DATA COMMUNICATION AND NETWORKING Chapter 12

Communication sending or receiving information Beating of drums Mirrors reflecting sunlight Homing pigeons Telegraph, telephone Computers … Data Communication

DATA COMMUNICATION Exchange of data between two devices wired or wireless transmission medium Communication system (collection of hardware, software …) Transfer of dataMethod of transfer Preservation of the data during the transfer process Delivery The system must deliver data to the correct or the intended destination. Accuracy The system must deliver data accurately (error free). Timeliness The system must deliver data in a timely manner without enough time lags.

Five components of a data Communication System 1. Message It is the information to be communicated. Popular forms of information include text, pictures, audio, video etc. 2. Sender It is the device which sends the data messages. It can be a computer, workstation, telephone handset etc. 3. Receiver It is the device which receives the data messages. It can be a computer, workstation, telephone handset etc. 4. Transmission Medium It is the physical path by which a message travels from sender to receiver. Some examples include twisted-pair wire, coaxial cable, radio-waves etc. 5. Protocol It is a set of rules that governs the data communications. It represents an agreement between the communicating devices. Without a protocol, two devices may be connected but not communicating.

Data Transmission Modes Data in a simplex channel is always one way. Simplex channels are not often used because it is not possible to send back error or control signals to the transmit end. An example of a simplex channel in a computer system is the interface between the keyboard and the computer, in that key codes need only be sent one way from the keyboard to the computer system. Simplex A half duplex channel can send and receive, but not at the same time. Its like a one-lane bridge where two way traffic must give way in order to cross. Only one end transmits at a time, the other end receives. Half Duplex Data can travel in both directions simultaneously. There is no need to switch from transmit to receive mode like in half duplex. Its like a two lane bridge on a two-lane highway. Full Duplex

Analog & Digital Transmission information changes continuously and can take on many different values. An analog clock’s hands move constantly, displaying time on a continuous scale. Analog information is characterized by discrete states. A light bulb, for example, is on or off. A digital clock represents the time in one- minute intervals and doesn’t change its numbers again until the next minute. A digital clock can represent exact minutes but not the seconds that pass in between. Digital

Analog & Digital Transmission … Analog Signals- Sine waves Amplitude Frequency Wavelength Digital

Data Communication Measurement Narrowband Services 64 Kbps or less channels Wideband Services 1.5 Mbps to 45 Mbps (North American) 2 Mbps to 34 Mbps (International) Broadband Services 45 Mbps or greater (North American) 34 Mbps or greater (International) It Changes

Transmission Media

Radio Frequency Propogation

Modulation

Multiplexing

Multiplexing …

Synchronization- Controlling time Asynchronous Transmission Each character of data is treated independently Synchronous Transmission For sending large blocks of data Control schemes Character-oriented Bit-oriented 6.17

Switching 4 Employee Office Direct Lines to each of them! Point to point communication Impractical & Wasteful Route calls by making temporary connection!

Use Switches or Exchanges Some switches are directly connected to a comminication device while others are dedicated to route/forward information

Circuit switching Major Attributes Dedicated fixed BW channel Data (sent/received) path is determined by the circuit Data path does not change within the lifetime of connection Simple method. Used in Public Service Telephone Network (PSTN) Disadvantage? Waste when there is no data flowing Cannot change the circuit after it is established even if there are other (cheaper) routes possible

Packet Switching Major Attributes Focuses on data communication (vs. voice) Break data into packets Package Assembler and Disassembler (PAD) Packets from a single message will not necessarily follow the same route Packet Header Destination Priority … Packet Switching Exchange (PSE) Efficient? “Message Switching” is obsolete

Computer Network Standalone versus Networked Environment How can we connect (physically)? Network Operating Systems Manage multiple computers on a network Client/Server (NOS) Client request and server serves Access to resources Peer to peer network (NOS?) Equal peer nodes Both server & client Music/File sharing!

Client/Server How it works Client sends request for service to server Server fulfills request and send results to client Client and server may share processing Benefits Reduces volume of data traffic Allows faster response for each client Nodes can be less expensive computers

AttributeP2PClient/Server Centralization of resource and data NoYes Maintenance costLowHigh Needs staffs, support Installation ProcessSimpleRequires experts CostLow- no dedicated serverRequires a dedicated server SecurityLowHigh ReliabilityHigh- all independent nodes Server down- network down Standalone Vs. Networked Environment Topology – Physical layout of components

Computer Network LAN MAN WAN CAN

LAN- Local Area Network Connections over short distances through communications media Connecting LANs Bridge – connects networks with similar protocols Router – directs traffic via best path IP switches Replacing routers Less expensive Faster Gateway Connects LANs with dissimilar protocols Performs protocol conversion Components PCs Network cable NIC

WAN- Wide Area Network Link computers in geographically distant locations

Network Topology Bus topology Ring topology Star topology Tree topology Mesh topology Check the textbook

OSI Model Textbook P 445

Network Devices NIC Repeater Hub Bridge Switch Router Gateway P449