In this paper, we derived analytical expression of traffic parameters of M/G/1/K queuing system to observe performance of a router with finite buffer length in context of cost analysis. Four different types of service time distributions (Exponential, K-Erlangian, Hyper Exponential and Long tailed distribution) are considered to evaluate mean queue length and probability of overflow of buffer with change in offered traffic intensity. Finally a cost function is evaluated considering cost of loosing calls, cost of customer waiting in queue, cost of service of processor and cost of buffer to observe relative cost of four different cases of service time distribution of M/G/1/K queuing system.