Appendix B SIP Call Flows
Call Flow Scenarios for Successful Calls
Step | Action |
| Description | |||
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6 |
| Gateway 1 sends an Alert message to User A. The Alert | ||||
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| message indicates that Gateway 1 has received a 180 | |
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| Ringing response from the Cisco SIP IP phone. User A | |
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| hears the ringback tone that indicates that User B is being | |
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| alerted. | |
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7 | 200 |
| The Cisco SIP IP phone sends a SIP 200 OK response to | |||
| Gateway 1 |
| Gateway 1. The 200 OK response notifies Gateway 1 that | |||
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| the connection has been made. | |
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8 |
| Gateway 1 sends a Connect message to PBX A. The | ||||
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| Connect message notifies PBX A that the connection has | |
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| been made. | |
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9 |
| Gateway 1 sends a SIP ACK to the Cisco SIP IP phone. The | ||||
| IP phone |
| ACK confirms that Gateway 1 has received the 200 OK | |||
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| response. The call session is now active. | |
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10 | Connect |
| PBX A acknowledges Gateway 1’s Connect message. | |||
| Gateway 1 |
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11 |
| User B transfers User A’s call to User C and then hangs up. | ||||
| Gateway 1 |
| The Cisco SIP IP phone sends a SIP BYE request to | |||
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| Gateway 1. The SIP BYE request includes the Also header. | |
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| In this scenario, the Also header indicates that User C | |
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| needs to be brought into the call while User B hangs up. | |
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| This header distinguishes the call transfer BYE request | |
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| from a normal disconnect BYE request. | |
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| The | |
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| request, however, Cisco’s implementation does not require | |
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| the header to complete the transfer. If the | |
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| header is included, the INVITE sent to the | |
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| party will include the | |
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| the | |
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| header. | |
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12 | 200 |
| Gateway 1 sends a SIP 200 OK message to the Cisco SIP | |||
| SIP IP phone |
| IP phone. The 200 OK response notifies the Cisco SIP IP | |||
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| phone that the BYE request has been received. The call | |
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| session between User A and User B is now terminated. | |
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| Cisco SIP IP Phone 7960 Administrator Guide | |||
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