1. Introduction

Data Communication Data Data Communication Information presented in whatever form is agreed upon by the parties creating and using the data Binary information units (0s and 1s) Data Communication Exchange of data between two devices via transmission medium Fundamental Characteristics Delivery: deliver data to correct destination Accuracy: deliver data accurately Timeliness: Deliver data in a timely manner Delivering data as they are produced, in the same order that they are produced, and without significant delay Real-time transmission

Data Communication System Component

Data Communication System Components (cont.) Message Information (data) to be communicated Sender Device sending data message Receiver Device receiving message Medium Physical path by which a message travels Protocol Set of rules governing data communication Agreement between communicating devices

Direction of Data Flow Simplex Unidirectional communication Keyboard, monitor

Direction of Data Flow (cont.) Half-duplex Both transmit and receive, but not at the same time Walkie-talkie

Direction of Data Flow (cont.) Full-duplex Transmit and receive simultaneously Telephone network

Network Network A set of devices (nodes) connected by communication links

Network Criteria Performance Reliability Security Throughput, delay, jitter, loss… Factors including number of users, type of transmission medium, hardware, software Reliability Frequency of failure, recovery time of a network after a failure, network’s robustness in a catastrophe Security Protecting data from unauthorized access

Physical Structure Type of Connection Point-to-Point Provide a dedicated link between two devices Reserve entire capacity of the channel for transmission between two devices

Physical Structure (cont.) Type of Connection (cont.) Multipoint (or Multidrop) More than two devices share a single link Spatially shared: several devices use link simultaneously Timeshare:users must take turns

Physical Structure (cont.) Physical Topology The way in which a network is laid out physically

Physical Structure (cont.) Physical Topology (cont.) Mesh Every device has a dedicated p-to-p link to every other device Guarantee data load between two devices Robust, meaning one link failure does not halt entire system Privacy or security Easy fault identification and fault isolation Amount of cabling and number of I/O ports required (n(n-1)/2)

Physical Structure (cont.) Physical Topology (cont.) Star Dedicated p-to-p link to central controller (hub) Less expensive than mesh Easy to install and reconfigure due to only one link and one I/O port Robustness due to easy fault identification and fault isolation More cabling than other topologies (tree, ring, bus) Single failure problem

Physical Structure (cont.) Physical Topology (cont.) Bus Multipoint configuration Ease of installation Limited number of taps a bus can support and distance Difficult reconfiguration and isolation

Physical Structure (cont.) Physical Topology (cont.) Ring Dedicated p-to-p configuration with two devices on either side Easy to install and reconfigure Simplified fault isolation Unidirectional traffic A break in the ring can disable entire network

Categories of Networks Classification of interconnected processors by scale

Categories of Networks (cont.) Local Area Network (LAN) Privately owned and limited size to a few kilometers Allow resources to be shared between PCs or workstations Bus, ring or star

Categories of Networks (cont.) Metropolitan Area Network (MAN) Extend over an entire city Single network or a means of connecting LANS into a larger network (ex) Telco.s provide a popular MAN service called SMDS (Switched Multi-megabit Data Services)

Categories of Networks (cont.) Wide Area Network (WAN) Provide long-distance transmission of data over large geographical areas (country or continent) Utilize public, leased, or private communication equipment Enterprise Network WAN that is wholly owned and used by a single company

Categories of Networks (cont.) Internetworks internetworks or internet Collection of interconnected networks

Brief History of Internet ARPANET Advanced Research Projects Agency (ARPA) in the DOD : presented ideas of ARPANET, 1967 Reality : 1969 (UCLA, UCSB, SRI, U of Utah) Birth of the Internet Vint Cerf and Bob Kahn devised to interconnect networks, in 1972 Presented TCP concepts in 1973; later, TCP  splitting into TCP and IP In 1983, TCP/IP became to official protocol for the ARPANET

Internet Today More than 36 million hosts More than 134,000 networks

Internet Specific worldwide internet

Protocols Set of rules (conventions) governing data communications Key Element Syntax Structure or format of data, meaning the order in which they are presented Semantics Meaning of each section of bits Timing Two characteristics: when data should be sent and how fast they can be sent Entity Anything capable of sending or receiving information

Standards Standard Categories De Jure standards De Facto Standards Essential in creating and maintaining an open and competitive market and in guaranteeing national and international interoperability Categories De Jure standards Legislated by an officially recognized body De Facto Standards Have not been approved by an organized body but have been adopted as standards through widespread use

Standard Organizations Standards Creation Committees International Standards Organization (ISO) International Telecommunications Union-Telecommunication Standards Sector (ITU-T, formerly CCITT) American National Standards Institute (ANSI) Institute of Electrical and Electronics Engineers (IEEE) Electronic Industries Association (EIA)

Standard Organizations (cont.) Forum Developed by special-interest groups to accommodate the need for working models and agreements and to facilitate the standardization process Speed acceptance and use of technologies in telecommunications community Frame relay forum, ATM forum and ATM consortium Internet Society (ISOC) and Internet Engineering Task Force (IETF) Regulatory Agencies Government agencies regulating all communications technology FCC

Internet Standards Internet Standard A thoroughly tested specification that is useful to and adhered by those who work with the Internet A specification begins as an Internet draft Working document with no official status and six-month life-time RFC (Request for Comment) Recommendation from Internet authorities