Data Communications and Networking Overview Chapter 1 Data Communications and Networking Overview Data Communication

A Communications Model Key elements of a simple model of communications: (Purpose: the exchange of data between two parties) Source generates data to be transmitted (e.g. telephones & PCs) Transmitter Converts data into transmittable electromagnetic signals Transmission System Carries data (single transmission line or network) Receiver Converts received signal into data Destination Takes incoming data Data Communication

Simplified Communications Model - Diagram TUNALI Data Communication

Communications Tasks Transmission system utilization Make efficient use of transmission facilities Interfacing A device must interface to cummunicate Signal generation Capable of being propagated through the transmission system, interpretable as data at the receiver Synchronization The receiver must be able to determine when a signal begins to arrive and when it ends Exchange management The two parties must cooperate (transmit simultaneously or take turn, data format) Error detection and correction In all communications systems, there is a potential for error Data Communication

Communications Tasks Flow control Sending data faster than destination can be processed Addressing Only intended destination system must receive the data Routing Specific route through the network Recovery Resume activity at the point of interruption or restore the state Message formatting Form of the data to be exchanged Security Receiver may wish the data have not been altered in transit, .. Network management Configuring the system, monitoring its status Data Communication

Simplified Data Communications Model

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) Data Communication

Wide Area Networks Large geographical area Crossing public rights of way Consists of a number of interconnected switching nodes Alternative technologies Circuit switching Packet switching Frame relay Asynchronous Transfer Mode (ATM) Data Communication

Circuit Switching Dedicated communications path established for the duration of the conversation Path: a connected sequence of physical links between nodes e.g. telephone network Data Communication

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 Used for terminal to computer and computer to computer communications Data Communication

Frame Relay Packet switching systems have large overheads to compensate for errors Modern systems are more reliable Errors can be caught in end system Most overhead for error control is stripped out Data Communication

Asynchronous Transfer Mode ATM Evolution of frame relay Little overhead for error control Fixed packet (called cell) length Constant data rate using packet switching technique (by using small – fixed sized cells) By using a fixed packet length, the processing overhead is reduced Data Communication

Local Area Networks Smaller scope Building or small campus Usually owned by same organization as attached devices There may be a substantial capital invesment for both purchase and maintenance One user for network management responsibility Data rates much higher Data Communication

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

Metropolitan Area Networks MAN Middle ground between LAN and WAN Private or public networks that provide high capacity at low costs Large area Data Communication

Networking Configuration Data Communication

Further Reading Stallings, W. Data and Computer Communications (7th edition), Prentice Hall, Upper Saddle River NJ, chapter 1 Data Communication