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Date: Fri, 12 Jan 1996 13:28:59 -0800
From: Sean Eric Fagan <sef@kithrup.com>
Message-Id: <199601122128.NAA25756@kithrup.com>
To: hackers@freebsd.org
Subject: Re: Status of ISDN drivers
Sender: owner-hackers@freebsd.org
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>My impression was that you got 56k*2 + 16k, where the 16k was for routing
>and control type information, but could be used for your data if your ISP
>was connected to the same phone switch as you.

It's considerably more complex than that (here in the Colonies, that is; I
don't know about the rest of the world).

If you are making a call to another ISDN line in the same Central Office
(CO) as yourself, then each B channel will be able to get 64k (with the
caveat that, early in the game, sometimes each B line was really just a
channel from a T1 connection, so would be limited to 56k; however, that
hasn't been the case for a long time now).

If you place a call to an ISDN line connected to another CO, then it depends
on how the phone company or companies in question are set up.  Around here,
for example, many CO's don't have the updated equipment, and so each channel
can only be 56k between CO's.  That means that each B channel is limited to
56k.

With updated equipment, then you can have a full 64k between an ISDN line in
Santa Cruz and an ISDN line in Tokyo.  But all the connections along the way
need to have the right equipment.

Each D channel is 8k.  A "normal" ISDN line has two B channels and one D
channel.

Also, don't forget that, in telephony, 'k' means "1000", not "1024."

Sean.