Data and Computer Communications Chapter 1 Data Communications

Data and Computer Communications Chapter 1 – Data Communications, Data Networks, and the Internet Eighth Edition by William Stallings Lecture slides by Lawrie Brown

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

Data Communications, Data Networks, and the Internet Ø Data communications l deals with the transmission of signals in a reliable and efficient manner. Ø Networking l deals with the technology and architecture of the communications networks used to interconnect communicating devices.

Data Communications, Data Networks, and the Internet Ø The computer communications revolution has produced several remarkable facts: l l l There is no fundamental difference between data processing (computers) and data communications (transmission and switching equipment). There are no fundamental differences among data, voice, and video communications. The distinction among single-processor computer, multiprocessor computer, local network, metropolitan network, and long-haul network has blurred.

Contemporary Data Comms Ø Effective and efficient data communication and networking facilities are vital to any enterprise. Ø Three different forces have consistently driven the architecture and evolution of data communications and networking facilities

Contemporary Data Comms Ø traffic growth at a high & steady rate l l l office automation remote access, Online transactions Ø development of new services l increases the demand for high-capacity networking and transmission facilities Ø advances in technology

Contemporary Data Comms 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

Internet Elements

Internet Architecture

Example Configuration

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