Assume that the time of failure T of a telephone switching system is exponentially distributed with a failure rate $\displaystyle \lambda$. Find the maximum likelihood estimate of the failure rate from a random sample $\displaystyle T_1 = t_1, T_2 = t_2, ...........T_n=t_n$ of a n times to failure.

I dont know whether to use exponential as stated in the question or to use Poisson as the parameter passed is of possion!!!!!!!!!!