Week 4 of OpenEdMOOC is about Creating, Finding, and Using Open Educational Resources. I don’t plan do fulfill the task of delivering a 1 hour lecture using OERs, but I was curious how much I would be able to find and how much I would need to create by myself. I was surprised how easy it was to find things. This is the short message of this post.
If you are interested in a little example from the History of Data Communication, read on.
I have long thought that one day I should create a little graphic, perhaps even an animation, about the OSI 7 layers model, because whenever I saw such a graphic on the web, I was frustrated that it did not emphasize the few aspects that I found fascinating when we built prototype OSI networks.
The basic idea of the services is very simple: Think of two 7-story buildings. In the left-hand one, on the 7th floor, someone wants to send a message to their peer on the 7th floor of the other building. For this purpose, he or she just turns to their aides on the floor below to get this done, without need to think about how all the lower 6 floors of all buildings will collectively delivery that service. The aides on floor 6, in turn, use the services of the all the lower 5 floors in just the same way, and so on.
Now all graphical descriptions that I had seen on the web, enumerated the seven services one after the other, in a loveless way, as if it was a bothersome obligation, such that the listener (if he was not yet asleep) found himself wondering: now what is the difference between transport layer (4) and network layer (3) whose descriptions sounded pretty much the same? (Or likewise, between TCP and IP?) Graphics that left out any 3-floor buildings in between, did not make clear the relaying and routing function of layer 3 and the end-to-end function of layer 4.
Today, the first OER that I found was sufficiently emphasizing both sorts of stacks. I think this is good news.
Source: lecture 1, slide 18, from MIT OCW, CC-BY-NC-SA.