Chapter 9: Network Connectivity

Overview

The Ethernet is now so pervasive that even embedded systems can no longer ignore it. Ethernet is a bit more complicated than simple RS-232 as a communication interface, but it is also priceless once you get it up and running.

The TCP/IP protocol stack is encapsulated into protocol layers . Each layer of the protocol considers the layer above it to be just a block of data (or payload). Thats all the layer knows . The payload for Ethernet is IP or ARP, the payload for IP is ICMP, UDP or TCP (and others), and then UDP and TCP carry others (like TFTP, HTTP, and FTP). FTP rides on TCP, TCP rides on IP, and IP rides on Ethernet. You can think of the TCP/IP protocol stack as a line of dump trucks . Each truck is small enough to fit inside the one in front of it. The front dump truck doesnt care what is inside its cargo area, so the fact that it is another smaller dump truck makes no difference. Each truck transfers its payload from source to destination. What happens to the payload after the transfer is of no concern to the dump truck that just dumped it.

Note 

If you really want to learn about networking, buy a book on networking. I cant cover the whole subject in this chapter. The goal of this chapter is to discuss briefly some of the basic protocols and step through what is needed to connect an embedded system to an IP network.

To connect an embedded system to an IP network, you must interface with some Ethernet device and write a packet processor.