Appendix B SIP Call Flows
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| Call Flow Scenarios for Successful Calls |
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Step | Action | Description | |
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10 | 200 | Cisco SIP IP phone C sends a SIP 200 OK response to | |
| to Cisco SIP IP phone B | Cisco SIP IP phone B. The 200 OK response notifies Cisco | |
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| SIP IP phone B that the connection has been made. | |
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| If Cisco SIP IP phone C supports the media capability | |
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| advertised in the INVITE message sent by Cisco SIP IP | |
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| phone B, it advertises the intersection of its own and Cisco | |
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| SIP IP phone B’s media capability in the 200 OK response. | |
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| If Cisco SIP IP phone C does not support the media | |
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| capability advertised by Cisco SIP IP phone B, it sends | |
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| back a 400 Bad Request response with a 304 Warning | |
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| header field. | |
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11 | Cisco SIP IP phone B sends a SIP ACK to Cisco SIP IP | ||
| Cisco SIP IP phone C | phone C. The ACK confirms that Cisco SIP IP phone B has | |
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| received the 200 OK response from Cisco SIP IP phone C. | |
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| The ACK might contain a message body with the final | |
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| session description to be used by Cisco SIP IP phone C. If | |
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| the message body of the ACK is empty, Cisco SIP IP phone | |
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| C uses the session description in the INVITE request. | |
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A | |||
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12 | Cisco SIP IP phone B sends a | ||
| to Cisco SIP IP phone A | SIP IP phone A with the same call ID as the previous | |
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| INVITE and new SDP session parameters (IP address), | |
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| which are used to reestablish the call. | |
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| Call_ID=1 | |
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| SDP: c=IN IP4 181.23.250.2 | |
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| To reestablish the call between phone A and phone B, the | |
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| IP address of phone B is inserted into the c= SDP field. | |
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13 | 200 | Cisco SIP IP phone A sends a SIP 200 OK response to | |
| to Cisco SIP IP phone B | Cisco SIP IP phone B. | |
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14 | Cisco SIP IP phone B sends a SIP ACK to Cisco SIP IP | ||
| Cisco SIP IP phone A | phone A. The ACK confirms that Cisco SIP IP phone B has | |
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| received the 200 OK response from Cisco SIP IP phone A. | |
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SIP IP phone B acts as a bridge mixing the RTP channel between User A and User B with the channel between User B and User C; establishing a conference bridge between User A and User C.
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| Cisco SIP IP Phone 7960 Administrator Guide |
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