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.
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.
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.
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.
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.
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.
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.
