Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!ucsd!ucbvax!SLOTH.NCSL.NIST.GOV!glenn
From: glenn@SLOTH.NCSL.NIST.GOV (K. Robert Glenn)
Newsgroups: comp.protocols.iso
Subject: Re: Route Recording in ISO 8473
Message-ID: <9010121202.AA08027@sloth.ncsl.nist.gov>
Date: 12 Oct 90 12:02:44 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: National Institute of Standards and Technology (NIST)
Lines: 46



>Unfortunatly fragements which follow different routes and which have
>the Compelete Route Recording selected will never reach an ES.

Why?  I don't see the logic here.

>Lost fragements will also cause the PDU to never reach an ES.

The complete PDU will not reach the ES, but parts of it might causing the
ES to generate and send an ER PDU (if permitted).

>It is mandatory for IS's to be able to reaseemble.

Table 10 in the IS version states that the reassemble PDU function is an 
implementation option for ISs(Fowarding systems).

>Although it is never mentioned in the standard, IS's should foward
>all PDU fragments through the same route if Complete Route Recording or
>Security is set. Both these functions require 
>the PDU to be dropped if the PDU cannot be reassembled.
>If the users does not want to lose PDU's due to the fragements
>travelling different paths the Partial Route Recording should
>be used. 
>Complete Route Record gives the user the actual path that the PDU
>traversed. It is interesting to note that if there is not enough
>room in the head to add the Network Entity Title, conformant 
>systems MAY still attempt to reassemble the PDU and drop 
>it if it cannot be reassembled.
>However if it can reassemble the PDU, the PDU is forwarded without
>the addition of the NET.
>
>Brad Kemp
>Locus Computing Corp
>bhk@locus.com			uunet!lcc!bhk
>

Very little is mentioned in the standard about Security.  The only thing
I can find concerning the Security function discarding PDUs, is that
if an 8473 implementation receives a PDU with the Security option 
in use and the implementation does not support Security, then the
PDU is discarded.  

K. Robert Glenn
N.I.S.T.
glenn@osi3.ncsl.nist.gov