$($a$)$ State three reasons for twisting data transmission cables.

$(3$ marks$)$

$($b$)$ With the aid of a ray diagram and refractive index profile, explain signal propagation in a multi$-$mode graded index fiber optic cable.

$(7$ marks$)$

$2602/305$

March$/$April $2024$

$3$

Turn over

$($c$)$ An optic fiber cable is made up of glass with core refractive index of $1\mathrm{.}57.$ The acceptance angle of the fiber is $20\mathrm{.}62.$ Light to the optical system is launched from air. Determine the:

$($i$)$ numerical aperture;

$($ii$)$ cladding refractive index;

$($iii$)$ critical angle.

$(6$ marks$)$

$($d$)$ Describe each of the following stations used in high level data link control $($HDLC$)$ protocol:

$($i$)$ primary station;

$($ii$)$ secondary station.

$(4$ marks$)$