Category: communication Technologies

Switching Techniques In large networks, there may be more than one paths for transmitting data from sender to receiver. Selecting a path that data must take out of the available options is called switching. There are two popular switching techniques – circuit switching and packet switching. Circuit Switching When a dedicated path is established for data transmission between sender and receiver, it is called circuit switching. When any network node wants to send data, be it audio, video, text or any other type of information, a call request signal is sent to the receiver and acknowledged back to ensure availability of dedicated path. This dedicated path is then used to send data. ARPANET used circuit switching for communication over the network. Advantages of Circuit Switching Circuit switching provides these advantages over other switching techniques − Once path is set up, the only delay is in data transmission speed No problem of congestion or garbled message Disadvantages of Circuit Switching Circuit switching has its disadvantages too − Long set up time is required A request token must travel to the receiver and then acknowledged before any transmission can happen Line may be held up for a long time Packet Switching As we discussed, the major problem with circuit switching is that it needs a dedicated line for transmission. In packet switching, data is broken down into small packets with each packet having source and destination addresses, travelling from one router to the next router. Learning working make money

Communication Technologies – Terminologies Before we dive into details of networking, let us discuss some common terms associated with data communication. Channel Physical medium like cables over which information is exchanged is called channel. Transmission channel may be analog or digital. As the name suggests, analog channels transmit data using analog signals while digital channels transmit data using digital signals. In popular network terminology, path over which data is sent or received is called data channel. This data channel may be a tangible medium like copper wire cables or broadcast medium like radio waves. Data Transfer Rate The speed of data transferred or received over transmission channel, measured per unit time, is called data transfer rate. The smallest unit of measurement is bits per second (bps). 1 bps means 1 bit (0 or 1) of data is transferred in 1 second. Here are some commonly used data transfer rates − 1 Bps = 1 Byte per second = 8 bits per second 1 kbps = 1 kilobit per second = 1024 bits per second 1 Mbps = 1 Megabit per second = 1024 Kbps 1 Gbps = 1 Gigabit per second = 1024 Mbps Bandwidth Data transfer rates that can be supported by a network is called its bandwidth. It is measured in bits per second (bps). Modern day networks provide bandwidth in Kbps, Mbps and Gbps. Some of the factors affecting a network’s bandwidth include − Network devices used Protocols used Number of users connected Network overheads like collision, errors, etc. Throughput Throughput is the actual speed with which data gets transferred over the network. Besides transmitting the actual data, network bandwidth is used for transmitting error messages, acknowledgement frames, etc. Throughput is a better measurement of network speed, efficiency and capacity utilization rather than bandwidth. Protocol Protocol is a set of rules and regulations used by devices to communicate over the network. Just like humans, computers also need rules to ensure successful communication. If two people start speaking at the same time or in different languages when no interpreter is present, no meaningful exchange of information can occur. Similarly, devices connected on the network need to follow rules defining situations like when and how to transmit data, when to receive data, how to give error-free message, etc. Some common protocols used over the Internet are − Transmission Control Protocol Internet Protocol Point to Point Protocol File Transfer Protocol Hypertext Transfer Protocol Internet Message Access Protocol Learning working make money

Communication Technologies Tutorial Job Search Exchange of information through the use of speech, signs or symbols is called communication. When early humans started speaking, some 5,00,000 years ago, that was the first mode of communication. Communication over a long distance when people who are communicating are not in direct line of each other’s site is called telecommunication. Invention of telephone and establishment of commercial telephony in 1878 marked a turnaround in communication systems and real telecommunication was born. Telephones slowly gave way to television, videophone, satellite and finally computer networks. Computer networks have revolutionized modern day communication and communication technologies. In this tutorial, we will discuss in detail how networks have evolved since the first network known as ARPANET. We will also discuss the hardware and software components of networking and the concept of global communication via Internet. Audience This tutorial is designed for anyone who wants to understand the basic concepts of networking and how a network functions. Prerequisites There are no prerequisites for this course except an appetite for learning how networks in general and Internet in particular operate. Learning working make money

Communication Technologies – Transmission Media For any networking to be effective, raw stream of data is to be transported from one device to other over some medium. Various transmission media can be used for transfer of data. These transmission media may be of two types − Guided − In guided media, transmitted data travels through cabling system that has a fixed path. For example, copper wires, fibre optic wires, etc. Unguided − In unguided media, transmitted data travels through free space in form of electromagnetic signal. For example, radio waves, lasers, etc. Each transmission media has its own advantages and disadvantages in terms of bandwidth, speed, delay, cost per bit, ease of installation and maintenance, etc. Let’s discuss some of the most commonly used media in detail. Twisted Pair Cable Copper wires are the most common wires used for transmitting signals because of good performance at low costs. They are most commonly used in telephone lines. However, if two or more wires are lying together, they can interfere with each other’s signals. To reduce this electromagnetic interference, pair of copper wires are twisted together in helical shape like a DNA molecule. Such twisted copper wires are called twisted pair. To reduce interference between nearby twisted pairs, the twist rates are different for each pair. Up to 25 twisted pair are put together in a protective covering to form twisted pair cables that are the backbone of telephone systems and Ethernet networks. Advantages of twisted pair cable Twisted pair cable are the oldest and most popular cables all over the world. This is due to the many advantages that they offer − Trained personnel easily available due to shallow learning curve Can be used for both analog and digital transmissions Least expensive for short distances Entire network does not go down if a part of network is damaged Disadvantages of twisted pair cable With its many advantages, twisted pair cables offer some disadvantages too − Signal cannot travel long distances without repeaters High error rate for distances greater than 100m Very thin and hence breaks easily Not suitable for broadband connections Shielding twisted pair cable To counter the tendency of twisted pair cables to pick up noise signals, wires are shielded in the following three ways − Each twisted pair is shielded. Set of multiple twisted pairs in the cable is shielded. Each twisted pair and then all the pairs are shielded. Such twisted pairs are called shielded twisted pair (STP) cables. The wires that are not shielded but simply bundled together in a protective sheath are called unshielded twisted pair (UTP) cables. These cables can have maximum length of 100 metres. Shielding makes the cable bulky, so UTP are more popular than STP. UTP cables are used as the last mile network connection in homes and offices. Coaxial Cable Coaxial cables are copper cables with better shielding than twisted pair cables, so that transmitted signals may travel longer distances at higher speeds. A coaxial cable consists of these layers, starting from the innermost − Stiff copper wire as core Insulating material surrounding the core Closely woven braided mesh of conducting material surrounding the insulator Protective plastic sheath encasing the wire Coaxial cables are widely used for cable TV connections and LANs. Advantages of Coaxial Cables These are the advantages of coaxial cables − Excellent noise immunity Signals can travel longer distances at higher speeds, e.g. 1 to 2 Gbps for 1 Km cable Can be used for both analog and digital signals Inexpensive as compared to fibre optic cables Easy to install and maintain Disadvantages of Coaxial Cables These are some of the disadvantages of coaxial cables − Expensive as compared to twisted pair cables Not compatible with twisted pair cables Optical Fibre Thin glass or plastic threads used to transmit data using light waves are called optical fibre. Light Emitting Diodes (LEDs) or Laser Diodes (LDs) emit light waves at the source, which is read by a detector at the other end. Optical fibre cable has a bundle of such threads or fibres bundled together in a protective covering. Each fibre is made up of these three layers, starting with the innermost layer − Core made of high quality silica glass or plastic Cladding made of high quality silica glass or plastic, with a lower refractive index than the core Protective outer covering called buffer Note that both core and cladding are made of similar material. However, as refractive index of the cladding is lower, any stray light wave trying to escape the core is reflected back due to total internal reflection. Optical fibre is rapidly replacing copper wires in telephone lines, internet communication and even cable TV connections because transmitted data can travel very long distances without weakening. Single node fibre optic cable can have maximum segment length of 2 kms and bandwidth of up to 100 Mbps. Multi-node fibre optic cable can have maximum segment length of 100 kms and bandwidth up to 2 Gbps. Advantages of Optical Fibre Optical fibre is fast replacing copper wires because of these advantages that it offers − High bandwidth Immune to electromagnetic interference Suitable for industrial and noisy areas Signals carrying data can travel long distances without weakening Disadvantages of Optical Fibre Despite long segment lengths and high bandwidth, using optical fibre may not be a viable option for every one due to these disadvantages − Optical fibre cables are expensive Sophisticated technology required for manufacturing, installing and maintaining optical fibre cables Light waves are unidirectional, so two frequencies are required for full duplex transmission Infrared Low frequency infrared waves are used for very short distance communication like TV remote, wireless speakers, automatic doors, hand held devices etc. Infrared signals can propagate within a room but cannot penetrate walls. However, due to such short range, it is considered to be one of the most secure transmission modes. Radio Wave Transmission of data using radio frequencies is called radio-wave transmission. We all are familiar with radio channels that broadcast entertainment

History Of Networking ARPANET – the First Network ARPANET − Advanced Research Projects Agency Network − the granddad of Internet was a network established by the US Department of Defense (DOD). The work for establishing the network started in the early 1960s and DOD sponsored major research work, which resulted in development on initial protocols, languages and frameworks for network communication. It had four nodes at University of California at Los Angeles (UCLA), Stanford Research Institute (SRI), University of California at Santa Barbara (UCSB) and University of Utah. On October 29, 1969, the first message was exchanged between UCLA and SRI. E-mail was created by Roy Tomlinson in 1972 at Bolt Beranek and Newman, Inc. (BBN) after UCLA was connected to BBN. Internet ARPANET expanded to connect DOD with those universities of the US that were carrying out defense-related research. It covered most of the major universities across the country. The concept of networking got a boost when University College of London (UK) and Royal Radar Network (Norway) connected to the ARPANET and a network of networks was formed. The term Internet was coined by Vinton Cerf, Yogen Dalal and Carl Sunshine of Stanford University to describe this network of networks. Together they also developed protocols to facilitate information exchange over the Internet. Transmission Control Protocol (TCP) still forms the backbone of networking. Telenet Telenet was the first commercial adaptation of ARPANET introduced in 1974. With this the concept of Internet Service Provider (ISP) was also introduced. The main function of an ISP is to provide uninterrupted Internet connection to its customers at affordable rates. World Wide Web With commercialization of internet, more and more networks were developed in different part of the world. Each network used different protocols for communicating over the network. This prevented different networks from connecting together seamlessly. In the 1980s, Tim Berners-Lee led a group of Computer scientists at CERN, Switzerland, to create a seamless network of varied networks, called the World Wide Web (WWW). World Wide Web is a complex web of websites and web pages connected together through hypertexts. Hypertext is a word or group of words linking to another web page of the same or different website. When the hypertext is clicked, another web page opens. The evolution from ARPANET to WWW was possible due to many new achievements by researchers and computer scientists all over the world. Here are some of those developments − Year Milestone 1957 Advanced Research Project Agency formed by US 1969 ARPANET became functional 1970 ARPANET connected to BBNs 1972 Roy Tomlinson develops network messaging or E-mail. Symbol @ comes to mean “at” 1973 APRANET connected to Royal Radar Network of Norway 1974 Term Internet coined First commercial use of ARPANET, Telenet, is approved 1982 TCP/IP introduced as standard protocol on ARPANET 1983 Domain Name System introduced 1986 National Science Foundation brings connectivity to more people with its NSFNET program 1990 ARPANET decommissioned First web browser Nexus developed HTML developed 2002-2004 Web 2.0 is born Learning working make money

Communication Technologies – Web Services Let us discuss some terms commonly used with regard to the Internet. WWW WWW is the acronym for World Wide Web. WWW is an information space inhabited by interlinked documents and other media that can be accessed via the Internet. WWW was invented by British scientist Tim Berners-Lee in 1989 and developed the first web browser in 1990 to facilitate exchange of information through the use of interlinked hypertexts. A text that contains link to another piece of text is called hypertext. The web resources were identified by a unique name called URL to avoid confusion. World Wide Web has revolutionized the way we create, store and exchange information. Success of WWW can be attributed to these factors − User friendly Use of multimedia Interlinking of pages through hypertexts Interactive HTML HTML stands for Hypertext Markup Language. A language designed such that parts of text can be marked to specify its structure, layout and style in context of the whole page is called a markup language. Its primary function is defining, processing and presenting text. HTML is the standard language for creating web pages and web applications, and loading them in web browsers. Like WWW it was created by Time Berners-Lee to enable users to access pages from any page easily. When you send request for a page, the web server sends file in HTML form. This HTML file is interpreted by the web browser and displayed. XML XML stands for eXtensible Markup Language. It is a markup language designed to store and transport data in safe, secure and correct way. As the word extensible indicates, XML provides users with a tool to define their own language, especially to display documents on the Internet. Any XML document has two parts – structure and content. Let’s take an example to understand this. Suppose your school library wants to create a database of magazines it subscribes to. This is the CATALOG XML file that needs to be created. <CATALOG> <MAGAZINE> <TITLE>Magic Pot</TITLE> <PUBLISHER>MM Publications</PUBLISHER> <FREQUENCY>Weekly</FREQUENCY> <PRICE>15</PRICE> </MAGAZINE> <MAGAZINE> <TITLE>Competition Refresher</TITLE> <PUBLISHER>Bright Publications</PUBLISHER> <FREQUENCY>Monthly</FREQUENC> <PRICE>100</PRICE> </MAGAZINE> </CATALOG> Each magazine has title, publisher, frequency and price information stored about it. This is the structure of catalog. Values like Magic Pot, MM Publication, Monthly, Weekly, etc. are the content. This XML file has information about all the magazines available in the library. Remember that this file will not do anything on its own. But another piece of code can be easily written to extract, analyze and present data stored here. HTTP HTTP stands for Hypertext Transfer Protocol. It is the most fundamental protocol used for transferring text, graphics, image, video and other multimedia files on the World Wide Web. HTTP is an application layer protocol of the TCP/IP suite in client-server networking model and was outlined for the first time by Time Berners-Lee, father of World Wide Web. HTTP is a request-response protocol. Here is how it functions − Client submits request to HTTP. TCP connection is established with the server. After necessary processing server sends back status request as well as a message. The message may have the requested content or an error message. An HTTP request is called method. Some of the most popular methods are GET, PUT, POST, CONNECT, etc. Methods that have in-built security mechanisms are called safe methods while others are called unsafe. The version of HTTP that is completely secure is HTTPS where S stands for secure. Here all methods are secure. An example of use of HTTP protocol is − The user is requesting (by clicking on a link) the index page of video tutorials on the tutorialspoint.com website. Other parts of the request are discussed later in the chapter. Domain Names Domain name is a unique name given to a server to identify it on the World Wide Web. In the example request given earlier − tutorialspoint.com is the domain name. Domain name has multiple parts called labels separated by dots. Let us discuss the labels of this domain name. The right most label .com is called top level domain (TLD). Other examples of TLDs include .net, .org, .co, .au, etc. The label left to the TLD, i.e. tutorialspoint, is the second level domain. In the above image, .co label in .co.uk is second level domain and .uk is the TLD. www is simply a label used to create the subdomain of tutorialspoint.com. Another label could be ftp to create the subdomain ftp.tutorialspoint.com. This logical tree structure of domain names, starting from top level domain to lower level domain names is called domain name hierarchy. Root of the domain name hierarchy is nameless. The maximum length of complete domain name is 253 ASCII characters. URL URL stands for Uniform Resource Locator. URL refers to the location of a web resource on computer network and mechanism for retrieving it. Let us continue with the above example − This complete string is a URL. Let’s discuss its parts − index.htm is the resource (web page in this case) that needs to be retrieved www.tutorialspoint.com is the server on which this page is located videotutorials is the folder on server where the resource is located www.tutorialspoint.com/videotutorials is the complete pathname of the resource https is the protocol to be used to retrieve the resource URL is displayed in the address bar of the web browser. Websites Website is a set of web pages under a single domain name. Web page is a text document located on a server and connected to the World Wide Web through hypertexts. Using the image depicting domain name hierarchy, these are the websites that can be constructed − www.tutorialspoint.com ftp.tutorialspoint.com indianrail.gov.in cbse.nic.in Note that there is no protocol associated with websites 3 and 4 but they will still load, using their default protocol. Web Browsers Web browser is an application software for accessing, retrieving, presenting and traversing any resource identified by a URL on the World Wide Web. Most popular web browsers include − Chrome Internet Explorer Firefox Apple

Wireless Technologies Wireless connection to internet is very common these days. Often an external modem is connected to the Internet and other devices connect to it wirelessly. This eliminated the need for last mile or first mile wiring. There are two ways of connecting to the Internet wirelessly – Wi-Fi and WiMAx. Wi-Fi Wi-Fi is the acronym for wireless fidelity. Wi-Fi technology is used to achieve connection to the Internet without a direct cable between device and Internet Service Provider. Wi-Fi enabled device and wireless router are required for setting up a Wi-Fi connection. These are some characteristics of wireless Internet connection − Range of 100 yards Insecure connection Throughput of 10-12 Mbps If a PC or laptop does not have Wi-Fi capacity, it can be added using a Wi-Fi card. The physical area of the network which provides Internet access through Wi-Fi is called Wi-Fi hotspot. Hotspots can be set up at home, office or any public space like airport, railway stations, etc. Hotspots themselves are connected to the network through wires. WiMax To overcome the drawback of Wi-Fi connections, WiMax (Worldwide Interoperability for Microwave Access) was developed. WiMax is a collection of wireless communication standards based on IEEE 802.16. WiMax provides multiple physical layer and media access control (MAC) options. WiMax Forum, established in 2001, is the principal body responsible to ensure conformity and interoperability among various commercial vendors. These are some of the characteristics of WiMax − Broadband wireless access Range of 6 miles Multilevel encryption available Throughput of 72 Mbps The main components of a WiMax unit are − WiMax Base Station − It is a tower similar to mobile towers and connected to Internet through high speed wired connection. WiMax Subscriber Unit (SU) − It is a WiMax version of wireless modem. The only difference is that modem is connected to the Internet through cable connection whereas WiMax SU receives Internet connection wirelessly through microwaves. Learning working make money

Communication Technologies – Mobile Since the introduction of first commercial mobile phone in 1983 by Motorola, mobile technology has come a long way. Be it technology, protocols, services offered or speed, the changes in mobile telephony have been recorded as generation of mobile communication. Here we will discuss the basic features of these generations that differentiate it from the previous generations. 1G Technology 1G refers to the first generation of wireless mobile communication where analog signals were used to transmit data. It was introduced in the US in early 1980s and designed exclusively for voice communication. Some characteristics of 1G communication are − Speeds up to 2.4 kbps Poor voice quality Large phones with limited battery life No data security 2G Technology 2G refers to the second generation of mobile telephony which used digital signals for the first time. It was launched in Finland in 1991 and used GSM technology. Some prominent characteristics of 2G communication are − Data speeds up to 64 kbps Text and multimedia messaging possible Better quality than 1G When GPRS technology was introduced, it enabled web browsing, e-mail services and fast upload/download speeds. 2G with GPRS is also referred as 2.5G, a step short of next mobile generation. 3G Technology Third generation (3G) of mobile telephony began with the start of the new millennium and offered major advancement over previous generations. Some of the characteristics of this generation are − Data speeds of 144 kbps to 2 Mbps High speed web browsing Running web based applications like video conferencing, multimedia e-mails, etc. Fast and easy transfer of audio and video files 3D gaming Every coin has two sides. Here are some downsides of 3G technology − Expensive mobile phones High infrastructure costs like licensing fees and mobile towers Trained personnel required for infrastructure set up The intermediate generation, 3.5G grouped together dissimilar mobile telephony and data technologies and paved way for the next generation of mobile communication. 4G Technology Keeping up the trend of a new mobile generation every decade, fourth generation (4G) of mobile communication was introduced in 2011. Its major characteristics are − Speeds of 100 Mbps to 1 Gbps Mobile web access High definition mobile TV Cloud computing IP telephony Learning working make money

Types of Networks Networks can be categorized depending on size, complexity, level of security, or geographical range. We will discuss some of the most popular topologies based on geographical spread. PAN PAN is the acronym for Personal Area Network. PAN is the interconnection between devices within the range of a person’s private space, typically within a range of 10 metres. If you have transferred images or songs from your laptop to mobile or from mobile to your friend’s mobile using Bluetooth, you have set up and used a personal area network. A person can connect her laptop, smart phone, personal digital assistant and portable printer in a network at home. This network could be fully Wi-Fi or a combination of wired and wireless. LAN LAN or Local Area Network is a wired network spread over a single site like an office, building or manufacturing unit. LAN is set up to when team members need to share software and hardware resources with each other but not with the outside world. Typical software resources include official documents, user manuals, employee handbook, etc. Hardware resources that can be easily shared over the network include printer, fax machines, modems, memory space, etc. This decreases infrastructure costs for the organization drastically. A LAN may be set up using wired or wireless connections. A LAN that is completely wireless is called Wireless LAN or WLAN. MAN MAN is the acronym for Metropolitan Area Network. It is a network spread over a city, college campus or a small region. MAN is larger than a LAN and typically spread over several kilometres. Objective of MAN is to share hardware and software resources, thereby decreasing infrastructure costs. MAN can be built by connecting several LANs. The most common example of MAN is cable TV network. WAN WAN or Wide Area Network is spread over a country or many countries. WAN is typically a network of many LANs, MANs and WANs. Network is set up using wired or wireless connections, depending on availability and reliability. The most common example of WAN is the Internet. Learning working make money

Network Security Computer networks are an integral part of our personal and professional lives because we carry out lots of day-to-day activities through the Internet or local organizational network. The downside of this is that huge amount of data, from official documents to personal details, gets shared over the network. So it becomes necessary to ensure that the data is not accessed by unauthorized people. Practices adopted to monitor and prevent unauthorized access and misuse of network resources and data on them is called network security. A network has two components – hardware and software. Both these components have their own vulnerability to threats. Threat is a possible risk that might exploit a network weakness to breach security and cause harm. Examples of hardware threats include − Improper installation Use of unsecure components Electromagnetic interference from external sources Extreme weather conditions Lack of disaster planning Hardware threats form only 10% of network security threats worldwide because the components need to be accessed physically. 90% threats are through software vulnerabilities. Here we discuss the major types of software security threats. Virus A virus is a malicious program or malware that attaches itself to a host and makes multiple copies of itself (like a real virus!), slowing down, corrupting or destroying the system. Some harmful activities that can be undertaken by a virus are − Taking up memory space Accessing private information like credit card details Flashing unwanted messages on user screen Corrupting data Spamming e-mail contacts Viruses mostly attack Windows systems. Till a few years ago, Mac systems were deemed immune from viruses, however now a handful of viruses for them exist as well. Viruses spread through e-mails and need a host program to function. Whenever a new program runs on the infected system, the virus attaches itself to that program. If you are an expert who tinkers with the OS files, they can get infected too. Trojan Horse Trojan horse is a malware that hides itself within another program like games or documents and harms the system. As it is masked within another program that appears harmless, the user is not aware of the threat. It functions in a way similar to viruses in that it needs a host program to attach itself and harms systems in the same ways. Trojan horses spread through emails and exchange of data through hard drives or pen drives. Even worms could spread Trojan horses. Worms Worms are autonomous programs sent by the attacker to infect a system by replicating itself. They usually infect multitasking systems that are connected to a network. Some of the harmful activities undertaken by worms include − Accessing and relaying back passwords stored on the system Interrupt OS functioning Disrupt services provided by the system Install viruses or Trojan horses Spams Electronic junk mail, unsolicited mail or junk newsroom postings are called spam. Sending multiple unsolicited mails simultaneously is called spamming. Spamming is usually done as part of marketing tactics to announce a product or share political or social views with a wide base of people. The first spam mail was sent by Gary Thuerk on ARPANET in 1978 to announce launch of new model of Digital Equipment Corporation computers. It was sent to 393 recipients and together with lots of hue and cry it generated sales for the company as well. Almost all mail servers give you the option of stopping spams by marking a received mail as junk. You should take care to share your email ID only with trusted people or websites, who will not sell them to spammers. Learning working make money