Chapter 9 Communications and Networks

Communications Computer communications are…  The process by which two or more computers or devices transfer data, instructions, and information

Sending device — initiates instruction to transmit data, instructions, or information The requirements for successful communications are… Communications Communications device — connects the communications channel to the receiving device Receiving device — accepts transmission of data, instructions, or information Communications device — connects the sending device to the communications channel Communications channel — media on which data, instructions, or information travel

Uses of Computer Communications Uses of communications technology include… WebWebInternetInternet Instant Messaging Internet Telephony NewsgroupsNewsgroups Chat Rooms Web Folders Fax Machine or Computer Fax/Modem Video Conferencing FTPFTP

Uses of Computer Communications Wireless messaging services include… Wireless instant messaging Wireless instant messaging allows wireless mobile devices to exchange messages Text messaging Text messaging allows users to send and receive short text messages on a smart phone or PDA Picture messaging Picture messaging allows users to send graphics, pictures, video clips, sound files, and short text messages

Uses of Computer Communications Public Internet access points and cybercafés are…  Public Internet access point allows wireless connection to Internet in a public location  Cybercafés are coffee shops that provide the use of computers for Internet access

Uses of Computer Communications What is a global positioning system (GPS)? Step 1. GPS satellites orbit Earth. Every thousandth of a second, each satellite sends a signal that indicates its current position to the GPS server. Step 2. A GPS receiver (such as in a car, a PDA, a watch, a handheld device, or a collar) determines its location on Earth by analyzing at least 3 separate satellite signals from the 24 satellites in orbit.

Uses of Computer Communications Collaboration and groupware are:  Microsoft’s NetMeeting allows collaboration  Groupware is software that allows people to share information  Collaboration is working with other users all of whom are connected to a network

Uses of Computer Communications Voice mail and web services are:  Voice mail is a voice message converted into a digital form  Web services describe standardised software that enables programmers to create applications that communicate with other remote computers over the Internet

Networks A network is…  A collection of computers and devices connected via communications devices and transmission media

Networks A Local Area Network (LAN) is…  A network in a limited geographical area such as a home or office building  Wireless LAN (WLAN)  A Metropolitan Area Network (MAN) is a connection of LANs within a city or town

Networks What is a Wide Area Network (WAN)?  Network that covers large geographic area using many types of media  Internet is world’s largest WAN

Networks A client/server network is…  One or more computers that act as servers and other computers, or clients, that access those servers

Networks A Peer-to-Peer Network is…  Simple network that connects fewer than 10 computers  Each computer, or peer, has equal capabilities  There are no dedicated server computers

Networks The Internet Peer-to-Peer (P2P) system…  Enables users to connect to each other’s hard disks and exchange files directly over the Internet

Networks A Bus Network is…  Where all computers and devices are connect to a central cable, or bus  Is an example of a network topology (layout of devices in network)  Other popular topologies include ring and star

Networks A Ring Network is where…  A cable forms a closed ring (or loop), with all computers and devices arranged along it  Data travels from device to device around the entire ring in one direction

Networks A Star Network is where…  All devices connect to a central device, called a hub (or switch)  All data transferred from one computer to another passes through this hub (or switch)  This is the most common LAN topology used today

Networks An Intranet… Extranet allows customers or suppliers to access part of a company’s Intranet Typically includes connection to InternetMakes information accessible to employeesInternal network that uses Internet technologies

Network Communications Standards Ethernet and token ring are: Ethernet technology allows computers to contend for access to a network  If two computers send data at the same time, a collision occurs and the computers must send again Token ring technology controls access to the network by requiring a devices to pass a special signal, called a token

Network Communications Standards TCP/IP and are:  TCP/IP (Transmission Control Protocol/Internet Protocol) this technology transmits data by breaking it up into small pieces, or packets  Commonly used for Internet transmissions  is family of standards for wireless LANs

Network Communications Standards Bluetooth is…  Short-range radio waves that transmit data between Bluetooth devices

Network Communications Standards IrDA, RFID, and WAP are: (IrDA) Infra Red Data Association (IrDA) Infra Red Data Association specification allows data to be transferred wirelessly via infrared light waves (WAP)Wireless Applications Protocol (WAP) Wireless Applications Protocol allows wireless mobile devices to access Internet (RFID)Radio Frequency Identification (RFID) Radio Frequency Identification uses radio signals to communicate with a tag placed in an object

Communications Software Communications software includes… Programs that help users establish a connection to the Internet, other network, or another computer Programs that help users manage the transmission of data, instructions, and information Programs that provide an interface for users to communicate with one another

Communications Over the Telephone Network The Public Switched Telephone Network (PSTN)?  Worldwide telephone system that handles voice-oriented telephone calls

Communications Over the Telephone Network A dial-up line…  Temporary connection using telephone line for communications  Costs no more than making regular call  Computers at any two locations can establish a connection using modems and telephone network

Communications Over the Telephone Network A dedicated line is…  Four types are:  ISDN  DSL (e.g. ADSL)  T-carrier line  ATM  An always-on connection between two communications devices

Communications Devices Other examples of communications devices are: Common types are dial-up modems, ISDN and DSL modems, cable modems, network cards, wireless access points, routers, and hubs ISDN and DSL modems send and receive data from ISDN and DSL lines

Communications Devices A dial-up modem…  Converts digital signals to analog signals and vice versa  Notebook computers often use PC Card modem

Communications Devices ISDN and DSL modems are… Communications devices that send and receive digital ISDN and DSL signals Usually external devices in which one end connects to a telephone line and the other end connects to a port on the system unit

Communications Devices A cable modem…  Sends and receives data over cable television network  Much faster than dial-up modem or ISDN  Sometimes called a broadband modem

Communications Devices A wireless modem…  Allows access to the Web wirelessly from a notebook computer, a PDA, a smart phone, or other mobile device  Typically use the same waves used by cellular telephones

Communications Devices A network card is…  An adapter card, PC Card, or compact flash card that enables a computer or other device to access a network  Sometimes called network interface card (NIC)

Communications Devices A wireless access point is…  A central communications device that allows computers and devices to transfer data wirelessly among themselves or to a wired network

Communications Devices A router…  Connects computers and transmits data to the correct destination on a network  Routers forward data on the Internet using fastest available path

Communications Devices A hub is…  A device that provides a central point for cables in a network

Home Networks a home network has…  Multiple computers connected in the home  Several types of home networks  Ethernet — connect computers via cable  Powerline cable — use electrical lines in house  Phoneline — use telephone lines  HomeRF (radio frequency) — wireless LAN

Communications Channel A communication channel is…  Transmission media on which data travels in a communications system Bandwidth is the amount of data that can travel over a channel Transmission media are materials capable of carrying one or more signals

Communications Channel How is a request sent over the Internet using a communications channel? Step 1. The sending device requests information using either a physical transmission media or a wireless transmission media. Step 2. When the request leaves the ISP, it travels over T1 lines, microwave stations, earth-based stations, and communications satellites until it reaches the Internet backbone. Step 3. The request travels over T3 lines along the Internet backbone. Step 4. The Request travels over T1 lines until it reaches the destination network server.

Physical Transmission Media Physical transmission media is…  Wire, cable, and other tangible materials used to send communications signals

Physical Transmission Media Twisted-pair cable and coaxial cable are…  Twisted-pair cable is used for telephone systems and network cabling  Coaxial cable is often used for cable television wiring Twisted Pair CableCoaxial Cable

Physical Transmission Media Fiber-optic cable is…  Capable of carrying significantly more data at faster speeds than wire cables  Less susceptible to interference (noise) and, therefore, more secure  Smaller size (thinner and lighter)

Wireless Transmission Media Wireless transmission media is…  Used when inconvenient, impractical, or impossible to install cables  Includes Bluetooth and IrDA

Wireless Transmission Media Broadcast Radio and Cellular Radio are:  Broadcast radio distributes radio signals over long and short distances  Cellular radio is form of broadcast radio used for mobile communications

Wireless Transmission Media A microwave station is…  Earth-based reflective dish used for microwave communications  Must transmit in straight line with no obstructions

Wireless Transmission Media A communications satellite is…  A space station that receives microwave signals from earth-based station, amplifies signals, and broadcasts signals back to any number of earth- based stations