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Article View: comp.protocols.iso
Article #859

NSAP Encoding in X.25/PLP-1984

#859
From: Jim Fraser
Date: Tue, 20 Nov 1990 14:50
29 lines
1950 bytes
I have noticed an inconsistency between ISO and CCITT documents
regarding encoding of NSAP addresses when X.25/PLP-1984 is used
to provide the ISO CONS.

In ISO/IS 8878 "Use of X.25 to provide the OSI connection-mode
network service" (1st ed.), section 6.2.2, it is specified that
NSAP addresses carried in the address field (AF) and address
extension field (AEF) of X.25 packets are in the preferred binary
encoding defined in ISO 8348/Add. 2 "Network Layer Addressing".
Thus, the AEF may contain hexadecimal digits.

However, in CCITT rec. X.25(1984), annex G, sections G3.1 and
G3.2, it is specified that the AEF is encoded in binary coded
decimal. Also, in the DIS version of ISO 8208, section 15.3.2,
it is also specified that the AEF is encoded in BCD.

Does the IS version of ISO 8208 allow binary encoding of the
AEF?

I realise that there is a further inconsistency in the maximum
length of NSAPS (CCITT 1984 = 32 digits, ISO = 40 digits), and
that both of these are resolved in the 1988 version of X.25.
However, I am concerned about the situation with X.25 1984.
Is there any widely accepted resolution of these inconsistencies?
How have other implementors resolved this?

                                   Jim Fraser,
                                   Concurrent Computer Corporation,
                                   Slough, U.K.
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From: jf@concurrent.co.uk (Jim Fraser)
Newsgroups: comp.protocols.iso
Subject: NSAP Encoding in X.25/PLP-1984
Keywords: CONS, NSAPs, X.25
Message-ID: <1008@sl10c.concurrent.co.uk>
Date: 20 Nov 90 14:50:01 GMT
Sender: info@concurrent.co.uk
Reply-To: jf@concurrent.co.uk (Jim Fraser)
Organization: Concurrent Computer Corp (ESDG), Slough, U.K.
Lines: 29