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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| 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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| 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 | 302 Moved | SIP redirect server sends a SIP 302 Moved temporarily | ||
| redirect server to SIP proxy | message to the SIP proxy server. The message indicates | ||
| server | that User B is not available at SIP phone B and includes | ||
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| instructions to locate User B at Cisco SIP IP phone C. | ||
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4 | SIP proxy server sends a SIP INVITE request to Cisco SIP | |||
| Cisco SIP IP phone C | IP phone C. The INVITE request is an invitation to User C | ||
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| to participate in a call session. | ||
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5 | 180 | Cisco SIP IP phone C sends a SIP 180 Ringing response to | ||
| phone C to SIP proxy server | the SIP proxy server. | ||
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| Cisco SIP IP Phone 7960 Administrator Guide |
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