Browse Prior Art Database

Specification of the Internet Protocol (IP) timestamp option (RFC0781)

IP.com Disclosure Number: IPCOM000003830D
Original Publication Date: 1981-May-01
Included in the Prior Art Database: 2000-Sep-13
Document File: 2 page(s) / 4K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

Z. Su: AUTHOR

Abstract

Packet switching is store-and-forward by nature. Network delay is a therefore a critical performance measure for packet-switching communications. A catenet is a system of packet-switched communication networks interconnected via gateways [Cerf 78]. The catenet "link" delays are thus variable. Their measurement, the measurement of delays across member networks of a catenet, becomes important for catenet investigations.

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RFC 781 Zaw-Sing Su

SRI

May 1981

A SPECIFICATION OF THE INTERNET PROTOCOL (IP) TIMESTAMP OPTION

I. INTRODUCTION

Packet switching is store-and-forward by nature. Network delay is a

therefore a critical performance measure for packet-switching communications.

A catenet is a system of packet-switched communication networks interconnected

via gateways [Cerf 78]. The catenet "link" delays are thus variable. Their

measurement, the measurement of delays across member networks of a catenet,

becomes important for catenet investigations.

An effective way to measure catenet delays is by means of packet header

timestamping. Header timestamping allows monitoring of catenet delays for

user traffic, such as the case of Ft. Bragg users accessing ISID across the

catenet. Packet header timestamping is also compatible with the use of test

packets for catenet delay measurement. Another advantage of header

timestamping is that since it is an IP option, the gateway imposes little

difference in the treatment of such a packet. In this note, a specification

of the timestamp option format for IP is presented.

Measurement of one-way delay, either end-to-end or across an individual

network, requires that device clocks be synchronized, using such facilities as

WWVB clocks [Mills 81]. This specification assumes this capability in the

gateways and involved network hosts.

II. FORMAT SPECIFICATION

As an IP option, the contents of the first two octets are dictated by the

IP header format to be option type and option length in octets [Postel 80].

The next two octets are used to control this option.

0 7 15 23 31

+---------------+---------------+---------------+---------------+

| type | length | offset |overflw| flags |

+---------------+---------------+---------------+---------------+

| internet ID |

+---------------+---------------+---------------+---------------+

| time stamp |

+---------------+---------------+---------------+---------------+

.

.

.

option type = 68 decimal (i.e., option class = 2 and option number = 4);

option length = the number of octets with a maximum of 40 (limited by

IHL = 15);

offset = the number of octets from the beginning of this option to the

end of timestamps (i.e., the begi...