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