received and delivered packet n. However, if packet n is lost, both it and packet
n + 1 will eventually be retransmitted as a result of the GBN retransmission rule at
the sender. Thus, the receiver can simply discard packet n + 1. The advantage of this
approach is the simplicity of receiver buffering—the receiver need not buffer any
out-of-order packets. Thus, while the sender must maintain the upper and lower
bounds of its window and the position of nextseqnum within this window, the
only piece of information the receiver need maintain is the sequence number of the
next in-order packet. This value is held in the variable expectedseqnum, shown
in the receiver FSM in Figure 3.21. Of course, the disadvantage of throwing away a
correctly received packet is that the subsequent retransmission of that packet might
be lost or garbled and thus even more retransmissions would be required.