If the frame is sent at the enhanced rate, the data portion may have up to two
or three times as many bits because each symbol carries 2 or 3 bits instead of 1 bit. These data are preceded by a guard field and a synchronization pattern that is
used to switch to the faster data rate. That is, the access code and header are carried at the basic rate and only the data portion is carried at the faster rate.
Enhanced-rate frames end with a short trailer.