Network address translation in session initiation protocol based application

Abstract

Improved techniques are disclosed for providing network address translation (NAT) in a session initiation protocol (SIP) based application. For example, a method for use in a router for performing NAT on a SIP message associated with a session being initiated between a first device and at least a second device, wherein the first device is part of a first network and the second device is part of a second network, includes the following steps. A SIP message is obtained from the first device, wherein a header field of the SIP message includes a local address and local port number usable by the first device on the first network. A port number to be associated with the session being initiated is randomly selected. The randomly selected port number is usable on the second network. An association (e.g., a binding) is generated between the randomly selected port number and a global address usable on the second network, the local address and the local port number. The local address and the local port number are substituted in the header field of the SIP message with the global address and the randomly selected port number thereby generating an address-translated SIP message. The address-translated SIP message is sent to the second device on the second network. The randomly selected port number may serve as a unique identifier for the session being initiated.