Q & A on Packets, frames, datagrams and PDUs Q: I have what I hope will be a very quick and easy question for you to answer regarding the usage of the terms "packet" and "frame" in relation to the OSI or TCP/IP protocol models. Is it common and/or correct to use those terms interchangeably? (As Microsoft does.) Or, are they distinct terms in relation to the models? A: In the TCP/IP world and in everyday use, term "packet" is fairly generic -- it refers to any small unit of data used in networking systems. The term "frame" refers to the packets that are defined by hardware (i.e., layers 1-2). Thus, it is correct (and more precise) to refer to the packets used on an Ethernet as "Ethernet frames", while the packets sent across the Internet are called "datagrams". People from the ISO world tend to use the wordy and ambiguous phrase "Protocol Data Unit (PDU)" instead of "packet" or "frame".