t.sharon-a.frank 1 internet resources discovery (ird) introduction to the internet/www
Post on 19-Dec-2015
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Introduction to the Internet
• Internet Resources/Services
• What is the Internet
• Standards/Protocols
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Internet Resources/Services
• 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?
• 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
running network apps
• communication links– fiber, copper, radio, satellite
• routers: forward packets (chunks) of data thru network
local ISP
companynetwork
regional ISP
router workstation
servermobile
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Internet Infrastructure
Router Router
RouterRouter
Router
Regional andNational Providers (ISP)
CorporateNetwork
CampusEthernet
LAN LANWAN
Interconnected Network
Local Area
PrivateDedicated
PublicCircuit Switched
MetropolitanArea
Public Packet Switched
Local Area
Bridge
Gateway
Router
Gateway
RouterISDN
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Who Runs the Internet?
• “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
… specific messages sent
… specific actions taken when messages received, or other events
network protocols:• machines rather than
humans• all communication activity
in Internet governed by protocols
protocols define format, order of messages sent and
received among network entities, and actions taken on message
transmission, receipt
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What’s a protocol?
a human protocol and a computer network protocol:
Q: Other human protocol ?
Hi
Hi
Got thetime?
2:00
TCP connection req.
TCP connectionreply.Get http://gaia.cs.umass.edu/index.htm
<file>time
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TCP/IP
IP
TCP
InternetIP
TCP
• 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.
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IP Packet
Packet Data
From: 192.112.36.5
To: 128.174.5.6
Packet EnvelopeIP Address
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IP Properties
• IP will get it there, but…– 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.
Network Delay is Variable
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Protocols in the TCP/IP Model
TELNET FTP SMTP DNS
TCP UDP
IP
ARPANET SATNETPacketradio LAN
Application
Transport
Network
Physical+data link
Networks
Protocols
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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)
• Map Domain Name to IP Address
• Domain Names must be Unique
• Domain Names have many Parts
• Suffix of Domain Names Significant
cs.biu.ac.il www.netscape.com www.cmu.edu
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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
Domain name server
in IsraelUser’s computerin Israel User’s computer
in USA
Internet
Name
IP Address
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DNS - Domain Name Lookup
Domain name server
in Israel
Domain name server in USAUser’s computer
in IsraelUser’s computer
in USA
Internet
Name Name
IP Address
IP Address
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Uniform Resource Locator (URL)
• Protocol: http, ftp, gopher...
• Domain-Name (or IP-address)
• Port (for security purposes)
• Directory
• File-Name
Protocol://domain-name:port/directory/file-name
Example: http://www.cs.biu.ac.il:8080/~taly/mm/index.html
URL is an address of a Web page in the Internet.