good morning world INTRODUCTION
In this unit you will be introduced to data communication and computer networking. Every day we share information using electronic devices such as phones, have you ever imagine that the main reason this happens is as a result of networking. It is important to have knowledge about networking as Librarians are involved in the provision of information.
5.1 Networking
Computer data communication
Data communication is the process of transferring information signals from one point to another for the purpose of sharing information. Computer communication is a process of which involves the transfer or sharing of data programs and information between two or more computers. This forms a communication system, in this case defined as, a system that transmits electronic data from one location to another through either wired or wireless communication channels. O’Leary, T. J and O’Leary, I. L. (2003) observe that every communication system has four (4) basic elements and these are:
(a) Sending and Receiving Devices. These are specialized communication devices which are able to originate and accept information, data or instruction signals.
(b) Communication Channel. This is the actual connecting or transmitting medium which is used to carry information signals, these media come either as wired or wireless channels
(c) Communication Devices/Connection Devices. These are devices which provide an interface between the sending devices and the receiving devices and the communication channel. They convent outgoing signals into a format that is acceptable by the communication channels.
(d) Data Transmission Specifications. These are the rules and procedures coordinating the sending and receiving devices by precisely defining how the signals will be sent across the communication channels.
5.2 COMMUNICATION CHANNELS
These come in two main forms but perform the same functions. They may be guided (wired/physical) and unguided (wireless/communication channels)
5.2.1 PHYSICAL COMMUNICATION CHANNELS
These are media of communication which use solid materials to connect sending and receiving devices. Examples of physical channels of communication are:
1. Twisted pair cable
2. Coaxial cable
3. Fiber optics
- Twisted pair cables
These are a physical data communication channels which involve two conductors wound together for the purpose of cancelling out electromagnetic interface from external sources and crosstalk from neighboring wires. They are the most common and earliest form of cable data transmission. The twisted pair cables have advantages and disadvantages.
- Coaxial cables
These are high frequency data transmission cables consisting of a round conducting wire surrounded by an insulating spacer which is further surrounded by a cylindrical conducting shealth which is surrounded by a final insulating layer known as a jacket.
These cables are rarely affected by electromagnetic interference because of the space and the spacer found in between the internal conducting material and the outer conductor. These cables are popular with television or video data transmission
| Advantages | Disadvantages |
| 1. rarely affected by electromagnetic interferences | 1. comparatively expensive |
| 2. data transmission capacity is also better than the twisted cables | 2. speed and capacity of data transmission has been superseded |
| 3. suited for video, television data transmission | 3.Do not provide a bigger data transfer capacity |
| 4. have a protective jacket which protects them from external environments |
- Fiber optics/optic fiber
These are data transmission media made out of glass or plastic fibres designed to guide light along its length by confining it as much as possible in a propagating way. These fibre optics are small or tiny in size, therefore, a number of them can be put together to form one big communication channel. This fibre optics has an opening through which light passes and the diameter of these openings determine the speed of data transmission.
| Advantages | Disadvantages |
| 1. small in size and are able to carry a lot of data | 1. comparatively expensive |
| 2. the fastest data transmission cables at the moment | 2. labour intensive at installation |
| 3. immune to electromagnetic interference and cross talking | 3. expensive per meter and high maintenance costs |
| 4. Used in explosive environments without any danger of igniting an explosion. |
5.2.1 WIRELESS OR UNGUIDED CHANNELS
Wireless connections do not use a solid substance to connect the sending and receiving devices. It uses air in most cases to transmit data signals. Some examples of wireless channels include the following:
a. Infrared
This is a type of wireless communication that uses light waves to communicate over short distances. It is sometimes referred to as “line of sight communication”. This is so because light waves can only travel in straight lines. This channel requires the sending and receiving device to be in clear view. One of the most common applications of this channel is on portable devices such as phones.
b. Microwave
This channel uses high frequency radio waves. Like infrared, microwave provides a line of sight communication. This channel is good when sending data between buildings within the same location. In order to transmit information using this method over long distances, the waves must be relayed by using antennas and relay stations.
c. Satellite
Here, a satellite orbits above the earth and collects information from relay stations. Satellite communication is used to send huge volumes of data. Data is sent from relay stations and the orbiting satellite distributes this information to other relay stations worldwide. The process of sending data to the orbiting satellite is called up linking while the process of receiving information from the orbiting satellite is called downlinking. One of the most popular applications of this channel is global positioning. The main advantages of this channel are that it has a wide coverage and is not affected by physical barriers such as water, hills etc. The main drawbacks are that it is expensive and is usually affected by bad weather.
5.1.1 NETWORKs
For business to operate effectively and efficiently in the highly competitive business world there is need for proper communication in organisations, networks provide channels for information to flow continuously between people in different organisations or different departments within an organisation. A network can be defined as a communication system that links two or more computers and peripheral devices and enable them transfer data between the components, it can also be said to be a set of hardware devices connected together logically or physically to allow them exchange and share resources. It allows computers to exchange data. In computer networks, networked computing devices pass data to each other along data connections (network links). The connections between nodes are established using either cable media or wireless media. The best-known computer network is the Internet.
Advantages of networking
- Effective communication
- Facilitates hardware sharing
- Promotes new ways of working
- Provides entertainment opportunities
- Enables sharing and dissemination of information
- Reduces costs as compared to traditional communication
Disadvantages of networking
- High costs of initial set up and administration
- When implementing or upgrading the network there is usually practical difficulties.
- Breaks in service can be very disruptive.
- Hardware and software costs
- Security is reduced due increased access points to sensitive data.
- Promotes undesired sharing of information
- Promotes illegal or undesired behaviour
Different types of networks
There are different types of networks, in this course we shall discuss two mostly used networks these are:
- Local Area Network (LAN)
- Wide Area Network (WAN)
- Local Area Network
This connects computers within a limited geographical area for example a building. Typically LANs span distances less than a mile; they are widely used by universities and colleges to share resources. Local area networks provide benefits such as economy and flexibility. People in the organisation can share costly equipment for instance a number of computers can share the laser jet printer. Sometimes LANs can be connected without cables they are then referred to as Wireless Local Area Networks
- Wide Area Network
Wide area networks are networks with a wider geographical coverage. They are usually made up of two or more LANs. They cover distances greater than 100 miles; they use satellites to reach users. The biggest WAN is the internet which spans the entire globe.
5.2.2 Network topologies
How different nodes in a network are connected to each other and how they communicate is determined by the network's topology. Network Topology refers to layout of a network and how different nodes in a network are connected to each other and how they communicate. Topologies are either physical (the physical layout of devices on a network) or logical (the way that the signals act on the network media, or the way that the data passes through the network from one device to the next). In order to understand network topologies you must first know what a network is? A network is a group of two or more computer systems linked together. The following are the five common network topologies.
1. Mesh Topology
Mesh Topology: In a mesh network, devices are connected with many redundant interconnections between network nodes. In a true mesh topology every node has a connection to every other node in the network. There are two types of mesh topologies:
Full mesh topology: occurs when every node has a circuit connecting it to every other node in a network. Full mesh is very expensive to implement but yields the greatest amount of redundancy, so in the event that one of those nodes fails, network traffic can be directed to any of the other nodes. Full mesh is usually reserved for backbone networks.
Partial mesh topology: is less expensive to implement and yields less redundancy than full mesh topology. With partial mesh, some nodes are organized in a full mesh scheme but others are only connected to one or two in the network. Partial mesh topology is commonly found in peripheral networks connected to a full meshed backbone.
2. Star Topology
Star Topology: In a star network devices are connected to a central computer, called a hub. Nodes communicate across the network by passing data through the hub.
Main Advantage: In a star network, one malfunctioning node doesn't affect the rest of the network.
Main Disadvantage: If the central computer fails, the entire network becomes unusable.
3. Bus Topology
Bus Topology: In networking a bus is the central cable -- the main wire -- that connects all devices on a local-area network (LAN). It is also called the backbone. This is often used to describe the main network connections composing the Internet. Bus networks are relatively inexpensive and easy to install for small networks. Ethernet systems use a bus topology.
Main Advantage: It's easy to connect a computer or device and typically it requires less cable than a star topology.
Main Disadvantage: The entire network shuts down if there is a break in the main wire and it can be difficult to identify the problem if the network shuts down.
4. Ring Topology
Ring Topology: A local-area network (LAN) whose topology is a ring. That is, all of the nodes are connected in a closed loop. Messages travel around the ring, with each node reading those messages addressed to it.
Main Advantage: One main advantage to a ring network is that it can span longer distances than other types of networks, such as bus networks, because each node regenerates messages as they pass through it.
5. Tree Topology
Tree Topology: This is a "hybrid" topology that combines characteristics of linear bus and star topologies. In a tree network, groups of star-configured networks are connected to a linear bus backbone cable.
Main Advantage: A Tree topology is a good choice for large computer networks as the tree topology "divides" the whole network into parts that are more easily manageable.
Main Disadvantage: The entire network depends on a central hub and a failure of the central hub can cripple the whole network.
5.2.3 The internet
The Internet is the largest example of a network. It is a global system of interconnected governmental, academic, corporate, public, and private computer networks. It is a “network of networks”. It is based on the networking technologies of the Internet Protocol Suite. It is the successor of the Advanced Research Projects Agency Network (ARPANET) developed by DARPA of the United States Department of Defense. The Internet is also the communications backbone underlying the World Wide Web (WWW).
Participants in the Internet use a diverse array of methods of several hundred documented, and often standardized, protocols compatible with the Internet Protocol Suite and an addressing system (IP addresses) administered by the Internet Assigned Numbers Authority and address registries.
The language prevalent on the internet is English and this is mainly due to its origin that is associated with the United States where English is the main language.
Services offered by the internet
The internet provides a number of services to the users among them the following:
I. World Wide Web (WWW)
It covers 90% of the internet. This is a large set of interlinked documents, images and other resources that are linked by hyperlinks and the Universal Resource Locator (URL). The URL brings together documents that belong to particular organisations. The websites are usually designed using the hypertext mark-up language (html). You need to have a web browser in order to access the World Wide Web. A web browser is software that allows one to navigate the web. Examples of web browsers include Internet explorer, fire fox, opera mini etc. Searching for information on web is keyword driven using search engines
Search engines are programs that search documents for specified keywords and returns a list of the documents where the keywords were found. A search engine is really a general class of programs, however, the term is often used to specifically describe systems like Google, Bing and Yahoo! it enables users to search for documents on the World Wide Web. Typically, Web search engines work by sending out a spider to fetch as many documents as possible. Another program, called an indexer, then reads these documents and creates an index based on the words contained in each document. Each search engine uses a proprietary algorithm to create its indices such that, ideally, only meaningful results are returned for each. I. Email service
This simply refers to electronic messages. E-mail is a way of sending letters or messages between computers and other electronic devices. This is by far one of the most popular internet facilities. It works under email protocols which are guidelines that are used to send data from one computer to another. An e-mail address is very important for one to access this service. The three important parts of an e-mail address are as follow;
a) The domain code, this is the last part of the address. It identifies the geographical or organisational description. For example ed. for educational organisations, zm for Zambia etc
b) Domain name, it represents the organisation that manages your mails
c) Username, the unique name that distinguishes you from the rest
User name domain code
[[1]]
Domain name
The following are the advantages and disadvantages of using the email service
| Advantages | Disadvantages |
| • Provides a quicker way of sending messages | •it promotes illegal behaviour such as pornography |
| allow attaching other documents to the documents being sent | •it is difficult to verify the information |
| •The same message can be sent to a lot of people at once | •it is a source of viruses |
| It is an economical mode of communicating | •it is source junk mails |
| •it has contributed to cyber crime |
II. Discussion groups
The internet allows a number of people with similar ideas and interests to communicate through this service. For one to have access to discussion groups they need to have a special identity usually an email address is used. The following are some of the discussion groups available:
- Mailing Lists: These are a list which allows members to communicate by sending messages to a list of addresses. Each message is copied and sent through e-mail to every member of the mailing list. To participate in a mailing list, one needs to have an e-mail request to the mailing list
- News Group: News groups unlike mailing lists use a special net of computers called USERNET. Each of those computers maintains a news group listing. This computer saves the messages on its system and periodically shares its recent messages with other computers in the USERNET. Unlike the mailing lists, USERNET do not send a message to each of the members but rather the members check individual contributions to particular news group by going through the USERNET
- Instant Messaging (I.M): This is an internet communication technology that creates the possibility of real time, text-based communication between two or more participants over the internet or some other form of network such as intranets or extranets. What separates instant messaging from other technologies such as e-mail is the fact that instant messaging happens in real time before your eyes. Instant messaging therefore allows effective and efficient communication featuring immediate receipt of acknowledgement or reply. In certain cases, instant messaging involves other/certain features which makes it even more popular and interactive for example, using webcams which will facilitate video conferencing.
Other facilities offered by the internet
i. Facebook
ii. Twitter
iii. Tell-net
iv. File transfer protocols, etc
Basic requirements to have Internet
There are basically four main elements needed for one to effectively connect to the internet. The following are the basic elements:
- Computer
A computer is an electronic machine programmed to manipulate data. For one to connect to the internet, a computer is needed so as to generate signals needed for communication and provide an interface through which people can communicate
- MODEM (Modulator/ Demodulator)
This is a communication device that is used to convert information signals from digital to analogue and vice versa. Most computers are digital computers as they generate digital signals but these signals are transmitted using telephone lines which understand analogue data.
- Telephone lines
These are the actual media through which data is transmitted from one computer to another
- Internet Service Provider
These are companies or institution that link computers to the internet gateway. These companies have the rights and technologies to facilitate internet connectivity. Examples of such companies in Zambia are Copper net, Zamnet etc
| 1. What is the difference between the internet and the www?
2. When was the internet first used? 3. Define a web browser and a search engine. Give examples in each case. 4. Why use the internet? |
In this unit you learnt the meaning of networking in computers, the types of networks, channels of data transmission, the internet and the services it provides. Take note of the merits and demerits associated with each service provided. You are encouraged to use networks so as to appreciate them more.
Further readings
Chaffey, D. (2006). Business Information Systems, Derby: Financial Times Press.
Stallings, W. (2000). Data and Computer Communication, 6th ed. New Delhi: Pearson Education.
Timothy.J and Linda O’leary. (2005) Computing Essentials. Boston: McGraw Hill.
UNIT 6: ERGONOMICS
Learning outcomes: On completion of the unit, you will be able to:
1 Explain Ergonomics
2 Identify physical health hazards
3 Apply safety measures
Learning conditions: You must have access to:
- Library
- Internet connectivity
- Computers
- Sample devices
Duration:
You will be expected to spend a minimum of 15 hours on this unit
INTRODUCTION
In this unit you will be introduce to data communication and computer networking. Every day we share information using electronic devices such as phones, have you ever imagine that the main reason this happens is as a result of networking. It is important to have knowledge about networking as Librarians are involved in the provision of information.
5.1 Networking
ERGONOMICS
Computers have become a common business tool because they increase productivity. Unfortunately, there are certain ways in which computers may eventually make people less productive. Many of the people involved in data entry and extensive word processing or internet use are the victims. Problems that come as a result of incorrect usage of computers have generated great interest in the field of ergonomics. O’Leary. T and O’Leary. L. (2003) defines ergonomics as the study of human factors related to things they use. As the use of computers increase so is the interest in ergonomic. People are devising ways that can increase productivity and avoid health risks. Ergonomic issues are looked at in the following ways:
- Physical health
Sitting in front of a screen in an awkward position for long hours may lead to problems like eyestrain, headache and back pain. These problems can be resolved as follows:
§ Eyestrain and headaches, eyes are made to work better in situations that are not very bright. Using computers for long hours at a closer range would create eyestrain, headaches and double vision. In order to avoid this, take short breaks of about 15 minutes, avoid computers that flicker, keep computer screens away from heavy exposure of light, make sure that the screen is brighter than normal light.
§ Back pain and neck pain, these usually come as a result of people using monitors and keyboards in improper positions. To avoid such problems make sure equipment are adjustable. You should adjust your chair for height and angle, and the chair should have good back support. Keyboards should be detachable and use a footrest to reduce leg fatigue
§ Repetitive strain injury is as a result of fast repetitive work that causes the neck, wrist, hand and arm to pain. To avoid this use suitable keyboards and take regular breaks
- Mental health
Computer technology create some irritants that may be mental in nature
§ Noise, computing can be quite noisy. Printers, fans and vibrating system unit can cause problem that are health related. Acoustical tiles and sound muffling can help in this case.
§ Electronic monitoring, workers who are watched using computer aid monitoring systems suffers more health problems than their counterparts monitored by human supervisors.