Network communication devices allow computers, servers, printers and
other devices to send data to each other. They are used to route data by
repeating "as is" what is sent, or running a complex
method of dividing the data and performing error checks before
retrieving the data. Communication can be between two adjacent
computers, a computer to a printer, or computers across wide-area
networks. These devices ensure that data sent is routed and received by
the intended device in the network.
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Hubs or Repeaters
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A hub is the simplest network communication device and is commonly used for local area networks with a small number of computers. It is called a repeater because it repeats the signal it received from a computer to all other computers in the network. The disadvantage of this is that the signal it receives, more often than not, is not intended to all computers. This causes unnecessary network traffic and bandwidth consumption because it doesn't discriminate to whom a signal will be sent. It is up to the receiving computers to decide whether it is for them or not. When a file is being copied from one computer to another, signals are transmitted during the transfer, which contain information like the IP addresses and computer names of the sender and recipient. Computers receive these signals and check whether or not the recipient's IP address and computer name match theirs. Another disadvantage happens when computers are sending and receiving data all at the same time. Without the proper routing mechanism, collision occurs because of all the signals being sent around. It can slow down a network or even bring it down.
Bridges
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A bridge is used to create segments in a network. Think of an office with different departments. There are departments that communicate with each other regularly and there are those that rarely need something from each other. A bridge can connect two departments that transfer data regularly while separate the others that do not. A bridge checks if the destination computer is part of its segment before sending. If it is not, it drops the signal. It essentially lessens network traffic and congestion, but a bridge cannot route data that is not part of its segment. Another communication device would need to take that part.
Switches
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A switch has many ports that can be used to connect different network segments. Different departments, even those that rarely communicate, can send files from one another because a switch looks at the destination computer's IP or MAC address, then finds the shortest route within the network to send it. Switches are replacing hubs and bridges in local and wide area networks because of its routing mechanism, but it can route data only to computers belonging to the subnets connected to the switch. If the computer does not belong to a subnet it recognizes, it drops the data altogether.
Routers
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A router takes off where a switch cannot. It is a device that has its own routing table, which contains IP addresses internal and external to the network. It can route data from computers not even belonging to the same subnet by passing the data off to another router, which passes it on to another until it reaches the destination computer. These "hops" from one router to another is what makes Internet communication possible, where one computer from one side of the world can send a file or an email to the other side of the world.
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