jf@concurrent.co.uk (Jim Fraser) (11/20/90)
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.