a$)$ Expand the acronyms and describe the basic difference in the operation between IEEE $802\mathrm{.}3($CSMA$/$CD$)$ and IEEE $802\mathrm{.}11($CSMA$/$CA$)$ Medium Access Control methods. $(5$ marks$)$

b$)$ Briefly describe the operation of CSMA$/$CA as used in Wi$-$Fi$,$ in the case of a hidden node. $(5$ marks$)$