LAN Topologies

network topologies

Talking about the Local area network, we should be familiar with the concept of the LAN topology that we use. There are many types of LAN topologies for different types of networks. We should also be familiar between physical topology and logical topology. Physical topology describes the layout of a network media such as copper cable, fiber optic cable, and most popular today is the wireless. While the logical topology is concerned about logical path through the network that data can take from one place to another.

The following are basic types of LAN topology

• Bus
• Star
• Ring
• Mesh
• Hybrids

But in this chapter we consider only in three types of it, Bus, Star, and ring

Bus topology

w  All network nodes connect to the bus, which is a single communications channel, such as twisted pair, coaxial cable, or fiber optic cable.

Advantages:

 LAN Bus topology is very simple and inexpensive to implement, there is only one main trunk.    

Disadvantages:

• LAN Bus topology requires proper termination on both ends of the bus. Improper termination will cause the network to be malfunction     
• One single trunk cable becomes a single point of failure, one break, causes all the network impact.
• Difficult in troubleshooting since you only have one single cable to share for all the computers on the network.

Star topology:

All network nodes connect to a single computer, typically the file server.

Advantages:

Any single failure of the port will not impact the whole network. See also

Installation of the cable in each port will not disrupt LAN services

No termination needed like in bus topology.

Ring topology:

Network nodes are connected to adjacent nodes to form a closed loop.

In a ring topology, access to the network is controlled through a token that is passed from node to node as the arbitration mechanism. Each node takes its turn at claiming the token as the token passes from neighbor to neighbor, and when a node possesses the token, it takes its turn to transmit onto the ring

Advantages:

• No collision detection mechanism is required, so Token ring provides greater overall bandwidth use.
• Troubleshooting is easy by the fact that each node only knows its upstream and downstream neighbors.

Disadvantages:

• The firmware required to manage the ring is somewhat complicated and must be on every network card that participates in the ring
• Expensive to implement and mostly the LANs today use Ethernet technology which dominate the market today.



Many application need data and the data should be organized so that any department in the company sue it. A huge number of data make difficult to manage it. In the past the firms are using files and document for storing the data that make difficult to find whatever you need.



Why data are difficult to manage?

*The amount of data are increasing rapidly.

*Data are scatter and it is form various place.

*Data come from internal and external sources.

*Data come from the web and it record what are doing there.     

The data level:

Data started with bit that is smallest unit of data. A group of bits called byte that single character. When grouping of those characters called a filed. A related field called record. Finally, the group of related field called database.

What data base do?

It minimize data redundant , data isolation, data inconsistency.

It maximize data securities , data integrity and data independent

 

the important issue in information systems

This chapter is long but interesting because it shows some interesting methods  that  related to information systems also related to our life. There are many issues one of these issues is ethical issue. Ethics means what is right and wrong. Also there is a code of ethics that is rules in any organization that they should follow to protect their organization and their employees. There are four categories of ethical issues the important from these is privacy issues. Privacy is what belong to us and not to share with others but the privacy not absolute because sometimes the society need it.

The second categories is threat to information security. Threat is danger that happen in any system.

Exposure: damage that can be result.

Vulnerability: possibility the system damage.

Risk:  probability that damage happen.

There are two type of threat:

Unintentional Treat: human errors, environmental and computer system design.

Intentional Threats: hacker, cracker and social enginneing.

  

chapter(1)

Information system: get right information for right people at right time.

differences between Data, information and knowledge:

Data: things, event or activities that have not been orgnized.

for example: number, figure and images

Information: Data that have been orgnized. For example, the grade of student with their name or ID.

Knowledge: Data that have been proccesed for understanding and experiences. 

Information technology architecture: is map or plan of the information in the organization. It give information about the current and how to improve it.

Application program: computer program designed to support specific task.

information systems change among the change in the need of the firm.

 Organizational employees:

Clerical worker: who support manager such as secretaries.

Lower level managers: make day to day operation.

Middle managers: make tactical decision such as short term planning.

Knowledge workers: professional employees such as telecommunication engineer in Omantel.

Executives: the top manager who make decision.