Computer Networks - Transmission Media PDF

COMPUTER NETWORKS -PART II TRANSMISSION MEDIA Transmission media carries a signal from one computer to another. It is grouped into two types Guided media or Wired Technology: The data signal physically gets transferred from the transmitting computer to...

COMPUTER NETWORKS -PART II TRANSMISSION MEDIA Transmission media carries a signal from one computer to another. It is grouped into two types Guided media or Wired Technology: The data signal physically gets transferred from the transmitting computer to the receiving computer through the wired transmission medium. Unguided media or Wireless Technology: The data is transmitted through waves Guided media or Wired Technology Waves are guided or there is a physical connection between the two computers hence the data physically transferred from one computer to another. Twisted pair cable\Ethernet Cable: It is a transmission medium consisting of two insulated wires in a regular spiral pattern. These are also used for short and medium range telephone communication. It is capable of carrying signal over long distances without the use of repeaters. This is of the suitable option if the length of the cable is more than a few hundred meters. The twisting of wires prevents cross talk. Types of Twisted Pair Cables A twisted-pair cable is a cable made by intertwining two separate insulated wires. There are two types of twisted pair cable- Shielded twisted pair Cable (STP) and Unshielded twisted pair Cable. Shielded cable is used in older telephone networks and network and data communications to reduce outside interference. Used for television signals and also by large corporations in building security systems. Advantages Disadvantages It is simple low weight, easy to install Low bandwidth capabilities, cannot be and maintain. used for broadband applications Capable of carrying a signal over long It can pick up noise signals distances without amplification Being thin in size, it is likely to break (repeater). easily Physically flexible Inexpensive medium for low speed applications where the distance between the nodes is relatively small. Coaxial cables: A coaxial cable consists of a central copper wire surrounded by PVC (poly vinyl chloride) insulation over which a sleeve of copper mesh is covered. The metal sleeve is again shielded by an outer shield of thick PVC material These are more expensive than twisted pair cables but perform better. Advantages Disadvantages Data transmission characteristics are better than that of Expensive compared twisted pair. to twisted pair cable Not compatible with It can be used for broadband communication i.e. several twisted pair cable channels can be transmitted simultaneously. These are difficult to It offers high bandwidth (up to 400 mbps). manage and reconfigure as It can be used as the basis for shared cable network. compared to twisted Transmission quality of co-axial cable is better than pair cable. twisted pair cable Fiber optic Cables: These cables are made of thin long strands of glass or glass like material which carry light from a source at one end of the fiber to the detector. The light sources are either laser diodes (LD) or light emitting diodes (LED). The data to be transmitted is modulated onto a light beam using frequency modulation techniques. At receivers end the signals are demodulated, Optical fibers offer a very high bandwidth and this makes it capable for multichannel communication. It consists of three pieces the core, cladding and protective coating. These cables are highly durable and offer excellent performance but are expensive. Advantages Disadvantages It is immune to electrical and magnetic It is difficult to install and maintain since interference they are quite fragile It is highly suitable for harsh industrial It is the most expensive of all cables environments Connecting two fibers or even the light It guarantees secure transmission and has source with the cable is a difficult a very high transmission capacity process. Hence connection loss is a problem  It can be used for broadband Light can reach the receiver out of phase transmission. Unguided Transmission media: Infrared Communication: The infrared light transmits data through the air and can propagates throughout a room. Infrared communication requires a transceiver (a combination of transmitter and receiver) in both devices that communicate. Infrared communication is playing an important role in wireless data communication due to the popularity of laptop computers, personal digital assistants(PDAs), digital cameras, mobile phones, pagers , TV remote and other devices but being a line-of-sight transmission , it is sensitive to fog and other atmospheric conditions. Advantages Disadvantages Power consumption is less It can only be used for short range Circuitry is simple and inexpensive communication Since it is having short range of Infrared wave transmission cannot communication hence it is considered pass through obstructions like walls, to be a secure mode of transmission. buildings etc. Radio waves: Transmission which makes use of radio wave frequencies is called radio wave transmission It is used in the following areas: Radio Television GPS systems Wireless networks etc. The transmitter encodes the message onto a sine wave and transmits it with radio waves. The receiver receives the radio waves and decodes it. It uses antennas to radiate and capture the signal. Advantages Disadvantages Radio-wave transmission offers mobility. Insecure communication It is easy to communicate through radio Susceptible to weather changes. waves in difficult terrains since there is no need of digging and laying cables. Radio waves can travel through long distances in all directions. Also they can easily pass through obstacles like a  building so they can be used for both indoor and outdoor communication. It offers freedom from land acquisition rights that are required for laying, repairing the cables. Microwave waves: It is an electromagnetic wave in the frequency range of about 2 to 40 GHz (high frequency radio signal). Microwave transmission consists of transmitter, receiver and atmosphere. Like radio waves, microwaves can pass through obstacles viz. buildings, mountains etc. Microwaves offer a line of sight method of communication. A transmitter and receiver of a microwave system are mounted on very high towers and both should be visible to each other (line of sight) In case of microwave transmission, curvature of the earth, mountains and other structures often block the line of sight. Hence several repeater stations are required for long distance transmission thereby increasing the cost considerably. It is generally used for long distance telephonic communications. Advantages Disadvantages Microwave transmission does not Signals become weak after travelling a certain require the expense of laying distance and so require amplification. To overcome cables. this problem, repeaters are used at regular It can carry 25000 voice channels at intervals (25-30 kms). The data signals are the same time. received, amplified and then retransmitted. This Since no cables are to be laid down makes it a very expensive mode of communication. so it offers ease of communication Installation and maintenance of microwave links over difficult terrains like hilly turns out be a very expensive affair. areas. The transmission is affected by weather conditions like rain, thunderstorms etc.  COMPUTER NETWORKS- PART V NETWORK PROTOCOL Protocols Protocol is a set of standard rules that the communicating parties — the sender, the receiver, and all other intermediate devices need to follow. It defines the standardized format for data packets, techniques for detecting and correcting errors and so on. Protocols also define: how computers identify one another on a network. the form to which the data should be converted for transit. how to decide whether the data received is for that node or to be forwarded to another node. ensuring that all the data have reached the destination without any loss. how to rearrange the packets and process them at the destination Types of network protocols are: 1. HTTP 2. FTP 3. TCP/IP 4. SLIP/PPP 5. SMTP 6. POP3 7. HTTPS 8. TELNET 9. VOIP HTTP: HTTP is the protocol that is used for transferring hypertext between two computers and is particularly used on the World Wide Web. It is a TCP/IP based communication protocol and provides a standard for Web browsers and servers to communicate.  Hypertext is the text that is specially coded using a standard coding language called Hyper Text Markup Language (HTML). HTTP defines how messages are formatted and transmitted, and what actions Web servers and browsers should take in response to various commands. For e.g. , when you enter a URL in your browser, this actually sends an HTTP command to the Web server directing it to fetch and transmit the requested Web page. HTTP is based on Client/Server(request-response) principle that runs over TCP. HTTP has three important features 1. Firstly, it is connectionless- After a request is made, the client disconnects from the server and waits for a response. To process the request, the server has to re-establish the connection with the client. 2. HTTP is media independent -This means any type of data(text ,images , sound , video etc.) can be sent by HTTP as long as both the client and server know how to handle the data content. 3. HTTP is stateless - This is because the server and the client are aware of each other only during a request. Afterwards, they get disconnected. File Transfer Protocol (FTP): It is a protocol used for transferring files between computers over a TCP/IP based network such as internet. It is commonly used for uploading pages to a website. When a user requests for a file transfer with another system, FTP sets up a connection between the two nodes for accessing the file. Optionally, the user can authenticate using user ID and password. The user then specifies the file name and location of the desired file. After that, another connection sets up and the file transfer happens directly between the two machines. It is the simplest and most secure way to exchange files over the Internet. The objectives of FTP are: To promote sharing of files (computer programs and/or data). To encourage indirect or implicit use of remote computers. To shield a user from variations in file storage systems among different hosts. To transfer data reliably, and efficiently. TCP/IP (Transmission Control Protocol/Internet Protocol).  It is the base communication protocol of the Internet. It consists of two major components: TCP and IP. Communication between two computers on internet is done using TCP/IP protocol. TCP - is responsible for verifying the correct delivery of data from client to server. Data can be lost in the intermediate network. TCP adds support to detect errors or lost data and to trigger retransmission until the data is correctly and completely received. IP - is responsible for moving packet of data from node to node. IP forwards each packet based on a four-byte destination address (the IP number). The Internet authorities assign ranges of numbers to different organizations. The organizations assign groups of their numbers to departments. IP operates on gateway machines that move data from department to organization to region and then around the world. Point-to-Point Protocol (PPP): It is a protocol for direct communication between two computers, typically a personal computer connected by phone line to a server. For example, an Internet Service Provider(ISP) may provide you with a PPP connection so that the ISP's server can respond to your requests, pass them on to the Internet, and forward your requested Internet responses back to you. PPP defines the format of frame to be exchanged between devices on one or multiple links and also defines the authenticity of the two devices. It supports various authentication schemes such as Password Authentication Protocol (PAP) and Challenge Handshake Authentication Protocol (CHAP). Email Protocols Simple Mail transfer protocol (SMTP) allows transmission of email over the Internet. Most email software is designed to use SMTP for communication purposes when sending email. It only works for outgoing messages. When an email has to be sent, the address of their Internet Service Provider's SMTP server has to be given. The actual mail transfer is done through Message Transfer Agents (MTA). So, the client computer must have a client MTA and the server must have a server MTA.  Most servers these days actually use a slightly updated version of the SMTP protocol called ESMTP (Extended Simple Mail Transfer Protocol). It is a TCP/IP based communication protocol and provides a standard for Web browsers and servers to communicate. Disadvantage of SMTP is that it relatively easy to send messages with fake sender address. Post Office Protocol Version 3 (POP3) Post Office Protocol 3 or POP3 is the third version of a widespread method of receiving email which receives and holds email for an individual until they pick it up. SMTP has a disadvantage that if the destination computer is not online, mails cannot be received. So, the SMTP server receives the mail on behalf of every host and the respective host then interacts with the SMTP server to retrieve messages by using a client server protocol called POP3. POP3 makes it easy for anyone to check their email if their email program is configured properly to work with the protocol. It is extremely common among most mail servers because of its simplicity and high success rate and minimum errors. Many popular email programs, including Microsoft Outlook, are automatically designed to work with POP3. Each POP3 mail server has a different address, which is usually provided to an individual by their web hosting company. This address must be entered into the email program so that the program can connect effectively with the protocol. The individuals receiving POP3 email will have to input their username and password in order to successfully receive email. Remote Access Protocol (Telnet) Telnet is the main internet protocol for creating a connection with a remote machine. It allows you to connect to remote computers (called remote hosts) over a TCP/IP network (such as the Internet). Once your telnet client establishes a connection to the remote host, your client becomes a virtual terminal, allowing you to communicate with the remote host from your computer with whatever privileges you may have been granted to the specific application and data on that host computer. Chat Protocol and VOIP A real time informal communication over the Internet is chatting. A chat program is software which is required for chatting over the internet. AOL Instant Messenger, Campfire, Internet Messenger, MSN Messenger are some commonly used chat programs. In order to chat, the user should have an account on a chatting program. A phone call is a voice based chat while online chat is textual conversation Internet Relay Chat (IRC) IRC protocol is used for chatting. It provides chatting between a groups or between two individuals. It is based on client/server model. The IRC client sends and receives messages to and from an IRC server. The IRC server transports the message from one client to another. The IRC server is linked to many other servers to form an IRC network. IRC server identifies every user through a unique nickname. VOIP VOIP stands for voice over internet protocol. It enables the transfer of voice using packet switched network rather than using public switched telephone network. By using VOIP software, phone calls can be done using standard internet connection. This method of making phone calls is much cheaper than convectional way because the service of Telecommunication Company is not used. There are three different methods of VoIP service in common use today: ATA - ATA stands for analog-to-digital converted. It is used to connect the telephone device to the computer. It takes the analog signals from the phone and converts them to digital signals. These digital signals can be transmitted over the internet. Some providers also are bundling ATAs free with their service. IP phones - IP phones appear much like an ordinary telephone or cordless phone. They are directly connected to the router or the LAN. They have all the hardware and software necessary right on board to handle the IP call.  IP Phones are sometimes called VoIP telephones, SIP phones or Soft phones. Computer-to-computer - It is the most easy and simplest way to use VoIP. The basic hardware requirements are as follows: Computer Internet Speakers Microphone The only cost involved with computer - to- computer VoIP is the monthly ISP fee Video Conferencing It is a communication technology that integrated video and audio to connect users anywhere in the world as if they were in the same room. It allows you to conduct meetings or trainings without the need for all of the participants to be in a single location, so it saves time and money. Eg., Skype, Microsoft Teams etc. Wireless/Mobile Communication protocols: GSM (Global System for Mobile communications): It is the most widely used digital cellular system. It is basically circuit switched network. Developed in Europe in1980s and become international standard in Europe, Asia, Africa and Australia. And the frequency is up to 1800 MHz. But in US used 1900MHz so not compatible with international standard. GSM Technology uses TDMA (Time Division Multiple access) to support up to eight calls simultaneously. Any GSM handset with SIM (Subscriber Identity Module) card can be used in any country that uses this standard. GSM digitizes and compresses voice data, then sends it down a channel with other streams of user data, each in its own time slot. GSM systems use encryption to make phone calls more secure SIM ( Subscriber Identification Module) is an integrated circuit that securely stores the International Mobile Subscriber Identity and related key used to identify and authenticate subscribers on telephony devices. GPRS (General Packet Radio Service) is a technology for radio transmission of small packets of data esp. between mobile devices and internet. GPRS provides a high- speed data transfer, typically between 56Kbits per second to 110kbits per second It is suited for sending and receiving small data as well as large volumes of data. GSM digitizes and compresses voice data, then sends it down a channel with  other streams of user data, each in its own time slot. GSM systems use encryption to make phone calls more secure. WLL (Wireless Local Loop): It is a system that connects subscribers to the public switched telephone network using radio signals. The WLL unit consists of a radio transceiver and the WLL interface assembled in one metal box. MULTIPLE ACCESS TECHNIQUES Multiple Access is the use of multiplexing techniques to provide communication service to multiple users over a single channel. It allows for many users at one time by sharing a finite amountof spectrum. The three types of multiple access techniques are: FDMA (Frequency Division Multiple Access) In this, each user utilizes a portion of the frequency bandwidth available. Each user has its own frequency domain. TDMA (Time Division Multiple Access) In this, each user is allowed to transmit only within specified time intervals. Different users transmit in different time slots. When users transmit, they occupy the whole frequency bandwidth. CDMA (Code Division Multiple Access) CDMA uses a spread-spectrum technique where data is sent in small pieces over a number of discrete frequencies. In this, each user is allocated a unique code sequence. On the sender's end, the data signal is encoded using the given unique code. The receiver decodes the signal according the unique code and recovers the original data. Mobile Telecommunication Technologies Mobile communication is based on cellular networks. A cellular network is nothing but a radio network. In this network, land is divided into areas called cells. Every cell in the network has a transmitter and a receiver known as cell site or base station. Each cell in the network uses different frequency for the transmission of signals. When joined together these cells provide radio coverage over a large geographical area. The network of cells enables the mobile devices to communicate even if they are moving from one cell to another via base stations. Mobile System Terms FDMA- It stands for Frequency Division Multiple Access. In this, each user utilizes a portion of the frequency bandwidth available. Each user has its own frequency domain. CDMA- It stands for Code Division Multiple Access. In this, each user is allocated a unique code sequence. On the sender's end, the data signal is encoded using the given unique code. The receiver decodes the signal according the unique code and recovers the original data. TDMA- It stands for Time Division Multiple Access. In this, each user is allowed to transmit only within specified time intervals. Different users transmit in different time slots. When users transmit, they occupy the whole frequency bandwidth. 1G: It stands for "first generation," refers to the first generation of wireless telecommunication technology, more popularly known as cellphones and came around 1982. The 1G mobile system was based on the analog cellular technology. They only had voice facility available and were based on circuit-switched technology. In 1G mobile systems voice was modulated to a frequency of about 150MHz and higher. They used radio towers for transmission. The major drawbacks of the 1G system were its low capacity, poor voice links and no security. 2G: It is second-generation wireless telephone technology and came around 1991. They used digital signals for transmissions of voice.  2G enabled the mobile systems to provide paging, SMS, voicemail and fax services. Both voice and data conversations were digitally encrypted. The 2G system was based on GSM technology. With GSM, all subscriber and wireless provider information is stored on interchangeable modules known as SIM (Subscriber Identification Module) cards. By swapping out the SIM card, users can painlessly switch phones or providers. They used circuit switching. 2.5G The mobile technology using packet switched domain instead of circuit switched domain were termed as 2.5G mobile systems. They used GPRS (General Packet Radio Service) in addition to GSM. With 2.5G services like MMS, sending pictures through e-mail became possible. GPRS technology was also a major step towards 3G mobile system. 3G: It is third generation of developments in wireless technology in mobile communications, introduced around 2001. It follows 1G and 2G. The 3G technology adds multimedia facilities to 2G phones by allowing video, audio, and graphics applications. With the advent of 3G technology watching streaming video or video telephony became a reality. 3G mobile systems are also known as Universal Mobile Telecommunications System (UMTS) or IMT-2000. They can sustain higher data rates and open the door to many Internet style applications. 4G: 4G networks will be based on packet switching only. It will be able to support faster transmission. They are projected to provide speeds up to 100 Mbps while moving and 1Gbps while stationary. It is a wireless access technology. 4G can provide better-than-TV quality images , video-links and user services include IP telephony, ultrabroadband internet access, gaming services and High Definition Television (HDTV) streamed multimedia. 5G: 5G is the fifth generation of wireless communication technologies supporting cellular data networks. 5G is expected to allow data transfer in Gbps, which is much faster than 4G. It is expected to be able to support all the devices of the future such as connected vehicles and the Internet of Things. Mobile Processor It is a CPU chip designed for tablets, smartphones and other portable devices. Mobile processors use lower voltages and are designed to run cooler than the CPUs in desktop computers. The most widely used mobile processors are ARM (Advanced Risk machine) chips.  COMPUTER NETWORKS -PART III NETWORK DEVICES Modem: The device that can convert digital data into analog signal (modulator) at the sender’s site and converts back analog signal to digital signal (demodulator) at the receiver’s end. Two types of modems are: External – Connected externally to a computer. Internal – Fixed within a computer. RJ45 connector: RJ45 -Registered Jack 45 is an eight-pin connector that is used exclusively with Ethernet cables for networking. It is a standard networking interface that can be seen at the end of all network cables. Basically, it is a small plastic plug that fits into RJ-45 jacks of the Ethernet cards present in various computing devices. Ethernet Card is a network adapter used to set up a wired network. It acts as an interface between computer and the network. It is a circuit board mounted on the motherboard of a computer. Ethernet cards can support data transfer between 10 Mbps and 1 Gbps (1000 Mbps). Ethernet cards are also called as network interface cards (NICs). Repeater: It is a network device used to regenerate data and voice signals received from an incoming packet and transmits to another segment in the network. (It takes incoming packets, analyze the packets and move the packets to another network.) Hub: An Ethernet hub is a network device used to connect different devices through wires. Data arriving on any of the lines are sent out on all the others. The limitation of Hub is that if data from two devices come at the same time, they will collide.  Switch: It is a network device used to interconnect computers on a network. When it receives a data packet, it forwards the packet directly to the recipient device by looking up the MAC address. A hub forward each incoming packet to all the hub ports, while a switch forwards each incoming packet to the specified recipient. A switch does not forward the signals which are noisy or corrupted. It drops such signals and asks the sender to resend it. Router is a network device that can receive the data, analyse it and transmit it to other networks. A router connects a local area network to the internet. Compared to a hub or a switch, a router has advanced capabilities as it can analyse the data being carried over a network, decide/alter how it is packaged, and send it to another network of a different type. For example, data has been divided into packets of a certain size. Suppose these packets are to be carried over a different type of network which cannot handle bigger packets. In such a case, the data is to be repackaged as smaller packets and then sent over the network by a router. A router can be wired or wireless. A wireless router can provide Wi-Fi access to smartphones and other devices. Usually, such routers also contain some ports to provide wired Internet access. These days, home Wi-Fi routers perform the dual task of a router and a modem/switch. These routers connect to incoming broadband lines, from ISP (Internet Service Provider), and convert them to digital data for computing devices to process Gateway: It is a network device used to connect dissimilar networks. The gateway establishes an intelligent connection between a local network and external network (LAN with the internet). It handles messages, addresses and protocol conversions necessary to deliver a message from one network to another. Wifi card: A wireless adapter is a hardware device that is generally attached to a computer or other workstation device to allow it to connect to a wireless system.  COMPUTER NETWORKS PART IV NETWORK TOPOLOGIES AND TYPES The arrangement of computers and other peripherals in a network is called its topology. Common network topologies are Bus, Star , Tree, Mesh and Ring. Bus (Linear): Bus topology is a series of computers connected to a backbone. If any node has to send some information to any other node, it sends the signal to the backbone. The signal travels through the entire length of the backbone and is received by the node for which it is intended. Data is transmitted in small blocks called packets. Each packet has a header containing the destination address. All computers connected to the bus receive the data but only that computer accepts it whose address matches the address attached with data. It works well for smaller networks. Advantages Disadvantages Short cable length results in Fault diagnosis is very difficult less installation cost In case of cable (backbone) or terminator fault, the Easy to extend: Additional entire network breaks down. nodes can be easily connected Reconfiguration is needed if repeaters are to be to the existing bus network at added. If the central bus becomes too long, the any point. repeaters might have to be used to amplify the signal. It is simple and reliable. Nodes must be intelligent to receive its packets. Efficiency of Bus network reduces, as the number of devices connected to it increases. Security is very low because all the computers receive the sent signal from the source. Star: In star topology each node is directly connected to a hub/switch by a single path. If any node has to send some information to any other node, it sends the signal to the hub/switch. This signal is then broadcast to all the nodes but is accepted by the intended node(s).  Advantages Disadvantages Failure of a single connection does not Long cable length as each node is affect the entire network. It just connected to the central node leading involves disconnecting one node from to increase in installation cost. an otherwise fully functional network. Addition of a new node involves This also helps in easy reconfiguration connection to the central node, hence of the network. difficult in expansion of network Fault detection is easier. Dependent on central node, hence if Simple access protocol. the central node fails, the entire Effective, efficient and fast network is disrupted. Tree/ Hybrid: It integrates multiple star topology together onto a bus. The network looks like an inverted tree with the central root branching and sub-branching down to the nodes. When the signal reaches the end of the transmission medium, it is absorbed by the terminators. Tree topology is best suited for applications which have a hierarchical flow of data and control. Such topologies are usually realised in WANs where multiple LANs are connected. Those LANs may be in the form of a ring, bus or star. Advantages Disadvantages It is easier to add new nodes to the Dependent on root computer. If the network root node fails, the entire network is It is easier to isolate a defective node disrupted. from the network. Complex access protocols. Error detection and correction is easy. As more and more nodes and Each segment is provided with segments are added, the maintenance dedicated point-to-point wiring to the becomes difficult. central hub. Scalability of the network depends on If one segment is damaged, other the type of cable used. segments are not affected. Ring Topology: It is a network in circular shape and every node will have one node on either side of it. Data is accepted from one of the neighboring nodes and is transmitted onwards to another. Thus, data travels in one direction only, from one node to node around the ring. After passing through each node, it returns to sending node, which removes it.  Advantages Disadvantages Short cable length. Node failure causes entire network Less connections are needed that failure increases the network reliability. Difficult to diagnose faults No wiring closet space required Network reconfiguration is difficult Suitable for optical fibres Less secure and less reliable Mesh Topology: In this topology, each communicating device is connected to every other device in the network. Advantages Disadvantages Handles large amount of traffic since Wiring is complex multiple nodes can transmit data Cabling cost is high in creating such simultaneously. networks More reliable in the sense that even if There are many redundant or a node gets down, it does not cause unutilized connections. any break in the transmission of data between other nodes. More secure as compared to other topologies because each cable between two nodes carries different data. Types of Networks: PAN (Personal Area Network) LAN (Local Area Network) MAN (Metropolitan Area Network) WAN (Wide Area Network) PAN (Personal Area Network) A Personal Area Network (subset of LAN) is a computer network organized around an individual person.  Personal area networks typically involve a mobile computer, a cell phone and/or a handheld computing device such as a PDA. To transfer files including email and calendar appointments, digital photos and music. Personal area networks can be constructed with cables or be wireless. USB and FireWire technologies often link together a wired PAN, while wireless PANs typically use Bluetooth or sometimes infrared connections. Bluetooth PANs generally cover a range of less than 10meters. LAN (Local Area Network) A network in which the devices are connected over a relatively short distance. They are generally privately-owned networks within a single building or campus, can be extended up to 1km. Many users can share expensive devices, such as laser printers, as well as data on the LAN. We also have WLAN (Wireless LAN) which is based on wireless network. One LAN can even be connected to other LANs over any distance via telephone lines and radio waves. LAN is comparatively secure as only authentic users in the network can access other computers or shared resources. Data transfer in LAN is quite high, and usually varies from 10 Mbps to 1000 Mbps. MAN (Metropolitan Area Network) Bigger version of LAN. It might cover few buildings in a city and might either be private or public. This is a network which spans a physical area (in the range of 5 and 50 km diameter) that is larger than a LAN but smaller than a WAN. MANs are usually characterized by very high-speed connections using optical fibers or other digital media and provides up- link services to wide area networks (WANs) and the Internet. Data transfer rate in MAN also ranges in Mbps, but it is considerably less as compared to LAN. Cable TV network or cable based broadband internet services are examples of MAN. WAN (Wide Area Network) WAN spans a large geographical area, often a country or a continent and uses various commercial and private communication lines to connect computers. The internet is the largest WAN, spanning the entire earth. Difference between LAN and internet? LAN Internet It is confined to a one building or No specific geographical area. nearby buildings It is a collection of different LANs. Example of WAN.  COMPUTER NETWORKS - PART I EVOLUTION AND DATA COMMUNICATION TERMINOLOGIES 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. Two computers are said to be interconnected if they are capable of exchanging information. In a network, people can share files and peripherals such as modems, printers, backup drives, or CD-ROM drives. Each computer on the network is called a node and hence, a network is a series of points or nodes interconnected by communication paths (transmission media). When networks at multiple locations are connected using services available from phone companies, people can send e-mail, share links to the global Internet, or conduct video conferences in real time with other remote users. Evolution of Networking Arpanet (Advance Research Projects Administration Network) – first network by Department of Defence of USA in 1969 to connect the academic and research institutions located at different places for scientific collaborations. Later ARPA was renamed by DARPA (Defence Advanced Research Projects Agency). In mid 80s, the National Science Foundation created a new high capacity network called NSFnet which allowed only academic research on its network. Private companies built their own networks, which were later interconnected along with ARPANET and NSFnet to form Internet. Arpanet used Network Control Protocol (NCP) as transmission protocol. Later NCP was replaced with TCP/IP. In 1990, the Berners-Lee at CERN developed HTML and URL, thus giving birth to World Wide Web (www) First version of Wi-fi standard was introduced in 1997. Need For Networking 1) Resource sharing - files and peripherals a) Sharing of files and software Files and folders can be backed up to local or remote shares. Software can be installed centrally rather than on each machine which proves to be much cheaper than buying licenses for every machine. b) Sharing Peripherals Networks enable us to share such resources and hence reduce the operational cost of any organization. c) Sharing storage Storage can be distributed and thus database load can be shared on the network. This even proves to be cost effective. 2) Improving communication A computer network can provide a powerful, fast and reliable communication medium among the users of various computers on the network. With the help of internet we can communicate efficiently and easily via email, instant messaging, chat rooms, telephone, video telephone calls, and video conferencing. 3) Access to remote database Booking tickets 4) Instant availability & Low cost Disadvantages of networking 1) Threat to data A computer network may be used by unauthorized users to steal or corrupt the data and even to deploy computer viruses or computer worms on the network. File security has to be taken care of especially if connected to WANs. 2) Difficult to set up The systems on a network are more sophisticated and complex to run. Setting up a network, may turn out to be a difficult task. Larger networks may also be very costly to set up and maintain. Requirements of a Network Every network includes: At least two computers - Server or Client workstation. Network Interface Cards (NIC) A connection medium, usually a wire or cable, although wireless communication between networked computers and peripherals is also possible. Network Operating system software, such as Microsoft Windows NT or 2000, Novell NetWare, Unix and Linux. Internet (network of networks) It connects many smaller networks together and allows all the computers to exchange information with each other through a common set of rules for communication. These rules are called protocols. Internet uses Transmission Control Protocol/Internet Protocol (TCP/IP). Programs such as web browsers, File Transfer Protocol (FTP) clients, and email clients are some of the most common ways through which the users work on the Internet. Interspace It is a client/server software program that allow multiple users to communicate online with real-time audio, video and text chat in dynamic 3D environments.  Network Terminologies Nodes (Workstations) A computer becomes a node (also called a workstation) as soon as it is attached to a network. Each user on a network works on a workstation. Server A computer that facilitates sharing of data, software and hardware resources on the network is known as the server. Each server has a unique name by which it is identified by all the nodes on the network. Network Interface Unit (NIU) A network interface unit is a device that is attached to each of the workstations and the server which helps to establish communication between the server and workstations. The NIC basically acts like an interpreter and is also known as Terminal Access Point (TAP) or Network Interface card (NIC). The NIC manufacturer assigns a unique physical address to each NIC card and this physical address is known as the MAC address. Data Communication Terminology Concept of Communication Data Communication is the transfer of data or information between a source and a receiver through a medium. The source transmits the data and the receiver receives it. Components of data Communication The five major components of a data communication system are a Message, a Sender, a Receiver, a Transmission Medium and Protocol. The message is the information to be communicated. This can be anything from text and pictures to audio and video. A Sender is a device which sends the data messages. This can be anything from a computer or laptop, to a workstation or a mobile phone. A Receiver is pretty much the same, except it is receiving the information. Generally, receivers can also send, but sometimes they clash in terms of compatibility due to differences in technology. A Transmission Medium is the physical path by which a message travels from sender to receiver. This can be by wire, or wireless. It can be by coaxial cable, fibre optics, or by radio waves. The Protocol is the final piece. These are the rules that govern the data communications and transfers. It represents an agreement between the communicating devices, i.e. The agreement to allow the sender access to deliver to the receiver unchallenged. Data Channel A channel is the medium used to carry information or data from one point to another. It may refer to the entire physical medium, such as a telephone line, optical fibre, coaxial cable or twisted pair wire, or, it may refer to one of the several carrier frequencies transmitted simultaneously within the line. Measuring Capacity of Communication Media Baud It is the unit of measurement for the information carrying capacity of a communication channel. It is synonymous with bps. Bits Per Second (bps) It refers to the speed at which data transfer is measured. It generally used to measure the speed of information through a high-speed phone lines or modems. Bandwidth It refers to the difference between the highest and lowest frequencies of a transmission channel. It is directly proportional to the amount of data transmitted or received per unit time. Higher the bandwidth, higher the data transfer rate. Frequency is measured in cycles per second i.e., hertz 1000 cycles per second-kilohertz (kHz). 1000 kHz-mega hertz (MHz). 1000 MHz-Giga hertz (GHz). 1000 GHz- Tera hertz (THz). Data Transfer Rate It represents the amount of data transferred per second by a communication channel or a computing or storage device. It is measured in units of bits per second (bps). 1000 bits per second – kbps 1000 bytes per second- Kbps (Kilo bps) Million bits per second – mbps (mega bits ber second) Million bytes per second – mbps (mega bits ber second) MBps stands for Megabyte per second whereas Mbps stands for Megabit per second. Identifying Nodes in a Networked Communication Each node in a network should be uniquely identified so that a network device can identify the sender and receiver and decide a routing path to transmit data. MAC Address MAC stands for Media Access Control. The MAC address, also known as the physical or hardware address, is a unique value associated with a network adapter called a NIC. The MAC address is engraved on NIC at the time of manufacturing and thus it is a permanent address and cannot be changed under any circumstances. The machine on which the NIC is attached, can be physically identified on the network using its MAC address. Each MAC address is a 12-digit hexadecimal numbers (48 bits in length), of which the first six digits (24 bits)contain the manufacturer’s ID called Organisational Unique Identifier (OUI) and the later six digits (24 bits) represents the serial number assigned to the card by the manufacturer. E.g., CC-2F-71-43-F9-B3 OUI Unique serial Number IP Address IP address (Internet Protocol address), is a unique address that can be used to uniquely identify each node in a network. The IP addresses are assigned to each node in a network that uses the Internet Protocol for communication. IP address can change if a node is removed from one network and connected to another network. The initial IP Address called version 4 (IPV4 in short), is a 32 bit numeric address, written as four numbers separated by periods, where each number is the decimal (base-10) representation for an 8-bit binary (base-2) number and each can take any value from 0 - 255. E.g., 192.168.0. As the no of devices connected to the network increased. New version IP6 was proposed. It is represented by eight groups of hexadecimal (base-16) numbers separated by colons. E.g., 2001:8f8:1827:84f4:1124:c0c3:b299:c66a Switching Techniques Switching techniques are to transfer data across networks efficiently. Circuit switching. Message Switching. Packet Switching. Circuit Switching Circuit switching is a technique in which a dedicated and complete physical connection is established between two nodes and through this dedicated communication channel, the nodes may communicate. The circuit guarantees the full bandwidth of the channel and remains connected for the duration of the communication session. Even if no communication is taking place in a dedicated circuit, that channel still remains unavailable to other users (idle channels). Example - analogue telephone network. When a call is made from one telephone to another, switches within the telephone exchange create a continuous wire circuit between the two telephones, for as long as the call lasts. Message Switching  The source computer sends data to the switching office first, which stores the data. It then looks for a free link to another switching office and then sends data to this office. This process is continued till data reaches destination. This is also called store and forward. Electronic mail (e-mail) and voice mail are examples of message switching systems. Packet Switching The message is divided into small packets of fixed size which are sent across the communication network separately. With message switching there is no limit on block size, in contrast packet switching places a tight upper limit on block size. Packets are stored in the main memory. Each packet contains a "header" with information necessary for routing the packet from source to destination. Each packet in a data stream is independent. The main advantage of packet-switching is that the packets from many different sources can share a line, allowing for very efficient use of the communication medium. With current technology, packets are generally accepted onto the network on a first-come, first-served basis. If the network becomes overloaded, packets are delayed or discarded ("dropped"). This method of data transmission became the fundamental networking technology behind the internet and most Local Area Networks. Comparison of different switching techniques Circuit Switching Packet Switching/ Message Switching Reserves required band width in Acquires and releases bandwidth as it is advance needed. Data is sent after a physical connection No direct connection between two between two devices are established devices, hence packet contains source and destination address along with the data The charge is based on distance and The charge is based on number of bytes time and connect time. Similarities between Message and Packet switching techniques Message switching Packet switching Acquires and releases bandwidth as Acquires and releases bandwidth as it is needed. it is needed. Use store and forward method Use store and forward method The charge is based on number of The charge is based on number of bytes and connect time. bytes and connect time. Differences between Message and Packet switching Message switching Packet switching  A single block of data is sent to the Data is divided into small packets destination. The size of the block is not fixed. The packet size is fixed Data packet is stored on the disk Data packets are stored in main memory. Time taken to access a data packet Time taken to access a data packet is more is reduced  COMPUTER NETWORKS- PART VI INTRODUCTION TO WEB SERVICES WWW(World Wide Web) It is an Internet service, based on a common set of protocols that allows the server to distribute documents across the internet in a standard way. Hyper Text Markup Language (HTML): It is a predominant markup language used for presenting information in web pages. eXtensible Markup Language (XML): It is a specification for designing markup language. It is a simplified subset of Standard Generalized Mark-up Language (SGML) for representing structured information on the Web. Advantage of XML over HTML: The first benefit of XML is that because you are writing your own markup language, you are not restricted to a limited set of tags defined by proprietary vendors. Rather than waiting for standard bodies to adopt tag set enhancements or for browser companies to adopt each other’s standards, with XML, you can create your own set of tags at your own pace. Hypertext is text displayed on computer with hyperlinks to other text that the reader can immediately access, usually by a mouse click or keypress sequence. Hyper Text Transfer Protocol (HTTP): It is the underlying protocol used by the World Wide Web. HTTP defines how messages are formatted and transmitted, and what actions web servers and browsers should take in response to various commands. Domain Names: A domain name is an identification string that defines a region of administrative authority, or control in the internet. Eg: www.microsoft.com where microsoft is the domain name. URL: A Uniform Resource Locator (URL) is a specific character string that constitutes a reference to an Internet resource. It is also referred to as a web address. 3 types of URLs – Absolute URL-complete internet address path ie http://www.java.sun.com/index.htm Relative URL – it contains the path from subdirectory or the file name itself. ie images/photo.jpg Fragment URL – it is a name given as a bookmark Protocol Address: An Internet Protocol address (IP address) is a numerical label assigned to each device (e.g., computer, printer) participating in a computer network that uses the Internet Protocol for communication. The format of an IP address is a 32-bit numeric address written as four numbers separated by periods. Eg: 1.160.10.240. In a network every machine can be identified by a unique IP address associated with it and thus help in providing network security to every system connected in a network. Website: It is a collection of web pages belonging to a person or organization. Eg: http://www.microsoft.com Web browser: It is a client application that requests, receives and displays HTML pages. Eg: Internet Explorer, Mozilla. Web Servers: It is a software that accepts requests over HTTP and delivers HTML pages and image files. Web Hosting: It is a service that allocates space for customers to showcase their websites on computer servers connected to the internet. Web Scripting: Client side Scripting: It occurs on the client side of a client server system. For example, on the World Wide Web, the scripting languages like Javascripts, VB Scripts, PHP are client-side because they are executed by the web browser in the client. Server side Scripting: It is a web server technology in which a user's request is verified by running a script directly on the web server to generate dynamic web pages. It is usually used to provide interactive web sites that interface to databases or other data stores. Active Server Pages(ASP), Java Server Pages (JSP), PHP(Personal Home Page),. Web 2.0 (for social networking): It is associated with web applications that facilitate information sharing, interoperability, user centered design on World Wide Web. A Web 2.0 site allows users to interact and collaborate with each other in a social media. Open Source Concepts: Open Source Software: (OSS) is a computer software that is available in source code form. The source code and certain other rights normally reserved for copyright holders are provided under a software license that permits users to study, change, improve and at times also to distribute the software. Eg: Mozilla (Web browser and email client), MySQL (database) Freeware: It is a computer software available for use at no cost or for an optional fee, but usually with one or more restricted usage rights. Eg: ImgBurn (CD writing software), Adobe Flash Player (vedio player) Shareware: It is a software that comes with permission for people to redistribute copies, but says that user has to pay a license fee if he continues to use a copy of it. Eg: WinAVI Video Converter 7.1, Adobe Acrobat 8 Professional.