From: tjr@cbnewsc.cb.att.com (thomas.j.roberts)
Newsgroups: comp.dcom.isdn
Subject: Re: DTMF interaction on ISDN
Date: 16 Oct 92 16:07:34 GMT
Article-I.D.: cbnewsc.1992Oct16.160734.6215
Organization: AT&T

From article <1992Oct14.082857.4571@ericsson.se>, by etxorst@eos.ericsson.se (Torsten Lif):
> [...]
> No, the way I see it, DTMF is needed only when an ISDN set calls
> outside of the digital world and that's a whole new can o'worms.

Well, here in the U.S., DTMF is also used when communicating with
voice-mail systems, which may well be all-digital. To me it seems
to be the SAME "can o' worms" we've always had....
 
> [Discussion of switching between DTMF mode and "normal (Q.931) mode"]
>
> You want the function to switch between D-channel dialling and DTMF
> signalling to be intuitive and easy to do but at the same time so
> foolproof that there's no way for the user to get stuck where he can't
> answer a "call waiting" because he's in DTMF. Congratulations, whoever
> got stuck with designing this function into a phone. You just won the
> booby prize, fella'.

It never happens to me, simply because the station set can easily
tell which mode to use: while dialing, the keypad dials Q.931 on
the D-channel; after dialing is complete (CALL PROCEEDING message),
the keypad dials DTMF on the active B-channel. There is NEVER a problem
or ambiguity - "Call Waiting" and such things are handled by special
buttons - NOT by the keypad (by keypad I mean the buttons 0-9*# ONLY).
This is very similar to old analog phones - "Call Waiting" and such
need a HOOK-FLASH before dialing, so the switch can know to listen
to the DTMF. All of the special buttons always "dial" using appropriate
Q.931 messages:
	If I hit a "Speed call" button after a connection
	is established, NOTHING HAPPENS (other than its green light 
	blinks, indicating an error).
	If I hit a "Call Appearance" button after a connection
	is established, the current call is put on hold, and
	I get dial-tone to make another call (which I can conference
	to the first call if I wish). The set knows to use Q.931
	when dialing this second call.
	Etc.
 
> Then, when you're done, you can start thinking about how to implement a
> similar functionality using user-user-info when the call actually is
> end-to-end ISDN. How do you switch the keypad between "dialling" mode
> and "u-u-info" mode? Do you send digits one by one (could be expensive
> if billing is "per package") or in batches (how do you terminate a
> batch)? If the other party provides responses by u-u-info, how do you
> present them? Does your phone have a display? Can it handle non-numeric
> info? How many characters? How many lines? What do you do when the CO
> sends a "display" element and the other party sends a u-u-info at the
> same time?

This is why user-to-user signaling is rarely used, especially by
"normal" ISDN station sets (aka telephones). Since users will continue
to want to communicate with old equipment, user-to-user signaling
is not universal -- in practice the considerations you raise will
probably prevent it from being useful except in special situations
(which I expect to be mostly computer-to-computer (where computer
can be any "smart" equipment)). I know of no "normal" ISDN telephones
which use user-to-user signaling at all (but I haven't looked).

> Sorry if I sound negative, but this is about the point where I got
> disillusioned by ISDN. The ISDN "LEGO" blocks are great for building
> the foundation of your house, but when you reach the upper floors you
> find that some shape blocks are missing and others don't quite fit
> together. It's going to be a long time and lots of trial-and-horror
> before all equipment actually works together in the way it was intended
> to.

Well, I have had a quite positive experience with ISDN. I have YET
to find a situation where my ISDN phone could not do what I wanted
(within reasonable expectations). All of the equipment I use works
together as it was intended.
NONE of the problems you discuss about switching dialing modes has 
EVER happened to me.  In fact, the ISDN phones around here are a BIG
hit compared to our previous analog system.
Most-used features:
	1) Distinctive ringing, so each person can identify his/her
	   own phone when some phone down the hall is ringing.
	2) AUDIX (voice mail). This GREATLY reduces "telephone tag".
	   It is much better than individual answering machines, and
	   more flexible, and cheaper.
	3) Simple conferencing - 3-way and 6-way conferences are
	   easy and straightforward to set up, with no obscure
	   */# dialing codes to remember or look up. Simply use
	   the "Conference" button.
	4) Speed calling - I have 24 individual buttons with their
	   own labels, no obscure dialing codes to remember.
	5) X.25 over the D channel to connect a user's terminal
	   or PC to the outside world (and we use such networking
	   VERY heavily).
(And I didn't even mention Caller-ID, which is nice, but not really
necessary). Not all of these features may be available everywhere
ISDN exists.

	I have had an AT&T 7507 ISDN phone for about 2 years now,
	served by an AT&T 5ESS(Rg) Switch in Naperville, IL USA.
	Our entire campus (~7000 people, 7 buildings) has had ISDN
	service from Illinois Bell (the local telephone company)
	for about 2 years. This message was created on a UNIX(Tm)
	machine (which happens to be 300 miles away) using my PC
	as a terminal emulator talking to the UNIX system via
	D-channel X.25.

Tom Roberts	att!ihlpl!tjrob		TJROB@IHLPL.ATT.COM
AT&T Bell Laboratories