Internet Overview

1Internet Technology

Internet Technology

What is the Internet?

An internet is a set of computer networks that are connected to each other (e.g. intranet).

The Internet is a world-wide set of networks that interoperate using TCP/IP protocols.

► Think of “communication software” or “standards” when you see “protocol”

► more on TCP/IP and other protocols later…

A global channel for digital communication and data exchange.

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Internet Technology

What is the Internet?

widit.knu.ac.kr155.230.194.245

www.whitehouse.gov96.16.242.135

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google.com74.125.224.72

How does the Internet work?

Postal Analogy► Common language

• e.g., Korean, English► A letter► An envelope

• stamped & addressed► Physical delivery

• via the postal stream

Internet► Application protocols

• HTTP, SMTP, SSH, SFTP► Digitized data► Communication protocols

• TCP/IP► Connection to the Internet

• NIC, wire/wireless, routers

Internet Technology 4

Internet Technology

Networking Basics:Main considerations for the Internet

Need homogeneous communications between heterogeneous hardware and software.

► Communication Protocols• Transmission Control Protocol / Internet Protocol

► Addressing System• Domain Name System (Service)

► Layered Networking Structure

Need efficient method of data exchange for a distributed and decentralized system

► Client-Server model

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Networking Basics:Circuit and Packet Switching

Internet Technology

Packet Switched Communication

Circuit Switched Communication

Dedicated Line

Sender Receiver

Data broken up into packets

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Internet Technology

Communication Protocol

TCP (Transmission Control Protocol)► Responsible for ensuring reliable & accurate delivery of data

• e.g., error-checking, end-to-end acknowledgement, etc.► Breaks up a file to transmit into a set of TCP “segments”.

• TCP header contains sequence #, ACK, checksum

IP (Internet Protocol)► Method for Routing Data

• Defines how packets reach specified destination► Best-effort delivery (i.e. connectionless, unreliable)

• data corruption, lost packets can occur► Encapsulates a TCP segment in an IP packet

• IP header contains the source/destination IP address

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Internet Technology

Internet Protocols Application Layer Protocols

Application layer protocols► ensure that the sender and receiver are speaking the same

language, and that the letter can be interpreted► HTTP, FTP, SMTP , Telnet/SSH

HyperText Transfer Protocol

File Transfer Protocol

Simple Mail Transfer Protocol

Telnet Protocol

Transmission Control Protocol

Internet Protocol

IP Packet LAN8

Internet Technology

Networking Basics:Four Layer Model

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• Applications Interface• e.g., HTTP, SMTP, SSHApplications

• Reliable Delivery• i.e., TCPTransport

• Source to Destination• i.e., IPNetwork

• Hosts, routers, wires, etc.Physical

Internet Technology

How does the Internet work? Communication on the Internet

Data

Packet Packet Packet

Application(e.g. Chrome)

Network Interface(i.e. TCP/IP)

Data

Packet Packet Packet

Application(e.g. Web server)

Network Interface(i.e. TCP/IP)

Physical (wire, router, hosts)

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Internet Technology

Internet Addressing

IP address ► a unique number assigned to a host ► assigned by IANA ► e.g. 155.230.194.245

Hostname► a human-readable name assigned to a host► named by organizations► e.g. widit.knu.ac.kr

Domain name► a name assigned to an entity. ► e.g. knu.ac.kr

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Internet Technology

Internet Addressing: Domain Name System (DNS)

Hostname to IP Address mapping system► DNS servers store the name/address pair.► Applications use resolvers query DNS servers.

Main Characteristics► Hierarchical

• Sub-domains on the left (e.g. lis.knu.ac.kr)

► Distributed• Authoritative name servers for each domain & sub-domains• When a DNS server is missing an entry, next server is checked• A client (resolver) must know at least 1 DNS server

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Internet Technology

Internet Addressing: DNS is Hierarchical

.edu

unc.eduncsu.edu duke.edu

med.unc.educs.unc.edu ils.unc.edu

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Internet Technology

Internet Addressing Hostname vs. IP Address

SpecificityMost Least

Top Level Domain

Specificity

Assigned locallyIANA assigned155.230.194.245

widit.knu.ac.kr

Least Most

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Internet Technology

Internet Addressing:Anatomy of a URL

URL stands for Universal Resource Locator► sometimes seen as Uniform Resource Locator

http:// knu.ac.kr /~kiyang/teaching/IT/s13/schedule.htm

Protocol Domain Item requested

Fully qualified resource name

• Certain protocols assume certain ports (e.g., http → port 80)• When non-standard port is use, it can be specified in the URL - e.g., http://widit.knu.ac.kr:8800/

widit.

Hostname

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Internet Technology

ClientInitiates a Connection

Server Waits & Responds to Incoming Connections

Client Application Server Applicationprogram running on

client machine(e.g., Internet Explorer)

Application Protocol(HTTP)

Client-Server Model

155.230.194.233 155.230.194.245

program running on server machine

(e.g., Apache Web Server)

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Internet Technology

Client-Server Model: Overview Servers

► Can be hardware (computers) or software (programs)► One computer can run many server applications.

• e.g., http (web), ftp, email, telnet, etc.• Server Address = IP address + port number

► Each server application listens on a different port• e.g., http → 80, SMTP → 25, telnet → 23, ssh → 22, ftp → 21

Clients► There can be many clients for a given application► People interface with them directly

• HTTP Clients: Internet Explorer, Firefox, Chrome• Email Clients: Outlook, Pine, Lotus Notes• Telnet/SSH Clients: Putty, SSH Secure Shell

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Web Authoring

18Internet Technology

Publishing HTML Content Creation Mode #1

► Create HTML pages on the local PC using Notepad, Dreamweaver, etc.► Upload the files to the server to be displayed on the Web

Content Creation Mode #2► Create HTML pages directly on the server using pico, vi, etc.

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Edit

Edit

Publish

Publish

Display

Display

upload

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An Opte Project visualization of routing paths through a portion of the Internet