So sánh token bus và token ring năm 2024

Token Bus was a 4 Mbps Local Area Networking technology created by IBM to connect their terminals to IBM mainframes. Token bus utilized a copper coaxial cable to connect multiple end stations (terminals, wokstations, shared printers etc.) to the mainframe. The coaxial cable served as a common communication bus and a token was created by the Token Bus protocol to manage or 'arbitrate' access to the bus. Any station that holds the token packet has permission to transmit data. The station releases the token when it is done communicating or when a higher priority device needs to transmit (such as the mainframe). This keeps two or more devices from transmitting information on the bus at the same time and accidentally destroying the transmitted data.

Token Bus suffered from two limitations. Any failure in the bus caused all the devices beyond the failure to be unable to communicate with the rest of the network. Second, adding more stations to the bus was somewhat difficult. Any new station that was improperly attached was unlikely to be able to communicate and all devices beyond it were also affected. Thus, token bus networks were seen as somewhat unreliable and difficult to expand and upgrade.

Token Ring

Token Ring was created by IBM to compete with what became known as the DIX Standard of Ethernet (DEC/Intel/Xerox) and to improve upon their previous Token Bus technology. Up until that time, IBM had produced solutions that started from the mainframe and ran all the way to the desktop (or dumb terminal), allowing them to extend their SNA protocol from the AS400's all the way down to the end user. Mainframes were so expensive that many large corporations that purchased a mainframe as far back as 30-40 years ago are still using these mainframe devices, so Token Ring is still out there and you will encounter it. Token Ring is also still in use where high reliability and redundancy are important--such as in large military craft.

Token Ring comes in standard 4 and 16 Mbsp and high-speed Token Ring at 100Mbps(IEEE 802.5t) and 1Gbps (IEEE 802.5v). Many mainframes (and until recently, ALL IBM mainframes) used a Front End Processor (FEP) with either a Line Interface Coupler (LIC) at 56kbps, or a Token-ring Interface Coupler (TIC) at 16 Mbps. Cisco still produces FEP cards for their routers (as of 2004).

Token Ring uses a based topology and passes a token around the network to control access to the network wiring. This token passing scheme makes conflicts in accessing the wire unlikely and therefore total throughput is as high as typical Ethernet and Fast Ethernet networks. The Token Ring protocol also provides features for allowing delay-sensitive traffic, to share the network with other data, which is key to a mainframe's operation. This feature is not available in any other LAN protocol, except Asynchronous Transfer Mode (ATM).

Token Ring does come with a higher price tag because token ring hardware is more complex and more expensive to manufacture. As a network technology, token ring is passing out of use because it has a maximum speed of 16 Mbps which is slow by today's gigabit Ethernet standards.

A Token Bus Network is a network protocol used to transmit data. In a Token Bus Network, a virtual ring is formed between nodes/stations and token is transferred from one station to another in a sequential manner. Each node in a Token Bus Network knows the address of its successor and predecessor and can transmit data if it has the token.

A Token Ring Network is similar to a Token Bus Network but it works around the physical ring instead of a virtual ring. A token is passed from one node to another in a sequential manner and each node can transfer data when it has the token.

Read through this article to find out more about Token Bus Network and Token Ring Network and how these two networks are different from each other.

What is Token Bus Network?

The "token bus" is a network that uses a virtual ring on a coaxial wire to implement the Token Ring protocol. A token is transmitted between network nodes, and only the node with the token is allowed to broadcast. The token is sent on to the next node in the virtual ring if a node has nothing to communicate. Because each node in the ring must know the address of its neighbor, a specific protocol is required to notify the other nodes of connections to and disconnections from the ring.

Token Ring earned a reputation for being unstable and difficult to update due to issues addressing device failures and adding additional stations to a network. Bus networks, such as Ethernet, offered a more flexible and stable physical design, but Ethernet's access protocol couldn't guarantee a maximum duration for any station to wait to access the network. Thus it was believed to be unsuitable for manufacturing automation applications.

Token bus protocol combines the advantages of a physical bus network with the deterministic access mechanism of a Token Ring network.

IEEE standard 802.4 standardized the token bus. It was primarily employed in industrial settings. General Motors utilized the Token Bus to standardize its Manufacturing Automation Protocol (MAP).

What is Token Ring Network?

Token Ring is a type of computer network that is used to create local area networks. IBM first presented it in 1984, and IEEE 802.5 was standardized in 1989.

It makes use of a token, which is a three-byte frame that is transmitted around a logical ring of workstations or servers. This token passing is a channel access mechanism that ensures that all stations have equal access and avoids station collisions of contention-based access methods.

Data transfer on a Token Ring takes place in the following manner −

• On the ring, empty information frames are constantly exchanged.
• A computer seizes the token when it has a message to send. After then, the computer will be able to send the frame.
• The frame is subsequently inspected by each workstation in turn.
• The workstation that declares itself as the message's destination copies the message from the frame and changes the token back to 0.

Difference between Token Bus Network and Token Ring Network

The following table highlight the major differences between Token Bus Network and the Token Ring Network.

Key Token Bus Network Token Ring Network Ring Type In a Token Bus network, the token rotates within a virtual ring of nodes. In a Token Ring network, the token rotates within an actual ring of nodes. Usage The token bus system is primarily intended for large industries. The token ring network, on the other hand, is intended for use in workplaces. IEEE Standard Token Bus Network is part of IEEE 802.4 standards. Token Ring Network is part of IEEE 802.5 standards. Bandwidth Capacity Token Bus network provides high bandwidth. Token Ring network bandwidth is lesser as compared to Token Bus network bandwidth. Network Topology Token Bus network uses Bus topology. Token Ring network uses Star topology. Maximum Response Time The maximum time to reach the last station in the Token Bus network is not easy to calculate. The maximum time to reach the last station in the Token Ring network can be calculated easily.

Conclusion

Token Bus LAN standard is defined by IEEE 802.4. Stations connected on a Bus are structured in a logical ring in token passing techniques. In this procedure, only the station having a token is being permitted to transmit frames.

Token Ring standards are described in IEEE 802.5. When all stations in a token ring are idle, a specific bit pattern called the token cycles around the ring. The physical positions of the stations on the ring define the token sequence.