Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!rutgers!ucsd!ucbvax!hsi.UUCP!stevens
From: stevens@hsi.UUCP (Richard Stevens)
Newsgroups: comp.protocols.ibm
Subject: SNA reliability above DLC
Message-ID: <8809220906.AA11914@jade.berkeley.edu>
Date: 21 Sep 88 20:01:16 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Reply-To: Richard Stevens 
Organization: The Internet
Lines: 16

After going through a many SNA manuals, including the friendly FAPLs,
I've come to realize that SNA provides no reliability in terms
of a checksum at any level above the data link.  Obviously you'll
have the data link reliability (16-bit CRC for SDLC, 32-bit FCS
for the token ring, etc.), but unlike TCP, UDP or Xerox's IDP,
there is no "checksum".  Am I missing something ??

I'll assume the designers of SNA assumed that a DLC check was
adequate.  Do TCP or UDP really need a checksum, especially when
running over an Ethernet, say ?  I see that ISO only specifies the
use of a checksum for TP-4.

        Richard Stevens
        Health Systems International, New Haven, CT
           stevens@hsi.uu.net
           ... { uunet | yale } ! hsi ! stevens