LECTURE 1 (1).pdf

 Unit - 1 ▪ For example, the manufacturers of Apple's iPhone OS, Google's Android' Microsoft Windows Mobile, Research In Motion's Blackberry OS. Attribute of Mobility U...

 Unit - 1 ▪ For example, the manufacturers of Apple's iPhone OS, Google's Android' Microsoft Windows Mobile, Research In Motion's Blackberry OS. Attribute of Mobility User Mobility o User should be able to move from one physical location to another location and use the same service. o Example: User moves from London to New York and uses the Internet in either place to access the corporate application. Network Mobility o User should be able to move from one network to another network and use the same service. o Example: User moves from Hong Kong to Singapore and uses the same GSM phone to access the corporate application. Bearer Mobility o User should be able to move from one bearer to another while using the same service. o Example: User is unable to access the WAP bearer due to some problem in the GSM network then he should be able to use voice or SMS bearer to access that same corporate application. o Like Hike Messenger Device Mobility o User should be able to move from one device to another and use the same service. o Example: User is using a PC to do his work. During the day, while he is on the street he would like to use his mobile to access the corporate application. Session Mobility o A user session should be able to move from one user - agent environment to another. o Example: An unfinished session moving from a mobile device to a desktop computer is a good example. Service Mobility o User should be able to move from one service to another. o Example: User is writing a mail. Suddenly, he needs to refer to something else. In a PC, user simply opens another service and moves between them. User should be able to do the same in small wireless devices. Host Mobility o User should be able to move while the device is a host computer. o Example: The laptop computer of a user is a host for grid computing network. It is connected to a LAN port. Suddenly, the user realizes that he needs to leave for an offsite meeting. He disconnects from the LAN and should get connected to wireless LAN while his laptop being the host for grid computing network. 2 Poul Isaac De Chavez ([email protected])  Unit - 1 Limitation of Mobile Computing Limitations of the wireless network o Heterogeneity of fragmented networks o Frequent disconnections o Limited communication bandwidth Limitations imposed by mobility o Lack of mobility awareness by system / applications o Route breakages Limitations of the mobile computer o Short battery lifetime o Limited capacities (memory, processing speed, etc.) Introduction of Wireless Communication Wireless Communication involves the transmission of information over a distance without the help of wires, cables or any other forms of electrical conductors. It is a term that connecting and communicating between two or more devices using a wireless signal through wireless communication technologies and devices. Figure 2: Wireless Communication The transmitted distance can be anywhere between a few meters (for example: a television's remote control) and thousands of kilometers (for example: radio communication). Wireless communication can be used for cellular telephony, wireless access to the internet, wireless home networking, and so on. Applications of Wireless Communication 1. GPS Units 2. Wireless keyboard-mouse 3 Poul Isaac De Chavez ([email protected])  Unit - 1 3. Headsets 4. Radio Receivers 5. Satellite Television 6. Broadcast Television 7. Cordless Telephones etc… Signals - Basics A signal is an electrical or electromagnetic current that is used for carrying data from one device or network to another. It is the key component behind virtually all: o Communication o Computing o Networking o Electronic devices A signal can be either analog or digital. Here, we are concerned with electromagnetic signals used as a means to transmit information. An electromagnetic signal is a function of time, but it can also be expressed as a function of frequency; that is, the signal consists of components of different frequencies. o Time Domain o Frequency Domain The frequency domain view of a signal is far more important to an understanding of data transmission than a time domain view. As a function of time, an electromagnetic signal can be either analog or digital. An analog signal is one in which the signal intensity varies in a smooth fashion over time. In other words, there are no breaks or discontinuities in the signal. A digital signal is one in which the signal intensity maintains a constant level for some period of time and then changes to another constant level. Figure 3: Analog and Digital Waveforms 4 Poul Isaac De Chavez ([email protected])  Unit - 1 Figure shows examples of both kinds of signals. The analog signal might represent speech, and the digital signal might represent binary 1s and 0s. Periodic signal: An analog or digital signal pattern that repeats over time. Aperiodic signal: An analog or digital signal pattern that doesn't repeat over time. Figure 4: Periodic and Aperiodic Signal Peak amplitude (A): Maximum value or strength of the signal over time. Typically measured in volts. Frequency (f): Rate, in cycles per second, or Hertz (Hz), at which the signal repeats. Phase (): A measurement of the relative position in time within a single period of a signal. Wavelength (): A distance occupied by a single cycle of the signal. o Example: Speed of light is v = 3x108 m/s. Wavelength is f = v (or  = vT) Figure 5: Different terms of waveform Analog and Digital Data Transmission The terms analog and digital correspond, roughly, to continuous and discrete, respectively. These two terms are used frequently in data communications in at least three contexts: o Data 5 Poul Isaac De Chavez ([email protected])  Unit - 1 o Signals o Transmission We define data as entities that convey meaning, or information. Signals are electric or electromagnetic representations of data. Transmission is the communication of data by the propagation and processing of signals. Analog data take on continuous values in some interval. o For example, voice and video are continuously varying patterns of intensity. o Most data collected by sensors, such as temperature and pressure, are continuous valued. Digital data take on discrete values. o Examples are text and integers. Figure 6: Analog and Digital Data An analog signal is a continuously varying electromagnetic wave that may be propagated over a variety of media, depending on frequency. o Examples are copper wire media, such as twisted pair and coaxial cable; fiber optic cable; and atmosphere or space propagation (wireless). Figure 7: Analog and Digital Signaling of Analog and Digital Data 6 Poul Isaac De Chavez ([email protected])  Unit - 1 Guided media, which are those that provide a channel from one device to another, include twisted-pair cable, coaxial cable, and fiber-optic cable. A signal travelling along any of these media is directed and contained by the physical limit of the medium. A. Magnetic Media One of the most common ways to transport data from one computer to another is to write them onto magnetic tape or removable media (e.g., recordable DVDs), physically transport the tape or disks to the destination machine, and read them back in again. Although this method is not as sophisticated as using a geosynchronous communication satellite, it is often more cost effective, especially for applications in which high bandwidth or cost per bit transported is the key factor. B. Twisted Pair A twisted pair consists of two insulated copper wires, typically about 1 mm thick. The wires are twisted together in a helical form, just like a DNA molecule. Twisting is done because two parallel wires constitute a fine antenna. When the wires are twisted, the waves from different twists cancel out, so the wire radiates less effectively. Figure 11: Twisted Pair Cable Why cable is twisted? If the two wires are parallel, the effect of these unwanted signals is not the same in both wires because they are at different locations relatives to the noise or crosstalk sources. This results in a difference at the receiver. By twisting the pair, a balance is maintained. Types of Twisted-Pair Cable 1) Unshielded twisted-pair (UTP) Twisted pair cabling comes in several varieties, two of which are important for computer networks. Category 3 twisted pairs consist of two insulated wires gently twisted together. Category 5 is the more advanced twisted pairs were introduced. They are similar to category 3 pairs, but with more twists per centimeter, which results in less crosstalk and a better-quality signal over longer distances, making them more suitable for high-speed computer communication. 10 Poul Isaac De Chavez ([email protected])  Unit - 1 Latest categories are 6 and 7, which are capable of handling signals with bandwidths of 250 MHz and 600 MHz, respectively (versus a mere 16 MHz and 100 MHz for categories 3 and 5, respectively). Figure 12: Unshielded twisted-pair 2) Shielded twisted-pair (STP). STP cable has a metal foil or braided mesh covering that encases each pair of insulated conductors. Metal casing improves the quality of cable by preventing the penetration of noise or crosstalk. It is bulkier and more expensive. Applications: o Used in telephone lines to provide voice and data channels. o The DSL lines uses by telephone companies use the high-bandwidth capability of UTP cables. o LANs, such as 10Base-T, 100Base-T, also uses twisted-pair cables. Figure 13: UTP and STP Cable C. Coaxial Cable It has better shielding than twisted pairs, so it can span longer distances at higher speeds. Two kinds of coaxial cable are widely used. One kind, 50-ohm cable, is commonly used when it is intended for digital transmission from the start. The other kind, 75-ohm cable, is commonly used for analog transmission and cable television but is becoming more important with the advent of Internet over cable. A coaxial cable consists of a stiff copper wire as the core, surrounded by an insulating material. The insulator is encased by a cylindrical conductor, often as a closely-woven braided mesh. The outer conductor is covered in a protective plastic sheath. The construction and shielding of the coaxial cable give it a good combination of high bandwidth and excellent noise immunity. 11 Poul Isaac De Chavez ([email protected])  Unit - 1 The bandwidth possible depends on the cable quality, length, and signal-to-noise ratio of the data signal. Modern cables have a bandwidth of close to 1 GHz. Coaxial cables used to be widely used within the telephone system for long-distance lines but have now largely been replaced by fiber optics on long-haul routes. Figure 14: Coaxial Cable D. Fiber Optics A fiber-optic cable is made of glass or plastic and transmits signals in the form of light. Optical fibers use reflection to guide light through a channel. A glass or plastic core is surrounded by a cladding of less dense glass or plastic. The difference in density of the two materials must be such that a beam of light moving through a core is reflected off the cladding instead of being refracted into it. Figure 15: Fiber Optic Cable Fiber optic cables are similar to coax, except without the braid. Figure shows a single fiber viewed from the side. At the center is the glass core through which the light propagates. The core is surrounded by a glass cladding with a lower index of refraction than the core, to keep all the light in the core. Next comes a thin plastic jacket to protect the cladding. Fibers are typically grouped in bundles, protected by an outer sheath. Figure shows a sheath with three fibers. Unguided (Wireless) transmission media A. Radio Transmission C. Infrared B. Microwave Transmission D. Light wave Transmission 12 Poul Isaac De Chavez ([email protected])  Unit - 1 Unguided media transport electromagnetic waves without using a physical conductor. This type of communication is often referred to as wireless communication. A. Radio Transmission Radio waves are easy to generate, can travel long distances, and can penetrate buildings easily, so they are widely used for communication, both indoors and outdoors. Radio waves also are omnidirectional, meaning that they travel in all directions from the source, so the transmitter and receiver do not have to be carefully aligned physically. The properties of radio waves are frequency dependent. At low frequencies, radio waves pass through obstacles well, but the power falls off sharply with distance from the source, roughly as 1/r2 in air. At high frequencies, radio waves tend to travel in straight lines and bounce off obstacles. They are also absorbed by rain. At all frequencies, radio waves are subject to interference from motors and other electrical equipment. In the VLF, LF, and MF bands, radio waves follow the curvature of the earth. In the HF they bounce off the ionosphere B. Microwave Transmission Since the microwaves travel in a straight line, if the towers are too far apart, the earth will get in the way.Consequently, repeaters are needed periodically. Unlike radio waves at lower frequencies, microwaves do not pass through buildings well. In addition, even though the beam may be well focused at the transmitter, there is still some divergence in space. Above 100 MHz, the waves travel in straight lines and can therefore be narrowly focused. Concentrating all the energy into a small beam using a parabolic antenna gives a much higher signal to noise ratio. Advantages: o No right way is needed (compared to wired media). o Relatively inexpensive. o Simple to install. Disadvantages: o Do not pass through buildings well. o Multipath fading problem (the delayed waves cancel the signal). o Absorption by rain above 8 GHz. o Severe shortage of spectrum. C. Infrared 13 Poul Isaac De Chavez ([email protected])  Unit - 1 Unguided infrared and millimeter waves are widely used for short-range communication. The remote controls used on televisions, VCRs, and stereos all use infrared communication. They are relatively directional, cheap, and easy to build but have a major drawback: they do not pass through solid objects (try standing between your remote control and your television and see if it still works). In general, as we go from long-wave radio toward visible light, the waves behave more and more like light and less and less like radio. On the other hand, the fact that infrared waves do not pass through solid walls well is also a plus. It means that an infrared system in one room of a building will not interfere with a similar system in adjacent rooms or buildings. Furthermore, security of infrared systems against eavesdropping is better than that of radio systems precisely for this reason. Therefore, no government license is needed to operate an infrared system, in contrast to radio systems, which must be licensed outside the ISM bands. Communication Network Communication networks can be categories by their size as well as their purpose. The size of a network can be expressed by the geographic area. Some of the different networks based on size are: o LAN – Local Area Network o MAN – Metropolitan Area Network o WAN – Wide Area Network LAN (Local Area Network) It is privately-owned networks within a single building or campus of up to a few kilometers in size. They are widely used to connect personal computers and workstations in company offices and factories to share resources (e.g., printers) and exchange information. LANs are easy to design and troubleshoot In LAN, all the machines are connected to a single cable. Different types of topologies such as Bus, Ring, Star, and Tree are used. The data rates for LAN range from 4 to 16 Mbps. They transfer data at high speeds (higher bandwidth). They exist in a limited geographical area. Connectivity and resources, especially the transmission media, usually are managed by the company which running the LAN. 14 Poul Isaac De Chavez ([email protected])  Unit - 1 Figure 16: Local Area Network MAN (Metropolitan Area Network) A metropolitan area network, or MAN, covers a city. The best-known example of a MAN is the cable television network available in many cities. A MAN is basically a bigger version of a LAN and normally uses similar technology. At first, the companies began jumping into the business, getting contracts from city governments to wire up an entire city. The next step was television programming and even entire channels designed for cable only. Often these channels were highly specialized, such as all news, all sports, all cooking, and so on. Figure 17: Metropolitan Area Network WAN (Wide Area Network) WAN, spans a large geographical area, often a country or continent. It contains a collection of machines intended for running user (i.e., application) programs. We will follow traditional usage and call these machines hosts. 15 Poul Isaac De Chavez ([email protected])  Unit - 1 The hosts are connected by a communication subnet, or just subnet for short. In most wide area networks, the subnet consists of two distinct components: transmission lines and switching elements. Transmission lines move bits between machines. The communication between different users of WAN is established using leased telephone lines or satellite links and similar channels. Figure 18: Wide Area Network What Is the Internet? The Internet is a computer network that interconnects hundreds of millions of computing devices throughout the world. When two computers are connected over the Internet, they can send and receive all kinds of information such as text, graphics, voice, video, and computer programs. 16 Poul Isaac De Chavez ([email protected])  Unit - 1 Figure 19: Some pieces of the Internet Switching Techniques For transmission of data beyond a local area, communication is typically achieved by transmitting data from source to destination through a network of intermediate switching nodes; this switched network design is sometimes used to implement LANs and MANs as well. Switching Techniques - In large networks there might be multiple paths linking sender and receiver. Information may be switched as it travels through various communication channels. Circuit Switching Circuit switching is used in public telephone networks and is the basis for private networks built on leased-lines. 17 Poul Isaac De Chavez ([email protected])  Unit - 1 o Store and forward mechanism Each packet contains some portion of the user data plus control info needed for proper functioning of the network. A key element of packet-switching networks is whether the internal operation is datagram or virtual circuit (VC). o With internal VCs, a route is defined between two endpoints and all packets for that VC follow the same route. o With internal diagrams, each packet is treated independently, and packets intended for the same destination may follow different routes. Examples of packet switching networks are X.25, Frame Relay, ATM and IP. Figure 21: Packet Switching 19 Poul Isaac De Chavez ([email protected])  Unit - 1 Station breaks long message into packets. Packets sent one at a time to the network. Packets handled in two ways: 1. Datagram ▪ Each packet treated independently ▪ Packets can take any practical route ▪ Packets may arrive out of order ▪ Packets may go missing ▪ Up to receiver to re-order packets and recover from missing packets 2. Virtual Circuit ▪ Preplanned route established before any packets sent. ▪ Once route is established, all the packets between the two communicating parties follow the same route through the network ▪ Call request and call accept packets establish connection (handshake) ▪ Each packet contains a Virtual Circuit Identifier (VCI) instead of destination address ▪ No routing decisions required for each packet ▪ Clear request to drop circuit ▪ Not a dedicated path What is Protocol? A protocol defines rules and conventions for communication between network devices. A protocol defines the format and the order of messages exchanged between two or more communicating entities, as well as the actions taken on the transmission and/or receipt of a message or other event. The key features of protocol are as follows: Syntax: Concerns the format of the data blocks Semantics: Includes control information for coordination and error handling Timing: Includes speed matching and sequencing Example: HTTP, IP, FTP etc… 20 Poul Isaac De Chavez ([email protected])  Unit - 1 Figure 22: A human protocol and a computer network protocol It defines those computers of the network used at the edge of the network. These computers are known as hosts or end system. Host can be classified into the following two types: o Clients: Refer to the computer systems that request servers for the completion of a task. The clients are generally called desktop PCs or workstations. o Servers: Refer to the computer systems that receive requests from the clients and process them. After the processing is complete, the servers send a reply to the clients who sent the request. The concept of clients and servers is essential in the network design. The various networks design models are as follows: Peer to Peer network A group of computers is connected together so that users can share resources and information. There is no central location for authenticating users, storing files, or accessing resources. This means that users must remember which computers in the workgroup have the shared resource or information that they want to access. Advantage: o It is easy to setup. o There is no need of any committed server as each peer acts as both server and client. o The network implementation is quite cheap. o The resources of a peer can be shared with other peers very easily in the network. 21 Poul Isaac De Chavez ([email protected])  Unit - 1 Figure 23: Network Edge - Peer to Peer and Client/Server Network Disadvantage: o The speed of the network decreases due to heavy usage. o It is not easy to keep track of information on each computer. o There is on central backup of files and folders. o Network and data security are weak. Client/Server network A client/server network is a system where one or more computers called clients connect to a central computer named a server to share or use resources. The client requests a service from server, which may include running an application, querying database, printing a document, or performing a backup or recovery procedure. The request made by the client is held by server. A client/server network is that the files and resources are centralized. This means that a computer, the server, can hold them and other computers can access them. Advantage: o The server system holds the shared files. o The server system can be scheduled to take the file backups automatically. o Network access is provided only to authorize users through user security at the server. o The server system is a kind of central repository for sharing printer with clients. o Internet access, e-mail routing, and such other networking tasks are quite easily managed by the server. o The software applications shared by the server are accessible to the clients. Disadvantage: o The implementation of the network is quite expensive. o A network operating system is essential. o If server fails, the entire network crashes. 22 Poul Isaac De Chavez ([email protected])  Unit - 1 Protocols layers and their service model OSI Layer Architecture OSI model is based on a proposal developed by the International Standards Organization (ISO) as a first step toward international standardization of the protocols used in the various layers. It was revised in 1995. The model is called the ISO OSI (Open Systems Interconnection) Reference Model because it deals with connecting open systems—that is, systems that are open for communication with other systems. The OSI model has seven layers. 1. Physical Layer 2. Data Link Layer 3. Network Layer 4. Transport Layer 5. Session Layer 6. Presentation Layer 7. Application Layer Physical Layer The physical layer coordinates the function required to carry a bit stream over a physical medium. It deals with the mechanical and electrical specifications of the interface and transmission medium. It also defines the procedures and functions that physical devices and interfaces have to perform for transmission to occur. The physical layer is concerned with the following: o Physical characteristics of interface and medium o Representation of bits o Data rate o Synchronization of bits o Line configuration o Physical topology o Transmission mode 23 Poul Isaac De Chavez ([email protected])  Unit - 1 Figure 24: OSI Reference Model Data Link Layer The data link layer transforms the physical layer, a raw transmission facility, to a reliable link. It makes the physical layer appear error-free to the upper layer. The data link layer is concerned with the following: o Framing o Physical addressing o Flow control o Error control o Access control Network Layer The network layer is responsible for the source-to-destination delivery of a packet, possibly across multiple networks. The network layer is concerned with the following: o Logical addressing o Routing 24 Poul Isaac De Chavez ([email protected])  Unit - 1 Transport Layer The transport layer is responsible for process-to-process delivery of the entire message. A process is an application program running on a host. The transport layer ensures that the whole message arrives intact and in order, overseeing both error control and flow control at the source-to-destination level. The transport layer is concerned with the following: o Service-point addressing o Segmentation and reassembly o Connection control o Flow control o Error control Session Layer The session layer is the network dialog controller. It establishes, maintains, and synchronizes the interaction among communicating systems. The session layer is concerned with the following: o Dialog control o Synchronization Presentation Layer The presentation layer is concerned with the syntax (language rule) and semantics (meaning of each rule) of the information exchanged between two systems. The presentation layer is concerned with the following: o Translation o Encryption o Compression Application Layer The application layer enables the user, whether human or software, to access the network. It provides user interfaces and support for services such as electronic mail, remote file access and transfer, shared database management, and other types of distributed information services. The application layer is concerned with the following: Network virtual terminal o File transfer, access, and management o Mail services o Directory services TCP/IP Reference Model Transmission Control Protocol/Internet Protocol (TCP/IP) protocol suite is the engine for the Internet and networks worldwide. TCP/IP either combines several OSI layers into a single layer, or does not use certain layers at all. TCP/IP is a set of protocols developed to allow cooperating computers to share resources across the network. The TCP/IP model has five layers. 25 Poul Isaac De Chavez ([email protected])  Unit - 1 1. Application Layer 2. Transport Layer 3. Internet Layer 4. Data Link Layer 5. Physical Network Figure 25: TCP/IP Reference Model Application Layer The application layer is provided by the program that uses TCP/IP for communication. An application is a user process cooperating with another process usually on a different host (there is also a benefit to application communication within a single host). Examples: Telnet and the File Transfer Protocol (FTP) etc… Transport Layer The transport layer provides the end-to-end data transfer by delivering data from an application to its remote peer. Multiple applications can be supported simultaneously. The most-used transport layer protocol is the Transmission Control Protocol (TCP), which provides: o Connection-oriented reliable data delivery o Duplicate data suppression o Congestion control o Flow control. Another transport layer protocol is the User Datagram Protocol (UDP), which provides: o Connectionless o Unreliable 26 Poul Isaac De Chavez ([email protected])  Unit - 1 o Best-effort service. UDP is used by applications that need a fast transport mechanism and can tolerate the loss of some data. Internetwork Layer The internetwork layer also called the internet layer or the network layer. It is provides the “virtual network” image of an internet this layer shields the higher levels from the physical network architecture below it. Internet Protocol (IP) is the most important protocol in this layer. It is a connectionless protocol that does not assume reliability from lower layers. IP does not provide reliability, flow control, or error recovery. IP provides a routing function that attempts to deliver transmitted messages to their destination. These message units in an IP network are called an IP datagram. Example: IP, ICMP, IGMP, ARP, and RARP. Network Interface Layer The network interface layer, also called the link layer or the data-link layer or Host to Network Layer. It is the interface to the actual network hardware. This interface may or may not provide reliable delivery, and may be packet or stream oriented. Example: IEEE 802.2, X.25,ATM, FDDI Physical Network Layer The physical network layer specifies the characteristics of the hardware to be used for the network. For example, it specifies: o The physical characteristics of the communications media o Standards such as IEEE 802.3 o The specification for Ethernet network media, and RS-232 o The specification for standard pin connectors. Internetworking An interconnected set of networks may appear simply as a larger network. This entire configuration is often referred to as an internet. Internetworking Terms Communication Network: o A facility that provides a data transfer service among devices attached to the network. Internet: 27 Poul Isaac De Chavez ([email protected])  Unit - 1 o A collection of communication networks interconnected by bridge and /or routers. Intranet: o An internet used by single organization that provides the key Internet application, especially the World Wide Web. o An intranet operates within the organization for internal purpose and can exist as an isolated, self-contained internet, or may have links to the internet. End Systems: o A device attached to one of the networks of an internet that is used to support end-user application or services. Intermediate System: o A device used to connect two networks and permit communication between end systems attached to different networks. Bridge: o A bridge is a type of computer network device that provides interconnection with other bridge networks that use the same protocol. o Bridge devices work at the data link layer of the Open System Interconnect (OSI) model, connecting two different networks together and providing communication between them. o Bridges are similar to repeaters and hubs in that they broadcast data to every node. o However, bridges maintain the media access control (MAC) address table as soon as they discover new segments, so subsequent transmissions are sent to only to the desired recipient. o Bridges are also known as Layer 2 switches. Router: o A router is a device that analyzes the contents of data packets transmitted within a network or to another network. o Routers determine whether the source and destination are on the same network or whether data must be transferred from one network type to another, which requires encapsulating the data packet with routing protocol header information. o Router operates at layer 3 of the OSI model. 28 Poul Isaac De Chavez ([email protected])