Computer Glossary of Terms - Page 2

Computer Glossary - Letters S through V

Computer Glossary

SAPs (service access points): represent internal software addresses in the sending or receiving computer

SAR (segmentation and reassembly): the process used to fragment and rebuild packets that allows them to be transported across asynchronous transfer mode (ATM)

SDH (synchronous digital hierarchy): international counterpart of SONET

SDRAM (synchronous dynamic random access memory): version of DRAM that allows for increased speed

SEAL (simple and efficient AAL): method of relaying ATM (asynchronous transfer mode) cells between ATM Layer and a higher layer

Section layer: layer of the OSI physical layer that creates frames, monitors the conditions of the transmission between the SONET equipment, and converts optical signals to and from electrical signals

Security routines: protect data and applications from unauthorized use, execution, or change

Semaphores: messages sent when a file is opened that prevent other users from opening the same file at the same time and compromising the integrity of the data

Serial port: handles data one bit at a time traveling sequentially across a single line from one device to the next

Server: a computer that provides services to the other workstations

Simplex transmission: the information always flows from the transmitter to one or more receivers with no provision for a return signal; like radio and TV broadcasts

SMLI (stateful multi-layer inspection): similar to application gateways; however, no proxy is used between the network and the Internet

SMLIS (stateful multilayer inspection servers): sophisticated firewalls that inspect each frame for suspicious communications

SMTP (simple mail transfer protocol): electronic mail service that allows a user to send or receive messages

SNA (systems network architecture): IBM’s mainframe network standards

SNMP (simple network management protocol):application layer protocol in the TCP/IP family; provides remote network management capabilities to a network administrator; implemented with centralized management stations that collect network information from agents throughout the network; can also send commands to the agents to alter the configuration or status of remote devices

SOCKS (an abbreviation of SOCKetS): protocol for handling TCP though a proxy server; library of software added to an individual application for secure communication through the firewall

SOCKS servers: specialized servers for prearranged communications through a firewall

TDM (time-division multiplexing): used in the T1 frame format; different channels are multiplexed by being assigned their own individual time slots

Threads: individual processes within a single application

Three-layer Network Model: shows network communications as a set of three conversations

Transmitter: source that generates the message or data

Transport layer: layer that is responsible for delivering information in sequence and to the correct end-user

Trap: SNMP protocol function used by the agent in a managed device to report important events or alarms

Topology: the physical (how the wires are laid out) and/or logical (how the wires work) arrangement of the devices on the network

UART (universal asynchronous receiver/transmitter): a computer component that handles asynchronous serial communication; pronounced U-art

UDP (user datagram protocol): connectionless, unreliable protocol that exchanges datagrams without acknowledgments or guaranteed delivery; requires error processing and retransmission by other protocols

USB (universal serial bus) port: designed to replace the RS-232 connection with one that can handle up to 127 devices; comes in 15 Mbps or 12 Mbps speed

USENET (USEr NETwork): Internet service that enables open forum discussions with people all over the world through newsgroups

User interface: how you interact with the computer

Utility routines: diagnostic, tracing, monitoring, and resource housekeeping functions

UTP (unshielded twisted-pair): the most common cable used in computer networking

VBR (variable bit rate): transmissions that are not time sensitive - the receiving computer can reconstruct the information regardless of how quickly or in what order the parts are received; also called “bursty” transmission

VCI (virtual channel identifier): identifies the virtual channel between ATM switch nodes

VoIP (Voice over Internet Protocol): routing of voice conversations over the Internet or through any other IP-based network; also called telephone, broadband phone

Volatile memory: chips that lose whatever information they are holding if power is interrupted

VPI (virtual path identifier): traces the virtual path, from endpoint-to-endpoint, through the ATM network