[Asterisk-Users] Dual Timing Sources

[qrss at keitz.org]

The following information is accurate for a situation where both T1s are
connected to telco switches and the telco is therefore providing the
timing signals. If one of the T1s is point to point (such as a tie line)
then this information may or may not apply depending upon what's on the
remote end.

Configuring one of your T1s as the primary timing source tells Asterisk to
sync to that T1's data stream as a reference clock for all data moving in
and out of the system. Since both T1s are from the same provider, all
clocks will be in sync. Even T1s from different providers are going to be
pretty much in sync. You should be able to pick either T1 as your primary
clock source. You can have only one primary clock source.

The secondary timing source only comes into play when the first one fails.
If the T1 that is your primary clock source fails, then Asterisk will
begin using the secondary source. Without a secondary clock source
configured, most equipment would instead switch to an internal clock
source which would cause slips on the non-failed T1. Configuring a
secondary clock source can help to ensure that you don't lose both T1s
just because the primary fails.

If possible, you should select whichever T1 is least likely to fail as
your primary clock source. If there is no way to determine that, then just
pick one.

If you are interested in some detailed information about what timing is
and how it works, this link looks pretty good:

http://www.oreilly.com/catalog/t1survival/chapter/ch05.html

> Ok.. I sort of lied.. it's the same CLEC but two different switches..
> was told by them since they are different switches I needed primary
> timing.... so in theory it should work if I set it as secondary.. ok
> we'll try!
>
> Just out of curiousity.. what happens if I set both as 1 (primary?)