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  • SAA (Systems Application Architecture) IBM's common application development environment, enabling software to be developed to run on a broad range of IBM hardware, under a range of operating systems: MVS/ESA, VM/ESA, OS/400 and OS/2 EE. This is achieved through a set of standard interfaces for applications (programming), user and communications.
  • SDH (Synchronous Digital Hierarchy) ITU-TS synchronous transmission standards aligned with Sonet above 155Mbit/s, aimed at network operators. Designed with ATM in mind, SDH has many advantages over existing transmission technologies including flexibility in managing the transmission, reconfiguration and control and switching at data rates to 622Mbit/s and beyond. SDH-based networks are being implemented by operators in various parts of Europe and developed by major players such as Alcatel and Northern Telecom.
  • SDLC (Synchronous Data Link Control) An IBM protocol for use in SNA (System Network Architecture) environments. It controls an individual link while catering for other network needs and can operate over full or half duplex lines. SDLC is a bit oriented protocol, using a variety of patterns to flag the beginning and end of a frame or packet. Different bit patterns are used to convey address, control and header fields which accompany the transmission and guide the frame to its destination.
  • SDV segment delay value

  • Segment A bus LAN term meaning an electrically continuous piece of the bus. Segments can be joined together using repeaters or bridges.
  • Serial interface Hardware for sending and receiving data one bit at a time.
  • Server A node that permits other nodes on the LAN to access its resources. The server may be dedicated, in which case this is its sole function, or non-dedicated, where the node can be used in other ways, such as a workstation.
  • Service point IBM network management term for a system that allows non-SNA equipment and network components to be incorporated into an SNA management structure.
  • Services A general term for resources made available by a server to other nodes on the network. In Microsoft LAN Manager terminology, this concept is broadened to include all main components of the LAN Manager software.
  • Session A logical connection between two nodes on a network for the exchange of data; alternatively, any live link between any two data devices, such as a minicomputer and a dumb terminal. A session is also used simply to describe connection time. Session Layer Level Five of the OSI data communications model, drawn up by the ISO, ensures the management of dialogue between applications by providing the protocols for assembling physical messages into logical messages to all dialogue between end systems.
  • SFD start-of-frame delimiter
  • SGMP (Simple Gateway Monitoring Protocol) A predecessor of SNMP.
  • Shielded Twisted Pair A twisted pair of cables surrounded by a wire gauze shield, commonly used by IBM.
  • Simplex A communications system or link which can only carry a signal in one direction.

  • SIR (Speaker Independent [Voice] Recognition) Technologies for the automated conversion of speech to accurate and meaningful textual information, typically ASCII. It typically accepts input from callers to voice processors where callers are using rotary dial instead of DTMF phones. SIR products have deliberately limited vocabularies, but are increasing due to the vast installed base of non-DTMF phones.
  • Slotted Ring A LAN architecture that continually carries a constant number of fixed length packets or slots round the ring. The nodes then use, by replacement, empty slots as they pass through, to transmit data. All the nodes have the ability to recognize empty slots or addressed to them. This network architecture is also known as a Cambridge Ring.
  • Smart wiring hub A network concentrator enabling multiple media to be supported and managed from a central location. When supporting structured wiring systems, smart hubs provide port management.
  • SMB (Server Message Block) A Microsoft - originated distributed system which enables access to another computer's files and peripherals over the network as if they were local.
  • SMDS (Switched Multimegabit Data Services) A public packet-switched high-speed data service that extends LAN-like performance to MANs and WANs with no distance limit. Although reflecting DQDB MAN standards, SMDS can also run over ATM. It offers variable data packet size, Virtual Private Network and Closed User Group features, transmission rates up to 34Mbit/s today and 150Mbit/s in the future.
  • SMF single-mode fiber
  • SMTP (Simple Mail Transfer Protocol) The TCP/IP standard protocol for transferring electronic mail messages from one machine to another. SMTP specifies how two mail systems interact and the format of control messages they exchange to transfer mail.
  • SNA (Systems Network Architecture) IBM's layered communications protocol for sending data between IBM hardware and software. Shortly to celebrate its Pearl anniversary (it was first announced way back in September 1974), it is defined today in terms of a stack of seven layers. While there is some commonalty between the layers of OSI and SNA, it is difficult to make a direct mapping. SNA has traditionally been a hierarchical network architecture for homogeneous networking between IBM systems, but in the 'new' SNA IBM has added increasing support for peer to peer networking through the development of Advanced Peer to Peer Communications. SNA is managed through the NetView network management system.

  • SNADS (SNA Distribution Services) A standardized asynchronous distribution service architecture for the transmission of files or jobs around an IBM SNA network. It is implemented as a transaction service of the SNA network.
  • SNI (SNA Network Interconnect) (In IBM SNA) The way in which autonomous SNA networks can be connected, while still allowing them to be independently managed.
  • SNMP (Simple Network Management Protocol) A transmission protocol defined by the IAB in RFC1157 for TCP/IP-based network management, widely accepted as a de facto standard for LAN network management. SNMP is used to monitor IP gateways and their networks. It defines a set of variables that the gateway must keep and specifies that all operations on the gateway are a side-effect of fetching or storing to the data variables. It consists of three parts: structure of management information (SMI), Management Information Base (MIB) and the protocol itself. The SMI and MIB define and store the set of managed entities; SNMP itself conveys information to and from these entities. The public domain standard is based on the operational experience of TCP/IP internetworks within Darpa/NSFnet.
  • SNMPv2 A combination of two proposed updates to SNMP: Secure SNMP and Simple Management Protocol. Its 12 documents and 400 pages define everything from SMI to a Manager-to-Manager MIB, plus much-needed security improvements.
  • Sockets IBM term for software interfaces that allow two Unix application programs to talk via TCP/IP protocols.
  • Sonet (Synchronous Optical NETwork) Transport network for synchronously multiplexed tributary signals. The standard defines a set of transmission rates, signals and interfaces for fiber optic transmission. Sonet is also an emerging standard proposed by Bellcore (Bell Communications Research, the standards organization of the US Bell Operating companies) for a synchronous optical transmission protocol. The broadband fiber network it supports is formed by a family of network elements conforming to the Sonet interface requirements. The basic electrical signal runs at 51.840Mbit/s - approximately 51 times the bandwidth of a standard US, Ti leased line (1.544Mbit/s). Sonet grows in multiples of the basic signal into the multi-Gigabit range. It is intended to be able to add and drop lower bit rate signals from the higher bit rate signal without needing electrical demultiplexing.

  • Source Routing IEEE standard for 802.5 Token Ring environments from an IBM development. A workstation (source) determines the router through the LAN internetwork. It sends a "discovery" or explorer packet along all active paths in the network, eventually reaching the destination host. Once received, the packet is sent back to the originator. Along the way, each bridge traversed adds its designator to the discovery packet. When it arrives at the originator, it contains complete routing information and the originator can send its data with that information attached. SR-compliant bridges generally need less processing power since most of the work is done by the originating workstation. A liability of SR is that the number of discovery packets traversing the network increases dramatically as the number of Token Ring LAN segments and internetworking devices between the stations grows.
  • Source Routing Transparent (SRT) An algorithm under consideration by IEEE combining Transparent Bridging for Ethernet networks and Source Routing of Token Ring networks for interconnectivity of the two LAN types. Upward migration to FDDI is guaranteed. The bridge applies either TB or SR logic to each frame according to frame type.
  • Spanning Tree Algorithm Part of an IEEE standard. A mechanism for detecting and preventing loops from occurring in a multi-bridged environment. When three or more LAN segments are connected by bridges, a loop can occur. As a bridge forwards all packets which are not recognized as being local, some packets can circulate for long periods of time, eventually degrading system performance. This algorithm ensures only one path connects any pair of stations, selecting one bridge as the 'root' bridge, with the highest priority one as identifier, from which all paths should radiate.
  • SPD Start_of_Packet delimiter
  • Speech Concatenation Voice processing term for economical digitized speech playback. It uses independently recorded files of phrases or file segments linked under application program control to produce a customized response in natural sounding language. Examples could be bank balances or bus schedules. It is done for speed and economy, lending itself to limited, structured vocabularies that are best stored in ram or readily accessible from disk.
  • Spool (Simultaneous Peripheral Operation On Line) A program or device that controls the flow of data to an outputting device such as a printer. Spooling means that a user can send data to a device which is already occupied and can rest assured that the data will be passed onto the desired destination as soon as possible. Spooling of printer output is achieved on a LAN by means of a print server. It is also important in WANs for providing a buffer for time non-critical applications such as Electronic Mail and File Transfer.

  • Spoofing A method of fooling network end stations into believing that keep-alive signals have come from and return to the host. Polls are received and returned locally at either end of the network and are transmitted only over the open network if there is a condition change. The result is a non-time critical network with a minimum of keep-alive traffic between deterministic end stations, while retaining the opportunity to send flags should an end station alter its state. The synchronous approach harks back to unreliable circuits and the need to check end station existence at regular intervals. Now networks are more reliable, spoofing by routers is an acceptable compromise.
  • SQE(T) (Signal Quality Error [Test]) Function of transceivers immediately acter its attached computer has transmitted on to the LAN. The transceiver sends a simple test signal over the AUI back to the computer, ensuring the computer knows it has a working connection. Because it acts as a confidence check and "pulses" down the line, it is also called a heartbeat.
  • SQL (Structured Query Language) A standardized query language that can be used for querying databases across a network in client/server applications. It can be used to interrogate the database, and extension to the language allow the database to be updated through it as well.
  • SR symbol rate
  • SSD start-of-stream delimiter
  • STA station management entity
  • Standalone server In LAN Manager terminology, a server that maintains its own user accounts database and does not participate in logon security.
  • Star Topology A network layout or design in which each node is connected to a central hub. The hub establishes, maintains and terminates all connections between the nodes. In a LAN, the hub is likely to be a workstation, whereas in larger multi-point networks the hub is more likely to a multiplexer.
  • SDTM (Statistical Time Division Multiplexing) A technique whereby a multiplexer apportions time on a dynamic basis only to those channels which are active.

  • Store and forward A buffering technique in which messages or packets are received in their entirety by an intermediary, ever if the ultimate recipient is not presently able to receive, This is used exclusively in the context of electronic mail across wide area networks, and occasionally for terminal I/O.
  • StreetTalk Banyan Systems' directory system which provides a distributed database of names addresses accessible from Vines.
  • STP shielded twisted pair (copper)
  • Sub-Area Network The original hierarchical approach used in the construction of IBM SNA backbone networks. The structure of a Sub-Area Network is predefined. The relationship between the components of the network and the links is generated into the software in the host systems involved. The network can, however, be modified without having to re-build the definition of the entire network. A new node can de added by defining it in the adjacent nodes to which it is directly attached. Such a network is constructed around a backbone of communications controllers to which the host systems are attached.
  • SVC (Switched Virtual Circuit) A temporary virtual circuit between two users.
  • Switch Equipment used to connect and distribute communications between a trunk line or backbone and individual nodes.
  • Switched attachment The IBM term for linking devices to host computers through a PBX capable of handling data switching.
  • Synchronous transmission A method of communication in which data is sent in blocks, without the reed for start and stop bits between each byte. Synchronization is achieved by sending a clock signal along with the data, and by sending special bit patterns to denote the start of each block.
  • SSCP (Systems Services Control Point) In an IBM S NA environment the SSCP resides in a host processor and is responsible for central control, directory services and operational functions in the network; either alone or in combination with SSCPs in other processors.


The Net is the Automation.
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composed by JohnBlack '01

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