Ethernet and Token Ring are examples of this layer. Many people neither use the term PDU nor the term frame, but call every unit of data traveling over a network a "packet." See OSI model and packet.

For Ethernet frames – and many other types of packets – that number ... reassemble the fragments before processing the protocol data unit (PDU). But there’s a danger when an application ...

When a bridge receives a bridge protocol data unit (BPDU), issued in response to the topology change, it begins STP by selecting a root bridge that will serve as the central bridge through which ...

at which time readies the MAC protocol data units (PPDU) for transmission. To reduce the dependence on the MAC on the Physical Medium Dependent (PMD) sublayer (discussed next) for each transmission, ...