Path: utzoo!attcan!uunet!ogicse!dali.cs.montana.edu!uakari.primate.wisc.edu!dogie.macc.wisc.edu!vms.macc.wisc.edu
From: jrosen@vms.macc.wisc.edu (Jay Rosenbloom)
Newsgroups: comp.dcom.lans
Subject: DECnet problem/protocol question
Message-ID: <4084@dogie.macc.wisc.edu>
Date: 23 Jul 90 22:54:34 GMT
Sender: news@dogie.macc.wisc.edu
Organization: University of Wisconsin Academic Computing Center
Lines: 30

I'm trying to help someone copy a file between DECnet systems using the VMS
COPY command and we are getting the message "-RMS-E-CRC, network DAP level CRC
check failed"  when RMS closes the target file .  The source machine is a
microvax I running VMS 4.5.  We have tried several target machines with no 
success.  The one target that seemed most likely to succeed (but didn't) was
also a VMS 4.5 machine on the same cable segment (in the same room) as the
source machine.   We also tried different files.  Very small files (less than a
couple hundred  blocks) worked.  I diff'ed versions of a file where all the
blocks copied but failed with the above error message and found multi-bit
differences in some records so I believe that DAPs CRC check is working (i.e.
the data really is getting corrupted).

One thing that is a little surprising to me is that DAP is detecting  the error
and not a lower layer protocol (would it be NSP?).  I think I read somewhere
that NSP was originally designed to run on top of a reliable  data link layer
(DDCMP), perhaps obviating the need in NSP to check for data errors between
nodes on the same line.  

Can anyone explain why DAP appears to be detecting the errors and not an
underlying transport layer?  It seems like the transport layer is not detecting
bad packets and doing retransmissions.  Maybe it does, but it's just not
effective.

I'd really appreciate it if a DECnet guru could shed some light on 
this!

-Jay
.............................................................................
Jay Rosenbloom / 608-262-9421 / jrosen@macc.wisc.edu / jrosen@wiscmacc      
Univ. of Wisconsin/Madison, Madison Academic Computing Center, Network Support