Types of communication devices

Types of communication devices Task 1a Identify and explain types of communication devices PDAs PDA stands for personal digital assistant. PDAs are like hand held computers. PDAs are used as mobile phones, they are used for e-mail, web browsing and as media players. PDAs are touch screen devices and the only keypad is built into the device. Wireless Network Interface Card Wireless NICs are network cards that connect to computer networks. These computer networks are radio based. Regular NICs connect wired through Ethernet cables. Wireless network interface cards work in modes: infrastructure and ad hoc. When using infrastructure mode, you need an access point to connect to. When using ad hoc mode you do not need to connect to an access point, instead you connect to other wireless devices. However, you need to be using the same channel and the same SSID. Switches Switches send packets to different IP addresses. Switches are an important part of a network because they speed things up. Switches allow direct communication between computers efficiently. LAN switches create a series of networks that only contain two devices. Routers Routers connect multiple devices to the internet at the same time. A router is a network device that forwards information. It can connect two or more logical subnets to the interface of the router. These subnets are not always mapped one to one. Routers store MAC addresses from computers that have used it to get on the internet. Bridges A network bridge connects network segments together. Network bridges are like network hubs because they connect network segments at the physical layer; however network bridges analyse data packets on other segments of the network. A bridge processes the information it receives and then works out the MAC address using the bridge. Computers A computer is a machine that follows instructions to manipulate data. Computers are very versatile because they have a lot of programs on them which make them different from calculators. As long as a computer has enough storage capacity and time it can out any computational task, no matter how large the task. Wireless keyboard and Mouse A wireless keyboard connects to the computer by using infrared or Bluetooth signals. An infrared wireless keyboard requires the signal from the keyboard to the computer to be in a straight line for the signal to reach the computer properly. Wireless mice work in the same way. They use infrared radio frequency signals to connect with the computer. Printers In laser printers, they scan the paper to make sure that the paper is in correctly. Then the print on the ink on the paper one line at a time until the print job is finished. All other printers work in the same way. Mobile phone with WAP Mobile phones that have WAP enabled allow users to browse the internet on their phone. It lets users use the phone like a computer and only lets users download music, videos and browse headlines. Radio A walkie talkie works on a half duplex transmission. It allows people to communicate from a distance. However, it only allows people to talk one at a time. Also other people with other walkie talkies can listen in on conversations. GPS (SAT NAV) GPS stands for global positioning system. There lots of satellites that transmit signals to the ground. GPS devices do not transmit signals they only receive them. To work well GPS devices require a clear sky and dont work well in forested areas. WI FI Wireless networks use radio waves like radios and mobile phones. Devices using wireless internet receive radio waves and internet connection. Wireless routers translate data into radio signals and send it to devices using the router to get on the internet. Chapter 2 Simplex Simplex transmission either sends or receives data. It allows transmission in one direction. Half duplex Half duplex transmission allows two people to communicate with each other. However, it only allows one person to speak at a time. Full duplex Full duplex transmission allows two people two communicate at the same and lets them both talk at the same time. Serial Serial data travels one bit at a time. It travels through data cables in straight lines, like single file. The data travels quickly because it travels one bit at a time. Parallel Parallel data travels simultaneously eight bits at a time. This can be faster than simplex transmission as parallel travels more bits at a time. However, it can also be slower than serial at times because parallel transmission needs wider cables to travel at its fastest speed. Infra-red Infrared radiation is electromagnetic. Infrared waves travel at a frequency that makes it invisible the naked eye. This is because its wavelength is larger than light. But its wavelength is less than microwaves. Radio link A radio link is a two way system of communication. A radio link is used to provide control over two different points from a distance. They send and receive radio waves. Laser Laser stands for light amplification by stimulated emission of radiation. It emits light using a process called stimulated emission within the electromagnetic radiation. The light that a laser emits is a narrow low-divergence beam. Optical lenses are used to convert these beams. Bandwidth Bandwidth travels in bits. Different bandwidths travel at different rates. Bandwidth is what is used to connect to the internet. Every internet connection has a bandwidth capacity and is measured in hertz. Synchronous Synchronous transmission synchronises transmission speeds when sending and receiving at each end of the transmission clock. Data is constantly streamed into both ends of the transmission clock and does not start and stop. Asynchronous Unlike synchronous transmission, asynchronous transmission starts and stops. Asynchronous transmission allows data to travel ten bits at a time. It adds a one or a zero to the start and end of a binary code. The first added digit is to let the transmission know data is coming through and the other at the end of the code is to let the transmission know that the code has ended. Digital Digital system technology uses discontinuous values. The discontinuous values include numbers, letters and icons. It also uses continuous values which include sounds and images. Analogue Analogue data travels in continuous streams. Analogue is more accurate than digital because digital uses ones and zeros which means they can only approximate audio and video signals. Error detection and correction There are several techniques that can be used to reduce data transmission errors: Parity checking and CRC are a couple of techniques. Parity checking Parity checking uses a parity bit. This is a bit that is added to a number of bits with the value one to make sure that it is odd or even. There are two parity bits: even and odd. When even, the parity bit is set to one if the total amount of ones is odd therefore making it even. When using an odd parity bit the parity bit is set to one if the amount of ones is even therefore making the amount odd. CRC CRC is a non secure hash function. CRC detects changes to raw computer data. A CRC enabled device calculates a short fixed binary sequence for each block of data. It sends or receives them at the same time. The device repeats the calculation when a block is sent or received and contains a data error if the result does not match. Chapter 3 TCP/IP Tcp/ip stands for internet protocol suite. The internet protocol suite is made up of a set of protocols that can be used on a computer network. Tcp/ip is made up of layers. These layers are the link layer, the internet layer, the transport layer and the application layer. SMTP SMTP stands for simple mail transfer protocol. The SMTP is what transfers the email data from one computer to another. The SMTP body is the entire message and is different from the message body. FTP FTP works similar to web pages. Every FTP server file is given a url so other computers ca find it when they are connected to the internet. Users can use web browsers or FTP clients to upload and download files. UPnP UPnP is used as a way of automatically forwarding ports so people dont have to do it manually. UPnP stands for universal plug and play. The goal of UPnP is to allow devices to connect to the internet effortlessly and simplify installation of devices and networks. Bluetooth Bluetooth is an open wireless protocol. It allows data exchange over a short distance. The data is transferred using radio waves from stationary mobile devices. This creates personal area networks. Stationary Bluetooth mobile devices can connect to multiple devices at a time, avoiding synchronisation problems.