic, they can skew the results of the measurement, and in extreme cases cause congestion and denial of service. The measurements themselves could be harmed by routers giving measurement traffic a different priority than "normal" traffic, or by an attacker injecting artificial measurement traffic. If routers can recognize measurement traffic and treat it separately, the - measurements will not reflect actual user traffic. If an attacker - injects artificial traffic that is accepted as legitimate, the loss - rate will be artificially lowered. Therefore, the measurement - methodologies SHOULD include appropriate techniques to reduce the - probability measurement traffic can be distinguished from "normal" - traffic. Authentication techniques, such as digital signatures, may - be used where appropriate to guard against injected traffic attacks. + measurements will not reflect actual user traffic. Therefore, the + measurement methodologies SHOULD include appropriate techniques to + reduce the probability measurement traffic can be distinguished from + "normal" traffic. + + If an attacker injects packets emulating traffic that are accepted as + legitimate, the loss ratio or other measured values could be + corrupted. 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 This memo makes no requests of IANA. 8. Acknowledgements Special thanks are due to Vern Paxson of Lawrence Berkeley Labs for his helpful comments on issues of clock uncertainty and statistics. Thanks also to Garry Couch, Will Leland, Andy Scherrer, Sean Shapira, and Roland Wittig for several useful suggestions. -9. Refetrences (temporary) - - [1] Paxson, V., Almes, G., Mahdavi, J. and M. Mathis, "Framework for - IP Performance Metrics", RFC 2330, May 1998. - - [2] Almes, G., Kalidindi, S. and M. Zekauskas, "A One-way Packet - Loss Metric for IPPM", RFC 2680, September 1999. - - [3] Mills, D., "Network Time Protocol (v3)", RFC 1305, April 1992. - - [4] Mahdavi J. and V. Paxson, "IPPM Metrics for Measuring - Connectivity", RFC 2678, September 1999. - - [5] Postel, J., "Internet Protocol", STD 5, RFC 791, September 1981. - - [6] Bradner, S., "Key words for use in RFCs to Indicate Requirement - Levels", BCP 14, RFC 2119, March 1997. - - [7] Bradner, S., "The Internet Standards Process -- Revision 3", BCP - 9, RFC 2026, October 1996. +9. References -10. References +9.1. Normative References -10.1. Normative References + [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, September + 1981. [RFC2026] Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9, RFC 2026, October 1996. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2330] Paxson, V., Almes, G., Mahdavi, J., and M. Mathis, "Framework for IP Performance Metrics", RFC 2330, May 1998. + [RFC2678] Mahdavi, J. and V. Paxson, "IPPM Metrics for Measuring + Connectivity", RFC 2678, September 1999. + [RFC2679] Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way Delay Metric for IPPM", RFC 2679, September 1999. [RFC2680] Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way Packet Loss Metric for IPPM", RFC 2680, September 1999. [RFC3432] Raisanen, V., Grotefeld, G., and A. Morton, "Network performance measurement with periodic streams", RFC 3432, November 2002. @@ -1015,55 +1058,80 @@ Babiarz, "A Two-Way Active Measurement Protocol (TWAMP)", RFC 5357, October 2008. [RFC5657] Dusseault, L. and R. Sparks, "Guidance on Interoperation and Implementation Reports for Advancement to Draft Standard", BCP 9, RFC 5657, September 2009. [RFC5835] Morton, A. and S. Van den Berghe, "Framework for Metric Composition", RFC 5835, April 2010. + [RFC5905] Mills, D., Martin, J., Burbank, J., and W. Kasch, "Network + Time Protocol Version 4: Protocol and Algorithms + Specification", RFC 5905, June 2010. + [RFC6049] Morton, A. and E. Stephan, "Spatial Composition of Metrics", RFC 6049, January 2011. [RFC6576] Geib, R., Morton, A., Fardid, R., and A. Steinmitz, "IP Performance Metrics (IPPM) Standard Advancement Testing", BCP 176, RFC 6576, March 2012. [RFC6703] Morton, A., Ramachandran, G., and G. Maguluri, "Reporting IP Network Performance Metrics: Different Points of View", RFC 6703, August 2012. -10.2. Informative References + [RFC7321] McGrew, D. and P. Hoffman, "Cryptographic Algorithm + Implementation Requirements and Usage Guidance for + Encapsulating Security Payload (ESP) and Authentication + Header (AH)", RFC 7321, August 2014. + +9.2. Informative References [ADK] Scholz, F. and M. Stephens, "K-sample Anderson-Darling Tests of fit, for continuous and discrete cases", University of Washington, Technical Report No. 81, May 1986. [I-D.ietf-ippm-testplan-rfc2679] Ciavattone, L., Geib, R., Morton, A., and M. Wieser, "Test Plan and Results Supporting Advancement of RFC 2679 on the Standards Track", draft-ietf-ippm-testplan-rfc2679-03 (work in progress), September 2012. [RFC3931] Lau, J., Townsley, M., and I. Goyret, "Layer Two Tunneling Protocol - Version 3 (L2TPv3)", RFC 3931, March 2005. + [RFC4737] Morton, A., Ciavattone, L., Ramachandran, G., Shalunov, + S., and J. Perser, "Packet Reordering Metrics", RFC 4737, + November 2006. + + [RFC6390] Clark, A. and B. Claise, "Guidelines for Considering New + Performance Metric Development", BCP 170, RFC 6390, + October 2011. + + [RFC6808] Ciavattone, L., Geib, R., Morton, A., and M. Wieser, "Test + Plan and Results Supporting Advancement of RFC 2679 on the + Standards Track", RFC 6808, December 2012. + Authors' Addresses Guy Almes Texas A&M + Email: galmes@tamu.edu + Sunil Kalidindi Ixia + Email: skalidindi@ixiacom.com + Matt Zekauskas Internet2 Email: matt@internet2.edu Al Morton (editor) AT&T Labs 200 Laurel Avenue South Middletown, NJ 07748 USA