ks and the PSTN Although tremendous amounts of time and money have been spent in developing the intelligence that provides the PSTN telephony features we know today, opera- tors are seeking ways to consolidate voice and data traffic, platforms, and services in order to reduce the operational, maintenance, and initial costs of the network. IP-based networks are now considered the best path to building converged net- works from which integrated services can be offered. There are many benefits asso- ciated with an IP network, including less expensive equipment, easier deployment, higher bandwidth, and the opportunity for many enhanced services. These new IP- based services include unified messaging, IP telephony, IP-based virtual private networks (IP VPNs), IPTV, and mobile IP, among many others. Both fixed and mobile operators are choosing to deploy such all-IP infrastructures, which include support for SS7 signaling protocols. Given the substantial presence of circuit-switched networks that continue to deliver high-quality voice and data connections and still have plenty of useful life, it is clear that an integration solution is required to interconnect the PSTN and the growing number of IP networks. The charter of the IETF Signaling Transport (SIGTRAN) Working Group, established in 1999, is to develop and standardize the SS7 and Next-Generation Networks messages and protocols necessary to carry mobile and PSTN signaling over IP net- works (i.e., SS7 over IP). The SIGTRAN Working Group has defined a new architec- tural model that enables the evolution to an all-IP network. This new model defines the appropriate protocols required for converging the PSTN and IP networks. The SIGTRAN protocols provide all the functionality needed to support SS7 signaling over IP networks, including flow control; in-sequence delivery of signaling mes- sages within a single control stream; identification of the originating and terminat- ing signaling points; identification of voice circuits; error detection, retransmission, and other