Cisco 7960G Administration Manual page 154

Call Flow Scenarios for Failed Calls
Called Number Does Not Answer
Figure B-22
not answer.
Figure B-22 Called Number Does Not Answer
Phone User A
Step Action
INVITE—Phone A to Phone B
1.
2. 180 Ringing—Phone B to
Phone A
3. CANCEL (Ring
Timeout)—Phone A to Phone B
200 OK—Phone B to Phone A
4.
Cisco Unified IP Phone 7960G and 7940G Administration Guide for Release 8.0 (SIP)
B-54
illustrates an unsuccessful call in which User A initiates a call to User B, but User B does
SIP IP
IP
1. INVITE B
2. 180 Ringing
3. CANCEL
4. 200 OK
5. 487 Request Cancelled
6. ACK
Description
Phone A sends a SIP INVITE request to Phone B. The request is an invitation to
User B to participate in a call session. In the INVITE request:
The phone number of B is inserted in the Request-URI field in the form of a
•
SIP URL. The SIP URL identifies the address of B and takes a form similar
to an e-mail address (user@host, where user is the telephone number and host
is either a domain name or a numeric network address). For example, the
Request-URI field in the INVITE request to B appears as "INVITE
sip:555-0199@companyb.com; user=phone." The "user=phone" parameter
distinquishes that the Request-URI address is a telephone number rather than
a username.
Phone A is identified as the call session initiator in the From field.
•
A unique numeric identifier is assigned to the call and is inserted in the
•
Call-ID field.
The transaction number within a single call leg is identified in the CSeq field.
•
The media capability A is ready to receive is specified.
•
Phone B sends a SIP 180 Ringing response to Phone A.
Phone A sends a CANCEL request to Phone B to cancel the invitation.
Phone B sends a SIP 200 OK response to Phone A. The response confirms receipt
of the cancellation request.
IP Network
Appendix B SIP Call Flows
SIP IP
Phone User B
IP
OL-7890-01