1// Client negotiates AccECN and starts sending 2// AccECN option in last ACK and data segments 3// Middlebox accepts AccECN option but some packets 4// are lost due to congestion. Client should 5// continue to send AccECN option 6 7`./defaults.sh 8sysctl -q net.ipv4.tcp_ecn=3 9sysctl -q net.ipv4.tcp_ecn_option=2 10` 11 12+0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 4 13+.002 ... 0.102 connect(4, ..., ...) = 0 14 15+.002 > [noecn] SEWA 0:0(0) <mss 1460,sackOK,TS val 100 ecr 0,nop,wscale 8> 16+0.1 < [ect0] SW. 0:0(0) ack 1 win 32767 <mss 1024,ECN e0b 1 ceb 0 e1b 1,nop,nop,nop,sackOK,nop,wscale 8> 17+.002 > [ect0] A. 1:1(0) ack 1 <ECN e1b 1 ceb 0 e0b 1,nop> 18 19// Send 20+0.01 write(4, ..., 3000) = 3000 21+.002 > [ect0] .5 1:1013(1012) ack 1 <ECN e1b 1 ceb 0 e0b 1,nop> 22+.002 > [ect0] P.5 1013:2025(1012) ack 1 <ECN e1b 1 ceb 0 e0b 1,nop> 23+.002 > [ect0] P.5 2025:3001(976) ack 1 <ECN e1b 1 ceb 0 e0b 1,nop> 24 25// First two segments were lost due to congestion as SACK was 26// received acknowledging 3rd segment 27+0.1 < [ect0] .5 1:1(0) ack 1 win 264 <ECN e1b 1 ceb 0 e0b 977,nop,nop,nop,sack 2025:3001> 28 29// Since data with option was SACKed, we can 30// continue to use AccECN option for the rest of 31// the connection. This one is a rexmt 32+.02~+0.5 > [ect0] .5 1:1013(1012) ack 1 <ECN e1b 1 ceb 0 e0b 1,nop> 33+0.1 < [ect0] .5 1:1(0) ack 3001 win 264 <ECN e1b 1 ceb 0 e0b 3000,nop> 34 35// Send new data, it should contain AccECN option 36+0.01 write(4, ..., 2000) = 2000 37+.002 > [ect0] .5 3001:4013(1012) ack 1 <ECN e1b 1 ceb 0 e0b 1,nop> 38+.002 > [ect0] P.5 4013:5001(988) ack 1 <ECN e1b 1 ceb 0 e0b 1,nop> 39