tact and uses the NetWare IPX protocols as its delivery mechanism. SRTP (Secure Real-Time Transport Protocol) A security profile for RTP that adds confi- dentiality, message authentication, and replay protection to RTP. It provides a framework for encryption and message authentication of RTP and RTCP streams. S/S (Start/Stop) signaling A form of asynchronous communication line control that uses start elements and stop elements to control the transfer of data over a communication line. Each group of signals representing a character is preceded by a start signal and followed by a stop element. Glossary SS7 (Signaling System 7) SS7 (Signaling System 7) A group of telephony signaling protocols used in the PSTN to set up calls and provide services. SS7 is characterized by high-speed circuit switching and out-of- band signaling using SS7 nodes. The SS7 network sets up and tears down a call, handles all the routing decisions, and supports all telephony services, such as 800 numbers, call forwarding, caller ID, and local number portability. Because the signaling network is separate, a voice circuit is not tied up until a connection is made between two parties. SS7 gateway A device that allows an interface between circuit-switched networks (with their powerful SS7 infrastructure) and packet-switched networks for support of traditional telephony applications. SSL (Secure Sockets Layer) A commonly used protocol for managing the security of a message transmission on the Internet. SSP (service-switching point) A switch that originates or terminates a call. ST connector A type of connector used on optical fiber cable, using a twist and lock cou- pling similar to the BNC connector that is used with thinnet. star A network topology in which nodes are connected to a single central hub rather than each other, forming a star-shaped configuration. If the hub is an intelligent device that controls the nodes' access to the network, the star topology is called active; when the hub is only a wiring connector, it is called passive. stati