Each year 1.5 million shelter animals are euthanized (670,000 dogs and 860,000 cats).
Source: ASPCA. The solution is not to shelter unwanted pets, but to
SHUT DOWN THE PET MILLS.
Anyone who wants a pet will just have to adapt a great pet from a shelter.
Video - Introducing the OSI Model
Transcript + My Comments
This video by Kevin Wallace introduces the OSI networking model. Keven's videos
teach networking in a light conversational way, with emphasis on retaining the
information for the purpose of passing the CompTIA Network+ certification exam.
A fundamental concept in the study of networking is the OSI model. OSI stands
for Open Systems Interconnect and it's a model of networks that was put together
by the ISO (International Standards Organization).
The OSI model is made up of seven different layers and there are different memory
aids to help you memorize these layers, and you would certainly want to memorize
these for certification.
If we start at the bottom, down at the physical layer, that's layer 1, the
physical layer is followed by the data link layer, layer 2, and then we have the
network layer at layer 3, the transport layer at layer 4, the session layer at
layer at layer 5, the presentation layer at layer 6, and finally the application
layer at layer 7.
The trick to memorizing the names of the layers is to memorize the acrostic
"Please Do Not Throw Sausage Pizza Away".
Note: In case you didn't know the meaning of the word acrostic (neither did I)
from the American Heritage Dictionary:acrostic - a poem or series of
lines in which the certain letters, usually the first in each line, form a name,
motto, or message when when read in sequence. I guess when studying for the
CompTIA Network+ certification exam (or any other exam) it is wise to use lots
The first letters of the acrostic reminding us of:
Of course, this starts at the bottom of the OSI model and goes up. If we prefer
to start at the top and go down, we can remember the acrostic "All People Seem To
Need Data Processing".
There are a lot of metaphors to explain what goes on at the different layers of
the OSI model. The metaphor Kevin prefers is to compare the OSI model to a bookshelf.
Kevin points out, that on the bookshelf behind him in the video, he doesn't use
one of the shelves, it contains no books.
His point is; you don't have to populate every layer of the OSI model. The OSI
model is a REFERENCE model, it doesn't have to apply to every single networking
scenario. It's just a general guideline. It was made to apply not just to IP based
networks, but also to IPX networks, and Apple-talk network. Kind of a one-size-fits-all model.