1. What Is the Purpose of the Components Required for Successful Communications, and What Are Various Sending and Receiving Devices?
Computer communications describes a process in which two or more computers or devices transfer data, instructions, and information. Today, even the smallest computers and devices can communicate directly with one another, with hundreds of computers on a company network, or with millions of other computers.
For successful communications, you need the following:
• A sending device that initiates an instruction to transmit data, instructions, or information.
• A communications device that connects the sending device to a communications channel.
• A communications channel, or transmission media on which the data, instructions, or information travel.
• A communications device that connects the communications channel to a receiving device.
• A receiving device that accepts the transmission of data, instructions, or information.
Some devices that serve as sending devices and receiving devices are
(a) mainframe computers,
(b) servers,
(c) desktop computers,
(d) notebook computers,
(e) smart phones,
(f) Internet-enabled portable media players,
(g) handheld game consoles, and
(h) GPS receivers.
The communications channel consists of telephone and power lines, cable television and other underground lines, microwave stations, and satellites.
2. How Are Computer Communications Used?
Computer communications are everywhere. Many require that users subscribe to an Internet access provider. With other computer communications, an organization such as a business or school provides communications services to employees, students, or customers.
The following pages discuss a variety of computer communications. Communications technologies include blogs, chat rooms, e-mail, fax, FTP, instant messaging, newsgroups, RSS, video conferencing, VoIP, Web, Web folders, and wikis. Users can send and receive wireless messages to and from smart phones, cell phones, handheld game consoles, and other mobile devices using text messaging, picture messaging and video messaging, and wireless instant messaging. People connect wirelessly to the Internet through a wireless Internet access point. A hot spot is a wireless network that provides Internet connections to mobile computers and devices. A cybercafé is a coffeehouse, restaurant, or other location that provides computers with Internet access. A global positioning system (GPS) analyzes signals sent by satellites to determine an earth-based receiver’s geographic location. Many software products provide a means to collaborate, or work online with other users connected to a server. Groupware is software that helps groups of people work on projects or share information over a network.
Voice mail allows someone to leave a voice message for one or more people. Web services describe standardized software that enables programmers to create applications that communicate with other remote computers.
3. What Are the Advantages of Using a Network, and How Are LANs, MANs, and WANs Different?
a network is a collection of computers and devices connected together via communications devices and transmission media. Many businesses network their computers together to facilitate communications, share hardware, share data and information, share software, and transfer funds.
• Facilitating communications — Using a network, people communicate efficiently and easily via e-mail, instant messaging, chat rooms, blogs, wikis, online social networks, video telephone calls, online meetings, video conferencing, VoIP, wireless messaging services, and groupware.
• Sharing hardware — In a networked environment, each computer on the network can have access to hardware on the network. Business and home users network their hardware to save money.
• Sharing data and information — In a networked environment, any authorized computer user can access data and information stored on other computers on the network.
• Sharing software — Users connected to a network have access to software on the network.
To support multiple users’ access of software, most vendors sell network versions or site licenses of their software, which usually cost less than buying individual copies of the software for each computer.
• Transferring funds — Called electronic funds transfer (EFT ), it allows users connected to a network to transfer money from one bank account to another via transmission media.
LANs, MANs, and WANs
Networks usually are classified as a local area network, metropolitan area network, or wide area network. The main differentiation among these classifications is their area of coverage.
· LAN (local area network) is a network that connects computers and devices in a limited geographical area such as a home, school computer laboratory, office building, or closely positioned group of buildings. Each computer or device on the network, called a node, often shares resources such as printers, large hard disks, and programs.Often, the nodes are connected via cables.
· MAN (metropolitan area network) is a high-speed network that connects local area networks in a metropolitan area such as a city or town and handles the bulk of communications activity across that region. A MAN typically includes one or more LANs, but covers a smaller geographic area than a WAN. A MAN usually is managed by a consortium of users or by a single network provider that sells the service to the users. Local and state governments, for example, regulate some MANs. Telephone companies, cable television operators, and other organizations provide users with connections to the MAN.
· WAN (wide area network) is a network that covers a large geographic area (such as a city, country, or the world) using a communications channel that combines many types of media such as telephone lines, cables, and radio waves (Figure 9-12). A WAN can be one large network or can consist of two or more LANs connected together. The Internet is the world’s largest WAN.
4. How Are a Client/Server and Peer-to-Peer Network Different, and How Does a P2P Network Work?
· Client/Server
On a client/server network, one or more computers act as a server, and the other computers on the network request services from the server. A server, sometimes called a host computer, controls access to the hardware, software, and other resources on the network and provides a centralized storage area for programs, data, and information. The clients are other computers and mobile devices on the network that rely on the server for its resources. For example, a server might store a database of customers. Clients on the network (company employees) access the customer database on the server.
· Peer-to-Peer
One type of peer-to-peer network is a simple, inexpensive network that typically connects fewer than 10 computers. Each computer, called a peer, has equal responsibilities and capabilities, sharing hardware (such as a printer), data, or information with other computers on the peer-to-peer network. Each computer stores files on its own storage devices. Thus, each computer on the network contains both the server operating system and application software. All computers on the network share any peripheral device(s).attached to any computer. For example, one computer may have a laser printer and a scanner, while another has an ink-jet printer and an external hard disk. Peer-to-peer networks are ideal for very small businesses and home users.
· Another type of peer-to-peer, called P2P, describes an Internet network on which users access each other’s hard disks and exchange files directly over the Internet. This type of peer-to peer network sometimes is called a file sharing network because users with compatible software and an Internet connection copy files from someone else’s hard disk to their hard disks. As more users connect to the network, each user has access to shared files on other users’ hard disks. When users log off the network, others no longer have access to their hard disks.
5. How Are a Star Network, Bus Network, and Ring Network Different?
· Star Network
On a star network, all of the computers and devices (nodes) on the network connect to a central device, thus forming a star. Two types of devices that provide a common central connection point for nodes on the network are a hub and a switch. All data that transfers from one node to another passes through the hub or switch. Star networks are fairly easy to install and maintain. Nodes can be added to and removed from the network with little or no disruption to the network. On a star network, if one node fails, only that node is affected. The other nodes continue to operate normally. If the hub or switch fails, however, the entire network is inoperable until the device is repaired. Most large star networks, therefore, keep backup hubs or switches available in case the primary one fails.
· Bus Network
A bus network consists of a single central cable, to which all computers and other devices connect. The bus is the physical cable that connects the computers and other devices. The bus in a bus network transmits data, instructions, and information in both directions. When a sending device transmits data, the address of the receiving device is included with the transmission so that the data is routed to the appropriate receiving device. Bus networks are popular on LANs because they are inexpensive and easy to install. One advantage of the bus network is that computers and other devices can be attached and detached at any point on the bus without disturbing the rest of the network.
· Ring Network
On a ring network, a cable forms a closed loop (ring) with all computers and devices arranged along the ring. Data transmitted on a ring network travels from device to device around the entire ring, in one direction. When a computer or device sends data, the data travels to each computer on the ring until it reaches its destination. If a computer or device on a ring network fails, the entire network potentially could stop functioning. A ring network can span a larger distance than a bus network, but it is more difficult to install. The ring topology primarily is used for LANs, but also is used in WANs.
6. What Are Various Network Communications Standards?
A network standard defines guidelines that specify the way computers access a medium, the type(s) of medium, the speeds on different types of networks, and the type of physical cable or wireless technology used. Network communications standards include the following. Ethernet specifies that no central computer or device on the network should control when data can be transmitted. Token ring requires devices to share or pass a special signal, called a token. TCP/IP divides data into packets. Wi-Fi identifies any network based on the 802.11 standards for wireless communications. Bluetooth uses short-range radio waves to transmit data. UWB specifies how two UWB devices use short-range radio waves to communicate at high speeds. IrDA transmits data wirelessly via infrared light waves. RFID uses radio signals for communications. WiMAX is a network standard developed by IEEE that specifies how wireless devices communicate over the air in a wide area. The Wireless Application Protocol (WAP) specifies how some mobile devices can display Internet content.
7. What Is the Purpose of Communications Software?
Communications software consists of programs that (1) help users establish a connection to another computer or network; (2) manage the transmission of data, instructions, and information; and (3) provide an interface for users to communicate with one another. The first two are system software and the third is application software. Chapter 3 presented a variety of examples of application software for communications: e-mail, FTP, Web browser, newsgroup/message boards, chat rooms, instant messaging, video conferencing, and VoIP. Sometimes, communications devices are preprogrammed to accomplish communications tasks. Other communications devices require separate communications software to ensure proper transmission of data. Communications software works with the network standards and protocols just discussed to ensure data moves through the network or the Internet correctly. Communications software usually is bundled with the operating system or purchased network devices. Communications software helps users establish a connection to another computer or network; manages the transmission of data, instructions, and information; and provides an interface for users to communicate with one another.
8. What Are Various Types of Lines for Communications over the Telephone Network?
· Dial-Up Lines
A dial-up line is a temporary connection that uses one or more analog telephone lines for communications. A dial-up connection is not permanent. a dial-up line to connect computers costs no more than making a regular telephone call.
· Dedicated Lines
Satellite local access area local telephone company A dedicated line is a type of always on connection that is established between two communications devices (unlike a dial-up line where the connection is reestablished each time it is used). The quality and consistency of the connection on a dedicated line are better than a dial-up line because dedicated lines provide a constant connection. Businesses often use dedicated lines to connect geographically distant offices. Dedicated lines can be either analog or digital. Digital lines increasingly are connecting home and business users to networks around the globe because they transmit data and information at faster rates than analog lines. Five types of digital dedicated lines are ISDN lines, DSL, FTTP, T-carrier lines, and ATM.
· ISDN Lines
For the small business and home user, an ISDN line provides faster transfer rates than dial-up telephone lines. Not as widely used today as in the past, ISDN (Integrated Services Digital Network) is a set of standards for digital transmission of data over standard copper telephone lines. With ISDN, the same telephone line that could carry only one computer signal now can carry three or more signals at once through the same line, using a technique called multiplexing.
· DSL
DSL is a popular digital line alternative for the small business or home user. DSL (Digital Subscriber Line) transmits at fast speeds on existing standard copper telephone wiring.
Some DSL installations include a dial tone, providing users with both voice and data communications. These DSL installations often require that filters be installed to reduce noise interference when voice communications share the same line. ADSL is one of the more popular types of DSLs. As shown in Figure 9-25, ADSL (asymmetric digital subscriber line) is a type of DSL that supports faster transfer rates when receiving data (the downstream rate) than when sending data (the upstream rate). ADSL is ideal for Internet access because most users download more information from the Internet than they upload.
· FTTP
FTTP, which stands for Fiber to the Premises, uses fiber-optic cable to provide extremely high-speed Internet access to a user’s physical permanent location. Two specific types of FTTP are FTTH and FTTB. FTTH (Fiber to the Home) provides home users with Internet access via fiber-optic cable. Similarly, FTTB (Fiber to the Building) refers to small businesses that use fiber-optic cables to access the Internet. With FTTP service, an optical terminal at your location receives the signals and transfers them to a router connected to your computer. As the cost of installing fiber decreases, more homes and businesses will opt for this high-speed Internet access.
· T-Carrier Lines
A T-carrier line is any of several types of long-distance digital telephone lines that carry multiple signals over a single communications line. Where as a standard dial-up telephone line carries only one signal, digital T-carrier lines use multiplexing so that multiple signals share the line. T-carrier lines provide very fast data transfer rates. Only medium to large companies usually can afford the investment in T-carrier lines because these lines are so expensive.
· ATM
ATM (Asynchronous Transfer Mode) is a service that carries voice, data, video, and multimedia at very high speeds. Telephone networks, the Internet, and other networks with large amounts of traffic use ATM. Some experts predict that ATM eventually will become the Internet standard for data transmission, replacing T3 lines.
9. What Are Commonly Used Communications Devices?
A communications device is hardware capable of transmitting data between a sending device and a receiving device. A dial-up modem converts digital signals to analog signals and analog signals to digital signals. So that data can travel along analog telephone lines. A digital modem sends and receives data and information to and from a digital line. An ISDN modem transmits digital data to and from an ISDN line, while a DSL modem transmits digital data to and from a DSL line. A cable modem, sometimes called a broadband modem, is a digital modem that sends and receives digital data over the cable television network. A wireless modem uses the cell phone network to connect to the Internet wirelessly from mobile computers and devices. A network card enables a computer or device that does not have built-in networking capability to access a network. A wireless access point allows computers and devices to transfer data wirelessly. A router connects multiple computers or other routers together and transmits data to its correct destination on the network. A hub or switch is a device that provides a central point for cables in a network.
10. How Can a Home Network Be Set Up?
A home network connects multiple computers and devices in a home. An Ethernet network connects each computer to a hub with a physical cable. A home power line cable network uses the same lines that bring electricity into the house. A phone line network uses existing telephone lines in a home. Most home networks use a Wi-Fi network.
11. What Are Various Physical and Wireless Transmission Media?
· Twisted-Pair Cable
One of the more widely used transmission media for network cabling and telephone systems is twisted-pair cable. Twisted-pair cable consists of one or more twisted-pair wires bundled together. Each twisted-pair wire consists of two separate insulated copper wires that are twisted together. The wires are twisted together to reduce noise. Noise is an electrical disturbance that can degrade communications.
· Coaxial Cable
Coaxial cable, often referred to as coax (pronounced KO-ax), consists of a single copper wire surrounded by at least three layers: (1) an insulating material, (2) a woven or braided metal, and (3) a plastic outer coating (Figure 9-37). Cable television (CATV) network wiring often uses coaxial cable because it can be cabled over longer distances than twisted-pair cable. Most of today’s computer networks, however, do not use coaxial cable because other transmission media such as fiber-optic cable transmit signals at faster rates.
· Fiber-Optic Cable
The core of a fiber-optic cable consists of dozens or hundreds of thin strands of glass or plastic that use light to transmit signals. Each strand, called an optical fiber, is as thin as a human hair. Inside the fiber-optic cable, an insulating glass cladding and a protective coating surround each optical fiber. Fiber-optic cables have the following advantages over cables that use wire, such as twisted-pair and coaxial cables:
• Capability of carrying significantly more signals than wire cables
• Faster data transmission
• Less susceptible to noise (interference) from other devices such as a copy machine
• Better security for signals during transmission because they are less susceptible to noise
• Smaller size (much thinner and lighter weight)
· Broadcast radio distributes radio signals through the air over long and short distances.
· Cellular radio is a form of broadcast radio that is used widely for mobile communications.
· Microwaves are radio waves that provide a high speed signal transmission.
· A communications satellite is a space station that receives microwave signals from an earth-based station, amplifies the signals, and broadcasts the signals back over a wide area.
