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Table of contents
1.
Introduction
2.
What is a Token Bus?
2.1.
How does the Token Bus work?
3.
Frame Format of Token Bus
4.
What is a Token Ring?
4.1.
How does the Token Ring work?
5.
Advantages of Token Bus
6.
Disadvantages of Token Bus
7.
Differences Between Token Ring and Token Bus
8.
Frequently Asked Questions
8.1.
What is the token bus method?
8.2.
What is the speed of token bus?
8.3.
What is IEEE standard 802.4 and token bus?
8.4.
What is token ring and token bus map with IEEE 802 standard?
8.5.
Is token ring used in LAN?
9.
Conclusion
Last Updated: Apr 17, 2024
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Token Bus and Token Ring

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Introduction

There is little difference between a token bus network and a token ring network, i.e., the token bus is more expensive than the token ring. Token ring networks are intended for offices, while token bus networks are designed for large industries. 

Computer Networks

IEEE 802.4 defines Token Bus networks, and IEEE 802.5 specifies the Token Ring. So, in what other ways does the Token Ring differ from Token Bus? Let's find the answer to this question further in this blog.

What is a Token Bus?

The token bus uses linear or tree-shaped cables to connect the stations. Still, in reality, the stations are connected over a network implementing a Token Ring protocol over a virtual ring. 

IBM created Token Bus for connecting their terminals with IBM mainframes as a local area network technology that provided 4 Mbps bandwidth.

The Token Ring combines the features of Ethernet (bus topology) and Token Bus. According to the MAC addresses of the stations, the logical Ring is formed in descending order.

How does the Token Bus work?

The diagram below illustrates this:

There are copper coaxial cables connecting the stations, but logically all the stations are connected. In Token Bus, a token is created to manage access to the coaxial cable that serves as a communication bus.

Token Bus

At each station, a token is passed. A station can only send data after it has captured the token before sending the data. Each user passes the token in a sequence.

It was used primarily for industrial applications. Manufacturing Automation Protocol (MAP) standardization was conducted using the token bus at General Motors. These concepts are similar to that of Token Ring networks. One main difference between the busses is that their ends do not come together to form a ring.

The Manufacturing Automation Systems and flexible manufacturing system (FMS) developed a modified Token bus protocol to guarantee packet delivery and transmission delay.

Also see, Message Switching in Computer Networks.

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Frame Format of Token Bus

The various fields of the frame format are - 

  • Preamble: Synchronization bits for frame alignment.
  • Frame Control: Control information about the frame.
  • Destination Address: Address of the intended recipient.
  • Source Address: Address of the sender.
  • Data: Payload containing information.
  • Checksum: Error detection mechanism.
  • End Delimiter: Marks the end of the frame.

What is a Token Ring?

IBM created the Token Ring in 1984 to improve their previous technology, Token Bus.

A token is made up of three bytes. Token Ring is a ring-based protocol that transmits data sequentially from one station to another using a token over a physical ring. A control token circles the Ring to control access.

Among the standard Token Ring, speeds are 4 and 16 Mbps, and high-speed Token Ring at 100 Mbps (IEEE 802.5t).

How does the Token Ring work?

In the following example, we have four stations, station1, station2, station3, and station4, connected via a ring topology. What are your options for finding out which station is currently transmitting and not transmitting right now? If they all send simultaneously, there will be a collision. In this case, token passing is necessary. Token passing allows communication between nodes in which a packet called a token is exchanged between nodes

Token Ring

Here is how data is transmitted:

The Ring continuously circulates empty information frames. Computers send messages by inserting a token in an empty frame, followed by a message and a destination identifier.

Each workstation then examines the frame. The destination workstation copies the message from the frame and changes the takeback to 0.

Upon returning the frame to the source, the token is set to 0 and copied the message. That message is then removed from the frame.

In the meantime, the "empty" frame circulates. When a workstation has a message to send, it is ready to receive it. The transmission is unidirectional, or one-way.

A mainframe's operation is critical to the operation of the Token Ring protocol, which can share the network with other data while allowing delay-sensitive traffic. LAN protocols with this feature are only available in Asynchronous Transfer Mode (ATM) at the data link layer.

Must Recommended Topic, Internal and External Fragmentation and Basic Networking Commands and Subnetting in Computer Networks

Advantages of Token Bus

The advantages of Token Bus are:

  • Deterministic Access: Ensures fair and controlled access to the network.
  • Collision-Free: Prevents collisions as only one node can transmit at a time.
  • Scalability: Can support a large number of nodes without performance degradation.
  • Priority Scheme: Allows for the implementation of priority-based access control.
  • Fault Tolerance: Token passing allows the network to recover from node failures swiftly.

Disadvantages of Token Bus

The disadvantages of Token Bus are:

  • Single Point of Failure: A malfunction of the token control station can disrupt the entire network.
  • Limited Bandwidth: The token passing mechanism may lead to inefficient bandwidth utilization.
  • Token Circulation Overhead: The token circulating through the network introduces latency.
  • Complexity: Requires sophisticated protocols for token passing and error handling.
  • Dependency on Physical Topology: Requires a physical bus topology, limiting flexibility in network layout changes.

Differences Between Token Ring and Token Bus

BasisToken BusToken Ring
TopologyBus topology is used for token bus networks.Star topology is used for token ring networks.
Token Passing MechanismToken contention-based accessDeterministic token passing
Collision HandlingCollisions handled with CSMA/CDRare collisions due to token passing
Failure ImpactFailures localized to affected bus segmentSingle device failure disrupts the network
EfficiencyVariable performance due to token contentionPredictable and deterministic performance
Implementation ComplexityCan be more complex due to collision handlingRelatively simpler implementation


You can also read about the network models in computer network.

Explore more:

Frequently Asked Questions

What is the token bus method?

The token bus method is a network access control mechanism where nodes pass a token to access the shared communication medium, ensuring orderly data transmission.

What is the speed of token bus?

The speed of token bus networks typically ranges from 1 to 10 Mbps.

What is IEEE standard 802.4 and token bus?

IEEE standard 802.4 defines the token bus protocol, specifying rules for token passing and access control in local area networks.

What is token ring and token bus map with IEEE 802 standard?

Token Ring is defined in IEEE 802.5 standard and Token Bus is defined in IEEE 802.4 standard.

Is token ring used in LAN?

Yes, Token Ring was used in LANs but is now less common.

Conclusion

This article is all about what is Token Ring and Token Bus are. Tokens are passed over a virtual network in a token bus network. In a token ring network, they are passed over a physical network. Then, we have also seen how they work.

Recommended Reading:


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