Please refer ->

Check slide 11 - 14 (**Notice efficiency can not be greater then 1**. :)

http://www.sce.carleton.ca/faculty/lambadaris/courses/521/homeworks/solutions_2.pdf

http://www.eecs.yorku.ca/course_archive/2010-11/F/3213/CSE3213_11_FlowErrorControl_F2010.pdf

Mainly for G-back-N proof -->

Efficiency is defined as the ratio of the time required to transmit a packet, TRANSP, to the average time it takes for a packet to be transmitted, E(T),

Efficiency = TRANSP/ E(T)

From the above description we can calculate E(T) as follows:

E(T) = (1 − p)TRANSP + p(time-out + E(T)).