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Transcript 
Computer Networks and the Internet
• Internet Service Providers (ISP)
• Networks
– WAN Wide Area Network
– LAN Local Area Network
• Computers
– Sneakernet
• Sharing
• ARPA
• Internet
Phone vs. Data
•
•
•
•
Point to Point
Single Address per line
All calls to a Central Office
Party (Shared) Lines
Telephone Communications
World
Logan
Central
Office
USU
Central Office
Trunks (Fiber and Copper)
Switch Control
Console
Subscribers
(Mostly
Copper
Wire)
Cross point
Switch
Electrical Parameters
• Voltage (Electromotive Force)
• Current (Amperes, # of electrons flowing)
• Resistance (conversion of energy)
– ohms
• Impedance (Alternating Current
Resistance)
– Henrys (inductors), farads (capacitors)
Electrical Circuit
•
DC
Capacitor (Farads)
6Volts
Voltage
Source
Inductor (Henrys)
Resistor (Ohms)
Components
• Resistor
– Turns electrical energy into heat linearly
• Capacitor
– Holds electrical charge, discharges logarithmically
• Inductor
– Holds electrical energy as magnetism, discharges
logarithmically
Square Wave
Fast Square Wave
Logarithmic Curve
Exponential Curve
Sine Wave
Transmission Line Equivalent
Transmission Speeds
•
•
•
•
•
•
•
Cycles per second (Hertz)
Bits per second
Baud
1GB/sec (Ethernet)
100MB/sec (Ethernet)
10MB/sec (Ethernet)
1.544MB/sec (DS1)
Twisted Pair Transmission Line
• Category 3
• Category 5 (More twists per inch)
Transmission Line details
•
•
•
•
Characteristic Impedance
Termination
Length Limitations
Loss due to
– Resistance
– Crosstalk
– Mutual Inductance
• Radiation
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
Fiber Optics
• Single Mode
Light Source
Light Detector
• Multimode
Light Detector
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
Conversations
Airplane Trip
•
•
•
•
•
•
Ticket (purchased)
Baggage (check)
Gates (load)
Takeoff
Routing
Routing
Ticket (complain)
Baggage (claim)
Gates (unload)
Landing
Routing
Communication Subsystems
Typical layers in a communication subsystem
System 1
System 2
Application
Application
Presentation
Presentation
Program 1 (Session)
Program 2 (Session)
Transport
Network
Data Link
Physical Link
The layers communicate via protocols
Transport
Network
Data Link
Physical Link
Communication Subsystems
Typical layers in a communication subsystem
System 1
System 2
Application
Application
WSFTP,Netscape
Presentation
Session
Transport
Network
Data Link
Physical Link
FTP, HTTP
Sockets
TCP,SPX
IP,IPX
Ethernet
Wire
The layers communicate via protocols
Presentation
Session
Transport
Network
Data Link
Physical Link
Physical Layer
• Operates on the wire using the following
standards:
• Fiber Optic (long distances)
• Ethernet (twisted pair, fiber, coax)
• PPP (twisted pair phone lines)
Link Layer
• Operates using the following standards:
– Ethernet protocol
• Most LANS
– PPP (Point to Point Protocol)
• Phones Lines
• DSL
Network Layer
• Operates using the following standards:
– TCP/IP (Tranmission Control Protocol/Internet
Protocol
– IPX (Internet Packet Exchange)
– AppleTalk
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