Business data communications 5e by stallings chapter 04

Internet Terminology• Central Office CO • Customer Premises Equipment CPE • Internet Service Provider ISP • Network Access Point NAP • Network Service Provider NSP... Connecting to the I

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,

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)

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

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

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

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

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