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Chapter 7
Networking: Computer Connections
1
Basic Components of a
Network
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Sending device
Communications link
Receiving device
Data Transmission Methods
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Digital transmission
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Distinct pulses
0’s and 1’s
Data Transmission Methods
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Analog transmission
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Continuous electrical signal
Carrier wave
Amplitude -- height of each wave
Frequency -- number of times the
wave repeats per second
Data Transmission Devices
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Modem (MOdulator/DEModulator)
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Capable of 56,000 bps (56 Kbps)
bps = bits per second
Receive speed limited to 53 Kbps
Transmit speed limited to 31 Kbps
← FCC restrictions
Data Transmission Devices
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ISDN
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-- Integrated Services Digital Network
Digital data
Speeds of 128,000 bps
Connect and talk on the phone at the same time
Requires an adapter & upgraded phone service
Expensive to set up + requires monthly fees
Data Transmission Devices
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DSL
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– Digital Subscriber Line
Conventional telephone lines
DSL modem: converts digital  analog
Many times faster than 56K modem
Computer and voice share phone line
Must be within 3 miles of telephone
company switching office
Data Transmission Devices
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Cable modems
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Coaxial cables
Does not interfere with cable TV
Up to 10 million bps
Always on
Shared capacity: More users mean slower
Security problem
Data Transmission Devices
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Cellular Modems
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Useful for people on the move
Slow speed
Transmission Types
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Asynchronous transmission
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Start/stop transmission
Low-speed communications
Transmission Types
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Synchronous transmission
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Blocks of data transmitted at a time
More complex and expensive
Faster transmission
Transmission Types
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Simplex
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Half-duplex
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One direction only
Either direction
Only one way at a time
Full-duplex
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Both directions at once
Communications Media
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Bandwidth = range of
frequencies that
medium can carry
Wire pair (twisted
pair)
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Inexpensive
Telephone systems
NOISE
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Electrical interference
Anything that disrupts the signal
High voltage equipment
Lightning
Even the sun can cause noise
Communications Media
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Shielded twisted pair
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Protective sheath
Reduces noise
Increases speed
Communications Media
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Coaxial cable
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Higher bandwidth
Less susceptible to noise
Cable TV systems
Communications Media
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Fiber optics
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Transmits using light
Higher bandwidth
Immune to electrical
noise
More security
Communications Media
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Microwave transmission
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Line-of-sight
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Relay stations
High speed
Weather can cause
interference
Communications Media
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Satellite transmission
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Microwave transmission
Satellite acting as relay
Long distance
Satellite Transmission
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Uplink – signal travels from the earth to
the satellite
Downlink – signal travels from the
satellite to the earth
Geosynchronous orbit – communication
satellites stay positioned over the same
point on the earth
Protocols
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Set of rules to exchange data
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What form of data transmission will be
used?
What is the transmission speed?
What duplex setting is needed?
Without a protocol, computers cannot
communicate with each other
Protocols
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Standards
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Assists with coordination
TCP/IP
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Transmission Control Protocol/Internet Protocol
Permits any computer to communicate with the
internet
Network Topologies
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Topology = the physical
layout of a network
Star network
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Central computer (hub)
Prevents collisions
Node failure—no effect on
overall network
Hub failure—network fails
Network Topologies
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Ring network
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Circular connection in one
direction
No danger from collisions
Node failure — entire
network fails
Network Topologies
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Bus network
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All nodes attached to a single line
Collisions result in re-send
Node failure—no effect on overall network
Wide Area Networks
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Large geographical area
Dial-up service
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Temporary connection
POTS
Dedicated service
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Permanent connection
Own dedicated circuits
Leased lines
Network Software
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File transfer software (FTP)
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Download – copy a file from another computer to
your computer
Upload – copy a file from your computer to
another computer
Local Area Network
Components
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PCs
Network cable
Network Interface Card (NIC)
Connecting LANs
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Bridge
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Router
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Connects LANs with similar protocols
Directs traffic to best path
Gateway
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Connects LANs with varying protocols
Uses of Networks
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E-mail
Facsimile (FAX)
Groupware
Teleconferencing and video
conferencing
Uses of Networks
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Electronic Fund Transfers
ATM
Telecommuting
Online services
The Internet