Data Communication and Computer Networks PDF

Data communication and computer networks (CoSc2032) Chapter One Part II Introduction to Computer Networks  Main topics  Types of Computer Networks  Transmission Medias  Network Topology  Network Protocol...

Data communication and computer networks (CoSc2032) Chapter One Part II Introduction to Computer Networks  Main topics  Types of Computer Networks  Transmission Medias  Network Topology  Network Protocol Stacks  Introduction to Computer Networks  The term network means two or more connected computers (other communication devices) that can share resources like data, applications, office machines, an Internet connection, or some combination of these. OR  Computer network to mean a collection of autonomous computers interconnected by a single technology.  connecting together of computers and other devices is called a network, and the concept of connected computers sharing resources is called networking.  The connection be via a copper wire, fiber optics, microwaves, infrared, Wi-Fi and communication satellites can also be used.  Networks come in many sizes (small, medium or large), shapes (physical  Introduction to Computer Net cont’d…  Two computers are said to be interconnected if they are able to exchange information. Media:  Cable  Components of a compute networks.  Wire  Microwave … Hardware:  Computer Software: Network Design:  Network card  Network OS Logical layout  Routers  Utilities … Physical layout …  Modem …  Uses of Computer Networks  Contd. 1. Resource sharing 2. Means of communication  The goal of network is to make all programs, equipment, and especially data available to anyone on the network without regard to the physical location of the – E-mail resource and the user. – Videoconferencing  An obvious and widespread example is having a group of office workers share a – Chatting common printer. – E-commerce  None of the individuals really needs a private printer, and a high-volume – Game networked printer is often cheaper, faster, and easier to maintain than a large – …. collection of individual printers. 3. Centralizing administration  Information sharing is more important than physical resource sharing and support – Database  To undertake parallel processing – Banks  To share databases – ….  Applications of Computer Networks  Business application  Wireless network  Home application  Sensor network  Wearable Internet access computers Entertainment  Science and Ubiquitous computing Research  Transportation Radio Frequency  Weather forecasting Identification (RFID) and others.  Introduction to computer Net cont’d… Social Issues  Computer networks allow ordinary citizens to distribute and view content in ways that were not previously possible.  Social networks, message boards, content sharing sites, and a host of other applications allow people to share their views.  The trouble comes with topics that people actually care about, like politics, religion, or sex.  The other issue is copyright, to handle this some automated systems that search peer-to-peer networks and fire off warnings to network operators and users who are suspected of trespassing copyright.  Privacy also a big problem in this regard. For example, Google can read your email (at least the subject in order) and show you advertisements based on your interests (i.e. information domain) if you use its email service, Gmail. However, it is totally the violation of individuals as well as companies privacy right, stated under legal documents and constitutions.  Network Types There are basically four categories of networks based on its size and geographical coverage. 1. Personal Area network 2. Local Area Network (LAN) 3. Metropolitan Area Network (MAN) 4. Wide Area Network (WAN)  Introduction to Computer net cont….. Types of Computer Networks Personal Area Networks It is the smallest network of A personal area network (PAN) is a computer computers. network used for data transmission among Bluetooth or other infrared- enabled devices could be used to devices such as computers, telephones, connect devices. tablets and personal digital assistants. It has a 10-metre range of connectivity. It can cover up to 30 feet in diameter. PAN network enables a single person's personal devices to connect with each other.  Local area network (LAN)  A local area network (LAN) is the basic building block of any computer network.  A LAN can range from simple (two computers connected by a cable) to complex (hundreds of connected computers and peripherals throughout a major corporation).  The distinguishing feature of a LAN is that it is confined to a limited geographic area and the topology it used.  A local area network (LAN) is usually privately owned and links the devices in a single office, factory building, or campus.  LANs are widely used to connect personal computers, laptop, PDA, Smart phones and other consumer electronics to let them share resources and exchange information.  Currently, LAN size is limited to a few kilometers(1km-10kms).  Early LANs had data rates in the 4 to 16 megabits per second (Mbps) range. Today, however, speeds are normally 100 or 1000 Mbps Contd.  Metropolitan Area Network (MAN)  A metropolitan area network (MAN) is a network with a size between a LAN and a WAN.  It normally covers the area inside a town or a city.  It is designed for customers who need a high-speed connectivity, normally to the Internet, and have endpoints spread over a city or part of city.  A good example of a MAN is the part of the telephone company network that can provide a high-speed DSL line to the customer.  Another example is the cable TV network that originally was designed for cable TV, but today can also be used for high-speed data connection to the Internet.  Recently MAN develop in high-speed, which has been standardized as IEEE 802.16 and is popularly known as WiMAX (Worldwide Interoperability for Microwave MAN cont’d Metropolitan Area Network are local area network (LAN) interconnections. A Metropolitan Area Network can range in size from 5 to 50 km. Data rates range from moderate to high. It is scalability, cost efficiency and enhanced security than others.  Wide Area Network  A wide area network (WAN) provides long-distance transmission of data, image, audio, and video information over large geographic areas that may comprise a country, a continent, or even the whole world.  A WAN can be as complex as the backbones that connect the Internet or as simple as a dial-up line that connects a home computer to the Internet. We normally refer to the first as a switched WAN and to the second as a point- to-point WAN.  The switched WAN connects the end systems, which usually comprise a router (internetworking connecting device) that connects to another LAN or WAN.  The point-to-point WAN is normally a line leased from a telephone or cable TV provider that connects a home computer or a small LAN to an Internet service provider (lSP). This type of WAN is often used to provide Internet Wide Area Network… It covers large geographical area, and use of leased telecommunication lines. Difficult to Design and Maintains slower data transfer rates. High Bandwidth than others Network type based on connection A network is two or more devices connected through links. A link is a communications pathway that transfers data from one device to another. For visualization purposes, it is simplest to imagine any link as a line drawn between two points. For communication to occur, two devices must be connected in some way to the same link at the same time. There are two possible types of connections: point-to- point and multipoint.  Network type based on connection…. Point-to-Point network Point to Multipoint Network A point-to-point connection provides a dedicated A multipoint (also called multi drop) link between two devices. connection is one in which more than The entire capacity of the link is reserved for two specific devices share a single transmission between those two devices. link. In a multipoint environment, the Most point-to-point connections use an actual length of wire or cable to connect the two ends, capacity of the channel is shared, either but other options, such as microwave or satellite spatially or temporally. links, are also possible. If several devices can use the link When you change television channels by infrared simultaneously, it is a spatially shared remote control, you are establishing a point-to- connection. point connection between the remote control and If users must take turns, it is a the television's control system. timeshared connection.  Network Topology  The term topology refers to the way in which a network is laid out physically. Two or more devices connect to a link; two or more links form a topology.  The topology of a network is the geometric representation of the relationship of all the links and linking devices (usually called nodes) to one another.  Physical and logical topologies that are very different. – Physical topology refers to the way in which the endpoints, or stations, attached to the network are interconnected. – Logical topology refers the way of data transmission among communication device on the existing physical topology  There are five basic topologies possible: mesh, star, bus, ring and hybrid.  Bus Topology  Full-duplex operation between the station and the tap allows data to be transmitted onto the bus and received from the bus.  A bus topology, is multipoint connection.  One long cable acts as a backbone to link all the devices in a network  Bus topology uses CSMA/CD, a protocol that helps devices share the bandwidth evenly without having two devices transmit at the same time on the network medium.  CSMA/CD was created to overcome the problem of those collisions that occur when packets are transmitted simultaneously from different nodes.  Nodes are connected to the bus cable by drop lines and taps.  A drop line is a connection running between the device and the main cable.  A tap is a connector that either splices into the main cable or punctures the sheathing of a cable to create a contact with the metallic core.  Advantages and Disadvantages of Bus Topology Advantages of Bus topology  Ease of installation.  uses less cabling than mesh or star topologies  Each drop line has to reach only as far as the nearest point on the backbone. Disadvantages of Bus topology  difficult reconnection and fault isolation. A bus is usually designed to be optimally efficient at installation.  It can therefore be difficult to add new devices.  In addition, a fault or break in the bus cable stops all transmission, even between devices on the same side of the problem.  Adding new devices may therefore require modification or replacement of the backbone.  Star Topology  In a star topology, each device has a dedicated point-to-point link only to a central controller, usually called a hub and it is full duplex.  The term dedicated means that the link carries traffic only between the two devices it connects.  The devices are not directly linked to one another.  Unlike a mesh topology, a star topology does not allow direct traffic between devices.  The controller acts as an exchange: If one device wants to send data to another, it sends the data to the controller, which then relays the data to the other connected device  There are two alternatives for the operation of the central node.  One approach is for the central node to operate in a broadcast fashion (using hub).  Another approach is for the central node to act as a frame-switching device. An incoming frame is buffered in the node and then retransmitted on an outgoing link to the destination station.  Advantest and Disadvantages of Star Advantages of Star topology  A star topology is less expensive than a mesh topology.  Easy to install and reconfigure.  Far less cabling needs to be housed,  Other advantages include robustness. If one link fails, only that link is affected. All other links remain active. Dis advantages of star Topology  Dependency of the whole topology on one single point, the hub. If the hub goes down, the whole system is dead.  Each node must be linked to central hub for this reason, often more cabling is required in a star than in some other topologies (such as ring or bus).  Ring Topology  In a ring topology, each device has a dedicated point-to-point connection with only the two devices on either side of it.  A signal is passed along the ring in one direction, from device to device, until it reaches its destination.  Computers are connected on a single circle of cable. Unlike the bus topology, there are no terminated ends.  Signals travel around the loop in one direction and pass through each computer  The method by which the data is transmitted around the ring is called token passing. A token is a special series of bits that contains control information.  Each computer acts as a repeater to boost the signal and send it to the next computer. Advantages and Disadvantages of Ring Advantages of Ring Topology  A ring is relatively easy to install and reconfigure. Each device is linked to only its immediate neighbors (either physically or logically).  To add or delete a device requires changing only two connections.  In addition, fault isolation is simplified. Disadvantages of Ring Topology In a simple ring, a break in the ring (such as a disabled station) can disable the entire network. This weakness can be solved by using a dual ring or a switch capable of closing off the break. Today, the need for higher-speed LANs has made this topology less popular.  Mesh topology In a mesh topology, every device has a dedicated point-to-point link to every other device. To find the number of physical links in a fully connected mesh network with n nodes, we first consider that each node must be connected to every other node. Node 1 must be connected to n - I nodes, node 2 must be connected to n – 1 nodes, and finally node n must be connected to n - 1 nodes. We need n(n - 1) physical links. However, if each physical link allows communication in both directions (duplex mode), we can divide the number of links by 2. In other words, we can say that in a mesh topology, we need n(n -1) /2 duplex-mode links. To accommodate that many links, every device on the network must have n – 1 input/output (I/O) ports to be connected to the other n - 1 stations. Advantages and Disadvantages of Mesh Topology Advantages  Eliminating the traffic problems that can occur when links must be shared by multiple devices.  mesh topology is robust. If one link becomes unusable, it does not incapacitate the entire system  Third, there is the advantage of privacy or security. When every message travels along a dedicated line, only the intended recipient sees it. Physical boundaries prevent other users from gaining access to messages. Disadvantages  The main disadvantages of a mesh are related to the amount of cabling and the number of I/O ports required.  First, because every device must be connected to every other device, installation and reconnection are difficult.  Second, the sheer bulk of the wiring can be greater than the available space (in walls, ceilings, or floors) can accommodate.  Finally, the hardware required to connect each link (I/O ports and cable) can be prohibitively expensive  Hybrid Topology  Hybrid topology is a combination of two or more types of physical or logical network topologies working together within the same network.  Selecting the Right Topology In the process of selecting appropriate network type you must first answer the following questions: How much cash do you have? How much fault tolerance do you really need? How scalable does your network need to be? How easy the installation and maintenance of a network?  Network Models by Capability 1. Peer to Peer (P2P)  Computers on the network communicate with each others as equals and each computer is responsible for making its own resources available to other computers on the network.  The computers existing in a peer-to-peer network can be client machines that access resources and server machines that provide them to other computers.  This works really well if there’s not a huge number of users on the network, each user handles backing things up locally, and your network doesn’t require a lot of security.  2. Client-server model  Two clients using a single server at a time  In instead of the request going directly to the machine with the desired resource, a client machine’s request for a resource goes to the main server, which responds by handling security and directing the client to the resource it wants.  Client/Server vs. Peer-to-Peer: Advantages and Disadvantages Client/Server Model Peer-to-Peer Model Advantages: Advantages:  Very secure OS.  Uses less expensive networks.  Better performance.  Easy to administer.  Centralized servers, easy to manage.  Contain both network operating system and  Centralized backups. application software.  High reliability.  Ideal for small business and home users (up to 10 computers). Disadvantages:  Disadvantages: Expensive administration.  Individual user performance easily affected.  More hardware intensive.  Not very secure.  Hard to back up. Connection Options 1. DSL((Digital Subscriber Line):Allow both voice and internet data can flow over the same telephone line at the same time. Has a modem which filters the voice and data. DSL represents a high-speed connection but, it is not as fast as cabling connection. 2.Cable Broadband Cable is typically provided by the same provider that provides cable television to its customers. you have experienced slow speed connection because your neighbors are also using the same cable line at the same time.  Transmission Medias  The transmission medium is the physical path between transmitter and receiver in a data transmission system.  Transmission media can be classified as guided or unguided.  In both cases, communication is in the form of electromagnetic waves.  With guided media, the waves are guided along a solid medium, such  GUIDED TRANSMSSION MEDIA  For guided transmission media, the transmission capacity, in terms of either data rate or bandwidth, depends critically on the distance and on whether the medium is point-to-point or multipoint, such as in a local area network (LAN).  Guided media, which are those that provide a conduit from one device to another, include twisted-pair cable, coaxial cable, and fiber-optic cable.  A signal traveling along any of these media is directed and contained by the physical limits of the medium.  Twisted-pair and coaxial cable use metallic (copper) conductors that accept and transport signals in the form of electric current.  Optical fiber is a cable that accepts and transports signals in the form of light. Guided Media cont’d….. Twisted Pair Cable Coaxial cable Fiber optics  Twisted-Pair Cable  A twisted pair consists of two conductors (normally copper), each with its own plastic insulation, twisted together, as shown in the figure below.  One of the wires is used to carry signals to the receiver, and the other is used only as a ground reference.  The twisting tends to decrease the crosstalk interference between adjacent pairs in a cable.  Ethernet operating over twisted-pair cabling is commonly used within a building for LANs supporting personal computers with the data rate of 100 Mbps to 10 Gbps.  Twisted pair may be used to transmit both analog (amplifiers in every 5 to 6 KM) and digital (repeaters in every 2 to 3 KM) transmission.  twisted pair cable is limited in distance, bandwidth, and data rate than others.  Signal attenuation of twisted pair is a very strong function of frequency compared to other cables.  Twisted-pair cabling is also susceptible to signal reflections, or return loss, caused by impedance mismatches along the length of the transmission line and crosstalk from adjacent twisted pairs or  Transmission Medias cont… Types of Twisted Pair Cable Twisted pair cables are mainly categorized into two, namely, Shielded (STP) and Unshielded (UTP) Twisted Pair cable. Shielded twisted pair cable has three forms. 1. Each pair of wires is individually shielded with metallic foil, generally referred to as foil twisted pair (FTP). 2. There is a foil or braid shield inside the jacket covering all wires (as a group). This configuration is sometimes designated as screened twisted pair (F/UTP). 3. There is a shield around each individual pair, as well as around the entire group of wires. This is referred to as fully shielded twisted pair or shielded/foil twisted pair (S/FTP). Transmission Medias cont….. Twisted Pair Cabling Twisted pair cables are terminated with RJ-45 connectors, is a common copper-based medium for interconnecting devices in the network. Different situations may require different UTP cabling with different wiring conventions. The following are main cable types that are obtained by using specific wiring conventions: – Ethernet Straight-through: in order to connect different kinds of networking devices like PC to Switch, Switch to router and others. – Ethernet Crossover: used to interconnect similar devices (i.e. PC to PC , Switch to Switch, Router to Router) – Rollover: used to interlink PC to other networking devices for configuration purpose only.  Transmission Medias cont….. Coaxial cable Coaxial cable consists of two conductors, it is constructed to permit it to operate over a wider range of frequencies. It consists of a hollow outer cylindrical conductor that surrounds a single inner wire conductor. The inner conductor is held in place by insulating rings. The outer conductor is covered with a jacket or shield. Coaxial cable can be used over longer distances and support more stations on a shared line than twisted pair.  Transmission Medias cont…. Coaxial Cable cont….. Because of its shielded, concentric construction, coaxial cable is much less susceptible to interference and crosstalk than twisted pair. The principal constraints on performance are attenuation, thermal noise, and intermodulation noise. 1. Thin net cable(10base2) : is a flexible coaxial cable about 0.64 centimeters (0.25 inches) thick. Carry a signal for 200 meters 2. Thick cable(10base5) :is a relatively rigid coaxial cable about 1.27 centimeters (0.5 inches) in diameter. carry a signal for 500 meters. Applications of Coaxial Cable – Television distribution – Long-distance telephone transmission – Short-run computer system links – Local area networks (in early age of LAN)  Transmission Medias cont…. Fiber Optics Fiber-optic cabling uses either glass or plastic fibers to guide light impulses from source to destination. The bits are encoded on the fiber as light impulses. Optical fiber cabling is capable of very large raw data bandwidth rates. An optical fiber strand (also called an optical waveguide) has a cylindrical shape and consists of three concentric sections: the core, the cladding, and the Jacket.  Unguided Media Where: MWA-Mobile Wireless Access FWA-Fixed Wireless Access NWA-Nomadic Wireless Access  Unguided Media cont… Types of Wireless Networks Standards for wireless data communications cover both the Data Link and Physical layers. Four common standards are: IEEE 802.11 - is a Wireless LAN (WLAN) technology that uses a Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) media access process. IEEE 802.15 - Wireless WPAN, commonly known as "Bluetooth", uses a device pairing process to communicate over distances from 1 to 100 meters. IEEE 802.16 - Commonly known as WiMAX (Worldwide Interoperability for Microwave Access), uses a point-to-multipoint topology to provide wireless broadband access. Global System for Mobile Communications (GSM) - Includes Physical layer specifications that enable the implementation of the Layer 2 General Packet Radio Service (GPRS) protocol to provide data transfer over mobile cellular telephony networks. Other wireless technologies such as satellite communications provide data network connectivity for locations without another means of connection. Unguided (Wireless) media cont…. Wireless media carry electromagnetic signals at radio and microwave frequencies that represent the binary digits of data communications. Wireless data communication technologies are good in open environments. However, buildings and structures, and the local terrain, will limit the effective coverage. In addition, wireless is susceptible to different kinds interference from home appliances. Each frequency band has its advantages and disadvantages. Popular mobile systems congregate toward lower frequencies, lower frequencies mean longer wavelengths that travel further, but it has a bandwidth limitation. In contrast, higher frequencies can provide sufficient bandwidth but their shorter wavelengths make for shorter traveling distances. Unguided signals can travel from the source to destination in several ways: ground propagation, sky propagation, and line-of-sight propagation.  Wireless Transmission Types Performance metrics Bandwidth Throughput Latency Capacity Radio wave 3KHz_1GHZ  ground +sky propagation Micro wave 1GZ-299 GHZ  Sky+ line of sight Infrared 300GHZ-400THZ  Line of sight  Network Protocol Stacks Protocol is an agreement between the communicating parties on how communication is to proceed. A protocol layer can be implemented in software, in hardware, or in a combination of the two. A set of layers and protocols is called a network architecture. The specification of an architecture must contain enough information to allow an implementer to write the program or build the hardware for each layer so that it will correctly obey the appropriate protocol. A list of the protocols used by a certain system, one protocol per layer, is called a protocol stack. The entities comprising the corresponding layers on different machines are called peers. The peers may be software processes, hardware devices, or even human beings. Contd.  Network Protocol Stack cont….. The Need for Layer Architecture We use layered architecture in networking for the following reasons: – It reduces design and implementation complexity of the software as well as the hardware. – It helps to easily replace one layer with a completely different protocol or implementation without affecting the upper or lower layers in the architecture. – Standards can be developed independently and simultaneously for each layer. Some researchers and networking engineers are strongly opposed to layering, because: – One layer may duplicate lower-layer functionality. – Functionality at one layer may need information that is present only in another layer; this violates the goal of separation of layers.  Network Protocol Stack cont…. Open System Interconnection (OSI)Reference Model It is considered as the primary architectural model for inter-computer communications. It ensures greater compatibility and interoperability between various types of network technologies. Divides the problem of moving information between computers over a network medium into SEVEN smaller and more manageable problems (modules). The model define how each layer communicates and works with the layers immediately above and below it. Each layer communicates with the same layer’s software or hardware on other computers (on the other node). The lower 4 layers are concerned with the flow of data from end to end through the network. The upper three layers of the OSI model are orientated more toward services to the applications. Data is Encapsulated with the necessary protocol information as it moves down the layers before network transit. Network Protocol Stack cont…..  Network Protocol Stack cont…… OSI Reference Model cont….. The principles that were applied to arrive at the seven layers: 1. A layer should be created where a different abstraction is needed. 2. Each layer should perform a well-defined function. 3. The function of each layer should be chosen with an eye toward defining internationally standardized protocols. 4. The layer boundaries should be chosen to minimize the information flow across the interfaces. 5. The number of layers should be large enough that distinct functions need not be thrown together in the same layer out of necessity and small enough that the architecture does not become unwieldy.  Network Protocol Stack cont….. TCP/IP (Internet) Reference Model OSI TCP/IP Internet Used in the grandparent of all wide area Protocol computer networks, the Advanced Research Projects Agency Network (ARPANet). Application Application Application Developed by Department of Defense (DoD) to Presentation ensure and preserve data integrity as well as Session maintain communication in the time of catastrophic war. Transport Transport Transport Condensed version of OSI model contains five Network Internet Internet layers instead of seven. It is independent of the Network access Data Link Link Link methods, Frame format, & Medium. Physical Physical Network Protocol Stack cont…… Protocols in TCP/IP Reference Model Network Protocol Stack cont….. Comparison of the OSI and TCP/IP Reference Models Three concepts (i.e. services, interfaces and protocols) are central to the OSI model. But the TCP/IP model did not originally clearly distinguish these concepts. The biggest contribution of the OSI model is that it makes the distinction between these three concepts explicit. Protocols in the OSI model are better hidden than in the TCP/IP model and can be replaced easily by new technology. The OSI reference model was devised before the corresponding protocols were invented. The downside of this ordering was that the designers did not have much experience with the subject and did not have a good idea of which functionality to put in which layer.  Comparison of the OSI and TCP/IP Reference Models …. With TCP/IP the reverse was true. There was no problem with the protocols fitting the model. The only trouble was that the model did not fit any other protocol stacks. Another difference is OSI supports both connectionless and connection oriented communication in the network layer, but only connection-oriented communication in the transport layer and TCP/IP supports only connectionless in the network layer but both in the transport layer.  Network Protocol Stack cont…… A Critique of the OSI Model and Protocols 1. Bad timing. 2. Bad technology. 3. Bad implementations. 4. Bad politics.  The choice of seven layers was more political than technical, and two of the layers (session and presentation) are nearly empty, whereas two other ones (data link and network) are overfull.  Network Protocol Stack cont….. A Critique of the TCP/IP Reference Model Not clearly distinguish the concepts of services, interfaces, and protocols. Not much of a guide for designing new networks using new technologies. It is not general and is poorly suited to describing any protocol stack other than TCP/IP. For example, Bluetooth is completely impossible. The link layer is not a layer but it is an interface (between the network and data link layers). The TCP/IP model does not distinguish between the physical and data link layers. These are completely different. The protocol implementations were then distributed free, which resulted in their becoming widely used, deeply entrenched, and thus hard to replace.  NEXT Chapter Two Data Link Layer