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From: motcid!benyukhi@uunet.uu.net (Ed Benyukhis)
Newsgroups: comp.dcom.telecom
Subject: Re: Data Lines vs. Voice Lines
Message-ID: <12623@accuvax.nwu.edu>
Date: 25 Sep 90 17:39:20 GMT
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X-Telecom-Digest: Volume 10, Issue 680, Message 7 of 10


In article <12545@accuvax.nwu.edu>, motcid!crocker@uunet.uu.net
(Ronald T. Crocker) writes:

>  From my experience (former Bell Labs), the type of multiplexing that
> you describe above (item 3) is not typical of any switches (digital or
> analog) that I am familiar with.  Most telephony connections are
> "circuit-switched", i.e. equivalent to hooking a pair of wires between
> the two parties.  The only "packet-switched" connections that I know
> of are those for ISDN packet data (B or D channel), and these are
> handled as "special cases," at least in the 5E.  
	      ^^^^^^^^^^^^^ 
I agree that most connections are circuit-switched and that most calls
are POTS type calls. But what is so special about B/D channel packet
switching???

> Voice is not packet data.  It is not treated in a packet manner.
  ^^^^^^^^^^^^^^^^^^^^^^^^
It could be.  VSCS (FAA) at Bell Labs is implementing just that i.e.
Packatizing voice for air traffic controllers communications.  Voice
packatezation perhaps warrants some discussion/explanation by someone
more familiar with the process.  How about it Pat????

> Whatever happens to be on the voice channel is digitized (PCM),
> transmitted across digital carrier facilities (T1) to another switch,
> decoded to the equivalent analog signal, and played out of the
> receiver in the handset.  No where in this loop is anything trying to
> figure out if the digitized voice signal represents "quiet".  T1 is
> simply a multiplexed digital version of 24 analog trunks.  Voice-grade
						             ^^^^^^^^^^^
> lines are 64Kbps, T1 channels are [nominally] 64Kbps.  Maybe if there
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 
When you say Voice Grade Lines, are you referring to th subscriber
loops??  And if you are, than, how about BRI connection piping 144Kbps
over a wire pair.  And even this can be increased by playing tricks
with the loading coils.  Also, depending on the Super Frame format,
you might not even get a 64Kbps clear channel on the T1 either.

In general, these are long and, at times, complex subject matters.


Regards,

Ed Benyukhis, Motorola, CID.
(708)632-4658