Chapter1 computer networking

COMPUTER NETWORKING Introduction The advent of computer and communication technology have changed our daily life. Observe the following daily life examples- Watching Cable TV Cash Withdrawal from ATM Sending and receiving E-mails Booking Railway or Air-lines Tickets. Sending and receiving SMS through Mobile. What is a Network – A computer network is a collection of interconnected computers and other devices which are able to communicate with each other and share hardware and software resources. Advantages/Why we build a Network? 1. Sharing Resources: To share data and peripherals among users irrespective of their physical location. Ex. Sharing database, program files, printer and scanners etc. 2. Improved Communication: Enables reliable, secure and faster communication between users. It saves our time. 3 Reduced Communication cost: Using today’s public network we can send a large quantity of data at very low cost. Internet and Mobile network playing a very important role in sending and receiving text, image, audio and video data. 4. Offers easy communication methods: Example - E-mail, SMS etc. Components of a Network Sender: A device or a computer that sends the data. Receiver: A device or a computer that receives the data. Message: Information to be communicated. It may be text, images, sound or video. Medium: A transmission medium is a physical path through which the data flows from sender to receiver. A cable, fiber-optics or radio waves can be the medium. Protocol: A set of rules that manage data communication. It represents an agreement between the communicating devices.

Networking Hardware- To form a computer network a lot of hardware devices are required. Some of these devices along with their functionalities are mentioned below : Transmission Media- Def- A transmission medium is a medium of data transfer over a network. It can be wired or wireless. Wired Media – A number of various types of cables are used to transfer data over computer networks. These are twisted pair cable, co-axial cable, and optical fiber cable. 1. Twisted pair cable – Most widely used cable for creating small computer networks. It contains four twisted pairs covered in an outer shield. An RJ-45 connecter is used to connect this cable to a computer. It is of two types: 1. UTP (Unshielded (unprotected) Twisted Pair): As the name suggest in UTP cables individual pairs are not shielded (protected). UTP Cable UTP Cable with RJ-45 Connector (Registered Jack) Characteristics – 1. Low-cost cable available for setting up small networks. 2. Thin and flexible cable and therefore it offers ease of installation. 3. Carry data upto a length of 100m. 2. STP (Shielded Twisted Pair) – It is the same cable as the UTP, but with each pair shielded individually. An outer shield then covers all the pairs like in UTP.

Characteristics – 1. As compared to UTP, STP offers better immunity (resistance) against internal and external electromagnetic interferences. 2. Expensive than UTP cable. 3. As compared to UTP cable, STP cable is difficult to install. 2. Coaxial Cable ( or coax) – Coaxial cables are group of specially wrapped & insulated wire lines. They consist of a central copper wire surrounded by a PVC insulation over which there is a sleeve (cover) mesh. The copper wire sleeve is shielded again by an outer shield. Signal is transmitted by inner copper wire. It is most common in cable TV network. Characteristics : 1. It can carry data for a large distance ( 185m to 500m) . 2. Bulkier and less flexible than twisted pair. 3.Due to its thickness and less flexibility, it is difficult to install as compared to twisted pair cable. 4. Data transmission is better than twisted pair. 5. Much higher noise immunity. 3. Optical Fiber Cable – Optical fibers are hair-thin threads of glass or plastic. Optical fiber can transmit data at much higher speed than copper wires or coaxial cables with no significant loss over long distances. An optical fiber has following parts: Core - It is the thin glass rod at the center through which the light travels Cladding (covering) - It is the outer optical material surrounding the core that reflects the light back into the core Buffer coating - It is the plastic coating that protects the cable from damage and moisture

Characteristics : 1. Can carry data for a very large distance. 2. Most efficient cable available for network. 3. Especially skilled people are required to install optical fiber cable. 4. Most expensive. 5. less susceptible to noise Wireless Media (Unguided media): 1.No physical link established between two or more devices, communicating wirelessly. Wireless signals are spread over in the air and are received and interpreted by appropriate antennas. 2.Electromagnetic waves are used for wireless communication over computer networks. 3.No physical medium is necessary for wireless signals, making them a versatile way to build a network. Radio wave – Radio waves are used for communication over distances ranging from a few meters upto covering an entire city and can penetrate (go through) buildings easily. Examples of Radio Waves transmission: - Cordless phones, AM AND FM radio broadcast, Garage door openers. Characteristics : 1. These waves are Omni-directional, so the transmitting and receiving antennas need not be aligned. 2. Ease of communication over difficult terrain (Area of land). 3. Relatively inexpensive than wired media. 4. Permission from concerned authorities is required for use of radio wave transmission. 5. Less secure mode of transmission

Microwave – Microwave signals travel in straight lines and cannot penetrate any solid object. Therefore for long distance microwave communication, high towers are built and microwave antennas are put on their tops. An example of usage of microwaves for communication is as follows: In the big cities where land is very costly and a lot of formalities have to be completed to get permission to dig land for cabling, microwave antennas can be put on top of high rise buildings and communication can be started in a short time. Characteristics : 1. Faster than radio communication. 2. Ease of communication over difficult terrain. 3. The transmission is in straight line so the transmitting and receiving antennas need to be properly aligned. 4. Relatively inexpensive than wired media. 5. Free from land acquisition rights. 1. Satellite Link - Satellite links are used for very long distance wireless communication which may range from intercity to worldwide. Transmission from the earth to a satellite is known as uplink. Transmission from a satellite to the earth is known as downlink.

Characteristics : 1. Area coverage very large. 2. Fast communication. 3. Very expensive. 4. Requires legal permission. 5. Normally owned by governments or by government approved organizations of various countries 4. Bluetooth – Bluetooth technology uses radio waves. This technology is used for short range wireless communication (approx. 10m). Characteristics: 1. Slow data transfer rate. 2. Used for short range communication. 3. Line of sight between communicating devices is not required. 5. Infrared Waves – These waves are used for short range communication (approx. 5m). It is inexpensive compared to other mechanisms. Examples – Home-entertainment remote-control devices, Cordless mouse.

Characteristics: 1. No government permission is required. 2. The waves do not cross any solid object in between. 3. Does not require an antenna. 4. Transmission is safe. Node – A node is a device which is directly connected to a computer network. It can be a computer or any other device like scanner, printer etc. Network Devices – Other than transmission media many other devices are required to form computer networks. Some of these devices are : 1. NIC - Any computer which has to be part of a computer network must have an NIC (Network Interface Card) installed in it. A computer communicates with other computer on a network with the help of NIC only. 2. Hub – A hub is an electronic device that connects several nodes to build a network and redirects the received information to all the connected nodes in broadcast mode. Hubs can be passive or active. Active hubs – Electrically amplify the signals as it moves from one connected device to another. Passive hub – Allow the signals to pass from one computer to another without any change.

http://www.youtube.com/watch?v=NxEyelY8R0s&list=PLC57B37876E E50A15 3. Switch – A switch is an intelligent device that connects several nodes to build a network and redirect the received information only to the intended node. Switch can be considered advance from of hub. 4. Repeater – A repeater is a device that is used to regenerate a signal which is on the way through a communication channel. A repeater regenerates the received signal and re-transmits it to its destination.

5. Gateway – A gateway is a device, which is used to connect different types of network and perform the necessary translation so that the connected networks can communicate properly. Network Topologies – The way in which the computers or other devices are physically interconnected to build a network is called a Topology. The most popular topologies are: 1. Bus topology – In this topology all nodes are connected to a main cable called backbone. If any node has to send some information to any other node, it sends the signal to the backbone. The signals travels through the entire length of the backbone and is received by the node for which it is intended. Characteristics: 1. It is easy to install. 2. It requires less cable length and hence it is cost effective. 3. In case of cable fault, the entire network breaks down. 4. Easy to add additional node. 5. Failure of a node does not affect the network.

2. Star Topology – In this topology each node is directly connected to a switch/hub. Each node requires a single cable. Any communication between the node must pass through the central node. Star topology generally requires more cable than bus topology. Characteristics : 1. It is easy to install. 2. Failure of hub/switch leads to failure of entire network. 3. It requires more cable than bus topology. 4. It is easy to add and remove additional node. 5. If any node other than host node fails, remaining nodes are unaffected. 3. Tree topology - Tree topology is a combination of bus and star topology. It is used to combine multiple star topology networks. All these stars are connected together like a bus. Characteristics: 1. It offers easy way of network expansion. 2. Even if one network (star) fails, the other networks remain connected and working.

Types of Networks A computer network may span any amount of geographical area. It can be on a table, in a room, in a building, in a city, in a country, across continents or around the world. On the basis of area covered computer network are classified as : 1. Personal Area Network (PAN) - A PAN is network of communicating devices ( Computer, Phone, Camera, MP3/MP4 Players) in the proximity(nearness) of an individual. This range is typically upto 10 meters. Example – Transfer songs from one cell phone to another, when files are transferred from PC to an MP3 player. A PAN can be set up using guided media (USB cable) or unguided media (Bluetooth, Infrared). 2. Local Area Network (LAN) – Small computer networks that are limited to a localized area (e.g. an office, a building or a factory, home, school) are known as Local Area Network. A LAN is managed by a single person or organization. It can cover an area of a few meters to a few kilometers. A LAN can be set up using wired media (UTP cables, Co-axial cables etc.) or wireless media (Infrared, radio waves).

3. Metropolitan Area Network (MAN) – Metropolitan Area Networks are the networks spread over a city. For example , cable TV networks, interconnected offices of a state government. A MAN is typically owned and operated by a single entity such as a govt. body or a large corporation. 4. Wide Area Network (WAN) – These are the networks spread over large distances says across countries or even continents. WANs usually contain a number of interconnected individual computers, LANs, MANs, and may be other WANS. Example – Internet. Area of coverage – No upper limit.

Identification of computers and users over a network MAC (Media Access Control) address – A MAC address is a unique 12 digit ( 6 digits for manufacturer code and 6 digits for serial number ) hexadecimal number assigned to each NIC. MAC address of an NIC never changes. example 00:A0:C9 : 14:C8:35 first six digit 00:A0:C9 indicates manufacturer code and the last digit 14:C8:35 are Serial number . IP Address – An IP (Internet Protocol ) address is a unique number assigned to each node on a network. IP address are expressed in decimal format. For example following is an IP address : 202.27.94.137 IP address setting of a node can be changed by the user. An IP address is a group of four bytes (or 32 bits). IP address Vs MAC Address – The IP address is assigned by the network administrator or the internet service provider while the MAC address is

assigned by the manufacturer. Thus if a computer is transferred from one network to another, its IP address gets changed where as the MAC address remains the same. Domain Name – The system which assigns names to computers (web server) and maintain a database of these names and corresponding IP address. A domain generally contains following parts: 1. Top level domain name or primary domain name such as .com, .net, .org, .edu, .in etc. 2. Sub-domain name(s) example – cbse.nic.in in – is the primary domain name nic – is the sub-domain of in cbase - is the sub-domain of nic. Generic Domain Names : .com- commercial business .edu - educational institutions .gov - gevt. Agencies .mil - Military .net - Network organizations .org - Organizations (nonprofit)

Domain Name Resolution – Domain Name Resolution is the process of getting the corresponding IP address from a domain name. Attack on Network Security: Some kinds of attack on network security are as follows: Denial of service attacks: Denial of service attacks are those attacks that prevent the legitimate (valid) users of the system, from accessing or using the resources, information and capabilities of the system. Examples of such attacks are: 1. Denial of Access to information: Corrupting, Encrypting or changing the status of information so that it is not accessible (available) to its valid user. 2. Denial of access to application: Forced shutting of an application as soon as the users open it. 3. Denial of access to Resources: Blocking a resource, may be a printer or scanner or USB port, of a computer from proper working. 4. Denial of access to a website: Continuously sending bulk request to a website so that it is not available to any other user. Intrusion Problems: An Intrusion problem is an attempt to mischievously steal some information from someone's computer. Examples of Intrusion are: Snooping (to find out private things about somebody) – refers to gaining unauthorised access to another person's or organization's data. This may be done in a number of ways: a. By getting someone’s login information. b. Reading the files in an unauthorized manner. c. Using some software which keeps track of the activities and data being sent or received on someone’s computer.

Eavesdropping (To listen secretly to the private conversation of others) – Refers to gaining unauthorized access to another person’s or organization’s data while the data is on its way on the network. this may be done in a number of ways: 1. By setting up parallel telephone lines. 2. By installing some software in the target computer. 3. By installing some receiver which capture the data while on its way. Network Security: refers to all activities undertaken to protect a computer network from attacks to its security. Various techniques used for network security are given below: 1. Login-password: By assigning login names and strong password to the users of a system, it can be ensured that only authorized people access a computer. 2. Firewall: A firewall is a hardware device or software that controls the incoming and outgoing network traffic. A firewall permits only the data to enter or leave a computer/Network for which permission have been granted by the computer/network administrator. 3. Anti Virus Software: Anti-virus software’s work against not only the virus but also against almost all kind kinds of malware. 4. File Permissions: by giving appropriate rights to respective users, computer security as well as network security can be increased.

ANSWER THE FOLLOWING QUESTIONS 1. Tara Nathani wants to upload and download files from/to a remote internet server, write the name of the relevant communication protocol, which will let her do the same. Ans – FTP (File Transfer Protocol). 2. Define any two threats of Network Security. 3. Which protocol is used for the transfer of hyper text documents on the internet? Ans – HTTP (Hyper Text Transfer Protocol) 4. Which transmission media should be used to transfer data across two continents at very high speed? 5. Give two examples of guided media and two examples of unguided media Ans – Guided media - Twisted pair cable, Coaxial cable Unguided media – Microwave, radio wave. 6. Why a switch is called an intelligent hub? 7. When is a repeater used in a computer network? 8. Two engineers in the same room have connected their Palm-top using Bluetooth for working on a group presentation. Out of the following, what kind of network have they formed? LAN, MAN, PAN, WAN 9. Two neighbourhood schools, at a distance of 120 meters from each other, decide to join their LANs using UTP cable so that they can share their e-learning resources. But after joining their LANs they are not able to share the resources due to loss of signal in-between. Which device should they use so that the signal is amplified in-between ? 10. How would you extract manufacturer-id and card no. from a MAC address ? Ans – The first three bytes of a MAC address represent manufacturer-id and the last three bytes of a MAC address represent card-no.

11. Sujata says that the following numbers indicate an address : 208.77.188.166 What is the above address called ? To which object/device is it assigned? Ans : The above address is called an IP address or Internet Protocol Address. It is assigned to devices participating in a network. 12. Jai Khanna is confused between the terms Domain Name and URL. Explain the difference with the help of appropriate examples of each Ans- A URL (Uniform Resource Locator) is the complete address of a document on the web, whereas a domain name specifies the location of document’s web server. A domain name is a component of the URL used to access web sites. For example the web address http://www.example.net/index.html is a URL. in this URL www.example.net is the domain name. 13. Ms. Taufiq Ahmed wants to prevent unauthorized access to/form his company’s local area network. Write the name of a system (software/hardware) , which he should install to do the same. 14. Beauty Lines Fashion Inc. is a fashion company, with design unit and market unit 135 meters away from each other. The company recently connected their LANs using Ethernet cable to share the stock related information. But after joining their LANs, they are not able to share the resources due to loss of signal in-between. Which device out of the following should you suggest to be installed for a smooth communication ? (i) UPS (ii) Modem (iii) Repeater 15. Which of the following is not a feature of Networking ? (i) Resource sharing (ii) Uninterrupted Power Supply (iii) Reduced cost (iv) Reliability 16. Identify the type of Topology from the following:

(i) If each node is connected with the help of independent cable with the help of a central switching (communication controller ) (ii) If each node is connected with the help of a single co-axial cabel. 17. Define following with reference to Threats to Network Security : (i) Trojan Horse (ii) Worm 18. Give one advantage and one disadvantage of using Star topology over bus topology. Ans : Advantage - As compared to Bus topology it gives far much better performance, signals don’t necessarily get transmitted to all the workstations. Disadvantage - Longer cable length. 19. Write the name of the most suitable wireless communication channels for each of the following situations. (i) (i) Communication between two offices in different countries. (ii) To transfer the data from one mobile phone to another. 20. Expand the following term: (i) HTTP (ii) FTP 21. What do you understand by Network Security? Name two common threats to it. Ans : Network security is needed to protect data during their transmission and to guarantee that data transmissions are authentic. 1. Trojan horse programs 2. Worms 22.

14. ABC Pvt. Ltd. Has set up its new center at Manglore for its offices and web based activities. It has four buildings as shown in the diagram below : Center to center distances between various buildings Number of computers (a)Suggest a cable layout of connections between the buildings. (b)Suggest the most suitable place (i.e., building) to house the server of this organization with a suitable reason. (c) Suggest the placement of the following devices with justification : (i) Repeater (ii) Hub/Switch Ans : (a) Two layouts are being suggested any of which may be considered : Layout Option 1 : Layout Option 2 : A to B 50 m B to G 150 m G to L 25 m A to L 170 m B to L 125 m A to G 90 m A 25 B 50 G 125 L 10 A B G L A B G L A B G L

(b) The most suitable place/building to house the server of this organization would be building G, as this building contains the maximum number of computers, thus decreasing the cabling cost for most of the computers as well as increasing the efficiency of the maximum computers in the network. Also housing the server here will make most of the traffic local. (c) (i) For Layout 1, since the cabling distance between A to G, and that between B to G are quite large, so a repeater each, would ideally be needed along their path to avoid loss of signals during the course of data flow in these routes. For layout 2, since the distance between building A to G is large so a repeater would ideally be placed in between this path (ii) in both the layouts, a hub/switch each would be needed in all the buildings, to interconnect the group of cables from the different computers in each building. Layout 1 Repeater Repeater A B G L RepeaterA B G L Repeater Repeater A B G L Hub Hub Hub Hub

Bus Topology A bus topology consists of a main run of cable with a terminator at each end. All nodes like workstations, printers, laptops servers etc., are connected to the linear cable. The terminator is used to absorb the signal when the signal reaches the end, preventing signal bounce. When using bus topology, when a computer sends out a signal, the signal travels the cable length in both directions from the sending computer. When the signal reaches the end of the cable length, it bounces back and returns in the direction it came from. This is known as signal bounce. Signal bounce will create problem in network, because if another signal is sent on the cable length at the same time, the two signals will collide. Definition Noise Noise is unwanted electrical or electromagnetic energy that degrades the quality of signals and data. Noise occurs in digital and analog systems, and can affect files and communications of all types, including text, programs, images, and audio. In a hard-wired circuit such as a telephone-line-based Internet hookup, external noise is picked up from appliances in the vicinity (neighborhood), from electrical transformers, from the atmosphere, and even from outer space. Normally this noise is of little or no consequence. However, during severe thunderstorms, or in locations were many electrical appliances are in use, external noise can affect communications. In an Internet hookup it slows down the data transfer rate, because the system must adjust its speed to match conditions on the line. Polyvinyl Chloride Amplitude Modulation Frequency Modulation What is the difference between HTTP and FTP?

- Both HTTP and FTP are file transfer protocols based on TCP, and they are published in RFC (Request for Comments). - HTTP is used to transfer the content of a web page from web server to a client’s web browser, while FTP is used to both upload and download files between FTP server and FTP client. So, HTTP is referred as a one-way system and FTP is grouped under two-way system. - When using an URL including http, it means that the user is connecting to a web server, and when using an URL containing ftp, it says that the user is working with a file server. - HTTP transfer only the web page content to the web browser in order to view it, and the transferred file is not copied to the memory, but FTP transfers the entire file to the other device, and also it is saved in the memory space. - FTP generally requires a user login to the server in order to exchange files, but HTTP does not need authentication for that. - FTP is more efficient in transferring larger files, whereas HTTP is more efficient for transferring smaller files such as web pages.

Chapter1 computer networking

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Chapter1 computer networking