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Chapter 5: The Internet

Chapter 5: The Internet. Business Data Communications, 5e. Internet History. Evolved from ARPANet (Defense Department’s Advanced Research Projects Agency Network) ARPANet was developed in 1969, and was the first packet-switching network

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Chapter 5: The Internet

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  1. Chapter 5: The Internet Business Data Communications, 5e

  2. Internet History • Evolved from ARPANet (Defense Department’s Advanced Research Projects Agency Network) • ARPANet was developed in 1969, and was the first packet-switching network • Initially, included only four nodes: UCLA, UCSB, Utah, and SRI

  3. Switching Methods • Circuit Switching: Requires a dedicated communication path for duration of transmission; wastes bandwidth, but minimizes delays • Message Switching: Entire path is not dedicated, but long delays result from intermediate storage and repetition of message • Packet Switching: Specialized message switching, with very little delay

  4. Early Applications & Protocols • Telnet/FTP (1972/73) • Distributed Email (1972) • TCP/IP (1982-83) • DNS (1984)

  5. Internet Components

  6. NSF and the Internet • In the 1980s, NSFNet extended packet-switched networking to non-ARPA organization; eventually replaced ARPANet • Instituted Acceptable Use Policies to control use • CIX (Commercial Internet eXchange) was developed to provide commercial internetworking

  7. The World Wide Web • Concept proposed by Tim Berners-Lee in 1989, prototype WWW developed at CERN in 1991 • First graphical browser (Mosaic) developed by Mark Andreessen at NCSA • Client-server system with browsers as clients, and a variety of media types stored on servers • Uses HTTP (hypertext transfer protocol) for retrieving files

  8. Internet Terminology • Central Office (CO) • Customer Premises Equipment (CPE) • Internet Service Provider (ISP) • Network Access Point (NAP) • Network Service Provider (NSP) • Point of Presence (POP)

  9. Connecting to the Internet • End users get connectivity from an ISP (internet service provider) • Home users use dial-up, ADSL, cable modems, satellite • Businesses use dedicated circuits connected to LANs • ISPs use “wholesalers” called network service providers and high speed (T-3 or higher) connections

  10. Commercial Internet Use • ARPANet and NSF limited use to research and development • Early commercial use primarily information dissemination • EDI transactions gradually moved to the Internet • WWW growth in 1990s has led to increased direct sales

  11. Internet Addressing • 32-bit global internet address • Includes network and host identifiers • Dotted decimal notation • 11000000 11100100 00010001 00111001 (binary) • 192.228.17.57 (decimal)

  12. Domain Name System • 32-bit IP addresses have two drawbacks • Routers can’t keep track of every network path • Users can’t remember dotted decimals easily • Domain names address these problems by providing a name for each network domain (hosts under the control of a given entity) • See Figure 4.5 for example of a domain name tree, and table 4.2 for a list of top-level domain names

  13. DNS Components • Domain name space • Tree-structured name space to identify all internet resources • DNS database • Stored in a distributed database • Name servers • Server programs that hold information about a specific portion of the domain name tree • Resolvers • Programs that extract information from name servers based on client requests

  14. DNS Database • Hierarchical database containing resource records (RRs) (name, IP address, other info about hosts). • Variable-depth hierarchy for names • essentially unlimited levels • uses . as the level delimiter in names • Distributed database: • resides in DNS servers throughout the Internet • Distribution controlled by the database • database divided into thousands of separately managed zones, • distribution and update of records controlled by database software.

  15. DNS Server Hierarchy • Each name server configured for a specific local zone • Includes subdomains and associated RRs • Authoritative source for that portion of hierarchy • Root servers are at top of hierarchy • Different root servers for different top level domains • Some redundancy within domain spaces to prevent bottlenecks

  16. DNS Operation • User program requests IP address for a domain name • Resolver module in local host or ISP formulates query for local name server (same domain as the resolver) • Local name server checks local database/cache • if found returns IP address to the requestor. • If not found, queries other available name servers, starting down from the root of the DNS tree or as high up the treeas possible. • When response is received, local name server stores the name/address mapping in local cache • User program receives IP address or error message.

  17. DNS Name Resolution • Query begins with name resolver located in the user host system • If requested name not in cache, query sent to local DNS server • returns an address immediately, or • returns address after querying other servers • Two possible types of queries • Recursive • Iterative

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