A classic example of a communication device is a computer modem, which converts a computer's digital information to an analog signal for transmission over a telephone line. Similarly, a modem receives analog signals, and converts them to digital, for processing by the computer. This process is called modulation/demodulation, from which the modem gets its name.
Communication device errors
Any time a communication device encounters problems communicating with another device, you may encounter a communication error. Below is a list of general steps that can be verified when this error is encountered. If your communication device uses a wire, make sure it is firmly connected.
Make sure the proper drivers are installed and that no errors or conflicts are occurring with the driver, and that the device is detected.
If your communication device requires settings, make sure they're correct. For example, a network card requires the proper IP, DNS, and Subnet settings to establish a connection with the network, and be able to find its route to other network devices.
Why do computers need communication devices?
A computer can work fine without a communication device. However, for a computer to communicate with other computers, they need a communication device. For example, for your computer to connect to the Internet to view this web page, it needs a communication device. Without a communication device, you'd have to use a sneaker net to transfer or share data between computers.
A communications device is any type of hardware capable of transmitting data, instructions, and information between a sending device and a receiving device. One type of communications device that connects a communications channel to a sending or receiving device such as a com- puter is a modem. Computers process data as digital signals. Data, instructions, and information travel along a communications channel in either analog or digital form, depending on the com- munications channel. An analog signal consists of a continuous electrical wave. A digital signal consists of individual electrical pulses that represent bits grouped together into bytes.
For communications channels that use digital signals (such as cable television lines), the modem transfers the digital signals between the computer and the communications channel. If a communications channel uses analog signals (such as some telephone lines), however, the modem first converts between analog and digital signals.
The following pages describe the following types of communications devices: dial-up modems, ISDN and DSL modems, cable modems, wireless modems, network cards, wireless access points, and routers.
Dial-Up Modems
As previously discussed, a computer’s digital signals must be converted to analog signals before they are transmitted over standard telephone lines. The communications device that performs this conversion is a modem, sometimes called a dial-up modem. The word, modem, is derived from the combination of the words, modulate, to change into an analog signal, and demodulate, to convert an analog signal into a digital signal.
A modem usually is in the form of an adapter card that you insert in an expansion slot on a com- puter’s motherboard. One end of a standard telephone cord attaches to a port on the modem card and the other end plugs into a telephone outlet.
ISDN and DSL Modems
If you access the Internet using ISDN or DSL, you need a communications device to send and receive the digital ISDN or DSL signals. An ISDN modem sends digital data and information from a computer to an ISDN line and receives digital data and information from an ISDN line. A DSL modem sends digital data and information from a computer to a DSL line and receives digital data and information from a DSL line. ISDN and DSL modems usually are external devices, in which one end connects to the telephone line and the other end connects to a port on the system unit.
Cable Modems
A cable modem is a digital modem that sends and receives digital data over the cable television (CATV) network (Figure 8-18). With more than 110 million homes wired for cable television, cable modems provide a faster Internet access alternative to dial-up for the home user and have speeds similar to DSL. Cable modems currently can transmit data at speeds that are much faster than either a dial-up modem or ISDN.
Wireless Modems
Some mobile users have a wireless modem that uses the cell phone network to connect to the Internet wirelessly from a notebook computer, a smart phone, or other mobile device (Figure 8-19). Wireless modems, which have an external or built-in antenna, are available as PC Cards, ExpressCard modules, and flash cards. Network Cards
A network card is an adapter card, PC Card, ExpressCard module, USB network adapter, or flash card that enables a computer or device that does not have networking capability to access a network. The network card coordinates the transmission and receipt of data, instructions, and information to and from the computer or device containing the network card.Network cards are available in a variety of styles (Figure 8-20). A network card for a desktop computer is an adapter card that has a port to which a cable connects. A network card for mobile computers and devices is in the form of a PC Card, ExpressCard module, USB network adapter, or a flash card. Network cards that provide wireless data transmission also are available. This type of card, sometimes called a wireless network card, often has an antenna.
A network card follows the guidelines of a particular network communications standard, such as Ethernet or token ring. An Ethernet card is the most common type of network card.
A wireless access point is a central communications device that allows com- puters and devices to transfer data wirelessly among themselves or to transfer data wire- lessly to a wired network (Figure 8-7 on page 303). Wireless access points have high-quality antennas for optimal signals.
Routers
A router is a communications device that connects multiple computers or other routers together and transmits data to its correct desti- nation on the network. A router can be used on any size of network. On the largest scale, routers along the Internet backbone forward data packets to their destination using the fastest available path. For smaller business and home networks, a router allows multiple computers to share a single high-speed Internet connection such as a cable modem or DSL modem (Figure 8-21). These routers connect from 2 to 250 computers.
To prevent unauthorized users from accessing files and computers, many routers are protected by a built-in firewall, called a hardware firewall. Some also have built-in antivirus protection. Today’s routers or combination wireless access point/routers are easy to configure and secure against unauthorized access.
Identify and explain types of communication devices
PDA’s
PDA stands for personal digital assistant. PDA’s are like hand held computers. PDA’s are used as mobile phones, they are used for e-mail, web browsing and as media players. PDA’s are touch screen devices and the only keypad is built into the device.
Wireless Network Interface Card
Wireless NIC’s are network cards that connect to computer networks. These computer networks are radio based. Regular NIC’s 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 don’t 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.
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