Internet Overview 1Internet 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.world-wide set of networks ► 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

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

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

Networking Basics: Main considerations for the Internet Need homogeneous communications between heterogeneous hardware and software. ► Communication Protocols T ransmission C ontrol P rotocol / I nternet P rotocol ► Addressing System D omain N ame S ystem (Service) ► Layered Networking Structure Need efficient method of data exchange for a distributed and decentralized system ► Client-Server model 5

Networking Basics: Circuit and Packet Switching Internet Technology Packet Switched Communication Circuit Switched Communication Dedicated Line Sender Receiver Data broken up into packets 6

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 7

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 H yper T ext T ransfer P rotocol F ile T ransfer P rotocol S imple M ail T ransfer P rotocol T elnet P rotocol T ransmission C ontrol P rotocol I nternet P rotocol IP Packet 8

Internet Technology Networking Basics: Four Layer Model 9 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

Internet Technology How does the Internet work? Communication on the Internet Data Packet Application (e.g. Chrome) Network Interface (i.e. TCP/IP) Data Packet Application (e.g. Web server) Network Interface (i.e. TCP/IP) Physical (wire, router, hosts) 10

Internet Technology Internet Addressing IP address ► a unique number assigned to a host ► assigned by IANAIANA ► 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

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 12

Internet Technology Internet Addressing: DNS is Hierarchical.edu unc.edu ncsu.eduduke.edu med.unc.educs.unc.eduils.unc.edu 13

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

Internet Technology Internet Addressing: Anatomy of a URL URL stands for Universal Resource Locator ► sometimes seen as Uniform Resource Locator knu.ac.kr/~kiyang/teaching/IT/s13/schedule.htm ProtocolDomainItem 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., widit. Hostname 15

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

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, , 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 Clients: Outlook, Pine, Lotus Notes Telnet/SSH Clients: Putty, SSH Secure Shell 17

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. Internet Tecnology 19 Edit Publish Display upload

Internet Technology 20 An Opte Project visualization of routing paths through a portion of the InternetOpte Projectrouting paths