(Representation of

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(Representation of )URLs, IP addressesin the
computer era

• 114 Lecture 8

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U-R-L
http//www.wellesley.edu/Resources/about/index.htm
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

• gov - Government agencies
• edu - Educational institutions
• org - Organizations (nonprofit)
• mil - Military
• com - commercial business
• net - Network organizations
• ca Canada
• kz

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(No Transcript)
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URL invoking a web program
http//www.db-url.com/website-monitor.html?gclidC
LfYzO_bq5QodzReMiw
http//wiki.answers.com/Q/What_does_URL_mean
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Clients and Servers
THE INTERNET
download
upload
Client Computers
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You have been enumerated

• Every server is enumerated in an IP address
• IPv4 32 bits written as 4 decimal numerals up to
  256, e.g. 149.130.12.213 (Wellesley College)
• How many addresses can it represent?
• IPv6 128 bits written as 8 blocks of 4 hex
  digits each, e.g. AF4323BCCAA10045A5B290ACF
  FEE8080
• How many addresses are in IPv6?
• Client translates URLs to IP addresses, e.g.
  cs.wellesley.edu ? 149.130.136.19
• Uses authoritative sites for address
  translationa.k.a Domain Name Server (DNS)

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What is your IP address?
IP Internet Protocol
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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.
Senator Ted Stevens, Chair, Comm. on Commerce,
Science and Transportation(charged with
regulating the internet)
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What is the Internet?
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No really, what is it?
https//www.youtube.com/watch?vewrBalT_eBM
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(Communicating through )HTTP and TCP/IP
Protocolsin the web era

• 114 Lecture 9

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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

client
routers
modem
server
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ARPAnet, 1971
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Sending and receiving information
Handshake
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TCP/IP vs Postal Mail Protocols
TCP Higher Level Protocols
IP Lower Level Protocols
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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

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Message pipelining

• When the message is segmented into packets, the
  network is said to pipeline message transmission.

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

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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

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Traceroute from gaia.cs.umass.edu
3 delay measurements
1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms 2
border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145)
1 ms 1 ms 2 ms 3 cht-vbns.gw.umass.edu
(128.119.3.130) 6 ms 5 ms 5 ms 4
jn1-at1-0-0-19.wor.vbns.net (204.147.132.129) 16
ms 11 ms 13 ms 5 jn1-so7-0-0-0.wae.vbns.net
(204.147.136.136) 21 ms 18 ms 18 ms 6
abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22
ms 18 ms 22 ms 7 nycm-wash.abilene.ucaid.edu
(198.32.8.46) 22 ms 22 ms 22 ms 8
62.40.103.253 (62.40.103.253) 104 ms 109 ms 106
ms 9 de2-1.de1.de.geant.net (62.40.96.129) 109
ms 102 ms 104 ms 10 de.fr1.fr.geant.net
(62.40.96.50) 113 ms 121 ms 114 ms 11
renater-gw.fr1.fr.geant.net (62.40.103.54) 112
ms 114 ms 112 ms 12 nio-n2.cssi.renater.fr
(193.51.206.13) 111 ms 114 ms 116 ms 13
nice.cssi.renater.fr (195.220.98.102) 123 ms
125 ms 124 ms 14 r3t2-nice.cssi.renater.fr
(195.220.98.110) 126 ms 126 ms 124 ms 15
eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135
ms 128 ms 133 ms 16 194.214.211.25
(194.214.211.25) 126 ms 128 ms 126 ms 17
18 19 fantasia.eurecom.fr
(193.55.113.142) 132 ms 128 ms 136 ms
trans-oceanic link
no response
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HTTP HyperText Transfer Protocol

• HTTP is the Webs 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).

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HTTP/1.0 nonpersistent connection
http//www.someSchool.edu/someDir/file.html
1a. Client initiates a TCP connection to
www.someSchool.edu
1b. Server at host www.someSchool.edu accepts
connection and acknowledges.

• Client sends HTTP request for file
• /someDir/file.html

3. Server receives message, finds and sends
file in HTTP response.

1. Client receives response.terminates connection,
   examines file, and may request other files.

5. Steps 2, 3, 4 are repeated for
each requested file.
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HTTP request message
request line (GET, POST, HEAD commands)
GET /someDir/file.html HTTP/1.0 Host
www.someSchool.edu User-agent
Mozilla/4.0 Connection close Accept-languageen,
fr
header lines
Carriage return, line feed indicates end of
message
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HTTP response message
status line (protocol status code status phrase)
HTTP/1.0 200 OK Connection close Date Thu, 06
Aug 1998 120015 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 ...
header lines
requested HTML file
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Testing HTTP using telnet

• Opens TCP connection to port 80
• Issues a GET request to HTTP server (you must
  hit carriage return twice at the end).

• Type
• telnet cs.wellesley.edu 80
• Type
• GET /mir/index.html HTTP/1.0

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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

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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 25