-=> Quoting Bo Simonsen to Roy J. Tellason <=-

 BS> Hello Roy!

 BS> May 05 20:00 03, Roy J. Tellason wrote to Bo Simonsen:
 
 BS>> The most normal is 30B+D, here in Denmark. Or 2B+D (normal ISDN). 
 
 BS>> But actually can one D channel handle so mutch? As far as i know
 BS>> isn't it more than 9600 bps.
 
 RJT> I could be mistaken,  but I seem to recall it being something like 
 RJT> 16Kbps in bandwidth...

 BS> You're right.. We can calculate it with that method.

 BS> In the US is a B channel 56 kps... because the D channel is shared, so

Nope. The B channels are 64k *if you are running data over them*.

For voice traffic *some* trunks use "robbed bit" signalling, which
means that Voice is actually running at 56k. Same data rate, just *7*
bits guaranteed available. 
 
Since a lot of phone companies charged more for data (often with
charges per "block" of data added on top) folks would just send the
data using tricks in the ISDN gear to encode the data at 7 bits for
transmission and reasemble it at the far end.

Either way, you are sending 8k *bytes* per second, but at 56k you only
get to use the 7 most significant bits of each byte.

The actual "bit robbing" only uses 1 bit out of every 8 bytes. So the
effect on digital voice is essentially invisible. But since you can be
sure how many channels your link goes over, and they aren't likely to
be synchronized as to which byte they steal the bit from, you have to
assume that the LSB of *all* bytes is bad.


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