Ciao... devi usare la dichiarazione api RasGetConnectionStatistics.. ecco la sintassi in visual basic 6:
Declare Function RasGetConnectionStatistics Lib 
\"RasApi32.DLL\" (ByVal hRasConn As Long, lpStatistics 
As RAS_STATS) As Long
la struttura di lpStatics è:
Type RAS_STATS
	dwSize As Long
	dwBytesXmited As Long
	dwBytesRcved As Long
	dwFramesXmited As Long
	dwFramesRcved As Long
	dwCrcErr As Long
	dwTimeoutErr As Long
	dwAlignmentErr As Long
	dwHardwareOverrunErr As Long
	dwFramingErr As Long
	dwBufferOverrunErr As Long
	dwCompressionRatioIn As Long
	dwCompressionRatioOut As Long
	dwBps As Long
	dwConnectDuration As Long
End Type
il parametro che ti interessa è dwBytesXmited.. che ha i bites trasmessi al secondo durante la connessione..
Spero di esserti stato d'aiuto...
Saluti...