Re: some questions of tcp congestion window

[Dong Fang <yp.fangdong@gmail.com>]

On 08/08/2013 03:26 PM, Dong Fang wrote:
> hi, all
>
> I'am reading the tcp/ip network source code(kernel 3.10), i was
> fogged by the congestion window. so, i want to confirm something
> about it:
>
> Note: sack is disable. and A is sender, B is receiver.
>
> 1. at time t, the number of packets in flight is 100. like this：
>     u, u+1, u+2, ..., u+99
>     and suppose u is lost and all other packets are not. so bwtween
>     t:t+RTT we would have retransmitted u and received 99 dupack.
>     all of this dupack's ack == u, right?
>
>     when A recieved 3 dupack, it changed to TCP_CA_Recovery state.
>     in this state, the congestion window won't grow any more.
>     then, A retransmit U packet. after that, if A receive a new ack,
>     acked all the packets in flight, so the sock state is changed
>     to TCP_CA_Open. right?
>
> 2. at time t, the number of packets in flight is 100, like this:
>     u, u+1, u+2, ..., u+99
>     and suppose u and u+5 is lost and all other packets are not.
>     between t:t+RTT, we should have retransmitted u and received 99
>     dupack, all of this dupack's ack == u, right?
>
>     when A recieved 3 dupack, it changed to Recovery state, then
>     retransmit U packet, after that, if A receive a new ack,
>     this ack is only acked for u+5, at this time, current sshresh =
>     cwnd/2 + 5(the first 5 packets was acked), but cwnd > sshresh.
>     so A won't send any packets to B, and B won't send any ack to
>     A too, because B have beed send 99 dupack and 1 new ack, it
>     have done its work, right? the only way to let B send ack to
>     A is, the retransmit timeout of u+5 packet.
>
>     when A was retransmit u+5 packet to B, then B send packet ack
>     for u+100 to A, this time, the A's cwnd == sshresh << 1, enter
>     CA progress, right?
can anybody help me? :)