Okay, so, today was the first of two series of lectures on the Internet.

we really looked at how your messages get across the Internet.

We looked at routing as the main focus.

we looked at, we started off by

looking at two fundamental concepts behind the Internet.

first of packet switching, right, was which became

to be the fundamental paradigm behind the Internet.

And we looked at distributed hierarchy, right tiers of

ISPs, tier one, tier two, tier three and so on.

That's how it's

spatially divided. then we looked at routing.

We spent most of our time talking about routing.

the three functions of routing.

Addressing in terms of IP addresses and subnets.

We looked at DHCP and NAT routing protocols.

we really focused on just the concepts behind

the simper one of RIP the Routing Information Protocol.

there's other ones, there's OSPF and then that's when we're doing Intra-AS.

Then there's Inter-AS routing, which would include BGP, Border Gateway Protocol.

And then we looked at forwarding, right?

How the router physically takes the packet, looks at the

destination address, and sends it off the corresponding output port.

we looked at the shortest path problem, right?

and again, remember shortest path means minimum cost.

It doesn't mean least number of hops.

Unless you're considering costs, all the costs to be one or two,

any single number for all the costs.

and we looked at the Bellman-ford algorithm which

is one way to solve the shortest path problem.

There's different ways, there's always Dijkstra's algorithm and so on.

But the Bellman-ford algorithm forms the basis for the

Routing Information Protocol, which is why we looked at that.

And that really explained a lot of the main ideas behind routing.

so, some major themes here.

First is again we saw iterative and distributed algorithms.

Bellman-ford is an iterative algorithm.

It's not distributed but we can make it

distributed by making it the Routing Information Protocol.

Where we have message passing between each of the routers, explicit message passing.

We have graphs again, this is another time we saw graphs here.

the graph of a routers, in this case, where nodes are routers the links are

physical connections, the graphs are directed and they're weighted too.

So, the links

have weights on them.

And then again, the Network of Networks, right?

So, the Internet is really the Network of Networks bottom line.

first of all, spatially it's divided into different tiers of ISP's.

Then, also, all the different types of networks

that we deal with, like social networks on Facebook.

Facebook network is part of the Internet, you know, it's part of the web.

there's all different networks that are just

consisted of, and connected by, this thing

that we call the Internet nowadays. And it's really changed our lives a lot.

So, I hope you enjoyed this lecture and I'm

looking forward to seeing you in the next one.