Path: utzoo!utgpu!watmath!clyde!att!rutgers!mailrus!purdue!decwrl!vixie
From: vixie@decwrl.dec.com (Paul Vixie)
Newsgroups: comp.dcom.lans
Subject: Re: Need configuration info for various DEC ethernet widgets
Message-ID: <108@gnome6.pa.dec.com>
Date: 20 Nov 88 08:13:31 GMT
References: <3607@phri.UUCP>
Organization: DEC Western Research Lab
Lines: 41

Since I'm now surrounded by DEC Ethernet widgetry, I can answer most of this.

# 	The question is, just what *is* a DESPR?  The Dec-Direct catalog I
# have says little of value about the various widgets they make other than to
# say that the DESPR is a repeater.

It is.  Just look at how big it is compared to a DESTA and you can tell that
something serious is going on in there.  It's not a bridge, though -- it
doesn't filter packets, it just sends them along.

# If he shorts out his thin cable, will that do anything bad to my net?

Nope.  And you don't need to worry about him terminating his thin segment,
either.  Everyone else on that thin segment should worry -- I suggest you
use DEMPRs if they will fit into the logic; DESPR's are useful only inside
a single office where there are fewer people to yell at you when you screw
something up.

# Do I have to count the effective length of his thin segments and the number
# of taps he has against the maximum limits of my cable?

Sortof.  It doesn't affect the number of taps but it does the number of
stations.  That is, a tap with nobody on it doesn't count (here, anyway).
As for length, yes, you need to keep it in mind since the propagation
delay from furthest station to furthest station is going up.  I'm not
sure if the DESPR does CS/MA, if that's what you're asking.  It seems like
it would have to, and if it does, one of the reasons for keeping the cable
short goes away: collision detection domains won't extend past the DESPR.
You still have to worry about propagation delay if your protocol cares.
(IP/TCP doesn't care, but parts of DECNET do.)

# What about the rule that says you can't have more than two repeaters
# between any pair of taps on the network?
# Does his DESPR count as a repeater in this sense?
# What about DELNI and TCL multiport xceiver boxes, do they count as repeaters?

Good questions, but you've exhausted my knowledge.  Anybody else know?
-- 
Paul Vixie
Work:    vixie@decwrl.dec.com    decwrl!vixie    +1 415 853 6600
Play:    paul@vixie.sf.ca.us     vixie!paul      +1 415 864 7013