Repeater: operates at physical layers of os i model. Digital signals or analog signals that carry digital data can only be transmitted over a limited distance. After a certain distance attenuation or noise endangers the integrity of that data. Repeaters reproduce and transmit the received digital data. This new signal is the exact duplicate of the original signals. Repeaters offer simple means to extend a network, increased traffic on the network is introduced.

This increased network congestion may not be acceptable in some situations. Switch: Communication networks may be categorized by the architecture and techniques they use to transfer data. The following types of networks are in common. Broadcast communication networks.

Local area networks. Packet radio networks. Satellite networks. In broadcast communication networks, there are no intermediate switching nodes.

Each node in the network is attached to share communication medium. Ethernet and Arc net are examples of broadcast communication networks. Switched communication networks: Circuit switched networks Message switched networks. Packet switched networks.

In switched communication network networks there may be multiple paths linking sender and receiver. Data is transmitted from source to destination by being routed through the networks nodes. This is called switching. Bridges: are limited to extend the network distance up to the network limitations. Bridges are useful to extend the network when dealing with one network. Also bridges limit entire company to use one network.

At last when using bridges a failure in the network affects the entire network and thus the entire company. Routers: can extend the network beyond the limitations of a network by connecting two or more networks. Routers allow extending the network by dealing with many networks. Routers also allow you to use a backbone network for faster transfer of information across the different networks. Routers provide the flexibility to use a different network at each department according to its needs. It also allows the network to operate, as it was, not a part of the larger internet work.

Failure of one network on the larger network does not affect other networks. HUB: a central device in a star typology that provides a common connection among the nodes. There is dynamic hub and non dynamic hub.