Episode 08

The “Seven-Layer” Vocabulary of Modern Internetworking

Segment 5 of 5

Several of the networking movies published at AskMisterWizard.com have referred to the concept of encapsulation, and by now, viewers should be clear that one message can contain another message inside. This concept can be carried forward to several layers of messages within messages. And it is commonplace for the various layers of the ISO model to be represented as a package inside a package, or a message inside a message at successively larger sizes at the various layers as they encapsulate one another.

To help you visualize this concept in the context of the Internet and a local area network, we might go so far as to illustrate several envelopes inside envelopes, inside one another with a small envelope on the right inserted into successively larger envelopes layer by layer, and finally into a very large envelope at the left. We could label each of those envelopes with the layers associated with a particular OSI level of intelligence, and also with the kind of functionality performed by the Internet at that corresponding layer. This allows us to map the real exercise of the Internet with the vocabulary of the OSI in a way that we can visualize with our eyes to make it memorable.

Accordingly, let me draw your attention to these images showing a series of envelopes. At the large end, I have wrapped the envelopes in an Ethernet cable, representing layer one (the “physical” layer). The physical layer is well-represented by an Ethernet cable. Inner layers are encapsulated inside outer layers in transit, and removed from those outer layers upon delivery. Ultimately, the destination application layer receives the same information that was originally sent at the source application layer. And incidentally, at each intermediate layer in between, the destination side receives the same information originally input at the source side: layer by layer, match by match, which makes the layers tend to be interchangeable, and this in turn makes our network and its applications far easier to write, and more interoperable.

This is the text from the movie entitled "7-LayerVocabulary of Modern Internetworking", published at www.AskMisterWizard.com. (The text also includes a few small, static illustrations from the movie). You can learn more about the video version and purchase an inexpensive personal license to view it by clicking right here. You can learn more about our "Internet Series" of licensed videos by clicking here.


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