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From: tozz@hpindda.HP.COM (Bob Tausworthe)
Newsgroups: comp.protocols.iso
Subject: Re: X.224 (Transport) state table question
Message-ID: <5560075@hpindda.HP.COM>
Date: 8 Aug 90 00:26:58 GMT
References: <1990Aug6.111420.13755@idt.unit.no>
Organization: HP Information Networks, Cupertino, CA
Lines: 47

> / hpindda:comp.protocols.iso / harald.alvestrand@elab-runit.sintef.no / 12:32 am  Aug  7, 1990 /
> In article <1990Aug6.235903.23530@mel.dit.csiro.au>, 
> ajw@mel.dit.csiro.au (Andrew Waugh) writes:
> 
> > Class 0 Transport only uses the implicit variant of normal release
> > (see 6.7.1).
> 
> Sorry, but no. This bit me too, once.
> DRs ARE used in class zero, but ONLY to refuse incoming CRs.
> This is done so you can pass the disconnect code, I think.
> The procedure in ISO 8073-1986 (I think this has the same numbering as
> X.224) is
> in chapter 6.6 (connection refusal), not 6.7 (normal release).
> 
> So my question, rephrased, is:
> After completing the refusal procedure in 6.6.3, when, if ever, should
> the responder
> disconnect the network connection?
> 
>                       Harald Tveit Alvestrand
>                       ISO hacker
> ----------

When I read the spec, the statement which kept going around in my head was:
  In TP0, the lifetime of the transport connection is directly correlated
  with the lifetime of the network connection.
  
I see two possibilities:

  1) Send DR then disconnect the network connection. This has one
     small problem that depending on the X.25 implementation, the
     NDISind could be received by the other side before the DR
     (or the DR would never be received). If this isn't a problem on
     your implementation, then go for it.

  2) Send the DR and go into CLOSED. When the other side receives the DR
     it will disconnect the network connection. So just add the following
     to your state table: If present state is CLOSED and you receive a
     NDISind, clean up network connection datastructures, and goto state
     CLOSED. Something like this is well within the conventions stated in
     A.1.3 (what to do if a state intersection is blank [like NDISind/CLOSED])

I like (2) better than (1). 

			      bob tausworthe
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These are my own opinions, unfortunately, not my employers.