Transcript ird0-2_int

Internet Resources Discovery (IRD)
Introduction to the
Internet/WWW
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Introduction to the Internet
• Internet Resources/Services
• What is the Internet
• Standards/Protocols
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Internet Resources/Services
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Electronic Mail (E-Mail)
News (Usenet)
File Transfer (FTP)
Remote Login (Telnet)
Information Browsing (Gopher)
Automated Title Search (Archie, Veronica)
Automatic Content Search (WAIS)
Advanced Browsing (WWW)
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Internet Resources Discovery (IRD)
• Resources discovery - locating unfamiliar
resources.
• Resources can be documents, files, users and
services, both textual and multimedia.
• IRD is resource discovery on the internet and in
the Web.
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What is the Internet?
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Internet is a Multi-Network Architecture
Internet = Interconnected Network
Internet is based on TCP/IP Protocol Set
IP = Internet Protocol
TCP = Transmission Control Protocol
Based on former ARPANET by DOD
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What’s the Internet: “nuts and bolts” view
• millions of connected
computing devices: hosts,
end-systems
– pc’s workstations, servers
– PDA’s phones, toasters
router
server
regional ISP
– fiber, copper, radio, satellite
• routers: forward packets
(chunks) of data thru network
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mobile
local ISP
running network apps
• communication links
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workstation
company
network
Internet Infrastructure
LAN
Corporate
Network
Router
WAN
LAN
Campus
Ethernet
Regional and
National Providers (ISP)
Router
Router
Router
Router
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Interconnected Network
Private
Dedicated
Public
Circuit Switched
Router
Local Area
ISDN
Bridge
Router
Metropolitan
Area
Local Area
Gateway
Gateway
Public
Packet Switched
Who Runs the Internet?
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“nobody”
Standards:Internet Engineering Task Force (later…)
Numbers: IANA (Internet Assigned Numbers Authority)
Names: Internic (US), RIPE (Europe),…
Network: ISPs (Internet Service Providers), NAPs
(Network Access Points),…
• Fibers: telephone companies (mostly)
• Content: thousands of companies, universities,
individuals,…
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What’s a protocol?
human protocols:
• “what’s the time?”
• “I have a question”
• introductions
network protocols:
• machines rather than
humans
• all communication activity
in Internet governed by
protocols
… specific messages sent
protocols define format,
order of messages sent and
… specific actions taken
when messages received,received among network entities,
and actions taken on message
or other events
transmission, receipt
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What’s a protocol?
a human protocol and a computer network protocol:
Hi
TCP connection
req.
Hi
TCP connection
reply.
Got the
time?
Get http://gaia.cs.umass.edu/index.htm
2:00
<file>
time
Q: Other human protocol?
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TCP/IP
• TCP breaks the message data into pieces
Data
IP Packet
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TCP/IP
• TCP takes a long message and breaks it up:
– Each piece has a sequence number.
– Each piece is sent using IP:
• Destination has enough info to reassemble message.
• Will request missing piece until all is there.
TCP
IP
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TCP
Internet
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IP
IP Packet
Packet Data
From: 192.112.36.5
To: 128.174.5.6
IP Address
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Packet Envelope
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IP Properties
• IP will get it there, but…
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Network Delay is Variable
Message might be lost, or sent out of order.
Message can’t be too long (about 1K max).
For email, web, want reliable transfer of big files.
Still doesn’t say for which process a packet is intended:
• Message come to a machine, but are handled by a
process.
• Like a house with many people in it.
• Solution is TCP.
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Protocols in the TCP/IP Model
Protocols
Application
Transport
TELNET
FTP
TCP
IP
ARPANET
SATNET
Networks
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DNS
UDP
Network
Physical+
data link
SMTP
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Packet
radio
LAN
Internet/WWW Standards
• Internet
– Domain Name System (DNS)
• WWW
– Uniform Resource Locator (URL)
– Hypertext Markup Language (HTML)
– Hypertext Transfer Protocol (HTTP)
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Domain Name Service (DNS)
cs.biu.ac.il
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www.netscape.com
www.cmu.edu
Map Domain Name to IP Address
Domain Names must be Unique
Domain Names have many Parts
Suffix of Domain Names Significant
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Domain Names
cs.biu.ac.il
il
ac
tau
biu
cs
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DNS - Domain Name Lookup
• Search in cache
• Search in local repository
– If the name is in the same domain
– If the name was retrieved lately
• Ask other servers
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DNS - Domain Name Lookup
User’s computer
in Israel
Domain name
server
in Israel
User’s computer
in USA
Name
IP Address
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Internet
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DNS - Domain Name Lookup
User’s computer
in Israel
Domain name
server
in Israel
Name
Domain name
server
in USA
Name
IP Address
IP Address
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Internet
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User’s computer
in USA
Uniform Resource Locator (URL)
URL is an address of a Web page in the Internet.
Protocol://domain-name:port/directory/file-name
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Protocol: http, ftp, gopher...
Domain-Name (or IP-address)
Port (for security purposes)
Directory
File-Name
Example: http://www.cs.biu.ac.il:8080/~taly/mm/index.html
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