[asterisk-users] One PRI card with 2 (or more) Telcos

[Kevin P. Fleming]

On 03/18/2011 01:23 PM, Tiago Geada wrote:
> Hi! I can try that tho. Where do I configure what timer to use??!

If your telcos are not synchronizing their network clocks to each other, 
you will not be able to solve this problem on a multi-port Digium T1/E1 
card. Digium T1/E1 cards select a single master clock (either the 
onboard clock or the clock recovered from one of the spans) to use as 
the 'board clock', which is then used to transmit data on all the spans. 
If the master clock is not in synchronization with the clocks at the 
other end of those spans, then bit slips will occur and cause various 
sorts of problems. This is why a card is always configured to use the 
recovered clock from a telco span if there is one, because the onboard 
clock would never by in sync with it.

If you have a board connected to two telcos and their clocks are not 
synchronized, not only will you have trouble using a Digium card, but 
even using a card that can handle using multiple transmit clocks at once 
will not solve the underlying bit slip problem that will occur if you 
ever connect a channel from Telco1 to a channel from Telco2. If you 
*never* connect channels between Telcos, then you don't have to worry 
about that problem, but if you do, at some point during the call there 
will be buffer overruns or underruns and there will be some effect (for 
a normal voice call, the effect might be a short audio artifact, and 
fairly harmless... unless the call is a modem or FAX call, in which case 
it could cause the call to fail).

For your sanity, I would strongly suggest that you don't connect spans 
from multiple telcos/networks/etc. on a single card, but keep each span 
provider on their own card.

-- 
Kevin P. Fleming
Digium, Inc. | Director of Software Technologies
Jabber: kfleming at digium.com | SIP: kpfleming at digium.com | Skype: kpfleming
445 Jan Davis Drive NW - Huntsville, AL 35806 - USA
Check us out at www.digium.com & www.asterisk.org