Cisco IP Phone not working on AT&T DSL?

[hummer3331973]

Hi-

Has anyone here encountered using Cisco 7960 IP phone on an AT&T DSL and not work (failed to register)? Have tried the same unit on a Comcast internet line and I have no problem.

In both instances, I connect the 7960 directly behind the telco modem thus no firewall is involve.

Any clue?

 

[mtashiro]

Are you connecting to a CallManager at you corporate location or using a third party service using Cisco phones?

 

[hummer3331973]

I'm using a third-party service provider.

 

[mtashiro]

I am assuming that the IP phone is behind a DSL router. does the DSL router allow the ports that are needed for the IP Phone?

 

[hummer3331973]

Yes it do, because I have another VoIP provider (this time using Polycom) and I can use the same DSL and it's working.

 

[hummer3331973]

I found a work-around on this problem. I put a Linksys DSL Router with 4-port switch in between the DSL modem (AT&T provided) and my 7960 and it works.

But I'm still guessing why..