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PA2AGA > TCPDIG 09.06.96 19:07l 173 Lines 6254 Bytes #-10988 (0) @ EU
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Subject: TCP-Group Digest 96/120
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TCP-Group Digest Fri, 7 Jun 96 Volume 96 : Issue 120
Today's Topics:
nntp date/time stamp (3 msgs)
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----------------------------------------------------------------------
Date: Thu, 06 Jun 96 05:49:00 -0000
From: mikebw@bilow.bilow.uu.ids.net (Mike Bilow)
Subject: nntp date/time stamp
Brian Kantor wrote in a message to Mike Bilow:
BK> That said, I think you'll find most implementations return a
BK> millisecond-accurate time of day. But don't count on it.
BK> If you want to sync clocks, use NTP.
In addition to NTP as defined in RFC1305, attention should be drawn to SNTP as
defined in RFC1361. Basically, SNTP describes a mechanism for querying a
standard NTP server for less critical synchronization than can be achieved by
a
full NTP client. Since there is no IP-based protocol that spans the rather
wide gap between the one-second granularity of the port 37 Time Protocol as
defined in RFC868 and the sub-nanosecond granularity of full NTP, using SNTP
represents a very reasonable option for simplified timekeeping where accuracy
to within a few tens of milliseconds is usual but not guaranteed.
-- Mike
------------------------------
Date: Thu, 6 Jun 96 13:11:06 BST
From: A.D.S.Benham@nortel.co.uk
Subject: nntp date/time stamp
In my area, when we first used NOS for NNTP we found that the time
synchronisation was a major problem.
The NNTP client keeps a note of the last time it polled the server,
and sends a "NEWNEWS" command with that time when it next polls the
server.
The sync problem arises because the =client= holds the time, but asks
the server for articles received since that time.
With early versions of NOS, the client didn't send the "GMT" option
on the "NEWNEWS" request, and the server didn't process it. This meant
that the "NEWNEWS" timestamp was treated at both ends as being in local
time. If the client and server were in different timezones, bad things
happened: worst case, no news was transferred.
When I helped produce UKNOS from JNOS, I had a big fix of the NNTP code.
Firstly, I made the "NEWNEWS" request use the "GMT" option, and made
the server act on it.
Then I made the server respond to the "DATE" extension command. This
returns the server's time in GMT, so the client can store that.
On the client side, when it was about to start a poll I made it issue
a "DATE" command. If it gets a 111 reply, I use that time. If it gets
a 500 reply, I make an RDATE (port 37) connection to the NNTP server.
RDATE returns (in GMT) the number of seconds since 1-Jan-1970. If the
RDATE connection succeeds, I use that time. If RDATE fails, then I
take the clients own time (in GMT) and then subtract 5 minutes.
The upshot is that the client has two goes at finding out what the
server's current time is. If both fail, then it takes its own time minus
5 minutes - this allows a 5 minute drift between server and client idea
of time (this is only important in one direction of drift, but since
the client doesn't know what the server's time is to know which way
it's offset....).
The UKNOS NNTP code is on ftp.ucsd.edu and ftp.demon.co.uk if anyone
wants to port the changes. I see that JNOS has imported some of the
changes, but not the most important one of making the "NEWNEWS"
transactions use the "GMT" option.
NTP is the real answer, but I suspect it won't be that good on heavily
shared 1200 baud channels ..
73, Andrew G8FSL
--
Andrew Benham A.D.S.Benham@nortel.co.uk
Nortel Ltd, 140 Greenway, Harlow Business Park,
Harlow, Essex CM19 5QD, United Kingdom
Tel: +44 1279 402372 Fax: +44 1279 405746
------------------------------
Date: Thu, 6 Jun 1996 14:16:13 -0400
From: crompton@nadc.nadc.navy.mil (D. Crompton)
Subject: nntp date/time stamp
Andrews NNTP updates are worth using! I have used many in my code
version. I do however suggest to all of my users that they use RDATE
with me as the server, especially if they use NNTP. This is not
integrated into the code but happens periodically - say 2-3 times a day.
I use NTP on my Linux system. JNOS rdates from there. This has worked
well for us.
Doug
------------------------------
Date: Thu, 6 Jun 1996 15:53:47 +0200 (MET DST)
From: "Lionel.GRESSE" <gresse@atalante.aix.ensam.fr>
unsubscribe
------------------------------
Date: Thu, 6 Jun 1996 12:14:35 +0000 (GMT)
From: "Curtis D. Levin" <cdlevin@shadow.net>
unsub cdlevin@shadow.net tcp-group
end
_________________________________________________________________
| Curtis D. Levin | Team Os/2 | kd4zkw.ampr.org [44.98.2.22] |
| cdlevin@shadow.net ~~~~~~~~~~~~| kd4zkw@amsat.org |
| http://www.shadow.net/~cdlevin | kd4zkw@ae4ej.#MIAFL.USA.NOAM |
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
------------------------------
End of TCP-Group Digest V96 #120
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