diff --git a/internal/multiplex/frameSorter.go b/internal/multiplex/frameSorter.go
index 6738893..0679673 100644
--- a/internal/multiplex/frameSorter.go
+++ b/internal/multiplex/frameSorter.go
@@ -2,7 +2,9 @@ package multiplex
 
 import (
 	"container/heap"
-	//"log"
+	"io"
+
+	log "github.com/sirupsen/logrus"
 )
 
 // The data is multiplexed through several TCP connections, therefore the
@@ -50,73 +52,101 @@ func (sh *sorterHeap) Pop() interface{} {
 	return x
 }
 
-func (s *Stream) writeNewFrame(f *Frame) {
-	s.newFrameCh <- f
+type frameSorter struct {
+	nextRecvSeq uint32
+	rev         int
+	sh          sorterHeap
+	wrapMode    bool
+
+	// New frames are received through newFrameCh by frameSorter
+	newFrameCh chan *Frame
+
+	output io.WriteCloser
+}
+
+func NewFrameSorter(output io.WriteCloser) *frameSorter {
+	fs := &frameSorter{
+		sh:         []*frameNode{},
+		newFrameCh: make(chan *Frame, 1024),
+		rev:        0,
+		output:     output,
+	}
+	go fs.recvNewFrame()
+	return fs
+}
+
+func (fs *frameSorter) writeNewFrame(f *Frame) {
+	fs.newFrameCh <- f
+}
+func (fs *frameSorter) Close() error {
+	fs.newFrameCh <- nil
+	return nil
 }
 
 // recvNewFrame is a forever running loop which receives frames unordered,
 // cache and order them and send them into sortedBufCh
-func (s *Stream) recvNewFrame() {
+func (fs *frameSorter) recvNewFrame() {
+	defer log.Tracef("a recvNewFrame has returned gracefully")
 	for {
-		f := <-s.newFrameCh
+		f := <-fs.newFrameCh
 		if f == nil {
 			return
 		}
 
-		// when there's no ooo packages in heap and we receive the next package in order
-		if len(s.sh) == 0 && f.Seq == s.nextRecvSeq {
+		// when there'fs no ooo packages in heap and we receive the next package in order
+		if len(fs.sh) == 0 && f.Seq == fs.nextRecvSeq {
 			if f.Closing == 1 {
 				// empty data indicates closing signal
-				s.passiveClose()
+				fs.output.Close()
 				return
 			} else {
-				s.sortedBuf.Write(f.Payload)
-				s.nextRecvSeq += 1
-				if s.nextRecvSeq == 0 { // getting wrapped
-					s.rev += 1
-					s.wrapMode = false
+				fs.output.Write(f.Payload)
+				fs.nextRecvSeq += 1
+				if fs.nextRecvSeq == 0 { // getting wrapped
+					fs.rev += 1
+					fs.wrapMode = false
 				}
 			}
 			continue
 		}
 
-		fs := &frameNode{
+		node := &frameNode{
 			trueSeq: 0,
 			frame:   f,
 		}
 
-		if f.Seq < s.nextRecvSeq {
+		if f.Seq < fs.nextRecvSeq {
 			// For the ease of demonstration, assume seq is uint8, i.e. it wraps around after 255
 			// e.g. we are on rev=0 (wrap has not happened yet)
 			// and we get the order of recv as 253 254 0 1
 			// after 254, nextN should be 255, but 0 is received and 0 < 255
 			// now 0 should have a trueSeq of 256
-			if !s.wrapMode {
+			if !fs.wrapMode {
 				// wrapMode is true when the latest seq is wrapped but nextN is not
-				s.wrapMode = true
+				fs.wrapMode = true
 			}
-			fs.trueSeq = uint64(1<<32)*uint64(s.rev+1) + uint64(f.Seq) + 1
+			node.trueSeq = uint64(1<<32)*uint64(fs.rev+1) + uint64(f.Seq) + 1
 			// +1 because wrapped 0 should have trueSeq of 256 instead of 255
 			// when this bit was run on 1, the trueSeq of 1 would become 256
 		} else {
-			fs.trueSeq = uint64(1<<32)*uint64(s.rev) + uint64(f.Seq)
+			node.trueSeq = uint64(1<<32)*uint64(fs.rev) + uint64(f.Seq)
 			// when this bit was run on 255, the trueSeq of 255 would be 255
 		}
 
-		heap.Push(&s.sh, fs)
+		heap.Push(&fs.sh, node)
 		// Keep popping from the heap until empty or to the point that the wanted seq was not received
-		for len(s.sh) > 0 && s.sh[0].frame.Seq == s.nextRecvSeq {
-			f = heap.Pop(&s.sh).(*frameNode).frame
+		for len(fs.sh) > 0 && fs.sh[0].frame.Seq == fs.nextRecvSeq {
+			f = heap.Pop(&fs.sh).(*frameNode).frame
 			if f.Closing == 1 {
 				// empty data indicates closing signal
-				s.passiveClose()
+				fs.output.Close()
 				return
 			} else {
-				s.sortedBuf.Write(f.Payload)
-				s.nextRecvSeq += 1
-				if s.nextRecvSeq == 0 { // getting wrapped
-					s.rev += 1
-					s.wrapMode = false
+				fs.output.Write(f.Payload)
+				fs.nextRecvSeq += 1
+				if fs.nextRecvSeq == 0 { // getting wrapped
+					fs.rev += 1
+					fs.wrapMode = false
 				}
 			}
 		}
diff --git a/internal/multiplex/frameSorter_test.go b/internal/multiplex/frameSorter_test.go
index 39c3b99..0524caa 100644
--- a/internal/multiplex/frameSorter_test.go
+++ b/internal/multiplex/frameSorter_test.go
@@ -1,21 +1,32 @@
 package multiplex
 
 import (
+	"bytes"
 	"encoding/binary"
+	"time"
+
 	//"log"
 	"sort"
 	"testing"
 )
 
+type BufferReaderWriterCloser struct {
+	*bytes.Buffer
+}
+
+func (b *BufferReaderWriterCloser) Close() error {
+	return nil
+}
 func TestRecvNewFrame(t *testing.T) {
 	inOrder := []uint64{5, 6, 7, 8, 9, 10, 11}
 	outOfOrder0 := []uint64{5, 7, 8, 6, 11, 10, 9}
 	outOfOrder1 := []uint64{1, 96, 47, 2, 29, 18, 60, 8, 74, 22, 82, 58, 44, 51, 57, 71, 90, 94, 68, 83, 61, 91, 39, 97, 85, 63, 46, 73, 54, 84, 76, 98, 93, 79, 75, 50, 67, 37, 92, 99, 42, 77, 17, 16, 38, 3, 100, 24, 31, 7, 36, 40, 86, 64, 34, 45, 12, 5, 9, 27, 21, 26, 35, 6, 65, 69, 53, 4, 48, 28, 30, 56, 32, 11, 80, 66, 25, 41, 78, 13, 88, 62, 15, 70, 49, 43, 72, 23, 10, 55, 52, 95, 14, 59, 87, 33, 19, 20, 81, 89}
 	outOfOrderWrap0 := []uint64{1<<32 - 5, 1<<32 + 3, 1 << 32, 1<<32 - 3, 1<<32 - 4, 1<<32 + 2, 1<<32 - 2, 1<<32 - 1, 1<<32 + 1}
-	sets := [][]uint64{inOrder, outOfOrder0, outOfOrder1, outOfOrderWrap0}
-	for _, set := range sets {
-		stream := makeStream(1, &Session{})
-		stream.nextRecvSeq = uint32(set[0])
+
+	sortedBuf := &BufferReaderWriterCloser{new(bytes.Buffer)}
+	test := func(set []uint64, ct *testing.T) {
+		fs := NewFrameSorter(sortedBuf)
+		fs.nextRecvSeq = uint32(set[0])
 		for _, n := range set {
 			bu64 := make([]byte, 8)
 			binary.BigEndian.PutUint64(bu64, n)
@@ -23,33 +34,49 @@ func TestRecvNewFrame(t *testing.T) {
 				Seq:     uint32(n),
 				Payload: bu64,
 			}
-			stream.writeNewFrame(frame)
+			fs.writeNewFrame(frame)
 		}
 
-		var testSorted []uint32
+		time.Sleep(100 * time.Microsecond)
+
+		var sortedResult []uint64
 		for x := 0; x < len(set); x++ {
 			oct := make([]byte, 8)
-			stream.sortedBuf.Read(oct)
+			n, err := sortedBuf.Read(oct)
+			if n != 8 || err != nil {
+				ct.Error("failed to read from sorted Buf", n, err)
+			}
 			//log.Print(p)
-			testSorted = append(testSorted, uint32(binary.BigEndian.Uint64(oct)))
-		}
-		sorted64 := make([]uint64, len(set))
-		copy(sorted64, set)
-		sort.Slice(sorted64, func(i, j int) bool { return sorted64[i] < sorted64[j] })
-		sorted32 := make([]uint32, len(set))
-		for i, _ := range sorted64 {
-			sorted32[i] = uint32(sorted64[i])
+			sortedResult = append(sortedResult, binary.BigEndian.Uint64(oct))
 		}
+		targetSorted := make([]uint64, len(set))
+		copy(targetSorted, set)
+		sort.Slice(targetSorted, func(i, j int) bool { return targetSorted[i] < targetSorted[j] })
 
-		for i, _ := range sorted32 {
-			if sorted32[i] != testSorted[i] {
-				t.Error(
-					"For", set,
-					"expecting", sorted32,
-					"got", testSorted,
-				)
+		for i, _ := range targetSorted {
+			if sortedResult[i] != targetSorted[i] {
+				goto fail
 			}
 		}
-		stream.newFrameCh <- nil
+		fs.Close()
+		return
+	fail:
+		ct.Error(
+			"expecting", targetSorted,
+			"got", sortedResult,
+		)
 	}
+
+	t.Run("in order", func(t *testing.T) {
+		test(inOrder, t)
+	})
+	t.Run("out of order0", func(t *testing.T) {
+		test(outOfOrder0, t)
+	})
+	t.Run("out of order1", func(t *testing.T) {
+		test(outOfOrder1, t)
+	})
+	t.Run("out of order wrap", func(t *testing.T) {
+		test(outOfOrderWrap0, t)
+	})
 }
diff --git a/internal/multiplex/stream.go b/internal/multiplex/stream.go
index 1d17af7..cbc5b7b 100644
--- a/internal/multiplex/stream.go
+++ b/internal/multiplex/stream.go
@@ -19,17 +19,10 @@ type Stream struct {
 
 	session *Session
 
-	// Explanations of the following 4 fields can be found in frameSorter.go
-	nextRecvSeq uint32
-	rev         int
-	sh          sorterHeap
-	wrapMode    bool
-
-	// New frames are received through newFrameCh by frameSorter
-	newFrameCh chan *Frame
-
 	sortedBuf *bufferedPipe
 
+	sorter *frameSorter
+
 	// atomic
 	nextSendSeq uint32
 
@@ -42,15 +35,16 @@ type Stream struct {
 }
 
 func makeStream(id uint32, sesh *Session) *Stream {
+	buf := NewBufferedPipe()
+
 	stream := &Stream{
-		id:         id,
-		session:    sesh,
-		sh:         []*frameNode{},
-		newFrameCh: make(chan *Frame, 1024),
-		sortedBuf:  NewBufferedPipe(),
-		obfsBuf:    make([]byte, 17000),
+		id:        id,
+		session:   sesh,
+		sortedBuf: buf,
+		obfsBuf:   make([]byte, 17000),
+		sorter:    NewFrameSorter(buf),
 	}
-	go stream.recvNewFrame()
+
 	log.Tracef("stream %v opened", id)
 	return stream
 }
@@ -108,7 +102,7 @@ func (s *Stream) Write(in []byte) (n int, err error) {
 // the necessary steps to mark the stream as closed and to release resources
 func (s *Stream) _close() {
 	atomic.StoreUint32(&s.closed, 1)
-	s.newFrameCh <- nil // this will trigger frameSorter to return
+	s.sorter.Close() // this will trigger frameSorter to return
 	s.sortedBuf.Close()
 }
 
diff --git a/internal/multiplex/switchboard.go b/internal/multiplex/switchboard.go
index d43720a..a0788b7 100644
--- a/internal/multiplex/switchboard.go
+++ b/internal/multiplex/switchboard.go
@@ -148,7 +148,7 @@ func (sb *switchboard) deplex(ce *connEnclave) {
 		// (this happens when ss-server and ss-local closes the stream
 		// simutaneously), we don't do anything
 		if stream != nil {
-			stream.writeNewFrame(frame)
+			stream.sorter.writeNewFrame(frame)
 		}
 	}
 }