diff --git a/Commands.go b/Commands.go
index bec0161..5b785b3 100644
--- a/Commands.go
+++ b/Commands.go
@@ -240,7 +240,7 @@ func SendChatAll(text string) {
 // cmdTransfer handles an incoming transfer message
 func (peer *PeerInfo) cmdTransfer(msg *protocol.MessageTransfer, connection *Connection) {
 	// Only UDT protocol is currently supported for file transfer.
-	if msg.TransferProtocol != 0 {
+	if msg.TransferProtocol != protocol.TransferProtocolUDT {
 		return
 	}
 
diff --git a/Transfer UDT.go b/Transfer UDT.go
index b41ce01..ea8f827 100644
--- a/Transfer UDT.go	
+++ b/Transfer UDT.go	
@@ -36,7 +36,9 @@ func (peer *PeerInfo) startFileTransferUDT(hash []byte, fileSize uint64, offset,
 		limit = fileSize - offset
 	}
 
-	virtualConnection := newVirtualPacketConn(peer, 0, hash, offset, limit)
+	virtualConnection := newVirtualPacketConn(peer, func(data []byte, sequenceNumber uint32) {
+		peer.sendTransfer(data, protocol.TransferControlActive, 0, hash, offset, limit, sequenceNumber)
+	})
 
 	// register the sequence since packets are sent bi-directional
 	virtualConnection.sequenceNumber = sequenceNumber
@@ -67,7 +69,9 @@ func (peer *PeerInfo) startFileTransferUDT(hash []byte, fileSize uint64, offset,
 // The caller must call udtConn.Close() when done. Do not use any of the closing functions of virtualConn.
 // Limit is optional. 0 means the entire file.
 func (peer *PeerInfo) FileTransferRequestUDT(hash []byte, offset, limit uint64) (udtConn net.Conn, virtualConn *virtualPacketConn, err error) {
-	virtualConn = newVirtualPacketConn(peer, 0, hash, offset, limit)
+	virtualConn = newVirtualPacketConn(peer, func(data []byte, sequenceNumber uint32) {
+		peer.sendTransfer(data, protocol.TransferControlActive, protocol.TransferProtocolUDT, hash, offset, limit, sequenceNumber)
+	})
 
 	// new sequence
 	sequence := networks.Sequences.NewSequenceBi(peer.PublicKey, &peer.messageSequence, virtualConn, transferSequenceTimeout, virtualConn.sequenceTerminate)
@@ -84,7 +88,7 @@ func (peer *PeerInfo) FileTransferRequestUDT(hash []byte, offset, limit uint64)
 	udtListener := udt.ListenUDT(udtConfig, virtualConn, virtualConn.incomingData, virtualConn.outgoingData, virtualConn.terminationSignal)
 
 	// request file transfer
-	peer.sendTransfer(nil, protocol.TransferControlRequestStart, virtualConn.transferProtocol, hash, offset, limit, virtualConn.sequenceNumber)
+	peer.sendTransfer(nil, protocol.TransferControlRequestStart, protocol.TransferProtocolUDT, hash, offset, limit, virtualConn.sequenceNumber)
 
 	// accept the connection
 	udtConn, err = udtListener.Accept()
diff --git a/Transfer Virtual Connection.go b/Transfer Virtual Connection.go
index 5090b6e..e8388b9 100644
--- a/Transfer Virtual Connection.go	
+++ b/Transfer Virtual Connection.go	
@@ -11,19 +11,14 @@ package core
 
 import (
 	"sync"
-
-	"github.com/PeernetOfficial/core/protocol"
 )
 
 // virtualPacketConn is a virtual connection.
 type virtualPacketConn struct {
 	peer *PeerInfo
 
-	// Transfer settings
-	transferProtocol uint8  // 0 = UDT
-	hash             []byte // The requested hash.
-	offset           uint64 // Offset to start reading.
-	limit            uint64 // Limit of bytes to read at the offset.
+	// function to send data to the remote peer
+	sendData func(data []byte, sequenceNumber uint32)
 
 	// Sequence number from the first outgoing or incoming packet.
 	sequenceNumber uint32
@@ -40,13 +35,10 @@ type virtualPacketConn struct {
 }
 
 // newVirtualPacketConn creates a new virtual connection (both incomign and outgoing).
-func newVirtualPacketConn(peer *PeerInfo, protocol uint8, hash []byte, offset, limit uint64) (v *virtualPacketConn) {
+func newVirtualPacketConn(peer *PeerInfo, sendData func(data []byte, sequenceNumber uint32)) (v *virtualPacketConn) {
 	v = &virtualPacketConn{
 		peer:              peer,
-		transferProtocol:  protocol,
-		hash:              hash,
-		offset:            offset,
-		limit:             limit,
+		sendData:          sendData,
 		incomingData:      make(chan []byte, 100),
 		outgoingData:      make(chan []byte),
 		terminationSignal: make(chan struct{}),
@@ -62,7 +54,7 @@ func (v *virtualPacketConn) writeForward() {
 	for {
 		select {
 		case data := <-v.outgoingData:
-			v.peer.sendTransfer(data, protocol.TransferControlActive, v.transferProtocol, v.hash, v.offset, v.limit, v.sequenceNumber)
+			v.sendData(data, v.sequenceNumber)
 
 		case <-v.terminationSignal:
 			return
diff --git a/protocol/Message Encoding Transfer.go b/protocol/Message Encoding Transfer.go
index 729a348..4c3f547 100644
--- a/protocol/Message Encoding Transfer.go	
+++ b/protocol/Message Encoding Transfer.go	
@@ -8,6 +8,14 @@ Offset  Size   Info
 0       1      Control
 1       1      Transfer Protocol
 2       32     File Hash
+
+Control = 0: Request Start
+34      8      Offset to start reading in the file
+42      8      Limit of bytes to read at the offset
+
+Offset + limit must not exceed the file size.
+
+Control = 3: Active
 34      ?      Embedded protocol data
 
 */
@@ -40,6 +48,8 @@ const (
 	TransferControlTerminate    = 3 // Terminate
 )
 
+const TransferProtocolUDT = 0 // Indicates that UDT is used as embedded transfer protocol.
+
 const transferPayloadHeaderSize = 34
 
 // DecodeTransfer decodes a transfer message