Internet Overview. Introduction to Internet Technology Overview of Web Authoring. Internet Technology 1

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1 Internet Overview Introduction to Overview of Web Authoring 1

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/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. 2

3 What is the Internet? google.com widit.knu.ac.kr

4 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 4

5 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 5

6 Networking Basics: Circuit and Packet Switching Circuit Switched Communication - Dedicated line Hello Who s calling? Sender Packet Switched Communication - Data is broken up into packets Receiver A B C A C B A B C 6

7 Networking Structure: Four Layer Model Applications Transport Network Applications Interface e.g., HTTP, SMTP, SSH Reliable Delivery i.e., TCP Source to Destination i.e., IP Physical Hosts, routers, wires, etc. 7

8 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 8

9 Communication Protocols Applications Layer 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 9

10 Communication on the Internet Application (e.g. Chrome) 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) 10

11 Internet Addressing IP address An unique number assigned to a host Assigned by IANA e.g 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 11

12 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 12

13 Internet Addressing: DNS is Hierarchical.edu ncsu.edu unc.edu duke.edu cs.unc.edu med.unc.edu ils.unc.edu 13

14 Internet Addressing: Hostname vs. IP Address widit.knu.ac.kr Most Specificity Least Top Level Domain IANA assigned Assigned locally Least Specificity Most 14

15 Internet Addressing: Anatomy of a URL URL stands for Universal Resource Locator a.k.a. Uniform Resource Locator Protocol Hostname Domain Item requested widit. knu.ac.kr /~kiyang/teaching/it/s16/schedule.htm 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 15

16 Client-Server Model Client Initiates a Connection Server Waits & Responds to Incoming Connections Client Application program running on the client machine (e.g., Internet Explorer) Application Protocol (e.g., HTTP) Server Application program running on the server machine (e.g., Apache Web Server) 16

17 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, , 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 http server SMTP server SSH server There can be many clients for a server application People interface with them directly HTTP Clients: Internet Explorer, Firefox, Chrome http client SMTP client http client http client SMTP client SSH client Clients: Outlook, Pine, Lotus Notes Telnet/SSH Clients: Putty, SSH Secure Shell 17

18 Web Authoring 18

19 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 Display Publish upload Edit Display Publish Internet Tecnology 19

20 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? 20

21 An Opte Project visualization of routing paths through a portion of the Internet 21

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