Different Types of Data Networks

Networking
As the name implies, networking is the connecting together of PC's and printers to allow resources to be shared. There are various methods of doing this, such as peer to peer, client/server, and main frames which serve dumb terminals. All of the examples on this page can be connected via Cat 5/5e/6 cabling by using adapters or baluns. Adapters convert whatever connectors are normally used to RJ45, and baluns also match the impedance to that of the systems normal cabling environment.

Peer to Peer
Peer to peer networking is usually found in small offices, shops, and nowadays even in homes. This method allows PC's to access information which is kept on any of the machines that are connected to the network, and to print to any of the printers on the network. This can become impractical however, when the amount of machines or the amount of traffic on the network starts to impact on the speed in which information can be accessed.

Client/Server
Another method is client/server networking, this system employs dedicated PC's or file server's which hold a companies information data bases in one location. Each of the users on the network can access files from the servers, and save files to the servers. This keeps all critical data in one place, and gives each user a dedicated link to that information. Keeping all of a company's data on one machine also has the added advantage making it easier to backup.

Main Frame
In the days before PC's, information was stored on a "main frame" and accessed by terminals which where connected to it. This was, in effect, like having one computer with lots of individual keyboards and screens all working the same machine. These "dumb terminals" had no processing power of their own and relied on the processing power of the main frame computer to do all the work. Some systems today, such as the IBM AS400, are often mistakenly referred to as main frames, when in actual fact they are mini computers. They can however, have dumb terminals connected to them just as the main frames of the 60's and 70's did.

IBM 3270
This is a main frame type system which uses coaxial cable to connect dumb terminals to a controller. The topology is a hierarchical star configuration where the controllers are star wired from the 3270 and positioned around the building, the terminals are then star wired from the controllers. The controllers are beige coloured boxes which measure about 18" high and 24" wide. Baluns for the 3270 are widely available to allow these terminals to connect over Cat 5 cabling.

IBM System 36 & 38
Again, a main frame type system but with a star/bus topology and using twinaxial cable (like coax but having two cores). The System 36 and 38 are large blue and white machines with built in consoles, each of their ports support 7 devices which can be terminals or printers. The devices are daisy chained from the machines workstation controller ports, linking in and out of the terminals and printers. On sites where Type 1 or Cat 5 cable has been installed, it is usual to find 'star concentrators' or 'Loop Wiring Concentrators' (LWC), these simply carry out the daisy chaining of the terminals at the patch cabinet to enable the building to be star wired. This makes a more flexible system as the terminals do not need to be grouped in the same geographical area to be daisy chained. This means that if a person were to move to a different location in the building, they would simply plug their terminal into the nearest data outlet and re-patch the connection in the cabinet. In the past a move such as this would mean finding the nearest available line, diverting it in and out of the re-positioned terminal, and then re-addressing it.

IBM AS400
This is the successor to the System 38 and its native environment is also a star/bus topology using twinaxial cable. However AS400's can also be connected over an Ethernet or Token Ring network just like a PC or a server. The advantage of this is the reliability of a main frame, with the speed and flexibility of a PC.

AS400's used to be large beige boxes that filled the air conditioned computer rooms of only a few years ago. Each rack could contain disk drives, processors or tape backup devices and required dedicated three phase supplies to power them. The modern AS400's are sleek black machines which are considerably smaller than their older counterparts, but with more processing power.

Some networks use a PC as a server and serial connections to attach other PC's which need access to the information stored on the server. These systems are becoming increasingly rare, usually found in small offices and shops where speed is not an issue. Each PC is connected via a screened multicore cable to what is sometimes referred to as a 'terminal server board'. These can also be wired with Category 5 cabling via an adapter, the adapter simply changes the serial connection from either a 25 or 9 way D type, to an RJ45 socket.

ARCnet
This was developed at about the same time as Ethernet (1970's) by the Datapoint Corporation, but due to its proprietary nature, it wasn't as widely accepted as Ethernet or Token Ring.

ARCnet uses a polling system whereby one machine becomes the master controller, and polls each of the other machines on the network to see if they have any data to transmit. Each machine has to wait for its turn before it can use the network and this makes it quite a reliable system. The original ARCnet only had a signal speed of 2.5Mbps and although a 20Mbps version (ARCnet Plus) was introduced in 1992, it still didn't become very popular.

This is quite a rare system these days but as it was once one of the main three, it is worth mentioning.