CS461 Data Communications and Computer Networks PDF

CS461 Data Comms & Networks Motivation Model Data Comms Data Communications and Computer Networks Basics Networks The Internet Examples CS461: Computer Networks HiLCoE School of Computer...

CS461 Data Comms & Networks Motivation Model Data Comms Data Communications and Computer Networks Basics Networks The Internet Examples CS461: Computer Networks HiLCoE School of Computer Science and Technology  CS461 Contents Data Comms & Networks Motivation Motivation Model Data Comms Networks A Communications Model The Internet Data Communications Networks The Internet Examples  CS461 What Is Data Communications? Data Comms & Networks IThe term “telecommunication” means communication Motivation at a distance. Model IWhen we communicate we are sharing information Data Comms I Local sharing, e.g. face-to-face Networks I Remote sharing, e.g. over some distance The Internet I Data: information being shared or information presented in whatever form is agreed upon by the parties creating and using the data, e.g. text, num- bers, images, audio, video I Data Communications: exchange of data between two (or more) devices via some transmission medium such as a wire cable.  CS461 Effective Data Communications Data Comms & Networks Delivery: the data must be delivered to the correct Motivation destination Model Accuracy: the data received must be accurate Data Comms Networks representation of the data sent The Internet Timeliness: the data should be delivered within a reasonable time  CS461 Contents Data Comms & Networks Motivation Motivation Model Data Comms Networks A Communications Model The Internet Data Communications Networks The Internet Examples  CS461 Simplified Communications Model Data Comms & Networks Motivation Model Data Comms Networks The Internet Source: Device that generates data to be transmitted Transmitter: Converts data from source into transmittable signals Transmission system: Carries data from source to destination Receiver: Converts received signal into data Destination: Takes and uses incoming data  CS461 Overview of Data Communications Data Comms & Networks A data communication system has 5 components Motivation Model Data Comms Networks The Internet Message: the information to be communicated (text, numbers, pictures, sound, video - or combinations) Sender: the device - computer, video camera,... Receiver: still the device Medium: the physical path by which a message travels from sender to receiver Protocol: the set of rules that govern data communi- cations; an agreement between the communicating de- vices  CS461 Simplified Communications Model Data Comms & Networks Motivation An Example Model Data Comms Networks The Internet  CS461 Communications Tasks Data Comms & Networks Simplified communications model makes it look easy... but Motivation there are many tasks to be performed in a data Model communications system Data Comms Networks The Internet  CS461 Communications Tasks Data Comms & Networks Transmission System Utilization Motivation - the need to make efficienct use of transmission facilities Model that are typically shared among a number of communicating Data Comms devices Networks - Multiplexing The Internet - Congestion Control techniques Signal generation - The properties of the signal capable of being propagated through the transmission system. Interpretable as data at the receiver Error Detection and Correction - In all communication systems, there is a potential for error that should be detected and corrected  CS461 Communications Tasks Data Comms & Networks Addressing and Routing Motivation - A source system must somehow indicate the identity of the Model intended destination Data Comms - a specific route must be chosen from many alternative Networks routes The Internet Flow control -required to assure that the source does not overwhelm the destination by sending data faster than they can be processed and absorbed Message formatting both sides must use the same binary code for characters Security authentication message integrity  CS461 Categorizing Communication Technologies Data Comms & Networks Data Communications: transmitting signals in reliable and Motivation efficient manner; focusses on individual links Model Networks: communications across set of links; Wide Area Data Comms Networks Networks, Local Are Networks, The Internet The Internet  CS461 Contents Data Comms & Networks Motivation Motivation Model Data Comms Networks A Communications Model The Internet Data Communications Networks The Internet Examples  CS461 A Data Communications Model Data Comms & Networks Motivation Model Data Comms Networks The Internet  CS461 Transmission Line Data Comms & Networks I Transmission line (or system) is key part of Motivation communications system Model I “Link” between transmitter and receiver Data Comms Networks I Needs to provide required capacity, with acceptable The Internet reliability at minimum cost  CS461 The Transmission of Information Data Comms & Networks Motivation Transmission and Transmission Media Model I How to convert information into transmittable Data Comms electromagnetic signal? Networks I What transmission media to use? The Internet Communication Techniques I How to encode information into a signal? I How to deal with errors? Transmission Efficiency I How to efficiently utilize/share communications system?  CS461 Contents Data Comms & Networks Motivation Motivation Model Data Comms Networks A Communications Model The Internet Data Communications Networks The Internet Examples  CS461 Networks Data Comms & Networks I Demand for any user to communicate with any other Motivation machine/user Model I Require: Data Comms I Communication software (see The Internet) Networks I Communication network technologies: WANs and LANs The Internet  CS461 Wide Area Networks Data Comms & Networks I Span a large geographical area Motivation I Require crossing of public right-of-ways Model Data Comms I Rely on links of common carriers (telecommunication Networks companies) The Internet I Carries data of multiple organisations I How to find path across a network? I How to deliver data across the network? I Example technologies: ATM, Frame Relay, SDH  CS461 Local Area Networks Data Comms & Networks I Small coverage area, e.g. building, campus Motivation I Owned and operated by organisation owning end-devices Model Data Comms I Higher internal (per user) data rates compared to WANs Networks I How to arrange nodes in a LAN? The Internet I How to share LAN amongst multiple users? I Example technologies: Ethernet, Wireless LAN  CS461 Contents Data Comms & Networks Motivation Motivation Model Data Comms Networks A Communications Model The Internet Data Communications Networks The Internet Examples  CS461 The Internet Data Comms & Networks Motivation Origins Model I Evolved from US Department of Defence research Data Comms network, ARPANET (developed in 1969) Networks The Internet I Used packet switching technology (whereas telephone networks used circuit switching) I Development and standardization of the Internet suite of protocols: TCP/IP What is The Internet? I Collection of networks connected together using common software: Internet Protocol (IP) I Although network technologies differ, any computer can communicate with any other computer (providing they are using IP)  CS461 Key Elements of the Internet Data Comms & Networks Hosts, routers and (sub-)networks Motivation Model Data Comms Networks The Internet  CS461 Simplified View of Portion of Internet Data Comms & Networks Motivation Model Data Comms Networks The Internet Introduction to Networking  Introduction Old paradigm: – A single powerful computer serving all the needs of an organization – Sneaker-net -- Method of sharing data by copying it to a disk and carrying it from computer to computer New paradigm – Computer networks: a large number of separate (autonomous) but internetworked (being able to exchange information) computers doing the job Merging of computer and communications technologies – no geographical barrier Connection: copper wire, fiber optics, microwaves, infrared, communication satellites, …  Definition: – A computer network is an interconnected collection of autonomous computers Interconnected - two computers have the ability to exchange information using some transmission media e.g., copper cabling, fiber optics, or radio. Autonomous - no one computer controls any other computer (i.e. no computer can forcibly start or stop another computer) Computers can be PC’s, workstations and other “specialized” computers such as hubs, switches and routers The computers can be geographically located anywhere Network Categories:  based on size, ownership, the distance it covers  Local Area Network (LAN): usually privately owned and links devices in a single office, building or campus  Wide Area Network (WAN): covering large geographic area; may utilize public, leased, or private communications equipment – Metropolitan Area Network (MAN): designed to extend over an entire city; it may be a single network or interconnected LANs – Personal Area Network (PAN): meant for one person; e.g. a wireless network connecting a computer with its mouse, keyboard and printer  Network Architecture : includes the type of computers on the network and determines how network resources are handled Two common types – Peer-to-peer – Client/Server Peer-to-peer – Each node considered as equal in terms of resource sharing and responsibilities – pros Easy to set up Less expensive Demands moderate level of skill to administer User is able to control their own resources – Cons Only < 10 nodes Very low level of security Performance suffers when a computer is accessed – Peer-to-peer networks are good choices for environments where: There are 10 users or fewer Users share resources, such as printers, but no specialised servers exist Security is not an issue The organization and the network will experience only limited growth within the foreseeable future  Client Server Model – Consists of a group clients connected to a server – Server – with more RAM, larger hard disk, more processing power… Pros Sharing Resources Security Number of Users - A server-based network can support thousands of users Cons more complex to install, configure, and manage Expensive Servers in networking 1. File and Print Servers manage user access and use of file and printer resources. 2. Application Servers make the server side of client/server applications, as well as the data, available to clients. an application server differs from a file and print server. With a file and print server, the data or file is downloaded to the computer making the request. With an application server, the database stays on the server and only the results of a request are downloaded to the computer making the request. 3. Mail Servers operate like application servers in that there are separate server and client applications, with data selectively downloaded from the server to the client. 4. Fax Servers – manage fax traffic into and out of the network by sharing one or more fax modem boards. 5. Directory Services Servers – enable users to locate, store, and secure information on the network.  Network Topology  Topology refers to the way in which multiple devices are interconnected via communication links.  There are two types of topology: physical and logical.  Physical Topology  Refers to the way in which a network is laid out physically  Refers to the arrangement or physical layout of computers, cables, and other components on the network  Can be referred as Physical layout, Design, Diagram, Map  Two or more devices connect to a link; two or more links form a topology  Logical topology  is bound to network protocols and describe how data is moved across the network  A network's topology affects its capabilities  The choice of one topology over another will have an impact on the  Types of equipment that the network needs  Growth of the network – scalability  Way the network managed  Four basic topologies are possible: mesh, star, bus, ring  Bus  multipoint (one long cable acts as a backbone to link all the devices in the network)  advantages  ease of installation; less cabling than star or mesh  disadvantages  signal reflection at the taps can cause degradation in quality (soln: limit the number and spacing of devices connected to a given length of cable)  difficult reconnection (adding new devices) and fault isolation  a fault in the bus cable stops all transmission  Star  each device has a dedicated point-to-point link only to a central controller, usually called a Concentrator  Advantages  robust; a failure of a link has no effect on others  fault identification and isolation are easy  less expensive than mesh (but more expensive than others)  Disadvantage  Single point of failure  Requires more cable length than a linear topology  More expensive than linear bus topologies because of the cost of the concentrators.  Ring  each device has a dedicated point-to-point connection only with 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  each device incorporates a repeater (to regenerate bits received before passing it)  Advantages  Equal access for all users  Each workstation has full access speed to the ring  As workstation numbers increase performance diminishes slightly  Disadvantages  Costly Wiring  Difficult Connections  Expensive Adaptor Cards  Mesh  every device has a dedicated point-to-point link to every other device  every device must have n-1 I/O ports  Advantages  no traffic problem  robust; a failure of a link has no effect on others  privacy or security  fault identification and isolation are easy  Disadvantages  amount of cabling and I/O ports needed (expensive)  Hybrid topology  A combination of two network topologies.  E.g. star and mesh Internetworking – Interconnection among or between public, private, commercial, industrial, or governmental networks – Called also internet – Three variants Intranet Extranet Internet – Intranet a set of networks that is under the control of a single administrative entity – Internet worldwide interconnection of networks  – Extranet internetwork that is limited in scope to a single organization or entity but which also has limited connections to the networks of one or more other usually, but not necessarily, trusted organizations or entities  Mode of transmission  refers to the direction of signal flow between two linked devices  It can be  Simplex: unidirectional, only one of the devices can transmit  E.g. TV transmission  Half-duplex: both can transmit and receive, but not at the same time  E.g. wireless handset (walkie-Talkie)  Full-duplex: both can transmit and receive at the same time  E.g. Telephone transmission  Transmission media Is a physical media that carries a signal from the transmitter to the receiver The information or signal transmitted from one device to another is through electromagnetic signals. Electromagnetic signals include power, voice, radio, waves, infrared light, visible light, ultraviolet light, X-rays, and gamma rays. These signals can travel trough vacuum, air or any other transmission medium The measurement of the quantity of data that can be passed down (transmitted) a communication link in a given time is done in terms of bandwidth In digital circuits, bandwidth is measured in bits per second (bps)  Two basic categories – Guided – Unguided – Guided – uses a cabling system that guides the signals along a specific path E.g. Fiber Optics, Twisted Pair, Coaxial Cable etc… – Unguided – consists of a means for the data signals to travel but nothing to guide them along a specific path - wireless Example: Radio wave, Satellite, etc.  Types of connection  Point-to-point: provides a dedicated link between two devices  Multipoint: more than two devices share (spatially - simultaneously - or temporally by taking turns) a single link  Direct link: signals propagate directly from transmitter to receiver  No intermediate devices other than amplifiers or repeaters  This can apply to both guided and unguided medium  Indirect link  Systems connected through a switched communication network