Router: Routers are devices which connect two are more networks that use similar protocol. A router consists of hard ware and software. Routers operate at a network layer of O.S.I model. Routers use logical and physical address to connect two or more logically separate network. They make this connection by organizing the large network into logical network segment (some times small sub network or sub nets). Each of these sub nets is given a logical address. Data is grouped into packets or block of data.
Advantages of Router: They use high level of intelligence to rout data. Routers can also act as a bridge to handle non rout able protocols such as NetBEUI (Network Bios Extended User Interface)
Disadvantages of Router:
High level of intelligence takes more processing time which can affect performance
Routers are very complicated which installation and maintenance difficult.
2) Gateways: Gateways are devices which connect two are more networks that use different protocols. They are similar in function to routes but they are more powerful and intelligent devices. A gateway can actually convert data so that network with an application on a computers on the other side of the gateway e.g a get way can receive email messages in one format in convert them into another format. Gateway can operate at all seven layer of OSI model. Since Gateway perform data conversion so they are slower in speed and very expensive devices.
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3) Repeaters: Repeaters are used within network to extend the length of communication. Data process through transmission media in the farm of waves or signals. The transmission media weaken signals that move through it. The weakening of signal is called attenuation. If the data is to be transmitted beyond the maximum length of a communication media, signals have amplified. The devices that are used to amplify the signals are called repeaters. Repeaters work at the physical layer of OSI model. Repeaters are normally two ports boxes that connect two segments. As a signal comes in one port, it is regenerated and sends out to the other port.
Advantages of Repeater:
Repeaters easily extend the length of network.
They require no processing over head, so very little if any performance degradation occurs.
It can connect signals from the same network type that use different types of cables.
Disadvantages of Repeaters:
Repeaters cannot be used to connect segments of different network types.
They cannot be used to segment traffic on a network to reduce congestion .
Many types of network have a limit on the number of network s that can be used at once .
4) Bridges: Bridges are used to connect similar network segments. A bridge does not pass or signals it receives. When a bridge receives a signal, it determines its destination by looking at its destination and it sends the signals towards it. For example in an above figure a bridge has been used to join two network segments A AND B.
When the bridge receives the signals it read address of both sender and receiver. If the sender is a computer in segment A and the receiver is also segment A, it would not pass the signals to the segments B. It will however pass signals if the sender is in one segment and the receiver in other segment. Bridge works at the data link layer of O.S.I model.
Advantages of Bridges:
Bridge extends network segments by connecting them together to make one logical network.
They can affect the segment traffic between networks by filtering data if it does not need to pass.
Like repeaters they can connect similar network types with different cabling.
Disadvantages of Bridges:
Bridge possess information about the data they receive with can slow performance.
5) Hub: Hubs are basically multi ports repeaters for U.T.P cables. Some hubs have ports for other type of cable such as coaxial cable. Hubs range in size from four ports up to and for specific to the network types. These are some hubs which are
I. Passive Hub
II. Active Hub
III. Switch/ Intelligent Hub
Passive Hub: It provides no signal regeneration. They are simply cables connected together so that the signal is broken out to other nodes with out regeneration. These are not used often today because of loss of cable length that is allowed.
Active Hub: It acts as repeaters and regenerates the data signals to all ports. They have no real intelligence to tell weather the signal needs to go to all ports that is blindly repeated.
Switch Hub: Switches are multi ports bridges. They filter traffic between the ports on the switch by using the address of computers transmitting to them.
Switches can be used when data performance is needed or when collision need to be reduce.
Advantages of Hub
Hubs need almost no configuration.
Active hub can extend maximum network media distance.
No processing is done at the hub to slow down performance
Disadvantages of Hub
Passive hubs can greatly limit maximum media distance.
Hubs have no intelligence to filter traffic so all data is send out on all ports whether it is need or not.
Since hubs can act as repeaters the network using them must follow the same rules as repeaters
6) Modem: The device that converts digital signals into analog signals and analog signals to digital signals is called Modem. The word modem stands for modulation and demodulation. The process of converting digital signals to analog signals is called modulation. The process of converting analog signals to digital signals is called demodulation. Modems are used with computers to transfer data from one computer to another computer through telephone lines.
Modems have two connections these are.
Analog connection: The connection between the modem and the telephone line is called analog connection.
Types of Modem
THERE ARE TWO TYPES OF MODEMS
Digital connection: The connection of modem to computer is called digital connection
INTERNAL MODEM: It fits into expansion slots inside the computer. It is directly linked to the telephone lines through the telephone jack. It is normally less inexpensive than external modem. Its transmission speed is also less external modem.
EXTERNAL MODEM: It is the external unit of computer and is connected to the computer through serial port. It is also linked to the telephone line through a telephone jack. External modems are expensive and have more operation features and high transmission speed.
Advantages of Modem
Inexpensive hardware and telephone lines.
ii. Easy to setup and maintain.
Disadvantages of Modem
i. Very slow performance.
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