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SAP (Service Access Point)
Service Access Point or SAP is an identifying label for network endpoints used in OSI networking. Service Access
Points are series of interface points, SAP interfaces between protocol layers. So, SAP creates Interfaces between
protocol layers. The protocol for each layer is concerned with providing a peer-to-peer service with the corresponding
layer at the other end of the path (a hop for the lower three layers, end-to-end for the upper four). Each layer
uses the services of the layers below it, by communicating via a Service Access Point (SAP).
Peer to peer communication using the services of a lower layer
During peer-to-peer communication, information at the sender, i.e. PDU (Protocol Data Unit), flows down through
each of the lower layers in the same node. At the lowest (physical layer) the information passes over the communications
cable to the corresponding physical layer entity. When information is received, the information, SDU (Service Data
Unit), is passed up to the next higher layer.
The boundaries between adjacent layers in the same system are called Interfaces. Service Primitives are used to
pass the information, and the protocol entity to which the information is delivered is called a SAP (Service Access
Point).
Examples of SAPs are the type field in the MAC (Medium Access Control) protocol, the address field in HDLC, the
protocol field in the IP network header, and the port identifier in UDP and TCP.
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SAP (Systems, Applications and Products in Data Processing)
SAP is the leading Enterprise Information and Management Package worldwide from the German software company, SAP
AG. The name SAP stands for Systems, Applications and Products in Data Processing. Use of this package makes it
possible to track and manage, in real-time, sales, production, finance accounting and human resources in an enterprise.
Traditional computer information systems used by many businesses today have been developed to accomplish some specific
tasks and provide reports and analysis of events that have already taken place. Examples are accounting general
ledger systems. Occasionally, some systems operate in a "real-time" mode that is, have up to date information
in them and can be used to actually control events. A typical company has many separate systems to manage different
processes like production, sales and accounting. Each of these systems has its own databases and seldom passes
information to other systems in a timely manner.
SAP takes a different approach. There is only one information system in an enterprise, SAP. All applications access
common data. Real events in the business initiate transactions. Accounting is done automatically by events in sales
and production. Sales can see when products can be delivered. Production schedules are driven by sales. The whole
system is designed to be real-time and not historical. SAP structure embodies what are considered the "best
business practices". A company implementing SAP adapts it operations to it to achieve its efficiencies and
power. The process of adapting procedures to the SAP model involves "Business Process Re-engineering"
which is a logical analysis of the events and relationships that exist in an enterprise's operations.
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Script
A type of computer code than can be directly executed by a program that understands the language in which the script
is written. Scripts do not need to be compiled to be run. Also known as calling script. A record of keystrokes
and commands that can be played back in order to automate routing tasks, such as logging on to an online service.
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SCSI (Small Computer System Interface)
SCSI is a standard that allows multiple devices to be connected in daisy-chain fashion. So, SCSI is an interface
controller that allows several peripherals to be connected to the same port on a computer..
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SDLC (Synchronous Data Link Control)
SDLC is the IBM® standard protocol, superseding bisynchronous (BSC).
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SDRAM (Synchronous Dynamic Random Access Memory)
SDRAM incorporates new features that make it faster than standard DRAM and EDO memory. SDRAM times all address,
data and control signals to a CPU's system clock. This function eliminates the bandwidth bottleneck between the
memory and CPU to maximize overall system performance. SDRAM can run at much higher clock speeds than conventional
memory. SDRAM actually synchronizes itself with the CPU's bus and is capable of running at 100MHz and 133MHz, about
three times faster than conventional FPM RAM, and about twice as fast EDO DRAM and BEDO DRAM.
SDRAM (synchronous DRAM) is a generic name for various kinds of dynamic random access memory (DRAM) that are synchronized
with the clock speed that the microprocessor is optimized for. This tends to increase the number of instructions
that the processor can perform in a given time. The speed of SDRAM is rated in MHz rather than in nanoseconds (ns).
This makes it easier to compare the bus speed and the RAM chip speed. You can convert the RAM clock speed to nanoseconds
by dividing the chip speed into 1 billion ns (which is one second). For example, an 83 MHz RAM would be equivalent
to 12 ns.
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Search Engine
A program that search one or more documents for specified keywords and returns a list of locations where those
keywords were found. Although search engine is really a general class of programs, the term is often used to specifically
describe systems like Alta Vista and Excite that enables user to search for documents on the World Wide Web and
in USENET newsgroups.
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Sector
The tracks on a harddisk are divided into sectors. Clusters contains from 1 to 64 sectors. So, sector is a part
of each track defined with magnetic marking and an ID number. Sectors have a sector header and an ECC (Error Correction
Code). In modern drives, sectors are numbered sequentially.
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Segment
Segment refers to a section of cable on a network. In Ethernet networks, two types of segments are defined. A populated
or trunk segment is a network cable that has one or more nodes attached to it. A link segment is a cable that connects
a computer to an interconnecting device, such as a repeater or concentrator, or connects an interconnecting device
to another interconnecting device.
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Server
A computer that offers services on a network. On the World Wide Web, a server is a computer that runs the Web server
software which responds to HTTP protocol requests. Also called host.
A server is a computer that is configured (via software and hardware) to provide files to one or more other computers.
Opposite of client. Simply, a computer that provides resources, such as files or other information. Common
Internet servers include file servers and name servers Domain Name Service.
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Server-side image map
An image map that passes the coordinates of the mouse pointer to a CGI handler routine on the server. Server-side
image maps require your server to compute the target URL of the hyperlink based on the mouse pointer coordinates.
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Session Layer
Session Layer provides the user's interface to the network. Determines when the session is begun or opened, how
long it is used, and when it is closed. It controls the transmission of data during the session and supports security
and name lookup enabling computers to locate each other.
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SGML (Standard Generalized Markup Language)
An ISO (International Standards Organization) markup language for representing documents on computers. HTML is
based on SGML concepts. SGML (Standard Generalized Markup Language), a system for organizing and tagging elements
of a document. SGML was developed and standardized by the International Organization for Standards (ISO) in 1986.
SGML itself does not specify any particular formatting; rather, it specifies the rules for tagging elements. These
tags can then be interpreted to format elements in different ways.
SGML is used widely to manage large documents that are subject to frequent revisions and need to be printed in
different formats. Because it is a large and complex system, it is not yet widely used on personal computers. However,
the growth of Internet, and especially the World Wide Web, is creating renewed interest in SGML because the World
Wide Web uses HTML, which is one way of defining and interpreting tags according to SGML rules.
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Short-Haul Modem
Short-Haul Modem is a DCE device that amplifies a data signal for transmission over cable for distances beyond
the RS-232 limit of 50 feet, even up to several miles. Also called "limited-distance modem" (LDM) or
"short-haul modem" (SHM).
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Signalling Protocol
Signalling Protocol defines a standard set of information elements and a method of transport in order to enable
components of a network to interoperate. Signalling provides the ability to transfer information inside networks,
between different networks, and more importantly between the customers that use the network services for which
we charge. There are two types of signalling:
1. Channel Associated Signalling (CAS), where the signalling information is carried down the same physical
channel as the voice or data.
2. Common Channel Signalling (CCS) concentrates the signalling information in a single dedicated channel,
such that all of the signalling information for many voice channels in a telephony system can be conveyed over
a single channel dedicated to signalling.
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Signalling System Number 7
Signalling System Number 7 (SS7, C7, No 7) is an example of a common channel signalling system, defined for use
in public switched networks where large numbers of circuits are switched between subscribers. SS7 is a global standard
used throughout the world within networks and on international interconnects, it is the signalling technology inside
the network that delivers (Integrated Services Digital Network) ISDN, mobile/wireless and Intelligent Networking.
The subscribers or service users access the network using an Access protocol, such as multi-frequency dialling
or ISDN. These types of protocol are targeted at providing services to the subscribers, allowing interaction of
the subscriber with the network. Inside the network however, a reliable and robust method of signalling is required,
this is provided by SS7.
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S Interface
S Interface is the standard 4-wire interface between an ISDN terminal adapter and the network channel termination.
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SLIP / PPP (Serial Line Internet Protocol / Point to Point Protocol)
SLIP/PPP is a compromise between a direct internet connection and host dial-up access is to use SLIP (Serial Line
Internet Protocol) or PPP (Point to Point Protocol). SLIP/PPP refers to both SLIP and/or PPP - they are similar
in many ways. SLIP/PPP provides the ability to transport TCP/IP traffic over serial lines, such as dial-up telephone
lines, between two computers. Both computers run some sort of TCP/IP based network software. This allows users
to get direct internet access from the PC with just a simple modem and a telephone line and run GUI based web browser,
ftp client and other networked resources.
SLIP/PPP is a form of direct internet connection in the sense that the computer has a communications link to the
internet, even if it is via a service provider and the computer has the networking software that can communicate
by using TCP/IP with other computers on the internet and that the computer has an identifying address (IP address)
at which it can be contacted by other computers on the internet.
SLIP/PPP vs. Host Dial-Up Access
Both SLIP and normal dial-up access involve dialing into a remote computer system (which is directly on the internet)
and logging in. The key distinction is that with SLIP, the PC is communicating using native TCP/IP with other computers
on the internet while with normal host dial-up, the PC simply acts as a dumb terminal to the remote computer which
then communicates with other computers on the internet using native TCP/IP.
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Slot
Slot is a physical connector on a motherboard to hold an expansion card, SIMM, DIMM, or a processor card in
place.
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SMTP (Simple Mail Transfer Protocol)
A protocol used to transfer email. SMTP transfers mail from server to server, and the end user must use POP
to transfer the messages to their machine.
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Socket
Socket is a receptacle usually on a motherboard in what processors or chips can be inserted into.
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Speed of Data Transfer
Speed of Data Transfer is the rate at which information travels through a network, usually measured in megabits
per second.
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SPID (Service Profile IDentifier)
SPID (Service Profile IDentifier) is a number assigned to an ISDN line by the ISDN service provider that identifies
certain characteristics of the line.
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Star Topology
Star Topology is a LAN topology in which each node on a network is connected directly to a central network hub
or concentrator.
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Star-Wired Ring
Star-Wired Ring is a Network topology that connects network devices (such as computers and printers) in a complete
circle.
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Statistical Multiplexing
Statistical Multiplexing is a multiplexing technique in which bandwidth is dynamically allocated on the basis of
need.
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Streaming
Audio, video, and text available for viewing on your computer even as it is in the process of downloading to your
system from a Web site.
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Switched Line
Switched Line is a communications link, such as the public telephone network, for which the physical path may vary
with each usage.
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Synchronous Transmission
Synchronous Transmission is a transmission in which data bits are sent at a fixed rate with the transmitter and
receiver synchronized. Synchronized transmission eliminates the need for start and stop bits. Compare with asynchronous
transmission.
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System Registry
System Registry stores the system configuration files used by Windows 95, 98and NT, to store settings about user
preferences, installed software, hardware and drivers, and other settings required for Windows to run correctly.
The system updates the registry every time you add new hardware or a new program to your system.
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