Asynchronous and Synchronous

1
Asynchronous and Synchronous

• Asynchronous Transmission
• Low speed
• Modem needed
• Transmitted as needed
• Start/stop bits used
• Synchronous Transmission
• High speed
• Source and destination in synch
• No start/stop bits needed

2
Data Communications Hardware

• Data communication hardware is used to transmit
  digital information
• There are many devices that enable data
  communication
• Concentrators
• Hubs
• Bridges
• Routers
• Brouters
• NIC
• Modems
• And more

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The Standard Telephone-Link Modem

• Modulator-demodulator
• Converts digital signals to analog signals for
  transmission over phone lines
• Internal and external
• Usually a voice/data/fax modem

4
Other Modems

• Cable modem
• Supports cable Internet
• DSL modem
• High-speed Internet connection using fiber-optic
  cable

5
Network Interface Cards

• Allows exchange of data via a LAN

6
Terminals

• Enables both input and output from a remote
  computer system
• Dumb and smart terminals
• Examples
• VDT (hospitals and airports)
• Windows terminals
• Telephone terminals
• Special function (ATMs)

7
Networks

• Networks are about sharing and communicating
• Networks allow printers, data, Internet access,
  and more to be shared

8
Network Topologies

• Network topology is a description of the possible
  physical connections within a network
• It is a configuration of hardware and it shows
  which pairs of nodes can communicate

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Network Topology - Star

• Easy to install/not that expensive
• Computers are concentrated into a star pattern
  using hubs or switches
• Hubs broadcast data to all devices
• Switches can be used instead of hubs
• Switches can help segment data traffic but are
  more expensive
• If there is a break in the cable it does not
  disturb the other computers

10
Network Topology - Ring

• Uses different hardware
• More expensive
• Complex to install
• Data is passed around the ring until it reaches
  its destination
• Best at passing data with less collisions

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Network Topology - Bus

• Least expensive/easiest to setup
• Uses coax cable
• Computers are daisy chained together in a linear
  bus
• Data packets are sent along the coax cables
• All computers hear data sent out

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Network protocols transmission control

• Token ring one-way communication around ring
  network
• Ethernet
• Uses carrier sense, multiple access with
  collision detection (CSMA/CD)
• Popular for bus networks
• Like a conversation in small group

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Communication over a ring network
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Communication over a bus network
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Types of Networks

• Local Area Network (LAN)
• Small network
• Usually confined to a building or an office floor
• Wide Area Network (WAN)
• Two or more LANs connected together
• The Internet is an example

16
Connecting networks

• Bridge connects two compatible networks
• Router connects two incompatible networks
• Resulting network is called an internet

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The distinction between a bridge and a router
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A typical approach to connecting to the Internet
19
Electronic mail

• Mail server set up by domain owner
• Mail sent from domain members goes through mail
  server
• Mail sent to domain members is collected by mail
  server
• Mail delivered to clients on demand
• POP3
• IMAP

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Package-shipping example
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Following a message through the Internet
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Wide Area Network Example
B
A Source
E Destination
D
C
Possible paths A-B-E A-B-D-E
A-C-D-E
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Home Network

• Home networks are becoming more popular
• Home networks are typically peer-to-peer
• A router keeps track of all the computers inside
  the home network
• The computers are configured with fake IP
  addresses that allows them to communicate
• Setup for a home computer is fairly easy