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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

• 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

• TCP breaks the message data into pieces

Data

IP Packet

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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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Domain Names

ilac

biutau

cs.biu.ac.il

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

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.