Communications and Networks Chapter 9 ITSC 1401, Intro to Computers Instructor: Glenda H. Easter.

Communications and Communications and NetworksNetworksChapter 9Chapter 9

ITSC 1401, Intro to Computers

Instructor: Glenda H. Easter

Communications and Networking, Chapter 9

CommunicationsCommunicationsand Networkingand Networking

Define the components required for successful communications

Describe uses of communications

Identify the various types of transmission media

Explain the purpose of communications software

CommunicationsCommunicationsand Networkingand Networking

Describe commonly used communications devices

Explain the difference between a local area network and a wide area network

Understand the various communications protocols

Identify uses of intranets and extranets

ConnectivityConnectivity

Connectivity is the ability for two or more computers to exchange information, share data and resources.Connectivity can be achieved in two ways:

Telecommunications (computers and telephones)Direct Access (computers and networks)A communication channel isanother word for telecommunications.

ConnectivityConnectivity

In order for connectivity to occur, you need either

a modem (Modulator/Demodulator) or

a network card

CommunicationsCommunications

What is needed for communications?Sending device

Conversion from data into signals

Communications channel

Conversion from signals to data

Receiving device

Uses of CommunicationsUses of Communications

E-mail Videoconferencing

Voice mail Groupware

Fax Instant Messaging

Telecommuting Smartphones

How Computer Communications How Computer Communications Work Work (Continued)(Continued)

Uses of CommunicationsUses of Communications

Global Positioning System

Bulletin Board System

The InternetThe Web

E-commerce

Telephony

Structure of the Internet Animation

Hardware

Channels-Wired Transmission Media

Twisted-Pair Cable

Coaxial Cable

Fiber-optic Cable

CommunicationsCommunications Channels Channels

Twisted pair - telephone wireCoaxial cable - used by cable television

companiesFiber optic cable - thin wires of glass fiberInfrared transmission - a beam of infrared lightMicrowave transmission - Radio signals

beamed between earth stationsSatellite transmission - Radio signals beamed

between satellites and earth stations

Physical Transmission MediaPhysical Transmission MediaTwisted-pair cable

Hundreds of wires connected together like those used for telephone lines.

Can often use a building’s existing unused telephone wiring.

This usage avoids having wiring strung over ceiling tiles (which may violate fire code and result in interference from fluorescent light fixtures).

Most buildings are wired with two (2) or three (3) pairs of wire to each wall outlet.

Twisted Pair CableTwisted Pair Cable

Physical Transmission MediaPhysical Transmission Media

Coaxial cable (coax)High-frequency line that has a solid cooper core

Cable TV

Not as susceptible to noise

Physical Transmission Media Physical Transmission Media (Continued)(Continued)

Coaxial cable has the disadvantage that to add or remove a node, cables may have to be disconnected and reattached.

Special “T” connectors have to be placed along the cable for stations to connect to, and the ends of the cable need to have end-cap connectors called terminators.

Coaxial cable is used for Ethernet networks.

Coaxial Cable (Coax)Coaxial Cable (Coax)

Fiber-optic cableTransfers data as pulses of light through tubes of glass. This is what is used for cellular telephones and microwave transmissions.

Carries many signals

High speed

Less susceptible to noise

Better security

Smaller size

Fiber Optic Cable (Continued):Installation requires special training because the cable cannot be simply cut or soldered as electrical wiring can.

Network interface cards are specific to the computer in which they are installed and to the type of network to which they are connecting.

Fiber-Optic CableFiber-Optic Cable

HardwareHardware

Channels-Wireless Transmission Modes

Cellular Telephone

Microwave Transmission

Satellite Transmission

Communication Links Communication Links (Continued)(Continued)Microwave

Microwaves are high-frequency radio waves that travel in straight lines through the air.

These can only be transmitted over short distances.

SatellitesUsed as microwave relay stations.

Orbit about 22,000 miles above the earth.

Can be used to send large volumes of data.

Wireless Transmission MediaWireless Transmission Media

Broadcast RadioLong distance

Station frequencies assigned by FCC• AM

• FM

Susceptible to noise

Cellular RadioCellular telephone

Mobile telephone switching office (MTSO)

MicrowavesHigh-speed

Microwave stations

Line-of-sight transmission

Communications SatelliteSpace station receives signals and re-transmits the signals

• Uplink

• Downlink

Communications SatelliteCommunications Satellite

Transmissions CharacteristicsTransmissions Characteristics

Signal Type: Analog or DigitalAnalog signals are continuous wave

Digital signals are electrical pulses

Transmissions ModesTransmissions Modes

Transmission Modes: Asynchronous and Synchronous

Asynchronous - irregular intervals

Synchronous - regular intervals

Transmission ModesTransmission Modes

Asynchronous is the most common and is the transmission mode used by personal computers.

It is slower because data is sent and received one byte at a time. With Asynchronous transmission the following example would be applicable:Computer A -- Start Bit -- Stop Bit -- Computer B

Transmission Modes Transmission Modes (Continued)(Continued)

Synchronous allows several bytes or blocks of information to be sent within timed intervals. Data is flowing in both directions at the same time.Computer A Computer BComputer A Computer B

This is usually the transmission mode used by mainframes.

Transmissions DirectionsTransmissions Directions

There are three directions or modes of data flow in a data communications system:

Transmission Direction: Simplex, Half-Duplex, and Full-Duplex

Simplex - one direction only

Half-duplex - either direction, but only one direction at a time

Full-duplex - both directions at the same time

Transmission Direction: Simplex, Transmission Direction: Simplex, Half-Duplex, and Full-DuplexHalf-Duplex, and Full-Duplex

Simplex Data FlowSimplex Data Flow

Data travels in only one direction.

It is not frequently used in data communication systems today.

Half DuplexHalf Duplex

Data travels in both directions, but not simultaneously.

It is frequently used for linking microcomputers by telephone lines to other microcomputers, minicomputers, and mainframes.

Full-DuplexFull-Duplex

Data is transmitted back and forth at the same time.

It is the fastest and most efficient form of two-way communication.

It requires special equipment and is used primarily for mainframe communications.

The capacity of aparticular medium to carry information

Twisted-pair has the lowest bandwidth

Aside from microwave and satellite, fiber optic has the highest

Transmission ratesTransmission ratesBandwidthBandwidth

BandwidthBandwidth

Bandwidth is the bits per second transmission capability of a channel.It is written as bps (Bits per Second)There are three types of bandwidth:

Voiceband - Used for microcomputer transmission.Medium Band used mainly with minicomputers and mainframes.Broadband used for very high speed computers

The Telephone NetworkThe Telephone Network

Public switched telephone network (PSTN)

Plain old telephone service (POTS)

Uses variety of media

The PSTN in PerspectiveThe PSTN in Perspective

As a caller moves from one area to another, a new cell site steps in to keep the signal strong. The sites are connected to a Mobile Telephone Switching Office (MTSO), which is connected to the standard PSTN telephone system.

Sender of call

receiver of call

Dial-Up LinesTemporary connection

Same cost as regular phone call

Quality cannot be controlled by the user

Speeds and Costs of Various Speeds and Costs of Various Telephone ConnectionsTelephone Connections

Dedicated LinesISDN lines

Digital subscriber lines

T-carrier lines

Asynchronous transfer mode (ATM)

Digital Subscriber LineDigital Subscriber LineSuper fast speed

Always on access

Simultaneous voice call and Internet access

Dedicated connection

Bandwidth doesn’t have to be shared; thereby, speeding up the process.

Hook up DSL to TV or run full-length movies over computer. Will be able to download video to hard drive.

Example of Communications’ Example of Communications’ ChannelChannel

0 1 1 0 0

0 1 1 0

SoftwareSoftware

Communications Software

Communications SoftwareCommunications Software

Dialing

File transfer

Terminal emulation

Internet access

Communications SoftwareCommunications Software

Communication Communication DevicesDevices

Modems - Internal/External/Fax/ModemsAnalog SignalsDigital SignalsDemodulation

• from analog to digital

Modulation• from digital to analog

Modem Types and General Modem Types and General InformationInformationModems were developed to share and process data.External Modems connect with a serial port.Internal Modems consists of a plug-in circuit board inside the system unit.Wireless Modems are similar to the external modem that connects to the computer’s serial port. These receive data through the air.Modems allow dial-up access.

Wide Area Networks (WAN)Wide Area Networks (WAN)

Wide Area Networks (WAN)Network covers a large geographical area

Usually consists of two or more LANs connected by a router

Wide Area Networks (WAN)Wide Area Networks (WAN)

A type of private A type of private networknetwork

Uses all types of Uses all types of media to connectmedia to connect

Can cross great Can cross great distancesdistances

Wide Area Networks (WANs)Wide Area Networks (WANs)

WANs connect computers over long distances.

They have the widest scope of connectivity.

WANs use microwave relays and satellites as a medium of transmission.

The most widely used WAN is the Internet.

Wide Area Network (WAN)Wide Area Network (WAN)

Metropolitan Area Network Metropolitan Area Network (MAN)(MAN)

Metropolitan Area Network (MAN)A backbone network that connects local area networks in a metropolitan area

Typically includes one or more LANs, but in a smaller area than a WAN

Network ArchitectureNetwork Architecture

A computer network is a communications system connecting two or more computers that work together

to exchange informationto share resources

Communications channels can be connected in different arrangements, or networks. The way networks are arranged and how their resources are shared is referred to as a network architecture.

Local Area Local Area NetworksNetworks

Star Topology

Bus Topology

Ring Topology

TopologyTopology

• The physical layout of the cables that connect the nodes of the network.

Star TopologyStar Topology

• Places a hub in the center of the network nodes. Groups of data are routed through the central hub to their destinations.

• Star: the hub is in the center of the network nodes.

• The entire network goes down only if the hub is lost.

Star TopologyStar Topology(Client/Server Architecture)(Client/Server Architecture)

In a Star Topology, each point could represent a computer terminal, and it is connected at the center by a host computer.

Star provides for timesharing where users share time on a central computer.

E Host

Star TopologyStar Topology (Client/Server Architecture) (Client/Server Architecture)

Uses the polling method of control.

With polling, each deviceon the system isgiven a turn tosend its message.

Star Topology (Continued)Star Topology (Continued)

Each machine is called a client or node.

Your central host connects to the nodes or machines.

A node is any device that shares resources on a network.

If the host or server dies, everything goes down.

Star TopologyStar Topology

Ring TopologyRing Topology

• Connects the nodes of the network in a circular chain in which each node is connected to the next.

• If a connection is lost, the entire network goes down.

• Ring: each node is chained to the next.

This is the oldest type of networking system.Each arrow representsa computer terminal.If Computer A tries tosend information to Computer B, and ComputerB is busy, it will send the information back to Auntil B is no longer busy.

Bus TopologyBus Topology

• A single conduit to which all the network nodes and peripheral devices are attached.

Bus: a single path connects all devices.

A broken path can bring down all connected devices.

Bus TopologyBus TopologyThis is the type of set-up that exists in the Computer Lab. This the most popular type of network.Each device in the network handles its own communications control. There is no host; each node manages part of the network.The terminals are connected to a communications channel.

Printer

ProtocolsProtocols

Protocols are sets of communication rules or standards for the exchange of information between computer systems.

A communications software package helps define the protocol, such as speed and modes for connecting with another microcomputer.

Communications ProtocolsCommunications Protocols

EthernetDeveloped by Xerox in 1976

Communications and Networks Chapter 9 ITSC 1401, Intro to Computers Instructor: Glenda H. Easter.

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