778 CHAPTER 30 Security Issues in VoIP Telecommunication Networks Vonage phone MITM INVITE Vonage server(s) ATT proxy servers MITM2 ATT phone 407 proxy-authentication required ACK INVITE (credentials) 100 TRYING 180 RINGING 200 OK ACK RTP stream BYE 200 OK RTP stream RTP stream RTP stream BYE X X INVITE 100 TRYING 180 RINGING 200 OK ACK RTP stream BYE 200 OK RTP stream BYE FIGURE 30-18 Bye drop billing attack. 30.5.5. Bye Drop Billing Attack BYE drop billing attacks prolong calls by sim- ply dropping the BYE message from the caller or callee. In the experiment, the call lasted for 2 min and the MITMs intercepted the BYE messages from the SIP phone and replied with a 200 OK message, creating a bogus RTP stream between the MITMs. With the attack, the call lasted about 218 min before the servers sent a BYE message to terminate the call. The call activity in the Vonage SIP showed 240 min of billable call time though the actual call lasted for merely 2 min. With the billing attacks on the mobile phone helping the service provider to gain money for unused calls, it also presents inconvenience to the user with call teardowns during a conver- sation. These vulnerabilities in the system make it unreliable and insecure. P2PSIP is an alterna- tive to the traditional server-based system and expected to avoid these vulnerabilities from the server-based service. Eventually, P2PSIP is still vulnerable to the common attacks because of the underlying SIP signaling. In the next section, we will go through some of the potential vulnera- bilities in the P2PSIP telecommunication and the recommendation/solutions to control the exploits during communication. 30.6. SECURITY REQUIREMENTS OF A P2P TELECOMMUNICATION NETWORK There are a number of commercial P2P-based VoIP systems that have been developed. Among