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Setting the SIP Response Code to return when all your lines are busy

SIP is based on request/response transactions. Each transaction consists of a SIP request and at least one response.

“486 Busy Here”

When the carrier sends in a request to start a new call, and there are no more licenses to fill that request, the system responds to the INVITE with a “486 Busy Here”.

This can be configured to return any other SIP response code by setting this value in the HmpElementsServer.exe.config file:

<setting name="ServerBusyResponse" serializeAs="String">

When this is set to zero, then the default “486 Busy Here” is sent.

“503 Service Unavailable”

When this is set to some other code, like 503, then a “503 Service Unavailable” is returned.

Valid SIP Codes

Valid SIP codes can be seen here:

Your Carrier’s Response

What your carrier decides when it receives one of these codes is defined by your carrier. Some carriers will play a busy signal, others will not. Some will play a message that the number cannot be reached. Some carriers can be defined to roll the call over to a backup IP address; it all depends on your carrier.

OPTIONS Requests

If your carrier supports OPTIONS requests you can give the carrier a “heads-up” about your server’s status. Please see this article on our wiki: SIP Options in HMP Elements

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