Data Communication Data Communications Data communication system components

Data Communication

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

Data Communication Modems q A computers voice is digital; that is, it consists of on/off pulses representing 1 s and 0 s. q A device called modem (short for modulatordemodulator) is needed to translate these digital signals into analog signals that can travel over standard telephone lines. q In its modulation phase, the modem turns the computers digital signals into analog signals, which are then transmitted across the telephone line. q 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. Uploading Downloading 4

Using Digital Data Connections 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. Some of the better known are called integrated services digital network (ISDN), T 1(1. 544 Mbps), T 3(44. 736 Mbps), DSL, cable modems, and ATM (Asynchronous transfer mode). 5

Wireless Networks Wireless: 802. 11 q The wireless standard that is becoming popular follows the family of specifications called 802. 11 or Wi-Fi. q The 802. 11 b standard describes specification for wireless speeds upto 11 Mbps, which is a little faster than the slowest form of Ethernet(10 Mbps) but much faster than the typical 1. 5 Mbps high end DSL connection. q The 802. 11 g standard describes specification for wireless LANs that provide 20+ Mbps connection speed. 6

Wireless Networks Wireless Access Point q. Wireless firewall switch router Wireless Adapter q. Wireless adapter card (wireless NIC) 7

Data Communications n Protocol A set of rules that govern the data communication. n Without a protocol, devices may be connected but not communicating. 8

Data Communications Mode Data flow between two devices can occur in 3 ways n Simplex The communication is unidirectional (i. e. on one way). One sends and the other only receives. n Ex. : Keyboards and traditional monitors, television broadcasting n Half-Duplex Each station can both transmit and receive but not at the same time. n n Ex. : Walkie-talkies Full-Duplex Both stations can transmit and receive simultaneously. n Ex. : Telephone network 9

Data Communications 10

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: n n Asynchronous transmission Synchronous transmission 11

Asynchronous Transmission Also called start/stop transmission n n Start bit transmitted at the beginning of each group of bits Stop bit sent at end of each group Data is transmitted one byte at a time 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 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 2. Unguided Media 14

Communications Media Guided /Bounded Media: Communication devices are directly linked with each other via cables or physical media i. e. n n n Wire pairs Coaxial cables Fiber optics Unguided /unbounded /Wireless Media Data is communicated between communicating devices in the form of wave n Microwave transmission n Satellite transmission 15

Guided Media : Wire Pairs Also known as twisted pair n Two wires twisted around each other to reduce electrical interference Inexpensive It is used for short distance data communication. Easily affected by electromagnetic waves and noise n Noise - anything that causes signal distortion 16

Coaxial Cable Coaxial cable consists of a copper wire 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 lost. 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 only has to be converted into light 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 n It means signals travel in straight line and cannot bend Requires microwave stations approximately every 20 -30 miles Offers high speed transmission Susceptible to weather conditions 19

Satellite Transmission A form of microwave transmission n Satellite acts as relay station Components n n Earth station sends and receives signal to satellite 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. 20

3 G -4 G 3 G phones, are supposed to send and receive voice and data at speed of up to 2 megabits per second eventually, which is similar to rates offered by broadband internet connections. Hewlett-Packard is already looking beyond 3 G to 4 G wireless technology. Its partner in this endeavor is NTT Do. Co. Mo Inc. , a unit of Japanese company Nippon Telephone & Telegraph Corp. Do. Co. Mo has become famous for helping to raise interest in 3 G with its commercially popular “i-mode” platform. This is a widely successful service in Japan that features an always on connection and delivery of all kinds of internet data from news to games to music.

3 G -4 G Among the 4 G issues H-P scientists are tackling, according to one account, are scalable coding, error-resisting coding, and transcoding. Scalable coding is a way to code video streams to work on many different devices. Error-resisting coding prevents transmissions from breaking up. Transcoding is a process of converting compressed video to any playback format.

Rules of communications: Protocol - a set of rules for the exchange of data between a terminal and a computer or two computers n Agreement on how data is to be sent and receipt acknowledged n Needed to allow computers from different vendors to communicate n Transmission Control Protocol/Internet Protocol (TCP/IP) permits any computer to communicate with the Internet 23