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Path: utzoo!watmath!deepthot!julian
From: julian@deepthot.UUCP (Julian Davies)
Newsgroups: net.dcom
Subject: Re: X.25 - changing parameters on a remote PAD - X.29? How?
Message-ID: <213@deepthot.UUCP>
Date: Fri, 9-Mar-84 12:24:51 EST
Article-I.D.: deepthot.213
Posted: Fri Mar  9 12:24:51 1984
Date-Received: Sat, 10-Mar-84 14:23:04 EST
References: <3473@utcsrgv.UUCP>
Organization: UWO CS, London Canada
Lines: 26

Yes, the remote PAD can be changed with X.29 procedures.  This is
impossible unless you are handling the full X.25 service (Datapac-3000
in Canada).  You have to be able to send and receive data packets with
the Q (Qualifier) bit set.
  In theory, one PAD can read and control another, when both ends of
the VC are on PADs, but there is no protocol defined for a user of
an asynchronous terminal to read or set PAD parameters at the *far*
end, only for one's own local PAD  (X.28).

  X.29 defines uses of the call user information at VC setup, and also
the user data packets with Q bit set.  The latter packets have the
data field in the following format  (Fig. 2/X.29 (1980))

Octet 1		0 0 0 0 | msg code
      2		parameter reference
      3		parameter value
      4		parameter reference	-- if more than one
		....

Message code:	0010 - Set
		0100 - Read
		0110 - Set and read
		0000 - parameter indication

In PAD read messages, the 'value' fields are set zero -- the
indication packet will come back with values filled in.