[Asterisk-Users] Channel bank timing

[Andrew Kohlsmith]

On Sunday 25 December 2005 18:39, Chris Mason (Lists) wrote:
> Can anyone help me understand channel bank timing? I have a server with
> a Sangoma A104 T1 card connected to two channel banks and I am having
> audio problems that is clearly timing errors. I thought I understood how
> to configure it but clearly I don't.
> All my incoming lines are PSTN, I do not have access to PRI. All my
> extension phones are SIP. My asterisk version is 1.2.1.

Tell the Channel Banks clock to the line, and have the Sangoma card NOT sync 
to anything (i.e. the A104 is the master, the channel banks the slaves).

Basically clocking works this way:  Each end of a T1 sends data generated by 
an on-board clock.  These two clocks (one at each side) needs to be in 
perfect sync with each other or you get frame slips and other nasties.  The 
solution is to have one of these clocks lock or synchronize to the far side.  
This is know by several names, among them "line clock", "recovered clock", 
"slave clock", etc.  The side that is not trying to synchronize is also known 
my several names... "master clock", "internal clock", etc.

So it comes down to this:  One side must synchronize its clock to the other 
side (which does NOT do this) or you will have frame slips.  The Digium 
multi-span T1/E1 cards can only slave to one clock for the whole card, 
whereas the Sangoma cards are a little different and can have each span slave 
to its own clock.

For your particular application it doesn't matter.  Have the card provide sync 
(be the master, internal, etc.) and have the channel banks recover clock (be 
the slave, use line clock, etc.) from the line.

Hopefully that helps.  :-)

> Channel bank 1: Adtran 600 with 12 FXO:
> Timing set to Network on CB
> /etc/zapata.conf: span=1,0,0,esf,b8zs
>
> Channel Bank 2: Adtran 750 with 12 FXO
> Timing set to loop on channel bank controller
> span=2,0,0,esf,b8zs

That looks perfect.  Make sure that you really are setting that.  IIRC the 
Sangoma card needs to have its clock set with the wancfg utility and not just 
ztcfg.

-A.