Transcript High-speed digital telecommunications networks that are national or

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TELECOMMUNICATIONS
AND NETWORKS
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Telecommunications
Communicating information via electronic means over
some distance
Information SuperHighway
High-speed digital telecommunications networks that
are national or worldwide in scope and accessible by the
general public
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Components of a Telecommunications
System
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Computers
I/O devices
Communications channels – cables, telephone lines
Communications Processors – modems, multiplexors
Communications Software
Uses Protocols
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Types of Signals
• Analog signal
– Continuous waveform
– Voice communications
• Digital signal
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Discrete waveform
Two states: 0 and 1
On-off electrical pulses
Data communications
• Modem
– Translates b/t digital and analog
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Communications Channels
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The links by which data or voice are transmitted
Twisted wire
Coaxial cable
Fiber-optic cable
Wireless
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microwave
Satellite and other wireless channels
Pagers
Cellular phones
PCS
PDAs
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Transmission Speed
• Transmission
– Bits per second (bps)
• Bandwidth
– Range of frequencies that can be accommodated on a
channel
– Greater range  Greater bandwidth  Greater
capacity
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Speeds and Costs
Medium
Speed
Twisted wire
300 bps – 10 Mbps
Microwave
256 Kbps – 100 Mbps
Satellite
256 Kbps – 100 Mbps
Coaxial cable
56 Kbps – 200 Mbps
Fibre optic cable
500 Kbps – 6+ Tbps
Cost
Low
High
Bps=bits per second; Kbps=kilobits per second; Mbps=megabits per second;
Tbps=terabits per second
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Communications Processors
• Front- end processor
– Special purpose computer that manages communication for host computer in
a network
• Concentrator
– Computer that collects & temporarily stores messages from terminals for
batch transmission to host computer
• Multiplexer
– allows channel to carry data from multiple sources simultaneously
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Network Topologies: Star
All computers and
devices connected to a
central host computer
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Network Topologies: Bus
All computers are
linked by a
single circuit
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Network Topologies: Ring
All computers are
linked by a closed
loop
Data is passed in one
direction
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Local Networks
• Private branch exchange (PBX)
– Firm’s central switching system
– Handles digital and voice
• Local area network (LAN)
– Dedicated channels
– Limited distance (less than 700 metre radius)
– Higher capacity than PBX
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Typical LAN
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LAN Technology
• Gateway
– A communications processor that connects dissimilar networks
• Router
– A device that forwards packets of data between similar networks
• Bridge
– A device that connects segments of the same or similar networks
• Network operating system (NOS)
– Coordinates resources
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Wide Area Networks (WAN)
A telecommunications network that spans a large
geographical distance
• Switched lines
– Telephone lines used by a computer to send data
• Dedicated lines
– Continuously available
– Conditioned to transmit data at high speeds
• MAN and GAN
– Metropolitan and global area networks
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Network Technologies
• Packet Switching
– Data broken into small packets
– Packets are then routed in the most economical way
• Frame Relay
– A shared network service technology that packages data
into bundles
– Does not use error-correction
– Cheaper and faster than packet-switching
• Asynchronous Transfer Mode (ATM)
– Information parceled into 8-byte cells
– Data transmitted between computers of any vendor
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Network Technologies
• Integrated Services Digital Network (ISDN)
– Dialup: voice, data, image, video on single line
• Digital Subscriber Lines (DSL)
– Operate over existing telephone lines
– High speed transmissions
• Cable Modems
– Operates over cable lines to provide access to networks
• T1 Line
– Dedicated telephone line, rate of 1.544 Mbps
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Electronic Data Interchange (EDI)
Computer-to-computer exchange of standard
business transaction documents
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