SIP response handling

Last Updated : Apr 24, 2016 |

The following table describes how Session Manager handles SIP responses.

Response

Session Manager action

2xx

Session Manager completes a call.

3xx

422

423

484

5xx (other than 501-504)

6xx

Session Manager sends a response to the caller.

408

501 to 504

Session Manager maps an alternate IP address or entity link of a SIP entity to determine an alternate route for a call.

Note:

If a SIP message establishes early dialog, Session Manager cannot change the dialog, and therefore cannot alternate route calls. For any SIP 101-199 provisional message that establishes early dialog, Session Manager cannot determine an alternate route for the call.

4xx (except 408)

Session Manager does not try to map the alternate IP addresses or entity link of a SIP entity to establish a call, Session Manager tries to determine an alternate route for the call with another routing policy.

Note:

If a SIP message establishes early dialog, Session Manager cannot change the dialog, and therefore cannot alternate route calls. For any SIP 101-199 provisional message that establishes early dialog, Session Manager cannot determine an alternate route for the call.

IP alternate routing and Call Admission Control

When sending a request, Session Manager sets the timer B or timer F value as specified in the destination SIP entity. If a SIP entity is administered with an FQDN, the Session Manager resolves the FQDN into a list of IP addresses using DNS or the local host name resolution table. The IP address of the final destination determines the egress location. The IP address is compared with IP address patterns on the Location Details page. If a location matches, the location is identified as the destination location. If no IP address pattern matches, the location that is administered on the destination SIP entity, if any, is identified as destination location.

If timer B or timer F expires, Session Manager generates a 408 response to the request. Session Manager then tries other IP addresses for the same SIP entity. If all IP addresses have been tried without success, Session Manager tries the next routing policy on the prioritized list.

If Call Admission Control is administered for the location and the request causes the number of allowed calls to be exceeded, the request is rejected with a 488 response.