A cell-discard method has been developed for use in networks supporting TCP-over-ATM traffic with an unspecified bit rate. In this "concentrated cell discard" (CCD) method, when an ATM switch becomes congested, consecutive cells are discarded from the front of the buffer, and cell discarding is suspended for a specified period of time. This method prevents TCP timeouts, which are the main reason for the decreasing TCP throughput in today's TCP-over-ATM networks, and shortens the duration of the congestion by avoiding the long delay experienced with the TCP fast-retransmission algorithm before the sender's TCP receives duplicate acknowledgments. Even though CCD does not consider TCP packet size or boundaries, the throughput with CCD was found by computer simulation to actually be higher than with early packet discard.

This paper describes key technologies for implementing a large scale public voice telephony over ATM (VTOA) handling node system. VTOA is one of the most promising ATM applications. It allows network operating companies to provide a less expensive but relatively high quality telephone service, by employing voice data compression and the efficient transmission capability of AAL2. We propose a VTOA handling system architecture from several technical aspects, such as the optimum basis for the node, i.e., STM versus ATM, the appropriate network structure, and suitable signalling. These key points are evaluated from the standpoints of economy, ease of implementation, and extensibility. We believe that our proposed methods will be the basis for the construction of an efficient and cost-effective VTOA handling network.