Re: [AVT] CAS signalling events: draft-ietf-avt-rfc2833biscas-00.txt

[Tom Taylor <taylor at nortel.com>]

Oren Peleg wrote:
> I have a problem with the ABCD state definition. The ABCD bits should
> have a respective bit in the state regardless to the trunk framing
> method. E.g. when on A & B are used & A=0 & B=1, the state may be 0x0100
> up to 0x0111. The important issue here is that the bit in the state for
> A, B, C & D is constant no matter what is the framing method. This way
> if the framing method is different between sender & receiver, the biscas
> still support it. Also may be recommended to duplicate the AB value to
> the CD bits when only A & B are used. This will help some different
> framing methods to be synced.
>
> Regards,
>
> Oren P.

I just thought I would summarize the consequences of this change as I extend the 
logic throughout the document.  It probably improves consistency.

Basic mapping of single bit and two bit states to event codes:

A = 1 mapped to b1111, event code 159
A = 0 mapped to b0000, event code 144
AB = 11 mapped to b1111, event code 159
AB = 10 mapped to b1010, event code 154
AB = 01 mapped to b0101, event code 149
AB = 00 mapped to b0000, event code 144

Signalling System No. 5 line signals:
====================================

Both 2400 Hz and 2600 Hz present (clear-forward and release guard):
    still b0000 = event code 144 (no change)

Only 2400 Hz present (seizing, forward acknowledgement, answer):
    b0101 = event code 149 (change from 145)

Only 2600 Hz present (proceed-to-send, busy flash, clear-back, and forward transfer):
    b1010 = event code 154 (change from 146)

Neither tone present (pause between signals, stable state):
    b1111 = event code 159 (change from 147)

Signalling System R1 line signals:
=================================

2600 Hz present (on-hook):
    still b0000 = event code 144 (no change)

2600 Hz absent (off-hook):
    b1111 = event code 159 (change from 145)

Signalling System R2 analogue line signals:
==========================================

3825 Hz tone present (on-hook):
    still b0000 = event code 144 (no change)

3825 Hz tone absent (off-hook):
    b1111 = event code 159 (change from 145)

Signalling System R2 digital line signals:
=========================================

Note that the A bit from each end indicates the hook state, while the B bit 
indicates failure conditions (forward) and assignment of switching equipment 
(backward).

On-hook and idle (either end):
    b1010 = event code 154 (change from 146)

Calling end off-hook:
    b0000 = event code 144 (no change)

Called end line on-hook, switching equipment engaged (seizure ack / clear-back / 
blocked):
    b1111 = event code 159 (change from 147)

Called end line off-hook, switching equipment engaged (answered):
    b0101 = event code 149 (change from 145)

The inconsistency between interpretation of the A bit (1 = line idle) and the B 
bit (0 = switch idle) causes these codes to differ from those for similar states 
using analogue signalling.

Tom Taylor

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