Ethernet Video Series
Episode 08, Segment 02 of 05
The 7-Layer Vocabulary of Modern Internetworking
ISO / OSI Reference Model (continued)
Most computers today are controlled by “multitasking” or “multiprocessing”
operating systems that are running several programs, or tasks, at any given
moment. Even a typical small computer in a home is often running twenty or
thirty different programs all at once, and somehow, our message from the
Internet has to find the right program to receive and process it. Furthermore,
most modern operating systems are oriented around a multi-user philosophy, where
any of several people could be using the computer at any given time (sometimes,
two or three people at once; sometimes just one). But in any event, work has to
be associated with and attributed to a particular person among a group of
people, and because different people have grown up in different cultures and
speak different languages, reading and writing with different alphabets, it’s
also important that our Internet message is somehow able to express itself in an
appropriate character set and language.
So, stepping back and looking at this situation from the big picture demands that we allow a specific message, using a specific character set in a specific language, to be delivered or attributed to a specific person, using a specific program or process, on a specific computer inside our network, which is a subset of the world-wide Internet. This is a lot of selection and focus, and layer upon layer of intelligence.
At one end of this spectrum, the data represents real information in a useful format that will make real sense in a specific context to a specific person or a specific application; whereas, at the other end of the spectrum, the data just represents bits in transit from somewhere to somewhere else. In between these two extremes, various levels of intelligence can be individually identified, and perhaps interchanged with counterparts at the other end of the network at the same level of intelligence.
In the physical world, using the analogy of packages being transported by a postal service, we are already accustomed to thinking about counterparts at each end of the delivery, each performing similar functions. For example, the delivery van at the source end of a shipment has a counterpart delivery van at the destination. And the shipping company’s office at the source end of a shipment has a counterpart with a shipping company’s office at the destination end of a shipment.
Episode 08, Segment 03 of 05