In the
OSI model of computer networking, a frame is the
protocol data unit at the
data link layer. Frames are the result of the final layer of
encapsulation before the data is transmitted over the physical layer. A frame is "the unit of transmission in a link layer protocol, and consists of a link layer header followed by a packet." Each frame is separated from the next by an
interframe gap. A frame is a series of bits generally composed of frame synchronization bits, the
packet payload, and a
frame check sequence. Examples are
Ethernet frames,
Wi-Fi frames,
4G frames,
Point-to-Point Protocol (PPP) frames,
Fibre Channel frames, and
V.42 modem frames. Often, frames of several different sizes are nested inside each other. For example, when using
Point-to-Point Protocol (PPP) over
asynchronous serial communication, the eight bits of each individual byte are framed by start and stop bits, the payload data bytes in a network packet
are framed by the header and footer, and several packets can be framed with
frame boundary octets. ==Time-division multiplex==