A protocol stack or protocol tower (from the English protocol stack , also known as a protocol stack , network stack or network stack ) is a conceptual architecture of communication protocols in data transmission . Clearly, the individual logs are as consecutively numbered layers ( layers ) of a stack ( stacks arranged) above each other. Each layer uses the lower layer in the protocol stack to fulfill its specific task.
Data transmitted over a network is processed by one network protocol at a time. Upon receipt, each network protocol removes from the data that control information that is only intended for this protocol itself, and transfers the remaining data to the next higher network protocol. In the transmission direction, the control information is added before it is transferred to the next lower network protocol - a message therefore carries all the headers of the layers above on the line . An HTTP message that is sent via Ethernet can be illustrated as follows:
If the functions of a protocol layer are subdivided into individual processes that run independently of one another and one after the other, they can be divided into sub-layers.
The figure shows the sub-layers of Ethernet as an example of a protocol stack . The OSI model is shown as a reference . While Ethernet only has functions that are assigned to layer 1 (physical layer) and layer 2 (data link layer) in the OSI model, on closer inspection these two layers are broken down into 7 sub-layers in the Ethernet protocol stack.
This example shows a protocol stack which, with the current state of the art, which allows transmission speeds of 100 Mbit / s and more, is implemented entirely in an integrated circuit (IC), i.e. in hardware. Processes such as ATM are designed for significantly higher transmission speeds: With them, the network layer (layer 3) is also implemented in hardware.
The example also shows two interfaces between the protocol layers: the Media Dependent Interface MDI and the Media Independent Interface MII. The sub-layers of Ethernet were divided up in such a way that the layers above the MII are independent of the transmission medium, i.e. regardless of whether Ethernet is transmitted, for example, via a coaxial cable or an optical fiber . This made it possible to manufacture ICs with a standardized MII interface that are suitable for different transmission media and can therefore be produced cost-effectively in larger numbers.