ETHERNET and TCP/IP

Like nearly all standards in the field of data transmission, ETHERNET also follows the ISO/OSI layer model. Based on this reference model, the principle course of a transmission is described. Each of the 7 parts (layers) has a particular function and makes it available for the next higher layer.

The ETHERNET standard IEEE-802.3 defines the function of the two lowest layers. These layers consist of the following components and the Logical Link Control (LLC) which is described in the IEEE standard 802.2.

• Media Access Control Protocol (MAC)
• Physical Layer Signalling (PLS)
• Attachment Unit Interface (AUI)
• Medium Dependent Interface (MDI)
• Physical Medium Attachment (PMA)

Since the ISO/OSI model did not yet exist when the development of TCP/IP protocols started, these protocols are based on the DoD architecture. The DoD model cannot be clearly transferred to the ISO/OSI model. The following figure shows a comparison of ETHERNET in the ISO/OSI model and the TCP/IP protocols adapted to that model. This shall explain that ETHERNET does not necessarily mean TCP/IP (and vice versa). To be precise, TCP/IP is only based on ETHERNET and can also be used in other data networks (e.g. for satellite links). In return, TCP/IP is not the only protocol used in ETHERNET networks. Actually, TCP/IP is only one of numerous protocols which are used side by side.

ETHERNET in the ISO/OSI model