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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
CentralOffice USU
Logan
World
Central OfficeTrunks
SubscribersCross pointSwitch
Switch ControlConsole
(Fiber and Copper)
(MostlyCopperWire)
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
Capacitor (Farads)
Inductor (Henrys)
Resistor (Ohms)
VoltageSource
6Volts
• DC
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
• Multimode
Light Source Light Detector
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)Ticket (complain)
• Baggage (check) Baggage (claim)
• Gates (load) Gates (unload)
• Takeoff Landing
• Routing Routing
• Routing
Communication Subsystems
Physical Link
Data Link
Network
Transport
Physical Link
Data Link
Network
Transport
Program 2 (Session)
System 1 System 2
Typical layers in a communication subsystem
The layers communicate via protocolsThe layers communicate via protocols
Program 1 (Session)
Presentation Presentation
Application Application
Communication Subsystems
Physical Link
Data Link
Network
Transport
Physical Link
Data Link
Network
Transport
Session
System 1 System 2
Typical layers in a communication subsystem
The layers communicate via protocolsThe layers communicate via protocols
Session
Presentation Presentation
Application Application
Wire
Ethernet
IP,IPX
TCP,SPX
Sockets
FTP, HTTP
WSFTP,Netscape
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