Internet Overview

1. Internet Overview Internet Technology

2. 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/IPprotocols. • 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. Internet Technology

3. Local Area Network What is the Internet?An internet “kiyang.kmu.ac.kr” 203.247.29.10 “www.whitehouse.gov” 96.16.242.135 Internet Technology

4. How does the Internet work?What happens between Point A and Point B? Point A Point B Internet Technology

5. 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 • HTML, SMTP, SSH, SFTP • Digitized data • Communication protocols • TCP/IP • Connection to the Internet • NIC, wire/wireless, routers Internet Technology

6. 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 Internet Technology

7. Networking Basics:Circuit and Packet Switching Circuit Switched Communication Dedicated Line Packet Switched Communication Receiver Sender Data broken up into packets Internet Technology

8. 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 destination IP address Internet Technology

9. Internet ProtocolsApplication 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 Telnet Protocol HyperText Transfer Protocol File Transfer Protocol Simple Mail Transfer Protocol Transmission Control Protocol Internet Protocol LAN IP Packet Internet Technology

10. Networking Basics:Four Layer Model 10 Internet Technology

11. How does the Internet work?Communication on the Internet Application (e.g. Firefox) Application (e.g. Web server) Data Data Network Interface (i.e. TCP/IP) Network Interface (i.e. TCP/IP) Packet Packet Packet Packet Packet Packet Physical (wire, router, hosts) Internet Technology

12. Internet Addressing • IP address • a unique number assigned to a host • assigned by IANA • e.g.155.230.194.245 • Hostname • a unique 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 Internet Technology

13. 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 Internet Technology

14. Internet Addressing: DNS is Hierarchical .edu unc.edu ncsu.edu duke.edu cs.unc.edu med.unc.edu ils.unc.edu Internet Technology

15. Specificity Specificity Most Least Internet Addressing Hostname vs. IP Address widit.knu.ac.kr Top Level Domain 155.230.194.245 Assigned locally IANA assigned Most Least Internet Technology

16. Fully qualified resource name Internet Addressing:Anatomy of a URL • URL stands for Universal Resource Locator • sometimes seen as Uniform Resource Locator Hostname Protocol Domain Item requested knu.ac.kr /~kiyang/teaching/IT/s13/schedule.htm widit. http:// • 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/ Internet Technology

17. Client-Server Model Client Initiates a Connection Server Waits & Responds to Incoming Connections 155.230.194.233 155.230.194.245 Application Protocol (HTTP) Client Application Server Application program running on client machine (e.g., Internet Explorer) program running on server machine (e.g., Apache Web Server) Internet Technology

18. 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 Internet Technology

19. Web Authoring Internet Technology

20. 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. Edit Edit Publish Display Display upload Publish Internet Tecnology