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DCNET Internet Clock Service (RFC0778)

IP.com Disclosure Number: IPCOM000003826D
Original Publication Date: 1981-Apr-18
Included in the Prior Art Database: 2000-Sep-13
Document File: 4 page(s) / 9K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

D.L. Mills: AUTHOR

Abstract

Following is a description of the Internet Clock Service (ICS) provided by all DCNET hosts. The service, intended primarily for clock synchronization and one-way delay measurements with cooperating internet hosts, is provided using the Timestamp and Timestamp Reply messages of the proposed Internet Control Message Protocol (ICMP). In addition, in order to maintain compatability with present systems, this service will be provided for a limited time using the Echo and Echo Reply messages of the Gateway-Gateway Protocol (GGP). It should be understood that ICMP and GGP datagrams are normally considered tightly bound to the Internet Protocol (IP) itself and not directly accessable to the user on a TOPS-20 system, for example. These datagrams are treated somewhat differently from user datagrams in gateways and DCNET hosts in that certain internal queueing mechanisms are bypassed. Thus, they can be a useful tool in providing the most accurate and stable time reference. The prime motivation for this note is to promote the development of this service in other internet hosts and gateways so that the feasibility for its use thoughout the community can be assessed.

This text was extracted from a ASCII Text document.
This is the abbreviated version, containing approximately 31% of the total text.

RFC 778

DCNET Internet Clock Service

D.L. Mills, COMSAT Laboratories

18 April 1981

Introduction

Following is a description of the Internet Clock

Service (ICS) provided by all DCNET hosts. The service,

intended primarily for clock synchronization and one-way

delay measurements with cooperating internet hosts, is

provided using the Timestamp and Timestamp Reply messages of

the proposed Internet Control Message Protocol (ICMP). In

addition, in order to maintain compatability with present

systems, this service will be provided for a limited time

using the Echo and Echo Reply messages of the

Gateway-Gateway Protocol (GGP).

It should be understood that ICMP and GGP datagrams are

normally considered tightly bound to the Internet Protocol

(IP) itself and not directly accessable to the user on a

TOPS-20 system, for example. These datagrams are treated

somewhat differently from user datagrams in gateways and

DCNET hosts in that certain internal queueing mechanisms are

bypassed. Thus, they can be a useful tool in providing the

most accurate and stable time reference. The prime

motivation for this note is to promote the development of

this service in other internet hosts and gateways so that

the feasibility for its use thoughout the community can be

assessed.

ICS Datagrams and Timestamps

At present, the ICS is provided using either ICMP or

GGP datagrams. The only difference between these is that

ICMP uses protocol number 1 and GGP uses protocol number 3.

In the following these will be referred to interchangably as

ICS datagrams. ICS datagrams include an internet header

followed by an ICS header in the following format:

DCNET Internet Clock Service PAGE 2

0 1 2 3

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

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

| Type | Code | Sequence |

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

| Originate Timestamp |

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

| Receive Timestamp |

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

| Transmit Timestamp |

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

ICS Datagram Format

The originator fills in all three timestamp fields just

before the datagram is forwarded to the net. Each of these

fields contain the local time at origination. Although the

last two are redundant, they allow roundtrip delay

measurements to be made using remote hosts without

timestamping facilities. The "Type" field can be either 8

(GGP Echo) or 13 (ICMP Timestamp). The "Code" field should

be ze...