Circuit Switching:-
setup time = s , transmission time = x/b , propagation time= kd
so , total time = s + x /b + kd
Packet Switching:-
no setup time , the last bit is sent at t = x /b , the last packet must be retransmitted k − 1 times by intermediate routers, with each retransmission taking p /b sec. , propagation time= kd
so , total time = x /b + (k − 1)p /b + kd
Packet switching is faster if s > (k − 1)p /b.
Hence,
In Circuit switching total time t = s+(x/b)+kd
In Packet switching total time t = x /b + (k − 1)p /b + kd