My connection with server already is really poor - 120 ms ping in average.
I did a similar test to
www.google.com, testing response time over TCP, and got 160 milliseconds. Does Google have poor connectivity? TCP was not designed for quick response times.
I measure my ping through flash client - send packet with timestamp and immediatly send from server to client.
TCP, by design, delays up to 200 milliseconds to provide more effective network utilization. You are not measuring anything except TCP specifically doing what it is designed to do. If you look closely at the network traffic, you'll see that most of the TCP packets actually contain much more than two bytes of data.
You are expecting horribly inefficient behavior. Sending 30 packets per second each containing only two bytes of data is incredibly dumb and TCP isn't stupid enough to do that.
Don't call this "ping". That makes people think it's a network round-trip measurement rather than a measurement of response time over TCP.
Don't say "30 packets/s" unless you actually measured the network traffic. When you write some bytes to a TCP connection, there is no reason to expect that will correspond to a packet. Packets are network things. Writes to a TCP connection are application things. Confusing application and network level concepts will really mess you up when you deal with TCP.
Also, why are you doing so many small writes? Gather the data into larger writes. Yes, TCP will do this for you, but it's still much more efficient if you do this in your application.
If you're just doing these horrible small writes to test performance, just stop doing it. It won't give you useful data. If these horrible small writes replicate your actual usage scenario and response time is important, then you need to work on fixing your protocol so that it makes some kind of sense.