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What is Token Passing?
Token passing is a method used for network communication that allows devices to take turns transmitting data over a shared network medium. In this approach, a special control token is passed between devices, granting them temporary permission to transmit data. This token is passed sequentially, ensuring fair access to the network resources.
Basic Concepts of Token Passing
To understand the concept of token passing, let’s break down the basic concepts involved:
1. Token: The token is a special control frame that circulates within the network. It serves as a permission slip, allowing the device that possesses the token to send data over the network.
2. Token Ring: In a token passing network, devices are connected in a ring topology. The token circulates around this ring, hopping from one device to another in a predetermined order.
3. Token Passing Process: The token passing process involves devices waiting for their turn to possess the token. Only the device that possesses the token can transmit data. Once the device completes its transmission, it passes the token to the next device in the ring, allowing it to transmit data.
4. Fairness: Token passing ensures fairness by providing equal opportunity for each device to access the network. Each device gets a turn to possess the token, eliminating the possibility of one device monopolizing the network resources.
How Token Passing Works
Now that we understand the basic concepts, let’s delve into the workings of token passing:
1. Initialization: The token is initially assigned to a specific device in the network. This device is responsible for starting the token passing process.
2. Token Ownership: The device that possesses the token is the only one allowed to send data. Other devices in the network can only listen to the network traffic.
3. Data Transmission: When a device has the token, it can transmit data packets onto the network. These packets travel around the ring, reaching the intended destination. Other devices receive and process the data packets as they pass through.
4. Token Passing: Once a device completes its data transmission, it passes the token to the next device in the ring. The token continues to cycle around, allowing other devices to have their turn.
5. Token Loss or Failure: In the event of a token loss or a device failure, a predefined algorithm handles the situation. The algorithm ensures that the token is recovered or a new token is generated to maintain network operation.
Advantages and Disadvantages of Token Passing
Advantages:
– Fairness: Token passing ensures equal access to network resources, preventing any single device from monopolizing the network.
– Efficiency: This method avoids collisions that occur in contention-based access methods, leading to efficient data transmission.
– Simplicity: The token passing protocol is relatively simple to implement and manage.
Disadvantages:
– Centralized Control: Token passing networks require a central device to manage the token, which could create a single point of failure.
– Scalability: As the network grows larger, the time required for the token to complete a cycle and reach each device can increase, affecting overall network performance.
In conclusion, token passing is a method for network communication that ensures fair access to network resources. It employs a token that is passed between devices, allowing them to transmit data in a sequential order. While it has its advantages, it’s essential to consider the network size and potential single points of failure when implementing token passing.
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