HP-UX Java SIP Stack Programmer's Guide (February 2008)

10. The proxy server forwards the 200–OK response back to UA1.
11. UA1 sends an ACK directly to UA2.
Using the Redirect Server
This section discusses the steps involved in establishing a call that uses a redirect server.
Figure 1-4 illustrates the interaction between the user agents, redirect server, and the
location service while establishing a call.
Figure 1-4 Call Setup Using a Redirect Server
The following steps describe how a call is established using a redirect server:
1. UA1 sends an INVITE message to [e-mail]. UA1 notices the redirect
server red.seq.com in the signalling path.
2. The redirect server looks up host1's current location in the location service.
3. The location service provides host1's current location ([e-mail]).
4. The redirect server sends host1's current location to UA1 using a 302 response.
5. UA1 acknowledges the response by sending an ACK message to the redirect server.
6. UA1 directly sends an INVITE message to the sev.alp.com domain.
7. The sev.alp.com domain identifies the call to host1.
The host1 answers the call.
8. UA2 sends a 200–OK response to UA1.
9. UA1 acknowledges the response with an ACK message.
32 Introduction