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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3 | 200 | Cisco SIP IP phone B sends a SIP 200 OK response to | |
| to Cisco SIP IP phone A | Cisco SIP IP phone A. The 200 OK response notifies Cisco | |
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| SIP IP phone A that the connection has been made. | |
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| If Cisco SIP IP phone B supports the media capability | |
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| advertised in the INVITE message sent by Cisco SIP IP | |
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| phone A, it advertises the intersection of its own and Cisco | |
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| SIP IP phone A’s media capability in the 200 OK response. | |
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| If Cisco SIP IP phone B does not support the media | |
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| capability advertised by Cisco SIP IP phone A, 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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4 | Cisco SIP IP phone A sends a SIP ACK to Cisco SIP IP | ||
| Cisco SIP IP phone B | phone B. The ACK confirms that Cisco SIP IP phone A has | |
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| received the 200 OK response from Cisco SIP IP phone B. | |
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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 B. If | |
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| the message body of the ACK is empty, Cisco SIP IP phone | |
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| B uses the session description in the INVITE request. | |
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A
5 | Cisco SIP IP phone B sends a | |
| to Cisco SIP IP phone A | SIP IP phone A with new SDP session parameters |
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| (IP address), which are used to place the call on hold. |
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| Call_ID=1 |
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| SDP: c=IN IP4 0.0.0.0 |
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| The c= SDP field of the SIP INVITE contains an 0.0.0.0. |
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| This places the call in limbo. |
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6 | 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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7 | 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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The RTP channel between Cisco SIP IP phone A and Cisco SIP IP phone B is torn down. User A is put on hold.
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| Cisco SIP IP Phone 7960 Administrator Guide |
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