Frame Relay does not provide any information on flow and error control. As a result, no space is
reserved within the frame for this information. These functions are left to the upper layer protocols.
Frame Relay does provide congestion detection and can notify the upper layers of possible problems;
however, Frame Relay is primarily concerned only with the transmission and reception of data.
As a mechanism for data circuit identification, Frame Relay uses a DLCI number. Ten bits
of the two-byte Address field are used to define the DLCI. To a Frame Relay frame, the DLCI
is the most significant address in the header. Figure 36.11 depicts a Frame Relay frame.