Network Topology

 What Is Network?

Network is a collection of computers and devices connected together via communication devices and transmission media.

What Is Network Topology?

A network topology refers to the layout of the computers and devices in a communications network

It refers to both the physical and logical layout of a network.

Physical Topology Layout

• The arrangement of a cabling is the physical topology.

Logical Topology Layout

• The path that data travels between computers on a network.

The study of network topology recognizes three basic topologies:

1. Bus network topology
2. Star network topology
3. Ring network topology

Bus Network Topology

In local area networks where bus topology is used, each node is connected to a single cable. Each computer or server is connected to the single bus cable. A signal from the source travels in both directions to all machines connected on the bus cable until it finds the intended recipient. If the machine address does not match the intended address for the data, the machine ignores the data. Alternatively, if the data matches the machine address, the data is accepted. Since the bus topology consists of only one wire, it is rather inexpensive to implement when compared to other topologies. However, the low cost of implementing the technology is offset by the high cost of managing the network. Additionally, since only one cable is utilized, it can be the single point of failure. If the network cable is terminated on both ends and when without termination data transfer stop and when cable breaks, the entire network will be down.

Advantages 

1. It is easy to set-up and extend bus network.
2. Cable length required for this topology is the least compared to other networks.
3. Bus topology costs very less.
4. Linear Bus network is mostly used in small networks. Good for LAN.

Disadvantages 

1. There is a limit on central cable length and number of nodes that can be connected.
2. Dependency on central cable in this topology has its disadvantages.If the main cable (i.e. bus ) encounters   some problem, whole network breaks down. 
3. Proper termination is required to dump signals. Use of terminators is must.
4. It is difficult to detect and troubleshoot fault at individual station.
5. Maintenance costs can get higher with time.
6. Efficiency of Bus network reduces, as the number of devices connected to it increases.
7. It is not suitable for networks with heavy traffic. 
8. Security is very low because all the computers receive the sent signal from the source.

Ring Network Topology

A network topology that is set up in a circular fashion in which data travels around the ring in one direction and each device on the right acts as a repeater to keep the signal strong as it travels. Each device incorporates a receiver for the incoming signal and a transmitter to send the data on to the next device in the ring. The network is dependent on the ability of the signal to travel around the ring. When a device sends data, it must travel through each device on the ring until it reaches its destination. Every node is a critical link.

Advantages 

1. 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.
2. Even when the load on the network increases, its performance is better than that of Bus topology.
3. There is no need for network server to control the connectivity between workstations.
4. Additional components do not affect the performance of network.
5. Each computer has equal access to resources.

Disadvantages 

1. Each packet of data must pass through all the computers between source and destination. This makes it slower than Star topology.
2. If one workstation or port goes down, the entire network gets affected.
3. Network is highly dependent on the wire which connects different components. 
4. MAU’s and network cards are expensive as compared to Ethernet cards and hubs. 

Star Network Topology

In local area networks with a star topology, each network host is connected to a central hub with a point-to-point connection. In Star topology every node (computer workstation or any other peripheral) is connected to central node called hub or switch. The switch is the server and the peripherals are the clients. The network does not necessarily have to resemble a star to be classified as a star network, but all of the nodes on the network must be connected to one central device. All traffic that traverses the network passes through the central hub. The hub acts as a signal repeater. The star topology is considered the easiest topology to design and implement. An advantage of the star topology is the simplicity of adding additional nodes. The primary disadvantage of the star topology is that the hub represents a single point of failure.

Advantages 

1. As compared to Bus topology it gives far much better performance, signals don’t necessarily get transmitted to all the workstations. A sent signal reaches the intended destination after passing through no more than 3-4 devices and 2-3 links. Performance of the network is dependent on the capacity of central hub.
2. Easy to connect new nodes or devices. In star topology new nodes can be added easily without affecting rest of the network. Similarly components can also be removed easily.
3. Centralized management. It helps in monitoring the network.
4. Failure of one node or link doesn’t affect the rest of network. At the same time its easy to detect the failure and troubleshoot it.

Disadvantages 

1. Too much dependency on central device has its own drawbacks. If it fails whole network goes down.
2. The use of hub, a router or a switch as central device increases the overall cost of the network.
3. Performance and as well number of nodes which can be added in such topology is depended on capacity of central device.

What Is Internet?

According to wikipedia , Internet is the global system of interconnected computer networks that use the Internet protocol suite (TCP/IP) to link devices worldwide. It is a network of networks that consists of private, public, academic, business, and government networks of local to global scope, linked by a broad array of electronic, wireless, and optical networking technologies. The Internet carries an unlimited range of information resources and services, such as the inter-linked hypertext documents and applications of the World Wide Web (WWW), electronic mail, telephony, and file sharing.

Evolution Of The Internet

ARPANET

• ARPA which stands for Advance Research Project Agency ,  is created by US Department of Defense.
• The network is called ARPANET.
• The network became functional in September 1969
• Apranet had two main goals.

INTERNET2

• Internet2 is not a new network
• It is a research and development project
• In developing technology to ensure that the internet in the future can handle tomorrow's applications.