THE SNOOP PROTOCOL1-a snoop agent, is introduced at the AP (Access Point) that acts as the last2-The snoop agent monitors every packet that passes through the AP in eith3-he Snoop agent operates differently on TCP data and ACK channels, as w4-For data transfer from an MT to the FH, tcontrol procedures.
1-If BS sends duplicate A2 FH will think that there is congestion and lowers speed2-Disadvantage will send P4 and after P3 he will send P3 and P4. MH FH BS snoop agent P2 P1 P3 P1 P4 P2 X X Ack1 Ack1 Ack2 Ack2 Ack2 P3 P4 Ack3 Ack3 Ack4 Ack4
Advantages of Snoop protocol1-offered End-to-End connections for TCP2-prevents Fixed Host from generating congestion algorithms3-Improved performance4-decreased End-to-End Average delay.5-High throughput
Protocols combined with snoopprotocolTCP TahoeRenoNew RenoSACKVegas
Improvement of TCP protocolsusing snoop1-As expected, most TCP versions improve compared to theplain wireless environment without Snoop. For instance,TCP Tahoe, Reno and New Reno improve.2- However, two important aspects need furtherinvestigation. TCP Vegas, which was the worst performingversion without Snoop, now is the best performing version,and TCP SACK that was the best performing version withoutSnoop is now the worst version.
Snoop+ α Protocol1-snoop has a problem; when there are no duplicate ACKs, the Snoop protocol cannot notice the2- the Snoop+ α protocol to solve the Snoop protocol’s problem. Because the Snoop+ α agent ad
These ACKs fall into one of three categories:1-Duplicate ACK : this is an ACK identical to the previously received ACK nu2- A spurious ACK : this is an ACK whose number is less than that of the las3-A new ACK : this is an ACK not received previously by the snoop+ α agen
Procedure for packets lossFor data transfer from an FH (Fixed Host) to an MT, theSnoop agent caches unacknowledged TCP data segments,which it forwards to the TCP receiver, and monitors thecorresponding ACKs. In particular, it provides for:1.Retransmission of any lost data segments locally by1.using local timers or TCP duplicate acknowledgments toidentify packet loss, instead of waiting for the FH to do so.2. Suppressing the duplicate ACKs on their way fromthe MT back to the FH, thus avoiding fast retransmit andcongestion control at the latter.