Extension frequently going offline (aka “bouncing extension”)

When we refer to an extension “bouncing” we mean that it goes offline periodically, usually for a short period like a minute or two or less, and does that several times a day. During the period that an extension is offline, it will not receive incoming calls. It may be able to make outgoing calls for reasons explained below


What makes an extension go offline


Each extension communicates with IPFINITY’s infrastructure over protocol known as SIP which generally traverses over UDP. Periodically our infrastructure will “ping” each phone or device (such as an ATA) to verify that it is still online. This “ping” occurs over SIP (not ICMP) via an OPTIONS message. If the extension does not respond, our server retries. After two seconds of not receiving a response the extension is marked offline. We continue trying to “ping”, and if the extension starts responding again, it is marked online and will now be able to receive calls.


Underlying cause


In every case, except for a defective extension, the underlying cause is a network issue.


Typical network issues are:


NAT: This is the most common type of issue: such as a short NAT timeout (the NAT timeout must be at least 300 seconds), or a NAT table that is full.

SIPALG: Any device such as a firewall or router that functions as a SIP proxy or processes SIP messages can interfere with the SIP signalling and should be disallowed to do so. Frequently, routers and firewalls will have a feature called SIPALG enabled by default. This should be disabled to prevent interference with the SIP signalling.

Network congestion or packet loss: This is often a difficult problem to trace and requires network analysis tools to determine the source of packet loss.

Bad switch or port: if the problem is confined to a single extension or a few extensions on one switch, the problem could be the switch or some ports on that switch. Changing the cabling, switch and ports is a good way to bracket the underlying cause.

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