Path: utzoo!utgpu!water!watmath!clyde!cbosgd!ihnp4!ihlpf!dunn
From: dunn@ihlpf.ATT.COM
Newsgroups: sci.electronics
Subject: Re: Re: Home Automation Interest?
Message-ID: <3417@ihlpf.ATT.COM>
Date: 18 Jan 88 22:26:35 GMT
Sender: dunn@ihlpf.ATT.COM
Lines: 62

Gary Wells writes:
>
>I've never even heard of the DDB, but I do know a little about ISDN.  It is
>obvious from the above comment that Mr. Hauser knows nothing about ISDN
>(no offense, most people don't yet).  
>

Its amazing how people who are not fully informed will make comments about how
much others know (i.e. - a _little_ knowledge is a dangerous thing). Now, off
the soapbox.

ISDN will be (is) a totally digital telephone system, which means that your
phone will actually be a A/D converter and a D/A converter. All the signals
leaving and arriving at your phone will be digital. Here in the U.S. ISDN lines
will have 2 B channels ("bearer" channels, capable of 64K bits/sec, enough for
good voice quality, not to mention great data transmission) and 1 D channel
("data", 9.6K bits/sec, which will be used for control information and
generally slower data transmissions).  What you have to realize is that these
three channels will all be transmitted over the same two copper wires that you
now have in your home. In other words, the whole shebang is a packet switched
network, with some of the packets (the "B" channels) getting more priority
(airtime) than the othere channel (the "D" channel).

Since we have all these packets floating around, the CPE (customer premise
equipment) must be smart enough to identify when a packet is destined for it so
that it can grab the information and decode it (for a telephone this means grab
the digital information and turn it into analog for us to hear). CPE should
ignore any packets that are not for them. As far as I remember, there are 256
possible addresses per ISDN (2B+D) line. At least three of these addresses are
used for telephone communications ( one per B channel, so you can have two
phone conversations to different people with two different phones on the same
two copper wires, and one for the D channel phone control information), but 
this leaves ~200 addresses that are unused.

*********> POINT OF THE WHOLE POSTING <*********

Maybe some smart company will come up with control modules which plug into the
telephone wires going through your home. Each module would check the D channel
for data packets with its address on it. These packets could be sent from
inside the house, or from the next state. Each packet would contain control
information for the modules. The modules would ignore packets that do not
contain their address in the header. This way you could control up to ~200
devices in your home. Even better, future home appliances might have ISDN
interfaces built right in. To borrow a sentance from a instructor I had " you
could plug in your ISDN toaster right next to your ISDN coffee maker and
control them all from your ISDN alarm clock radio".

When ISDN becomes widely available (don't hold your breath, the hardware is
expensive for phone companies and individuals to buy, and at first only
corporate America will be able to purchase) then you will see all these
gadgets ( along with _real_ picture phones). Hope this clears some stuff up.

				Bill Dunn
				here on my last day at Bell Labs...
				(going to AT&T IS )

Disclaimer: I'm sure my employer does not endorse any ramblings I might have,
		even though they might agree.


			Bill Dunn
			ihnp4!ihlpf!dunn