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calling OK but no audio until I change the ADSL modem/router


ndemou
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we have a pbxnsip server on a public internet address (no NAT and no firewall in front of it) and we're trying to make calls from SIP phones behind various locations with whatever ADSL modem/router they have. In some locations calls are proceeding fine until the other party picks up the phone. At this point no one hears the other party. Trying another "el'cheapo" modem/router that I cary with me solved the problem.

 

In at least 3 occasions I had enough time to try all settings that seemed logical (and some illogical ones) with no success at the existing routers (I'm no firewall expert but I do know the basics - I can even understand ipfilter rules :-). Even really straightforward settings like forwarding ALL TCP/UDP traffic above port 1024 to the IP of the sip phone through the DMZ configuration of the router did not work.Is there anything else I can do to solve the problem or at least make it appear as rarely as possible (replacing the router and setting up a new one is really painful)?

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It is unbelieveable what kind of devices are out there in the router market. I have seen routers that have no expiration of NAT ports, and they just use 32 ports in a FIFO fashion. That router in a busy office was a nightmare troubleshooting why some phone calls just wont work!!!

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It is unbelieveable what kind of devices are out there in the router market. [...]

 

I've been burned by routers in at least 3 and possibly 4 out of about 10 locations. Do you also see such a high percentage of "will never work" routers? I've lost 2-3 hours with a linksys ADSL/wifi router and 1-2 hours with every other.

 

Is there a list "best practices" for router configuration than I can follow before giving up?

 

Lastly for people that ask me "what router should I buy to play nice with SIP?" is there some feature they should be checking before buying?

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I've been burned by routers in at least 3 and possibly 4 out of about 10 locations. Do you also see such a high percentage of "will never work" routers? I've lost 2-3 hours with a linksys ADSL/wifi router and 1-2 hours with every other.

 

Is there a list "best practices" for router configuration than I can follow before giving up?

 

Lastly for people that ask me "what router should I buy to play nice with SIP?" is there some feature they should be checking before buying?

 

I just disposed my private router collection. I tried to make a statistics on whoich router is using what type; but in the end the result was: Every router as it's own type. There is a interesting IETF document at http://tools.ietf.org/html/draft-jennings-...test-results-04 that tries to classify routers. IMHO just another reason to finally give up on NAT and move straight ahead to IPv6.

 

Or use TLS and encrypt the traffic between the phone and the PBX so that no "smart" routers can mess the SIP packets up! Security against vendors that want to do you something good, but unfortunately are unable to do so from their skill set.

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I just disposed my private router collection [...] Every router [is] it's own type. [...] IMHO just another reason to finally give up on NAT and move straight ahead to IPv6.

So if I got it right routers are what they are and if I don't get things working within the first 15minutes there's no use wasting my time except if...:

 

Or use TLS and encrypt the traffic between the phone and the PBX so that no "smart" routers can mess the SIP packets up!

thanks, I'll try to set it up using a snom phone.

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we have a pbxnsip server on a public internet address (no NAT and no firewall in front of it) and we're trying to make calls from SIP phones behind various locations with whatever ADSL modem/router they have. In some locations calls are proceeding fine until the other party picks up the phone. At this point no one hears the other party. Trying another "el'cheapo" modem/router that I cary with me solved the problem.

[...]

SOLVED :)

 

It was our mistake: there was a firewall after all and it was rejecting UDP packets coming to high ports. What's strange now is why on earth some routers had no problem sending audio to the server although UDP traffic was blocked!!! Any way all good now -- sorry for the false alarm.

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