Introduction to Types of LAN

LAN or a Local Area Network is a type of connectivity for the devices located in a specific geographical area. It is classified into four types based on the distribution method followed in the LAN network. They are called as ‘Ethernet’ for the LAN where a network is created as wired, ‘Token Ring’ for connected the devices in a circular ring pattern with the help of a token passed through the network for enabling the connection, ‘Token Bus’ for connecting the devices using coaxial cables and tokens, ‘FDDI or Fiber Distributed Data Interface’ for faster network connectivity via optical fiber cables and copper cables.

Classification of LAN

LANs are classified as below according to the methods used for sharing data:

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, the sender has to wait if there is already a data packet in the queue. After that, all the devices on the network check that packet to see if they are the recipients of that packet. The actual recipient then receives the packet.

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.

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

Starting Delimiter (SD): It signals the beginning of the token frame.
Access Control (AC): Contains the priority field, reservation field, a token bit, and a monitor bit.
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 a collision problem, 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.

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.

Conclusion – Types of LAN

All types of LAN have their specific importance and purpose of use, but they have their own limitations and problems as well. Like in the token ring, if a station shuts down, then the data packets keep on circulating, known as the orphan packet problem, then data corruption is also there. The token ring was previously widely used on LANs but has replaced by Ethernet due to expensive pricing as token ring products are more expensive than Ethernet at similar speeds, so it is very important to take note of all the details before using any kind of LAN.

Introduction to Types of LAN