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