Appendix B SIP Call Flows
|
| Call Flow Scenarios for Failed Calls |
|
|
|
| |
Step | Action | Description | |
|
|
| |
5 | 4xx/5xx/6xx | The Cisco SIP IP phone sends a class 4xx, 5xx, or class 6xx | |
| IP phone to Gateway 1 | failure response to Gateway 1. Depending on which class | |
|
| the failure response is, the call actions differ. | |
|
| If the Cisco SIP IP phone sends a class 4xx failure response | |
|
| (a definite failure response that is a client error), the request | |
|
| will not be retried without modification. | |
|
| If the Cisco SIP IP phone sends a class 5xx failure response | |
|
| (an indefinite failure that is a server error), the request is | |
|
| not terminated but rather other possible locations are tried. | |
|
| If the Cisco SIP IP phone sends a class 6xx failure response | |
|
| (a global error), the search for User B is terminated because | |
|
| the 6xx response indicates that a server has definite | |
|
| information about User B, but not for the particular | |
|
| instance indicated in the | |
|
| further searches for this user will fail. | |
|
|
| |
6 | Gateway 1 sends a Release message to PBX A. | ||
| A |
|
|
|
|
| |
7 | PBX A sends a Release message to Gateway 1. | ||
|
|
| |
8 | Gateway 1 sends a SIP ACK to the Cisco SIP IP phone. The | ||
| IP phone | ACK confirms that User A has received the 486 Busy Here | |
|
| response. The call session attempt is now being terminated. | |
|
|
| |
9 | Release | Gateway 1 sends a Release Complete message to PBX A | |
| to PBX A | and the call session attempt is terminated. | |
|
|
|
|
|
| Cisco SIP IP Phone 7960 Administrator Guide |
|
|
|
|
| ||
|
|
|
| |
|
|
|
