4.9.3 The Internet

Question 1

What is the structure of the internet?

Answer 1

Each continent uses backbone cables connected by trans-continental leased lines fed across the sea beds. ISPs connect directly to this backbone and distribute the Internet Connection to smaller providers who in turn provide access to individual homes and businesses

Question 2

What is packet switching?

Answer 2

A message is broken into a number of parts which are sent independently over the optimum route and reassembled at the destination

Question 3

What does a router do?

Answer 3

It receives data packets from one network and using the address provided by the packet, it forwards the packet on towards the correct network. Routers determine where to send packets according to a table of neighbouring networks or using an algorithm to determine the most efficient step for the packet. Each router knows which other routers are closest to it and by sharing information it allows the optimum route for a packet to be calculated

Question 4

What is a packet made up of?

Answer 4

A packet contains a header (senders and receivers IPs, protocol, packet number), a payload (the data) and a trailer (Checksum or CRC)

Question 5

What is a gateway?

Answer 5

A gateway is a node on a network that serves as an entrance to another network. In enterprises, the gateway is the computer that routes the traffic from a workstation to the outside network that is serving the Web pages. In homes, the gateway is the ISP that connects the user to the internet

Question 6

How is routing achieved across the Internet?

Answer 6

Routers find the optimum path using an algorithm called Dijkstra’s algorithm. Routing destinations are stored on the router for the nearby locations to send the packet to. Once the packet has reached a nearby router, the original router can only wait for a replying packet from the final destination