1. COMPUTER NETWORKS

2. COMMUNICATION
Communication is the act of conveying a massage from a sender to a receiver through some form of medium. Communication is not complete if the receiver does not understands the massage.

3. Analog and Digital Communications

4. Immune from Noise and Distortion
Parameters
Analog Communication
Digital Communication
Definiton
Analog Communication is the technology which uses Analog signal for the transmission of information.
Digital Communication is the technology which uses digital signal for the transmission of information.
Noise and Distortion
Get affected by Noise
Immune from Noise and Distortion
Error Probability
Error Probability is high due to parallax.
Error Probability is low
Hardware
Hardware is complicated and less flexible than digital system.
Hardware is flexible and less complicated than Analog system.
Cost
Low Cost
High Cost
Bandwidth Requirement
Low bandwidth requirement
High bandwidth Requirement
Power Requirement
High power is required
Low Power Requirement
Portability
Less Portable as the components are heavy
More portable due to compact equipments.
Modulation Used
Amplitude and Angle Modulation
Pulse coded Modulation or PCM, DPCM etc.
Representation of Signal
Analog signal can be represented by sine wave.
Digital signal is represented by square wave.
Signal Values
Consists of continuous values
Consists of discrete values
Example of Signal
Analog signal comprises of voice, sound etc.
Digital signals are used in computers

5. What is a Computer Network?
A system of interconnected computers and computerized peripherals (such as printers) is called network. In other words, a network is the interconnection of computers. This interconnection among computers facilitates information sharing among them. Computers may connect to each other by wired media or wireless media.

7. Computer Network Cont. Computer network must have the following:
Something to share(Data or Hardware Resources)
A pathway (Transmission Medium)
Rules for communication (Protocols : are rules that govern computer communication in a network)
Computers or digital communication devices( That send and receive signals)

8. Advantages of a Computer Network
It enhances communication and availability of information.
It allows for more convenient resource sharing.
It makes file sharing easier.
It is highly flexible.
It is an inexpensive system.
It boosts storage capacity.

9. Disadvantages of a Computer Network
It lacks independence
It poses security difficulties.
It lacks robustness.
It allows for more presence of computer viruses and malware.
Its light policing usage promotes negative acts.
It requires an efficient handler.
It requires an expensive set-up.

10. Personal Area Network TYPES OF NETWORKS
A Personal Area Network or simply PAN, is smallest network which is very personal to a user. This may include Bluetooth enabled devices or infra-red enabled devices. PAN has connectivity range up to 10 meters. PAN may include wireless computer keyboard and mouse, Bluetooth enabled headphones, wireless printers and TV remotes for example.

12. Local Area Network (LAN)
A computer network spanned inside a building and operated under single administrative system is generally termed as Local Area Network. Usually, Local Area Network covers an organizations offices, schools, college/universities etc. Number of systems may vary from as least as two to as much as 16 million
LAN provides a useful way of sharing resources between end users. Resources like Printers, File Servers, Scanners and internet is easy sharable among computers.

14. Metropolitan Area Network (MAN)
MAN, generally expands throughout a city such as cable TV network. It can be in form of Ethernet, Token-ring or ATM. Metro Ethernet is a service which is provided by ISPs. This service enables its users to expand their Local Area Networks. For example, MAN can help an organization to connect all of its offices in a City. MAN works in between Local Area Network and Wide Area Network. MAN provides uplink for LANs to WANs or Internet.

16. Wide Area Network (WAN)
This network covers a wide area which may span across provinces and even a whole country. Generally, telecommunication networks are Wide Area Network. These networks provides connectivity to MANs and LANs. Equipped with very high speed backbone, WAN uses very expensive network equipment.

17. Internet
A network of networks is called internet, or simply Internet. It is the largest network in existence on this planet. Internet hugely connects all WANs and it can have connection to LANs and Home networks. Internet enables its users to share and access enormous amount of information worldwide. It uses www, ftp, services, audio and video streaming etc. At huge level, internet works on Client-Server model.

18. Internet is widely deployed on World Wide Web services using HTML linked pages and is accessible by some client software known as Web Browsers. When a user requests a page using some web browser located on some Web Server anywhere in the world, the Web Server responds with the proper HTML page. The communication delay is very low.

19. The Internet is serving many proposes and is involved in many aspects of life. Some of them are:  Websites   Instant Messaging  Blogging  Social Media  Marketing  Networking  Resource Sharing  Audio and Video Streaming

20. Computer Network Topologies
Network Topology is the way computer systems or network equipment connected to each other. It is the architecture of computer systems in a network. Topologies may define both physical and logical aspect of the network.

21. Types of Network Topologies
Point-to-point (P2P)
Point-to-point networks contains exactly two hosts (computer or switches or routers or servers) connected back to back using a single piece of cable. Often, the receiving end of one host is connected to sending end of the other end and vice-versa.

23. Bus Topology In contrast to point-to-point, in bus topology all device share single communication line or cable. All devices are connected to this shared line. Bus topology may have problem while more than one hosts sending data at the same time. It is one of the simple forms of networking where a failure of a device does not affect the others. But failure of the shared communication line make all other devices fail.

25. Star Topology
All hosts in star topology are connected to a central device, known as Hub device, using a point-to-point connection. That is, there exists a point to point connection between hosts and Hub. hub acts as single point of failure. If hub fails, connectivity of all hosts to all other hosts fails. Every communication happens between hosts, goes through Hub only. Star topology is not expensive as to connect one more host, only one cable is required and configuration is simple.

27. Ring Topology
In ring topology, each host machine connects to exactly two other machines, creating a circular network structure. When one host tries to communicate or send message to a host which is not adjacent to it, the data travels through all intermediate hosts. To connect one more host in the existing structure administrator may need only one more extra cable. Failure of any host results in failure of the whole ring. Thus every connection in the ring is point of failure. There exists methods which employs one more backup ring.

29. Mesh Topology
In this type of topology, a host is connected to one or two or more than two hosts. This topology may have hosts
having point-to-point connection to every other hosts or may also have hosts which are having point to point
connection to few hosts only.

31. Tree Topology
Also known as Hierarchical Topology is the most common form of network topology in use present day. This topology imitates as extended Star Topology and inherits properties of Bus topology.
This topology divides the network in to multiple levels/layers of network. Mainly in LANs, a network is divided into three types of network devices. The lowest most is access-layer where users computer are attached. The middle layer is known as distribution layer, which works as mediator between upper layer and lower layer. The highest most layer is known as Core layer, and is central point of the network, i.e. root of the tree from which all nodes connect.

33. Daisy Chain
This topology connects all its hosts in a linear fashion. Similar to Ring topology, all hosts in this topology are connected to two hosts only, except the end hosts. That is if the end hosts in Daisy Chain are connected then it represents Ring topology. Each link in Daisy chain topology represents single point of failure.
Every link failure splits the network into two segment. Every intermediate host works as relay for its immediate hosts.

35. Hybrid Topology
A network structure whose design contains more than one topology is said to be Hybrid Topology. Hybrid topology inherits merits and demerits of all the incorporating topologies.

37. Communication Channels
A path through which information is transmitted from one place to another is called communication channel. It is also referred to as communication medium or link. The twisted pair wire, coaxial cable, fiber optic cable, microwave, satellite etc. are examples of communication channels.

38. In a communication channel, data is transmitted in the form of signals (analog signal). The data transmission is measured in bandwidth. The bandwidth will be higher if more signals can be transmitted. Actually, the bandwidth measures the amount of information that can be transmitted through the media within the given period of time. For analog signals, bandwidth is represented in hertz (Hz). It means number of signals transmitted per second. For digital signals, it is represented in bits per second (bps). Different transmission media have different bandwidths. The higher the bandwidth of the transmission media, the more information can be transmitted.

39. TYPES OF COMMUNICATION CHANNELS
Physical Transmission Media
Also called guided communication media, they are communication devices that are directly linked with each other via cables or physical media for transmission of data. The data signals are bounded to a cabling media. Therefore, guided media is also called bounded media. The guided media are usually used in LAN. The examples of guided or bounded media are: Twisted pair wire. Coaxial cable, Fiber optic cable.

40. Wireless transmission media
Also called unguided communication media, data is communicated between communication devices in the form of wave. Unguided media provides means to transmit data signals but does not guide them along a specific path. The data signals are not bounded to a cabling media. Therefore,. unguided media is also called unbounded media. This transmission medium is used when it is impossible to install the cables. The data can be transmitted all over the world through this medium. The examples of unguided or unbounded media are: Microwave, Satellite, Radio Broadcast, Cellular Radio.