--- 1/draft-ietf-ippm-loss-episode-metrics-03.txt 2012-01-18 15:13:57.302803735 +0100 +++ 2/draft-ietf-ippm-loss-episode-metrics-04.txt 2012-01-18 15:13:57.338755883 +0100 @@ -1,33 +1,33 @@ Network Working Group N. Duffield Internet-Draft AT&T Labs-Research Intended status: Standards Track A. Morton -Expires: April 29, 2012 AT&T Labs +Expires: July 20, 2012 AT&T Labs J. Sommers Colgate University - October 27, 2011 + January 17, 2012 Loss Episode Metrics for IPPM - draft-ietf-ippm-loss-episode-metrics-03 + draft-ietf-ippm-loss-episode-metrics-04 Abstract The IETF has developed a one way packet loss metric that measures the loss rate on a Poisson probe stream between two hosts. However, the impact of packet loss on applications is in general sensitive not just to the average loss rate, but also to the way in which packet losses are distributed in loss episodes (i.e., maximal sets of - consecutively lost probe packets). This draft defines one-way packet - loss episode metrics, specifically the frequency and average duration - of loss episodes, and a probing methodology under which the loss - episode metrics are to be measured. + consecutively lost probe packets). This document defines one-way + packet loss episode metrics, specifically the frequency and average + duration of loss episodes, and a probing methodology under which the + loss episode metrics are to be measured. Requirements Language 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] Status of this Memo This Internet-Draft is submitted in full conformance with the @@ -36,24 +36,24 @@ 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 April 29, 2012. + This Internet-Draft will expire on July 20, 2012. Copyright Notice - Copyright (c) 2011 IETF Trust and the persons identified as the + Copyright (c) 2012 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 @@ -113,21 +113,21 @@ 6. Loss Episode Metrics derived from Bi-Packet Loss Probing . . . 14 6.1. Geometric Stream: Loss Ratio . . . . . . . . . . . . . . . 15 6.1.1. Metric Name . . . . . . . . . . . . . . . . . . . . . 15 6.1.2. Metric Parameters . . . . . . . . . . . . . . . . . . 15 6.1.3. Metric Units . . . . . . . . . . . . . . . . . . . . . 16 6.1.4. Metric Definition . . . . . . . . . . . . . . . . . . 16 6.1.5. Discussion . . . . . . . . . . . . . . . . . . . . . . 16 6.1.6. Methodologies . . . . . . . . . . . . . . . . . . . . 16 6.1.7. Errors and Uncertainties . . . . . . . . . . . . . . . 16 6.1.8. Reporting the Metric . . . . . . . . . . . . . . . . . 16 - 6.2. Geometric Steam: Loss Episode Duration . . . . . . . . . . 16 + 6.2. Geometric Stream: Loss Episode Duration . . . . . . . . . 16 6.2.1. Metric Name . . . . . . . . . . . . . . . . . . . . . 16 6.2.2. Metric Parameters . . . . . . . . . . . . . . . . . . 16 6.2.3. Metric Units . . . . . . . . . . . . . . . . . . . . . 17 6.2.4. Metric Definition . . . . . . . . . . . . . . . . . . 17 6.2.5. Discussion . . . . . . . . . . . . . . . . . . . . . . 17 6.2.6. Methodologies . . . . . . . . . . . . . . . . . . . . 17 6.2.7. Errors and Uncertainties . . . . . . . . . . . . . . . 17 6.2.8. Reporting the Metric . . . . . . . . . . . . . . . . . 18 6.3. Geometric Stream: Loss Episode Frequency . . . . . . . . . 18 6.3.1. Metric Name . . . . . . . . . . . . . . . . . . . . . 18 @@ -140,53 +140,54 @@ 6.3.8. Reporting the Metric . . . . . . . . . . . . . . . . . 19 7. Applicability of Loss Episode Metrics . . . . . . . . . . . . 19 7.1. Relation to Gilbert Model . . . . . . . . . . . . . . . . 19 8. IPR Considerations . . . . . . . . . . . . . . . . . . . . . . 20 9. Security Considerations . . . . . . . . . . . . . . . . . . . 20 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 21 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21 12.1. Normative References . . . . . . . . . . . . . . . . . . . 21 12.2. Informative References . . . . . . . . . . . . . . . . . . 21 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22 1. Introduction 1.1. Background and Motivation Packet loss in the Internet is a complex phenomenon due to the bursty nature of traffic and congestion processes, influenced by both end- users and applications, and the operation of transport protocols such as TCP. For these reasons, the simplest model of packet loss--the single parameter Bernoulli (independent) loss model--does not represent the complexity of packet loss over periods of time. Correspondingly, a single loss metric--the average packet loss ratio over some period of time--arising, e.g., from a stream of Poisson probes as in [RFC2680] is not sufficient to determine the effect of packet loss on traffic in general. Moving beyond single parameter loss models, Markovian and Markov- modulated loss models involving transitions between a good and bad state, each with an associated loss rate, have been proposed by - Gilbert and more generally by Elliot. In principle, Markovian models - can be formulated over state spaces involving patterns of loss of any - desired number of packets. However further increase in the size of - the state space makes such models cumbersome both for parameter - estimation (accuracy decreases) and prediction in practice (due to - computational complexity and sensitivity to parameter inaccuracy). - In general, the relevance and importance of particular models can - change in time, e.g. in response to the advent of new applications - and services. For this reason we are drawn to empirical metrics that - do not depend on a particular model for their interpretation. + Gilbert [Gilbert] and more generally by Elliot [Elliot]. In + principle, Markovian models can be formulated over state spaces + involving patterns of loss of any desired number of packets. However + further increase in the size of the state space makes such models + cumbersome both for parameter estimation (accuracy decreases) and + prediction in practice (due to computational complexity and + sensitivity to parameter inaccuracy). In general, the relevance and + importance of particular models can change in time, e.g. in response + to the advent of new applications and services. For this reason we + are drawn to empirical metrics that do not depend on a particular + model for their interpretation. An empirical measure of packet loss complexity, the index of - dispersion of counts (IDC), comprise, for each t >0, the ratio v(t) \ + dispersion of counts (IDC), comprise, for each t >0, the ratio v(t) / a(t) of the variance v(t) and average a(t) of the number of losses over successive measurement windows of a duration t. However, a full characterization of packet loss over time requires specification of the IDC for each window size t>0. In the standards arena, loss pattern sample metrics are defined in [RFC3357]. Following the Gilbert-Elliot model, burst metrics specific for VoIP that characterize complete episodes of lost, transmitted and discarded packets are defined in [RFC3611] @@ -228,39 +229,41 @@ packet loss ratio, which can be recovered from the loss episode metrics upon dividing the average loss episode duration by the loss episode frequency. 3. the metrics provide the smallest possible increment in complexity beyond, but in the spirit of, the IPPM average packet loss ratio metrics [RFC2680] i.e., moving from a single metric (average packet loss ratio) to a pair of metrics (loss episode frequency and average loss episode duration). - The draft also describes a probing methodology under which loss + The document also describes a probing methodology under which loss episode metrics are to be measured. The methodology comprises sending probe packets in pairs, where packets within each probe pair have a fixed separation, and the time between pairs takes the form of a geometric distributed number multiplied by the same separation. This can be regarded a generalization of Poisson probing where the probes are pairs rather than single packets as in [RFC2680], and also of geometric probing described in [RFC2330]. However, it should be distinguished from back to back packet pairs whose change in separation on traversing a link is used to probe bandwidth. In this - draft, the separation between the packets in a pair is the temporal - resolution at which different loss episodes are to be distinguished. - One key feature of this methodology is its efficiency: it estimates - the average length of loss episodes without directly measuring the - complete episodes themselves. Instead, this information is encoded - in the observed relative frequencies of the 4 possible outcomes - arising from the loss or successful transmission of each of the two - packets of the probe pairs. This is distinct from the approach of - [RFC3611] that reports on directly measured episodes. + document, the separation between the packets in a pair is the + temporal resolution at which different loss episodes are to be + distinguished. The methodology does not measure episodes of loss of + consecutive background packets on the measured path. One key feature + of this methodology is its efficiency: it estimates the average + length of loss episodes without directly measuring the complete + episodes themselves. Instead, this information is encoded in the + observed relative frequencies of the 4 possible outcomes arising from + the loss or successful transmission of each of the two packets of the + probe pairs. This is distinct from the approach of [RFC3611] that + reports on directly measured episodes. The metrics defined in this memo are "derived metrics", according to Section 6.1 of [RFC2330] the IPPM framework. They are based on the singleton loss metric defined in Section 2 of [RFC2680] . 1.3. Outline and Contents o Section 2 defines the fundamental singleton metric for the possible outcomes of a probe pair: Type-P-One-way-Bi-Packet-Loss. @@ -321,39 +324,39 @@ value 0 or 1, where 0 signifies successful transmission of a packet and 1 signifies loss. The metric unit of Type-P-One-way-Bi-Packet-Loss is a Loss Pair. 2.4. Metric Definition 1. "The Type-P-One-way-Bi-Packet-Loss with parameters (Src, Dst, T1, T2, F, P) is (1,1)" means that Src sent the first bit of a Type-P packet to Dst at wire-time T1 and the first bit of a Type-P - packet to Dst a wire-time T2>T1, and that neither packet was + packet to Dst at wire-time T2>T1, and that neither packet was received at Dst. 2. The Type-P-One-way-Bi-Packet-Loss with parameters (Src, Dst, T1, T2, F, P) is (1,0)" means that Src sent the first bit of a Type-P packet to Dst at wire-time T1 and the first bit of a Type-P - packet to Dst a wire-time T2>T1, and that the first packet was + packet to Dst at wire-time T2>T1, and that the first packet was not received at Dst, and the second packet was received at Dst 3. The Type-P-One-way-Bi-Packet-Loss with parameters (Src, Dst, T1, T2, F, P) is (0,1)" means that Src sent the first bit of a Type-P packet to Dst at wire-time T1 and the first bit of a Type-P - packet to Dst a wire-time T2>T1, and that the first packet was + packet to Dst at wire-time T2>T1, and that the first packet was received at Dst, and the second packet was not received at Dst 4. The Type-P-One-way-Bi-Packet-Loss with parameters (Src, Dst, T1, T2, F, P) is (0,0)" means that Src sent the first bit of a Type-P packet to Dst at wire-time T1 and the first bit of a Type-P - packet to Dst a wire-time T2>T1, and that both packet were + packet to Dst at wire-time T2>T1, and that both packets were received at Dst. 2.5. Discussion The purpose of the selection function is to specify exactly which packets are to be used for measurement. The notion is taken from Section 2.5 of [RFC3393], where examples are discussed. 2.6. Methodologies @@ -411,24 +414,25 @@ with parameters (Src, Dst, Ti1, Ti2, Fi, P) where Fi is the restriction of the selection function F to the packet pair at time Ti1, Ti2. 3.5. Discussion The metric definition of Type-P-One-way-Bi-Packet-Loss-Stream is sufficiently general to describe the case where packets are sampled from a pre-existing stream. This is useful in the case that there is a general purpose measurement stream setup between two hosts, and we - which to select a substream from it for the purposes of loss episode - measurement. In the next section we specialize this somewhat to more - concretely describe a purpose built packet stream for loss episode - measurement. + wish to select a substream from it for the purposes of loss episode + measurement. Packet pairs selected as bi-packet loss probes need not + be consecutive within such a stream. In the next section we + specialize this somewhat to more concretely describe a purpose built + packet stream for loss episode measurement. 3.6. Methodologies The methodologies related to the Type-P-One-way-Packet-Loss metric in Section 2.6 of [RFC2680] are similar for the Type-P-One-way-Bi- Packet-Loss-Stream metric described above. In particular, the methodologies described in RFC 2680 apply to both packets of each pair. 3.7. Errors and Uncertainties @@ -662,21 +666,21 @@ o q, a launch probability o F, a selection function defining unambiguously the two packets from the stream selected for the metric. o P, the specification of the packet type, over and above the source and destination address 6.1.3. Metric Units - A number in the interval [0,1] + A decimal number in the interval [0,1] 6.1.4. Metric Definition The result obtained by computing the Bi-Packet-Loss-Ratio over a Type-P-One-way-Bi-Packet-Loss-Geometric-Stream sample with the metric parameters. 6.1.5. Discussion Type-P-One-way-Bi-Packet-Loss-Geometric-Stream-Ratio estimates the @@ -695,21 +699,21 @@ corresponding idealized version corresponding to q = 1. Estimation variance as it applies to Type-P-One-way-Bi-Packet-Loss-Geometric- Stream-Loss-Ratio is described in [SBDR08]. For other issues refer to Section 4.7 6.1.8. Reporting the Metric Refer to Section 4.8 -6.2. Geometric Steam: Loss Episode Duration +6.2. Geometric Stream: Loss Episode Duration 6.2.1. Metric Name Type-P-One-way-Bi-Packet-Loss-Geometric-Stream-Episode-Duration 6.2.2. Metric Parameters o Src, the IP address of a source host o Dst, the IP address of a destination host @@ -841,36 +845,36 @@ independent parameters, the Markov transition probabilities P(g|b) = 1- P(b|b) and P(b|g) = 1- P(g|g), where P(i|j) is the probability to transition from state j and step n to state i at step n+1. With these parameters, the fraction of steps spent in the bad state is P(b|g)/(P(b|g) + P(g|b)) while the average duration of a sojourn in the bad state is 1/P(g|b) steps. Now identify the steps of the Markov chain with the possible sending times of packets for a Type-P-One-way-Bi-Packet-Loss-Geometric-Stream with launch spacing d. Suppose the loss episode metrics Type-P-One- - way-Bi-Packet-Loss-Geometric-Stream-Ratio and ype-P-One-way-Bi- + way-Bi-Packet-Loss-Geometric-Stream-Ratio and Type-P-One-way-Bi- Packet-Loss-Geometric-Stream-Episode-Duration take the values r and m respectively. Then from the discussion in Section 6.2.5 the following can be equated: r = P(b|g)/(P(b|g) + P(g|b)) and m/d = 1/P(g|b). These relationships can be inverted in order to recover the Gilbert model parameters: P(g|b) = d/m and P(b|g)=d/m/(1/r - 1) 8. IPR Considerations An IPR disclosure concerning some of the material covered in this - draft has been made to the IETF: see + document has been made to the IETF: see https://datatracker.ietf.org/ipr/1354/ 9. 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 which run on the Internet. However,implementations of these metrics must be mindful of security and privacy concerns. @@ -893,20 +897,22 @@ 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: they involve no release of user data. 10. IANA Considerations + This document requests no actions from IANA. + 11. Acknowledgements 12. References 12.1. Normative References [RFC2680] Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way Packet Loss Metric for IPPM", RFC 2680, September 1999. [RFC3393] Demichelis, C. and P. Chimento, "IP Packet Delay Variation @@ -930,20 +936,27 @@ "Framework for IP Performance Metrics", RFC 2330, May 1998. [RFC3357] Koodli, R. and R. Ravikanth, "One-way Loss Pattern Sample Metrics", RFC 3357, August 2002. [SBDR08] IEEE/ACM Transactions on Networking, 16(2): 307-320, "A Geometric Approach to Improving Active Packet Loss Measurement", 2008. + [Gilbert] Gilbert, E.N., "Capacity of a Burst-Noise Channel. Bell + System Technical Journal 39 pp 1253-1265", 1960. + + [Elliot] Elliott, E.O., "Estimates of Error Rates for Codes on + Burst-Noise Channels. Bell System Technical Journal 42 pp + 1977-1997", 1963. + Authors' Addresses Nick Duffield AT&T Labs-Research 180 Park Avenue Florham Park, NJ 07932 USA Phone: +1 973 360 8726 Fax: +1 973 360 8871