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NOTES ON METHODOLOGY

OSI Model

A conceptual model of networking based on seven “layers”:

Layer	Description
Application	Provides networking options (an interface to transmit data) to programs running on the computer.
Presentation	Translates the data into a standardized format (so the receiving machine can read it); it also handles encryption, compression, or other transformations of the data.
Session	Sets up and maintains a connection with the other computer across the network (connection is unique to this communication).
Transport	Decides on a transport protocol (TCP or UDP) and then divides up the data to be sent over the network (TCP: segments; UDP: datagrams).
Network	[router level] Locates the destination computer via logical addressing (i.e., IP Addresses).
Data Link	[switch level] Identifies the MAC/hardware addresses of the machines on the network (mapping each IP Address to the device's MAC/hardware address). Runs a CRC for data integrity and then presents the data in a suitable format for transmission.
Physical	The hardware that communicates with electrical impules (1's and 0's) or light (on and off).

The machine that receives the transmssion does so on Layer 1, then passes the data up the stack to Layer 2, etc.