COMUTER NETWORK & NETWORK TOPOLOGY

Computer Network

Computer network is a collection of computers and other network devices which are connected with each other. A computer network allows the user to share resources which include information, software and peripheral devices such as printers, scanners etc. with other users in the network.

Computer networks are classified into different types according to the network size, level of required network security, amount of network traffic, needs of network users, level of administrative support available, network budget etc.                                        

 

Types of network

Computer network is categorized as per the geographical area to be covered by the network. There are three types of networks:

 

1. Local Area Network (LAN)

A local area network is a high-speed data network that covers a small geographical area such as a home, school, office building. It typically connects network devices in such a way that workstations, personal computers, printers, servers, and other devices can share data, programs etc.

 

2. Metropolitan Area Network (MAN)

A metropolitan area network is a network that covers a larger area. Larger than that of a LAN but smaller than a WAN. It covers larger geographical areas, such as cities or districts.

 

3. Wide Area Network (WAN)

A wide area network is a data communications network that covers a relatively broad geographical area which can span the globe and that often uses transmission facilities provided by common carriers, such as telephone companies. Internet is an example of wide area network.

COMPARISON CHART OF LAN, MAN AND WAN

	LAN	MAN	WAN
Distance	Limited-typically 1 meter-1 km	Limited-typically 1 km- 100 km	Unlimited- upto 10,000 km
Speed	High- Typically in excess of 10 Mbps, 100Mbps and 1000Mbps are standard	High- Typically 100 Mbps	Slower- 10-20 Mbps
Error Rate	Lowest	Moderate	Highest
Media	Locally owned – twisted pair wires, fiber optic cable, wireless (not satellite)	Locally owned and common carrier – twisted pair wires, fiber optic cable and wireless	Locally owned and common carrier- twisted pair wires, coaxial cable, fiber optic cable, wireless to include satellite
Cost	Low	High	Higher
Example	College, School, Hospital.	Small towns, City.	Country/Continent.

Network Topology

Network Topology describe the ways in which network devices are connected to create a network.

Network Topologies can be Physical (how the wires are interconnected) or Logical (determines the way in which the data actually passes through the network from one device to other). A network can be created by using point-to-point connection in which only two devices are connected to each other and in multi-point connection where many devices share the connection.

1. Bus Topology

Bus topology is a network topology in which all devices are connected to a single cable called backbone. The backbone functions as a shared communication medium that devices attach or tap into with an interface connector.

Suppose a device wants to communicate with another device on the network then it sends a broadcast message on the backbone cable and all other devices can see that message, but only the intended recipient actually accepts and processes the message. Bus topology is also known as linear topology.

When the signal reaches the end of the cable length, that signal returns in the direction it came from and that signal will create problem in the network. So, the terminators are used at both end of the backbone cable to absorb that unused signal.

 

Bus Topology Diagram

 

Advantages of Bus Topology

·         Easy to connect a network device to the network

·         Less expensive

·         Used in small networks

·         The failure of one device does not affect the entire network

Disadvantages of Bus Topology

·         A break in the backbone cable can cause the entire network shut down.

·         Terminators are required at both ends of the backbone cable.

·         Difficult to troubleshoot if the entire network shuts down.

·         Not meant to be used as a stand-alone solution in a large building.

·         The efficiency will be decrease, when the number of devices connected to the bus network increases.

2. Star Topology

In star topology all nodes (file server, workstations, and peripherals) are connected directly to a central network device such as hub or switch. The hub or switch takes a signal from any node and passes it to all the other connected nodes in the network. The hub or switch manages and controls all functions of the network.

If one node needs to send data to another node, it will send the data to the central connecting hub device. Then the hub device will relay the data to the intended recipient. This configuration is common with twisted pair cable; however, it can also be used with coaxial cable or fiber optic cable.

Star Topology Diagram

Advantages of Star Topology

·        Easy to install.

·        Easy to extend the network without disturbing to the entire network.

·        Easy to detect faults and to remove parts.

·        Easy to manage and maintain the network.

Disadvantages of Star Topology

·        If the central hub or switch goes down, the entire network will shut down

·        More expensive than bus topology because of the additional cost of the connecting devices.

·        Requires more cable length than a bus topology.

3. Ring Topology

In Ring Topology, all the nodes are connected to each-other in a circular manner to make a closed loop. Each node is connected to two adjacent neighbors. In ring topology, all data travels around the network, in one direction.

Ring topology can be categorized into two types:

In Single Ring Topology, all the nodes are connected to a single cable called primary ring and data travels only in one direction.

Dual Ring Topology consists of two independent primary and secondary rings. Data can travel in both the directions- clockwise or anti-clockwise. Secondary ring is redundant and is used only when primary stops functioning.

Ring Topology Diagram

Advantages of Ring Topology

·        This type of network topology is very organized. Each node gets to send the data when it receives an empty token. This helps to reduces chances of collision. Also, in ring topology all the traffic flows in only one direction at very high speed.

·        Even when the load on the network increases, its performance is better than that of Bus topology.

·        There is no need for network server to control the connectivity between workstations.

·        Additional components do not affect the performance of network. Each computer has equal access to resources. 

Disadvantages of Ring Topology 

·        Each packet of data must pass through all the computers between source and destination. This makes it slower than Star topology.

·        If one workstation or port goes down, the entire network gets affected.

·        Network is highly dependent on the wire which connects different components.

·        Device needed to connect computer and network cards are expensive as compared to Ethernet cards and hubs.

4. Mesh Topology

In a mesh network topology, each of the network devices are interconnected with one another and each device (node) transmits its own data as well as relay data from other devices. This topology provides many redundant connections. There are two types of mesh topology

Full Mesh Topology

In full mesh topology, each network device (node) is connected to every other device in the network. If one of the devices (nodes) goes down then the network traffic can be redirected to other devices (nodes). This topology is used only for backbone networks.

Partial Mesh Topology

In partial mesh topology, each network device (node) is indirectly connected to other devices in the network. It also reduces redundancy.

Mesh Topology Diagram

Advantages of Mesh topology 

·        It can manages to transmit high amount of traffic from one device to multiple devices simultaneously.

·        Even if one of the devices fails there is always an alternative path for data transmission. So data transfer doesn’t get affected.

·        Adding and removing devices in the topology can be done without disrupting other network devices (nodes).

Disadvantages of Mesh topology

·        Requires high number of cables for setting up the network topology.

·        Difficult to configure the mesh topology, as each node is connected to all other node.

·        Mesh topology is costly compared to the other network topologies.

5. Tree Topology

The structure of tree topology is a combination of bus and star topologies. It consists of groups of nodes connected as star topology. These groups of star network topologies are connected to a backbone cable of bus topology. Tree topologies allow for the expansion of an existing network, and enable schools to configure a network to meet their needs.
 

Tree Topology Diagram

Advantages of a Tree Topology

·        Fault identification and correction is easy.

·        Scalable as Expansion of existing network is easy

·        Point-to-point wiring for individual segments.

·        Networks divided into segments. Thus, failing of one segment does not affect the rest of the network.

Disadvantages of a Tree Topology

·        Costly

·        If the backbone line breaks, the entire segment goes down.

·        Difficult to configure than other network topologies.