TCP congestion window

TCP congestion window

[yi]

Dear all,
First, I apologize you for posing this message although I'm not on the list.

I have some questions. I made the following system call for getting tcp 
cwnd size of ongoing connection. However, I am always getting the value 
of "2", which is the initial tcp cwnd size, I think. What I really want 
to do is to trace tcp cwnd size when I download some big file using 
"wget"'s http file downloader. For it, I added a new system call shown 
below and modified the wget source code.

Please cc to me personally in reply. Thanks in advance.

Best Regards,
Yung Yi.

---------------------------------------------------------------------------
asmlinkage int sys_get_winsize(int sockfd)
{
    struct socket *sock;
    struct sock *sk;
    int err;
    sock = sockfd_lookup(sockfd, &err);

    if (!sock)
        return -1;

    sk = sock->sk;
    return sk->tp_pinfo.af_tcp.snd_cwnd;
}

Re: TCP congestion window

[Nagendra Singh Tomar]

Yi,
   First of all networking related questions should go to 
linux-net@vger.kernel.org. Now for ur question.
cwnd has got significance in the sending side of a TCP connection. Its the 
sender that keeps changing the cwnd based on the ACKs recvd. If you are 
using wget for downloading a file and you are expecting cwnd to change on 
the wget side, then the answer is that since wget is *only* receiving 
data, cwnd will not change on wget side. It will change on the other side.
If you are checking for cwnd on the other side then please ignore my 
answer.

Thanx
tomar


On Tue, 22 Jul 2003, yi wrote:

> Dear all,
> First, I apologize you for posing this message although I'm not on the
> list.
> 
> I have some questions. I made the following system call for getting tcp 
> cwnd size of ongoing connection. However, I am always getting the value 
> of "2", which is the initial tcp cwnd size, I think. What I really want 
> to do is to trace tcp cwnd size when I download some big file using 
> "wget"'s http file downloader. For it, I added a new system call shown 
> below and modified the wget source code.
> 
> Please cc to me personally in reply. Thanks in advance.
> 
> Best Regards,
> Yung Yi.
> 
> ------------------------------------------------------------------------
> ---
> asmlinkage int sys_get_winsize(int sockfd)
> {
>     struct socket *sock;
>     struct sock *sk;
>     int err;
>     sock = sockfd_lookup(sockfd, &err);
> 
>     if (!sock)
>         return -1;
> 
>     sk = sock->sk;
>     return sk->tp_pinfo.af_tcp.snd_cwnd;
> }
> 
> 
> -
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Re: TCP congestion window

[Pekka Pietikainen]

On Mon, Jul 21, 2003 at 05:07:02PM -0500, yi wrote:
> I have some questions. I made the following system call for getting tcp 
> cwnd size of ongoing connection. However, I am always getting the value 
> of "2", which is the initial tcp cwnd size, I think. What I really want 
> to do is to trace tcp cwnd size when I download some big file using 
> "wget"'s http file downloader. For it, I added a new system call shown 
> below and modified the wget source code.
Also what you want already exists, so no need to modify the kernel,
the TCP_INFO socket option (netinet/tcp.h should have the required
definitions in recent glibc)

  struct tcp_info info;
  int optlen=sizeof(struct tcp_info);
  if(getsockopt(sk->fd,SOL_TCP,TCP_INFO,(void *)&info,&optlen) < 0)
    return;
  printf("unacked: %d sacked: %d lost: %d retrans: %d fackets: %d\n",
                info.tcpi_unacked,info.tcpi_sacked,info.tcpi_lost,
                info.tcpi_retrans,info.tcpi_fackets);
  printf("pmtu: %d rcv_ssthresh: %d rtt: %d rttvar: %d snd_ssthresh:
	%d\nsnd_cwnd: %d advmss: %d reordering: %d\n",info.tcpi_pmtu,info.tcpi_rcv_ssthresh,
  info.tcpi_rtt,info.tcpi_rttvar,info.tcpi_snd_ssthresh,info.tcpi_snd_cwnd,info.tcpi_advmss,
          info.tcpi_reordering)

There's a few more that I don't print there, see the header file.

-- 
Pekka Pietikainen

Re: TCP congestion window

[Glen Turner]

Pekka Pietikainen wrote:

> Also what you want already exists, so no need to modify the kernel,
> the TCP_INFO socket option (netinet/tcp.h should have the required
> definitions in recent glibc)

There's also the Web100 patches at http://www.web100.org/
which add full TCP instrumentation, complete with a nice
set of GUI diagnostic tools.