Physical Medium Dependent

Physical Medium Dependent sublayers or PMDs further help to define the physical layer of computer network protocols. They define the details of transmission and reception of individual bits on a physical medium. These responsibilities encompass bit timing, signal encoding, interacting with the physical medium, and the properties of the cable, optical fiber, or wire itself. Common examples are specifications for Fast Ethernet, Gigabit Ethernet and 10 Gigabit Ethernet defined by the Institute of Electrical and Electronics Engineers (IEEE).

For cable modems Physical Medium Dependent sublayers define the physical sub-layer which also includes the MPEG sub-layer.^{[citation needed]}

Description

The Ethernet PMD sublayer is part of the Ethernet physical layer (PHY). The hierarchy is as follows:

Data Link Layer (Layer 2)
- LLC (Logical Link Control Sublayer)
- MAC (Media Access Control Sublayer)
  - RS (Reconciliation Sublayer) - This sublayer processes PHY Local/Remote Fault messages and handles DDR conversion
PHY Layer (Layer 1)
- PCS (Physical Coding Sublayer) - This sublayer performs auto-negotiation and coding such as 8b/10b
- PMA (Physical Medium Attachment Sublayer) - This sublayer performs PMA framing, octet synchronization/detection, and [math]\displaystyle{ x^7+x^6+1 }[/math] scrambling/descrambling
- PMD (Physical Medium Dependent Sublayer) - This sublayer consists of a transceiver for the physical medium