Which ARQ protocol retransmits only the specific frames that are lost or corrupted, while allowing out-of-order frames to be buffered?
Selective Repeat retransmits individual erroneous or lost frames and can buffer correctly received out-of-order frames.
In Go-Back-N ARQ, when a receiver gets an out-of-order frame, what does it normally do?
The standard GBN receiver accepts only the next expected frame; out-of-order frames are discarded and cumulative ACK behavior is used.
Which statement correctly distinguishes cumulative ACKs from selective ACKs?
A cumulative ACK indicates successful receipt through a particular point in the sequence.
A data-link protocol uses a 3-bit sequence number and Go-Back-N. What is the largest valid sender window?
For Go-Back-N, the sender window is at most $2^k - 1$, so $2^3 - 1$ = 7.
A data-link protocol uses a 4-bit sequence number and Selective Repeat. What is the largest safe sender window under the standard SR constraint?
Selective Repeat normally limits the window to half the sequence-number space: $2^{4-1}$ = 8.