Remoting communications client->server but with server->client too

I quess the server is listennig to a PORT number e.g. PORT_NUM=20000

on the client declare a TcpClient

Private Const READ_BUFFER_SIZE As Integer = 255
    Private client As TcpClient
    Private readBuffer(READ_BUFFER_SIZE) As Byte

on Loadform
            client = New TcpClient(HOST_IP, PORT_NUM)
            ' Start an asynchronous read invoking DoRead to avoid lagging the user interface.
            client.GetStream.BeginRead(readBuffer, 0, READ_BUFFER_SIZE, AddressOf DoRead, Nothing)

''' <summary>
    ''' This is the callback function for TcpClient.GetStream.Begin to get an asynchronous read.
    ''' </summary>
    ''' <param name="ar"></param>
    ''' <remarks></remarks>
    Private Sub DoRead(ByVal ar As IAsyncResult)
        Dim BytesRead As Integer = -1
        Dim strMessage As String = ""
        Try
            ' Finish asynchronous read into readBuffer and return number of bytes read.
            BytesRead = client.GetStream.EndRead(ar)
            If BytesRead < 1 Then
                Exit Sub    'If no bytes were read server has close.
            Else
                ' Convert the byte array the message was saved into, minus two for the Chr(13) and Chr(10)
                strMessage = Encoding.ASCII.GetString(readBuffer, 0, BytesRead - 2)
                ProcessCommands(strMessage)
                ' Start a new asynchronous read into readBuffer.
                client.GetStream.BeginRead(readBuffer, 0, READ_BUFFER_SIZE, AddressOf DoRead, Nothing)
            End If
        Catch e As Exception
        End Try
        BytesRead = Nothing : strMessage = Nothing
    End Sub

Now on the server side I use
  Private clients As New Hashtable
to store all connected clients
-when I get a clients query- I read it in a sub like...
 Private Sub OnLineReceived(ByVal sender As modul_UserConnection, ByVal data As String)
-so- I know the sender (client)
and
Private Sub ReplyToSender(ByVal strMessage As String, ByVal sender As modul_UserConnection)
        Try
            sender.SendData(strMessage)
        Catch ex As Exception
        End Try
    End Sub

    ' This subroutine uses a StreamWriter to send a message to the user.
    Public Sub SendData(ByVal Data As String)
        ' Synclock ensure that no other threads try to use the stream at the same time.
        SyncLock client.GetStream
            Dim writer As New IO.StreamWriter(client.GetStream)
            writer.Write(Data & Chr(13) & Chr(10))
            ' Make sure all data is sent now.
            writer.Flush()
        End SyncLock
    End Sub

but all depants on the way your class works....
if you can find your solution with the above ok...
-else-
I could send you the modul_UserConnection class to test it...

Have fun coding...

the SendData in the modul_UserConnection is...

    Public Event LineReceived(ByVal sender As modul_UserConnection, ByVal Data As String)

    ' This subroutine uses a StreamWriter to send a message to the user.
    Public Sub SendData(ByVal Data As String)
        ' Synclock ensure that no other threads try to use the stream at the same time.
        SyncLock client.GetStream
            Dim writer As New IO.StreamWriter(client.GetStream)
            writer.Write(Data & Chr(13) & Chr(10))
            ' Make sure all data is sent now.
            writer.Flush()
        End SyncLock
    End Sub

Hi, thank you for the answer, I'm really new with vb.net, I'll take your offert to have the modul_UserConnection Class, for see what you do exactly :)

Thank you very much!