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 | Connect | PBX A acknowledges Gateway 1’s Connect message. |
| Gateway 1 |
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10 | 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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11 | User B terminates the call session at his Cisco SIP IP phone | |
| Gateway 1 | and the phone sends a SIP BYE request to Gateway 1. The |
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| BYE request indicates that User B wants to release the call. |
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12 | Gateway 1 sends a Disconnect message to PBX A. | |
| PBX A |
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13 | PBX A sends a Release message to Gateway 1. | |
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14 | 200 | Gateway 1 sends a SIP 200 OK response to the Cisco SIP |
| SIP IP phone | IP phone. The 200 OK response notifies the phone that |
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| Gateway 1 has received the BYE request. |
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15 | Release | Gateway 1 sends a Release Complete message to PBX A |
| to PBX A | and the call session is terminated. |
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| Cisco SIP IP Phone 7960 Administrator Guide |
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