Path: utzoo!attcan!uunet!lll-winken!lll-tis!helios.ee.lbl.gov!pasteur!ucbvax!noah.arc.CDN!kenw
From: kenw@noah.arc.CDN (Ken Wallewein)
Newsgroups: comp.protocols.appletalk
Subject: Re: How to monitor AppleTalk networks
Message-ID: <1666*kenw@noah.arc.cdn>
Date: 27 May 88 14:51:00 GMT
References: <32990@linus.UUCP>
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 27

> Although PhoneNet is supposed to work
>over longer cable lengths than Appletalk cable, we experienced
>more anomalies when PhoneNet sections were tacked on.  When we
>disconnected the PhoneNet section, performance returned to normal.

  It worked fine for us. The fact that it didn't for you is, however, 
certainly not surprising.

> We suspect echos and standing waves are the culprit, caused by
>impedance mismatches, but we don't have hard evidence.  The
>phenomenon would be similar to TV ghosts caused by poor antenna
>cabling.  It would be nice to have a CRT display which would reveal
>echoes and standing waves so that cabling irregularities could be
>more easily diagnosed and corrected.  Right now it's a black art.

  Amen, brother! 

  What would be nice would be a TDR (Time Domain Reflectometer) like that used
on coax-based Ethernet (but less expensive, of course :-), or that new doodad 
that's used for tuning twisted-pair Ethernet. 

  There have been a couple of messages about strategic placement of 
terminating resistors, etc. However, nobody's really said how to decide WHERE 
to put them.

  There's a market here somewhere...

/kenw