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Chapter 7

Networking: Computer Connections

Basic Components of a Network Sending device Communications

link Receiving device

Data Transmission Methods

Digital transmission Distinct pulses 0’s and 1’s

Data Transmission Methods

Analog transmission Continuous electrical

signal Carrier wave Amplitude Frequency

-- height of each wave

-- number of times the wave repeats per second

Data Transmission Devices Modem (MOdulator/DEModulator)

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

ISDN 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

-- Integrated Services Digital Network

Data Transmission Devices

DSL 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

– Digital Subscriber Line

Data Transmission Devices

Cable modems 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

Cellular Modems Useful for people on the move Slow speed

Transmission Types Asynchronous transmission

Start/stop transmission Low-speed communications

Transmission Types Synchronous transmission

Blocks of data transmitted at a time More complex and expensive Faster transmission

Transmission Types

Simplex One direction only

Half-duplex Either direction Only one way at a time

Full-duplex Both directions at once

Communications Media

Bandwidth = range of frequencies that medium can carry

Wire pair (twisted pair) Inexpensive Telephone systems

NOISE

Electrical interference Anything that disrupts the signal High voltage equipment Lightning Even the sun can cause noise

Communications Media

Shielded twisted pair Protective sheath Reduces noise Increases speed

Communications Media

Coaxial cable Higher bandwidth Less susceptible to noise Cable TV systems

Communications Media Fiber optics

Transmits using light Higher bandwidth Immune to electrical

noise More security

Communications Media

Microwave transmission Line-of-sight

Relay stations High speed Weather can cause

interference

Communications Media Satellite

transmission Microwave

transmission Satellite acting as

relay Long distance

Satellite Transmission

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

Set of rules to exchange data 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

Standards Assists with coordination TCP/IP

Transmission Control Protocol/Internet Protocol

Permits any computer to communicate with the internet

Network Topologies Topology = the physical

layout of a network Star network

Central computer (hub) Prevents collisions Node failure—no effect on

overall network Hub failure—network fails

Network Topologies Ring network

Circular connection in one direction

No danger from collisions

Node failure — entire network fails

Network Topologies Bus network

All nodes attached to a single line Collisions result in re-send Node failure—no effect on overall

network

Wide Area Networks Large geographical area Dial-up service

Temporary connection POTS

Dedicated service Permanent connection Own dedicated circuits Leased lines

Network Software

File transfer software (FTP) Download – copy a file from another

computer to your computer Upload – copy a file from your computer to

another computer

Local Area Network Components

PCs Network cable Network Interface Card (NIC)

Connecting LANs

Bridge Connects LANs with similar protocols

Router Directs traffic to best path

Gateway Connects LANs with varying protocols

Uses of Networks

E-mail Facsimile (FAX) Groupware Teleconferencing and video

conferencing

Uses of Networks

Electronic Fund Transfers ATM Telecommuting Online services The Internet