The internet layer Skills: None IT concepts: layered protocols, the internet layer, IP protocol, router, dumb (“end-to- end,” “neutral”) networks This work is licensed under a Creative Commons Attribution-Noncommercial- Share Alike 3.0 License.

Internet concepts –Applications –Technology (Communication) –Implications for Internet skills –Application development –Content creation Where does this topic fit?

The initial vision: an IP address for every host direct, end-to-end connection

The TCP/IP protocol layers Application Transport Internet Data link Physical Get useful work done – retrieve Web pages, copy files, send and receive , etc. Make client-server connections and optionally control transmission speed, check for errors, etc. Route packets between networks Route data packets within the local area network Specify what medium connects two nodes, how binary ones and zeros are differentiated, etc, There are two transport layer protocols, TCP and UDP. Web applications use TCP because it checks for errors and controls speed.

The Internet consists of connected networks

Each network has a router at its edge

Data center Campus router The router at the edge of our campus network Firewall CSU router Responsibility of CSUDH 1 gbps AT&T Links from campus buildings Downtown LA

A client has a packet to send to a server The client and server are on different, Internet connected networks, so the packet must be routed across the Internet.

It is sent across the LAN to the router (using a data link protocol) There are four possible outgoing routers.

It uses information in local tables and makes a new decision for each packet. The LAN router picks the “best” of the four

Each router does the same thing

The next “hop”...

The packet reaches the destination network’s router

And is delivered to the server (using a data link protocol)

The complete route

What happens if something goes wrong? Perhaps a router breaks or is over capacity or a cable is cut

IP routes around the problem

By design, the Internet is dumb The InternetThe telephone network The telephone network is smart

The internet layer Skills: None IT concepts: layered protocols, the internet layer, IP protocol, router, dumb (“end-to- end,” “neutral”) networks This work is licensed under a Creative Commons Attribution-Noncommercial- Share Alike 3.0 License.

A few questions We asked what happens when something goes wrong – what sorts of things might go wrong? Would the route from host A to B necessarily be the same as the route from B to A? Might routes between two hosts change during the day? Might the time to traverse a route vary during the day?