$($b$)($i$)$ State three merits of scrambling in data encoding.

$($ii$)$ The data sequence: $101100000100001$ is encoded in high density bipolar $3$

$)$ scheme. Draw the resultant waveform.

$(7$ marks$)$

$($e$)$ A modem transmits $56,000$ bits per second using signalling elements chosen from a $4096$ constellation. Determine the:

$($i$)$ modulation scheme used;

$($ii$)$ number of bits which may be encoded in each signalling element;

$($iii$)$ baud $-$ rate of the modem. $=\frac{1}{5},f(\frac{1}{5}80)$

$(6$ marks$)$

$($d$)$ Draw the high $-$ level Data Link Control $($HDLC$)$ frame and state the function of any two fields.

$(5$ marks$)$