Introduction

Let’s remember where we are:

The data link layer allowed us to reliably send data from some source to the local router, using a cable, switch, etc., some device:

Now is the time is sending the data from the local router to the actual destination. For this we will need IP addresses, etc.

But, how does the internet look like? How do devices get an IP address? How does an IP packet look like? How do you route packets? Which protocols other than IP do we need and why? How do we deal with congestion?

In this lecture we will try to answer these questions.

Quick remainder: Connectionless and connection-oriented services

CONNECTIONLESS SERVICE

• routers use routing algorithms to decide where to send each packet individually.
• Used by Internet Protocol (IP).

CONNECTION-ORIENTED SERVICES

• When a connection is made, it's fixed.
• All packets follow this path.
• ISPs sometimes use this on top of IP.
• Router failure is critical here. The path will vanish.
• You need to setup a connection with agreement first.

Internet components and structure

We already talked about local area networks:

We can see devices, some switches and a router (or multiple ones), which can be wireless, normal cable router, etc. This router is known as the gateway router to the actual Internet.

Once we leave the local area network we are in an autonomous system:

An autonomous system is an area in the Internet consisting of routers (known as external routers or simply routers), controlled by a single service provider.

Furthermore, in the internet there exists multiple autonomous systems: