What is a Topology?
The physical topology of a network refers to the configuration of cables, computers, and other peripherals. Physical topology should not be confused with logical topology which is the method used to pass information between workstations. Logical topology was discussed in the Protocol chapter.
Main Types of Physical Topologies
The following sections discuss the physical topologies used in networks and other related topics.
Star topologies also may be implemented with Ethernet/cabled structures, wireless routers and/or other components. In many cases, the central hub is the server, and the additional nodes are clients. Benefits of a star network topology include the following: Has the ability to limit the impact of a single failure. A hub maybe a hub, a router or a switch. In star Topology, there exists a point-to-point connection between a node and hub device. The hub device takes a signal from any node and passes it to all the other nodes in the network. Star Topology Network Design, Diagram and Description. Here is the Star Topology Layout Picture for proper understanding this concept. It is clearly evident from the diagram that this Type of Topology works by using a central device to which all other Nodes like Clients, Servers and other Network Nodes are connected.
Linear Bus
A linear bus topology consists of a main run of cable with a terminator at each end (See fig. 1). All nodes (file server, workstations, and peripherals) are connected to the linear cable.
Advantages of a Linear Bus Topology
- Easy to connect a computer or peripheral to a linear bus.
- Requires less cable length than a star topology.
Disadvantages of a Linear Bus Topology
- Entire network shuts down if there is a break in the main cable.
- Terminators are required at both ends of the backbone cable.
- Difficult to identify the problem if the entire network shuts down.
- Not meant to be used as a stand-alone solution in a large building.
Star
A star topology is designed with each node (file server, workstations, and peripherals) connected directly to a central network hub, switch, or concentrator (See fig. 2).
Data on a star network passes through the hub, switch, or concentrator before continuing to its destination. The hub, switch, or concentrator manages and controls all functions of the network. It also acts as a repeater for the data flow. This configuration is common with twisted pair cable; however, it can also be used with coaxial cable or fiber optic cable.
Fig. 2. Star topology
Advantages of a Star Topology
- Easy to install and wire.
- No disruptions to the network when connecting or removing devices.
- Easy to detect faults and to remove parts.
Disadvantages of a Star Topology
- Requires more cable length than a linear topology.
- If the hub, switch, or concentrator fails, nodes attached are disabled.
- More expensive than linear bus topologies because of the cost of the hubs, etc.
Tree or Expanded Star
A tree topology combines characteristics of linear bus and star topologies. It consists of groups of star-configured workstations connected to a linear bus backbone cable (See fig. 3). Tree topologies allow for the expansion of an existing network, and enable schools to configure a network to meet their needs.
Advantages of a Tree Topology
- Point-to-point wiring for individual segments.
- Supported by several hardware and software venders.
Disadvantages of a Tree Topology
- Overall length of each segment is limited by the type of cabling used.
- If the backbone line breaks, the entire segment goes down.
- More difficult to configure and wire than other topologies.
5-4-3 Rule
A consideration in setting up a tree topology using Ethernet protocol is the 5-4-3 rule. One aspect of the Ethernet protocol requires that a signal sent out on the network cable reach every part of the network within a specified length of time. Each concentrator or repeater that a signal goes through adds a small amount of time. This leads to the rule that between any two nodes on the network there can only be a maximum of 5 segments, connected through 4 repeaters/concentrators. In addition, only 3 of the segments may be populated (trunk) segments if they are made of coaxial cable. A populated segment is one that has one or more nodes attached to it . In Figure 4, the 5-4-3 rule is adhered to. The furthest two nodes on the network have 4 segments and 3 repeaters/concentrators between them.
NOTE: This rule does not apply to other network protocols or Ethernet networks where all fiber optic cabling or a combination of a fiber backbone with UTP cabling is used. If there is a combination of fiber optic backbone and UTP cabling, the rule would translate to a 7-6-5 rule.The speed of networking switches is vastly improved over older technologies, and while every effort should be made to limit network segment traversal, efficient switching can allow much larger numbers of segments to be traversed with little or no impact to the network. Atmosphere vst keygen download windows 10.
Considerations When Choosing a Topology
- Money. A linear bus network may be the least expensive way to install a network; you do not have to purchase concentrators.
- Length of cable needed. The linear bus network uses shorter lengths of cable.
- Future growth. With a star topology, expanding a network is easily done by adding another concentrator.
- Cable type. The most common cable in schools is unshielded twisted pair, which is most often used with star topologies.
Summary Chart
Physical Topology | Common Cable | Common Protocol |
---|---|---|
Linear Bus | Twisted Pair Coaxial Fiber | Ethernet |
Star | Twisted Pair Fiber | Ethernet |
Tree | Twisted Pair Coaxial Fiber | Ethernet |
A topology is a relationship exist between the links and linking devices (nodes) to each other which is represented by a geometric representation. Star and Ring topology are the types of network topologies. The crucial difference between star and ring topology is that the star topology is suitable for a primary-secondary type of connection whereas ring topology is more convenient for the peer-to-peer connection.
The link is shared equally in the peer-to-peer connection. Inversely, in a primary-secondary relationship one device is used to control traffic and other devices must transmit the signal through it.
Content: Star Topology Vs Ring Topology
Comparison Chart
Basis for comparison | Star Topology | Ring Topology |
---|---|---|
Architecture structure | Peripheral nodes are linked to the central device known as a hub. | Every node has two branches connected to a node either side of it. |
Amount of cabling required | Larger | Less as compared to star topology |
Point of failure | Hub | Every node in the ring |
Data traversal | All data passes through the central network connection. | Data moves in only one direction around the ring till it arrives the destination. |
Network expansion | A new cable is plugged in from the new node to the hub. | In order to add a new node, a connection must be broken which turns down the network. |
Fault isolation | Easy | Difficult |
Troubleshooting | The other nodes are affected only in the case of a hub failure. | When a node goes down the information continues to transfer till the damaged node. |
Cost | High | Low |
Definition of Star Topology
Star Topology is the network architecture in which each device has a dedicated point-to-point link only to the central controller known as a hub. There is no direct link exists among the devices. It is dissimilar to mesh topology which allows direct traffic between the devices. In Star topology, the controller plays an important role and act as a mediator. When a device wants to send data to another, it first sends data to the controller which then relays the data to other connected devices.
Star topology needs only one link and I/O port to connect a device to another. That is the reason it is easy to install and reconfigure. The addition, deletion, replacement of the devices involves only one connection that is between that device and the hub. The cabling requirements are less in the star topology, but it is greater when we compare it with other topologies such as tree, ring and bus.
This topology is robust where even if the link fails, only that link is influenced and the other links remain active. It also makes fault identification and isolation easier. Hub observes link problems and bypasses faulty links.
Definition of Ring Topology
The Ring Topology connects each device with dedicated point-to-point line configuration to other two adjacent devices, and the first device connects to the last device. It passes a signal in only one direction from one device to other until it reaches the device sent the signal. A repeater is installed in each device in the ring. If a device receives a signal meant for another device, the device regenerates the bits and boosts the signal by using a repeater that is installed on each device and transfers them along. When the signal reaches the destination, the receiver sends back an acknowledgement to the sender.
Ring topology is easy to install and configure as each device is linked to its immediate neighbour. The addition, deletion and repositioning of a device just require changing only two connections. The only limitations are the traffic and media considerations, i.e., the maximum length of the ring and the number of devices.
The fault isolation in a ring can be simplified by using an alarm which alerts the network operator to the problem and its location. A signal is circulated continuously, if any device does not receive a signal within a specified time it can issue an alarm. Though, unidirectional nature of traffic can be disadvantageous for the network where even a single faulty cable can disable the entire network. This limitation can be overcome by employing a switch or a dual ring that is able to closing off the break.
Star Topology Cost Chart
Key Differences Between Star and Ring Topology
- In the star topology, each device is connected to a central node which sends the information received from one device to the other and act as a mediator. On the other hand, in the ring topology, each device has two nodes connected to either side of it, and the last node is connected to the first one.
- The star topology requires more cable than ring topology.
- Hub in the star topology is considered as a point of failure because the failure of any device would not affect the whole network, but if hub goes down, no data is transmitted across it. In contrast, each node in the ring topology is considered to be a point of failure as the failure of any device could significantly affect whole ring network.
- In a star topology, all the data travels through the central hub. As against, in the ring topology, the data passes through each node unidirectionally until it reaches the destination.
- To add new nodes to the ring network, a cable is used to connect the new device to the hub without influencing the rest of the network. On the contrary, the addition of new devices is done by breaking a connection which results in temporary unserviceable network till the new device is activated.
- Fault isolation is easier in star topology while it is quite difficult in the ring topology.
- Troubleshooting in the ring topology is simple, as the information continues to transfer through the rest of ring until reaching the point of failure. Conversely, in the star topology, the other devices are affected only when the connecting device goes down (Hub).
- Star topology is expensive than the ring because it requires central connecting device usually hub.
Conclusion
The star topology is used to connect primary-secondary type of connection whereas ring topology is used for peer-to-peer connections.