Thomas Kunz
Systems and Computer Engineering
409
Snoop: Description of Protocol
nprocessing ACKs from MH:
–new ACK:
common case, initiates cleaning up of snoop cache, update estimate of round-trip time for wireless link,
forward ACK to FH
–spurious
ACK: less than last ACK seen, happens rarely. Just drop ACK and continue
–duplicate
ACK: indicates packet loss, one of several actions:
npacket either not in cache or marked as retransmitted:
pass duplicate ACK on to FH
nfirst duplicated ACK for cached packet: retransmit
cached packet immediately and at high
priority, estimate number of expected duplicate
ACKs, based on # of packets sent after missing one
nexpected successive duplicate ACKs: ignore, we already
initiated retransmission. Since retransmission
happens at higher priority, we might not see
total number of expected duplicate ACKs