diff --git a/daemon/fw/pit-algorithm.hpp b/daemon/fw/pit-algorithm.hpp
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+/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
+/**
+ * Copyright (c) 2014-2016,  Regents of the University of California,
+ *                           Arizona Board of Regents,
+ *                           Colorado State University,
+ *                           University Pierre & Marie Curie, Sorbonne University,
+ *                           Washington University in St. Louis,
+ *                           Beijing Institute of Technology,
+ *                           The University of Memphis.
+ *
+ * This file is part of NFD (Named Data Networking Forwarding Daemon).
+ * See AUTHORS.md for complete list of NFD authors and contributors.
+ *
+ * NFD is free software: you can redistribute it and/or modify it under the terms
+ * of the GNU General Public License as published by the Free Software Foundation,
+ * either version 3 of the License, or (at your option) any later version.
+ *
+ * NFD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
+ * without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
+ * PURPOSE.  See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * NFD, e.g., in COPYING.md file.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef NFD_DAEMON_FW_PIT_ALGORITHM_HPP
+#define NFD_DAEMON_FW_PIT_ALGORITHM_HPP
+
+#include "table/pit-entry.hpp"
+
+/** \file
+ *  This file contains algorithms that operate on a PIT entry.
+ */
+
+namespace nfd {
+namespace fw {
+
+/** \brief contain Name prefix that affects namespace-based scope control
+ *  \sa http://redmine.named-data.net/projects/nfd/wiki/ScopeControl
+ */
+namespace scope_prefix {
+
+/** \brief ndn:/localhost
+ *
+ *  The localhost scope limits propagation to the applications on the originating host.
+ *
+ *  Interest and Data packets under prefix ndn:/localhost are restricted by these rules:
+ *  \li Interest can come from and go to local faces only.
+ *  \li Data can come from and go to local faces only.
+ */
+extern const Name LOCALHOST;
+
+/** \brief ndn:/localhop
+ *
+ *  The localhop scope limits propagation to no further than the next node.
+ *
+ *  Interest packets under prefix ndn:/localhop are restricted by these rules:
+ *  \li Interest can come from a local face or a non-local face.
+ *  \li If PIT entry has at least one in-record from a local face,
+ *      it can be forwarded to local faces and non-local faces.
+ *  \li If PIT entry has all in-records from non-local faces,
+ *      it can only be forwarded to local faces.
+ *  \li PIT entry can be satisfied by Data from any source.
+ *
+ *  Data packets under prefix ndn:/localhop are unrestricted.
+ */
+extern const Name LOCALHOP;
+
+} // namespace scope_prefix
+
+/** \brief determine whether forwarding the Interest in \p pitEntry to \p outFace would violate scope
+ *  \sa http://redmine.named-data.net/projects/nfd/wiki/ScopeControl
+ */
+bool
+violatesScope(const pit::Entry& pitEntry, const Face& outFace);
+
+/** \brief decide whether Interest can be forwarded to face
+ *
+ *  \return true if out-record of this face does not exist or has expired,
+ *          and there is an in-record not of this face,
+ *          and scope is not violated
+ *
+ *  \note This algorithm has a weakness that it does not permit consumer retransmissions
+ *        before out-record expires. Therefore, it's not recommended to use this function
+ *        in new strategies.
+ *  \todo find a better name for this function
+ */
+bool
+canForwardToLegacy(const pit::Entry& pitEntry, const Face& face);
+
+/** \brief indicates where duplicate Nonces are found
+ */
+enum DuplicateNonceWhere {
+  DUPLICATE_NONCE_NONE      = 0,        ///< no duplicate Nonce is found
+  DUPLICATE_NONCE_IN_SAME   = (1 << 0), ///< in-record of same face
+  DUPLICATE_NONCE_IN_OTHER  = (1 << 1), ///< in-record of other face
+  DUPLICATE_NONCE_OUT_SAME  = (1 << 2), ///< out-record of same face
+  DUPLICATE_NONCE_OUT_OTHER = (1 << 3)  ///< out-record of other face
+};
+
+/** \brief determine whether \p pitEntry has duplicate Nonce \p nonce
+ *  \return OR'ed DuplicateNonceWhere
+ */
+int
+findDuplicateNonce(const pit::Entry& pitEntry, uint32_t nonce, const Face& face);
+
+/** \brief determine whether \p pitEntry has any pending out-records
+ *  \return true if there is one or more unexpired OutRecords
+ *  \todo #3545 take Nack into consideration
+ */
+bool
+hasPendingOutRecords(const pit::Entry& pitEntry);
+
+} // namespace fw
+} // namespace nfd
+
+#endif // NFD_DAEMON_FW_PIT_ALGORITHM_HPP