1. Chapter 2 The Internet Underlying Architecture

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. Client/ Server Architecture Client: a Local PC, request some services from a server Server “Host”: More powerful central computer Client/ Server Model Client/ Server Model Client Request (website) Server The answer

9. 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