draft-ietf-ippm-delay-05.txt   draft-ietf-ippm-delay-06.txt 
Network Working Group G. Almes Network Working Group G. Almes
Internet Draft S. Kalidindi Internet Draft S. Kalidindi
Expiration Date: May 1999 M. Zekauskas Expiration Date: August 1999 M. Zekauskas
Advanced Network & Services Advanced Network & Services
November 1998 February 1999
A One-way Delay Metric for IPPM A One-way Delay Metric for IPPM
<draft-ietf-ippm-delay-05.txt> <draft-ietf-ippm-delay-06.txt>
1. Status of this Memo 1. Status of this Memo
This document is an Internet-Draft. Internet-Drafts are working This document is an Internet-Draft and is in full conformance with
documents of the Internet Engineering Task Force (IETF), its areas, all provisions of Section 10 of RFC2026.
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 Internet-Drafts are working documents of the Internet Engineering
months, and may be updated, replaced, or obsoleted by other documents Task Force (IETF), its areas, and its working groups. Note that
at any time. It is inappropriate to use Internet-Drafts as reference 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." material or to cite them other than as "work in progress."
To view the entire list of current Internet-Drafts, please check the The list of current Internet-Drafts can be accessed at
"1id-abstracts.txt" listing contained in the Internet-Drafts shadow http://www.ietf.org/ietf/1id-abstracts.txt
directories on ftp.is.co.za (Africa), nic.nordu.net (Northern
Europe), ftp.nis.garr.it (Southern Europe), munnari.oz.au (Pacific The list of Internet-Draft shadow directories can be accessed at
Rim), ftp.ietf.org (US East Coast), or ftp.isi.edu (US West Coast). http://www.ietf.org/shadow.html
This memo provides information for the Internet community. This memo This memo provides information for the Internet community. This memo
does not specify an Internet standard of any kind. Distribution of does not specify an Internet standard of any kind. Distribution of
this memo is unlimited. this memo is unlimited.
2. Introduction 2. Introduction
This memo defines a metric for one-way delay of packets across This memo defines a metric for one-way delay of packets across
Internet paths. It builds on notions introduced and discussed in the 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, RFC 2330 [1]; the reader is assumed to be
familiar with that document. familiar with that document.
This memo is intended to be parallel in structure to a companion This memo is intended to be parallel in structure to a companion
document for Packet Loss ("A Packet Loss Metric for IPPM" document for Packet Loss ("A Packet Loss Metric for IPPM"
<draft-ietf-ippm-loss-05.txt>) [2]. <draft-ietf-ippm-loss-06.txt>) [2].
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [6]. document are to be interpreted as described in RFC 2119 [6].
Although RFC 2119 was written with protocols in mind, the key words Although RFC 2119 was written with protocols in mind, the key words
are used in this document for similar reasons. They are used to are used in this document for similar reasons. They are used to
ensure the results of measurements from two different implementations ensure the results of measurements from two different implementations
are comparable, and to note instances when an implementation could are comparable, and to note instances when an implementation could
perturb the network. perturb the network.
skipping to change at page 3, line 41 skipping to change at page 3, line 42
direction may be radically different than provisioning in the direction may be radically different than provisioning in the
reverse direction, and thus the QoS guarantees differ. Measuring reverse direction, and thus the QoS guarantees differ. Measuring
the paths independently allows the verification of both the paths independently allows the verification of both
guarantees. guarantees.
It is outside the scope of this document to say precisely how delay It is outside the scope of this document to say precisely how delay
metrics would be applied to specific problems. metrics would be applied to specific problems.
2.2. General Issues Regarding Time 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 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. understood to be measured in seconds (and fractions) relative to UTC.
As described more fully in the Framework document, there are four As described more fully in the Framework document, there are four
distinct, but related notions of clock uncertainty: distinct, but related notions of clock uncertainty:
synchronization* synchronization*
measures the extent to which two clocks agree on what time it 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 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* accuracy*
measures the extent to which a given clock agrees with UTC. For 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. 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* resolution*
measures the precision of a given clock. For example, the clock 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 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* skew*
measures the change of accuracy, or of synchronization, with measures the change of accuracy, or of synchronization, with
time. For example, the clock on a given host might gain 1.3 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 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 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 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 to UTC, which threatens accuracy. We might also speak of the
skew of one clock relative to another clock, which threatens 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. A Singleton Definition for One-way Delay
3.1. Metric Name: 3.1. Metric Name:
Type-P-One-way-Delay Type-P-One-way-Delay
3.2. Metric Parameters: 3.2. Metric Parameters:
+ Src, the IP address of a host + Src, the IP address of a host
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be used where appropriate to guard against injected traffic attacks. be used where appropriate to guard against injected traffic attacks.
The privacy concerns of network measurement are limited by the active The privacy concerns of network measurement are limited by the active
measurements described in this memo. Unlike passive measurements, measurements described in this memo. Unlike passive measurements,
there can be no release of existing user data. there can be no release of existing user data.
7. Acknowledgements 7. Acknowledgements
Special thanks are due to Vern Paxson of Lawrence Berkeley Labs for Special thanks are due to Vern Paxson of Lawrence Berkeley Labs for
his helpful comments on issues of clock uncertainty and statistics. his helpful comments on issues of clock uncertainty and statistics.
Thanks also to Will Leland, Andy Scherrer, Sean Shapira, and Thanks also to Garry Couch, Will Leland, Andy Scherrer, Sean Shapira,
Roland Wittig for several useful suggestions. and Roland Wittig for several useful suggestions.
8. References 8. References
[1] V. Paxson, G. Almes, J. Mahdavi, and M. Mathis, "Framework for [1] V. Paxson, G. Almes, J. Mahdavi, and M. Mathis, "Framework for
IP Performance Metrics", RFC 2330, May 1998. IP Performance Metrics", RFC 2330, May 1998.
[2] G. Almes, S. Kalidindi, and M. Zekauskas, "A Packet Loss Metric [2] G. Almes, S. Kalidindi, and M. Zekauskas, "A One-way Packet Loss
for IPPM", Internet-Draft <draft-ietf-ippm-loss-05.txt>, August Metric for IPPM", Internet-Draft <draft-ietf-ippm-loss-06.txt>,
1998. February 1999.
[3] D. Mills, "Network Time Protocol (v3)", RFC 1305, April 1992. [3] D. Mills, "Network Time Protocol (v3)", RFC 1305, April 1992.
[4] J. Mahdavi and V. Paxson, "IPPM Metrics for Measuring [4] J. Mahdavi and V. Paxson, "IPPM Metrics for Measuring
Connectivity", Internet-Draft <draft-ietf-ippm- Connectivity", RFC 2498, January 1999.
connectivity-03.txt>, October 1998.
[5] J. Postel, "Internet Protocol", RFC 791, September 1981. [5] J. Postel, "Internet Protocol", RFC 791, September 1981.
[6] S. Bradner, "Key words for use in RFCs to Indicate Requirement [6] S. Bradner, "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, March 1997. Levels", RFC 2119, March 1997.
[7] S. Bradner, "The Internet Standards Process -- Revision 3", RFC
2026, October 1996.
9. Authors' Addresses 9. Authors' Addresses
Guy Almes Guy Almes
Advanced Network & Services, Inc. Advanced Network & Services, Inc.
200 Business Park Drive 200 Business Park Drive
Armonk, NY 10504 Armonk, NY 10504
USA USA
Phone: +1 914 765 1120 Phone: +1 914 765 1120
EMail: almes@advanced.org EMail: almes@advanced.org
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Matthew J. Zekauskas Matthew J. Zekauskas
Advanced Network & Services, Inc. Advanced Network & Services, Inc.
200 Buisiness Park Drive 200 Buisiness Park Drive
Armonk, NY 10504 Armonk, NY 10504
USA USA
Phone: +1 914 765 1112 Phone: +1 914 765 1112
EMail: matt@advanced.org EMail: matt@advanced.org
Expiration date: May, 1999 Expiration date: August, 1999
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