Ethernet is a layer 2 data link protocol that is widely used with the TCP/IP protocol, which resides at layers 3 and 4. To understand network communications, it is essential to learn about the protocol layers (see OSI model). The IP layer 3 breaks apart the data being transmitted into variable length packets, known as "Ethernet frames," up to 1,500 bytes long. Each frame has a header containing source and destination addresses and a trailer with error correction data. TCP/IP Ensures Complete Delivery Ethernet transmits the frames from one node to the next and only guarantees that if the frame arrives, it arrived intact. If a frame goes missing, it is none the wiser. However, the TCP part of TCP/IP ensures that the entire set of data has been delivered intact. For details about the protocols, see data link protocol, CSMA/CD, TCP/IP and Internet protocol.