Unity3D demo on iPhone cannot receive udp packets - iphone

Question

I wrote a udp send and receive unity3d plugin dll in c#, but it cannot receive any udp packets from server on iphone4s.
When server send a udp packet to the demo running on iphone4s, it cannot receive anything.
When server send a udp packet to the demo running on ipod touch 4, it works!Received the packet!
When server send a udp packet to the demo running in the Unity3d editor, it works ok!
I used Wireshark to capture the packets between client and server, it indeed captured the packet that server sent to the demo, but the client demo seems doesn't receive anythig.
Why?
internal class RudpNetInteractor
{
private Socket socket;
private EndPoint serverAddress;
internal RudpNetInteractor(IPEndPoint serverAddress)
{
this.rudpClient = rudpClient;
this.serverAddress = serverAddress;
}
internal void BuildConnection()
{
socket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
socket.Connect(serverAddress);
BeginReceive();
}
internal void Send(byte[] buffer)
{
socket.BeginSend(buffer, 0, buffer.Length, SocketFlags.None, new AsyncCallback(OnSend), null);
}
private void OnSend(IAsyncResult ar)
{
try
{
socket.EndSend(ar);
}
catch {}
}
internal void Destroy()
{
socket.Close();
socket = null;
}
private void OnReceive(IAsyncResult ar)
{
try
{
SocketReceiveInfo receiveInfo = (SocketReceiveInfo)ar.AsyncState;
Socket receiveSocket = receiveInfo.ReceiveSocket;
int len = receiveSocket.EndReceive(ar);
if (len > 0)
{
byte[] dest = new byte[len];
Array.Copy(receiveInfo.ReceiveBytes, dest, len);
Console.WriteLine(BitConverter.ToString(dest));
}
BeginReceive();
}
catch {}
}
private void BeginReceive()
{
byte[] receiveBytes = new byte[576];
SocketReceiveInfo info = new SocketReceiveInfo(receiveBytes, socket);
socket.BeginReceiveFrom(receiveBytes, 0, receiveBytes.Length, SocketFlags.None, ref serverAddress, new AsyncCallback(OnReceive), info);
}
}
internal class SocketReceiveInfo
{
private byte[] receiveBytes;
private Socket receiveSocket;
internal SocketReceiveInfo(byte[] receiveBytes, Socket receiveSocket)
{
this.receiveBytes = receiveBytes;
this.receiveSocket = receiveSocket;
}
internal byte[] ReceiveBytes
{
get { return receiveBytes; }
}
internal Socket ReceiveSocket
{
get { return receiveSocket; }
}
}