rdt3.0: channels with errors and loss
New assumption: underlying channel can also lose packets (data or ACKs)
- checksum, seq. #, ACKs, retransmissions will be of help, but not enough
Q: how to deal with loss?
- sender waits until certain data or ACK lost, then retransmits
- yuck: drawbacks?
Approach: sender waits “reasonable” amount of time for ACK
retransmits if no ACK received in this time
if pkt (or ACK) just delayed (not lost):
- retransmission will be duplicate, but use of seq. #’s already handles this
- receiver must specify seq # of pkt being ACKed