CS 115: COMPUTING FOR THE SOCIO-TECHNO WEB HOW THE INTERNET WORKS: HTTP, TCP/IP AND OTHER PROTOCOLS (

U-R-L  Uniform Resource Locator  T. B-L wanted URI: Universal Resource Identifier  It tells you where something is located, i.e., the name of the server that has it  It also tells you how you could get it Server and domainAccess method Static URL DocumentPath gov - Government agencies edu - Educational institutions org - Organizations (nonprofit) mil - Military com - commercial business net - Network organizations ca – Canada kz–…

2/11/2009 Harvard Bits 3

URL INVOKING A WEB PROGRAM Server and domainAccess method Dynamic URL ParameterWeb program Server and domainAccess method Dynamic fake URL Web program and parameter

CLIENTS AND SERVERS 5 Client Computers Web Server Web Server cs.wellesley.edu Server firstclass.wellesley.edu downloadupload THE INTERNET

YOUR ADDRESS IS ENUMERATED Every server is enumerated in an IP address IPv4: 32 bits written as 4 decimal numerals up to 256, e.g (Wellesley College) Wellesley College How many addresses can it represent? IPv6: 128 bits written as 8 blocks of 4 hex digits each, e.g. AF43:23BC:CAA1:0045:A5B2:90AC:FFEE:8080 How many addresses are in IPv6? Client translates URLs to IP addresses, e.g. cs.wellesley.edu  Uses authoritative sites for address translation a.k.a: “Domain Name Server” (DNS)DNS

WHAT IS *YOUR* IP ADDRESS? IP: Internet Protocol

WHAT IS THE INTERNET? “Ten movies streaming across that, that Internet, and what happens to your own personal Internet? I just the other day got...an Internet was sent by my staff at 10 o'clock in the morning on Friday. I got it yesterday [Tuesday]. Why? Because it got tangled up with all these things going on the Internet commercially. [...] They want to deliver vast amounts of information over the Internet. And again, the Internet is not something that you just dump something on. It's not a big truck. It's a series of tubes. And if you don't understand, those tubes can be filled and if they are filled, when you put your message in, it gets in line and it's going to be delayed by anyone that puts into that tube enormous amounts of material, enormous amounts of material.”Ten movies streaming across that, that Internet, and what happens to your own personal Internet? I just the other day got...an Internet was sent by my staff at 10 o'clock in the morning on Friday. I got it yesterday [Tuesday]. Why? Because it got tangled up with all these things going on the Internet commercially.They want to deliver vast amounts of information over the Internet. And again, the Internet is not something that you just dump something on. It's not a big truck. It's a series of tubes. And if you don't understand, those tubes can be filled and if they are filled, when you put your message in, it gets in line and it's going to be delayed by anyone that puts into that tube enormous amounts of material, enormous amounts of material Senator Ted Stevens, Chair, Comm. on Commerce, Science and Transportation (charged with regulating the internet)

WHAT IS THE INTERNET?

NO REALLY, WHAT IS IT? T_eBM

A NUTS AND BOLTS VIEW OF INTERNET The Internet is a network of networks consisting of: hosts (can be can be either clients or servers) communication links of varying bandwidths routers (switching devices) modems translate bits to travel correctly through wires and air A client program running on a host, following a protocol, requests and receives a file from a server program running on another system We call such programs processes Network Protocols and HTTP 1-11 client server routers modem

ARPANET,

SENDING AND RECEIVING INFORMATION Network Protocols and HTTP 1-13 Handshake

TCP/IP VS POSTAL MAIL PROTOCOLS 14 TCP ~ Higher Level Protocols IP ~ Lower Level Protocols

TCP/IP: BASIC PROTOCOLS TCP: Transport Control Protocol Creates logical connection b/w two machines on the network Makes connected machines think that they are directly connected Provides reliable, perfect transport of messages IP: Internet Protocol Breaks data into packets to move through routers Tries hard, but may drop packets We usually talk about TCP/IP TCP uses IP and guarantees delivery 15

MESSAGE PIPELINING When the message is segmented into packets, the network is said to pipeline message transmission. 1-16

Standards, although they are merely conventions, give rise to vast innovation, if they are well chosen, spare, and widely adopted.

PACKET SWITCHING Messages are broken into packets each of which travels from the source to destination through a maze of routers and links. Packet switching achieves much higher efficiency than full-file travel 1-18

TRACEROUTE FROM GAIA.CS.UMASS.EDU cs-gw ( ) 1 ms 1 ms 2 ms 2 border1-rt-fa5-1-0.gw.umass.edu ( ) 1 ms 1 ms 2 ms 3 cht-vbns.gw.umass.edu ( ) 6 ms 5 ms 5 ms 4 jn1-at wor.vbns.net ( ) 16 ms 11 ms 13 ms 5 jn1-so wae.vbns.net ( ) 21 ms 18 ms 18 ms 6 abilene-vbns.abilene.ucaid.edu ( ) 22 ms 18 ms 22 ms 7 nycm-wash.abilene.ucaid.edu ( ) 22 ms 22 ms 22 ms ( ) 104 ms 109 ms 106 ms 9 de2-1.de1.de.geant.net ( ) 109 ms 102 ms 104 ms 10 de.fr1.fr.geant.net ( ) 113 ms 121 ms 114 ms 11 renater-gw.fr1.fr.geant.net ( ) 112 ms 114 ms 112 ms 12 nio-n2.cssi.renater.fr ( ) 111 ms 114 ms 116 ms 13 nice.cssi.renater.fr ( ) 123 ms 125 ms 124 ms 14 r3t2-nice.cssi.renater.fr ( ) 126 ms 126 ms 124 ms 15 eurecom-valbonne.r3t2.ft.net ( ) 135 ms 128 ms 133 ms ( ) 126 ms 128 ms 126 ms 17 * * * 18 * * * 19 fantasia.eurecom.fr ( ) 132 ms 128 ms 136 ms 3 delay measurements no response trans-oceanic link

HTTP: HYPERTEXT TRANSFER PROTOCOL HTTP is the Web’s client/server protocol. User agent (browser) implements the client side of HTTP. Web pages generally consist of an HTML file which references other objects (JPEG, Java applet, video, audio clips). 1-20

HTTP/1.0 NONPERSISTENT CONNECTION a.Client initiates a TCP connection to 2.Client sends HTTP request for file /someDir/file.html 1b.Server at host accepts connection and acknowledges. 3.Server receives message, finds and sends file in HTTP response. 4.Client receives response. terminates connection, examines file, and may request other files. 5.Steps 2, 3, 4 are repeated for each requested file.

HTTP REQUEST MESSAGE 1-22 GET /someDir/file.html HTTP/1.0 Host: User-agent: Mozilla/4.0 Connection: close Accept-language:en,fr request line (GET, POST, HEAD commands) header lines Carriage return, line feed indicates end of message

HTTP RESPONSE MESSAGE 1-23 HTTP/ OK Connection: close Date: Thu, 06 Aug :00:15 GMT Server: Apache/1.3.0 (Unix) Last-Modified: Mon, 22 Jun 1998 …... Content-Length: 6821 Content-Type: text/html data data data data data... status line (protocol status code status phrase) header lines requested HTML file

TESTING HTTP USING TELNET Type: telnet cs.wellesley.edu 80 Type: GET /~mir/index.html HTTP/1.0 Opens TCP connection to port 80 Issues a GET request to HTTP server (you must hit carriage return twice at the end). 1-24

SOME HTTP RESPONSE STATUS CODES 200 OK request succeeded, requested object in this message 301 Moved Permanently requested object moved, new location specified in this message (Location) 400 Bad Request request message not understood by server 404 Not Found requested document not found on this server 505 HTTP Version Not Supported 1-25

SMTP (MAIL) PROTOCOL The sending process must simply specify the name or address of the host machine (hostname or IP address), and The process on that host that will handle the received message (port number). Mail port is usually