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CIS 115

How the Internet Works

Circuit Switching

Image Source: Wikipedia







Packet Switching - Paul Baran

Image Source: Wikipedia

7 Layer OSI Network Model

  • Application
  • Presentation
  • Session
  • Transport - TCP/UDP
  • Network - IPv4/IPv6
  • Data Link - Ethernet
  • Physical - 100BASE-T

Encapsulation

Image Source: Wikipedia

Physical - 100BASE-T

Image Source: Wikipedia

Data Link - Ethernet

Image Source: Wikipedia

Network - IPv4

IPv4 Packet Structure
Version InfoLength
Packet IDFlags & Offset
Protocol & TTLChecksum
Source IP Address
Destination IP Address
Data...

IPv4 vs. IPv6

IPv4: 32 bit Addresses
232 = 4,294,967,296

IPv6: 128 bit Addresses
2128 = 340,282,366,920,938,463,463,
374,607,431,768,211,456
or 340 Undecillion addresses

Network - IPv6

Image Source: Wikipedia

Image Source: XKCD

Transport - TCP

TCP Packet Structure
Source PortDest. Port
Sequence Number
Acknowledgement Number
OptionsLength
ChecksumUrgent
Data...

Transport - UDP

UDP Packet Structure
Source PortDest. Port
LengthChecksum
Data...

TCP vs. UDP

TCPUDP
Connection OrientedConnectionless
ReliableUnreliable
AcknowledgeNo Acknowledge

Applications

  • POP/SMTP/IMAP - Email
  • HTTP/FTP - World Wide Web
  • DNS/DHCP - Network Setup
  • SSH/RDP/Telnet - Connections

Domain Name System (DNS)
"Phonebook for the Internet"

  • www.ksu.edu → 129.130.8.49
  • www.google.com → 74.125.227.116
  • www.ibm.com → 129.42.60.216
  • www.yahoo.com → 98.138.253.109

Image Source: Wikipedia

DNS Lookup

Image Source: Wikipedia

Dynamic Host Configuration Protocol (DHCP)

Image Source: Tech Juice

HyperText Transfer Protocol (HTTP)

Image Source: Wikipedia

Image Source: Wikipedia

HTTP Commands

  • GET
  • POST
  • HEAD
  • PUT
  • DELETE

HTTP Status Codes

  • 200
  • 301
  • 403
  • 404
  • 500
  • 503

HTTP Status Codes

  • 200 - OK
  • 301 - Moved Permanently
  • 403 - Forbidden
  • 404 - Not Found
  • 500 - Internal Server Error
  • 503 - Service Unavailable

Assignments

  • Read and be prepared to discuss:
    • Tubes Chapter : The Whole Internet
  • Blog 8: TBD - Due 10/26 10:00 PM
  • Wiki Article Draft - Due Friday 10/23 10:00 PM

Blog 8: How has the Internet Influenced You?

The internet has been a major force in our lives for several decades now. Write about how the internet has influenced you as a person. Try and think about ways that you would be a different person if you didn’t have the internet. Things you can think about:

  • Instant Messaging, Email and Social Media
  • Online Gaming
  • Wikipedia and Simple Online Research
  • Availability of Media Online

DHCP Request

DHCP Response

DNS Lookup

DNS Response

HTTP Request

HTTP Response