Data and Computer Communications Chapter 1 Data Communications

Data and Computer Communications Chapter 1 – Data Communications, Data Networks, and the Internet

What is Data Communication Ø When we communicate we are sharing information Ø Local sharing (face to face) Ø Remote sharing (over some distance) Ø Data : information being shared (text, numbers, images, audio, video) Ø Data communication : exchange of data between two or more devices via some transmission medium

Effective Data communication Ø Delivery : the data must be delivered to the correct destination Ø Accuracy : the data received must be accurate representation of the data sent Ø Timeliness : the data should be delivered within a reasonable time

Data Communications, Data Networks, and the Internet Ø The fundamental problem of communication is that of reproducing at one point either exactly or approximately a message selected at another point - The Mathematical Theory of Communication, Claude Shannon

Contemporary Data Comms Ø trends l l l traffic growth at a high & steady rate development of new services advances in technology Ø significant change in requirements l l l emergence of high-speed LANs corporate WAN needs digital electronics

A Communications Model

Communications Tasks Transmission system utilization Addressing Interfacing Routing Signal generation Recovery Synchronization Message formatting Exchange management Security Error detection and correction Network management Flow control

Data Communications Model

Transmission Medium Ø selection is a basic choice l l internal use entirely up to business long-distance links made by carrier Ø rapid technology advances change mix l l fiber optic wireless Ø transmission costs still high Ø hence interest in efficiency improvements

Networking Ø growth of number & power of computers is driving need for interconnection Ø also seeing rapid integration of voice, data, image & video technologies Ø two broad categories of communications networks: l l Local Area Network (LAN) Wide Area Network (WAN)

Wide Area Networks Ø span a large geographical area Ø cross public rights of way Ø rely in part on common carrier circuits Ø alternative technologies used include: l l circuit switching packet switching frame relay Asynchronous Transfer Mode (ATM)

Circuit Switching Ø uses a dedicated communications path established for duration of conversation Ø comprising a sequence of physical links Ø with a dedicated logical channel Ø eg. telephone network

Packet Switching Ø data sent out of sequence Ø small chunks (packets) of data at a time Ø packets passed from node to node between source and destination Ø used for terminal to computer and computer to computer communications

Frame Relay Ø packet switching systems have large overheads to compensate for errors Ø modern systems are more reliable Ø errors can be caught in end system Ø Frame Relay provides higher speeds Ø with most error control overhead removed

Asynchronous Transfer Mode Ø ATM Ø evolution of frame relay Ø fixed packet (called cell) length Ø with little overhead for error control Ø anything from 10 Mbps to Gbps Ø constant data rate using packet switching technique with multiple virtual circuits

Local Area Networks Ø smaller scope l Building or small campus Ø usually owned by same organization as attached devices Ø data rates much higher Ø switched LANs, eg Ethernet Ø wireless LANs

Metropolitan Area Networks Ø MAN Ø middle ground between LAN and WAN Ø private or public network Ø high speed Ø large area

The Internet Ø Internet evolved from ARPANET l l first operational packet network applied to tactical radio & satellite nets also had a need for interoperability led to standardized TCP/IP protocols

What is the Internet Ø Collection of networks connected together using common software Ø Although network technologies differ, any computer can communicate with any ither computer

Internet Elements Host, routers, switch, etc

Internet Architecture

Example Configuration

Summary Ø introduced data communications needs Ø communications model Ø defined data communications Ø overview of networks Ø introduce Internet