Appendix B SIP Call Flows
Call Flow Scenarios for Successful Calls
Step | Action | Description |
1
| to SIP proxy server | SIP proxy server. The INVITE request is an invitation to |
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| User B to participate in a call session. |
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| In the INVITE request: |
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| • The phone number of User B is inserted in the |
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| |
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| URL identifies the address of User B and takes a form |
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| similar to an email address (user@host where user is |
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| the telephone number and host is either a domain name |
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| or a numeric network address). For example, the |
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| |
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| appears as “INVITE |
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| user=phone.” The “user=phone” parameter |
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| distinquishes that the |
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| telephone number rather than a user name. |
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| • Cisco SIP IP phone A is identified as the call session |
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| initiator in the From field. |
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| • A unique numeric identifier is assigned to the call and |
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| is inserted in the |
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| • The transaction number within a single call leg is |
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| identified in the CSeq field. |
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| • The media capability User A is ready to receive is |
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| specified. |
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2 | SIP proxy server sends the SIP INVITE request to the SIP | |
| SIP redirect server | redirect server. |
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3 | 300 Multiple | SIP redirect server sends a SIP 300 Multiple choices |
| redirect server to SIP proxy | message to the SIP proxy server. The message indicates |
| server | that User B can be reached either at SIP phone B or Cisco |
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| SIP IP phone C. |
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4 | SIP proxy server sends a SIP INVITE request to Cisco SIP | |
| Cisco SIP IP phone B | IP phone B. The INVITE request is an invitation to User B |
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| to participate in a call session. |
| Cisco SIP IP Phone 7960 Administrator Guide |
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