TDM Services over IP Networks

Time Division Multiplexing (TDM) circuits have been the backbone of communications over the past several decades. These circuits which provide reliable and low-delay services for voice, data and video transport, are migrating towards Internet Protocol (IP) based packet switched networks. The primary reason for the migration of these circuits is to reduce the cost of transport and management by having a converged network for all services. Due to the sheer magnitude of the installed legacy TDM equipment, this migration to "end-to-end IP" will go through a transitional phase where some services will continue to use legacy equipment, while the core network moves towards IP. In this transitional phase, there is a need for technology allowing seamless transmission of TDM services across the packet switch networks. The Internet Engineering Task Force (IETF) and International Telecommunication Union (ITU) provide specifications for interoperability to emulate TDM circuits over IP networks. These emulated services can be implemented using a gateway device that provides for inter-working function (IWF) between TDM and IP networks. The primary challenge of the gateway device is to provide the equivalent level of reliability and security of traditional TDM networks. To that extent, the gateway device must be able to achieve an equivalent level of synchronization of TDM circuits across the IP network and cope with packet impairments of the underlying IP network. In addition, the gateway can provide value added services such as echo cancellation, multicasting and IP security.