Business data communications 5e by stallings chapter 04

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