Chapter 5: The Internet Business Data Communications, 5e Internet History Evolved from ARPANet (Defense Departments 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) 188.8.131.52 (decimal)
Domain Name System 32-bit IP addresses have two drawbacks Routers cant keep track of every network path Users cant 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
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