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