SPGDCM@CMSA.BERKELEY.EDU (09/30/87)
MSG:FROM: SPGDCM --UCBCMSA TO: NETWORK --NETWORK 09/30/87 12:38:13
To: NETWORK --NETWORK Network Address
From: Doug Mosher <SPGDCM at UCBCMSA>
MVS/Tandem Systems Manager (415)642-5823
Evans 257, Univ. of California, Berkeley, CA 94720
Subject: ISDN notes
To: telecom@xx.lcs.mit.edu
Jim Davis asked for a pointer to ISDN specs, and did not want an answer to his
example question. I am, however, commenting on that question for others who
may be interested. I have some questions myself, and would rather not have to
research the spec.
My understanding is as follows:
Once a voice connection is completed, by existing equipment or by newly
proposed ISDN equipment, one may then send "in-band" (voice-frequency) tones
across the wire, and receive them at the other end, as one pleases. For
example, one could call existing answering machines, use bank information
services, use modems in the old style, or play Yankee Doodle for that matter.
If one wants, there will be newer ways to set up calls, signal, or send data;
but these are optional, require the user to do something new, etc. The
existing processes are not obsoleted.
An example of this, of sorts, is at UC Berkeley, where we use DMS-100
equipment. This equipment does all its "dialing", and even multi-button phone
operations, using out-of-band ISDN signalling. But once a connection is made,
(a) if one creates tones externally (external beepers, sponge-cup acoustic
couplers), and act upon these tones externally (at one's answering machine or
regular modem at the other end), the tones still act as before.
(b) the DMS-100 instruments even try to "help out"; normally the numeric
keypad actuates the newer ISDN signalling. But once a connection is made, the
system reacts to keypad use by emitting the older DTMF tones on the line, to
be helpful. The actual process is to use ISDN signalling from one's phone to
the central equipment, which then issues the DTMF tones on the circuit.
(c) the PHYSICAL connection to external devices such as direct-connect modems,
is, however, limited. To use a direct-connect modem here, or an answering
machine, one must order a different type of circuit.
We also participated in an experiment, during which I had a "DOV" unit (data
over voice) at my home, and we had special equipment at the University. My
home DOV box split the line into two plugs, one of which handled packet data
at "9600 baud", and the other of which acted exactly like my regular home
phone. While using my terminal on the new circuit, I could dial, send and
receive calls, run my answering machine, and even run a second terminal
connection using my modem, at the same time.
This leaves open one ambiguity. If both the sender and receiver use
"old-style" equipment, it appears things will remain the same and will work.
If one uses a newer style circuit to call an older-style circuit, some aspects
still operate. But if one adopts a newer ISDN circuit, for example at one's
home, will this be similar to the university DMS-100 equipment, and make me
forego my answering machine and modem, or will it be like the DOV connection,
and allow both?
8 ISDN notes