Computer Network Devices Adavantages and Disadvantages of Networking Devices

To create a flexible enterprise internetwork, it is necessary to interconnect individual local area network data link and wide area networking facilities, there are a number of different types of devices that can be used to accomplish this.

Each has its own unique uses and it is appropriate for different form of network interconnection. The type of device that is available for network interconnection can be divided into the following general categories

a.       Bridges

b.      Repeaters

c.       Routers

d.      Switches

e.      Connectors

Repeaters

The repeaters is the simplest facility used for network interconnection whose major function is to receive a signal from one LAN cable segments and to retransmitting, regenerate the signal at its original strength over one or more other cable segment. A repeater operates in OSI model physical layer and its transparent to all the protocols operating in the layers above the physical layer.

A specific LAN implementation usually places a limit on the physical size of a simple cable segments. The limit is based on the physical medium and transmission technique used

Repeaters allow network to be constructed to exit the size limit of a single, physical cable segment. The number of repeaters that can be used in tandem is generally limited by a particular LAN implementation. Using a repeater between two or more LAN cable segment requires that the same physical layer protocol be used to send signal over all the cable segment

Example

Two LAN cable segment is an Ethernet LAN that both used baseband transmission could be connected with a repeater. Different types of physical transmission medium can also be connected using a properly designed repeater as long as the they all handle similar type of signal.

Advantage of a repeater: It is simple in term of implementation cost

Disadvantages: Repeaters provide no method for isolating the traffic generated on one cable segment from  traffic generated by the other cable segment. When a repeater is used to connect cable segment A to segment B, whether or not there is s station on segment B that is the destination of the signal

Internetworking Bridges

The bridge is used to connect an extended Local Area Network and Bridges are more intelligent compare to repeaters. Bridges interconnect separate LAN data link rather than first cable segment. Some bridges learn the address of the stations that can be reached over each data link. They bridge (Isolate traffic) so they can selectively relay only traffic that need flows across each bridge. It operates in media Access Control. It is transparent to the protocol operating in the layers above the data link layer. A bridge interconnect network that use different transmission technique or Media Access Control Method. There are two types of bridges namely Spanning tree and source routing

Spanning Tree Bridges

They are used to form tree structure in which analogue active path connects any two stations in the extended LAN. The spanning tree bridges are transparent to ordinary station on the interconnected LANs. A spanning tree bridge learns appropriate route for friends by observing transmission that take place on the data links to which the bridge is connected. It then forwards frame over the appropriate data link when required.

Source Routing Bridges

They are typically used with token ring LAN, more than one path through source routing bridges can interconnect to any LAN station. The only difference is that each station is expected to know the route over which to send its frame. If a station does not know the route or if a previously known route is no longer active the station broadcast route discovery frames over the extended LAN and then determines from the responses the appropriate route to use

Routers

Computer routers provide the ability to route messages from one system to another where these may be multiple path between them. A router performs its function in OSI model network layer. Router can be use for traffic isolation, routing function, create subnets

Switches

in addition to repeaters, bridges and routers a variety of different types of switching facility can be use in constructing internet. The main purpose of interconnecting LAN data link segment is to allow a greater degree of sharing of common communication medium. Network interconnection devices allow a larger number of different network devices to be attached to the same LAN. All system attached to a LAN or extended LAN created using repeaters and bridges share the same physical transmission. Switching devices are devices designed for the opposite purpose of repeaters and bridges. In some cases when the number of devices attached to the same common transmission medium get too large, the transmission capacity can be exceeded especially when system are transmitting large quantity of data between them. One of the ideas of routers is to allow network segment to be interconnected also isolate one physical group of system from another