Chapter 1 Data Communications and Networks - Overview Data Communications deals with the transmission of signals in a reliable and effective manner. Topics covered include signal transmission, transmission media, signal encoding, interfacing, data link control, and multiplexing. Networking deals with the technology and architecture of the communication networks used to interconnect communicating devices (entities). Topics include LANs, WANs.

Data Communications between two devices Networks provide networking services between two entities The communications between two end-points uses Protocol

1.1 A Communications Model  Source Generates (binary) data to be transmitted  Transmitter Converts data into transmittable electromagnetic signals  Transmission system This can be a single transmission line or a complex network  Receiver Converts received signal into data  Destination Takes incoming data pp

Simplified Communications Model - Diagram p. 11

Communications Tasks Transmission system utilizationAddressing InterfacingRouting Signal generationRecovery SynchronizationMessage formatting Exchange managementSecurity Error detection and correctionNetwork management Flow control p. 12

1.2 Data Communications p. 13

1.3 Data Communication Networking  Point to point communication not usually practical Devices are too far apart Large set of devices would need impractical number of connections  Solution is a communications network Wide Area Network (WAN) Local Area Network (LAN) p. 14

Wide Area Networks  Large geographical area  Crossing public rights-of-ways  Rely in part on common carrier circuits  Alternative technologies Circuit switching Packet switching Frame relay Asynchronous Transfer Mode (ATM) pp

Circuit Switching  Dedicated communications path established for the duration of the conversation  Data transmission is rapid, without delay  This kind of switching is good for real-time services  The typical network which adopts this kind of switching is telephone network p. 15

Packet Switching  Data sent out of sequence  Small chunks (packets) of data at a time  Packets passed from node to node between source and destination  At each node, the entire packet is received, stored briefly, and then transmitted to the next node  Used for terminal to computer and computer to computer communications  There are two kinds of packet switching: Virtual circuit and datagram p. 15

 Packet switching systems have large overheads to compensate for errors  Modern systems are more reliable  Errors can be caught in the end system  Most overhead for error control is stripped out  Developed to take advantage of high data rates and low error rates p. 15 Frame Relay

Asynchronous Transfer Mode  ATM  Evolution of frame relay  Little overhead for error control  Fixed packet (called cell) length  Anything from 10 Mbps to Gbps  Constant data rate using packet switching technique p. 16

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 p. 16

LAN Configurations  Switched Switched Ethernet May be single or multiple switches ATM LAN Fibre Channel  Wireless Mobility Ease of installation pp

Metropolitan Area Networks  MAN  Middle ground between LAN and WAN  Private or public network  High speed  Large area p. 17

1.4 Networking Configuration p. 18

Standards  Required to allow for interoperability between equipments  Advantages Ensures a large market for equipment and software Allows products from different vendors to communicate  Disadvantages Freeze technology May be multiple standards for the same thing pp. 4-5

Standards Organizations  Internet Society  IEEE 802  ISO  ITU-T (formally CCITT)  ATM forum p. 5

Further Reading  Stallings, W. [2003] Data and Computer Communications (7th edition), Prentice Hall, Upper Saddle River NJ, chapter 1  Web site for Stallings book