telecom@ucbvax.ARPA (01/31/85)
From: Jon Solomon (the Moderator) <Telecom-Request@BBNCCA>
TELECOM Digest Wed, 30 Jan 85 16:37:29 EST Volume 4 : Issue 151
Today's Topics:
T1 is wonderful
Seperate AT&T and Local billing
Re: TELECOM Digest V4 #150
What's Gerard K O'Neil doing these days?
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Date: 29 Jan 85 06:58:40 PST
From: Murray.pa@XEROX.ARPA
Subject: T1 is wonderful
To: TELECOM@BBNCCA.ARPA
Cc: Murray.pa@XEROX.ARPA
We have a T1 link to a building a block away. It costs about $1500/month
as compared to roughly $1100/month for a 56KB line. (Straight PacTel
prices.)
The error rate is so low that I can't even see it. How about 0 for 10^7
packets. Are we just lucky? Anybody got any more data?
We built our own controller because I didn't find one that would connect
to a Multibus. Anybody know of one? I don't want it to do me any favors
(like talk TCP), just send and receive raw packets like a dumb ethernet
controller.
I don't know what a DMR-11 is like, but it probably won't be trivial to
interface it to a T1 line. The first problem is that the receive side
doesn't provide the clock on another pair of wires like RS232 modems do.
You have to watch the line, and derive the clock with a PLL. Another
problem is that you have to send ones occasionally. (15 zeros in a row
max and you must have at least 3 ones in every 24 bits.) SDLC packet
format meets this if you invert the data! The last problem I know about
is that the actual interfacing to the wires is more complicated that
just plugging in the 1488/1489 chips that everybody uses to talk to
RS232 lines. I got an analog wizard down the hall to design that part: 4
chips, 2 transformers, 2 transistors and a few resistors. There must be
a better way, but it works, it fits, and I didn't have any troubles with
it. If you do decide to design something, check out the RPT-81 from
Precision Monolithics and/or look at page 305, Electronic Design,
7-Jan-82.
If you are thinking of generic T1 links, like a microwave gizmo rather
than an official T1 line from your phone company, you may have some more
options. The one by GE (GemLink) is availiable with RS422 interfacing. I
don't know any more than it's an option on their data sheet. You should
also look into closed circuit TV versions if you are willing to do the
analog interfacing work. (I don't know much about it.) Then you can pick
the data rate. That might be helpful if something like your DMR-11
really tops out at 1Mb rather than the 1.5 that a T1 expects.
T1 is clearly a wonderful thing. The bypass market is going to support a
lot of companys making whizbang microwave and fiber boxes, and they are
all going to be talking T1. Interconnecting LANs that are scattered
around a campus is going to get dragged along for the ride. The prices
and flexibility can only get better.... Support your local T1 vendor.
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Date: 29 January 85 22:20-EST
From: Michael Grant <GRANT%UMDB.Bitnet@WISCVM.ARPA>
To: Telecom Digest <TELECOM@BBNCCA.ARPA>
Subject: Seperate AT&T and Local billing
As I see it, AT&T might ask there local company to withdraw local service if
a customer stopes paying there phone rental bill. After all, that phone IS
connected to the local suplier's line. And, anyway, AT&T still has some
ties to that local company, they can probebly drop little threats like
'Well, if you don't cut Mr. Shmo's phone for us because he's stopped paying
for his phone, we're not going to renew that service contract on all that
nice switching equipment we sold you.'
On the other hand....they may just ignore you until the bill got 'big enough'
to worry about.
-Mike Grant
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Date: Wed, 30 Jan 85 08:37:13 pst
From: hplabs!sdcrdcf!darrelj@Berkeley (Darrel VanBuer)
To: telecom@Berkeley
Subject: Re: TELECOM Digest V4 #150
Cc:
You can't generally use just a plain high-speed syncronous interface to a T1
facility because of coding restrictions (e.g. every 193rd bit must be a timing
slot, and often every 8th bit must be reserved for control signaling).
I.e. you have to follow the guidelines for the 24 telephone conversations which
might be there instead, leaving you a slightly stuttery 1.344 Mbps.
Darrel J. Van Buer, PhD
System Development Corp.
2500 Colorado Ave
Santa Monica, CA 90406
(213)820-4111 x5449
...{allegra,burdvax,cbosgd,hplabs,ihnp4,orstcs,sdcsvax,ucla-cs,akgua}
!sdcrdcf!darrelj
VANBUER@USC-ECL.ARPA
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Date: Wed 30 Jan 85 16:12:21-EST
From: Ralph W. Hyre Jr. <RALPHW@MIT-XX.ARPA>
Subject: What's Gerard K O'Neil doing these days?
To: telecom@BBNCCA.ARPA
I heard he was working on some kind of worldwide communications system,
but I don't know anything else? If anyone has an address of more information
I'd appreciate hearing about it. (Gerard K. O' Neil wrote 'The High Frontier',
which advocates building space colonies.)
- Ralph Hyre
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End of TELECOM Digest
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