1. CP476 Internet ComputingCh.1 # 1 Lecture 2. A Brief Introduction to the Internet The objective is to understand The history of Internet What the Internet is? How it works? What it does? How it was designed? How it was implemented? History of the Internet –In 1967, at an ACM meeting, ARPA presented the idea of ARPANE. Use Network Control Protocol (NCP) to control the communication between the hosts – In 1970, ARPA hosts implemented NCP. Four nodes were connected –In 1973, Cerf and Kahn devised the idea of gateway to serve as the intermediate hardware, and the Transport Control Protocol/Internetworking Protocol (TCP/IP) as software to transfer packet from one network to another – In 1977, an internet consisting of ARPANET, packet radio, and packet satellite was demonstrated. – In 1983, NCP was abolished, TCP/IP became official for ARPANET – MILNET was born in 1983, NSFNET was born in 1986, ARPANET replaced by NSFNET 1990. In 1995, ISP started –WWW application started in 1994

2. CP476 Internet ComputingCh.1 # 2 local ISP company network regional ISP router workstation server mobile Internet core What Is the Internet? –A collection of computers connected via communication links through routers – Hosts (or end systems) servers, workstations, mobile devices, etc. – Routers, or intermediate note Where and how can we access the Internet ? –Campus network, local ISP, regional ISP –Telephone lines (Dial-up, DNSL), TV cable, power line, wireless, satellite.

3. CP476 Internet ComputingCh.1 # 3 What the Internet Does? –Electronic mail (email): –File transfer –Remote log in –News group –Web browse –Internet Phone –Peer-to-peer –Many others, you name it. How Does the Internet Work? –Almost all Internet applications follows a request-response scheme with the client- server diagram – All requests and responds are through packet transfer. Sending and receiving packets follow communication protocols. –A packet sent from a host, goes through routers (store and forward) to arrive the destination host. A protocol defines types of messages exchanged fields in messages, rules for when and how messages of send/respond are processed.

4. CP476 Internet ComputingCh.1 # 4 –To make design manageable and efficient, and to make the Internet support multiple applications, and multiple networks, stack protocols were used Every application shares the same lower level transmission protocol: Internet Protocol (IP) Most applications use the Transport Control Protocol (TCP) as the middle level transportation protocol Others use the User Datagram Protocol (UDP) Different applications use different high level application protocols –IP is the fundamental protocol, which specifies the exact format of all datagram Performs the routing function rules for datagram processing by routers and hosts.

5. CP476 Internet ComputingCh.1 # 5 TCPUDP ARPRARPICMP IP IGMP SMTPFTPDNSHTTP Underlying LAN or WAN technology IP Phone Application layer Transport layer Network layer Data link layer Physical layer –Transmission Control Protocol (TCP) provide connection-oriented service (handshaking), reliable transport services between to two application programs. –TCP/IP is the packet transport protocol suite for most Internet applications. –HTTP defines how clients request Web page from the Web server and how servers transfer Web pages to clients

6. CP476 Internet ComputingCh.1 # 6 TCP/IP defines Internet Protocol (IP) Addresses –Every node has a unique numeric address of 32 bit binary bits in IPv4 (1981) 128 binary bits in IPv6 (1998) IP address is used by TCP/IP software Example: The IP address of WLU web server machine is 11000000 00110110 11110010 01111001 A readable format: divided into 4 sections, each represented in decimal number. 192.54.242.121 Physical address: each network card is identified by a 48 bit binary number, used for sending or receiving packets at physical level –Example: 00000000 00001110 10100110 10110011 10110101 00101100 or in six section of hex: 00-0E-A6-B3-B5-2C A domain name is an alias for IP address, easy for human use –Example: How to get the IP address of www.wlu.ca?www.wlu.ca

7. CP476 Internet ComputingCh.1 # 7 How are the addresses resolved? – Domain Name System (DNS) converts domain names to IPs as an application – IP address is mapped to physical address while transferring by ARP or RARP by data link layer The construction of packet – A message or request is generated from an application program. – The message is fragmented to segments, each will be sent individually to its destination and then reassembled. – Datagram: a segment plus TCP header: type of applications, IP address, data, etc. – Frame: a datagram combined with physical address, to be sent through physical links.

8. CP476 Internet ComputingCh.1 # 8 application transport Network Data link physical FTP, HTTP, etc Socket TCP software IP software routing IP address resolving M M M M H t H t H n H t H n H l message segment datagram frame How It Was Designed Layered approach –Abstraction, hide the detail of lower layers – Makes a complex system easier to deal with – Modularization: maintenance and updating Five layer scheme – Application: telnet, ftp, email, web browse – Transport: process-to-process data transfer – Network: routing of datagram – Data link: frame transmission between neighboring elements – Physical: bits on the wire

9. CP476 Internet ComputingCh.1 # 9 How Was It Implemented? –Socket: Interface between application and transport layers Send/receive messages to/from choice of transport protocol ability to fix a few parameters, buffer size –TCP/IP are integrated as a part of operation systems to handle the input and output packets –Implementation of TCP/IP software uses multiple concurrently executing processes. Process priority, process communication through ports, message passing mechanism Handing incoming packets Network interface hardware transfers incoming packets from network to computer’s memory and informs the OS the coming of the packet.

10. CP476 Internet ComputingCh.1 # 10 –If the datagram carries a TCP segment, then is sent to TCP port. A TCP process will be created to retrieve the packet from the queue, and process it: acknowledge, timer, drop, retransmission, deposit the data in buffer associated with a connection. –If the datagram carries a UDP packet. Usually it is handled directly by IP process, which check the protocol port number and deposits the UDP datagram on the appropriate port (queue), where an application program can extract it.

11. CP476 Internet ComputingCh.1 # 11 Device interface for net one TCP Output Process IP Process Hardware for net one Hardware for net two Operating system Ports for UDP datagrams TCP inputUDP input Queues for packet sent to IP Port for segments to TCP Device interface for net two Buffers In-coming packet processing

12. CP476 Internet ComputingCh.1 # 12 Outgoing packets handing for TCP packets –Connection must be established –Data must be placed in segment –Segments must be retransmitted until acknowledgements of recipient arrive. TCP uses two processes to do this –A tcpout process handles segmentation and transmission details. –A tcptimer process manages a timer, which prompts the tcpout for retransmission when timeout. tcptimer will be stopped by an acknowledge packet. –Once TCP produces a datagram, it is passed to an IP process to delivery

13. CP476 Internet ComputingCh.1 # 13 Device for net one TCP Timer Process TCP Output Process IP Process Hardware for net one Device for net two Hardware for net two Operating system Port for TCP output TCP outputUDP output Queues for out- going packets Outgoing packet processing