A network is a number of computers connected through some channel so that they may share some of the resources and allow access into them by users from other points.
Advantages of networking
a. Resources can be shared e.g. printers, computer files and programmes.
b. More even distribution of processing and other work by the computers and users.
c. More economic and fuller use of computers.
d. Allow for the provision of local facilities without loss of central control. e. Mutual support and a spirit of cooperation exist.
Disadvantages of networking.
a. There could be congestion at the shared resources. b. Control of information and confidentiality may be lost. c. The costs of the system may be considerable.
Wide Area Networks (WAN)
These are networks that are spread over large geographical areas. The telephone system is one such WAN. It is a long distant network of interconnected computers on separate sites, cities or even different countries.
Purposes of Implementation of WAN
-To get data from its source.
-Improve on the productivity of the system by improving the speed of processing - Allow for instant feedback and expansion of the system.
WAN hardware
Hosts - This provides users with processing software and access. The host is usually a
mainframe computer with microcomputers connected to it.
Front end Processors (FEP) & Back End Processors (BEP) - These are
minicomputers that are placed in front of (FEP) or at the back (BEP) of the main system CPU. These assist the main system CPU with accepting input perform the operations on it before forwarding it to the mainframe CPU for further processing or after the main system CPU to assist with the output activities. They generally manage communications. The main system CPU concentrates on process work without having to handle input and output activities.
Modems - This is short for Modulate Demodulate. Telephone lines that are common
link media between computers use the analogue signal whereas computers use digital signals. So there is need to convert the signals. From the sending computer, the digital signal should be modulated to analogue signal for transmission over the telephone link. At the receiving end the analogue signal has to be demodulated (converted back) into the digital signal.
Modulation can be done using a number of methods. Amplitude modulation (AM) where the amplitude is modified to represent binary digits 0 and 1. Frequency Modulation (FM) adjusts frequency to represent the bits 0 and 1. The Phase Shift Modulation adjusts a fixed amount so that 0 and 1 can correspond to different phase shifts.
Terminals - These are the microcomputers connected to the system on which the
users can work to sent data or access information. Terminals may be dump or intelligent. Dump terminals have limited memory and intelligence while intelligent terminals have processing and memory capabilities that they can process data themselves.
Multiplexor -it is a device that can subdivide one big channel so that many people can
use it at the same time. There are two types of multiplexors: time division and frequency division.
Time Division Multiplexors (TDM) - It slices multiple incoming signals into small time intervals that are then transmitted over a channel and then split by another TDM at the receiving end.
Time Slots Time
Frequency Division Multiplexor (FDM) - incoming signals on different frequency ranges are sent across a transmission medium at the same time. At the receiving end another FDM splits the frequencies into multiple signals again.
Terminal controllers/Concentrators- are used to connect many terminals to a single
line, they do not communicate directly with the FEP.
Protocol Converters - Because of the diversity of technology in communication, WANs are using various devices, channels, modes and codes. To allow for communication between and among all these protocol converters are used to translate different signals from one system to another. Typical protocol converters include HTTP (Hyper Text Transfer Protocol) used on Internet communications, TCP/IP.
Multiplexor
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MultiplexorWAN Software
In order for the WAN hardware to operate there should appropriate software which should include telecommunications access programmes that handle messages between the host's memory and the remote devices, this programme could be in the FEP. There is also the network control programme that has the work of running the network off the host by checking if terminals have messages to send, do editing of incoming messages.
Network concerns For the Manager
1. Reliability of the network - there should be minimal breakdown and errors in the system.
2. Response time of the Network - there should be less time spent on picking the required signals when required.
3. Costs of the Network - costs of setting up and maintaining the system may be considerable, so the manager should reduce these.
4. Compatibility of Software and hardware - hardware and the software should be compatible (capable of working together) otherwise there should at least be some conversion of either the software or the hardware to suit the other.
5. Access and Security of the System - with WAN there is greater risk of data being accessed by unauthorised people, there should be measures to reduce this risk e.g. use of passwords, physical access protection or through encryption (coding of data so that in the event that it is intercepted it may not be understood) WAN Topology Zimbabwe South Africa Terminals Host Modem Modem Multiplexor Multiplexor