User's Manual

106 Appendix A: Basic call flows
NN10029-111 Standard MCP 1.1 FP1 (02.02) April 2003 Copyright © 2003, Nortel Networks
Nortel Networks Confidential
The following steps provide more detail about the call flow:
1. Client A initiates the transfer of B to C. A selects blind transfer.
2. The SIP Application Module sends a Hold to B.
3. Client B sends a 200 OK message back to the SIP Application
Module. The 200 OK messages contain an Allow Header, which
lists the SIP methods that the client being transferred supports. If
Refer is in that list, then Refer is used for the transfer; otherwise,
Bye-Also is used.
4. SIP Application Module sends a 200 OK message back to Client A.
5. Ack message from Client A to the SIP Application Module.
6. Ack message from the SIP Application Module to Client B.
7. Client A sends Refer-to header with C’s information in it and a
Referred-by header with A’s information in it.
8. The SIP Application Module sends the Refer message to B.
9. 200 Accepted
10.200 Accepted
11. The SIP Application Module sends an Invite to B to establish the
new call between B and C.
12.Invite to C.
13.SIP Application Module receives a 486 Busy Here response from
Client C. This response could be any type of 4xx, 5xx, or 6xx error
message.
14.The SIP Application Module sends a Notify message to Client B.
The body of the Notify message contains the 486 Busy Here, in this
example
15.Client B responds with an Ack.
16.The SIP Application Module sends an Ack to Client C.
17.Client B Notifies Client A, through the SIP Application Module, that
Client C is Busy.
18.Notify goes to Client A.
19.Client A responds with a 200 OK.
20.200 OK to Client B.
21.There are now two possibilities:
• Invite (Unhold): Client A can re-establish the call to Client B, in
which case steps 22-26 apply.
• Bye: Client A can hang up, in which case this is the last step.