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From: srg@quick.UUCP
Newsgroups: comp.protocols.tcp-ip
Subject: Submission for mod-protocols-tcp-ip
Message-ID: <8704190722.AA17818@uw-apl>
Date: Sun, 19-Apr-87 01:16:46 EST
Article-I.D.: uw-apl.8704190722.AA17818
Posted: Sun Apr 19 01:16:46 1987
Date-Received: Sun, 19-Apr-87 17:45:53 EST
Sender: daemon@ucbvax.BERKELEY.EDU
Distribution: world
Organization: The ARPA Internet
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Path: quick!srg
From: srg@quick.UUCP (Spencer Garrett)
Newsgroups: mod.protocols.tcp-ip
Subject: Re: Time RFC 868
Summary: RTT can be estimated with 2 packets, not 4
Message-ID: <119@quick.UUCP>
Date: 19 Apr 87 06:16:45 GMT
References: <8704051517.a011510@Huey.UDEL.EDU> <194@cos.COM>
Organization: Quicksilver Engineering, Seattle
Lines: 11

In article <194@cos.COM>, howard@cos.UUCP (Howard Berkowitz) writes:
> the slave RETRANSMITS what it received.  The master
> then calculates the difference (in time units) between
> what it sent and what the slave received, and sends
> that as a correction factor.  ...

This same protocol could be done with 2 packets instead of 4.  The
originator (master) should estimate the round-trip time (RTT) using
its local clock instead of asking the responder (slave) to perform
that function.  The accuracy of the setting of the local clock is of
no consequence.  Only a time difference is needed.