ble. At this point, the Mist circuit has been established. The Lighthouse has knowledge of Alice's "name" (her pseudonym) but not her current position (just a way to get in touch with her). 20.5.2.4 Making a VoIP Call Bob wants to call Alice. Note that both users should have established a Mist circuit with their Lighthouses and be able communicate through them. Bob is aware that Alice's nickname is "Mother". The procedure is illustrated in Figure 20.4. 1) Bob (who has registered with the nickname "Father") creates a MIST packet towards its SIP Lighthouse and encapsulates a SIP INVITE request for the user "Mother". He sends this up to the Mist hierarchy. 2) LighthouseBob receives the packet, determines the destination user and looks up in the Mist registry for the corresponding Lighthouse. 3) LighthouseBob creates a Mist packet towards the LighthouseAlice and encapsulates the INVITE Request that he received. 4) LighthouseAlice receives the packet, which is the SIP redirect server, determines that the called person is "Mother" and looks in the binding table to locate her. 5) Upon retrieving the Mist routing information, it creates a Mist packet with the SIP INVITE request and sends it to her through the Mist circuit. 6) Alice receives the packet, determines that it is an INVITE request from her friend Bob (she knows that his nickname is "Father"). 7) Alice creates a SIP redirect packet to inform Bob about her current loca- tion, encrypts this message with Father's public key, and encapsulates everything in a Mist packet towards her Lighthouse. Note that the public key of Bob is based on his nickname. This is to enforce Bob's anonymity. 8) LighthouseAlice upon receiving the packet, determines that destination is LighthouseBob, encapsulates the content of Alice packet to a Mist packet and send it to LighthouseBob. 9) LighthouseBob forward the packet to Bob. 10) Bob, upon receiving, creates a SIP packet to acknowledge. At this point, Bob knows Alice's remote current address. C 2009 by Taylor & Francis Group, LLC SIP H