Post on 21-Dec-2015
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
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 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
Connecting LANs
Bridge Connects LANs with similar protocols
Router Directs traffic to best path
Gateway Connects LANs with varying protocols