what's the relationship between server_bytes_in and bytes_out ?

I wirte some code to get stream from remote server in live application

write the following code in application.onAppStart function in main.asc(application is live type) file.

        this.myNC= new NetConnection();

        this.myNC.onStatus = NC_onStatus;

        this.myNC.connect("rtmp://test.domain/live");

        trace("this.myNC.connect :: rtmp://test.domain/live");

Then :

function NC_onStatus(info)

{

        switch (info.code)

        {

                case "NetConnection.Connect.Success" :

                        application.myStream = Stream.get("stream");    //App stream

                        application.myStream.onStatus = NS_onStatus;

                        if (application.myStream)

                        {

                                application.myStream.play("stream",-2, -1,true,application.myNC); //If reset is true (1), any playing stream stops, and the playl

ist is reset. By default, the value is true

                        }

                        trace("Connect success!");

                        break;

                case "NetConnection.Connect.Failed" :

                        trace("connect origin failed!");

                        break;

                case "NetConnection.Connect.Rejected" :

                        trace("connect origin reject!");

                        break;

function NS_onStatus(info)

{

        trace(info.code);

}

When this vhost is running, I request the api of adminserver : getActiveVHostStats. But result of bytes_out field is very large.

And what's the relationship between server_bytes_in and bytes_out ?