When should keep alive be enabled on endpoint

When should keep alive with either Default, Options or Notify be enabled on an endpoint when the pbx is remotely hosted and endpoints are behind nat’d firewall?


This is an interesting topic for me as well. We are currently advising that the customer modify their UDP session timeout on their router for port 5060 to be 45 minutes while the phones register every 30 minutes. This will keep the session open so an inbound call won’t be blocked. On the Adtran, the command is “ip policy-timeout udp 5060 2700”. We have also discovered in the Grandstream that there are two options in recent firmware that could be useful. Accounts1–>Network Settings–>NAT Traversal–>Keep-Alive will send empty SDP messages to the PBX “periodically”. The manual doesn’t say what frequency. Alternatively under Accounts1–>SIP Settings Basic Settings–>Enable OPTIONS Keep Alive will send OPTIONS to the PBX to try to hold the session open.

When should you take some action? Every time. If the phone registers every 60 minutes, and the UDP session timeout on the router is 5 minutes, the router will end the phone session when the phone is idle because it thinks the session is over. Outbound calls will work because it starts a new session. When a call comes at the phone from the PBX after the phone is idle for longer than the router’s UDP session timeout, the firewall will block it as unsolicited traffic (It will do it’s job) since there is no session.

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I have been told before to not enable keep alive in endpoints while qualify is enabled in FreePBX for the endpoint(s). You bring up interesting comments because when I see phones becoming unreachable, its really problematic.

We don’t have control on clients routers in some cases. So there is no way to know the capabilities of the clients’ router.

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