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Chapter 7Chapter 7

Telecommunications – Part 1Telecommunications – Part 1

Outline

Telecommunications Model Analog SignalDigital Signal Communication media (twisted wire, coaxial cable, fibreoptic, microwave, satellite signalling)Computer NetworkLocal Area Network (LAN) Wide Area Network (WAN) Network HardwareNetwork SoftwareNetwork Topology Packet and Circuit Switching

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TelecommunicationsInformation Systems for

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Telecommunications

Telecommunications: Electronic data transfer (communications) over some a channel (medium).

Telecommunications system contains:

Sender & Receiver

Message - Data that is transmitted as a signal over a channel Channel - The medium by which data or voice are transmitted

between sender and receiver (e.g., twisted wire, optical cable, air—

microwave, satellite signaling)

Other equipment (switch, relay, modem, gateway, etc.)

sender receiverrelay

electronic signal (message)

channel

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Types of Signals

Analog signalContinuous waveformCan get all the rangesUse: voice communicationsExample: electrical light

Digital signalDiscrete waveformTwo states: 0 and 1 (On-off electrical pulses)Use: data communicationsExample: computer, computer nets

Modem (MOdulation / DEModulation)

Converts digital into analog, and analog into digital signals

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Medium Speed

Fiber optic cable 6 Tbps

Coaxial cable 1Gbps

Twisted wire Up to 1Gbps

Microwave 600 Mbps

Satellite 600 Mbps

bps=bits per second; Kbps=kilobits (103); Mbps=megabits (106); Gbps=gigabits (109); Tbps=terabits (1012)

Telecomm Media & Transmission Speeds

Total amount of data transmitted through a telecommunications channel measured as bits per second.

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Networks

Network - A set of nodes (computers, printers, and other equipment) and linking media.

Types of networks based on:

Topology (configurations of nodes and links; e.g., star network)

Geographic scope – LAN vs. WAN

Communications method – Circuit vs. Packet

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All computers are connected to a central node (e.g. hub, computer, switch, controller).

All communications between computers must pass through the central node.

Better communications control, but the central node is critical (high-risk).

hub, switch,controller, orcomputer

Star Network

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Bus Network

All computers are linked by a single circuit

All messages are broadcast to the entire network

Simple communications management as signals can travel both directions as needed, but collision possible.

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Ring Network

All computers are linked by a closed loop

Data is passed in one direction from one node to another

Better control and no collision, but communications management more complex than with bus.

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LAN vs. WAN

Local Area Network (LAN)

Network covering a smaller area (one or more buildings like campus)

Wide Area Network (WAN)

Network covering a larger area (a region, world)

Examples: IBM’s SNET, Internet

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Circuit Switching

Circuit Switching

Entire message travels

from switch to switch

Used for analog signals

(classical telephone

network)

Source: TechWeb

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Packet SwitchingPacket Switching

Sender breaks message into small packets Packets are routed in the most economical way by different routesReceiver reassembles the message Internet works this way

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Network Hardware

Router, Switch –most used todayDevices for managing communications on a network

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Network Software

Network Operating System (NOS)Software that routes and manages communications & resources (e.g., Ethernet OS for bus network, IBM toke Passing Ring OS for ring network, Windows Server and Client NOS)

Network ProtocolRules that govern communications between network nodes (e.g., how computers on a bus network communicate;

TCP/IP – how computers on different networks communicate)

NOS can support a certain protocol and more than one (TCP/IP today supported by most NOSes)

Transfer Control Protocol & Internet Protocol (TCP/IP)

Defines the Internet – how different networks (NOSes, hardware, application and system software) communicate with each other.Four layers:

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TCP

IP

Email (SMTP), file transfer (FTP,

HTTP

How Internet Works

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SMTP to TCP: “Take this messageand send it to thisemail address”.

TCP Breaks message intopackets and passes to IP.

IP Looks up Internet addresses and routers on the way toreceiver. Puts addresson each packet and passes to Network.

Puts packets on com-munication medium.

SMTP restores original formatof message and presents it.

TCP Put packets back to the Whole in proper orders and Checks sum of data received vs. sum sent.

IP Accepts packets and reports back to routers.

Gets packets off com-munication medium.

SENDER RECEIVER

See: How SMTP and TCP/IP work