Intro' to the TCP/IP Protocol Suite.
Protocol Layers
Dealing with the full complexity of even a simple p-t-p modem connection is
impossible for even the best network engineer. So to handle the complexity
engineers break down the problem of communicating between computers in to
boxes. Then to make things even simpler, they stack those boxes on top
of each other so each box only needs to worry about the box above of it,
and the box below it. At the highest level, TCP/IP breaks down into four
layers.
- Application Layer.
- This layer corresponds to the user/user application that is using the
network to communicate. It is conceptualised as an intimittent stream of
data to, and from, the application layer.
- Transport Layer.
- Most network technologies are inherently packet based. In TCP/IP the
transport layer provides two protocols to user applications, TCP and UDP.
TCP converts the unreliable packet based network technologies into the data
streams required by the conceptual Application Layer. The transport layer
is treated as a providing and recieving streams of packets.
- Network Layer.
- Each physical network provides a different means of specifiying the
destination of a data frame. However an internet can't be bound to any
specific physical network technology. So tcp/ip provides its own
addressing scheme. The Network layer's job is to provide best-effort
delivery of each packet from the Transport layer to the appropriate
machine.
- Network Interface.
- This layer encapsulates both the device driver, any OS system calls,
and the physical NIC/wires/cables/microwave link. As far as the Network
layer is concerned, all it has to provide the Network Interface is an
appropriately formed IP datagram for transmission to a specified machine.
I shall now deal with each layer's protocols in turn, bottom up.
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Andrae Muys