Communications• Computer communications describes a

process in which two or more computers or

devices transfer data, instructions, and

information.

Components of Communication

• A sending device that initiates an instruction to transmit data, instructions, or information. (Sender)

• A communications device that connects the sending device to a communications channel. (Encoder)

• A communications channel, or transmission media on which the data, instructions, or information travel. (Medium)

• A communications device that connects the communications channel to a receiving device. (Decoder)

• A receiving device that accepts the transmission of data, instructions, or information. (Reciever)

Networks• a network is a collection of computers and

devices connected together via communications

devices and transmission media.• A network can be internal to an organization

or span the world by connecting to the Internet.

Advantages of Network:

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, videoconferencing, 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 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.• Consumers use an ATM to access their

bank account. Businesses deposit payroll

checks directly in employees’ bank accounts.

LANs, MANs, and WANs• A local area network (LAN) is anetwork that connects computers and devices

in a limited geographical area such as a home,

school computer laboratory, office building

or closely positioned group ofbuildings.

Wireless LAN• A wireless LAN (WLAN) is a LAN that

uses no physical wires. Computers and devices

that access a wireless LAN must have built-in

wireless capability or the appropriate wireless

network card, USB network adapter,

ExpressCard module, PC Card, or flash card.

MANA metropolitan area network (MAN) isa 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.

WAN• A wide area network (WAN) is anetwork 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

Network Architectures• The design of computers, devices, and

media in a network, sometimes called

the network architecture, is categorized aseither client/server or peer-to-peer.

Client/Server• On a client/server network,one or more computers act as a server, andthe other computers on the network requestser vices from the server• A server, sometimes called a host computer, controls access to the hardware, software, andother resources on the network and providesa centralized storage area for programs, data,

and information.

Client/Server• The clients are other computersand mobile devices on the networkthat rely on the server for its resources.

For example, a server might store a database of

customers. Clients on the network (companyemployees) access the customer database onthe server.

Peer-to-Peer• One type of peer-to-peer networkis a simple, inexpensive network that typically

connects fewer than 10 computers.• Each computer, called a peer, has equal responsibilities and capabilities• Each computer stores files on its ownstorage devices. Thus, each computer on thenetwork contains both the server operatingsystem and application software.

Internet Peer-to-Peer• 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. (BitTorrent , Kazaa)

Internet

Network Topologies• A network topology refers to the layout of

the computers and devices in a communications

network.• Three commonly used network topologies

are star, bus, and ring.

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.• Star networks are fairly easy to install and

maintain. Nodes can be added to and removedfrom the network with little or no disruption to

the network.

Bus Network• A bus network consists of a single central cable, to which all computers and other devices connect.• 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 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.

Intranets• An intranet (intra means within) is an internal

network that uses Internet technologies.

• Intranets generally make company information accessible to employees and

facilitate working in groups.

IntranetsSimple intranet applications include:

• Electronic publishing• telephone directories• event calendars• procedure manuals• employee benefits• job postings

Extranets• Sometimes a company uses an extranet,which allows customers or suppliers to access

part of its intranet.• Package shipping companies, for example, allow customers to accesstheir intranet to print air bills, schedule pickups,

and even track shipped packages as thepackages travel to their destinations.

Network CommunicationsStandards

• A network standard defines guidelines that specify the way computers access the medium to which they are attached, the type(s) of medium used, the speeds used on different types of networks, and the type(s) of physical cable and/or the wireless technology used.

protocol• A standard that outlines characteristics

of how two network devices communicate

is called a protocol. Specifically, a protocol

may define data format, coding schemes, error handling, and sequencing techniques.

TCP/IP• TCP/IP is a network standard,specifically a protocol, that defines howmessages (data) are routed from one end of anetwork to the other, ensuring the data arrivescorrectly. • TCP/IP describes rules for dividingmessages into small pieces, called packets;providing addresses for each packet; checkingfor and detecting errors; sequencing packets;and regulating the flow of messages along thenetwork.

Ethernet• Ethernet is a network standard that specifies nocentral computer or device on the network (nodes)should control when data can be transmitted;that is, each node attempts to transmit data whenit determines the network is available to receivecommunications. • If two computers on an Ethernetnetwork attempt to send data at the same time,a collision will occur, and the computers mustattempt to send their messages again.

Token Ring• The token ring standard specifies thatcomputers and devices on the network shareor pass a special signal, called a token, in aunidirectional manner and in a preset order.• A token is a special series of bits that function likea ticket. The device with the token can transmit

data over the network. Only one token exists per

network. This ensures that only one computertransmits data at a time.

Example of How Communications Standards Work Together

Wi-Fi• Wi-Fi (wireless fidelity), which identifies

any network based on the 802.11 standards.

Developed by IEEE , 802.11 is a series of network standards that specifies how two wireless devices communicate over the air with each other.

Bluetooth• Bluetooth is a network standard, specificallya protocol, that defines how two Bluetoothdevices use short-range radio waves to transmit data. The data transfers between devices at a rate of up to 3 Mbps.

• A Bluetooth device contains a small chip thatallows it to communicate with other Bluetoothdevices. Examples of Bluetooth-enabled devicescan include desktop computers, notebook computers,

handheld computers, smart phones.

UWB• UWB, which stands for ultra-wideband, is a

network standard that specifies how two UWBdevices use short-range radio waves to communicate at high speeds with each other.

• At distances of 10 meters (about 33 feet), the data transfer rate is 110 Mbps. At closer distances, such as 2 meters (about 6.5 feet), the transfer rate is at least 480 Mbps.

IrDA• IrDA standard is used to transmit data wirelessly to each other via infrared (IR) light waves.

• The devices transfer data at rates from 115 Kbps (thousand bits per second) to 4 Mbps between their IrDA ports.

RFID• RFID (radio frequency identification) is a standard, specifically a protocol, that defines

how a network uses radio signals to communicate with a tag placed in or attached to an object, an animal, or a person. The tag, called a transponder, consists of an antenna and a memory chip that contains the information to be transmitted via radio waves.

WiMAX• WiMAX (Worldwide Interoperability forMicrowave Access), also known as 802.16, isa network standard developed by IEEE thatspecifies how wireless devices communicateover the air in a wide area. Using the WiMAX

standard, computers or devices with the appropriate WiMAX wireless capability communicate via radio waves with other computers or devices via a WiMAX tower.

TYPES OF WIMAX• Fixed wireless With fixed wireless

WiMAX, a customer accesses the Internetfrom a desktop computer at home or otherpermanent location.• Mobile wireless Mobile wireless WiMAX,

by contrast, enables users to access the WiMAXnetwork with mobile computers and mobiledevices such as smart phones.

WAP• The Wireless Application Protocol (WAP) is a standard , specifically a protocol, that specifies how some mobile devices such as smart phones can display the content of Internet services such as the Web, e-mail, and chat rooms.

A WAP-enabled smartphone.

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.

(3) provide an interface for users to communicate with one another.

Communications over theTelephone Network

• The public switched telephone network (PSTN)

is the worldwide telephone system that handles voice-oriented telephone calls.

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. Using

a dial-up line to connect computers costs no more than making a regular telephone call.

Dedicated Lines• A dedicated line is a type of always-onconnection 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.

Five types of digital dedicated lines

• ISDN lines• DSL• FTTP• T-carrier lines• ATM

Communications Devices• A communications device is any type of

hardware capable of transmitting data, instructions, and information between a sending device and a receiving device.

Dial-Up Modems• A dial-up modem is a communications

devicethat can convert digital signals to analog signals and analog signals to digital signals, so that data can travel along an analog telephone line.

Digital Modems• A digital modem is a communications

devicethat sends and receives data and information to and from a digital line.

• ISDN Modem• DSL Modem• CABLE Modem

Wireless Modems• 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 . Wireless modems, which have an external or built-in antenna, are available as USB flash drives, Express Card modules, PC Cards, and memory cards.

Wireless Modems

Network Cards• A network card, sometimes called a network

interface card (NIC pronounced nick), is a communications device that enables a computer or device that does not have built-in networking capability to access a network.

Network Cards

Routers• A router is a communications device

thatconnects multiple computers or other routers

together and transmits data to its correct destination on a network.

• A router can be used on any size of network.

Routers

Hubs and Switches• A hub or switch is a device that provides a central point for cables in a network.

• Larger networks typically use a hub, while smaller networks use a switch.

Hubs and Switches

Communications Channel• Communication channel is a way to connect or communicate to a network through physical or wireless media.

Types of communication channels

• Physical transmission media• Wireless transmission media

Physical transmission media

• Physical transmission media use wires to communicate or connect to network.

• Twisted-Pair Cable• Coaxial Cable• Fiber-Optic Cable

Twisted-Pair Cable• Twisted-pair cable consistsof 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

• (3) a plastic outer coating

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 .

Wireless Transmission Media

• A type of media in which wireless media is use to connect or communicate to a network.

• Infrared• Broadcast Radio• Cellular Radio• Microwaves• Communications Satellite

Infrared

• infrared (IR) is a wireless transmission medium that sends signals using infrared light waves. Mobile computers and devices, such as a mouse, printer, and smart phone, often have an IrDA port that enables the transfer of data from one device to another using infrared light waves.

Broadcast Radio• Broadcast radio is a wireless transmission

medium that distributes radio signals through

the air over long distances such as between cities, regions, and countries and short distances such as within an office or home.

Cellular Radio• Cellular radio is a form of broadcast radio that is used widely for mobile communications, specifically wireless modems and cell phones.

Microwaves• Microwaves are radio waves that provide

a high-speed signal transmission. Microwave

transmission, often called fixed wireless, involves sending signals from one microwave station to another . Microwaves can transmit

data at rates up to 4,500 times faster than a

dial-up modem.

Communications Satellite

• A communications satellite is a space

station that receives microwave signals from

an earth-based station, amplifies (strengthens)

the signals, and broadcasts the signals back

over a wide area to any number of earth-based

Stations.