andbook: Services, Technologies, and Security Communication binding table Communication binding table Source Destination Lighthouse Source Destination Lighthouse 100-A 254-C User B's User A's User binding table lighthouse lighthouse Downward HandleID User binding table User C Downward User B HandleID User B User C User A User B For User A use 412 For User B use 689 User B's User A's portal portal User B User A FIGURE 20.3 Establishment of a Mist communication path. Bob (Father) Lookup service LighthouseAlice Alice (Mother) LighthouseBob (redirect server) 1. MIST [SIP [INVITE mother@dpi.com]] 2. MIST [mother@dpi.com] 3. MIST [Lighthouse alice] 4. MIST [SIP [INVITE mother@dpi.com] 5. MIST [SIP [INVITE mother@dpi.com] 6. MIST [P_Father (SIP [302: Moved temporarily])] contact 3572@ffs.com 7. MIST [P_Father (SIP [302: Moved temporarily])] contact 3572 @ ffs.com 8. MIST [P_Father (SIP [302: moved temporarily])] contact: 3572@ffs.com 9. MIST [SIP [ACK]] 10. MIST [SIP [ACK]] 11. MIST [SIP [ACK]] 12. SIP [INVITE 3572@ffs.com] 13. SIP [200: ACK] 14. SIP [ACK] FIGURE 20.4 The message sequence chart when applying Mist in SIP. C 2009 by Taylor & Francis Group, LLC Anonymity in SIP 11) Therefore the next step is to send directly to her an SIP INVITE request. 12) They both acknowledge. The SIP circuit is established. Through the aforementioned procedure, the two users can place phone calls through the Mist without revealing their position. Therefore, it will be difficult for eavesdroppers to trace them and inference about their identity. 20.6 Conclusions In many Internet applications, end-user privacy is essential. This avoids the identification of sexual, political, social and economic preferences of the indi- vidual and upgrades the digital dignity. The VoIP paradigm, and the SIP as its dominant architecture, is one of the Internet services that is expected to pre- vail. Solving the privacy concerns might accelerate its success and broadness. This section addresses these concerns and suggests a solution that might be useful f