Networks & CommunicationsNetworks & CommunicationsIntroductionIntroduction

OverviewOverview Network TopologyNetwork Topology

– Bus NetworkBus Network– Ring NetworkRing Network– Star NetworkStar Network– Tree NetworkTree Network– Mesh NetworkMesh Network

Network CharacteristicsNetwork Characteristics Network ApplicationsNetwork Applications The InternetThe Internet

Bus NetworkBus Network

Bus NetworkBus Network A bus network is an arrangement in a local area network (LAN)

in which each node (workstation or other device) is connected to a main cable or link called the bus. The illustration shows a bus network with five nodes. Each node is shown as a sphere, the bus appears as a heavy horizontal line, and connections to the bus appear as vertical lines.

A bus network is simple and reliable. If one node fails to operate, all the rest can still communicate with each other. For a major disruption to take place, the bus itself must be broken somewhere. Bus networks are easy to expand. Additional nodes can be added anywhere along the bus.

There are several limitations to the bus network topology. The length of the bus is limited by cable loss. A bus network may not work well if the nodes are located at scattered points that do not lie near a common line.

Ring NetworkRing Network

Ring NetworkRing Network A ring network is a local area network (LAN) in which the

nodes (workstations or other devices) are connected in a closed loop configuration. Adjacent pairs of nodes are directly connected. Other pairs of nodes are indirectly connected, the data passing through one or more intermediate nodes. The illustration shows a ring network with five nodes. Each node is shown as a sphere, and connections are shown as straight lines. The connections can consist of wired or wireless links.

A break in the cable of a ring network may result in degraded data speed between pairs of workstations for which the data path is increased as a result of the break. If two breaks occur and they are not both in the same section of cable, some workstations will be cut off from some of the others. When system reliability is a critical concern, a bus network or star network may prove superior to a ring network. If redundancy is required, the mesh network topology may be preferable.

Star NetworkStar Network

Star NetworkStar Network A star network is a local area network (LAN) in which all nodes

(workstations or other devices) are directly connected to a common central computer. Every workstation is indirectly connected to every other through the central computer. In some star networks, the central computer can also operate as a workstation. The illustration shows a star network with five workstations (or six, if the central computer acts as a workstation). Each workstation is shown as a sphere, the central computer is shown as a larger sphere, and connections are shown as straight lines. The connections can be wired or wireless links.

In a star network, a cable failure will isolate the workstation that it links to the central computer, but only that workstation will be isolated. All the other workstations will continue to function normally, except that they will not be able to communicate with the isolated workstation. If any workstation goes down, none of the other workstations will be affected. But if the central computer goes down, the entire network will suffer degraded performance or complete failure. If redundancy is required, the mesh network topology may be preferable.

Tree (star-bus) NetworkTree (star-bus) Network

Tree NetworkTree Network In telecommunication networks, a tree network is a

combination of two or more star networks connected together. Each star network is a local area network in which there is a central computer or server to which all the workstations or nodes are directly linked. The central computers of the star networks are connected to a main cable called the bus. Thus, a tree network is a bus network of star networks. The illustration shows a tree network with five star networks interconnected. The workstations are shown as small spheres, the central computers of the star networks are shown as larger spheres, connections within star networks are shown as short lines, and the bus is shown as a backbone. The connections can consist of wire cables, optical fiber cables, or wireless links.

Tree NetworkTree Network In a tree network, a cable failure in one of the star networks

will isolate the workstation that it links to the central computer of that star network, but only that workstation will be isolated. All the other workstations will continue to function normally, except that they will not be able to communicate with the isolated workstation. If any workstation goes down, none of the other workstations will be affected. If a central computer goes down, the entire portion of the network served by it will suffer degraded performance or complete failure, but rest of the network will continue to function normally. If the bus is broken, serious network disruption may occur.

Mesh NetworkMesh Network

Mesh NetworkMesh Network A mesh network is a network that employs one of two

connection arrangements, full mesh topology or partial mesh topology. In the full mesh topology, each node (workstation or other device) is connected directly to each of the others. In the partial mesh topology, some nodes are connected to all the others, but some of the nodes are connected only to those other nodes with which they exchange the most data. The illustration shows a mesh network with eight nodes. Each node is shown as a sphere, and connections are shown as straight lines. The connections can be wired or wireless.

A mesh network is reliable and offers redundancy. If one node can no longer operate, all the rest can still communicate with each other, directly or through one or more intermediate nodes. Mesh networks work well when the nodes are located at scattered points that do not lie near a common line.

Mesh NetworkMesh Network The chief drawback of the mesh topology is expense, because

of the large number of cables and connections required. In some scenarios, a ring network or star network may prove more cost effective than a mesh network. If all the nodes lie near a common line, the bus network topology is often the best alternative in terms of cost.

Network CharacteristicsNetwork Characteristics Media used for connection

– Copper Cable– Fiber Optic Cable– Broadband Cable

Speed of connection Type of Signal

– Analog– Digital

Type of Data Movement– Full Duplex– Half Duplex– Simplex

Method of Movement– Asynchronous– Synchronous (polled)

Network ApplicationsNetwork Applications Email Web Servers & Browsers FTP Servers Instant Messaging

Server no purpose without the network Did not exist before networks were created New applications created daily, weekly,

annually

The InternetThe Internet Wide area Network Utilizes mesh topology TCP/IP is protocol used to drive the network

– FTP– HTTP– HTTPS– Telnet