--- 1/draft-ietf-ippm-delay-05.txt 2006-02-04 23:45:18.000000000 +0100 +++ 2/draft-ietf-ippm-delay-06.txt 2006-02-04 23:45:18.000000000 +0100 @@ -1,52 +1,55 @@ Network Working Group G. Almes Internet Draft S. Kalidindi -Expiration Date: May 1999 M. Zekauskas +Expiration Date: August 1999 M. Zekauskas Advanced Network & Services - November 1998 + February 1999 A One-way Delay Metric for IPPM - + 1. Status of this Memo - This document is an Internet-Draft. 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. + This document is an Internet-Draft and is in full conformance with + all provisions of Section 10 of RFC2026. - 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 + 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." - To view the entire list of current Internet-Drafts, please check the - "1id-abstracts.txt" listing contained in the Internet-Drafts shadow - directories on ftp.is.co.za (Africa), nic.nordu.net (Northern - Europe), ftp.nis.garr.it (Southern Europe), munnari.oz.au (Pacific - Rim), ftp.ietf.org (US East Coast), or ftp.isi.edu (US West Coast). + 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 This memo provides information for the Internet community. This memo does not specify an Internet standard of any kind. Distribution of this memo is unlimited. 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 familiar with that document. This memo is intended to be parallel in structure to a companion document for Packet Loss ("A Packet Loss Metric for IPPM" - ) [2]. + ) [2]. 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 [6]. 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. @@ -119,53 +122,71 @@ 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 + {Comment: the terminology below differs from that defined by ITU-T + documents (e.g., G.810, "Definitions and terminology for + synchronization networks" and I.356, "B-ISDN ATM layer cell transfer + performance"), but is consistent with the IPPM Framework document. + In general, these differences derive from the different backgrounds; + the ITU-T documents historically have a telephony origin, while the + authors of this document (and the Framework) have a computer systems + background. Although the terms defined below have no direct + equivalent in the ITU-T definitions, after our definitions we will + provide a rough mapping. However, note one potential confusion: our + definition of "clock" is the computer operating systems definition + denoting a time-of-day clock, while the ITU-T definition of clock + denotes a frequency reference.} + Whenever a time (i.e., a moment in history) is mentioned here, it is understood to be measured in seconds (and fractions) relative to UTC. As described more fully in the Framework document, there are four distinct, but related notions of clock uncertainty: synchronization* measures the extent to which two clocks agree on what time it is. For example, the clock on one host might be 5.4 msec ahead - of the clock on a second host. + of the clock on a second host. {Comment: A rough ITU-T + equivalent is "time error".} accuracy* measures the extent to which a given clock agrees with UTC. For example, the clock on a host might be 27.1 msec behind UTC. + {Comment: A rough ITU-T equivalent is "time error from UTC".} resolution* measures the precision of a given clock. For example, the clock on an old Unix host might tick only once every 10 msec, and thus - have a resolution of only 10 msec. + have a resolution of only 10 msec. {Comment: A very rough ITU-T + equivalent is "sampling period".} skew* measures the change of accuracy, or of synchronization, with time. For example, the clock on a given host might gain 1.3 msec per hour and thus be 27.1 msec behind UTC at one time and only 25.8 msec an hour later. In this case, we say that the clock of the given host has a skew of 1.3 msec per hour relative to UTC, which threatens accuracy. We might also speak of the skew of one clock relative to another clock, which threatens - synchronization. + synchronization. {Comment: A rough ITU-T equivalent is "time + drift".} 3. A Singleton Definition for One-way Delay 3.1. Metric Name: Type-P-One-way-Delay 3.2. Metric Parameters: + Src, the IP address of a host @@ -774,43 +795,45 @@ 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. 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 Will Leland, Andy Scherrer, Sean Shapira, and - Roland Wittig for several useful suggestions. + Thanks also to Garry Couch, Will Leland, Andy Scherrer, Sean Shapira, + and Roland Wittig for several useful suggestions. 8. References [1] V. Paxson, G. Almes, J. Mahdavi, and M. Mathis, "Framework for IP Performance Metrics", RFC 2330, May 1998. - [2] G. Almes, S. Kalidindi, and M. Zekauskas, "A Packet Loss Metric - for IPPM", Internet-Draft , August - 1998. + [2] G. Almes, S. Kalidindi, and M. Zekauskas, "A One-way Packet Loss + Metric for IPPM", Internet-Draft , + February 1999. [3] D. Mills, "Network Time Protocol (v3)", RFC 1305, April 1992. [4] J. Mahdavi and V. Paxson, "IPPM Metrics for Measuring - Connectivity", Internet-Draft , October 1998. + Connectivity", RFC 2498, January 1999. [5] J. Postel, "Internet Protocol", RFC 791, September 1981. [6] S. Bradner, "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, March 1997. + [7] S. Bradner, "The Internet Standards Process -- Revision 3", RFC + 2026, October 1996. + 9. Authors' Addresses Guy Almes Advanced Network & Services, Inc. 200 Business Park Drive Armonk, NY 10504 USA Phone: +1 914 765 1120 EMail: almes@advanced.org @@ -826,11 +848,11 @@ Matthew J. Zekauskas Advanced Network & Services, Inc. 200 Buisiness Park Drive Armonk, NY 10504 USA Phone: +1 914 765 1112 EMail: matt@advanced.org - Expiration date: May, 1999 + Expiration date: August, 1999