One key design decision for ATM was whether to use fixed$-$ or variable$-$length cells. Let us consider this decision from the point of view of efficiency. We can define transmission efficiency as

$N=$ Number of information octets $\frac{?}{?}$ Number of information octets $+$ Number of overhead octets

a$.$ Consider the use of fixed$-$length packets. In this case, the overhead consists of the header octets. Define

$L=$ Data field size of the cell in octet

$H=$ Header size of the cell in octets

$x=$ Number of information octets to be transmitted as a single message

Derive an expression for $N.$ Hint: The expression will need to use the operator $*,$ where $[Y]=$ the smallest integer greater than or equal to $Y.$