thin the set itself. Endpoints with authorization, encryption, QoS-aw speakers and microphones can be troubled by acoustic intelligent applications design for QoS echo. When an IP connection is inter-worked to the Transport layer Port-based access control, TCP rate circuit-switched network, it is necessary to cancel any control hybrid-induced echo that might be generated from a cir- Network layer Resource reservation, Type of Service cuit-switched endpoint. This cancellation should take bits, path controls, load balancing, place in the interworking device. Telephone users expect address-based access control, good conversational quality on a call. Only in the most protocol-based separation extreme cases (Earth to Moon) do they accept long Data link layer Frame prioritization (802.1p/Q), ATM delays without question. Frequent users of calls relayed Cell QoS, VLAN and VPN isolation, via satellite have some acceptance of long delays, and are logical port access control, path practiced in the required protocols, but most users are controls unwilling to accept such inconveniences on calls that are Physical layer Bit error correction, link diversity, path essentially "local." Although there is no specific break- controls, physical security, physical port down point, the generally accepted standard is that one- access way delays in excess of 150 ms or round-trip delays in excess of 300 ms are intolerable. Perhaps the most ob- vious contributor to latency is the audio packet propa- today's society without a telephone (even for calling gation delay across the network (although it is often not someone in the same office)? Imagine the inconvenience the major contributor). Propagation delays (including if the telephone system was frequently SO busy that you media access delays) can vary from a few milliseconds on could not even get a dial tone or if a telephone call sud- a LAN to hundreds of milliseconds and are strongly de- denly failed in the middle of a conversation? The same pendent on network loading and topology. The del