Nortel Networks NN10265-111 - Manual (Page 113)

MCS 5100 RTP Media Portal Basics
113 Copyright © Nortel Networks Limited 2006
The following steps provide more detail about the call flow:
1. Client A initiates a SIP session to Client B by sending an Invite
message to the SIP Application Module. Within the Invite message,
Client A includes SDP information that identifies the called address
(IP and port of B).
2. The SIP Application Module requests resources to support the half
call (connection) between client B and the RTP Media Portal. The
address and port of Client B are included in the request.
3. The RTP Media Portal allocates resources (an IP address and port)
for Client B. The new resources (A’) are returned to the SIP
Application Module in the response.
4. The SIP Application Module forwards the original invite to Client B,
substituting the address and port of Client A with the A’ resources
allocated by the RTP Media Portal.
5. Client B answers the incoming call. The SIP message sent to the
SIP Application Module contains the address and port of Client B.
6. The SIP Application Module requests resources to support the half
call (connection) between Client A and the RTP Media Portal. The
address and port of Client A are included in the request.
7. The RTP Media Portal allocates resources (an IP address and port)
for Client A. The new resources (B’) are returned to the SIP
Application Module in the response.
8. The SIP Application Module replaces the SDP information
identifying the terminating address (B) with information identifying
the terminating NAPT address (B’), and forwards on the OK
message to Client A. At this point, both clients have the correct
addresses to establish the media connection and media packets
are being sent and received.
9. Client B disconnects the call by sending a BYE message to the SIP
Application Module.
10. The SIP Application Module propagates the BYE to Client A.
11. The SIP Application Module tells the RTP Media Portal to free the
resources for Client B.
12. The SIP Application Module tells the RTP Media Portal to free the
resources for Client A.
13. The RTP Media Portal frees the resources and responds SIP
Application Module.
14. The RTP Media Portal frees the resources and responds to SIP
Application Module.