ii$)$ IEEE $802\mathrm{.}15\mathrm{.}4$ Standard specifies communication technologies for low$-$rate wireless personal area networks $($LR$-$WPANs$),$ including PHY & Medium Access Control $($MAC$).$

a$.$ Give two possible network topologies that can be used to configure IEEE $802\mathrm{.}15\mathrm{.}4$ MAC, and briefly explain their characteristics.

b$.$ There are two transfer mode in specified in IEEE $802\mathrm{.}15\mathrm{.}4$ MAC, what are they? Draw the diagram to show the differences between them