The Data Link layer provides the following services to the Network layer. Handling of transmission errors Regulation of data flow rate Framing One of the purposes of the Data Link layer is to form the stream of bits received by the physical layer into discrete units called frames. A frame can also be called a packet or block. It is a unit of transmission.
Frames are necessary for packet switched networks.
A frame generally has a header followed by the transmitted data. A trailer often follows the data. Pause between frames - Buffering and other actions can possibly remove the space between frames. The receiver can count the number of characters until it has received the predetermined count. Another method relies on the frame size being sent first.