A back-to-back user agent (B2BUA) is a type of SIP device that receives a SIP request, then reformulates the request and sends it out as a new request. Responses to the request are also reformulated and sent back in the opposite DIRECTION. For example, a B2BUA device can be USED to IMPLEMENT an anonymizer service in which two SIP UAs can communicate WITHOUT either party learning the other party’s URI, IP address, or any other information. The most common form of B2BUA present in SIP networks is application layer gateways (ALG).

A back-to-back user agent (B2BUA) is a type of SIP device that receives a SIP request, then reformulates the request and sends it out as a new request. Responses to the request are also reformulated and sent back in the opposite direction. For example, a B2BUA device can be used to implement an anonymizer service in which two SIP UAs can communicate without either party learning the other party’s URI, IP address, or any other information. The most common form of B2BUA present in SIP networks is application layer gateways (ALG).