The set of nodes are connected in the form of ring which is the token ring. Its a single shared medium. Each node in the network transmits the data following a distributing algorithm. Every frame of the data is analyzed by every node, where the destination node saves a copy as in the data frame header of the frame as it passes. If any devices in the network fail it renders the whole network which is overcome by the star topology. In this star topology it is connected centrally to a token ring hub. The Multi-station Access unit (MAU) is the hub which in terms acts as a relay. These units are required for the robustness and any change in the structure of the network like addition and removal of nodes.

A special sequence of bits circulating around the network is defined as the Token, wherein each node receives and forwards the token. A node possessing the frame to transmit upon the exposure of the token, it removes the ring off the token than inserting the frame in the ring. The frame on its way to the sender strips of the frame from the node and reinserts the token. The given node has an associated time called the THT or the token holding time for the hold of the token the definition emphasizes that it has an impact on utilization and fairness upon the network where the utilization is considered to be the bandwidth usage against that set on the allocated network.

PROS AND CONS OF NETWORK TOPOLOGIES

BUS TOPOLOGY

PROS

For small networks, bus topology is the appropriate topology. Implementation and handling the topology is easy.

CONS

Since it suits small networks, the length of the cable is small and this defines the length of the network in which the stations are connected. Only limited nodes can be functioned with the help of this topology.

RING TOPOLOGY

PROS

Data transferred between two nodes passes through the nodes present in between the source and the destination nodes. For managing topology, a separate central server is not needed.

CONS

If any node in the network fails it affects the flow of data transfer and also any change in the network affects the performance of the network

MESH TOPOLOGY

PROS

The main advantage of the network is it transmits data from one mode to multiple nodes.

CONS

Redundancy of the network connection happens in this topology because when one node is connected to multiple nodes the purpose of many connections in the network between nodes is of no purpose.

STAR TOPOLOGY

PROS

Isolation of network devices is achieved in this star topology. The operation of data transmission is simpler due to its nature of centralization.

CONS

The main functionality of the network devices in this topology is achieved by the central hub. If the central hub fails the data transfer in the entire network gets affected

TOKEN BUS

IBM developed token bus to connect IBM mainframe with the terminals. It is a 4Mbps LAN technology. The physical structure of a token bus comprises of copper coaxial cable which in term connects the mainframe of the network to many stations (workstations, terminals). The communication channel is achieved by the co-axial cable whereas the token bus protocol creates a token for the transmission of data. The station possessing the token has the right to transmit the data and the transmission occurs when the token is released by the station. Priority is given to devices such as mainframe for the data transmission. This kind transmission makes one or more devices to transmit data in the token bus.

Limitations of token bus

Failure of any device in the bus will affect the entire network.

More number of stations cannot be added to the network.

Newly added Stations which are not properly added to the network will be not being able to function properly in the network.

TOKEN RING

Source: Webopedia Computer Dictionary.

[ONLINE] Available at: http://www.webopedia.com/TERM/T/token_ring_network.html

IBM developed token ring, which is an upgrade to the technology developed before. A compete to the DIX (DEC/Intel/Xerox) standard of Ethernet is the token ring. The physical structure of the token ring is the ring structured network and it controls the access of the network by a token which is passed in the network. The final throughput is huge as the fast Ethernet and Ethernet for the token ring since conflicts takes place in accessing the network. The features of the token ring protocol are sharing the network, delay-sensitive traffic. These features are the main factors for the operation of a mainframe device. The maximum speed of token ring is 16Mbps which makes this out of use in front of today’s Ethernet standards. Token is highly expensive for its manufacture and its complexity.

Network Topology:

A complete configuration of the cables, peripherals, computers of a network completes the physical topology. The physical scope of the Topology should not be linked with the logical Topology that has been used to transfer information from one to another workstation.

Major Types – Network Topologies:

The term Topology refers to a connected layout of devices shared in a network. No we shall go ahead in the discussion of the standard Topologies from the computer networking.

An imagination of the shape of the network or the structure of virtual architecture is considered to be the topology. The structure or the shape is not mandatory to implement the exact physical layout of the present devices in the network. For instance the Home LAN shall be constructed in a circle physically and does not really need to determine the circle in the topology too. They shall be categorized as follows;

Star Topology

Ring Topology

Bus Topology

Tree Topology

Mesh Topology

Hybrid Topology

A solid or complex oriented network shall be built by the association of the hybrids of one or more of the basic scheduled topologies mentioned above.

Star Topology:

This Topology is mainly considered for the home networking. It normally facilitates a model of central connection called the HUB and this hub may not definitely be a HUB, it may consist of Router or a Switch or a Hub itself. The devices are connected to the Hub through the UTP Ethernet. A comparative study with the bus topologies the star topology consist of more usage of cables and the breakage of the network does only pull one computer network access down and not the complete set of LAN anyhow on the failure of the hub the entire network fails.

The general advantage of the Star Topology describes ease of installation and wiring without any disruptions caused to the network while connecting or disconnecting of any devices. They are easy to connect, remove or detect faults in and among the devices or the network.

The general Disadvantages of the Star Topology state’s some such as the increase in the necessary of the cable length. The Hub or the device used as hub fails to concentrate then the nodes attached shows to be inactive or disabled automatically. These topologies are considered to be more expensive than the existing linear topologies increasing the cost value of the concentrators.

The protocol access for the Star Topology is recognised to be the LocalTalk or the Ethernet. The token Ring uses a similar kind of topology known as the Star-Wired Ring.

Star-Wired Ring:

The outlook appearance of the Star-Wired Topology is to be the same model of the Star Topology. The MAU of the Star-Wired ring consist of the wiring that focuses on the transfer of information from one device to another in a ring or a circle as explained in the figure below. A Star-Wired Topology is been used in the Token Ring protocol.

Ring Topology:

Each and every device in this category has two exact neighbours for communication purposes and instances in the Ring network. The messages distributed travel through the ring in the same direction either clockwise or anti-clockwise failing the entire network on the account of breakage. If any cable or device is broken in the connection of the loop then they take the advantage of breaking the entire network. A typical usage of the FDDI, SONNET or any Token Ring topology is used for the implementation of the Ring Network. These kinds of topologies are enhanced in schools and some office enterprises.

An interesting topology in the network topology is the network topology. On the outline it looks like the group of computers which are connected in the form of circle. The network is redundant and collision-free topology. Being a ring, there are no terminator devices in this topology. The node gives information of data about destination address. According to the destination address given in the data sent in the frame it reaches the destination address and the data is given to destination from the frame. This ring topology is of another kind which is known as Dual-Ring topology. The second ring is being used when the first ring fails.

An illustration – Ring Topology:

Bus Topology:

These are networks and are not confused along with the Bus of the computers. These Networks are used as a common activity for the connection of the devices in the network. They are also known as the backbone of the networks. A shared connection shares the communication with another device by the medium through a single cable; they attach or tap along with the interface connector. A broadcast message is sent through the wire set in the network by the device that is need of communication and only the intended recipient formally receives, accepts and processes the messages.

Ethernet Bus topologies are in action with comparatively less usage of cables and are relatively easy in the process of installation on comparison with the alternatives. The cabling options differ as 10Base-2 (ThinNet) and 10Base-5 (ThickNet), as both are famous Ethernet cables for bus topologies. The bus topologies are best enhanced and reported with results in a limited active devices environment. If in the same case more number of computers are connected then the performance may be affected as they are only restricted to a limited number of computers. An additional problem such as the failure of the backbone shall result in the breakage of the entire network and may enter the stage of becoming unusable.

An illustration – Bus Topology:

Liner Bus Topology – Advantages:

The computer of the peripheral shall be attached easily with the linear bus. The requirement of the length of cable is less when compared with the Star Topologies.

Linear Bus Topology – Disadvantages:

A small break in the cable shuts the entire network. The backbone cable requires terminator at the both ends. A difficulty arises in the understanding of the problem in the shutting down of the system as a whole. This type of solution is never recommended for a stand-alone solution for a large building using large number of networking area.

Tree Topology:

Integrating multiple start topologies combined with the bus topology is known as the Tree topology. To define it easily the hub is the only device that connects to the tree directly, and defined as a each hub functioning to be a root from the tree of devices. The hybrid approach of the bus and the star topologies enhances the future of the network expandability that is proposed to better than the bus topology and the star topology. Whereas in the bus topologies the numbers of devices are limited due to the generation of traffic in broadcasting and in the Star topologies there are only limited number of hub points.

An illustration – Tree Topology:

Tree Topology – Advantages:

Individual segments including Point to Point wiring features.

Supported by different vendors and several hardware’s.

Tree Topology – Disadvantages:

The length of the overall segment is limited by the type of cable used.

The entire system goes down upon the breakage of the backbone line in the system.

The configuration is considerably more difficult other than other topologies.

Mesh Topology:

This is a topology that involves the concept of routes. The mesh topologies unlike the other topologies shall take any path from the source to the destination through several options as the messages sent in other network uses the same passage. In comparison with the ring topologies the messages though having a two cable path they travel only through one direction. Some of the Wide area network associate deploys the Mesh routing.

The connection of every single node together is specified as the Full Mesh topology. This shall create the most reliable and redundant networks especially for the large networks used in many organisations. Even though if one link or the other fails they should be able to get connected and linked through the other for the transferring of the data. The linking specifies more connect-ability issues creating a technique of involving a partial mesh topology for restriction of the calculation of the wires used for the linking of the computers for every device on a network.

The Partial mesh topology is more or less like the Full-mesh as the only difference is the connection of every device with another device on the network is not made instead implementing few routes alternatively. The partial-mesh topologies is been adopted for redundant connection and mostly in WAN’s between routers. A full mesh is defined as the part of a Mesh network where the complete device connects as depicted in the illustration below, some devices may also connect through indirect way empowering the partial mesh networks.

Hybrid Topology:

A hybrid topology is one where one or more network topologies exist.

Scenario 1: scenarios in which two different topologies connected together still can observe and maintain the same basic network character and hence cannot be considered as a Hybrid Network. For instance a tree network being connected to the same tree network is still the tree network. Therefore the hybrid network is said to be absolute when the two basic network topologies are associated and the topologies resulted failing to meet the basic topology definitions. Example: Two star topologies associated exhibits hybrid topology networks.

Scenario 2: two basic network topologies connected accrues the Hybrid Topology.

Token Bus:

The token ring network and the token bus network are similar processes wherein the station shall have the possession of a token earlier than the transmission on the network. On the other hand the determination of the topology and the understanding of the token-passing methodology are totally different. The IEEE 802.4 committee has expressed the standards of Token bus as the broadband networks in opposition with the Ethernet’s baseband transmission technique. The MAP, Manufacturing Automation Protocol for the manufacturing of the Floor networks uses the IEEE 802.4. Attached resource Computing Network (ARCNET) developed by the General Motors. Although it does not agree or confirm to IEEE 802.4 standards it comes under the Token Bus network only.

A group of workstations connected by huge long trunk cables of the network may be called as a topology. The workstations normally divide in a star configuration from the hubs comprising of the bus and the star topology. A group of user’s separated by a measured distance come under the category of the Token bus topology and they are determined to the best in structure among them. The token bus networks of the IEEE 802.4 are designed in the 75-ohm coaxial cable via the bus topology. The characteristics of the broadband for the IEEE 802.4 support the standard transmission simultaneously over different several channels.

The frames of data and tokens are transferred from one station to another in order of following the station addresses with numeric sequence. Hence the token rings are said to follow a logical ring than a physical ring. The token is passed from the last station to the first station through a numerical order pass. The token ring shall never follow the physical ring or ordering present in the workstation attachment to the cable. The stations may present in a different physical location in different orders than the transfer is said to be made. For instance the station 1 might be at one corner and station 2 be in another corner with station 3 present in the middle space.

Token bus is said to be present in some manufacturing environments while the Ethernet and the token ring methods have become more standard and prominent in many office environments.

Token and Token-Passing Access Methods:

A special controlled frame in the token bus. Token ring and Fibre Distributed Data Interface (FDDI) determining the station for the transmission of data on a shared network is defined as a Token.

A token that possess the node shall have the capability to transmit. Other than the contention based networks like the Ethernet, token based network workstations shall not complete the access for to the network. The token obtained station only can transmit whereas the other stations will rather wait for the token than to detect the access of the network in their own. In an occasion of two or more workstations attempting to access the network at the same time result in collisions in the Ethernet networks. These should get back and try again in a different time space that significantly reduces the performance as the workstation attached to the network increases.

A station takes access or control of a possession of a token and one bit is changed forming the Start of Frame Sequence (SFS) converted from the token in the token ring networks. The workstation may indicate the priority type that may be required for the transmission in the field that exist in the token. These priority settings are essentially a request in the future for the workstations in the exercise of the tokens. The other stations work their own priority levels comparing the workstations request. If the priority of the workstation is higher than the rest of the stations may grant access to the token with an extensive period.