Constantly losing TCPClient connection from application - vb.net

Question

I have an application which connects to a Zebra QLn420 label printer through a TCPClient connection to the printer's static IP address and port number.
We have been having some issues with the software "stalling" and skipping over some of the labels, and after investigating (by adding some logging capabilities to the software to write out to a text file each time it checks the connection and actually reconnects) I have noticed that the connection does not seem to stay open for more than one second (not a solid number, it can vary from less than a second to 5 seconds or more from my tests).
While testing at my desk, this is almost a non-issue because the signal strengths are so strong that it reconnects instantly, but out in the warehouse where this is actually used, in some areas the signal isn't so strong. The function which handles the connection will try to reconnect for up to 5 seconds twice, then display an error message and ask if they want to retry connecting.
I'm curious if anyone has experienced anything like this, and what can be done to resolve it. I understand that the software will lose connection with the printer occasionally, especially in the weaker signal areas. But I would like to find a way to keep the connection open until either I close it or the signal is too weak to keep it going, as I feel this has a lot to do with the "missing" labels and definitely impacts the speed of the software.
Below is my connection code (a combination of my own code and some snippets found online):
Public Class LabelPrinter
Private strIP as String = "xxx.xxx.xxx.xxx"
Private intPort As Integer = "6101"
Private client As System.Net.Sockets.TcpClient
Private blnConnected As Boolean = False
Private blnValidIP As Boolean = False
Private intTimeoutLength As Integer = 5000
Private TimeoutTime As New Timers.Timer
Private clntSockParams As ClientSocketParameters
Private Structure ClientSocketParameters
Public addrs As String
Public prt As Integer
End Structure
Public Sub New(Picker As Picker, newIP As String, newPort As Integer, Optional PrinterTimeout As Integer = 5000)
If newIP <> "" Then strIP = newIP
If newPort <> 0 Then intPort = newPort
intTimeoutLength = PrinterTimeout
If newIP = "" Or newPort = 0 Then Exit Sub
Dim ipAddress As System.Net.IPAddress = Nothing
If Not System.Net.IPAddress.TryParse(strIP, ipAddress) Then Exit Sub
End Sub
Public Function Connect() As Boolean
Try
'connect to printer via TcpClient, need ip address and port number
'connects without thread, hangs program for 10-20 seconds if printer is not turned on, replaced with code below to thread the connection and set timeout
'If client Is Nothing OrElse Not client.Connected Then
' client = New System.Net.Sockets.TcpClient
' client.Connect(strIP, intPort)
'End If
'RRB 02/10/15 - added for loop to try to connect twice each attempt instead of only once
For i As Integer = 1 To 2
If client Is Nothing OrElse Not client.Connected Then
'uses ClientSocketParameters structure to pass to recursive function ConnectionReturned()
clntSockParams = New ClientSocketParameters
clntSockParams.addrs = strIP
clntSockParams.prt = intPort
'create client and call BeginConnect (attempts to connect on separate thread until TimeoutTime has elapsed)
client = New System.Net.Sockets.TcpClient
client.SendTimeout = intTimeoutLength
client.ReceiveTimeout = intTimeoutLength
'setup timer with timeout length and start, if timer goes past intTimeoutLength, the Timeout() function is called which closes everything and leaves client = Nothing
AddHandler TimeoutTime.Elapsed, AddressOf Timeout
TimeoutTime.Interval = intTimeoutLength
TimeoutTime.Start()
client.BeginConnect(strIP, intPort, New AsyncCallback(AddressOf ConnectionReturned), clntSockParams)
'keeps the program from doing anything else until BeginConnect either succeeds or fails (due to connect on separate thread)
Do While TimeoutTime.Enabled
System.Threading.Thread.Sleep(500)
Loop
End If
'if TimeoutTime is elapsed and client is Nothing, connection didn't happen, throw an error
If client Is Nothing Then
blnConnected = False
Else
blnConnected = True
Exit For
End If
Next
Catch ex As Exception
blnConnected = False
End Try
Return blnConnected
End Function
Private Sub ConnectionReturned(ByVal ar As System.IAsyncResult)
'this method is called from the client.BeginConnect line in Connect(), make sure timer is running
If TimeoutTime.Enabled Then
'ensure client is initialized
If client Is Nothing Then client = New System.Net.Sockets.TcpClient
'keep calling ConnectionReturned until client.Connected is true
If client.Connected Then
TimeoutTime.Stop()
Else
Dim actualParameters As ClientSocketParameters = DirectCast(ar.AsyncState, ClientSocketParameters)
client.BeginConnect(actualParameters.addrs, actualParameters.prt, New AsyncCallback(AddressOf ConnectionReturned), clntSockParams)
End If
End If
End Sub
Private Sub Timeout(ByVal sender As Object, ByVal e As EventArgs)
'this method is only called if TimeoutTime elapsed, which means no connection was made. close the client object if needed, set to Nothing, and stop TimeoutTime
If TimeoutTime.Enabled Then
Try
client.Close()
Catch ex As Exception
End Try
client = Nothing
TimeoutTime.Stop()
End If
End Sub
Public Sub Disconnect()
'need to make sure StreamWriter connection and TcpClient connection to printer are closed
Try
client.Close()
Catch ex As Exception
End Try
client = Nothing
blnConnected = False
End Sub
End Class
Please let me know if more information is needed. I'm also open to alternative connection types, so long as the static IP and port can be used (over wifi connection).
EDIT: I've modified the code in my program to use the System.Net.Socket class, and the connection seems to hold steady in my initial tests. What would cause this connection method to work where TCPClient doesn't seem to, in the same location?