Interest in personal computers has usually focussed on the individual's use of a so-called stand-alone machines. But now it may be less important as the users around the country can be linked together over telephone lines/radio in a network. Direct-access processing generally involves on-line terminals located at or near data sources and their sources can be far away from CPU.
Historical background of communication:- In thd 100 years after the introduction of the telephone, a complex network of telecommunications systems was established to link locations throughout the world. The first linkage of computing and communication linkage began to start. Communication usages has grown steadily since then. Now most of micros, minis and large machines are able to communicate with each other.
Converging communication picture:- About 40 years ago, computing capability was obtained from computer vendors and communication service was supplied by telecommunication firms. The communication firms used some computer-controlled message-switching devices to improve their services and the computer vendors offered limited communications packages to sell data processing services.
                Today computer are an essential part of modern communication network and such a network is vital for the operation of many computer based management information systems. Several new terms have been coined to reflect the merger of computing and communication use communications. As more PC'S are attached to communication networks as more of the equipment in an organisational settings is linked together by data communications. The distinctions between computing and communications will get even more blurred.
Concepts of communications:- In a simple data communication system, terminals and other remote I/O devices are linked with one or more central processors to capture input data and receive output information. Connecting equipment and software, sometimes referred to as interface elements are used to bridge the different physical and operating environment that exist between I/O devices and control processors.
Data transmissions techniques:- A MODEM is Modulating/Demodulation device that converts the discrete steam of digital "on/off" electrical pulses generated by computing equipment into a type of continuosly variable analog wave patterns used transmit human voice. Digital pulses cannot effectively travel any distance over the transmission network that was designed years ago for  voice communications. Hence a MODEM is needed to modulate or convert the digital pulses in the analog wave patterns when telephone lines are used to transmit data. Similarly another modem is needed at the receiving end to demodulate or reconvert or recover the digital data from the transmitted signal.
               Where the I/O equipment at the remote stations are not likely to move, modem is hard-wired to this equipment. Some such direct-connect modems have built-in microprocessors and other specialised communication chips. These intelligent modems can automatically perform dialling, answering and disconnecting functions. But not all modems are hard wired where communication network is designed for all-digital transmissions modems are not required.
Data Transmission Channel:- A data transmission channel carries data from one location to the other and is classified as narrowband, voiceband and wideband categories. The wider the band the more data it can transmit in a given period of time. Telegraph lines are narrow band, channels with transmission rate of 5 to 30 characters per second ( CPS) where standard telephone lines are voiceband with rate in over 1000 CPS. Broadband channel are used for higher speeds ( over 100,000 CPS). Coaxial cables microwave circuits and communication satellites are used to provide these channels. Fibre optic cables and laser technology provides cheaper broadband channels in large numbers.
               In many cases, a terminal operator at a remote station uses a regular dial-up telephone switching network, calls a number at the CPU locations and enters data. When data volume is sufficient, it is economical to acquire dedicated or leased lines which can be used both for voice and data purposes.
Coordinating the Data Communication Environment:- The data communication environment has changed rapidly and much larger computing/communication networks are now in service. Coordination required for efficient network use is complex. Such networks may have hundreds of terminals and many small precessors located at dozens of dispersed sites. These sites in turn may be linked by different transmission channels to larger host computers. The task of network designer is to select and coordinate yhe network component so that the necessary data is moved to the right place, at the right time with a minimum of errors and at the lowest possible costs.
 COMMUNICATOR PROCESSOR:-A number of these processors are used in a network for the following purposes:-
A. Remote concentration of messages:- The remote concentrator reduces transmission costs by receiving terminal input from many low speed lines and smooth stream of data on a higher speed and more efficient transmission channel. Devices called multipliers also perform this concentration function. Micro processor equipped multiplexers perform mych like concentrators.
B. Message switching:- The message switching receives and analyses data messages from point in network, determines the destination and the proper routing and then forwards the messages to other network locatuons. If necessary, a message may be stored until an  appropriate outgoing line is available.
3. Packet switching:- The technique of packet switching has been specifically developed for high speed data transmission between the computers connected via broadband communication networks. Data to be transferred is assembled into packets, the size of which is optimized for the switching system concerned after taking into account such factors as the capacity or transmission rate on the interconnecting circuits the amount of store available at the switches and the likely transmissions time. The packets are short( 64/128/216 bytes) and may be independently routed. Thus the system can keep the traffic flowing by sending packets which are part of different transmission consecutively down a given circuit instead of having to keep the circuit open until a whole transmission is complete.
D. Front-end processing:- The front-end processor usually located at a central computer site. Its purpose is to relieve the main computer (host computer) of a number of functions required to interact with and control the communication network.
E.  The functions of a communication processor differs from one network to another. A message packet switching processor may also function as a remote concentrator. A front-end processor may perform message/packet switching functions and in less complex networks the host conputer may perform most or all the functions of the front-end processor.