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segment
A physical portion of a network is referred to as a segment. A network is composed of one or more physical segments.
segmentation
The process of dividing a long data transmission into smaller chunks that lower layer processes can handle is referred to as segmentation. See reassembly.
Sequenced Packet Exchange (SPX)
SPX is Novell NetWare's proprietary Transport Layer protocol.
serial bus
An I/O bus that carries 1 bit at a time is referred to as a serial bus. See bus and parallel bus.
Serial Line Internet Protocol (SLIP)
SLIP is not an official Internet standard, but a de facto standard included in many implementations of TCP/IP. It was originally developed for use over dedicated circuits or leased lines, and therefore does not include provisions for establishing a connection over the telephone network.
server
A server is any program that provides a service to a client program. This term is often used to refer to the computer that hosts the server program; however, a server program may also run on a computer that normally functions as a client. See client.
Server Message Block (SMB)
SMB is an Application/Presentation Layer protocol used between clients and servers on a LAN. Functions requiring LAN support, such as retrieving files from a file server, are translated into SMB commands before they are sent to the remote device. Applications use SMB "calls" to perform file operations across a network.
Simple Mail Transfer Protocol (SMTP)
SMTP is a protocol and set of processes that use the protocol to transfer e-mail messages between user mailboxes.
simplex
See duplex.
source code
Source code refers to the programming instructions a programmer writes using a programming language. The source code of most applications and OSs is compiled into a machine language format that computers can use (but people cannot read or alter). The compiled version of a program cannot be edited; however, the original source code can be changed and recompiled.
stack
A stack is a group of protocols that work together to provide data communication. In a stack, each protocol uses the services of the protocol below it, and provides services to the protocol above it.
standard
Standards are the technical specifications and working methods necessary for different vendors' equipment to interoperate. Standards enhance efficiency and usability; however, they generally do not protect life or limb.
subnet
A subnet is a subdivision of a network, in which users are grouped logically based on their network address. Subnets are formed by routers, thus each subnet is a separate broadcast domain.
switch
A switch is a device that operates at the Data Link Layer of the OSI model, using hardware addresses to forward frames between ports. Like a bridge, a switch can connect LANs or LAN segments of the same media access type, such as two Token Ring segments, or different types, such as Ethernet and Token Ring. Unlike a bridge, a switch dedicates the entire media bandwidth, such as 10-Mbps Ethernet, to each port-to-port connection.
synchronous
Synchronous communication is data communication controlled by a microprocessor clock, so that signals are permitted to start and stop at particular times. To use synchronous communication, the clock settings of the sending and receiving systems must match.
Synchronous Data Link Control (SDLC)
See High-Level Data Link Control (HDLC).
Synchronous Optical Network (SONET)
SONET is an optical transmission standard that defines a signal hierarchy. The basic building block is the STS-1 51.84-Mbps signal, chosen to accommodate a T3 signal. The STS designation refers to the interface for electrical signals. The optical signal standards are correspondingly designated OC-1, OC-2, and so on.
Systems Network Architecture (SNA)
SNA is IBM's architecture for computer networking. It was designed for transaction processing in mission-critical applications, often involving a large number of "dumb" terminals communicating with a mainframe. Typical transactions perform inquiries and update information in a database. For example, a commercial bank might have a number of 3270-type display units and printers in each of hundreds of branch offices that are used to access a central database in the home office.
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