File1, 2, & 3 for zmohammed:



When talking about data communication, the OSI model is the golden
reference model for how data is communicated between any two networked systems.
OSI stands for Open Standards Interconnect model and was created by the
International Standards Organization to overcome difficulties in
interoperation between networking technologies.
The OSI model specified the concept of layers and defined the function
offered on each layer. These layers are broken into seven different segments.
The layer go as followed; physical, data-link, network, transport, session,
presentation, and application.
The physical layer is the lowest layer in the model and is for
the purpose of maintaining and transmitting bits about physical connections
through mechanical, electrical and other functionalities. For example this
may be something like optical signals (optic fiber), or electromagnetic
waves (wireless networks).


The physical layer is the only layer that interacts with nature. After
data has been processed by all other layers, it finally reaches the physical
layer where the data hits the wire.
Before the data reaches the network layer, it has to pass through the
data-link layer. The main purpose of this layer is to send data between
neighboring devices on the network through signaling service. The two primary
functions are addressing and error-detection.
A good example of the data-link layer in action is the internet. The
data-link layer is the building block of the internet, so when you use the
internet, information passes through many instances of the data-link layer
before it reaches its final destination, each instance of the layer
warrants that the data is safe to go to the next destination in the network.


The network-layer provides the functional and procedural means
to transfer packets of data from a source computer to a destination computer
through one or more networks. Its function is used for packet forwarding,
managing quality of services, and forwarding local host domain messages
to the transport layer.
The standard protocol used by all networks at this layer is the
Internet protocol (IP). IP designates an address to every device on a
network. The function of this layer can be summarized by the term routing,
which is the process of selecting a path on the internet that can be used
to deliver data to a destination.
Routing is performed by devices called routers which connect two
or more networks and forward incoming packets to the appropriate connected
network. Since an address is defined by IP, the sender adds the destination's
IP address to the header of every data packet sent out on the network.

No lines are longer than 80 characters, TYVM. Other specified properties aren't being scored automatically at this time so this is not necessarily good news...