Documentation/networking/tcp.txt

   1 How the new TCP output machine [nyi] works.
   2
   3
   4 Data is kept on a single queue. The skb->users flag tells us if the frame is
   5 one that has been queued already. To add a frame we throw it on the end. Ack
   6 walks down the list from the start.
   7
   8 We keep a set of control flags
   9
  10
  11         sk->tcp_pend_event
  12
  13                 TCP_PEND_ACK                    Ack needed
  14                 TCP_ACK_NOW                     Needed now
  15                 TCP_WINDOW                      Window update check
  16                 TCP_WINZERO                     Zero probing
  17
  18
  19         sk->transmit_queue              The transmission frame begin
  20         sk->transmit_new                First new frame pointer
  21         sk->transmit_end                Where to add frames
  22
  23         sk->tcp_last_tx_ack             Last ack seen
  24         sk->tcp_dup_ack                 Dup ack count for fast retransmit
  25
  26
  27 Frames are queued for output by tcp_write. We do our best to send the frames
  28 off immediately if possible, but otherwise queue and compute the body
  29 checksum in the copy.
  30
  31 When a write is done we try to clear any pending events and piggy back them.
  32 If the window is full we queue full sized frames. On the first timeout in
  33 zero window we split this.
  34
  35 On a timer we walk the retransmit list to send any retransmits, update the
  36 backoff timers etc. A change of route table stamp causes a change of header
  37 and recompute. We add any new tcp level headers and refinish the checksum
  38 before sending.
  39