$($a$)$ Automatic repeat request $($ARQ$)$ mechanism is the action taken against lost frames, or damaged frames. With respect to buffer size issues, explain briefly the operation needs at the sender and at the receiver for the:

$($i$)$ Go$-$back$-$N ARQ

$(2$ marks$)$

$($ii$)$ Selective reject. ARQ

$(2$ marks$)$

$($b$)$ Draw a diagram to illustrate the Seven $(7)$ layers of an Open Systems Interconnection $($OSI$)$ model and briefly explain the function of each layer.

$(7$ marks$)$

$($c$)$ Indicated below are two $16-$bit integers, A and $B.$ By adding these two $16-$bit integers, calculate the sum and checksum.

$(3$ marks$)$

A: $1\{\begin{array}{ccc}\text{:}[1,& 1,1,1,0,0,1,1,0,0,1,1,0,0,1,1,& 0]\end{array}$

B: $1,1,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1$