Final answer:
In a network using selective-repeat protocol with m=4 and a sending window of size 8, the total number of frames that can be sent before an acknowledgment is required is 8 frames.
Step-by-step explanation:
When using the selective-repeat protocol in a network with a window size of 8 and a sequence number range of m=4, which means there are 2^4 or 16 different sequence numbers, the number of frames that can be sent before an acknowledgment is required is equal to the window size. This is because, in selective-repeat, each frame within the window can be sent independently and can be acknowledged independently.
Therefore, the correct answer to how many frames can be sent before an acknowledgment is required, given a sending window of size 8, is 8 frames (option b). Acknowledgments are not needed to be all received before reaching the end of the window, as the protocol allows for selective acknowledgment of individual frames within the window. This means frames can be sent out up to the limit of the window size before requiring an acknowledgment of at least the first frame sent in the sequence.