PDF of this tutorialWith the size and scope of packet networks approaching that of the PSTN, carriers have begun to seek ways to converge their voice and data traffic. Carriers are moving voice services to packet networks both to reduce internal costs and to provide more value-added and cost-effective services in an increasingly competitive environment. A recent study by Sprint Corporation found that data equipment was 70 percent less expensive than voice equipment, and data access lines were 60 to 80 percent cheaper than voice access lines. Maintenance of packet networks was 50 percent, while provisioning was 72 percent lower. However, consolidation of voice onto packet networks has, in the past, proven difficult. Just as the PSTN was not designed to carry data efficiently, data networks were not meant to accommodate voice applications or the value-added voice services that telephony users have come to expect. For example, the PSTN offers 99.9994-percent availability versus an average of 99.9 percent for data networks. Moreover, most packet networks utilize best-effort delivery techniques and pay little attention to ensuring the low delay and consistent delivery times required by voice applications. ATM networks offer intrinsic QoS capabilities for voice traffic, although few carriers were able to leverage them as a result of the lack of call signaling support (required to interwork with the SS7 network) in existing platforms. Yet ATM, with its installed base and voice-ready QoS, appears to be the best current method of quickly and cost-effectively migrating voice traffic from the PSTN to packet-based backbones.
