Computer Networks and the Internet

1
Computer Networks and the Internet

• Internet Service Providers (ISP)
• Networks
• WAN Wide Area Network
• LAN Local Area Network
• Computers
• Sneakernet
• Sharing
• ARPA
• Internet

2
Phone vs. Data

• Point to Point
• Single Address per line
• All calls to a Central Office
• Party (Shared) Lines

3
Telephone Communications
Central Office
USU
World
Logan
4
Central Office
Trunks
(Fiber and Copper)
Switch Control Console
Cross point Switch
Subscribers
(Mostly Copper Wire)
5
Electrical Parameters

• Voltage (Electromotive Force)
• Current (Amperes, of electrons flowing)
• Resistance (conversion of energy)
• ohms
• Impedance (Alternating Current Resistance)
• Henrys (inductors), farads (capacitors)

6
Electrical Circuit
Capacitor (Farads)

• DC

6Volts
Voltage
Source
Inductor (Henrys)
Resistor (Ohms)
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Components

• Resistor
• Turns electrical energy into heat linearly
• Capacitor
• Holds electrical charge, discharges
  logarithmically
• Inductor
• Holds electrical energy as magnetism, discharges
  logarithmically

8
Square Wave
9
Fast Square Wave
10
Logarithmic Curve
11
Exponential Curve
12
Sine Wave
13

Transmission Line Equivalent
14
Transmission Speeds

• Cycles per second (Hertz)
• Bits per second
• Baud
• 1GB/sec (Ethernet)
• 100MB/sec (Ethernet)
• 10MB/sec (Ethernet)
• 1.544MB/sec (DS1)

15
Twisted Pair Transmission Line

• Category 3
• Category 5 (More twists per inch)

16
Transmission Line details

• Characteristic Impedance
• Termination
• Length Limitations
• Loss due to
• Resistance
• Crosstalk
• Mutual Inductance
• Radiation

17
Transmission Line Losses

• Measured in DECIBELS
• Ratio of input voltage/current to output
  voltage/current
• DB 20log(voltage1/voltage2)
• 20 DB is 100 volts in and 10 volts out

18
Fiber Optics

• Single Mode
• Multimode

Light Detector
Light Source
Light Detector
19
Network Topologies

• Bus
• Simple but can be failure prone
• Star
• Simple, uses more wire than Bus, less failure
  prone
• Ring
• Like Bus system
• Mesh
• Redundant but complicated

20
Conversations
21
Airplane Trip

• Ticket (purchased) Ticket (complain)
• Baggage (check) Baggage (claim)
• Gates (load) Gates (unload)
• Takeoff Landing
• Routing Routing
• Routing

22
Communication Subsystems
Typical layers in a communication subsystem
System 1
System 2
Application
Application
Presentation
Presentation
Program 1 (Session)
Program 2 (Session)
Transport
Transport
Network
Network
Data Link
Data Link
Physical Link
Physical Link
The layers communicate via protocols
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Communication Subsystems
Typical layers in a communication subsystem
System 1
System 2
Application
Application
WSFTP,Netscape
Presentation
Presentation
FTP, HTTP
Session
Session
Sockets
Transport
Transport
TCP,SPX
Network
Network
IP,IPX
Data Link
Data Link
Ethernet
Physical Link
Physical Link
Wire
The layers communicate via protocols
24
Physical Layer

• Operates on the wire using the following
  standards
• Fiber Optic (long distances)
• Ethernet (twisted pair, fiber, coax)
• PPP (twisted pair phone lines)

25
Link Layer

• Operates using the following standards
• Ethernet protocol
• Most LANS
• PPP (Point to Point Protocol)
• Phones Lines
• DSL

26
Network Layer

• Operates using the following standards
• TCP/IP (Tranmission Control Protocol/Internet
  Protocol
• IPX (Internet Packet Exchange)
• AppleTalk