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Re: UCL Telex number - "40" or "54" in NSAP

Steve Hardcastle-Kille <S.Kille@cs.ucl.ac.uk> Thu, 05 March 1992 19:10 UTC

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To: Christian Huitema <Christian.Huitema@sophia.inria.fr>
cc: osi-ds@cs.ucl.ac.uk
Subject: Re: UCL Telex number - "40" or "54" in NSAP
Phone: +44-71-380-7294
In-reply-to: Your message of Mon, 17 Feb 92 11:24:34 +0000. <199202171024.AA11066@mitsou.inria.fr>
Date: Thu, 05 Mar 1992 10:47:39 +0000
Message-ID: <1144.699792459@UK.AC.UCL.CS>
From: Steve Hardcastle-Kille <S.Kille@cs.ucl.ac.uk>


 >From:  Christian Huitema <Christian.Huitema@fr.inria.sophia>
 >To:    osi-ds@uk.ac.ucl.cs
 >Subject: UCL Telex number - "40" or "54" in NSAP
 >Date:  Mon, 17 Feb 92 11:24:34 +0000

 >Pointing my nose out of the short names rat-hole, I just picked an ennoying
 >defect in the "interim NSAP encoding format" specified by Steve in RFC-1277.
 >
 >It contains tables explaining the various formats, e.g.
 >______________________________________
 >|Part___|_______IDP__________|________
 >|Comp___|__AFI__|___IDI______|Prefix_| ...
 >|Octet__|_______|____________|_1-2___|_...
 >|Value__|_Telex_|007_28722___|__02___|_...
 >|Ct_Dec_|__54___|007_28722___|__02___|_...
 >|Ct_Bin_|__54___|00_72_87_22_|__02___|_...
 >
 >In this, the Telex number of UCL is described as telex country code 7 (UK
 >or GB) + value 728722, padded with two non significant leading zeros. The
 >first two digits of the NSAP, the AFI, have the value 54, which described a
 >Telex based NSAP, with a decimal DSP.
 >
 >In order to align our environment with the RFC, we have programmed here a
 >syntax parser for RFC-1278. The problem is that, if we enter an NSAP as 
 >
 >	TELEX+ 728722
 >
 >what we obtain is NOT "54000728722", but rather "40000728722", i.e. using
 >the AFI "40" instead of "54". This is consistent with ISO-8348 add 2, which
 >specifies in paragraph 8.2.1.2:
 >
 >	....Two AFI values are associated with each combination that
 >	involves a variable length encoding..... The numerically lower 
 >	AFI value is used when the first significant digit in the IDI
 >	is nonzero. The numerically greater AFI value is used when the 
 >	first significant digit in the IDI is zero.
 >
 >The two values assigned for Telex IDI + digital DSP in ISO-8348 add 2 are
 >"40" and "54". All occurences of AFI=54 in RFC-1277 are erroneous. They
 >should be replaced by AFI=40.
 >
 >Christian Huitema

The telex number is 00728722 and not 728722 - thus it is a telex
address with leading zeros.   The AFI is therefore correct, and the
document is self consistent.


Steve

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