Session Initiation Protocol (SIP) is the Voice over IP signaling protocol that negotiates communications to and from Blueworx Voice Response. These communications can come from various SIP entities such as proxies, SIP registrars, phones, or other telephony servers. Secure SIP provides authentication, in addition to integrity and confidentiality of messages, and security for SIP communications on non-secure networks like the internet. Secure SIP can prevent attacks such as tampering with messages, or the impersonation of a user.
The concepts of authentication, integrity, and confidentiality are explained in Security. It is important to note that Secure SIP secures only the signaling data of a call. To secure the audio as well, you must enable Secure RTP.
Normally SIP uses one of UDP or TCP to send SIP messages, which are by default, sent to port 5060. Secure SIP uses TLS, itself built on top of TCP, which by default uses port 5061. If asked to choose a protocol for SIP messages, only TLS is secure.