$4)[15$ points$]$ Consider a $255$ Mbps Ethernet broadcast channel with CSMA$/$CD used by nodes A and B and suppose that A and B are directly connected by a $1,200$ meters long cable. The signal propagation speed on the cable is $\backslash (200,000\backslash$mathrm$\{$~km$\}/\backslash$mathrm$\{$sec$\}\backslash ).$ Suppose that node A starts transmitting a new frame initially, and, $0\mathrm{.}002$ msec before the first bit of node A$\text{'}$s transmission has propagated to node B$,$ node B also starts transmitting its frame.

$($a$)$ What is the minimum frame size to ensure that node A can detect the collision before completing its frame transmission? $(10$ points$)$

$($b$)$ What will happen if the chosen minimum frame size is too small? $(5$ points$)$