Hi,

Is this a bug?  (just kidding)

As the number of extensions we serve increases, we’re trying to avoid saturating our local bandwidth by proxying all of the media between endpoints.  This seems to work fine with the Linksys devices but not with Aastra in all scenarios.  The Aastras are configured with the NAT IP field populated appropriately and Rport (RFC 3581) enabled.

The FS server is behind a NAT firewall with SIP and RTP port ranges forwarded to it.  There are endpoints here on the same network as the switch, and there are remote endpoints behind their own NAT firewalls.  Everything works fine in Proxy Media mode but in bypass mode we see the following behavior:

Scenario 1:

Remote endpoint places a call to PSTN, FS negotiates bypass media between remote endpoint and PSTN gateway.  Call succeeds.

Scenario 2:

Remote endpoint places a call to another remote endpoint on same LAN.  Call succeeds.

Scenario 3:

Local endpoint places a call to PSTN gateway.  Call succeeds.

Scenario 4:

Remote endpoint places a call to local endpoint (or vice versa).  Call fails with no audio with Aastra devices on both ends, but if one of the endpoints is a LinkSys, the call succeeds.

I realize that I should be able to solve this problem with a local SBC like OpenSIPS/RTPproxy, but in the meantime I was hoping that there might be a setting that I was overlooking with the Aastra.  When I look at the SIP traffic for the call, FS appears to be negotiating the addresses/ports properly so I suspect that this problem is related to Aastra’s inability to deal with symmetric NAT.  The Linksys devices seem to be able to deal with it with FS’ help, presumably by doing some UDP hole-punching.

Phil Quesinberry

Q Systems Engineering, Inc.

Electronic Controls and Embedded Systems Development

(410) 969-8002

http://www.qsystemsengineering.com