Dahdi Timing Issues

Lab Setup Between Two Ports

Network Diagram:         ISDN T1(Port A) ---> Sangoma Board -> Asterisk -> SIP ---> Asterisk -> ISDN T1(Port B)

In this network diagram the clock on T1 (A) is slightly different than a clock on T1 (B). Therefore T1 (A) is pushing data quicker than T1(B) and this will cause a data underrun after sometime. When Sangoma cards are connected with a telco the telco uses ATOMIC clocks and they are synchronized. This is why a LAB setup will always exhibit this behavior.

This means if the network diagram is the following then the results will be better. 

Network Diagram TelcoA -- atomic clock A -- Sangoma T1 -- VoIP Sangoma T1 -- atomic clock B --- TelcoB

Bottom line, no matter what equipment he uses they will have this issue, unless their T1(A) and T1(B) clocks are 100% in-sync.