Ring topology

Ring topology:

The ring network is a local area network whose topology is a ring can be as simple as a circle or point to point connection of computers at dispersed locations with no central host computer or communications controller. That isall of the nodes are connected in a closed loop. Messages travel around the ring, with each node reading
those messages addressed to it. One of the advantages of ring networks is that they can span larger distances than they can span larger distances than other types of networks.

Star topologies

Star Topology:

The star network topology is frequently used to connect one or more small computers or peripheral devices to a large host computer. Many organizations use the star network or a variation of it in a time sharing system, in which several users are able to share a central  processor.

Star network is frequently used in a LAN to connect several micro computers to a central unit that works  as communication controller. Another common use of the star network is as a LAN to connect several microcomputers to a mainframe that allows access to an organization database.

The star topology as shown above has minimum line cost as only 4 lines are used. The routing function is performed two nodes by establishing a logical path between them. The system, however, crucially depends on E. If E breaks down the whole network would breakdown.

Network Topology

 When computers at different location are to be inter connected, one may do it in a number of ways. The different kinds of interconnections of computers in a communication subnet giver rise to topology or network topology.
There r different types of topologies they are
*Star topologies
*Ring topologies
*Tree topologies
*Bus topologies.

Network Basic

The advantages of establishing a computer networking by linking computers together, can be listed as follows :
*A large number of users belonging to same area or same organization but spread over at different places can communicate and share useful files, software  and information at right time via network of computers Thus leads to Resource sharing
* With a computer network you can avail the following services.
*Remote login
*E-mail
*Interactive entertainment
*Internet services
*Video conferencing 

Routers

Router

A router can be a “gateway” in TCP/IP connect internet connection. In communication networks, a router is a device that examines the d4estination address of a message or packet and selects the most effective roué for its transmission. It is used in complex, large networks where there are many path ways between users.

Thus job of the router is to know where packets of information are headed, to make sure they are addressed correctly, and to send them on their way by the most efficient route possible.

The router function by choosing.

·         Best path

·         Fastest path available

·         Least costly path

·         Currently available Path.

Routers are needed to connect network with protocol that function in similar ways, Whereas when the networks to be connected are using completely different protocols from each other, then a device that interprets and translates the different protocols are used in two distinct networks and this device is called as gate way.

Router operates network layer of OSI model

Routers are relatively expensive

Router cannot route some common protocol

Router focuses on protocol address

Router can accommodate multiple paths

Router can join two different networks

Network Basic

HUB

Hub is a central switching device for communication lines is star topology.It is a central switch box that permits multiple network devices connect to a local area network through a single point,

A hub can be a active hub or a passive hub. A passive hub adds nothing to the transmission except switching function. Where as a hub may contain necessary electronics that regenerate signals to boost strength as well monitor activity. Such hubs are known as intelligent hubs or Active hubs.

Hubs may be added to bus topologies

Network Basic

OSI Reference model

The OSI reference model has 7 layers.

*The physical layer

* Data link layer

*Network layer

*Transport layer

*Session layer

*Presentation layer

* Application layer

Each layer is defined for having associated with distinct functions. The functions performed by each layer can be described as below.

*The Physical layer: The layer defines the electrical and mechanical aspects of interfacing to a physical medium for transmitting dat. It also defines how physical links are setup, maintained and disconnected.

*The data link layer: This layer establishes an error free communication path between computers over the physical channel. It gives the standard for framing messages, checking integrity of messages received, accessing and using channels and sequencing of transmitted data.

*The Network layer: This layer determines the setting up of a logical path between computers in a network, message addressing to computers  and controlling message flow between computer nodes.

*The Transport layer: Once a path is established between computers it provides control standards for a communication session for enabling processes to exchange data reliably and sequentially, independent of which systems are communicating or their location in the network.

*The Presentation layer: This layer provides facilities to convert encoded transmitted data into forms which can displayed on a video terminal or printed.

*The Application layer: This layer provides services that directly support users such as file transfers, remote file access data base management etc,,