diff --git a/quic/core/session_notifier_interface.h b/quic/core/session_notifier_interface.h
new file mode 100644
index 0000000..83fc0f1
--- /dev/null
+++ b/quic/core/session_notifier_interface.h
@@ -0,0 +1,43 @@
+// Copyright (c) 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef QUICHE_QUIC_CORE_SESSION_NOTIFIER_INTERFACE_H_
+#define QUICHE_QUIC_CORE_SESSION_NOTIFIER_INTERFACE_H_
+
+#include "net/third_party/quiche/src/quic/core/frames/quic_frame.h"
+#include "net/third_party/quiche/src/quic/core/quic_time.h"
+
+namespace quic {
+
+// Pure virtual class to be notified when a packet containing a frame is acked
+// or lost.
+class QUIC_EXPORT_PRIVATE SessionNotifierInterface {
+ public:
+  virtual ~SessionNotifierInterface() {}
+
+  // Called when |frame| is acked. Returns true if any new data gets acked,
+  // returns false otherwise.
+  virtual bool OnFrameAcked(const QuicFrame& frame,
+                            QuicTime::Delta ack_delay_time) = 0;
+
+  // Called when |frame| is retransmitted.
+  virtual void OnStreamFrameRetransmitted(const QuicStreamFrame& frame) = 0;
+
+  // Called when |frame| is considered as lost.
+  virtual void OnFrameLost(const QuicFrame& frame) = 0;
+
+  // Called to retransmit |frames| with transmission |type|.
+  virtual void RetransmitFrames(const QuicFrames& frames,
+                                TransmissionType type) = 0;
+
+  // Returns true if |frame| is outstanding and waiting to be acked.
+  virtual bool IsFrameOutstanding(const QuicFrame& frame) const = 0;
+
+  // Returns true if crypto stream is waiting for acks.
+  virtual bool HasUnackedCryptoData() const = 0;
+};
+
+}  // namespace quic
+
+#endif  // QUICHE_QUIC_CORE_SESSION_NOTIFIER_INTERFACE_H_