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From: ijk@violin.att.com (Ihor J Kinal)
Newsgroups: comp.dcom.telecom
Subject: Re: Splitting Call Transmission Directions
Message-ID: <12315@accuvax.nwu.edu>
Date: 18 Sep 90 14:06:57 GMT
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X-Telecom-Digest: Volume 10, Issue 654, Message 3 of 7


Larry Lippman wrote:

> Also, I can think of no valid reason to split E-W and W-E
> routing between different transmission facilities.  *ALL* transmission
> facilities used for intertoll circuits are, by their very nature,
> bi-directional.  While I have seen all sorts of route diversity and
> failure protection switching, I have never seen anything that split
> transmission directions through different facilities.

The way I remember this, the reason that a split was put into effect
was excessive delay on satellite calls.  Remember that the satellites
are at approx 22,000 miles up.  Double that, and it means that we need
approx a quarter of a second to traverse in ONE direction. [Speed of
light = 186,000 m.p.s.].

If both sides went over satellite, that would mean a half-second of
extra delay from when one person stopped talking, until the next
person could possibly reply.  This much delay would then then cause
the original person to start talking again, to see if the distant
party was still there, leading to great confusion.


Ihor Kinal
att!cbnewsh!ijk

[Include standard disclaimers and although I work at Bell Labs, I
never did any work satellite communications - I'm just a software
person anyway.]