sample@ubc.CSNET (Rick Sample) (10/28/87)
Can someone tell me a reasonable rate for errors on the AppleTalk? Running Peek gives three types of errors: overruns, CRC errors, and time outs. Are collisions included in these errors? Is an error rate of 5% much more than normal? Seems rather high to me. What might cause such a high rate? We have been having a lot of trouble with a flaky appletalk, and I am trying to debug it. Any advice would be appreciated. Rick Sample, Computer Science, University of British Columbia
garrett@udel.EDU (Joel Garrett) (10/28/87)
In article <9083*sample@cs.ubc.cdn> sample@ubc.CSNET (Rick Sample) writes: >Running Peek gives three types of errors: overruns, CRC errors, >and time outs. Are collisions included in these errors? Is an >error rate of 5% much more than normal? Seems rather high to me. >What might cause such a high rate? > I'm not sure if this has a lot to do with it, but I think I remember reading somewhere (maybe in the BYTE article on Appletalk on Ethernet a while back) that the Appletalk interfaces on the Mac aren't buffered very deeply (ie either one packet or none at all, not sure which) so depending on what is going on on a receiving mac, it would be very easy to overrun its buffer (or the lack thereof) and also have timeouts. CRC errors are another story, no idea about that. Also, I've never measured the error rate on a "non-flaky" network (or for that matter on a "flaky one" ;-) so I wouldn't know what a "typical" error rate in either of these situations would be, though I'd think that 5% might not be out of line, especially if it is a busy net. Joel Garrett Research Associate University of Delaware Center for Composite Materials arpa: garrett@udel-ccm.arpa
LENOIL@XX.LCS.MIT.EDU.UUCP (10/28/87)
Date: 27 Oct 87 12:14 -0800
From: Rick Sample <sample%ubc.csnet@RELAY.CS.NET>
Subject: appletalk error rates
Can someone tell me a reasonable rate for errors on the AppleTalk?
Running Peek gives three types of errors: overruns, CRC errors,
and time outs. Are collisions included in these errors? Is an
error rate of 5% much more than normal? Seems rather high to me.
What might cause such a high rate?
We have been having a lot of trouble with a flaky appletalk, and I
am trying to debug it. Any advice would be appreciated.
A reasonable CRC rate for AppleTalk Personal Network cabling would be .1% of
the total packets. CRC errors in excess of that rate usually indicate an
unterminated network, or a network with a loop or spur.
Wrong: --M--M--M
Wrong: M--M
| |
M--M
Wrong: M--M--M--M
|
M
The least likely possibility (although it does occur) is a bad cable or
connection box. The brute force way to isolate the fault is to use a
binary search: cut your network in half and see which half produces the CRC
error; divide that segment in half, etc.
Robert Lenoil
Apple Computer Inc.
Network Systems Development
-------jww@sdcsvax.UCSD.EDU (Joel West) (10/29/87)
The SCC has a 3-character on-chip buffer; after that you
get a 'hardware overrun' (as the Serial Driver refers to it.)
As a consequence, characters must be sucked out of the SCC
every 95 microseconds or less; the same applies to shoving
them in during transmit.
--
Joel West (c/o UCSD)
Palomar Software, Inc., P.O. Box 2635, Vista, CA 92083
{ucbvax,ihnp4}!sdcsvax!jww jww@sdcsvax.ucsd.edukre@monet.Berkeley.EDU.UUCP (10/30/87)
Remember that when you see "overruns" from appletalk peek, its peek itself that had the overrun (ie: the peek process wasn't quick enough reading the packet). There's no way that "peek" can possibly know whether the real recipient node had an overrun or not. Similarly crc errors might be purely errors local to the mac running peek, though this is considerably less likely. These are likely to be real transmission problems, or collisions. kre
tdomae@NRTC.NORTHROP.COM (Terry Domae) (11/02/87)
You really don't have that many "overruns" on your network. The problem here is that your MAC can't keep up with the packets being transmitted over the appletalk network. If you use a MAC-II, I would venture to say that those errors would go away (as long as you don't use multi-finder it seems to have a terrible impact on appletalk traffic). /tpd