networks, such as Internet and other UNIX-based network systems, for the exchange of elec- tronic messages. SNA (Systems Network Architecture) (1) IBM's standardized relationship between Virtual Telecommunications Access Method (VTAM) and the NCP. (2) An architecture that spec- ifies how products connect and communicate with one another in a network. SNA is a design for total data communications system, encompassing every part of the communication network, from the user's application program at the central site to the terminal at a remote location. Glossary SNMP (Simple Network Management Protocol) SNMP (Simple Network Management Protocol) A standard low-level protocol monitor and manage nodes on a network. SNMP consists of agent software, which runs on the managed device, and manager software, which resides on a central system that polls the agents. SNMP is an alternative to CMIP. SNMPv2 (Simple Network Management Protocol version 2) A revision of SNMP that includes additional security features, the ability to transfer a large chunk of data at once, and the ability to communicate between SNMP management stations. SNR (signal-to-noise ratio) The relative power of a signal compared to the power of noise on a line, expressed in decibels. As the ratio decreases, it becomes more difficult to distinguish between information and interference. SOA (semiconductor optical amplifier) An optical amplifier that is built on a single chip. SOAs can be integrated into multifunction optical chips and can be less expensive than EDFAs. The disadvantage of SOAs is a higher signal-to-noise ratio. socket An interface to the transport layer of the OSI model that consists of a group of func- tions that can be called from a program written in C. The calls that make up sockets are system calls (i.e., they are direct calls to an operating system). Sockets permit an application program to access the services provided by TCP and UDP. SOFDMA (Scalable Orthogonal Frequency Division Multiple Access) A multicar- rier modulation technique in whi