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Service providers are presently seeking to increase their profits through low cost deployment of voice and leased line services over more efficient Ethernet and IP infrastructures. At the same time enterprises are looking for ways to take advantage of the promise of convergence by integrating their voice and data networks while preserving their investment in traditional PBX and TDM equipment. The voice-over-IP (VoIP) approach is maturing, but its deployment requires a certain level of investment in new network infrastructure and/or customer premises equipment (CPE).
TDM-over-IP (TDMoIP) is a technology that enables voice and leased-line services such as video and data to be offered inexpensively over service provider IP networks while retaining the reliability and quality of the public switched telephone network (PSTN). In this article, we'll discuss the technical challenges inherent in transporting TDM circuits over IP networks, how TDMoIP technology meets those challenges, and the standards shaping TDMoIP and related technologies.
Challenges of Transporting TDM
Conventional TDM networks are highly deterministic. A source device transmits one or more octets to a destination device via a dedicated-bandwidth channel every 125 μs. The circuit delay through a TDM network is predictably low and constant throughout the life of a connection. Timing is delivered along with the data, and the permitted variability (jitter and wander) of TDM clocks is tightly defined. In addition, the infrastructure supports a rich set of user features via a vast set of signaling protocols.
Packet-switched networks (PSNs), such as IP/multi-protocol label switching (MPLS) systems, are more efficient than TDM networks due to bandwidth sharing. However, this sharing leads to PSNs being inherently non-deterministic.
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