mptcp_skb_entail() # mptcp_output.c
mptcp_ack_retransmit_timer() # mptcp_output.c
--> tcp_transmit_skb() # kernel/net/ipv4/tcp_output.c
tcp_mtu_probe() # kernel/net/ipv4/tcp_output.c
tcp_write_xmit()
__tcp_retransmit_skb()
tcp_send_active_reset()
tcp_send_synack()
tcp_send_syn_data()
tcp_connect()
tcp_send_ack()
tcp_xmit_probe_skb()
tcp_write_wakeup()
--> tcp_transmit_skb() # kernel/net/ipv4/tcp_output.c
上面是 节点5: 112.26.[0-4].5，客户端
下面是 节点1: 112.26.[0-4].1，服务器
