Does anyone know how the 'keep alive' feature in Nortel Settings works? I have had some issues with remote 5010 phones disconnecting and reconnecting constantly. Others on the same system have no problems. We've done lots of troubleshooting on the sonic wall, and the remote router to no avail. I decided to adjust the 'keep alive' setting down to 30 seconds and that immediately stabilized all of the problem connections. I'm glad it's fixed, but the customer really wants to know what the root problem is that 'keep alive' is compensating for. The hover hint says the system checks on the 'sanity' of the remote phones. That seems less than technical.
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The UCx system "pings" each phone periodically. The "keep alive" value is the period of time between these "ping messages".
When you use remote phones, they are typically behind some router. In order to allow multiple devices to share its public Internet connection, the router implements network address translation (NAT). The router's NAT implementation maintains information about the mapping of internal addresses and port numbers and the assigned external port numbers (NAT sessions). These sessions allow the router to deliver requests from internal addresses and port number to devices on the Internet and match responses in order to deliver them back to the correct internal devices. These NAT sessions are valid for some period of time - typically it is around 1 minute, but it can be shorter (usually this NAT session timeout is configurable). If the router sees no packet from the internal device to the external destination for the "NAT session timeout" period, it closes the NAT session and frees the external port used for that session. Any packets received from Internet to that external port number are dropped by the router (i.e., not delivered to the internal device).
The UCx "keep alive" option name indicates that this value is related to messaging that is supposed to keep NAT sessions on remote routers alive. If the frequency used by the UCx system is lower than the router's configured NAT session timeout, the router would be closing NAT sessions and phones would be re-registering frequently. For example, if the UCx keep alive is 50 seconds, but the router's NAT timeout is 40 seconds, the router would close the NAT session for a phone behind it whenever the phone is idle.
The solution is either to increase the configured NAT timeout on the router or to reduce the keep alive timer on the UCx server. To keep the "keep alive messaging" to a reasonable level, it might be slightly better to change the router setting, but these days the Internet connection bandwidth isn't typically a concern, so there is pretty much no difference if you go either way.
In your case, the router is using a NAT session timeout that is less than the previous UCx keep alive value (whatever it was) but not less than 30 seconds. Setting the UCx keep alive to 30 seconds therefore solved the problem.
When you use remote phones, they are typically behind some router. In order to allow multiple devices to share its public Internet connection, the router implements network address translation (NAT). The router's NAT implementation maintains information about the mapping of internal addresses and port numbers and the assigned external port numbers (NAT sessions). These sessions allow the router to deliver requests from internal addresses and port number to devices on the Internet and match responses in order to deliver them back to the correct internal devices. These NAT sessions are valid for some period of time - typically it is around 1 minute, but it can be shorter (usually this NAT session timeout is configurable). If the router sees no packet from the internal device to the external destination for the "NAT session timeout" period, it closes the NAT session and frees the external port used for that session. Any packets received from Internet to that external port number are dropped by the router (i.e., not delivered to the internal device).
The UCx "keep alive" option name indicates that this value is related to messaging that is supposed to keep NAT sessions on remote routers alive. If the frequency used by the UCx system is lower than the router's configured NAT session timeout, the router would be closing NAT sessions and phones would be re-registering frequently. For example, if the UCx keep alive is 50 seconds, but the router's NAT timeout is 40 seconds, the router would close the NAT session for a phone behind it whenever the phone is idle.
The solution is either to increase the configured NAT timeout on the router or to reduce the keep alive timer on the UCx server. To keep the "keep alive messaging" to a reasonable level, it might be slightly better to change the router setting, but these days the Internet connection bandwidth isn't typically a concern, so there is pretty much no difference if you go either way.
In your case, the router is using a NAT session timeout that is less than the previous UCx keep alive value (whatever it was) but not less than 30 seconds. Setting the UCx keep alive to 30 seconds therefore solved the problem.
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