Lecture 2. A Brief Introduction to the Internet

1. 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 Lecture 2. A Brief Introduction to the Internet

2. 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. local ISP Internet core regional ISP router workstation server company network mobile

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. 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. Transmission Control Protocol (TCP) provideconnection-oriented service (handshaking), reliable transport services between to twoapplication 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 SMTP FTP DNS HTTP IP Phone Applicationlayer TCP UDP Transportlayer Networklayer IP ARP RARP ICMP IGMP Data linklayer Underlying LAN orWAN technology Physicallayer

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 softwareExample: The IP address of WLU web server machine is11000000 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: 000000000000111010100110101100111011010100101100 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?

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. application transport Network Data link physical H H H H H H t n t n l t • 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 FTP, HTTP, etc M message Socket TCP software M segment IP softwarerouting IP address resolving datagram M frame M

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 packetsNetwork interface hardware transfers incoming packets from network to computer’s memory and informs the OS the coming of the packet.

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 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. In-coming packet processing TCP input UDP input Ports for UDPdatagrams Buffers TCPOutput Process Port for segments to TCP IP Process Operating system Queues for packetsent to IP Device interfacefor net one Device interfacefor net two Hardwarefor net one Hardwarefor net two

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. Outgoing packet processing TCP output UDP output Port for TCP output TCPTimer Process TCPOutput Process Operating system IP Process Queues for out-going packets Devicefor net one Device for net two Hardwarefor net one Hardwarefor net two