physical layer (PHY)

In local area networks( LAN), the physical layer (PHY) corresponds in its functionality to the physical layer of the OSI reference model. The PHY sublayer lies below the MAC layer and is used for coding, decoding, synchronization of the station with the transmit clock and regeneration of the transmit clock. Furthermore, connection establishment, connection provisioning and maintenance and, if necessary, the restoration of physical connections between neighboring nodes are performed in this layer.

In order to do justice to the many different LAN variants, the OSI reference model for LAN applications was modified slightly and the LAN layer model was derived from it. The LAN layer model is modified by the respective working groups according to the requirements. In classic Ethernet, the physical layer (PHY) is divided into three sublayers: The Physical Layer Signalling( PLS), the Attachment Unit Interface( AUI) and the Medium Attachment Unit( MAU).

For Fast Ethernet, there are four different physical layer architectures, for 100Base- TX, 100Base-T4, 100Base-FX and 100Base- T2. In general, the physical layer consists of the Physical Coding Sublayer( PCS), Physical Media Attachment( PMA), Physical Medium Dependent( PMD) and the Autonegotiation Sublayer with the Autonegotiation Protocol( ANP) and is based on the Medium Dependent Interface( MDI). The individual sublayers have different characteristics in the different Fast Ethernet variants. This applies to all sublayers, from the coding to the connector.

In FDDI, the physical layer is divided into two parts. In addition to the PMD sublayer, which is available in various forms, there is also the physical layer (PHY).