Telecommunications & Networks

Chapter 6

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Communication Model

Message is communicated via a signal Transmission medium (communication channel)

“carries” the signal

Feedback

Encode Decode

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Telecommunications

Electronic transmission of signals, e.g., telephone, radio, television

Telecommunication medium: Anything that carries an electronic signal & interfaces between a sending device & a receiving device

Data Communications: A subset of telecommunications referring to the sending, transmission, & receiving of data -- typically between computer systems

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Communications & TelecommunicationsIn human speech, signals are transmitted through the

air; in telecommunications, signals are transmitted through various media

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Elements of Telecommunications

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Types of telecommunication Media (1)

Twisted Pair Insulated copper wire Electrical signals

Coaxial Cable Inner wire core surrounded by shielding Electrical signals Higher transmission speeds than twisted

pair Fiber-optic Cable

Extremely thin strands of glass bound together

Light pulse signals Very high transmission speeds

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Types of Telecommunication Media (2)

Microwave Satellite

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Types of Telecommunication Media (3)

Cellular transmission signals are transmitted to receivers & integrated into the regular network.

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Modems

Translate digital signals to analog for transmission over the Public Switched Telephone Network (PSTN)

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Carriers & Services (1)

Common Carriers: Long distance telephone companies (AT&T, Sprint)

Value-Added Carriers: Private telecom systems offering enhanced services for a fee

Switched Lines: Circuits that use switching equipment to allow one device to connect to other devices (typical phone lines)

Dedicated Lines: Point-to-point circuits with no switching or dialing

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Carriers & Services (2)

Private Branch Exchange (PBX)Telecommunications switching equipment that allows

users within an organization to share outside linesCapable of handling both voice & data traffic

Integrated Services Digital Network (ISDN)Uses existing telecommunications infrastructure to

simultaneously transmit digital voice, data, & videoBeing phased out in North America (cable & ADSL are

replacing this service) T1 Circuits

High speed dedicated lines (1.54 Mbps) Equivalent to 24 regular voice lines

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Types of Network Configurations

Ring Bus

Star

Hierarchical

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LANs & WANs

Local Area Network (LAN): Connects computer systems & devices in the same geographic area (can be ring, bus, hierarchical, star, hybrid)

Wide Area Network (WAN): Ties together large geographic regions using microwave & satellite transmission or telephone lines

International Network (Global Area Network: GAN): Links systems between countries

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Types of Computing Connectivity (1)

Terminal-to-Host Applications & databases

reside on host mainframe computer

User accesses applications via a “dumb” terminal

File ServerFile server transfers data &

programs to PCs on the network where the PCs perform most processing.

“Dumb”terminal

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Types of Computing Connectivity (2)

Client/ServerApplications & databases reside on specialized host

computers (servers)Processing is shared between the host server & the

clientClient & server may be different types of computers

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Advantages & Disadvantages of Client/Server Computing

AdvantagesReduced costs Improved performance Increased security

Disadvantages Increased costsLoss of controlComplex multi-vendor

environment

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Communication Software

Communications Software: Provides error checking, message formatting, communication logs, data security/privacy, & translation capabilities for networks

Network Operating System (NOS): Systems software that controls the devices on a network & allows them to communicate with each other

Network Management Software: Monitors the use of network resources, scans for viruses, & ensures compliance with software licenses

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Communication Protocols

Protocol: Rules that ensure communications among different types of computers from multiple manufacturersOpen Systems Interconnection (OSI): Leading protocol

“model”; comprised of 7 layersTransmission Control Protocol/Internet Protocol

(TCP/IP): Two communication protocols of the Internet that work together (rapidly overtaking OSI)

Systems Network Architecture (SNA): IBM’s proprietary communication protocol

Ethernet: Protocol standard developed for LANs using a bus topology

X.400 & X.500: Standards for message handling & network directories

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Bridges, Routers, Gateways, & Switches

Bridge: Connects two or more networks that use the same protocol at the media control sublayer of the data link layer

Router: Operates at the network level of the OSI model with more sophisticated addressing software than bridges; can determine preferred paths

Gateway : Operates at or above the OSI transport layer & links LANs or networks that employ different architectures & use dissimilar protocols

Switch: Switches data to its destination by a point-to-point (rather than shared) connection

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Telecommunications Applications (1)

Linking computers & data terminals: Download & upload information

Voice Mail: Enables users to send, receive, & save verbal messages, including sending the same message to a “group”

E-mail: Enables users to send, receive, & save text messages & attached documents

Telecommuting: Enables employees to work away from the office using PCs & networks to communicate electronically

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Telecommunications Applications (2)

VideoconferencingAllows participants to

conduct long-distance meetings “face to face” while eliminating travel

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Telecommunications Applications (3)

Electronic Data Interchange (EDI)

Uses networks to allow output from one organization’s system to be processed directly as input to another organization’s systems, without human

intervention; follows standards & procedures

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Case: Nav Canada, pages 284-285

Next Class: Chapter 7