System Administration Guide: IP Services

Data-Link Layer: Where Framing Takes Place

Data-link layer protocols, such as PPP, format the IP datagram into a frame. These protocols attach a third header and a footer to “frame” the datagram. The frame header includes a cyclic redundancy check (CRC) field that checks for errors as the frame travels over the network media. Then, the data-link layer passes the frame to the physical layer.