Lecture de port : 1 trame sur deux !

Bonjour,

Ci-dessous, le code qui me permet de capturer des trames envoyées par des devices distants via GPRS .

Voici le problème rencontré :

chaque 5 secondes, le boitier envoie sa position au serveur.
Celui-ci capture bien la trame mais seulement toutes les 10 secondes.

Si je paramètre la fréquence du boitier chaque 30 secondes, la réception se fera toutes les 60 secondes !

Il doit y avoir quelque chose avec le networkstream que j'ignore.
J'avoue ne pas comprendre pourquoi je ne capture que la moitié des trames.

Une idée ?

Merci d'avance

PS : l'appli tourne sur un serveur virtuel et sous web server 2008 R2
PS2 : le pb est le meme sur un pc classique
Code:
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Imports System.Net
Imports System.Net.Sockets
Imports System.Text
Imports System.IO
 
Public Class Module1
 
 
    Public Shared port As Integer = 65535
    Public Shared adresse_ip As String = "192.168.10.200"
 
    Public Delegate Sub Ajout(ByVal Valeur As String) 'declare un délégué pour insérer des datas dans le listbox
    Public Shared serverinfo As IPEndPoint = Nothing
    Public Shared counter As Integer 'Compteur pour le client connecté
    Public Shared incrementation As Integer = 0
 
 
    Private Sub BackgroundWorker1_DoWork(ByVal sender As Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork
 
            Dim ipAddress As IPAddress = Dns.GetHostEntry(adresse_ip).AddressList(0)
        Dim serverSocket As New TcpListener(ipAddress, port)
        Dim clientSocket As TcpClient = Nothing
 
        Dim date_socket As Date
        Dim ip_socket_connecté As String
 
        Try
            serverSocket.Start()
            Invoke(New Ajout(AddressOf msg), New Object() {Date.Now & " : Serveur démarré. Port " + port.ToString + " - " + ipAddress.ToString})
            counter = 0
                        While (True)
                counter += 1
                clientSocket = serverSocket.AcceptTcpClient()
                Invoke(New Ajout(AddressOf msg), New Object() {Date.Now & " : Client No: " + Convert.ToString(counter) + " Démarré ! " + " IP : " + clientSocket.Client.RemoteEndPoint.ToString})
 
                Console.WriteLine(" : Client No: " + Convert.ToString(counter) + " Démarré ! " + " IP : " + clientSocket.Client.RemoteEndPoint.ToString)
 
                date_socket = Date.Now 'Date
                ip_socket_connecté = clientSocket.Client.RemoteEndPoint.ToString 'IP
 
                Dim client As New handleClinet
                client.startClient(clientSocket, Convert.ToString(counter), ip_socket_connecté, date_socket)
            End While
 
            'clientSocket.Close()
            'serverSocket.Stop()
            Invoke(New Ajout(AddressOf msg), New Object() {"exit"})
        Catch ex As IOException
            Console.WriteLine(Date.Now.Date & " 000-IOEXCEPTION : Erreur : " & ex.Message)
 
        Catch ex As SocketException
            Console.WriteLine(Date.Now.Date & " 000-SOCKET : Erreur : " & ex.Message)
        End Try
    End Sub
 
    Public Class handleClinet
        Dim clientSocket As TcpClient
        Shared clNo As String 'Numéro du client
        Shared clIP As String 'Adresse ip du client connecté
        Shared clDate As Date 'Date et heure de la connection du client
 
        Shared chaine_SYNCHEADER As String = ""
        Shared chaine_SYNCID As String = ""
        Shared CHAINE_UNITID As String = ""
 
 
        Public Sub startClient(ByVal inClientSocket As TcpClient, ByVal clineNo As String, ByVal clineIP As String, ByVal clineDate As Date)
            Me.clientSocket = inClientSocket
            handleClinet.clNo = clineNo 'Numéro du client
            handleClinet.clIP = clineIP 'Adresse IP du client connecté
            handleClinet.clDate = clineDate 'Date du client connecté
            Dim ctThread As Threading.Thread = New Threading.Thread(AddressOf ecoute)
            ctThread.Start()
        End Sub
 
        Public Sub ecoute()
 
            Dim bytes(clientSocket.ReceiveBufferSize) As Byte
            'Dim bytes(10024) As Byte
 
            Dim networkStream As NetworkStream = clientSocket.GetStream()
 
            Dim valeur_true As Boolean = True
 
            While (clientSocket.Connected)
 
                Try
                    networkStream.Read(bytes, 0, CInt(clientSocket.ReceiveBufferSize))
                    'On dissocie le header pour déterminer le boitier et son ID
                    Dim sendbytes As [Byte]() = bytes
                    chaine_SYNCHEADER = ""
                    chaine_SYNCID = ""
                    CHAINE_UNITID = ""
 
                    chaine_SYNCHEADER = Hex(bytes(1)) & Hex(bytes(0))
                    chaine_SYNCID = Hex(bytes(3)) & Hex(bytes(2))
                    CHAINE_UNITID = Hex(bytes(7)) & Hex(bytes(6)) & Hex(bytes(5)) & Hex(bytes(4))
 
 
                    Select Case chaine_SYNCHEADER
                        Case "AB65"
                            networkStream.Write(sendbytes, 0, 8)
                            header_lu = True
 
                            Dim chaine_Serveur As String = ""
                            'Console.WriteLine(Date.Now & " " & HexaToDec(CHAINE_UNITID))
 
                    End Select
 
                Catch ex As IOException
                    Console.WriteLine("700 : " & ex.Message)
                End Try
 
 
                Try
 
                    If clientSocket.Connected = False Then
                        Console.WriteLine(Date.Now & " Clientsocket fermé, exit sub")
                        Exit Sub
                    End If
 
                    Dim networkStream2 As NetworkStream = clientSocket.GetStream()
                    Dim bytes2(clientSocket.ReceiveBufferSize) As Byte
 
                    If networkStream2.CanRead Then
                        Do
                            networkStream2.Read(bytes2, 0, CInt(clientSocket.ReceiveBufferSize))
 
                            Dim chaine_brute As String = ""
                            chaine_brute = Encoding.ASCII.GetString(bytes2)
                            chaine_brute = chaine_brute.Trim(Chr(&HA))
                            chaine_brute = chaine_brute.Trim(Chr(&HD))
                            Dim tabstring() As String = Split(chaine_brute, Chr(13))
 
 
                            'Traitement des données
 
 
                        Loop While networkStream2.DataAvailable
                    Else
                        Console.WriteLine("Lecture impossible du networkstream2 !")
                    End If
                Catch ex As IOException
                    Console.WriteLine("876 : " & ex.Message)
                Catch ex As SocketException
                    Console.WriteLine("880 : " & ex.Message)
                End Try
            End While
        End Sub
    End Class
End Class