Chapter 1 Introduction to Data Communications and Networking PDF

Chapter 1 Introduction 1.1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  1-1 DATA COMMUNICATIONS The term telecommunication means communication at a distance. The word data refers to information presented in whatever form...

Chapter 1 Introduction 1.1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  1-1 DATA COMMUNICATIONS The term telecommunication means communication at a distance. The word data refers to information presented in whatever form is agreed upon by the parties creating and using the data. Data communications are the exchange of data between two devices via some form of transmission medium such as a wire cable. 1.2  Effectiveness of a data communications system Delivery Correct destination Received by the intended device or user. Accuracy Delivering the data accurately without errors. Timeliness Deliver data in a timely manner. Especially in video & audio. Real time transmission. Delivering data as they are produced. Same order Without significant delay. Jitter Variation in the packet arrival time. 1.3  Components of a data communications system Message Information (data) to be communicated. Such as text, numbers, pictures, audio, and video. Sender Device that sends the data message. Computer, workstation, and video camera Receiver Device that receives the message. Computer, workstation, and telephone handset. Transmission medium Physical path by which a message travels from sender to receiver. Twisted pair wire, coaxial cable, and satellite. Protocol Set of rules that govern data communications. 1.4  Figure 1.1 Five components of data communication 1.5  Data flow Simplex The communication is unidirectional. Keyboard and monitors. Half-duplex Each station can both submit and receive, but not at the same time. Walkie-talkies Full-duplex Both stations can transmit and receive simultaneously. Telephone network. 1.6  Figure 1.2 Data flow (simplex, half-duplex, and full-duplex) 1.7  1-2 NETWORKS A network is a set of devices (often referred to as nodes) connected by communication links. A node can be a computer, printer, or any other device capable of sending and/or receiving data generated by other nodes on the network. 1.8  Distributed computing Most networks use distributed computing. A task is divided among multiple computers. 1.9  Network criteria Performance Can be measured in many ways. Transit time: the amount of time required for a message to travel from one device to another. Response time: the elapsed time between an inquiry and a response. Performance depends on: Number of users The type of transmission medium. Capability of the connected hardware. Efficiency of the software. Evaluated by throughput and delay. 1.10  Reliability Measured by: Frequency of failure. The time it takes a link to recover from a failure. Network’s robustness in a catastrophe. Security Protecting data from unauthorized access. Protecting data from damage. Implementing policies and procedures for recovery from breaches and data losses 1.11  Type of connection Point-to-point Dedicated link between two devices. The entire capacity is reserved from transmission between those two devices. Multipoint (Multidrop) More than two devices share a single link. Can be spatially or time shared connection 1.12  Figure 1.3 Types of connections: point-to-point and multipoint 1.13  Figure 1.4 Categories of topology 1.14  Categories of topology Mesh Every device has a dedicated point-to-point link to every other device. Number of links Simplex: n(n-1) Duplex: n(n-1) / 2 Connection of telephone regional offices. Star Each device has a dedicated point-to-point link only to a central controller usually called a hub. Used in LANs. 1.15  Bus One long cable connects links all the devices in a network. Nodes 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. Ring 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. Hybrid A main star topology with each branch connection several stations in a bus topology. 1.16  Figure 1.5 A fully connected mesh topology (five devices) 1.17  Figure 1.6 A star topology connecting four stations 1.18  Figure 1.7 A bus topology connecting three stations 1.19  Figure 1.8 A ring topology connecting six stations 1.20  Figure 1.9 A hybrid topology: a star backbone with three bus networks 1.21  Categories of networks Local Area Network Is privately owned and links the devices in a single office, building or campus. LAN size is limited to few kilometers. Sharing resources Hardware such as printer Software such as an application program. Speed: normally 100 or 1000 Mbps. 1.22  Wide Area Network Long transmission of data over large geographic areas. Country, continent, or the whole world. Switched WAN: connects the end systems, which usually comprise a router. Point-to-point WAN: is a line leased from telephone or cable TV provider that connects a home computer or a small LAN to an ISP. X.25, Frame relay, and asynchronous transfer mode (ATM). Metropolitan Area Network Is a network with a size between a LAN and a WAN. Town or a city. Cable TV network. 1.23  Figure 1.10 An isolated LAN connecting 12 computers to a hub in a closet 1.24  Figure 1.11 WANs: a switched WAN and a point-to-point WAN 1.25  Figure 1.12 A heterogeneous network made of four WANs and two LANs 1.26  1-3 THE INTERNET internet (internetwork) : two or more networks that can communicate with each other. Internet is a collaboration of more than hundreds of thousands of interconnected networks. 1.27  A brief history ARPANET was the first network (Four nodes – Group of universities). Small network of connected computers. Each computer is connected to a specialized computer, called interface message processor (IMP). IMPs would be connected to one another. IMP communicates with other IMPs as well as with its own attached host. Internetworking project (Vint and Bob) -Transmission control protocol (TCP) to achieve end-to-end delivery of packets. Then, TCP was splitted into TCP and Internetworking protocol (IP) IP handles datagram routing while TCP is responsible for higher level functions such as segmentation, reassembly, and error detection. The Internetworking protocol became known as TCP/IP. 1.28  Internet service providers (ISPs) International ISPs Connect nations together. National ISPs Backbone networks created and maintained by specialized companies (e.g. SprintLink). National ISPs are connected by complex switching stations called network access points (NAPs). Sometimes by private switching stations called peering points (normally operate at a high data rate – up to 600 Mbps). 1.29  Regional ISPs Smaller than National ISPs. Connected to one or more national ISPs. Smaller data rate. Local ISPs Provide direct service to end users. Can be connected to regional ISPs or directly to national ISPs. Local ISP can be: A company that just provides Internet services. A corporation that supplies services to its own employees. Non-profit organization such as a university, that runs its own network. 1.30  Figure 1.13 Hierarchical organization of the Internet 1.31  1-4 PROTOCOLS AND STANDARDS In this section, we define two widely used terms: protocols and standards. First, we define protocol, which is synonymous with rule. Then we discuss standards, which are agreed-upon rules. 1.32  Protocols Two entities (anything capable of sending or receiving information) can’t simply send bid streams to each other and expect to be understood. So, the entities must agree on a protocol. A protocol is a set of rules that data communications. 1.33  Key elements of protocol are: Syntax refers to the structure or format of the data first 8 bits = source address. Semantics refers to the meaning of each section of bits. How is a particular pattern to be interpreted. What action is to be taken based on that interpretation. e.g. does an address identify the route to be taken or the final destination of the message. Timing When data should be sent. How fast they can be sent. E.g. matching the speed between the sender and receiver. 1.34  Standards Two categories: De facto: Standards that have not been approved by an organized body but have been adopted as standards through widespread use. De jure: Standards that have been legislated by an officially recognized body. Standards are developed through the cooperation of standards creation committees, forums, and government regulatory agencies. 1.35  Standards creation committees International Organization for Standardization (ISO). International Telecommunication Union-Telecommunication standards sector (ITU-T). American National Standards Institute (ANSI). 1.36  Forums Many special-interest groups have developed forums made up of representatives from interested corporations. The forums work with universities and user to test, evaluate, and standardize new technologies. Regulatory agencies Government agencies that regulate all communications technology. e.g. Federal communications commission (FCC) in the US. Regulating radio. 1.37  Internet standard Is a thoroughly tested specification that is useful and adhered to those who work with the internet. A specification begins as an internet draft. Internet draft is a working document (work in progress) with no official status and a 6 month lifetime. After recommendation from the Internet authority, a draft may be published as a Request for Comment(RFC). Each RFC is edited, assigned a number, and made available to all interested parties. Then, RFC might become a standard after going through maturity levels. 1.38