Ethernet Delivers the Internet

Ethernet frames follow a pattern thatís very similar to telegrams. Inside the Ethernet frame, after the destination address, and the source Ethernet address, is the main message field. And that main message field inside the Ethernet frame can further be broken down into various sub-fields according to well-developed traditions and standards in the Ethernet community.

In fact, so many different people representing different organizations have had opinions and views and arguments about how to use the Ethernet message field that influential committees have been formed to create standards. Among the most important of these little sub-fields is one that tries to communicate a general description of the type of message and length of message transported inside this Ethernet frame. The exact formatting of the bits inside that little field have been a subject of considerable development and conflicting (some would say "confusing") evolution.

But itís not necessary that we understand those details. What is important is that we realize and trust that influential committees have agreed on the format by which information can be exchanged from one party to another, and that ultimately, our networking equipment can figure it out.

Probably the single most important message type that can be carried inside an Ethernet frame is an Internet protocol packet. This is the way Ethernet delivers the Internet.

I like to think of these committees and the protocols and standards that they create as if they are forms of the source that I use when I fill out my income tax reports every year. Thereís a place for every bit of information. And by following the form precisely, other people whoíve never met me can interpret details about my financial condition without very much confusion.

By following these well-established forms, or protocol conventions, the message field inside an Ethernet frame can carry many different kinds of messages. Our analogy with telegrams is valid here, too: Remember that the message inside a telegram often contained a postal address. In this same way, the IP packet, or Internet protocol packet, inside an Ethernet frame also contains an independent addressing system known as the IP address.


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