In-depth Comparison of TDMoIP and CESoPSN

Although not strictly relevant to a comparison of the two protocols as they have developed, some knowledge of the original design goals of the two development teams involved will assist the reader in understanding the divergent decisions and trade-offs made by designers of each technology. TDMoIP was designed by RAD Data Communications, a company whose major expertise is in access networks, and was thus constructed to function even as an access method for enterprises or a means for campus users to converge networks. The RAD development team did not believe that incumbent carriers would immediately abandon their highly reliable and fully functional TDM networks in favor of IP or even MPLS ones. They did believe that enterprises and alternative service providers would strive to cut costs and to maximize the return on their investment in broadband data networks. In fact, the great majority of the 12,000 TDMoIP ports deployed to date are used by enterprises, campuses, and alternative service providers. From the practical point of view, this viewpoint led to the development of devices that handled a relatively small number of ports, from a single T1 or E1 trunk, up to 16 trunks. From the protocol point of view, this viewpoint led to a strong emphasis on proper handling of fractional T1 or E1, necessitating full exploitation of TDM structure. Since enterprise customers do not usually have high quality clock sources, TDMoIP designers went to great lengths in designing adaptive clock recovery techniques that enable conformance with international standards even over degraded networks. Becuase enterprise networks are often unreliable and overloaded, TDMoIP designers considered the careful handling of packet loss to be critical. Since enterprise customers often have simple PBXs, and some users even wish to directly connect analog phones, RAD designers were concerned with robust and efficient transport of TDM signaling. Finally, RAD’s installed base of circuit emulation systems operating over ATM networks led the TDMoIP design team to prefer protocols that easily interwork with ATM CES. It is not a secret that Axerra, the company that developed CESoPSN, was founded by R&D personnel who left RAD for this purpose. Their vision was to elevate TDMoIP applications to the carrier level, providing a solution for the ‘carrier’s carrier’. This also explains their cooperation with proponents of SONET/SDH over packet networks. Since the CESoPSN team focused on a different client, if is not surprising that they de-emphasized various aspects important in TDMoIP’s design, while emphasizing others. Carriers require very large systems handling large numbers of trunks, constraining processing power per input trunk