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From: jdr@sloth.mlb.semi.harris.com (Jim Ray)
Newsgroups: comp.protocols.tcp-ip
Subject: Fiber link problems
Keywords: ODS, CISCO, FIBER
Message-ID: <1990Dec19.044936.4204@mlb.semi.harris.com>
Date: 19 Dec 90 04:49:36 GMT
Sender: news@mlb.semi.harris.com
Organization: Harris Semiconductor, Melbourne FL
Lines: 59
Nntp-Posting-Host: sloth.mlb.semi.harris.com

We are currently experiencing problems with a few fiber links between 
buidlings.

The links in question are connected via ODS 291 twisted pair box on
one net in one building to another ODS 291 twisted pair box ( using
a host port twisted pair connection ) which then connects to the remote 
buidling via the fiber network port.  The fiber then connects to the
remote building to a fiber tranceiver ( ODS 234 ) which then goes into
a TCL tranceiver and then to the remote lan.

     ---------------------    net a
         | <-- tcl tranceiver
         |
         |_|-----|
           |     |  ODS 291
           |     |           Acts as a full repeater
         --|     |
        |  -------
        | <------------twisted pair connecting host ports  ( 10 base t )
        |              
        ---|-----|
           |     |
           |     |  ODS 291   Acts as a full repeater
           -------
             |
             | <------------ fiber
            ...
             |
             |
            ---
            |  |  ODS 234 fiber tranceiver
            ----
             |
             |<---  tcl tranceiver
           --------------------   remote lan a

Symptoms:

    1) ping's with normal size packets work fine with about 1% loss
    2) ping's with 500 byte packets have 10 % loss
    3) ping's with 800 byte packets have 20 % loss
    4) ping's with 1500 byte packets have 38 % loss

    5) NFS of course does not like this at all -- since it opts for
       large packet sizes.
    6) Cisco routers connected to either side of lan a go into
       hibernation mode for from 20-40 seconds or so every 5-10 minutes,
       and occationally get interface resets ( keepalive time is 10
       seconds -- so 3 at 10 seconds == 30 ).
    7) Sniffer on either side see nothing out of the ordinary.
    8) hosts pinging and being ping'd don't see high error rate ( in
       netstat ).

This sounds like some type of retiming problem to me.  Anyone have any
ideas?
--
Jim Ray                                Harris Semiconductor
Internet:  jdr@semi.harris.com         PO Box 883   MS 62B-022
Phone:     (407) 729-5059              Melbourne, FL  32901