Data Communication

2 Data Communications Data communication system components: Message Message Information (data) to be communicated. Sender Sender Device that sends the data message. A computer, video camera, or any other device that can be connected to network etc. A computer, video camera, or any other device that can be connected to network etc. Receiver Receiver Device that receives the data message. A computer, a Television, etc. A computer, a Television, etc. Transmission medium Transmission medium The physical path by which a message travels from sender to receiver. Twisted pair, coaxial cable, optical fiber, radio waves. Twisted pair, coaxial cable, optical fiber, radio waves.

Data Communication Modems  A computers voice is digital; that is, it consists of on/off pulses representing 1s and 0s.  A device called modem (short for modulator- demodulator) is needed to translate these digital signals into analog signals that can travel over standard telephone lines.  In its modulation phase, the modem turns the computers digital signals into analog signals, which are then transmitted across the telephone line.  The reverse takes place during its demodulation phase, as the modem receives analog signals from the phone line and converts them into digital signals for the computer. 3

Uses for a modem File transfer is the process of exchanging files between computers, either through telephone lines or a network. UploadingDownloading 4

Broadband Connections The term broadband is used to describe any data connection that can transmit data faster than is possible through a standard dial up connection using a modem. Digital Subscriber Line (DSL) transmission speeds ranging from several hundred Kbps to millions of bits per second (Mbps) Digital Subscriber Line (DSL) transmission speeds ranging from several hundred Kbps to millions of bits per second (Mbps) Cable Modem transmission speeds of 1.5 Mbps or more. Cable Modem transmission speeds of 1.5 Mbps or more. Fiber speeds far exceeding current DSL or cable modem speeds, typically by tens or even hundreds of Mbps. Fiber speeds far exceeding current DSL or cable modem speeds, typically by tens or even hundreds of Mbps. Wireless Wireless speeds are comparable to DSL and cable modem speeds. Satellite receive (download) at a speed of about 500 Kbps and send (upload) at a speed of about 80 Kbps Satellite receive (download) at a speed of about 500 Kbps and send (upload) at a speed of about 80 Kbps Broadband over Power lines (BPL) Broadband over Power lines (BPL) speeds are comparable to DSL and cable modem speeds. 5

6 Data Communications Protocol Protocol A set of rules that govern the data communication. Without a protocol, devices may be connected but not communicating. Without a protocol, devices may be connected but not communicating.

7 Rules of communications: Protocol Protocol - a set of rules for the exchange of data between a terminal and a computer or two computers Agreement on how data is to be sent and receipt acknowledged Agreement on how data is to be sent and receipt acknowledged Needed to allow computers from different vendors to communicate Needed to allow computers from different vendors to communicate Transmission Control Protocol/Internet Protocol (TCP/IP) permits any computer to communicate with the Internet Transmission Control Protocol/Internet Protocol (TCP/IP) permits any computer to communicate with the Internet

8 Data Communications Mode Data flow between two devices can occur in 3 ways Simplex Simplex The communication is unidirectional (i.e. on one way). One sends and the other only receives. Ex.: Keyboards and traditional monitors, television broadcasting Ex.: Keyboards and traditional monitors, television broadcasting Half-Duplex Half-Duplex Each station can both transmit and receive but not at the same time. Ex.: Walkie-talkies Ex.: Walkie-talkies Full-Duplex Full-Duplex Both stations can transmit and receive simultaneously. Ex.: Telephone network Ex.: Telephone network

9 Data Communications

10 Coordinating sender and receiver device Coordinating sender and receiver device Sending data to remote location only works if receiving device is ready to accept it Two approaches to keeping devices in step: Asynchronous transmission Asynchronous transmission Synchronous transmission Synchronous transmission

11 Asynchronous Transmission Also called start/stop transmission Start bit transmitted at the beginning of each group of bits Start bit transmitted at the beginning of each group of bits Stop bit sent at end of each group Stop bit sent at end of each group Data is transmitted one byte at a time Data is transmitted one byte at a time Each group typically consists of one character Each group typically consists of one character Receiving device gets start signal and sets up mechanism to accept the group Used for low-speed communications

12 Synchronous Transmission Large block of characters transmitted Data is transmitted block by block or word by word Error-check bits make sure all characters received Much faster, but equipment is more expensive

13 Communications Media Communications Media Physical means of data transmission from one place to another Bandwidth is measure of the capacity of the communications link Types of Communications Media 1.Guided Media 1.Guided Media 2.Unguided Media 2.Unguided Media

14 Communications Media Guided /Bounded Media: Communication devices are directly linked with each other via cables or physical media i.e. Communication devices are directly linked with each other via cables or physical media i.e. Wire pairs Wire pairs Coaxial cables Coaxial cables Fiber optics Fiber optics Unguided /unbounded /Wireless Media Data is communicated between communicating devices in the form of wave Data is communicated between communicating devices in the form of wave Microwave transmission Microwave transmission Satellite transmission Satellite transmission

15 Guided Media : Wire Pairs Also known as twisted pair Two wires twisted around each other to reduce electrical interference Two wires twisted around each other to reduce electrical interferenceInexpensive It is used for short distance data communication. Easily affected by electromagnetic waves and noise Noise - anything that causes signal distortion Noise - anything that causes signal distortion

16 Coaxial Cable Coaxial cable consists of a copper wire core covered by insulating material. The insulated copper wire is covered by copper mesh. It protects the cable from electromagnetic waves. It is used for long distance data communication. It is more expensive than wire cable. Commonly used to connect to cable TV Higher bandwidth and less effected to noise than twisted pair

17 Fiber Optics It is also known as light pulse media. It is made up of thin glass fiber. It is thinner than a human hair. Data transfer rate of fiber optics is very fast. There is no chance of data loss. An important characteristics of fiber optics is refraction. Refraction is a characteristics of a material to either pass or reflect light. The advantage of fiber optic is that the data has to be converted into light only because it is already in binary form. It is very expensive and difficult to install. Use light instead of electricity to send data Much higher bandwidth than coaxial cable Immune to electrical interference It is very expensive and difficult to install

18 Microwave Transmission Microwaves are radio waves that are used to provide high-speed transmission Uses line-of-sight transmission of data signals It means signals travel in straight line and cannot bend It means signals travel in straight line and cannot bend Requires microwave stations approximately every miles Offers high speed transmission Susceptible to weather conditions

19 Satellite Transmission A form of microwave transmission Satellite acts as relay station Satellite acts as relay stationComponents Earth station sends and receives signal to satellite Earth station sends and receives signal to satellite Transponder receives and amplifies signal, changes frequency, and retransmits data Transponder receives and amplifies signal, changes frequency, and retransmits data Useful when signal must travel thousands of miles A large volume of data can be communicated at once. The disadvantage is that bad weather can affect the quality of satellite transmission.

Wireless Networks Wireless:  The wireless standard that is becoming popular follows the family of specifications called or Wi-Fi.  The b standard describes specification for wireless speeds upto 11 Mbps, which is a little faster than the slowest form of Ethernet(10Mbps) but much faster than the typical 1.5Mbps high end DSL connection.  The g standard describes specification for wireless LANs that provide 20+ Mbps connection speed. 20

Wireless Networks Wireless Access Point Wireless access points (WAPs) are specially configured nodes on wireless local area networks (WLANs). Access points act as a central transmitter and receiver of WLAN radio signals. Access points used in home or small business networks are generally small, dedicated hardware devices featuring a built-in network adapter, antenna, and radio transmitter. Access points support Wi-Fi wireless communication standards. 21