reshold (to 50 % of the previous one) significantly after congestion indications. This heavy speed reduction and the subsequent speed recovery, although quite fast, are called the slow start algorithm. TCP and Radio TCP is designed for high quality lines. As indicated before, however, the radio path might suffer from a low, unstable bandwidth, handovers, short periods of no connection, sometimes high BER and long, varying round trip delays (RTD). This does not fit TCP very well. BER causes packet loss. RTD is affected by buffering and serialization of data, propagation time and necessary retransmissions. The possible ways to retain a higher speed include cutting the RTD by using different TCP connections for the radio path and the rest of the path, replacing the retransmission mechanisms with a faster one, or making retransmissions only over the radio path. Alter- native retransmission methods require a mechanism at a lower level in the stack below TCP. Such a solution uses the radio link control (RLC) protocol at the link layer. How- ever, in the last case, TCP will experience delays when RLC retransmits, which might cause a congestion indication to TCP, invoking the slow start mechanism. Using different TCP connections between the terminating points has other drawbacks such as time for protocol translation and an impact on security (TCP is above IPsec in the stack, for example). With a delay from sending to reception of acknowledgement of up to 450 ms, which is not unrealistic with significant retransmissions at the radio path, the bandwidth-delay product for WCDMA operating at 384 kbit/s is 20 kbytes. At 64 kbit/s it is around Understanding Changing Telecommunications - Building a Successful Telecom Business 4 kbytes. This is the required number of outstanding bytes TCP needs to fully utilize the available bandwidth. A low bandwidth-delay product is the goal. TCP and High Speed Links As a result of research at the California Institute of Technology and other research units an alternative or at least a compleme