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Transcript of Internet new
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THE INTERNET
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The Internet
• The Internet: An internet that spans the world– Original goal was to develop a means of connecting
networks that would not be disrupted by local disasters.
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The Internet • An information system• Communication tool• A large network of computer systems
world wide• can be explored by using a Web Browser
• Services available through the Internet:• Email (Discussion groups , Chat Rooms, etc.)• Information search (including research)• Education (Online courses; virtual colleges)• Entertainment, News, and more…...
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Internet Architecture
• Internet Service Provider (ISP)• Access ISP: Provides connectivity to the Internet
– Traditional telephone (dial up connection)– Cable connections– Wireless
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Internet Composition
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A network protocol Is the set of very detailed rules, sequences, message formats, and procedures that computer systems use and understand when exchanging data with each other.
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Examples of Protocols– Transmission Control Protocol (TCP)– User Datagram Protocol(UDP)– File Transfer Protocol (FTP)– Hypertext Transfer Protocol (HTTP)– Simple Mail Transfer Protocol (SMTP)
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Transmission Control Protocol (TCP/IP)
• It is connection oriented.• It establish connection before data transfer • It divide the whole message in small parts known as
packets• It sends packets in order and it also receive in order
in destination
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User Datagram Protocol(UDP)
• It is not connection oriented.• It does not establish connection before data transfer • It divide the whole message in small parts known as
packets.• It sends packets to the available path on that
particular movement. • The packets are not received in order and it required
a addition mechanism for ordering the packets on destination.
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File transfer protocol
• Is a network protocol used for transfer data from one computer to another through a network such as Internet (is commonly used for copying files to and from other computers)
• FTP is a two-way system - it can be used to copy or move files from a server to a client computer as well as upload or transfer files from a client to a server
• FTP systems generally encode and transmit their data in binary sets which allow for faster data transfer
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What is an IP Address?
• An IP address is a unique global address for a network interface– An IP address:
- is a 32 bit long identifier
- encodes a network number (network prefix) and a host number.
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• The network prefix identifies a network and the host number identifies a specific host (actually, interface on the network).
Network prefix and host number
network prefix host number
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Dotted Decimal Notation
• IP addresses are written in a so-called dotted decimal notation
• Each byte is identified by a decimal number in the range [0..255]
• Example:
1000111110000000 10001001 100100001st Byte
= 128
2nd Byte
= 143
3rd Byte
= 137
4th Byte
= 144
128.143.137.144
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IP Addresses (continued)
• When IP addresses were originally created, they were called classful addresses– That is, each IP address fell into particular class– A particular class address has a unique network address
size and a unique host address size– There are basically five types of IP addresses: Classes A,
B, C, D and E
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IP Addresses (continued)
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IP Addresses (continued)
• When you examine the first decimal value in the dotted decimal notation:– All Class A addresses are in the range 0 - 127– All Class B addresses are in the range 128 - 191– All Class C addresses are in the range 192 – 223– All Class D addresses are in the range 224 – 239– All Class E addresses are in the range 240 - 255
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Name servers
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DNS• IP addresses are difficult to remember
– [email protected] would be difficult to remember– If JohnDoe’s mail server moves to another machine, then his e-mail address
would not be valid anymore– Something like [email protected] would be appropriate
• Need some mechanisms to translate wuzwuz.ucg.ie to the IP address– To solve this problem DNS was invented
• It is a hierarchical, domain-based naming scheme and a distributed database system for implementing naming scheme.
• Usage:– Map name onto an IP address, an application program calls an library
procedure, called resolver.– The resolver sends packet to a local DNS server which looks up the name and
returns the IP address to the resolver– The resolver returns the IP address to the application, which can establish an
TCP/IP connection with the destination (or send packets)
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URL – Uniform Resource Locator
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URL – Uniform Resource Locator
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Traditional Internet Applications
• Electronic Mail (email)– Domain mail server collects incoming mail and transmits
outgoing mail– Mail server delivers collected incoming mail to clients
via POP3 or IMAP
• File Transfer Protocol (FTP)• WWW (World Wide Web)
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World Wide Web (WWW) – a vast collection of information that’s connected like a
web– accessible through the Internet using connections called
hyperlinks– view the WWW resources through a program called a
Web Browser, such as:• Netscape Navigator • Internet Explorer
– Navigate through the WWW by pointing to and clicking on hyperlinks (underlined or boldfaced words,
phrases, icons, or images)– Also called Cyberspace or the Information Superhighway
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Architectural Overview
• Browser displays a page on the client machine– Click on a link, the browser sends a message to the abcd.com web server asking it for the
page– When page arrives, it is displayed; if it contains a hyperlink on a page on xyz.com, that is
clicked, then the browser will send a message to xyz.com server and the process continues
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HTML – HyperText Markup Language
• (a) HTML source code – Markup language containing explicit commands for formatting
• (b) Formatted page