CS6: Data Communication and Networking
Communication is one of the fundamental aspects of life. In this regard, electronic communication means have been developed on top of the traditional manual and mechanical modes of communication for individuals and organisations to communicate more effectively. A person can now communicate through contemporary media like mobile phones and over the internet.
It is therefore important that learners are introduced to basic data communication and ICT networking infrastructure and services in order to come to terms with contemporary data communication facilities.
Learning Outcome: The learner should develop basic skills, knowledge and expertise in the use of contemporary communication facilities like computers, mobile telephones, the Internet, among others.
DATA COMMUNICATION AND NETWORKING
Sub Topic 11.1: Introduction to Data Communication
Sub topic Objectives:
a. defining data communication.
b. explaining the elements of data communication (sender, receiver, messages, transmission media and protocol).
c. defining data communication tools
d. describing types of electronic data communication tools like computers, mobile phones, the Internet, among others.
e. comparing electronic and manual data communication tools (manual drums, bells and messengers).
f. defining data transmission media.
g. differentiating between physical transmission media and wireless transmission media.
h. describing services offered by data communication tools like E-mail, Skype, News groups, and instant messaging.
i. explaining the implications of using data communication services.
Definition of terminologies
Computer communication is the transmission of data and information over a channel between two computers. Communications between computers can be as simple as cabling two computers to the same printer.
A computer Network is a collection of two or more computers and devices connected by channels so that they can communicate with each other and share resources: Examples of resources
Encoding: This is the process through which Information (e.g. data, text, voice or video) from the sending device is converted into signals which the communication medium can carry.
Transmission: This is the process through which the signals are broad cast/ sent out through the medium to the receiving device.
Decoding: This is the process through which the signals are converted back into the information in its original form in the receiving device.
Telecommunication refers to transmission of data and information over a long-distance, eg television
Teleprocessing: This refers to access and modification of computer files located elsewhere.
Downloading: To Download is to transfer a file to your computer from another.
Uploading means to transfer a file from your computer to another.
Throughput refers to the rate of how much data is moved during a certain amount of time. The amount of signals that can travel over a communications channel sometimes is called the Bandwidth. The higher the bandwidth, the more data and information the channel can transmit.
Data Encryption: This is Process of converting data into coded form (cypher text) to prevent it from being read or understood by unauthorized people. Encrypted data is difficult to decode without a secret key
Communications Software:Â This refers to a set of instructions (software) needed by a computer before it starts sending and receiving data from other computers.
Importance of computer communication
Limitations of computer communication
Transmission media (Channels)
Transmission media refers to the physical materials that are used to transmit data between computers. For communications between computers that are linked by cable, there are three choices:
Twisted wire
Twisted pair cable comes in two varieties: Shielded and Unshielded Twisted Pair (UTP). UTP is the most popular
Advantages:
Disadvantage:
Coaxial cable
Coaxial cable consists of a single copper wire surrounded by at least three layers:
.
Advantages
Disadvantages
Fiber Optic Cable
Each strand, called an optical fiber, is as thin as a human hair. Each optical fiber is surrounded by an insulating glass cladding and a protective coating. Fiber-optic cables are used by many local and long-distance telephone companies, cable TV, and in high-traffic networks or as the main cable in a network.
Advantages:
Disadvantages:
Wireless telecommunications technologies transport digital communications without cables between communications devices. Wireless transmission media used in communications include broadcast radio, cellular radio, microwaves, communications satellites, and infrared & bluetooth.
Wireless transmission is more convenient than installing cables but it has Slower data transfer than hard-wired methods and it is also Subject to interference.
Microwave
Microwaves are high-frequency radio waves that are sent through the atmosphere and space to deliver telecommunications services, including TV distribution. It is dependent on line of sight.
Advantage:
Disadvantage:
Satellite
A satellite is basically a microwave station placed in outer space. The satellite receives a signal from the earth, amplifies it, and then rebroadcasts it at a different frequency to any number of earth-based stations.
Satellite In The Rays Of Light. 3D Scene.
Infrared and Bluetooth IrDA (Infrared Data Association) ports transmit data via infrared light waves. As long as the devices are within a few feet and nothing obstructs the path of the infrared light wave, data can be transferred without the use of cables.
Bluetooth port is an alternative to IrDA. Bluetooth technology uses radio waves to transmit data between two devices. Many computers, peripherals, smart phones, PDAs, cars, and other consumer electronics are Bluetooth-enabled, which means they contain a small chip that allow them to communicate with other Bluetooth-enabled computers and devices.
Physical transmission media and wireless transmission media
Advantages of physical over wireless transmission media
Disadvantages of physical transmission media
Services offered by data communication tools
Data communication tools offer services like Telephone, SMS, E-mail, Skype, Newsgroups and instant messaging.
Positive Implications
Negative Implications
DATA TRANSMISSION
Telecommunications involves the transmission of data, information, and instructions among computers. Any transmissions sent during these communications can be categorized by a number of characteristics including the signal type, transmission mode, transmission direction, and transmission rate.
Signal Type: Recall that computers produce digital signals yet telephone equipment originally was designed to carry only voice transmission in the form of an analog signal.
Analog Signals
An analog signal uses variations which are represented by a continuous waveform to convey information. It is particularly useful for wave data like sound waves. Analog signals are what normal phone line and sound speakers use.
Digital Signals
A digital signal is a series of discrete (discontinuous) bits which are simply the presence or absence of an electric pulse. The state of being on or off represents the binary digit of 1 or 0, respectively.
Advantages of digital signals include:
Transmission Modes
When two devices exchange data, the data flows between the devices as a continuous stream of bits.
There are two basic transmission techniques for separating the groups of bits: asynchronous transmission and synchronous transmission
Asynchronous transmission
Asynchronous transmission transmits one byte at a time over a line at random intervals. Each byte is framed by controls—a start bit for marking the beginning of the byte, a stop bit for marking the end of the byte, and a parity bit for error checking. Asynchronous transmission is relatively slow and used for low-speed transmission.
Synchronous transmission
Synchronous transmission transmits groups of bytes simultaneously at regular intervals. The beginning and ending of a block of bytes is determined by the timing of the sending device and receiving devices.
Although synchronous transmission requires more complicated and expensive communications devices, it provides much higher speeds and greater accuracy than asynchronous transmission.
Transmission Direction
The direction in which data flows along transmission media is characterized as
Simplex transmission
Simplex transmission sends data in one direction only. Simplex transmission is used only when the sending device does not require a response from the receiving device. One example of simplex transmission is television broadcasting.
Half-duplex transmission
Half-duplex transmission allows data transmission in either direction, but only one way at a time. Many fax machines, police radio calls, credit card verification systems and automatic teller machines use half-duplex transmission.
Full-duplex transmission
In full-duplex transmission, data can flow in both directions at the same time. A regular telephone line, for example, supports full-duplex transmission, allowing both parties to talk at same time.
Multiplex transmission
In multiplex transmission, several different types of signals can be carried at once through the same line. E.g. During Video calls where Images
Computer Networks
Unit Objectives
To be able to know the:
Networking hardware
Networking hardware includes all computers, peripherals and Communications devices that enable two or more computers to exchange items such as data, instructions, and information with each other.
Examples include: a server computer, clients/work stations, network interface card, modems, Hub/Switch, repeater, Router, etc.
1. SERVERÂ
A server is the host or central computer that manages the resources on a network. A server provides a centralized storage area for programs, data, and information.
A dedicated server is a server that performs a specific task. Examples of dedicated Servers include: file server, print server, database server, and a network server.
Roles of Dedicated Servers
Requirements of a server computer
2. NETWORK INTERFACE CARD
A network card, also called network interface card (NIC), is a device that enables the computer or device that does not have built-in networking capability to access a network.
3 MODEMS (signal converters)
The modem, is a device which Modulates a digital signal from computers into an analog one to send data out over the phone line. Then for an incoming signal it Demodulates, the analog signal into a digital one.
4. HUBS and SWITCHES
A hub, (also called a multi-station access unit (MAU)) is a device that provides a central point for cables in a network. Unlike the hubs, a switch does not broadcast the data to all the computers, it sends the data packets only to the destined computer.
5. REPEATER
A repeater is a device that accepts a signal from a transmission medium, amplifies it, and retransmits it over the medium. As a signal travels over a long distance, it undergoes a reduction in strength, an occurrence called attenuation.
7. NETWORK BRIDGE
A bridge connects two pieces of land together offering a path from one to another. A network bridge is device that connects two networks making each accessible to the other. A bridge knows all of the addresses on each side of the bridge and can send information accordingly.
8. MULTIPLEXER
A multiplexer is a device that combines two or more input signals from various devices into a single stream of data and then transmits it over a single transmission medium.
By combining the separate data streams into one, a multiplexer increases the efficiency of communications and reduces the need for using multiple separate transmission media.
Types of computer networks
A network can be relatively small or extensively large. The most common types of computer networks include
Local Area Network (LAN)
A local area network (LAN) is a network that connects computers in a small geographic area such as a building like a computer laboratory, or an office. The nodes are connected to the LAN via cables. A wireless LAN (WLAN) is a LAN that does not use physical wires, but uses wireless media such as radio waves.
The two kinds of LAN are peer-to-peer network and client/server network.
Peer-To-Peer Network
This is a type of network where each computer can share the hardware, data, or information located on any other computer on the network. Each computer stores files on its own storage devices. Each computer on the network contains both the network operating system and application software.
Advantages of a Peer To Peer Network (P2P)
Disadvantages of a Peer to Peer Network
Client/Server Network
A client/server network has one or more computers acting as a server while the other computers (i.e., clients) on the network can request services from the server. A client computer is a computer that can access the resources on a network. A server provides a centralized storage area for programs, data, and information. Most client/server networks have a network administrator who is in charge of the network.
Advantages of a Client/Server Network
Disadvantages of a Client /Server Network
PERSONAL AREA NETWORK (PAN)
A personal area network (PAN) is the interconnection of computer devices within the range of an individual person, typically within a range of 10 meters.
Wide area network (WAN)
A wide Area Network (WAN) is a network that covers a large geographic area. An example of a WAN is a network that connects the district office computers of a company across the country or across several counties in the world. Computers are often connected to a WAN via public networks such as the telephone system or by dedicated lines or satellites. The Internet is the world’s largest WAN.
Metropolitan area networks (MANs)
A metropolitan area network (MAN) is a large computer network that usually spans a city or a large campus. A MAN usually interconnects two or more LANs using a high-capacity backbone technology, such as fiber-optical links or other digital media. A MAN covers a smaller geographic area than a WAN.
A virtual private network (VPN) extends a private network across a public network, and enables users to send and receive data across shared or public networks as if their computing devices were directly connected to the private network. Applications running across the VPN may therefore benefit from the functionality, security, and management of the private network.
VPNs may allow employees to securely access a corporate intranet while located outside the office. They are used to securely connect geographically separated offices of an organization, creating one cohesive network.
Intranet, Extranet and Internet
QN: What is the difference between Intranet, Extranet and Internet?
Intranet
 Advantages of Installing a School Network
Disadvantages of Installing a School Network
EXTRANET
An extranet is a computer network that allows controlled access from the outside for specific business or educational purposes. Extranets are extensions to, or segments of, private intranet networks that have been built in many corporations for information sharing. Most extranets use the internet as the entry point for outsiders, a firewall configuration to limit access and a secure protocol for authenticating users
Advantages of extranet
Disadvantages of extranet
NETWORK TOPOLOGIES
A network topology is a description of the possible physical connections within a network. In other words, a topology is the physical arrangement of the devices in a communications network.
Three commonly used network topologies are bus, ring, and star. However, Most computer networks are hybrids—combinations of these topologies. In a network topology, any network hardware component is also called a node.
Bus topology
A bus or linear network topology consists of a single central cable that connects all computers and devices together. The physical cable that connects the computers and other devices is known as the bus or the backbone.
Merits of BUS Topology
Demerits of BUS Topology
Ring Topology
Ring network consists of a cable forming a closed ring, or loop, with all the computers and devices in a network. A ring network links all nodes together in a circular chain. The node examines any data that passes by to see if it is the addressee; if not, the data is passed on to the next node in the ring.
Advantages of Ring Topology
Demerits of a Ring Topology
Star Topology
On a star network, all of the computers and devices (nodes) on the network connect to a central hub or switch. All data that is transferred from one computer to another passes through the hub.
Merits of a Star Topology
Demerits of a Star Topology
Mesh Topology
This is the type of network topology in which each of the nodes of the network is connected to each of the other nodes in the network. Fully connected Mesh topology makes it possible for data to be simultaneously transmitted from any single node to all of the other nodes.
Merits of Mesh Topology
Demerits of Mesh Topology
Tree Topology
Tree network topology is also known as a the hierarchical network topology. This is because it contains different levels of hierarchy.
The type of network topology in which a central ‘root’ node (the top level of the hierarchy) is connected to one or more other nodes that are one level lower in the hierarchy (i.e., the second level),
Each of the second level nodes will also have one or more other nodes that are one level lower in the hierarchy (i.e., the third level) connected to it. The hierarchy of the tree is symmetrical – Each node in the network having a specific fixed number, of nodes connected to it at the next lower level in the hierarchy.
It usually has three layers: the core layer, the distribution layer and the Access layer.
Factors to consider When Choosing a Topology:
1.  Budget
A rule of thumb is to never make technology procurement decisions based on price alone. There’s no denying though that you can only cut your coat according to your cloth. If a topology is unaffordable, it’s off the table no matter how perfectly suited it might be for your situation.
In any case, irrespective of what your preferred topology is, there’ll almost always be a lower-priced alternative that’s nearly as effective. On pricing matters, bus and ring topologies are quite cost-effective while star, mesh, tree and hybrid topologies are expensive.
2.  Hardware Resources
Certain network topologies work best with certain hardware. And vise-versa. So before you make a decision on the topology to adopt, perform an inventory of your current hardware. You may also already have the hardware needed to implement a certain type of topology. So as opposed to buying everything from scratch, such existing resources give you a head start.
For instance, you may have hardware limitations such as the length of the network cable. In that case, you’d go for a topology that requires the least amount of cable for connecting nodes. Bus and star topologies perform pretty well in this regard.
3.  Ease of Implementation
If you’ll contract a third party to install and/or maintain your network, then the complexity of the network topology you choose is perhaps a non-issue. A competent networking professional will have the education and experience needed to comprehend what each topology entails and implement it accordingly.
However, if you expect to leave network implementation in the hands of novices or individuals without the requisite IT training, then the ease of the topology should be a major factor in your choice. In this case, the bus and star topologies score pretty well. The mesh, tree and hybrid, on the other hand, are complex and difficult for a layman to install or understand.
4.  Size of Network
How many devices are going to be on your network? How geographically dispersed are they? How far from the ‘center’ is the furthest device? Some topologies are inadequate or expensive when applied to large networks. A topology that works perfectly for a 5-device network may prove a disaster when applied to a 10,000-device organization.
Part of the inventorying process we referred to in point 2 should include determining the total number of devices to be interconnected. Armed with this information, you can choose the topology that would best serve the purpose. The tree topology works well with large networks. The bus topology is best suited for small organizations.
5.  Reliability
When it comes to reliability, network topologies aren’t created equal. If you are looking for high reliability because you are in an industry where even brief downtime and delays are frowned upon (e.g. banking), then network reliability is a fundamental consideration. Choose the topology that delivers the highest reliability.
Ring topology performs pretty well under heavy loads but is prone to a single point of failure. Star topology doesn’t depend on any node but the network will collapse if the hub fails. Mesh and hybrid topologies score highest on the reliability front.
6.  Future Expansion
If you expect your organization to grow in size in the medium to long-term, opt for a network topology that’s readily scalable. Identify the topology that’s easy to add new nodes to, without negatively affecting network performance or the user experience of other devices on the network.
The tree topology is perhaps the most compatible with future expansion requirements as it’s fairly easy to extend or shrink the network. The bus topology is also easy to expand but only to a certain extent which is why it would only work for small networks.
Choosing a network topology is one of the most important decisions you’ll make for your technology infrastructure and will have far-reaching ramifications over the long-term. A wrong choice can prove to be an expensive mistake. It’s a decision that requires careful thought in order to get it right from the start.
THIS VIDEO EXPLAINS MORE ABOUT COMPUTER COMMUNICATION
NETWORK PROTOCOLS
(Transmission Control Protocol/Internet Protocol)
WHAT BRINGS COMMUNICATION IN A NETWORK?
NB:Â 1,2&3 layers are physical and deal in transferring data from one device to another e.g. how one configures a switch, router
TRANSPORT LAYER
It links the two sub groups i.e. the upper (software) and the lower (hardware). Carry voice and data and It uses protocols i.e. UDP and TCP.
APPLICATION LAYER
RULES and Regulation FOR APPLICATION LAYER
In the lower 3 are physical devices.
PHYSICAL LAYER DEVICES (1)
DATA LINK LAYER DEVICES (2)
NETWORK LAYER DEVICES (3)
TRANSPORT LAYER DEVICES
Fibre optic cables that are normally used in backbones.
What is an IP address and why is it important?
IP stands for Internet Protocol. An IP address is a series of binary numbers that provide information about the network and the host (the computer or other device). These numbers are typically written as four numbers separated by dots in the older, IP Version 4 (IPv4) address numbering that is most common.
In other words, An IP address is a set of 4 numbers assigned to each device on a computer network. When we apply this definition for the internet, the IP address can be considered a numerical representation of a website address. For example, the domain google.com would go to the IP address 73.14.213.99.
IP address contains 4 octets, each octet can be represented by number 0-255 and separated by periods. For example, 192.168.100.2 is an IP address.
Why is it important?
ASSIGNMENT : CS6: Assignment on Data Communication and Networking MARKS : 25 DURATION : 45 minutes