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// Test fast retransmit with 4 packets outstanding, receiver sending SACKs.
// In this variant the receiver supports SACK.
// Establish a connection.
0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
+0 bind(3, ..., ...) = 0
+0 listen(3, 1) = 0
+0 < S 0:0(0) win 32792 <mss 1000,sackOK,nop,nop,nop,wscale 7>
+0 > S. 0:0(0) ack 1 <...>
+.1 < . 1:1(0) ack 1 win 32792
+0 accept(3, ..., ...) = 4
// Send 1 data segment and get an ACK, so cwnd is now 4.
+0 write(4, ..., 1000) = 1000
+0 > . 1:1001(1000) ack 1
+.1 < . 1:1(0) ack 1001 win 32792
// Write 4 data segments.
+0 write(4, ..., 4000) = 4000
+0 > . 1001:5001(4000) ack 1
// Get 3 SACKs.
+.1 < . 1:1(0) ack 1001 win 32792 <sack 2001:3001,nop,nop>
+0 < . 1:1(0) ack 1001 win 32792 <sack 2001:4001,nop,nop>
+0 < . 1:1(0) ack 1001 win 32792 <sack 2001:5001,nop,nop>
// We've received 3 duplicate ACKs, so we do a fast retransmit.
+0 > . 1001:3049(2048) ack 1
// Receiver ACKs all data.
+.1 < . 1:1(0) ack 6001 win 32792
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