Telecommunications & Networks

Chapter 8

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Chapter 8 Model

User

User ComputerHWSW

Connections

Internet

LANWAN

Voice/Telephone Systems

Network Operating SystemNetwork Management

SecurityAdministration

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Convergence

• Merging of technologies– Applications

• Edutainment (Bill Gates’ word for merging of education & entertainment, as in Typing Tutor)

• MS Windows expanding to include browser, email, etc.

– Hardware• Computers & communications formerly managed by two

different departments in an organization; now usually managed by one department

• Increasingly deregulated industries can now develop & produce in areas in which they were previously restricted

• Any place/any time/any device concept means one device to do almost anything

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Information Superhighway

• More than the Internet• ALL communications channels, no matter what

the bandwidth/speed• Used for all purposes

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Telecommunications System Components

• Computers/terminals• Communications channels (composed of

communications media)• Communications processors• Communications software

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Telecommunications System Functions

• Transmits information• Establishes interface between sender & receiver• Routes messages along most efficient paths• Performs elementary processing to ensure

message is received by right recipient• Edits message to ensure that message received

is same as message sent• Converts messages for speed & format

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Analog vs. Digital Signals

• Analog– Continuous wave– Telephone, television, radio– Signal attenuates, losing strength over distance– Repeated or amplified signal may not be exactly the

same as original signal• Digital

– Discrete signal (not continuous): on/off– Electric light switch (not rheostat)– Signal attenuates less– When repeated or amplified, signal is restored to original

pattern• Modem converts analog/digital signals

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Communications Channels #1

• Means by which signal is transmitted from one device to another

• Can use different kinds of transmission media

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Communications Channels #2

• Wired– Twisted wire (twisted pair; untwisted pair)

• Cheap, easy to install, slow

– Coaxial cable (thick & thin)• Reasonable, harder to install, faster

– Fibre optic cable (signal is light pulses, not electricity)• Expensive, hard to install, fastest• Originally backbone media, but now extended to buildings,

homes, etc.• Optical networks use fibre optic cable• DWDM (dense multiwave division multiplexing) means more

signal can be sent at one time: faster

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Communications Channels #3

• Wireless–Uses electromagnetic spectrum (EMS)–Ranges of frequencies of EMS assigned for different

functions–Microwave systems: line-of-sight, only 25-30 miles apart–Satellite systems: geosynchronous orbit (same concept

as line-of-sight), high orbit (22,000 miles above earth) vs. low orbit (much closer, can receive weaker signals from cheaper microwave stations)

–Paging systems, cellular telephones, personal communication services (PCS), personal digital assistants (PDA)

–Mobile data networks

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Speed

• Bandwidth: Range of frequencies that can be accommodated on a particular channel; greater the range, greater the transmission capacity

• Baud: Binary event representing signal change from positive to negative or vice versa; not the same as bit rate (bits per second – bps); bit rate generally higher than baud rate

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Communications Processors & Software

• Communication Processors– Front-end processor– Concentrator– Controller– Multiplexer (MUX)

• Software to run all of these processors– Network, access, & transmission control– Error detection/correction– Security

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Network Topologies #1

• Star– Central “hub” computer– All messages go through hub computer - centralization – If hub computer fails, network fails (single point of failure)

• Tree (extended star)

• Bus– Single circuit connects all computers– “Collisions” possible (depends on model)

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Network Topologies #2

• Ring– Computers connected in a circle,

data flow in only one direction– Failure of one computer may

crash network (solution: ring-star)

• Hybrid– Combination of more than

one of the three network topologies

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PBXs, LANs, & WANs #1

• PBX: Special purpose computer for handling telephone calls and data– Do not require special wiring (just telephone wiring)– Geographic scope limited– Cannot handle high volume data traffic

• LAN: Network over a limited distance with dedicated channels– Server– Gateway/bridge/router– Network operating system (NOS)– Peer-to-peer or client/server

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PBXs, LANs, & WANs #2

• WAN: Network over a larger distance that may use multiple, non-dedicated channels– Switched lines– Dedicated lines– Satellites, etc.

• Converged networks– Deliver voice, data, video, etc. in a single network

infrastructure– Unified messaging systems combine voice, fax, &

e-mail in one system

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Network Services & Broadband• VAN: Private, multipath, data-only, network

managed by a 3rd party that adds services, such as protocol conversion; cheaper than owning because costs are shared by subscribers

• Packet switching (X.25)• Broadband technologies

– Frame Relay– ATM (asynchronous transfer mode)– ISDN (Integrated Services Digital Network)– DSL (digital subscriber line)– Cable model– T1 line (T3)

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Telecommunications Technologies• E-Mail

• Groupware• Voice Mail• Fax• Teleconferencing

– Data-– Video-

• Digital information services– AOL, Yahoo!, MSN, Lexis

• Distance education (synchronous or async.)

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EDI

Electronic data interchange: Transfer of standardized data between computers of different organizations– Lowers transaction costs– Reduces paperwork & errors– Can lock in customers & suppliers– Can minimize inventory & inventory costs– Previously used private networks but moving toward

use of the Internet and XML

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Case: Monitoring Employees on Networks

• Is it ethical? Is there a yes or no answer to this question? If not, when is it ethical? When is it unethical?

• Do you believe that zero tolerance for personal use of computers while at work is an appropriate policy? Why yes or why not?

• ALWAYS ask what the policy is in your organization (including the U of M)

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Next Class

• Chapter 9: The Internet & The New IT Infrastructure

• Case Study: General Motors