snoop + alpha protocol

1. SNOOP+α
PROTOCOL

2. The snoop agent

3. THE SNOOP PROTOCOL
1-a snoop agent, is introduced at the AP (Access Point) that acts as the last
2-The snoop agent monitors every packet that passes through the AP in eith
3-he Snoop agent operates differently on TCP data and ACK channels, as w
4-For data transfer from an MT to the FH, t
control procedures.

4. 1-If BS sends duplicate A2 FH will think that there is congestion and lowers speed
2-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

5. Advantages of Snoop protocol
1-offered End-to-End connections for TCP
2-prevents Fixed Host from generating congestion algorithms
3-Improved performance
4-decreased End-to-End Average delay.
5-High throughput

6. Protocols combined with snoop
protocol
TCP Tahoe
Reno
New Reno
SACK
Vegas

7. Simulation Results

8. Improvement of TCP protocols
using snoop
1-As expected, most TCP versions improve compared to the
plain wireless environment without Snoop. For instance,
TCP Tahoe, Reno and New Reno improve.
2- However, two important aspects need further
investigation. TCP Vegas, which was the worst performing
version without Snoop, now is the best performing version,
and TCP SACK that was the best performing version without
Snoop is now the worst version.

9. Snoop+ α Protocol
1-snoop has a problem; when there are no duplicate ACKs, the Snoop protocol cannot notice the
2- the Snoop+ α protocol to solve the Snoop protocol’s problem. Because the Snoop+ α agent ad

10. These ACKs fall into one of three categories:
1-Duplicate ACK : this is an ACK identical to the previously received ACK nu
2- A spurious ACK : this is an ACK whose number is less than that of the las
3-A new ACK : this is an ACK not received previously by the snoop+ α agen

11. Procedure for packets loss
For data transfer from an FH (Fixed Host) to an MT, the
Snoop agent caches unacknowledged TCP data segments,
which it forwards to the TCP receiver, and monitors the
corresponding ACKs. In particular, it provides for:
1.Retransmission of any lost data segments locally by
1.using local timers or TCP duplicate acknowledgments to
identify packet loss, instead of waiting for the FH to do so.
2. Suppressing the duplicate ACKs on their way from
the MT back to the FH, thus avoiding fast retransmit and
congestion control at the latter.