• Category: Network
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Application Layer (Layer 7)

At the very top of the OSI Reference Model stack of layers, we find layer 7, the application layer. Continuing the trend that we saw in layers 5 and 6, this one too is named very appropriately: the application layer is the one that is used by network applications.

  • Category: Network
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Presentation Layer (Layer 6)

The presentation layer is the sixth layer of the OSI Reference Model protocol stack, and second from the top. It is different from the other layers in two key respects. First, it has a much more limited and specific function than the other layers; it's actually somewhat easy to describe, hurray! Second, it is used much less often than the other layers; in many types of connections it is not required.


  • Category: Network
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Session Layer (Layer 5)

The fifth layer in the OSI Reference Model is the session layer. As we proceed up the OSI layer stack from the bottom, the session layer is the first one where pretty much all practical matters related to the addressing, packaging and delivery of data are left behind—they are functions of layers four and below.
  • Category: Network
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Transport Layer (Layer 4)

The fourth and “middle” layer of the OSI Reference Model protocol stack is the transport layer. I consider the transport layer in some ways to be part of both the lower and upper “groups” of layers in the OSI model.

  • Category: Network
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Network Layer (Layer 3)

The third-lowest layer of the OSI Reference Model is the network layer. If the data link layer is the one that basically defines the boundaries of what is considered a network, the network layer is the one that defines how internetworks (interconnected networks) function.