DATA COMMUNICATION AND NETWORKING CHAPTER 1 - PRELIM JUNE 2005 DATA COMMUNICATION AND NETWORKING DATA COMMUNICATIONS Is the exchange of data between two devices via some form of transmission medium such as a wire cable. JUNE 2005 DATA COMMUNICATION AND NETWORING 3 Fundamental Characteristics: 1. Delivery. The system must deliver data to the correct destination. 2. Accuracy. The system must deliver the data accurately 3. Timeliness. The system must deliver data in a timely manner. JUNE 2005 DATA COMMUNICATION AND NETWORING Components 1. Message. Is the information (data) to be communicated. 2. Sender. Is the device that sends the data message. 3. Receiver. Is the device that receives the message. JUNE 2005 DATA COMMUNICATION AND NETWORING 4. Medium. Is the physical path by which a message travels from the sender to receiver. 5. Protocol. Is a set of rules that govern data communications. It represents an agreement between the communicating devices. JUNE 2005 DATA COMMUNICATION AND NETWORING Direction of Data Flow Transmission Modes 1. Simplex Mode, the communication is unidirectional. Only one of the two devices on a link can transmit; the other can only receive. 2. Half-Duplex, each station can both transmit and receive, but not at the same time. 3. Full-Duplex (also called duplex), both stations can transmit and receive simultaneously. JUNE 2005 DATA COMMUNICATION AND NETWORING NETWORKS Is a set of devices (often referred to as nodes) connected by communication links. JUNE 2005 DATA COMMUNICATION AND NETWORING Distributed Processing In which task is divided among multiple computers. Instead of a single large machine being responsible for all aspects of a process, separate computers (usually a PC or workstation) handle a subset. JUNE 2005 DATA COMMUNICATION AND NETWORING Network Criteria 1. Performance can be measured in many ways, including transit time and response time. The performance of a network depends on a number of factors, Number of users Type of transmission medium Capabilities of the connected hardware Efficiency of the software JUNE 2005 DATA COMMUNICATION AND NETWORING 2. Reliability is measured by, Frequency of failure Time it takes to recover from a failure Robustness in a catastrophe 3. Security issues include protecting data from, Unauthorized users viruses JUNE 2005 DATA COMMUNICATION AND NETWORING Physical Structures Line Configuration A network is two or more devices connected together through Links. Link is a communications pathway that transfers data from one device to another. JUNE 2005 DATA COMMUNICATION AND NETWORING There are two possible type of connections/line configurations: 1. Point-to-point, connection provides a dedicated link between two devices. The entire capacity of the link is reserved for transmission between those two devices. JUNE 2005 DATA COMMUNICATION AND NETWORING 2. Multipoint (also called multidrop)connection is one in which more than two specific devices share a single link. The capacity of the channel is shared, either spatially or temporally (timeshare). JUNE 2005 DATA COMMUNICATION AND NETWORING Physical 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. Is the geometric representation of the relationship of all the links and linking devices (usually called nodes) to one another. JUNE 2005 DATA COMMUNICATION AND NETWORING Four Basic Topologies: 1. Mesh. Every device has a dedicated point-to-point link to every other device. A fully connected mesh network has n(n- 1)/2 physical channels to link n devices. Every device on the network must have n-1 input/output (I/O) ports. JUNE 2005 DATA COMMUNICATION AND NETWORING Advantages of Mesh: a) Eliminates the traffic problems that can occur when links must be shared by multiple devices. b) Robust. If one link becomes unusable, it does not incapacitate the entire system. c) Privacy or Security d) Makes fault identification and fault isolation easy. Traffic can routed to avoid links with suspected problems. JUNE 2005 DATA COMMUNICATION AND NETWORING Disadvantages of Mesh: a) Because every device must be connected to every other device, installation and reconfiguration are difficult. b) The sheer bulk of the wiring can be greater than the available space (in walls, ceilings, or floors) can accommodate. c) The hardware required to connect each link (I/O ports and cable) can be prohibitively expensive. JUNE 2005 DATA COMMUNICATION AND NETWORING 2. Star. A topology in which each device has a dedicated point-to- point link only to a central controller, usually called a hub. 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. JUNE 2005 DATA COMMUNICATION AND NETWORING Advantages of Star: a) Less expensive than a mesh topology. b) Each device needs only one link and one I/O port to connect it to any number of others. Thus, make it easy to install and reconfigure. c) Less cabling needs to be housed, and additions, moves, and deletions involve only one connection: between that device and the hub. d) Robustness e) Easy fault identification and fault isolation. JUNE 2005 DATA COMMUNICATION AND NETWORING Disadvantages of Star: Each node must be linked to a central hub. For these reason more cabling is required in a star than in some other topologies (such as tree, ring, or bus). JUNE 2005 DATA COMMUNICATION AND NETWORING 3. Bus. A network topology in which all computers are attached to a shared medium (often a single cable). One long cable acts as a backbone to link all the devices in the network. Nodes are connected to the bus cable by drop lines and taps. Bus topology is multipoint. JUNE 2005 DATA COMMUNICATION AND NETWORING 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. JUNE 2005 DATA COMMUNICATION AND NETWORING Advantages of Bus: a) Ease of installation. b) Use less cabling than mesh, or star topologies. JUNE 2005 DATA COMMUNICATION AND NETWORING Disadvantages of Bus: a) Difficult reconfiguration and fault isolation. b) A fault or break in the bus cable stops all transmission, even between devices on the same side of the problem. The damage area reflects signals back in the direction of origin, creating noise in both directions. JUNE 2005 DATA COMMUNICATION AND NETWORING 4. 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 in the ring incorporates a repeater. JUNE 2005 DATA COMMUNICATION AND NETWORING Advantages of Ring: a) Easy to install and reconfigure. b) Fault isolation is simplified. JUNE 2005 DATA COMMUNICATION AND NETWORING Disadvantages of Ring: a) Unidirectional traffic. b) A break in the ring (such as disabled station) can disable the entire network. This weakness can be solved by using dual ring or a switch capable of closing off the break. JUNE 2005 DATA COMMUNICATION AND NETWORING Categories of Networks Size Ownership Distance it covers LAN Few Privately owned Links devices 2 PCs & a kilometers, in a single printer, in a licensing office building house or restrictions or campus office, 4 TO on the # of 16 Mbps range users per copy up to 100 of software or Mbps, voice, access of OS sound, & video peripherals, Bus, Ring, & star MAN 3 to 30 miles Maybe wholly Entire city, owned and may be a single operated by a network such as private company, cable TV or it maybe network, LAN to service provided LAN (co. use a by a public MAN to connect company, such as the LANs in all a local telephone offices company. throughout the city JUNE 2005 DATA COMMUNICATION AND NETWORING Categories of Networks Size Ownership Distance it covers WAN Unlimited # of Public leased Large Data, voice, miles through AT&T, geographical image & video MCI, SPRINT areas information. or private (country, communication continent, devices or whole world combination JUNE 2005 DATA COMMUNICATION AND NETWORING The Internet – A Brief History An internet (note the lowercase letter i) is two or more networks that can communicate with each other. The most notable internet is called the Internet (uppercase letter I), a collaboration of more than hundreds of thousands interconnected networks. JUNE 2005 DATA COMMUNICATION AND NETWORING Milestones Mid-1960s Mainframe computers in research organizations were stand-alone devices. ARPA in the DOD 1967 ACM meeting ARPA presented its ideas for ARPANET interface message processor (IMP). 1969 ARPANET was a reality. Four nodes: UCLA, UCSB, SRI, University of Utah Network Control Protocol (NCP) JUNE 2005 DATA COMMUNICATION AND NETWORING Milestones 1972 Vint Cerf and Bob Kahn collaborated on Internetting Project 1973 paper outlined the protocols to achieve end-to-end delivery of packets. Paper on TCP included concepts such as encapsulation, the datagram, and the functions of a gateway. TCP split into two protocols: TCP and IP IP would handle datagram routing TCP would be responsible for higher-level functions such as segmentation, reassembly, and error detection. The internetworking protocol became known as TCP/IP. JUNE 2005 DATA COMMUNICATION AND NETWORING PROTOCOLS AND STANDARDS Protocol Is a set of rules that govern data communication. For communication to occur they must agree on a protocol. A protocol defines what, how, when it is communicated. The key elements of a protocol are syntax, semantics, and timing. JUNE 2005 DATA COMMUNICATION AND NETWORING Key Elements of a Protocol 1. Syntax refers to the structure or format of the data, meaning the order in which they are presented. 2. Semantics refers to the meaning of each section of bits. How a particular pattern to be interpreted, and what action is to be taken based on that interpretation? JUNE 2005 DATA COMMUNICATION AND NETWORING Key Elements of a Protocol 3. Timing refers to two characteristics: when data should be sent and how fast they can be sent. JUNE 2005 DATA COMMUNICATION AND NETWORING Standards Standards are essential in creating and maintaining an open and competitive market. They provide guidelines to manufacturers, vendors, government agencies, and other service providers to ensure the kind of interconnectivity. JUNE 2005 DATA COMMUNICATION AND NETWORING Categories of Standards 1. De facto (by fact). Standards that have not been approved by an organized body but have been adopted as standards through widespread use. 2. De jure (by law). Those that have been legislated by an officially recognized body. JUNE 2005 DATA COMMUNICATION AND NETWORING Standard Organizations Standards are develop through the cooperation of standards creation committees, forums, and government regulatory agencies. JUNE 2005 DATA COMMUNICATION AND NETWORING Standard Creation Committees International Organization for Standardization (ISO) Multinational body Created in 1947 OSI International Telecommunication Union- Telecommunication Standards (ITU-T) Consultative Committee for International Telegraphy and Telephony (CCITT) Best known standards are V series: define transmission over public digital networks, and X series: define transmission over public digital networks. JUNE 2005 DATA COMMUNICATION AND NETWORING Standard Creation Committees American National Standards Institute (ANSI) U.S. voting representative to both ISO and ITU-T. Members include professional societies, industry associations, governmental and regulatory bodies, and consumer groups. Institute of Electrical and Electronics Engineers (IEEE) Largest national professional group involved in developing standards for computing, communication, electrical engineering, and electronics. Sponsored an important standard for LAN called Project 802 (e.g. 802.3, 802.4, 802.5) JUNE 2005 DATA COMMUNICATION AND NETWORING Standard Creation Committees Electronic Industries Association (EIA) An association of electronic manufacturers in the U.S. Responsible for developing the EIA-232-D, EIA-449, and EIA-530 define serial transmission between two digital devices (e.g. computer to modem) JUNE 2005 DATA COMMUNICATION AND NETWORING Forums Telecommunications technology development is moving faster than the ability of standard committees to ratify standards. Forums consist of representatives from corporations, they work with universities, and users that test, evaluate, and standardize new technologies. JUNE 2005 DATA COMMUNICATION AND NETWORING Regulatory Agencies All communications technology is subject to regulation by government agencies such as the Federal Communications Commission (FCC) in the United States. The purpose of these agencies is to protect the public interest by regulating radio, television, and wire/cable communications. JUNE 2005 DATA COMMUNICATION AND NETWORING
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