## The seven-layer OSI model

#### It is often the case that there are several types of signalling protocol running concurrently to control the information flow and processing within a network – some dealing with information on a bit-by-bit basis, such as error correction protocols, and some operating at a much higher level to ensure that whole files of data are packaged correctly and arrive in sequence after transmission. These various levels of protocol are often categorized in terms of their function within a now standardised seven-layer model, known as the OSI seven-layer model, as shown here. As the data passes through each layer of the network hierarchy, additional signalling information is usually added to pass information to the corresponding layers at the receive side. This can amount to a very large overhead for the system, particularly if the data packet size itself is small. |

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