Chapter 4: The Internet Business Data Communications, 6e.

Chapter 4: The Internet

Business Data Communications, 6e

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

Internet Domain Expansion

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

• Growth has led to the expansion of data mining for target marketing

Internet Addressing

• 32-bit binary numbers provide unique global Internet address

• Includes network and host identifiers• Dotted decimal notation [4 octets]

– 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)

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