chapter 4: the internet business data communications, 6e
TRANSCRIPT
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