At 10:58 PM 7/26/00, Mooney Drew-DMOONEY1 wrote:
>Wouldn't robbed bit signalling be
>implemented ONLY in customer-premise equipment?
If you have a T1 tie line between your PBXs for example, the circuit really
goes the Central Office for the phone company, of course. Doesn't their
equipment have to know about the robbed-bit signalling in order to handle
on-hook, off-hook, etc.? Just wondering. I'm a data person, not voice,
(except voice over data over voice, i.e. VoIP and VoFR using data T1 lines
that were originally designed for digital voice! ;-)
>On the subject of ESF - I think you guys might be
>confusing signalling with synchronization.
No, we're not confusing the two. We were quite clear that signalling
happens in the robbed bits. Synchronization happens in the framing bit,
which is the 193rd bit, outside the DS0s, as you say.
>I've never actually "ordered" a T1, but I have
>commissioned bunches of them, and configured
>them in switches [telephony, not IP!] and wireless
>network controllers - and in every instance, an
>AMI span has only had 56k available bandwidth, while
>any B8ZS span has 64k available - so - question to
>the transmission guru's [which I am not] would
>implementing robbed bit signalling on an AMI circuit
>reduce it's available bandwidth to 48k and on a
>B8ZS reduce the 64k to 56k?
Well, I wondered about that too. And it turns out that because AMI does not
handle consecutive 0s properly, a technique still in use in Digital Data
Services is to make every bit 8 a 1 and to use only the lower 7 bits. This
7/8 mode yields 56Kbps instead of the standard DS0 rate of 64 Kbps. This
technique also disallows the use of signalling bits.
B8ZS is an improvement to this situation. The gory details were in the
previous messages.
Also, someone sent around a terrific URL for T1 information, but it may
have been missed since it appeared in a discussion about BGP for some
unknown reason. The URL is here:
http://www.dcbnet.com/notes/9611t1.html
Are we having fun now!? ;-)
Priscilla
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Priscilla Oppenheimer
http://www.priscilla.com
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