'***************************************************************************
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'* ClassRTPAgent *
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'* *
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'* This class manages the RTP communications with a E301 module. *
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'* When you create an ClassRTPAgent objet (a RTPAgent) you must provide *
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'* the Destination IP and port to send the packets and the local port *
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'* where the E301 is sending us his packets. *
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'* Once created, you must call SendAudioPacket each time you have to send *
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'* a new audio packet and ReceiveAudioPacket when to need a new packet to *
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'* send to the audio system *
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'* *
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'* This routine implements a reception FIFO to absorbe the jitter in the *
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'* packet reception. But is NOT IMPLEMENTED the reordering of the incoming *
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'* packets. This would be necessary in some cases. *
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'* *
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'* EQUITEL C.V. February 2007 ALMDI*
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'***************************************************************************
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Imports System
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Imports System.Net
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Imports System.Net.Sockets
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Imports System.Threading
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Imports System.Text
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Imports System.IO
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Imports System.Net.NetworkInformation
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Imports System.Globalization
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Public Class ClassRTPAgent
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Implements System.IDisposable
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#Region "Constants and definitions"
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Private Const HeaderLength As Integer = 12
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Private Const AudioPacketLength As Integer = 160
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Private Const FIFOSize As Byte = 16
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Private Structure BuffStruct
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Public Data() As Byte
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End Structure
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#End Region
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#Region "Fields"
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Private mDisposed As Boolean = False
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Private mDestinationIP As String
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Private mDestinationPort As Integer
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Private mLocalPort As Integer
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Private mReceptionThread As Thread
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Private mUdpClient As UdpClient
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Private mOutputBuffer As BuffStruct
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Private mSequence As UInt32
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Private mTimestamp As UInt32
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Private mInputFIFO(FIFOSize) As BuffStruct
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Private mFIFOWritePointer As Integer = -1
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Private mFIFOReadPointer As Integer = -1
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#End Region
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#Region "Properties"
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Public Property DestinationIP() As String
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Get
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DestinationIP = mDestinationIP
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End Get
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Set(ByVal Value As String)
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mDestinationIP = Value
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End Set
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End Property
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Public Property DestinationPort() As Integer
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Get
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DestinationPort = mDestinationPort
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End Get
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Set(ByVal Value As Integer)
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mDestinationPort = Value
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End Set
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End Property
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Public Property LocalPort() As Integer
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Get
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LocalPort = mLocalPort
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End Get
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Set(ByVal Value As Integer)
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mLocalPort = Value
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End Set
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End Property
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#End Region
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#Region "CONSTRUCTOR / DESTRUCTOR"
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Public Sub New(ByVal DestinationIP As String, ByVal DestinationPort As Integer, ByVal LocalPort As Integer)
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Dim i As Integer
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mDestinationIP = DestinationIP
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mDestinationPort = DestinationPort
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mLocalPort = LocalPort
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mUdpClient = New UdpClient(mLocalPort)
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mSequence = 0
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mTimestamp = 0
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ReDim mOutputBuffer.Data(HeaderLength + AudioPacketLength)
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For i = 0 To FIFOSize - 1
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ReDim mInputFIFO(i).Data(HeaderLength + AudioPacketLength - 1)
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Next
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mReceptionThread = New Thread(AddressOf PacketReception)
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mReceptionThread.Start()
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End Sub
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Protected Overridable Sub Dispose(ByVal disposing As Boolean)
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If Not Me.mDisposed Then
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If disposing Then
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mReceptionThread.Abort()
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mReceptionThread = Nothing
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mUdpClient.Close()
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mUdpClient = Nothing
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End If
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End If
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Me.mDisposed = True
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End Sub
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Public Sub Dispose() Implements IDisposable.Dispose
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Dispose(True)
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GC.SuppressFinalize(Me)
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End Sub
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Protected Overrides Sub Finalize()
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Dispose(False)
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MyBase.Finalize()
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End Sub
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#End Region
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#Region "Private functions"
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Private Sub CreateRTPHeader(ByRef RTP_Buf As Byte(), ByVal Sequence As UInt32, ByVal TimeStamp As UInt32)
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'This routine creates the header for the RTP packet in accordance with the
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'RFC 3550:
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'
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' 0 1 2 3
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' 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
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' +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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' |V=2|P|X| CC |M| PT | sequence number |
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' +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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' | timestamp |
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' +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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' | synchronization source (SSRC) identifier |
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' +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
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' version (V): 2 bits
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' padding (P): 1 bit
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' extension (X): 1 bit
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' CSRC count (CC): 4 bits
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' marker (M): 1 bit
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' payload type (PT): 7 bits
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' sequence number: 16 bits
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' timestamp: 32 bits
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'First 32 bit word
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RTP_Buf(0) = &H80 'Version=2, P=X=CC=M=0
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RTP_Buf(1) = &H8 'Payload type =8 (as defined in RFC3551 for G711-A law)
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RTP_Buf(2) = (Sequence >> 8) And 255
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RTP_Buf(3) = (Sequence) And 255
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'Second word (TimeStamp)
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RTP_Buf(4) = (TimeStamp >> 24) And 255
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RTP_Buf(5) = (TimeStamp >> 16) And 255
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RTP_Buf(6) = (TimeStamp >> 8) And 255
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RTP_Buf(7) = (TimeStamp) And 255
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'Third word (SSRC = Sincronization Source Code)
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RTP_Buf(8) = &H12
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RTP_Buf(9) = &H34
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RTP_Buf(10) = &H56
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RTP_Buf(11) = &H78
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End Sub
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Private Function PCM_to_G711_A(ByVal PCMSample As Short) As Byte
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'This routine converts a 16 bit PCM sample to G711-A format
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Dim p As Short = PCMSample
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Dim a As Short
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If (p < 0) Then
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p = Not p
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a = &H0
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Else
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a = &H80
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End If
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p >>= 4
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If (p >= &H20) Then
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If (p >= &H100) Then
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p >>= 4
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a += &H40
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End If
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If (p >= &H40) Then
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p >>= 2
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a += &H20
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End If
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If (p >= &H20) Then
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p >>= 1
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a += &H10
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End If
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End If
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a += p
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Return a Xor &H55
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End Function
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Private Function G711_A_to_PCM(ByVal G711Sample As Byte) As Short
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'This routine converts a G711-A sample to PCM (16 bits)
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Dim sign As Byte
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Dim shift As UShort
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Dim linear As Short
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G711Sample = G711Sample Xor &H55
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sign = G711Sample And &H80
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linear = G711Sample And &H1F
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linear <<= 4
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linear += 8
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G711Sample = G711Sample And &H7F
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If (G711Sample >= &H20) Then
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linear = linear Or &H100
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shift = (G711Sample >> 4) - 1
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linear <<= shift
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End If
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If (sign = &H80) Then
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Return -linear
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Else
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Return linear
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End If
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End Function
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Private Sub PacketReception()
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'This routine reads the incoming RTP Packets from the localport
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'and passes them to the FIFO. When the FIFO is half-filled for
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'the first time, the FIFO reading is enabled
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Dim Packet(HeaderLength + AudioPacketLength - 1) As Byte
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Dim IpE As New System.Net.IPEndPoint(IPAddress.Any, mLocalPort)
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While True
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Try
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Packet = mUdpClient.Receive(IpE)
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mFIFOWritePointer += 1
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If mFIFOWritePointer = FIFOSize Then mFIFOWritePointer = 0
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mInputFIFO(mFIFOWritePointer).Data = Packet
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If (mFIFOWritePointer = FIFOSize / 2) And mFIFOReadPointer = -1 Then
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mFIFOReadPointer = 0
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End If
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Catch
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Console.WriteLine("Packet reception error")
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End Try
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End While
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End Sub
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#End Region
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#Region "Public functions"
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Public Sub SendAudioPacket(ByRef AudioPCM() As Short)
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'This processes the audio packet passed (in 16 bit/sample format)
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'converting it to G711-A format (8 bits per sample) and
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'creating an RTP packet wich is sent.
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Dim i As Integer
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CreateRTPHeader(mOutputBuffer.Data, mSequence, mTimestamp)
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For i = 0 To AudioPacketLength
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mOutputBuffer.Data(i + 12) = PCM_to_G711_A(AudioPCM(i))
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Next
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mUdpClient.Send(mOutputBuffer.Data, (HeaderLength + AudioPacketLength), mDestinationIP, mDestinationPort)
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mTimestamp += AudioPacketLength
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mSequence += 1
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End Sub
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Public Function ReceivedAudioPacket() As Short()
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'Returns the next audio packet in the FIFO properly converted to PCM format
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Dim P(AudioPacketLength) As Short
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Dim i As Integer
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If mFIFOReadPointer <> -1 Then
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For i = 0 To AudioPacketLength - 1
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P(i) = G711_A_to_PCM(mInputFIFO(mFIFOReadPointer).Data(i + HeaderLength))
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Next
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For i = AudioPacketLength To AudioPacketLength - 1
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P(i) = mInputFIFO(mFIFOReadPointer).Data(i + HeaderLength)
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Next
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mFIFOReadPointer += 1
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If mFIFOReadPointer = FIFOSize Then mFIFOReadPointer = 0
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Return P
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Else
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For i = 0 To AudioPacketLength - 1
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P(i) = 0
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Next
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Return P
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End If
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End Function
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#End Region
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End Class
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