Question

Draw and explain the different types of LAN devices with the help of neat diagram.

Answer 1

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A local area network (LAN) is a computer network that interconnects computers within a limited area such as a residence, school, laboratory, university campus or office building. By contrast, a wide area network (WAN) not only covers a larger geographic distance, but also generally involves leased telecommunication circuits. Following are types of LAN:

1. Ethernet

• It is a network protocol that controls how data is transferred over a local area network.
• In this type of LAN, the user is able to transfer data at a rate of more than 10 megabits per second.
• Firstly, the system checks the medium used for the transfer of data, if the medium is available then only the data transmission is done.
• It is used in wired local area networks.
• When a machine or machines want to communicate with each other on a network, they detect the main wire connecting all the devices which will be used to carry the data. If the main wire which is referred to as the carrier is available and free, which means no other machine on the network is transmitting any data, then the sender machine initiates sending the packets of data on the network.
• Whenever a packet is transmitted, if there is already a data packet in the queue the sender has to wait. After that, all the devices on the network check that packet to see if they are the recipients of that packet. The packet is then received by the actual recipient.

Ethernet LAN Diagram 222 22.59.01 222 22 59.02 222 22.59.03 222 22.59.04 222 22 59.05 222 22 59.06 222 22 59 07 222 22 59 08 222 22.59.09 Department Department 2 Department 3 Ethernet (222.22,0,2) 10.22 5909 10.22.59.10 - Deot. 1 10.22 59.11 - Dept. 2 10.22 59.12 - Dept. 3 Router - Fireware Department Printers IHIT

2. Token Ring

• It is a type of local area network in which all devices are connected in a ring arrangement.
• All the devices are connected in a circle and they receive a token as per their requirements. A token keeps on rotating in the circular ring.
• A token is used to avoid collisions of data. It is of 3 bytes and keeps on traveling in the ring of servers or workstations.

Destination Host D Host C Token Ring Source Data Packet Host A Host B

The details of three 1-byte fields of a free token frame are:

1. Starting Delimiter (SD): It signals the beginning of the token frame.
2. Access Control (AC): Contains the priority field, reservation field, a token bit, and a monitor bit.
3. Ending Delimiter (ED): It refers to the end of the token frame.

• A station can send data frames only if it has a token. After the data frame is received successfully, the tokens are made free or released.
• The computers are connected by a ring or also called as a star topology.
• The token is passed over the physical ring which is formed by the circular arrangement of stations and the coaxial cable network.
• In this type of LAN, it is possible to calculate the maximum time for a token to reach a station.
• It was developed to solve the problem of collision i.e. when two stations transmit simultaneously at the same time.
• A newer version called Fast Token Ring has been developed which can transfer data up to a rate of 100Mbps.

3. Token Bus

• This is also a type of Local Area Network developed by IBM.
• Token Bus standard uses copper cables which are coaxial for connecting multiple devices to the main large computers or workstations. The coaxial cable acts as the common communication bus.
• In this protocol also a token is created by this protocol to manage access for communication.
• Any computer that holds the token can transfer the data. The token is released when the station completes its data transmission or when a higher priority device needs to transmit (such as the mainframe).
• Due to the token freeing mechanism, there is no collision i.e. two or more devices can easily transmit information on the bus at the same time and the transmitted data is also saved from being destroying.
• It is similar to the token-ring network but the difference is that the ends of the network do not meet each other to form a ring. But the network gets terminated at both ends.
• In this protocol, the token or a small message which circulates among the devices of a computer network is passed along the virtual ring of stations connected to a LAN.
• The topology which is used is a bus or tree type that connects the stations.
• Each and every device is aware of the address of its preceding and succeeding device to transmit token to.
• Data transmission cannot be performed without a token.
• In this type of LAN topology, it is not possible to calculate the time for the token transfer. The working procedure of this token bus is the same as the token ring topology.
• These are used for industrial purposes like manufacturing etc.

TOKEN Station 1 Station 3 Station 5 Station 2 Station 4

4. Fiber Distributed Data Interface (FDDI)

• It is a LAN standard used for data transmission via optical media.
• Used for long-distance networks.
• Uses optical fiber and copper cable.
• It provides communication with fiber optic cables up to 200 kilometers at a speed of 100 Mbps.
• FDDI has two token rings, primary and secondary communication rings. One ring is for backup in the case when the primary one fails.
• The primary ring works and the second one remains free and is available for backup.
• It is extended to FDDI-2 for long-distance voice and multimedia communication.
• It is used for huge and fast data transfer such as in voice and video conferences, online lectures, news, etc.
• It was displaced by fast Ethernet, which is cheaper and has a faster data transfer rate.
• It is used in a large geographical scenario with thousands of end-users.

DAS DAS DAS CON Can be switched SAS SAS SAS CON SAS DAS = Dual attach station SAS = Single attach station CON = Concentrator

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