sockets - setReceiveBufferSize doesn't work...

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chrisrocker90@yahoo.com - 07 Feb 2006 17:53 GMT

I'm trying to set the receive (and send) size on a socket buffer.
However, it doesn't seem to work. When I compare it with the
advertised window size in the tcp header, there is no correlation. I
used a packet sniffer to read the outbound TCP header window size.

Heres the code:

destSocket = new Socket(destHost, destPort);
destSocket.setSendBufferSize(256);
destSocket.setReceiveBufferSize(256);
System.out.println(destSocket.getReceiveBufferSize());
System.out.println(destSocket.getSendBufferSize());

Reprinting the buffers sizes show the set method works; but as I said,
there is no change in the window size. I've tried several different
values, but none seem to take.

Am I misunderstanding the purpose of the socket buffer, or is it just
not working?

- Chris

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Gordon Beaton - 07 Feb 2006 18:10 GMT

> I'm trying to set the receive (and send) size on a socket buffer.
> However, it doesn't seem to work. When I compare it with the
[quoted text clipped - 8 lines]
> System.out.println(destSocket.getReceiveBufferSize());
> System.out.println(destSocket.getSendBufferSize());

Depending on the platform, it may be necessary to set the buffer sizes
before connecting, which you aren't doing here. Try creating an
unconnected Socket and setting the values before calling connect().

Also the value is only a hint and some platforms may use a larger
value than the one you suggest.

/gordon

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chrisrocker90@yahoo.com - 07 Feb 2006 19:52 GMT

Ok, I tried this:

    destSocket = new Socket();

    InetSocketAddress sa = new InetSocketAddress(destHost,
destPort);
destSocket.setSendBufferSize(16384);
destSocket.setReceiveBufferSize(16384);

System.out.println("destHost: " + destHost + ", destPort: " +
destPort);
System.out.println(destSocket.getReceiveBufferSize());
System.out.println(destSocket.getSendBufferSize());

     destSocket.connect(sa);

This output is this:

4000 3784 127.0.0.1
destHost: 127.0.0.1, destPort: 3784
16384
16384

But - the window size is still around 64K. The OS is Win2K. I guess
this is one of the operating systems which ignores the socket buffer
sizing. Is there a workaround to this, or a patch to the jvm or os, or
anything? Or should I write it in C (which I'm not that familiar with,
but if it works, well, it works).

Chris

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EJP - 08 Feb 2006 00:44 GMT

Chris,

Why are you using such small numbers? 256 and 16384? 64k would be more
like it these days.

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chrisrocker90@yahoo.com - 08 Feb 2006 15:05 GMT

EJP,

The numbers are abitrary at this point - I'm just trying to see if it
works, first. I've also tried numbers larger than 64k, with no luck.
What I'm really trying to do is use a TCP proxy to calculate the
bandwidth * delay product such that the receive buffer is appropriate
to the connection. That way, on a long fat pipe a large window could be
used, but on a thin pipe a much smaller window could be used. I'm
getting ready to quit on it for now, or move to C at the least, which I
also have my doubts about working on the winsock API.

- Chris

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EJP - 08 Feb 2006 23:37 GMT

> EJP,
>
[quoted text clipped - 6 lines]
> getting ready to quit on it for now, or move to C at the least, which I
> also have my doubts about working on the winsock API.

OK. The Windows default is 8k but this can be changed via a registry
setting called TcpWindowSize which may have happened in your case.

The platform is free to adjust the size you supply to
setSendBufferSize()/setReceiveBufferSize(), both upwards and downwards,
so your test with 256 is never going to work as expected because 256 is
far too small for any platform I am aware of.

The maximum is 64k-1 unless you use window scaling, which implies that
you have to set the buffer sizes prior to calling connect() for a
client, or on the ServerSocket for a server.

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chrisrocker90@yahoo.com - 09 Feb 2006 19:54 GMT

EJP,

Still no luck. I set the relevant registy entries as follows:

GlobalMaxTcpWindowSize: 65535
TcpWindowSize: 32760
TCP1323Opts: 1 (Supports scaling)

My program sets all buffer sizes on all sockets to 16834. It's done
before establishing a connection for them. It's a proxy server, so
there are 3 sockets, i.e. the server socket, the socket it spawns, and
the connection to the remote host.

However, despite all this, the packet sniffer shows the windows size to
be 32760. The initial syn opt shows that the windows scaling option is
0, i.e, don't scale the value.

Have you gotten this kind of thing to work on win2k before? Could it be
the Winsock implmentation? Also, have your worked on bandwidth * delay
and setting the buffer size? If so, how did it work out? I noticed
there is a lot more work being done on Linux in this area, but I'm
trying to make this cross-platform. Thanks for any advice you can
offer. I'm ready to give up on this one.

- Chris

Reply to this Message

Gordon Beaton - 09 Feb 2006 20:02 GMT

> My program sets all buffer sizes on all sockets to 16834. It's done
> before establishing a connection for them. It's a proxy server, so
> there are 3 sockets, i.e. the server socket, the socket it spawns, and
> the connection to the remote host.

Note that you must set the buffer sizes for the *ServerSocket* in
order for this to have an effect on the Sockets that are created from
it in response to arriving connections. This is because the Sockets
will inherit their values from the ServerSocket, and you have no other
chance to set them before they are connected.

/gordon

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chrisrocker90@yahoo.com - 09 Feb 2006 20:28 GMT

Unfortunately, I'm already doing that

public final static int BUFF_SIZE = 16834;

mainSocket = new ServerSocket();
mainSocket.setReceiveBufferSize(BUFF_SIZE);
InetSocketAddress serverPort = new InetSocketAddress ( SERVER_PORT
);
mainSocket.bind(serverPort);
System.out.println("mainSocket.getReceiveBufferSize(): " +
mainSocket.getReceiveBufferSize());

output is:

mainSocket.getReceiveBufferSize(): 16834

- Chris

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