Business data communications 5e by stallings chapter 04

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 • Initially, included only four nodes: UCLA, UCSB, Utah, and SRI 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 Early Applications & Protocols • • • • Telnet/FTP (1972/73) Distributed Email (1972) TCP/IP (1982-83) DNS (1984) Internet Components 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 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 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) 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 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 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) 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 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 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 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 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 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 ... 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... 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... – Programs that extract information from name servers based on client requests DNS Database • Hierarchical database containing resource records (RRs) (name, IP address, other info about hosts)