Chapter 2

The Internet Underlying Architecture

How the DNS works?

DNS: Domain Name System Visiting a website:- Write the address- IP will use the address and DNS

to deliver mail from PC to PC Domain types:

.com - .gov - .net - .mil - .org - .uk

How the DNS works?

Ex. NASA’s SPACElink Address

Spacelink.msfc.nasa.gov

The top domain (government)

The Nasa domain

Marshal Space Flight Center(a network in Nasa)

The Nasa computer that runs the Spacelink Program

How the DNS works? Name Servers:- Keep in track of changes- Work with DNS to ensure that email is

delivered to the right person- Make sure that you are sending to the

proper location- Routing all messages properly Name Servers contain tables that

match alphanumeric Internet Addresses to numeric IP Addresses

How Routers work?

The traffic cops of the Internet Routing steps:- Open the IP packets to read the

destination address- calculate the best route- Send the packet toward its final

destination or to another router and so on. Hops:

Routers or Gateways on any given path

How Routers work?

Router Physical Ports:

1. Input: receiving

2. Output: Sending Routing Operation:- Routing Process software runs (receiving)- Routing Table (Addresses Database)- Sending the packet to the output port- Send data to a router or to the destination

How Routers work?

Input Queue:A special holding area on the Router RAM A Router can have more than one queue Packets may be lost if the received

packets’ number exceed the queue’s capacity

TCP will re-sent the packet again if this happened

Client/ Server Architecture

Client: a Local PC, request some services from a server

Server “Host”: More powerful central computer

Client/ Server ModelClient/ Server Model

Client Request (website) Server

The answer

Client/ Server Architecture

Network Computer’s kinds:

Windows, Macintosh, Unix Connections to the server:

LAN – WAN – Phone Line Reason for set up this model: Information travel: HTTP

Hyper Text Transfer Protocol