old modems & a packet switcher

From: William Donzelli <william_at_ans.net>
Date: Mon Aug 3 12:10:08 1998

> With many of these devices, it takes (at least) two to tango, and of
> course you never find both together. (What is the sound of one statmux
> clapping?)

Well, after finding one, you will have a new goal of finding another one!
 
> Synchronous modems often didn't just carry the data from one end to
> the other, they also provided clock signals to the DTEs. Many DTEs
> expect to see those clock signals and won't originate them, so getting
> two nearby ones to talk over direct cabling can be an interesting
> proposition.

Lots of the stuff I have seen allows a user to insert an external clock -
this can be handy for testing in the real world. Providing the clock is no
big deal. Sure, it would be nice to get a dead-on clock for a T1, but as
long as you keep the circuit private, the clock can be fairly sloppy.
 
> Can you do this over dry copper, for short runs?

Yes, some people on this list get connected this way (T1s that run a whole
20 feet, CSU to CSU, with no frame in between). A horrible kludge in a
production environment, in my opinion, but it worked for quite a few
years. Recently someone at ANS suggested that we use a T3 the same way,
but he ended up being tarred and feathered.
 
> If so, would you want to? You mentioned in another post that you'd
> have to run conduit for FDDI, and that makes me think there might be
> some open space between hither and yon. Sure, you could run copper,
> but wouldn't electrical potential differences be a problem?

Differences as in losses due to the long run? That is what the Line Build
Out option is for (on most CSUs). T1s, with thier twisted pair,
differential design, tend to be pretty tough.
 
William Donzelli
william_at_ans.net
Received on Mon Aug 03 1998 - 12:10:08 BST