HP-UX C SIP Stack Programmer's Guide (Novembery 2007)

12 HP-UX C SIP Stack Programmer’s Guide
Entity Interaction
CALL PROXYING Figure 1-3 shows call set-up between two User Agents with the assistance of an
intermediate Proxy server.
Figure 1-3 Call Proxying Scenario
CALL FLOW
1. An INVITE message is sent to bob@ acme.com, but finds the
Proxy server sip.acme.com along the signaling path.
2. The Proxy server immediately responds with a 100 (Trying)
provisional response.
3. The Proxy server looks-up Bob’s current location in a Location
Service using a non-SIP protocol (For example, LDAP).
4. The Location Service returns Bob’s current location: SIP
address [e-mail].
User Agent
1
User Agent
2
1: INVITE
[e-mail]
2: 100/Trying
lab.acme.com
Proxy
Server
sip.acme.com
Location
Service
5: INVITE
bob@
lab.acme.com
6: 100/Trying
7: 180/Ringing
8: 180/Ringing
9: 200/OK
10: 200/OK
11: ACK [e-mail]
3: [e-mail] ?
4: [e-mail]
a.toon.com