-=> Quoting Bo Simonsen to Leonard Erickson <=-

 BS>> But actually can one D channel handle so mutch? As far as i know 
 BS>> isn't it more than 9600 bps. I can see it's enought to handle 
 BS>> signaling, caller-id transfering, etc. But to 30B channels? 
 
 LE> Remember, the D channel is only needed for call setup and tear-down.

 BS> Yep
 
 LE> *During* a call, there's no signalling for that B channel. Well, maybe
 LE> if you've got Call Waiting, or the version that incorporates Caller ID
 LE> for the second incoming call. 

 BS> That's right. But i think of if they were used for normal telephone
 BS> traffic, it sounds of a quite low speed. 

Not really. The aren't carrying any of the *voice* traffic. They are
simply a *control* channel. For "normal" phone system use, the phone
switches on each end use the D channel to tell each other when
something changes. 

That's a few bytes to set up a call and a few bytes to break down a
call. And *nothing* during a call. 

 LE> In some places in the US, in the early days of ISDN you could send 
 LE> data
 LE> over the D channel from your ISDN gear. Data *other* than the call
 LE> setup etc. 

 BS> I heard about it.. Was it cheeper than using the B channels, or was
 BS> there any other advantages of it? 

It was another data channel. I recall an early ISDN presentation to a
local PC users group. They were going to have email sent via the D
channel, with a "message light" on the ISDN box to let you know you had
email waiting.


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