Suppose now that in addition to corrupting bits, the underlying channel can lose
packets as well, a not-uncommon event in today’s computer networks (including the
Internet). Two additional concerns must now be addressed by the protocol: how to
detect packet loss and what to do when packet loss occurs. The use of checksumming, sequence numbers, ACK packets, and retransmissions—the techniques
already developed in rdt2.2—will allow us to answer the latter concern. Handling the first concern will require adding a new protocol mechanism.