The OSI Model
The OSI model is a seven layered standard which describes how a network is designed.
| 6 | Application layer | Program |
| 5 | Presentation layer | XDR or user routines |
| 4 | Session layer | RPC / sockets |
| 3 | Transport layer | TCP or UDP |
| 2 | Network layer | IP internet protocol. Routing occurs at this layer. |
| 1 | Data link layer | ethernet (protocols) |
| 0 | Physical layer | ethernet (electronics) |
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Physical layer - the sending of a signal across a wire. This includes the cable and the equipment necessary to boost, terminate and remove noise.
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Data link layer - Handshaking. This is the validation that what was sent along a cable actually arrived.
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Network layer - This layer of software remembers that machines are in communication. It establishes connections and deals with the delivery of data between the machines. This layer must understand about machine addresses since it has to deliver data from point to point.
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Transport layer - This layer builds packets (or datagrams) so the network layer can do it's job.
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Session layer - This is generally part of an operating system, and it helps a program set up a connection.
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Presentation layer - This helps interpret the data.
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Application layer - Programs and applications which send and receive data.
