The POS PHY Level 3 specification defines the interconnection of Physical Layer (PHY) devices to Link Layer devices, implementing Packet over SONET (POS). The POS PHY Level 3 interface covers all application bit rates up to 2.4 Gbit/s. This specification identifies the features and requirements of the design intended to be used in Link Layer devices. The design implements a POS PHY Level 3 Link Layer interface on one side while, on the other side, it talks to generic FIFOs. It is intended that the user application (Link Layer device) will interface with the generic FIFOs based on the interface described in this specification.