I've got the following configuration : 2 subnets (we'll call A and B) with IP phones in both. Internet access behind a NAT for each of them, and a routed VPN is set up between those 2 subnets. I am using a hosted SIP provider (same for both networks). IP phones are configured to work behind a NAT and use the hosted SIP proxy.

Calls to the outside and incoming calls work fine, going though the hosted provider.

Calls between phones in subnet A are established directly, ie the SIP traffic still goes to the hosted provider but the RTP traffic stays local. Same for calls within subnet B.

Calls from A to B or from B to A work too. However the RTP traffic does not go though the VPN and makes a round trip to the SIP provider which is not ideal.

What options do I have to improve on this last point ?

  • Are the phones peered directly to the SIP provider or is there any kind of intermediate sip proxy or local registration/gateway function? It might also help to know the make of the phones and the mechanism you're using to push configuration (i.e. managed vs local - see earlier question)
    – rnxrx
    Jul 13 '12 at 6:09

Only your SIP provider, or your SIP proxy administrator can do that. Otherwise if ICE protocol is supported by your provider and your phones too you can enable it and try to establish a direct media path.

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