Data Communication Lecture # 01 Introduction & Overview Course Instructor: Engr. Sana Ziafat
Grading Policy • Final Exam: 60% • Mid term Exam 20% • Assignments 5% • Quizzes: 15%
Quizzes may be announced or unannounced. • Exams are closed-book and extremely time limited. • Exams consist of design questions, numerical, maybe true-false and short answer questions.
TEXT BOOKS • Data Communications and Networking, 4/e • B.A. Forouzan, McGraw-Hill, 2003, ISBN 0-07-292354-7. • Data and Computer Communication by William Stallings (7th Edition) Prentice Hall.
Introduction • Data : Refers to information presented in whatever form is agreed upon by the parties creating and using data • Communication: When we communicate we are sharing information. This sharing can be remote or local…. Local face to face and remote at a distance
What is data communication? • Data communication- • Exchange of data between two devices via some form of transmission medium such as wire cable. • Defined as a subset of telecommunication involving the transmission of data to and from computers and components of computer systems.
History of Telecommunications • Invention of telegraph Samuel Morse – 1837 • Invention of telephone- Alexander Graham Bell – 1876 • Development of wireless By ??? – 1896 • Concept of universal access and growth of AT&T • Divestiture of AT&T—what year??
History of Telecommunications Continued…. • Telecommunications Act of 1996 • Three main developments that led to the growth of data communications systems: • Large-scale integration of circuits reduced the cost and size of terminals and comm equipment • Developments of software systems made establishment of communication networks easy • Competition among providers of transmission facilities reduced the cost of data circuits
Fundamental Characteristics • The effectiveness of a data communication system depend on four fundamental characteristics: • Delivery • Accuracy • Timelines • Jitter (variation in packet arrival time)
A Communications Model • Source • Generates data to be transmitted • Transmitter • Converts data into transmittable signals • Transmission system • Carries data • Receiver • Converts received signal into data • Destination • Takes incoming data
Key Communications Tasks • Transmission system utilization • Interfacing • Signal generation • Synchronization • Exchange management • Error detection and correction • Addressing and routing • Recovery • Message formatting • Security • Network management
Data REPRESENTATION • Data can be represented as • Text • Numbers • Images • Audio • Vedio
Direction of data flow Simplex Half Duplex Full Duplex
Network design Before looking inside a computer network, first agree on what a computer network is
Computer network ? Specialized to handle: Keystrokes Voice Video • Set of serial lines to attach terminals to mainframe ? • Telephone network carrying voice traffic ? • Cable network to disseminate video signals ?
Networks • Potential of networking: • move bits everywhere, cheaply, and with desired performance characteristics • Network provides “connectivity”
What is “Connectivity” ? • Direct or indirect accessto every other node in the network • Connectivity is the magic needed to communicate if you do not have a direct pt-pt physical link. • Tradeoff: Performance characteristics worse than true physical link!
A Network A network can be defined recursively as two or more nodes connected by a physical link Or two or more networks connected by one or more nodes
Transmission Technology Broadcast/ Multipoint Network Point – To – Point Network Single communication channel that is shared by all the machines on the network. Many connections between individual pairs of machines All the others receive “Packets” in certain contexts, sent by any machine. A packet may have to visit one or more intermediate machine. An address field within the packet specifies for whom it is intended. Routing algorithms play an important role in PTP networks. Multicasting: transmission to a subnet of the machines. Network Hardware
… Building Blocks • Nodes: PC, special-purpose hardware… • hosts • switches • Links: coax cable, optical fiber… • point-to-point • multiple access
Switched Networks • A network can be defined recursively as... • two or more nodes connected by a link • white nodes (switches) implement the network • colored nodes (hosts) use the network
Switched Networks • A network can be defined recursively as... • two or more networks connected by one or more nodes: internetworks • white nodes (router or gateway) interconnects the networks • a cloud denotes “any type of independent network”
Switching Strategies • Packet switching: store-and-forward messages • operates on discrete blocks of data • utilizes resources according to traffic demand • send/receive messages at variable rate • example: Internet • Circuit switching: carry bit streams • establishes a dedicated circuit • links reserved for use by communication channel • send/receive bit stream at constant rate • example: original telephone network
Networks: key issues • Network criteria • Performance • Transit time • Throughput • Delay • Reliability • Data transmitted are identical to data received. • Measured by the frequency of failure • The time it takes a link to recover from a failure • Security • Protecting data from unauthorized access
Terminology • The throughput or bandwidth of a channel is the number of bits it can transfer per second • The latency or delay of a channel is the time that elapses between sending information and the earliest possible reception of it
Network topologies • Topology defines the way hosts are connected to the network
Network topology issues A goal of any topology • highthroughput (bandwidth) • low latency
Advantages & disadvantages of mesh topology • Advantages - Dedicated links eliminate the traffic problem -Secure communication -Ease of fault identification & fault Isolation -Robust • Disadvantages -Large number I/O ports & cabling required -Installation & reconfiguration is difficult -Wiring can be greater than available space -Expensive
Advantages & disadvantages of star topology • Advantages -Less expensive than mesh topology -Installation & reconfiguration are easy -Robust - Ease of fault identification & fault Isolation -Required less cabling than mesh topology • Disadvantages -Dependency of whole topology on single point Application: High Speed LAN
Advantages & disadvantages of bus topology • Advantages -Ease of installation -Required less cabling • Disadvantages -Difficult reconnection &fault isolation -A fault or break stops all transmission
Advantages & disadvantages of bus topology • Advantages -Ease of installation & reconfiguration • Disadvantages -A break in ring can disable the entire link
What next ? • Hosts are directly or indirectly connected to each other • Nodes must be able to say which host it wants to communicate with
Addressing and Routing • Address: byte-string that identifies a node • usually unique • Routing: forwarding decisions • process of determining how to forward messages to the destination node based on its address • Types of addresses • unicast: node-specific • broadcast: all nodes on the network • multicast: some subset of nodes on the network
Wrap-up • A network can be constructed from nesting of networks • An address is required for each node that is reachable on the network • Address is used to route messages toward appropriate destination
LAN, WAN & MAN • Network in small geographical Area (Room, Building or a Campus) is called LAN (Local Area Network) • Network in a City is call MAN (Metropolitan Area Network) • Network spread geographically (Country or across Globe) is called WAN (Wide Area Network)
Local Area Networks • Smaller scope • Building or small campus • Usually owned by same organization as attached devices • Data rates much higher • Usually broadcast systems • Now some switched systems and ATM are being introduced
NETWORKS LAN CHARACTERISTICS LAN Size Transmission Technology MAN WAN Topology INTERNET Restricted in Size Single Cable 10 to 100 Mbps Low delay (ms) Very few Errors Megabits/Sec. (Unit) BUS (Ethernet) Ring (Token ring) Local Area Networks (Cont.)
MAN • Metropolitan Area Network • Support data and voice • No switching elements • Standard: DQDB (Distributed Queue Dual Bus) • Two unidirectional buses to which all the computers are connected. • Each bus has a head-end, a device that initiates transmission activity. • Traffic that is destined for a computer to the right of the sender uses the upper bus, traffics to the left uses the lower one.
Wide Area Networks • Large geographical area • Alternative technologies • Circuit switching • Packet switching • Frame relay • Asynchronous transfer mode (ATM)