Networking Chapter 6 Computer Connections Copyright Prentice Hall

Data Communications Data communications is transmitting processed data over communications lines. Copyright © Prentice

Data Processing Designs Data processing has evolved along these lines: • Centralized data processing

Factors in Network Design • Sending device • Communications Link • Receiving Device Copyright

Data Transmission— Digital Signal digital signal Copyright © Prentice Hall 2000 Digital signals are

Data Transmission— Analog Signal analog signal Copyright © Prentice Hall 2000 Most telephone lines

Data Transmission: Modulation The conversion of digital signals to analog signals is called modulation.

Data Transmission: Demodulation The conversion of analog signals into digital form is called demodulation.

Modems • Modems convert digital signals to analog and analog signals to digital •

Types of Modems • Direct-connect • External • Internal Copyright © Prentice Hall 2000

Types of Modems • External - connects via a cable to a variety of

Modem Data Speeds One measure of modem speed is how many bits per second

ISDN—Transmission Without a Modem ISDN (Integrated Services Digital Network) is designed to transmit a

Benefits of ISDN… • No need to convert to analog and back again •

Disadvantages of ISDN… • high initial costs • on-going monthly fees • possibly, a

Transmission Over Long Distances To make sure that the sending and receiving computers are

Asynchronous Transmission In this technique, a special start/stop signal surrounds each character sent. start

Synchronous Transmission In this technique, a starting bit pattern is sent, followed by a

Directing Traffic Data transmission can also be described by the direction the data is

Simplex is one-way flow of data. Television is an example of data moving in

Half-duplex allows for two-way data transmission, but only one direction at a time. An

Full-duplex is simultaneous, two-way transmission. Both parties can talk—even at the same time. The

Communications Links There are several kinds of communications links: • Wire pairs • Coaxial

Wire Pairs This is the most common way to link communications devices. It is

Coaxial Cables Instead of twisted pairs of wires, coaxial consists of one center wire

Fiber Optics Fiber optic technology uses light, not electricity, to send data. Cables are

Microwave In this form of communications link, data is sent as signals through the

Satellite This form of communications link requires earth stations and transponders. Earth stations send

Protocols SYN ACK Copyright © Prentice Hall 2000 • A protocol is a set

Network Topology Each computer device connected to the network is called a node. The

Star Network With star topology, there is a hub computer that is responsible for

Ring Network In this arrangement, nodes are connected in a circular pattern. Data travels

Bus Network For this arrangement, there is a single line to which all the

Wide Area Networks A network that links computers that are physically very distant from

WAN Communication WAN communication requires that smaller computers talk with larger ones. This is

Local Area Networks in the same room or building are called LANs (local area

LAN Components Since LANs do not use telephone lines, they have their own standard

LAN Network Cable A LAN Network cable can consist of wire pairs, coaxial or

LAN Network Interface Card This card is also called a NICs are needed to

LAN Bridge A bridge is needed to connect similar LANs to one another. Bridge

LAN Gateway… A gateway is used to connect dissimilar LANs or to connect a

Organizing LAN Resources There are two ways to organize the resources in a LAN:

Client/Server Networks The server usually does the processing for the client machines. server This

Peer-to-Peer LANs Peer-to-peer is designed to give all nodes equal status—no single computer is

Local Area Network Protocols • Ethernet • Token Ring Copyright © Prentice Hall 2000

• The Work of Networking Office Automation is the use of technology to

Electronic Mail (E-mail) E-mail is the process of sending typed messages directly from one

Facsimile (Fax) Personal computer users can send and receive faxes directly by means of

Groupware allows users to share and work on the same file—even when the users

Teleconferencing allows live, interactive work to be done with clients or team members who

Electronic Data Interchange (EDI) Using EDI, businesses can transmit invoices, purchase orders, and the

Electronic Fund Transfer (EFT) EFT allows people to pay for goods and services by

Telecommuting By telecommuting, employees are connected to their work computers from their homes. Copyright

Online Services Online services available include news, weather, shopping, games, educational materials, e-mail, forums,

The Internet is a network of networks. To work on the Internet means it

Conclusion The demand for data communications services is swelling. The modern computer user will

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Data Transmission— Digital Signal digital signal Copyright © Prentice Hall 2000 Digital signals are simply the presence or absence of an electrical impulse. Digital transmission sends data as distinct pulses. 5

Data Transmission— Analog Signal analog signal Copyright © Prentice Hall 2000 Most telephone lines require analog signals. Analog transmission sends data as a continuous electrical signal in the form of a wave. 6

Benefits of ISDN… • No need to convert to analog and back again • Speed—data can be transmitted at 128, 000 bps • Voice communication via telephone and data transmission can happen at same time since the ISDN circuitry uses two phone lines Copyright © Prentice Hall 2000 14

Transmission Over Long Distances To make sure that the sending and receiving computers are communicating with one another involves one of two techniques: • Asynchronous transmission • Synchronous transmission Copyright © Prentice Hall 2000 16

Asynchronous Transmission In this technique, a special start/stop signal surrounds each character sent. start character stop Asynchronous equipment is less expensive but yields slower transmission due to the frequent start/stop signals. Copyright © Prentice Hall 2000 17

Synchronous Transmission In this technique, a starting bit pattern is sent, followed by a continuous stream of characters; then an error check is sent, and finally, a stop bit. start message Copyright © Prentice Hall 2000 error check stop start message error check stop 18

Wire Pairs This is the most common way to link communications devices. It is also the least expensive. Wire pairs (or twisted pairs) is the same wiring used for telephone transmission. Copyright © Prentice Hall 2000 24

Coaxial Cables Instead of twisted pairs of wires, coaxial consists of one center wire within a shielded enclosure. Coaxial cables send a stronger, faster signal with less noise distortion than wire pair lines. Copyright © Prentice Hall 2000 25

Fiber Optics Fiber optic technology uses light, not electricity, to send data. Cables are made of glass fibers that guide light beams for miles. Fiber optics is faster, lighter, and less expensive than wire cables. Copyright © Prentice Hall 2000 26

Microwave In this form of communications link, data is sent as signals through the atmosphere from one relay station to another. Microwave transmissions offer speed, cost-effectiveness, and ease of implementation. Copyright © Prentice Hall 2000 27

Satellite This form of communications link requires earth stations and transponders. Earth stations send and receive signals. Transponders amplify the signal, change the frequency, and retransmit the data to a receiving earth station. Copyright © Prentice Hall 2000 28

Protocols SYN ACK Copyright © Prentice Hall 2000 • A protocol is a set of rules for the exchange of data between computers • The TCP/IP protocol permits any computer to communicate with the Internet 29

Network Topology Each computer device connected to the network is called a node. The topology of a network can be arranged in a variety of ways: • Star network • Ring network • Bus network Copyright © Prentice Hall 2000 30

WAN Communication WAN communication requires that smaller computers talk with larger ones. This is made possible with terminal emulation software. With file transfer software, files can be downloaded to the smaller computer or uploaded to the host computer. Copyright © Prentice Hall 2000 35

Local Area Networks in the same room or building are called LANs (local area networks). LANs allow sharing of computerrelated resources such as printers, hardware, secondary storage, software, and data. Copyright © Prentice Hall 2000 36

LAN Network Cable A LAN Network cable can consist of wire pairs, coaxial or fiber optic cabling or a combination of these. Some networks are wireless—using radio waves to broadcast signals. Copyright © Prentice Hall 2000 38

Client/Server Networks The server usually does the processing for the client machines. server This arrangement minimizes the amount of data being transferred and puts burden on the more powerful server. Copyright © Prentice Hall 2000 43

Peer-to-Peer LANs Peer-to-peer is designed to give all nodes equal status—no single computer is in control or stores all the files. This setup is slowed down during heavy use. Copyright © Prentice Hall 2000 44

Online Services Online services available include news, weather, shopping, games, educational materials, e-mail, forums, financial information, software product support, and access to the Internet. Copyright © Prentice Hall 2000 54

Conclusion The demand for data communications services is swelling. The modern computer user will need to be proficient at using these services in their work and home life. Copyright © Prentice Hall 2000 56