SA: Service Affecting
Service Affecting (SA) is a category of conditions that interrupt network traffic. On the other hand, non-service affecting refers to events that will not interrupt traffic.

SAC: Single-attached Concentrator
Single-attached Concentrator (SAC) is a FDDI or CDDI concentrator that connects to the network by being cascaded from the master port of another FDDI or CDDI concentrator.

Samba
Samba is an Open Source/Free Software suite that provides seamless file and print services to SMB/CIFS clients regardless which operating system -- Linux, Unix, IBM system 390, Open VMS or Windows -- it is based on. Samba can be run on multiple platforms including Microsoft Windows, UNIX, Linux, IBM System 390, OpenVMS, and other operating systems. Samba uses the TCP/IP protocol that is installed on the host server. When correctly configured, it allows that host to interact with a Microsoft Windows client or server as if it is a Windows file and print server. Samba is a software package that gives network administrators flexibility and freedom in terms of setup, configuration, and choice of systems and equipment.

Samba TNG
Samba TNG is a fork of Samba which provides file print and login services for various Microsoft Windows clients. It can integrate with a Windows Server domain, either as a Primary Domain Controller (PDC) or as a Domain Member. It can also be part of an Active Directory domain. Its Primary Domain Controller server functionality is rather complete, although due to lack of developer resources (and no funding at all), it has not been possible to keep Samba TNG completely up-to-date.

Sampling Rate
The sampling rate, also known as sample rate or sampling frequency, defines the number of samples per second taken from a continuous (analog) signal to make a discrete (digital) signal. It is measured in hertz (Hz). The inverse of the sampling frequency is the sampling period or sampling time, which is the time between samples.

SAN: Storage Area Network
Storage Area Network (SAN) is a high-speed network or subnetwork whose primary purpose is to transfer data between computer and storage systems. A storage device is a machine that contains nothing but a disk or disks for storing data. A SAN consists of a communication infrastructure, which provides physical connections; and a management layer, which organizes the connections, storage elements, and computer systems so that data transfer is secure and robust.

SAP: Service Access Point
Service Access Point (SAP) is a field defined by the IEEE 802.2 Logic Link Control (LLC) specification that is part of a LAN address specification. SAP includes two parts: destination service access point (DSAP) and source service access point (SSAP).

SAPI: Service Access Point Identifier
Service Access Point Identifier (SAPI), an Ethernet term, is an identifier given to a SAP (Service Access Point). The SAPI may identify the type of service, signaling, Data transfer, Management etc. required by the higher layer protocol.

SAR: Segmentation And Reassembly
Segmentation And Reassembly (SAR) is one of the two sublayers of the ATM Adaptation Layer (AAL), responsible for dividing (at the source) and reassembling (at the destination) the PDUs passed from the CS. The SAR sublayer takes the PDUs processed by the CS and, after dividing them into 48-byte pieces of payload data, passes them to the ATM layer for further processing.

SAS: Single Attachment Station
Single Attachment Station (SAS), also known as a Class B station, is a device attached only to the primary ring of an FDDI ring.

SAS: Statically Assigned Socket
Statically Assigned Socket(SAS) is a type of socket that is permanently reserved for use by a designated process. In an AppleTalk network, SASs are numbered 1 to 127; they are reserved for use by specific socket clients and for low-level built-in network services.

SB-ADPCM: Sub Band - Adaptive Differential Pulse Code Modulation
Sub Band - Adaptive Differential Pulse Code Modulation (SB-ADPCM) is an algorithm for compressing 7 KHz audio into 48, 56 or 64 KB/s channels. This technology is used in the specification G.722. SB-ADPCM is also the basis of another popular wideband coding scheme, APT-X.

SBus
SBus is a bus technology used in Sun SPARC-based workstations and servers. The SBus specification was adopted by the IEEE as a new bus standard (IEEE Std 1496-1993).

SC: Subscriber Connector
Subscriber Connector (SC) is a type of fiber optic connector used in 100BASE-FX fiber optic media systems.

Scan Line Fix Up
Scan Line Fix Up is a mechanism used for non-ECM (error correction mode) calls meant to eliminate fax failures caused by an excessive number of received page errors because of data loss. If data loss is detected, the data of the current scan line is discarded and replaced with the previous line or white space.

SCP: Service Control Point
Service Control Point (SCP) is an element of an SS7-based Intelligent Network that performs various service functions, such as number translation, call setup and teardown, and so on.

SCR: Sustainable Cell Rate
Sustainable Cell Rate(SRC) is an ATM parameter for traffic management. For Variable Bit Rate (VBR) connections, SCR determines the long-term average cell rate that can be transmitted.

SCTE: Serial Clock Transmit External
Serial Clock Transmit External (SCTE) is a timing signal that DTE echoes to DCE to maintain clocking. SCTE is designed to compensate for clock phase shift on long cables. When the DCE device uses SCTE instead of its internal clock to sample data from the DTE, it is better able to sample the data without error even if there is a phase shift in the cable.

SDCC: Section Data Communications Channel
Section Data Communications Channel (SDCC) is a SONET-embedded operations channel that is processed by each STE node in a network. It provides many data channels for maintenance and operations functions, such as orderwire, performance monitoring, and craft/OS data communication channel (DCN) extension.

SDSU: SMDS DSU
SMDS DSU is a type of Data Service Unit (DSU) for access to Switched Multimegabit Data Service (SMDS) via High-Speed Serial Interfaces (HSSIs) and other serial interfaces.

SDT: Standards Drafting Team
Standards Drafting Team (SDT) is an informal team formed by volunteers under a certain IETF working group to define a specific standard and draft the RFC and other documents.

SDU: Service Data Unit
Service Data Unit(SDU) is a unit of information from an upper-layer protocol that defines a service request to a lower-layer protocol.

SEAL: Simple And Efficient AAL
Simple And Efficient AAL(SEAL) is a scheme used by the ATM AAL5 in which the Segmentation And Reassembly (SAR) sublayer segments CS PDUs without adding additional fields.

SECAM
SECAM is an analog color television system first used in France, utilizing an 8 MHz-wide modulated signal. There are three varieties of SECAM: French SECAM (SECAM-L), used in France and its former colonies; SECAM-B/G, used in the Middle East, former East Germany and Greece; SECAM D/K, used in the Commonwealth of Independent States and Eastern Europe.

SECB: Severely Errored Cell Block
Severely Errored Cell Block (SECB), a term in the ATM ABR service, refers to a severely cell block outcome occurring when more than M errored cells, lost cells, or mis-inserted cell outcomes are observed in a received cell block.

SECBR: Severely Errored Cell Block Ratio
Severely Errored Cell Block Ratio (SECBR) is the ratio of severely errored cell blocks in a transmission in relation to the total cell blocks sent in a transmission associated with a given traffic load, orientation and distribution, as well as an integration period. i.e,
SECBR = Severely Errored Cell Blocks/Total Transmitted Cell Blocks
SECBR may cause the SUT to drop cells that may contain a portion of an IP datagram. This may cause IP and TCP packet loss.

Secondary Ring
Secondary Ring refers to one of the two rings making up an FDDI or CDDI ring. The secondary ring usually is reserved for use in the event of a failure of the primary ring

Section
Section, in networking, refers to a portion of a transmission facility, including terminating points between a terminal NE and a regenerator or two regenerators. A terminating point is the point after signal regeneration at which performance is monitored or can be monitored.

Section DCC: Section Data Communications Channel
Section Data Communications Channel (Section DCC or SDCC), a concept in Operational Support Services (OSS), is a 192-kbps data communications channel embedded in the section overhead for OAM&P traffic between two SONET network elements. It provides many data channels for maintenance and operations functions, such as orderwire, performance monitoring, and craft/OS data communication channel (DCN) extension.

Security Management
Security Management is one of five categories of network management defined by ISO for the management of OSI networks. Security management subsystems are responsible for controlling access to network resources.

Seed Router
Seed Router is router in an AppleTalk network that has the network number or cable range built into its port descriptor. The seed router defines the network number or cable range for other routers in that network segment and responds to configuration queries from non-seed routers on its connected AppleTalk network, allowing those routers to confirm or modify their configurations accordingly. Each AppleTalk network must have at least one seed router.

SEFS: Severely Errored Framing Second
Severely Errored Framing Second (SEFS) is a second with either one or more out-of-frame (OOF) defects or a detected AIS defect.

Segment
A segment in networking is a specially-configured subset of a larger network. A network segment is typically defined by devices controling the flow of packets into and out of the segment, including routers, switches, hubs, bridges. The purposes of network segmentation are to physically separate related computers into groups for increasing network performance and security. In Ethernet networks, for example, computers send broadcast packets only to computers within the same segment.

Selective Repeat ARQ
Selective Repeat ARQ is a specific instance of the Automatic Repeat-reQuest (ARQ) Protocol, in which the sending process continues to send a number of frames specified by a window size even after a frame loss. Unlike Go-Back-N ARQ, the receiving process will continue to accept and acknowledge frames sent after an initial error.

Selector
Selector, a concept in the OSI network, is an identifier of octet string used by an OSI entity to distinguish among multiple Service Access Point (SAP) at which it provides services to the layer above.

Sensor Network
A sensor network is a computer network of many, spacially distributed devices using sensors to monitor conditions at different locations, such as temperature, sound, vibration, pressure, motion or pollutants. Usually these devices are small and inexpensive, so that they can be produced and deployed in large numbers, and so their resources in terms of energy, memory, computational speed and bandwidth are severely constrained. Each device is equipped with a radio transceiver, a small microcontroller, and an energy source, usually a battery. The devices use each other to transport data to a monitoring computer.

Serial Transmission
Serial Transmission is a method of data transmission in which the bits of a data character are transmitted sequentially over a single channel.

Server Address
A server address is a number or string of characters uniquely identifying an interface to a networked computer that provides one or more services. A server address can be a numeric IP address on private networks or on the Internet, although human-friendly names consisting of alphanumeric characters can also be given. The human-friendly names are then converted into the numeric addresses that computers understand by other servers dedicated to that purpose called "DNS servers" (DNS:Domain Naming System). Naturally, a DNS server cannot have an alphanumeric address.

Server Socket
A server socket is an computer communications end point for new incoming connections. The server socket will accept incoming connections, handle all lower-level network traffic to finalize the incoming connection and then spawn a new connection that can be used to read from or write to, depending on the code. The server socket itself will still be available to accept other incoming connections.

Service Class
Service Class, a term used in Service Level Agreement (SLA) and Quality of Service (QoS), refers to a collection of service types/parameters required for a specific service offered. Each service class includes the attributes and values that define the type or quality of service associated with a given class. For example, data connectivity is a service class with the data-bandwidth as a service type.

Service Level
Service Level, a term used in Service Level Agreement (SLA) and Quality of Service (QoS), refers to various levels and qualities of services defined for each service type under a service class. For example, the service type called data-bandwidth might have service levels (a specific value of bandwidth) defined for VOIP, data communication, and downloads.

Service Package
Service Package is a service offering with certain Quality of Service (QoS) promises that a service provider offers to subscribers. A service class is selected for each service package, defining which service types make up the service package.

Service Point
Service Point is the interface between non-SNA devices and IBM Tivoli NetView that sends alerts from equipment unknown to the SNA environment.

Service Tuple
Service Tuple refers to a service type and level pair. For example, the service tuple data-bandwidth=45 Mbps consists of the service type data-bandwidth and the service level 45 Mbps.

Service Type
Service Type is a component of a service package that service providers offer to subscribers. For example, bandwidth might be a service type defined for a subscriber, indicating the minimum or maximum bandwidth the subscriber can use. One or more service levels is defined for each service type.

SES: Severely Errored Second
Severely Errored Second (SES), a measure in a T1 line, is the one-second-time interval during which the bit out-of-frame (OOF) error ratio is greater than a specified limit, and transmission performance is significantly degraded.

Session
Session, in general computer networking, refers to a virtual connection between two hosts by which network traffic is passed. In SNA, session a logical connection enabling two NAUs to communicate.

Session Layer
Session Layer is the layer 5 of the OSI 7 layers reference model. This layer establishes, manages, and terminates sessions between applications and manages the data exchange between presentation layer entities.

SETI: Search for ExtraTerrestrial Intelligence
Search for ExtraTerrestrial Intelligence (SETI) is an organized efforts by humans to detect intelligent aliens. A number of efforts with "SETI" in the project's name have been organized, including projects funded by the United States Government. The generic approach of SETI projects is to survey the sky to detect the existence of transmissions from a civilization on a distant planet - an approach widely endorsed by the scientific community as hard science.

SETI@home
Search for ExtraTerrestrial Intelligence(SETI) at Home (SETI@home) is a peer-to-peer computing project on the Internet that takes advantage of unused processing time in users' computers to analyze radio telescope data. The goal of SETI@home, which is administered by the University of California at Berkeley, is to detect intelligent life outside Earth. SETI@home searches for possible evidence of radio transmissions from extraterrestrial intelligence using data from the Arecibo radio telescope.

S-Frame: Supervisory Frame
Supervisory Frame (S-Frame) is one of three SDLC frame formats. The other two frames are information and unnumbered. Supervisory frames carry control parameters relative to the sequenced data transfer.

SG: Signaling Gateway
Signaling Gateway(SG) is a gateway that processes only signaling traffic (no bearer traffic.) For example, a gateway that terminates SS7 A-links is a signaling gateway.

Shadowing
Shadowing in computer networking is a form of replication in which well-defined units of information are copied to several other storage systems.

Shared Cable Modem
Shared Cable Modem refers to a single cable modem servicing multiple Customer Premise Equipments (CPEs). Shared Cable Modem is associated with multiple subscriber/accounts and is administered in the User Registrar Admin UI through a neighborhood.

SHDSL: Symmetric High-Bitrate Digital Subscriber Loop
Symmetric High-Bitrate Digital Subscriber Loop (SHDSL), a DSL variation, can transport data symmetrically at data rates from 192 Kbps to 2,320 Kbps. SHDSL utilizes a single copper wire pair, making it an affordable DSL option attractive to small businesses.

Shielded Cable
Shielded Cable has a layer of shielded insulation around the cable to reduce Electromagnetic Interference (EMI).

Ships In The Night Mode
Ships In The Night Mode refers to the capability to support both MPLS functions and ATM Forum protocols on the same physical interface, or on the same router or switch platform. In this mode, the two protocol stacks operate independently.

Shortest-path Routing
Shortest-path Routing is a routing method that minimizes distance or path cost through the application of an algorithm.

SID: Service ID
Service ID (SID) is a number that defines (at the MAC sublayer) a particular mapping between a cable modem (CM) and the Cable Modem Termination System (CMTS). The SID is used for the purpose of upstream bandwidth allocation and class-of-service management.

Signal Path
Signal Path is the route of a signal channel that carries signaling data.

Signal Unit Error Rate Monitor
Signal Unit Error Rate Monitor is an SS7 MTP 2 function that provides monitoring of signal unit events.

Signaling
Signalling refers to the process of setting-up communications links between two systems such as between a user system and a service provider system. Signaling is used in both traditional telephony and in packet-based communications. SS7/C7 is the most famous signaling system in telephony, while in data communication, the various VOIP signaling methods such as SIP and H.323 are introduced.

Signaling Gateway
Signaling Gateway (SG) is a gateway that processes only signaling traffic (no bearer traffic.) For example, a gateway that terminates SS7 A-links is a signaling gateway. In a VOIP nework, signaling Gateway is a device that sends and receives PSTN signalling at the edge of IP/ATM network. It backhauls the signalling to a Media Gateway Controller. The Signaling Gateway function may be co-resident with the Media Gateway function to process signaling associated with line or trunk terminations controlled by the Media Gateway.

Signaling Packet
Signaling Packet, in an ATM network, is generated by an ATM-connected device that wants to establish a connection with another such device. The signaling packet contains the ATM NSAP address of the desired ATM endpoint, as well as any QoS parameters required for the connection. If the endpoint can support the desired QoS, it responds with an accept message, and the connection is opened.

Signaling Point
Signaling Point is a node in a signaling network (such as SS7/C7 signaling network) that either originates and receives signaling messages, or transfers signaling messages from one signaling point to another.

Silicon switching
Silicon switching is a type of switching developed by Cisco Systems based on their Silicon Switch Engine (SSE), which provides high-speed, dedicated packet switching.

Simplex
Simplex refers to the capability for transmission in only one direction between a sending station and a receiving station. Broadcast television is an example of a simplex technology.

Single-vendor Network
Single-vendor Network refers to using equipment on an entire network from only one vendor. Single-vendor networks rarely suffer compatibility problems.

SIPRNet: Secret Internet Protocol Router Network
Secret Internet Protocol Router Network(SIPRNet) is a system of interconnected computer networks used by the U.S. Department of Defense to transmit classified information (up to and including information classified SECRET//NOFORN) by packet switching over the TCP/IP protocols in a "completely secure" environment. In other words, the SIPRNet is the DoDs classified version of the civilian Internet and together with its counterpart, the TOP SECRET/SCI Joint Worldwide Intelligence Communications System, JWICS, are revolutionizing the way classified information is disseminated to consumers.

SLA: Service Level Agreement
A Service Level Agreement (SLA) is a contract between a network Service Provider and a customer, which defines the terms of types of services, quality of services and the customer payment. A typical SLA includes the following items:
The minimum bandwidth allocated to the customer
The burst bandwidth for the customer
The number of users that can be served simultaneously
The schedule for notification in advance of network changes that may affect users
Dial-in access availability
Usage statistics that will be provided
The minimum network availability from the service provider, such as 99.9% up time or a maximum of down time of 1 minute per day.
The priority of the traffic per type of the customer
Customer technique support and services
Penalty provisions if the Service Provider does not meet the SLA

SLAC: Stanford Linear Accelerator Center
Stanford Linear Accelerator Center (SLAC) is one of the world's leading research laboratories, established in 1962 at Stanford University. SLAC's mission is to design, construct and operate state-of-the-art electron accelerators and related experimental facilities for use in high-energy physics and synchrotron radiation research.

Sliding Window Flow Control
Sliding Window Flow Control is a method of flow control in which a receiver gives the transmitter permission to transmit data until a window is full. When the window is full, the transmitter must stop transmitting until the receiver advertises a larger window. TCP, other transport protocols, and several data link layer protocols use this method of flow control.

Slot Time
Slot Time is the time required for an electronic pulse to travel the length of the maximum theoretical distance between two nodes. In CSMA/CD networks such as Ethernet, NICs wait a minimum of the slot time (which should be a constant, NOT dependent on the individual network -- i.e., it is a standard across all CSMA/CD networks that use a common NIC) before transmitting, allowing time (the maximum theoretical time - slot time) for the pulse to reach the NIC that intends to send.

Slotted Ring
Slotted Ring is a LAN architecture based on a ring topology in which the ring is divided into slots that circulate continuously. Slots can be either empty or full, and transmissions must start at the beginning of a slot.

SLSM: Static-length Subnet Mask
Static-length Subnet Mask (SLSM) refers to the usage of the same subnet mask for all subnets of a single Class A, B, or C network.

SMAC: Source MAC
Source MAC (SMAC) refers to the MAC address specified in the Source Address field of a packet.

SMF: Single-mode Fiber
Single-mode Fiber (SM Fiber or SMB), also called monomode fiber, is a fiber-optic cable with a narrow core that allows light to enter only at a single angle. Such cabling has a higher bandwidth than multimode fiber, but requires a light source with a narrow spectral width (for example, a laser).

SMI: Structure of Management Information
Structure of Management Information (SMI) is part of the Sinple Network Management Protocol (SNMP) which specifies rules used to define managed objects in the SNMP MIB. The SMI is divided into three parts: module definitions, object definitions, and trap definitions.

SMT: Station Management
Station Management(SMT) is an ANSI FDDI specification that defines how ring stations are managed.

SMUX: SNMP Multiplexing
SNMP multiplexing (SMUX) is a computer networking protocol used in implementing the Simple Network Management Protocol. It defines communications between the SNMP Agent and other processes.

SNA: System Network Architeture
The Systems Network Architecture (SNA) defined by IBM is one of the most popular network architecture models. Although now considered as a legacy networking model, SNA is still widely deployed. SNA was designed around the host-to-terminal communication model that IBM's mainframes use.

SNADS: SNA Distribution Services
SNA Distribution Services (SNADS), one of three SNA transaction services, consists of a set of SNA transaction programs that interconnect and cooperate to provide asynchronous distribution of information between end users.

SNI: SNA Network Interconnection
SNA Network Interconnection(SNI) is an IBM gateway connecting multiple SNA networks.

Sniffer
"Sniffer" as a product was originally created by Network General that monitors and analyses data traveling over a network. "Sniffer" actually is a trade marked product brand of Network General. However, due to its popularity among the IT professionals, the word "Sniffer" is widely used as a name for any products that are doing network traffic capturing and analysis.

SNMP Agent
Simple Network Management (SNMP) architecture assumes the existence of managers and agents. SNMP agent is a software module in a managed network device responsible for maintaining local management information and delivering that information to an SNMP manager via SNMP protocols. A management information exchange can be initiated by the manager (via polling) or by the agent (via a trap). Agents function as collection devices that gather and send data about the managed resource in response to a request from a manager.

SNMP Agent Extensibility
SNMP Agent Extensibility is an IETF working group with a mission to define standards-track technology for SNMP Agent Extensibility, or AgentX. The resulting technology specification will allow independently developed sub-agents to communicate with a master-agent running on an Internet device.

SNMP Communities
SNMP Communities is the authentication scheme that enables an intelligent network device to validate SNMP requests.

SNMP Group
SNMP group refers to a collection of objects providing basic instrumentation and control of an SNMP entity.

SNMP Manager
Simple Network Management (SNMP) architecture assumes the existence of managers and agents. A SNMP Manager, also known as SNMP Console, is a software module responsible for managing part or all of the configuration on behalf of network management applications and users. An agent is a software module in a managed device responsible for maintaining local management information and delivering that information to a manager via SNMP. A management information exchange can be initiated by the manager (via polling) or by the agent (via a trap).

SNMP MIB: SNMP Management Information Base
SNMP Management Information Base (SNMP MIB) is a database used to store the statistical data defined in the SNMP systems. It comprises a collection of objects in a (virtual) database used to manage entities (such as routers and switches) in a network. Objects in the MIB are defined using a subset of Abstract Syntax Notation One (ASN.1) called "Structure of Management Information Version 2 (SMIv2). MIB-I refers to the initial MIB definition; MIB-II refers to the later definition. SNMPv2 includes MIB-II and adds some new objects.

SNMP Objects
SNMP Objects refers to the data components in the SNMP Management Information Base (MIB) defined as part of SNMP. Objects in the MIB are defined using a subset of Abstract Syntax Notation One (ASN.1) called "Structure of Management Information Version 2 (SMIv2).

SNMP OID
SNMP Object Identifier (OID) is the value that is defined in specific MIB modules to identify a specific SNMP Object in the MIB database. SNMP OID is a period-delimited sequence of numbers of the form a.b.c...x.y.z. It is a unique identifier for an item of information that is part of an MIB. Typically OIDs can have names associated with them. OIDs are hierarchical in nature. Hence 1.2.3 comes before 1.3 but after 1.2.

SNMP Trap
SNMP traps are the messages sent by an SNMP agent to a manager that enable an agent to notify the management station of significant events by way of an unsolicited SNMP message. The idea behind the SNMP trap-directed notification is that: if a manager is responsible for a large number of devices, and each device has a large number of objects, it is impractical for him to poll or request information from every object on every device. The solution is for each agent on the managed device to notify the manager without solicitation. It does this by sending a message known as a trap of the event. After receiving the event, the manager displays it and may choose to take an action based on the event. For instance, the manager can poll the agent directly, or poll other associated device agents to get a better understanding of the event.

SNPA: Subnetwork Point of Attachment
Subnetwork Point of Attachment(SNPA) is a data link layer address (such as an Ethernet address, X.25 address, or Frame Relay DLCI address). SNPA addresses are used to configure a Connectionless Network Service (CLNS) route for an interface.

SNRM: Set Normal Response
Set Normal Response Mode(SNRM), one of commands in the HDLC protocol, places the secondary station into NRM. NRM does not allow the secondary station to send any unsolicited frames. Hence the primary station has control of the link.

SNRME: Set Normal Response Mode Extended
Set Normal Response Mode Extended(SNRME), one of commands in the HDLC protocol, increases the size of the control field to 2 octets instead of one in NRM. This is used for extended sequencing.

Socket
A socket represents a single connection between two network applications. Sockets are the combination of IP address plus corresponding TCP/UDP port numbers. Every paired of connected socket has a source IP/port and a destination IP/port. Users of Internet applications are normally aware of all except the local port number, this is allocated when connection is established and is almost entirely arbitrary unlike the well-known port numbers associated with popular applications. In AppleTalk network, socket functions in the same way except the detailed definition is different. Every application that uses AppleTalk Datagram Delivery Protocol (DDP) to transfer data must send or receive that data through a socket. The use of sockets allows DDP to determine for which application a packet is intended.

Socket Client
Socket Client is a software process or function implemented in an AppleTalk network node. An application that is associated with a specific socket through Datagram Delivery Protocol (DDP) is the client of that socket, or a socket client.

Socket Listener
Socket Listener in AppleTak network is the software provided by a socket client to receive datagrams addressed to the socket. Every socket-client application that uses Datagram Delivery Protocol (DDP) directly to transfer data must have associated with it a socket listener that receives datagrams addressed to the socket on behalf of that socket's client application.

Socket Number
Socket Number in AppleTalk network, is an 8-bit number that identifies a socket. A maximum of 254 different socket numbers can be assigned in an AppleTalk node.

Socket Pair
Socket Pair is a way to uniquely specify a connection in the TCP/IP network, i.e., source IP address, source port, destination IP address, destination port.

Soft phone
Soft phone is software that simulates a real phone and runs on a general purpose computer, rather than a dedicated device. It is usually used with a headset connected to the sound card of the PC or USB phone. Soft phone is an important component in a VOIP network.

Software flow control
Software flow control, also known as XOFF/XON flow control, refers to a flow control technique in a modem. With software flow control, when a modem needs to tell the other to pause, it sends a certain character, usually Control-S. When it is ready to resume, it sends a different character, such as Control-Q. Software flow control's only advantage is that it can use a serial cable with only three wires. Since software flow control regulates transmissions by sending certain characters, line noise could generate the character commanding a pause, thus hanging the transfer until the proper character (such as Control-Q) is sent. Also, binary files must never be sent using software flow control, as binary files can contain the control characters. Hardware, or RTS/CTS, flow control uses wires in the modem cable or, in the case of internal modems, hardware in the modem. This is faster and much more reliable than software flow control.

Software handshake
Software handshake is a type of computer handshake to indicate to each other when to start or stop sending data. In Software handshake, the handshaking signals between two computers which are carried by way of extra characters inserted into the data stream; for example, Control-Q (ASCII character 17) for start and Control-S (ASCII character 19) for stop, while a hardware handshake communicates the same information by voltage levels or pulses on wires.

Software handshaking
Software handshaking refers to the process of the transmission of extra data on a channel in order to control the device sending data in the other direction on that channel. For an EIA-232 connection, this means sending Control-S and Control-Q characters to stop and start transmission.

Software Generic
Software Generic refers to the system operating software release for general availability, for example, SUN Solaris 10 etc.

SOHO Network
A SOHO network is a Small office/home office local area network. SOHO networks generally are confined to a single room. Such networks generally use a small Ethernet switch or hub and cat 5 cabling, or a Wi-Fi wireless network.Generally SOHO networks are used to share files and other information as well as to share an Internet access connection. A SOHO network may also have a server which needs to be accessed.

SOHO: Small office, home office
Small office, home office (SOHO) refers to a specific group of people who work from home or very small companies. A large number of businesses fall under this category, having anywhere from 1 - 10 employees.

SONET Multiplexing
SONET multiplexing is the process of transfering low speed traffic to high speed traffic in a SONET network. It involves generation of the STS-1 signal for each tributary. The STS-1 signal contains the payload traffic plus transport overhead allowing for a variety of tributary types to be accommodated. An STS-n signal is created by interleaving bytes from n STS-1 signals that are mutually synchronized, so there is no timing adjustment required when going to higher level multiplex formats. Drop Module Interfaces (DMI) provide SONET/SDH formatting and multiplexing/demultiplexing of the STS-1 signal; ports for low-speed DS1/E1, DS3/E3, STS-1, OC-1 lines; and termination and framing services for tributaries.

Source Address
Source Address is the address of a network device that is sending data.

Source Node
A source node is the originating node of an end-to-end channel, path or session depending on the specific protocols used to establish such channel, path or session.

Source Port
Source Port refers to the the TCP/UDP port that a packet is sent from, while the destination port is the TCP/UDP port that a packet is received.

Source routing
Source routing is a method for specifying ahead of time the route a packet should take when traversing a routed internetwork.

SPAG: Standards Promotion and Application Group
Standards Promotion and Application Group(SPAG) is a group of European OSI manufacturers that chooses option subsets and publishes these in the "Guide to the Use of Standards" (GUS).

SPAN: Switched Port Analyzer
Switched Port Analyzer(SPAN) is a feature of many managed switches that extends the monitoring capabilities of existing network analyzers into a switched Ethernet environment. SPAN mirrors the traffic at one switched segment onto a predefined SPAN port. A network analyzer attached to the SPAN port can monitor traffic from any of the other switched ports.

Spanning Explorer Packet
Spanning Explorer Packet, also known as a limited-route explorer packet or a single-route explorer packet, is the a type of packet that follows a statically configured spanning tree when looking for paths in a Source-Route Bridging (SRB) network.

Spanning Tree
In the mathematical field of graph theory, a spanning tree of a connected, undirected graph is a tree composed of all the vertices and some (or perhaps all) of the edges of that graph. That is, every vertex is connected to the tree, but no cycles (or loops) are formed. In networking, Spanning tree is used as a type of loop-free subset of a network topology.

Spanning-tree Algorithm
Spanning-tree Algorithm is an algorithm used by spanning tree protocol to determine the best way to build a network based on spanning tree topology to avoid bridge loops (multiple paths linking one segment to another, resulting in an infinite loop situation). The algorithm is responsible for a bridge using only the most efficient path when faced with multiple paths. If the best path fails, the algorithm recalculates the network and finds the next best route.

SPE: Synchronous Payload Envelope
Synchronous Payload Envelope(SPE) is the payload carrying portion of the Synchronous Transport Signal (STS) in SONET. The SPE is used to transport a tributary signal across the synchronous network. In most cases, this signal is assembled at the point of entry to the synchronous network and is disassembled at the point of exit from the synchronous network. Within the synchronous network, the SPE is passed on intact between NEs on its route through the network.

Speed Matching
Speed Matching is a feature that provides sufficient buffering capability in a destination device to allow a high-speed source to transmit data at its maximum rate, even if the destination device is a lower-speed device.

SPF: Shortest Path First
Shortest Path First (SPF) is a routing algorithm that iterates on length of path to determine a shortest-path spanning tree. SPF is commonly used in link-state routing algorithms. It is sometimes called Dijkstra's algorithm.

Split-horizon Updates
Split-horizon Updates or Split Horizon is a routing technique in which information about routes is prevented from exiting the router interface through which that information was received. Split-horizon updates are useful in preventing routing loops.

SPNNI connection
SPNNI connection is a Cisco Proprietary Network to Network Interface for a Frame Relay connection between two VNSs in different areas or domains. The SPNNI connection gets its name from the proprietary Network-to-Network Interface protocol that operates over this connection.

Spooler
Spooler is an application that manages requests or jobs submitted to it for execution. Spoolers process the submitted requests in an orderly fashion from a queue. A print spooler is a common example of a spooler.

SQE: Signal Quality Error
Signal Quality Error (SQE), also called heartbeat, is designed to fix the problem in earlier versions of Ethernet where a host does not know if a transceiver is connected.

SR/TLB: Source-route Translational Bridging
Source-route Translational Bridging (SR/TLB) is a method of bridging where source-route stations can communicate with transparent bridge stations with the help of an intermediate bridge that translates between the two-bridge protocols.

SR: Short Reach
Short Reach (SR) refers to the distance specification for optical systems that operate effectively up to 3 km (1.8 mi).

SRB: Source-Route Bridging
Source Routing Bridging (SRB) is a method of bridging originated by IBM and popular in Token Ring networks. In an SRB network, the entire route to a destination is predetermined; in real time, prior to the sending of data to the destination. SRBs store and forward the frames as indicated by the route appearing in the appropriate frame field. Since its initial proposal, IBM has offered a new bridging standard: the source-route transparent (SRT) bridging solution. Although SRT bridging has achieved support, SRBs are still widely deployed.

SRT: Source-route Transparent Bridging
Source-route Transparent Bridging (SRT), originally introduced by IBM, is a bridging scheme that merges the two most prevalent bridging strategies: SRB and transparent bridging. Source routing transparent (SRT) bridging is standardized in Section 9 of the IEEE 802.2 standard. It allows source routing and transparent bridging to coexist on the same bridged network by using source routing with hosts that support it and transparent bridging otherwise.

SSAP: Source Service Access Point
Source Service Access Point(SSAP) is part of the Service Access Point (SAP) in the 802.2 LLC protocol that a network node designate in the Source field of a packet. The other part in the SAP is Destination Service Access Point DSAP.

SSCP: System Services Control Points
System Services Control Points(SSCP) are the management and control systems within an SNA network for managing network configuration, coordinating network operator and problem determination requests, and providing directory services and other session services for network end users

SSCP-PU Session
System Services Control Points(SSCP) Physical Unit (PU) session is used by SNA to allow an SSCP to manage the resources of a node through the PU. SSCPs can send requests to, and receive replies from, individual nodes in order to control the network configuration.

SSCS: Service Specific Convergence Sublayer
Service Specific Convergence Sublayer(SSCS) is one of the two sublayers of any ATM Adaptation Layer (AAL). SSCS, which is service dependent, offers assured data transmission. The SSCS can be null as well, in classical IP over ATM or LAN emulation implementations.

SSD Server: Service Selection Dashboard Server
Service Selection Dashboard (SSD) Server is a customizable Web-based application that works with the Service Selection Gateway (SSG) to allow end customers to login to and disconnect from proxy and passthrough services through a standard Web browser. After the customer logs in to the network of the service provider, an HTML Dashboard is populated with the services authorized for that user.

SSE: Silicon Switching Engine
Silicon Switching Engine(SSE) is a routing and switching mechanism that compares the data link or network layer header of an incoming packet to a silicon-switching cache, determines the appropriate action (routing or bridging), and forwards the packet to the proper interface. The SSE is encoded directly in the hardware of the SSP (Silicon Switch Processor). It therefore can perform switching independently of the system processor, making the execution of routing decisions much quicker than if they were encoded in software.

SSG: Service Selection Gateway
Service Selection Gateway(SSG) is a gateway that offers service providers a means for menu-based service selection. End users can select services from the Dashboard menu, and the SSG can set up and tear down proxy and passthrough network connections based on a selection of a user. The SSG accounts for the services selected so that service providers can bill for individual services.

SSP : Silicon Switch Processor
Silicon Switch Processor(SSP) is a high-performance silicon switch for some Cisco routers that provides distributed processing and control for interface processors. The SSP leverages the high-speed switching and routing capabilities of the Silicon Switch Engine (SSE) to increase aggregate router performance dramatically, minimizing performance bottlenecks at the interface points between the router and a high-speed backbone.

SSP: System Switch Processor
System Switch Processor(SSP) is a card that acts as an Ethernet switch and passes data between all system cards and to any other switches connected to the system.

Standby Monitor
Standby Monitor is a device placed in standby mode on a Token Ring network in case an active monitor fails.

Star Network
Star network refers to a network in which network nodes are connected to a central node, which rebroadcasts all transmissions received from any peripheral node to all peripheral nodes on the network, including the originating node. All peripheral nodes may thus communicate with all others by transmitting to, and receiving from, the central node only.

Star Topology
Star topology is one of the most common computer network topologies. The network nodes are connected to a central node, which rebroadcasts all transmissions received from any peripheral node to all peripheral nodes on the network, including the originating node. All peripheral nodes may thus communicate with all others by transmitting to, and receiving from, the central node only.

StarLAN
StarLAN was the first implementation of Ethernet computer networking on twisted pair wiring. Developed in the mid-1980s by members of the IEEE 802.3 standards committee, StarLAN ran at a speed of 1Mbit/s. This version of the standard was known as 1BASE5. It was adopted by other networking vendors such as Hewlett-Packard and Ungermann-Bass.

Startup Range
Startup Range is the range of values (from 65280 to 65534) from which an AppleTalk node selects the network number part of its provisional address if it has not saved another network number.

Static Route
Static Route refers to the route that is explicitly configured and entered into the routing table. Static routes take precedence over routes chosen by dynamic routing protocols.

Statistical Multiplexing
Statistical Multiplexing is a technique in which information from multiple logical channels can be transmitted across a single physical channel. Statistical multiplexing dynamically allocates bandwidth only to active input channels, making better use of available bandwidth and allowing more devices to be connected than with other multiplexing techniques. Also referred to as statistical time-division multiplexing or stat mux.

Stop-and-wait ARQ
Stop-and-wait ARQ is one kind of Automatic Repeat-reQuest (ARQ) method in which the communication is done one frame at time. After each frame the sender waits for ACK (acknowledgement) signal and doesn't send any further frames until it is received. If the received frame is damaged or lost, the receiver discards it and does not send an ACK. If a certain time, known as the timeout, passes without ACK, the sender sends the frame again.

Store And Forward Switching
Store And Forward Switching refers to a switching technique in which frames are completely processed before being forwarded out the appropriate port. This processing includes calculating the Cyclic Redundancy Check (CRC) and checking the destination address. In addition, frames must be temporarily stored until network resources are available to forward the message.

Store-and-Forward Switch
Store-and-forward switch refers to a switching device that stores a complete incoming data packet before it is sent out. Such switches are used when incoming and outgoing speeds differ or as a security measure.

Streaming
Streaming is a technique for transferring data such that it can be processed as a steady and continuous stream. Streaming technologies are widely used in transmiting large multimedia (voice, video and data) files quickly. With streaming, the client browser or plug-in can start displaying the multimedia data before the entire file has been transmitted.

Store And Forward
Store And Forward refers to a switching function whereby a message is transmitted to some intermediate relay point and temporarily stored before forwarding to the next relay point.

Store And Forward Packet Switching
Store And Forward Packet Switching refers to a switching technique in which frames are completely processed before being forwarded out the appropriate port. This processing includes calculating the Cyclic Redundancy Check (CRC) and checking the destination address. In addition, frames must be temporarily stored until network resources are available to forward the message.

Stream-oriented
Stream-oriented refers to a type of transport service that allows its client to send data in a continuous stream. The transport service guarantees that all data will be delivered to the other end in the same order as sent and without duplicates.

Stub Area
Stub Area a concept in the Open Shortest Path First (OSPF) network, refers to an area that carries a default route, intra-area routes, and interarea routes, but does not carry external routes. Virtual links cannot be configured across a stub area, and they cannot contain an Autonomous System Boundary Router (ASBR).

Stub Network
Stub Network refers to the network that has only a single connection to a router. A stub network may meet one or more of the following criteria: 1) A single OSPF area with no external routes (though it may have interarea and/or intra-area routes); 2) A single LAN which never carries packets between two remote hosts; all traffic is to and/or from local hosts (it may or may not be multiply-connected; but multiple routers on a stub network don't route to one another, they will only route packets into the LAN if it's destined for the LAN, and out from the LAN if it originated on the LAN); or 3) A network that is only accessible by one path.

STUN: Serial Tunnel
Serial Tunnel(STUN), a feature in Cisco routers, allowing two SDLC- or HDLC-compliant devices to connect to one another through an arbitrary multiprotocol topology (using Cisco routers) rather than through a direct serial link. STUN encapsulates SDLC frames in either the Transmission Control Protocol/Internet Protocol (TCP/IP) or the HDLC protocol. STUN provides a straight passthrough of all SDLC traffic (including control frames, such as Receiver Ready) end-to-end between Systems Network Architecture (SNA) devices.

Subarea
Subarea is a portion of an SNA network that consists of a subarea node and any attached links and peripheral nodes.

Subarea Node
Subarea Node is an SNA communication controller or host that handles complete network addresses.

Subchannel
Subchannel is a broadband terminology, that refers to a frequency-based subdivision creating a separate communications channel.

Subdomain
A subdomain, a term in the Domain Name System (DNS) hierarchy, is a domain that is part of a larger domain. A DNS hierarchy consists of the root-level domain at the top, underneath which are the top-level domains, followed by second-level domains and finally subdomains. Subdomains are separated by dots "." and are read from left to right, in descending specificity. Each consecutive subdomain contains all previous subdomains, and is contained by any subsequent subdomains. All subdomains are contained by the second-level domain, which is in turn contained by its top level domain. For example, domainname.com is a top level domain, subdomain.domainname.com is a subdomain.

Subinterface
Subinterface is one of the virtual interfaces on a single physical interface.

Subnet Address
Subnet Address is a portion of an IP address that is specified as the subnetwork by the subnet mask.

Subnet Broadcast Address
The subnet broadcast address is the address formed by setting all the host bits to 1 for a nonclassful address.

Subnet Mask
A subnet mask, also known as an address mask, is used to determine the number of bits used for the subnet and host portions of the address. The mask is a 32-bit value that uses one-bits for the network and subnet portions and zero-bits for the host portion. Subnet mask is an an eight byte address divided into 4 parts grouped by periods. Each part may range from 0 to 255. It identifies all the members of a subnet making them easier to reference.

Subnet: Sub Network
Sub-network (Subnet), also known as subnetwork, is a logical grouping of connected network devices in an organization. Typically, a subnet may represent all the machines at one geographic location, in one building, or on the same local area network (LAN). Network designers employ subnets as a way to partition networks into logical segments for better administration, improving performance and enhance network security. In addition, having an organization's network divided into subnets allows it to be connected to the Internet with a single shared network address, which helps ease the problem of Internet IP address exhaustion.

Subvector
Subvector is a data segment of a vector in an SNA message. A subvector consists of a length field, a key that describes the subvector type, and subvector specific data.

Successor
Successor, in EIGRP, is a neighboring router that could possibly be an alternative next-hop router to reach a particular subnet. Successors might or might not be feasible successors.

SUNET: Swedish University Computer Network
Swedish University Computer Network(SUNET) provides high-speed Internet access to academic institutions in Sweden. The current incarnation of the network, GigaSunet, provides 10 Gbit/s links between the cities hosting universities. It replaces the older network, SUNET-155, based mainly on 622 and 155 Mbit/s links.

Super-JANET
Super-JANET is the latest phase in the development of JANET, the UK educational and research network run by UKERNA. It uses SMDS and ATM to provide multiservice network facilities for many new applications, including multimedia conferencing.

Supernet
Supernet refers to an aggregation of IP network addresses advertised as a single classless network address. For example, given four Class C IP networks192.33.8.0, 192.33.9.0, 192.33.10.0, and 192.33.11.0each having the intrinsic network mask of 255.255.255.0, one can advertise the address 192.33.8.0 with a subnet mask of 255.255.252.0.

SURAnet: Southeastern Universities Research Association Network
Southeastern Universities Research Association Network(SURAnet) is the network connecting universities and other organizations in the Southeastern United States. SURAnet, originally funded by the NSF and a part of the NSFNET, is now part of BBN Planet.

SVC: Switched Virtual Circuit
Switched Virtual Circuit (SVC) is a type of virtual circuit (VC) that is set up dynamically when needed. An SVC can be equated to a dial connection in concept.

Switch
A switch is a networking device that connects network segments. There are two categories of switches: packet switch and circuit switch. Packet switch is for data networking operating typically at the layer two (Data Link Layer) of the OSI model. It is capable of inspecting the data packets as they are received, determining the source and destination device of that packet, and forwarding that packet appropriately. On the other hand, the circuit switch that establishes connections on demand and permits exclusive use of those connections until they are released. A circuit-switched network is a type of network in which a physical path is obtained for, and dedicated to, a single connection between two end-points in the network during the connection. The traditional voice phone service using PSTN (not the voice over IP) is circuit-switched.

Switched LAN
Switched LAN refers to a Local Area Network (LAN) in witch all nodes are connected using a LAN switch instead a Hub or bridge. The most popular network switch in the LAN environment is the Ethernet switch.

Switching
Switching is the process that establishes connections of different network segments. There are two main categories of switching: packet switching and circuit switching. Packet switching is for data networking in which data packets are transmitted individually to its detinaion according to certain algorithms. Circuit switching is a process that establishes connections on demand and permits exclusive use of those connections until they are released.

Symbolic Name
Symbolic Name is an alphanumeric name of a user in associated with an IP address. For example, the email address of a user is a symbolic name, which has the format of user@domain, e.g. jenny@javvin.com.

Symmetric network
In a symmetric computer network, all devices can transmit and receive data at equal rates. Asymmetric networks, on the other hand,support disproportianately more bandwidth in one direction than the other.

Synchronization
Synchronization refers to the process of establishment of common timing between sender and receiver.

Synchronous Mode
Synchronous Mode is a type of transmission in which the transmission and reception of all data is synchronized by a common clock and transmitted in blocks rather than individual characters. This mode gives higher data throughput than asynchronous mode, but can be less secure. Synchronous mode does not require a start-and-stop code as in asynchronous mode, and can also mean that the data stream has the same capacity in both directions. See also asynchronous mode.

Synchronous Transmission
Synchronous Transmission refers to the type of transmission in whitch digital signals are transmitted with precise clocking. Such signals have the same frequency, with individual characters encapsulated in control bits (called start bits and stop bits) that designate the beginning and the end of each character.

Synthetic Operation
Synthetic Operation is a probing operation in which packets sent into the network that appear to be user data traffic but actually measure network performance.

Sysgen: System generation
System generation(Sysgen) is the process of selecting optional parts of an operating system and of creating a particular operating system tailored to the requirements of a data processing installation.

SysOp: Systems Operator
Systems Operator(SysOp) refers to the administrator of a bulletin board system (BBS) or special-interest area of an online service or, historically, the operators of any computer system, especially a mainframe computer.

System Packet Interface
The System Packet Interface family of Interoperability Agreements from the Optical Internetworking Forum specify a packet level interface. A typical application of such a packet level interface is between a framer and a network processor. Another application of this interface might be between a packet processor ASIC and a traffic manager device.