Internet Overview • Introduction to Internet Technology • Overview of Web Authoring

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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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What is the Internet?

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widit.knu.ac.kr 155.230.194.245

www.whitehouse.gov 104.118.93.61

google.com 74.125.232.230

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

How does the Internet work? Key Components

Need homogeneous communications between heterogeneous hardware and software.

Communication Protocols →Transmission Control Protocol / Internet Protocol

Addressing System →Domain Name System (Service)

Networking Structure →Four Layer Model

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

Application Structure →Client Server Architecture/Model

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Networking Basics: Circuit and Packet Switching

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Packet Switched Communication - Data is broken up into packets

Circuit Switched Communication - Dedicated line

Sender Receiver

A B C A B C

A B

C

Hello

Who’s calling?

Networking Structure: Four Layer Model

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

• Reliable Delivery • i.e., TCP Transport

• Source to Destination • i.e., IP Network

• Hosts, routers, wires, etc. Physical

Communication Protocols Transport & Network Layers

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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Ensure that the sender and receiver are speaking the same language, and that the letter can be interpreted

HTTP, FTP, SMTP , Telnet/SSH

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HyperText Transfer Protocol

File Transfer Protocol

Simple Mail Transfer Protocol

Telnet Protocol

Transmission Control Protocol

Internet Protocol

IP Packet

Communication Protocols Applications Layer

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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)

Communication on the Internet

Internet Addressing

IP address An 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 Addressing: Domain Name System (DNS)

Hostname to IP Address mapping system DNS servers store the name-address pair. Applications use resolvers to 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 Addressing: DNS is Hierarchical

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.edu

unc.edu ncsu.edu duke.edu

med.unc.edu cs.unc.edu ils.unc.edu

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Internet Addressing: Hostname vs. IP Address

Specificity Most Least

Top Level Domain

Specificity

Assigned locally IANA assigned 155.230.194.245

widit.knu.ac.kr

Least Most

URL stands for Universal Resource Locator a.k.a. Uniform Resource Locator

Certain protocols assume certain ports (e.g., http → port 80) When non-standard port is use, it can be specified in the URL

→ http://widit.knu.ac.kr:8800/

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http:// knu.ac.kr /~kiyang/teaching/IT/s16/schedule.htm

Protocol Domain Item requested

Fully qualified resource name

widit.

Hostname

Internet Addressing: Anatomy of a URL

Client-Server Model

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Client Initiates a Connection

Server Waits & Responds to Incoming Connections

Client Application Server Application program running on the client machine

(e.g., Internet Explorer)

Application Protocol (e.g., HTTP)

155.230.194.233 155.230.194.245

program running on the server machine

(e.g., Apache Web Server)

Client-Server Model: Overview

Servers Can refer to 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 server 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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http server

SMTP server

SSH server

http client

http client

http client

SMTP client

SMTP client

SSH client

Web Authoring

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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

Q&A What is the Internet? How does it work? Describe Domain Name System Client-Server Model 4-Layer Model TCP/IP

How can you publish content on the Web?

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

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