Lecture # 01 Introduction Course Instructor: Engr. Sana Ziafat

Grading Policy Final Exam: 40% Mid term Exam20% Assignments5% Quizzes:15% Lab work20%

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  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

Simplified Communications Model - Diagram

Simplified Data Communications Model

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 1. Text 2. Numbers 3. Images 4. Audio 5. Video

Direction of data flow Simplex Half Duplex Full Duplex

Before looking inside a computer network, first agree on what a computer network is

Computer network ? Set of serial lines to attach terminals to mainframe ? Telephone network carrying voice traffic ? Cable network to disseminate video signals ? Specialized to handle: Keystrokes Voice Video

Networks Potential of networking: move bits everywhere, cheaply, and with desired performance characteristics Network provides “connectivity”

What is “Connectivity” ? Direct or indirect access to 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

Network Hardware 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.

Types of connections: point-to-point and multipoint

Simplified Network Model

Building Blocks Nodes: PC, special-purpose hardware… hosts switches Links: coax cable, optical fiber… point-to-point multiple access …

Switched Networks two or more nodes connected by a link white nodes (switches) implement the network colored nodes (hosts) use the network A network can be defined recursively as...

Switched Networks 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” A network can be defined recursively as...

Switching Strategies Circuit switching: carry bit streams a. establishes a dedicated circuit b. links reserved for use by communication channel c. send/receive bit stream at constant rate d. example: original telephone network Packet switching: store-and-forward messages a.operates on discrete blocks of data b.utilizes resources according to traffic demand c.send/receive messages at variable rate d.example: Internet

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 1.high throughput (bandwidth) 2.low latency A goal of any topology

Categories of Topology

Figure 1.5 A fully connected mesh topology (five devices)

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

A star topology connecting four stations

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

A bus topology connecting three stations

Advantages & disadvantages of bus topology  Advantages -Ease of installation -Required less cabling  Disadvantages -Difficult reconnection &fault isolation -A fault or break stops all transmission

A ring topology connecting six stations

Advantages & disadvantages of bus topology  Advantages -Ease of installation & reconfiguration  Disadvantages -A break in ring can disable the entire link

A hybrid topology: a star backbone with three bus networks

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

Local Area Networks (Cont.) NETWORKS LANMANWANINTERNET LAN CHARACTERISTICS SizeTransmission TechnologyTopology Restricted in Size Single Cable 10 to 100 Mbps Low delay (ms) Very few Errors Megabits/Sec. (Unit) BUS (Ethernet) Ring (Token ring)

MAN Metropolitan Area Network Support data and voice No switching elements 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)

Internet Collection of interconnected networks. Example: A collection of LAN ’ s connected by a WAN.

Applications   Searchable Data (Web Sites)  E-Commerce  News Groups  Internet Telephony (VoIP)  Video Conferencing  Chat Groups  Instant Messengers  Internet Radio

Research areas in Networking Routing Security Ad-hoc networks Wireless networks Protocols Quality of Service …

COURSE OUTLINE Network Models Encoding Schemes Bandwidth Utilization Different types of transmission medium Error detection & Correction IP addressing …

Readings Chapter 1: 1.1, 1.2 Data & Computer Communication seventh Edition, By William Stallings Chapter 1: 1.1, 1.2 (B. A Forouzan) Data Communications and Networking, By Behroz A Forozun

Q & A