diff --git a/usrsctplib/netinet/sctp_callout.h b/usrsctplib/netinet/sctp_callout.h
new file mode 100755
index 0000000..52a282f
--- /dev/null
+++ b/usrsctplib/netinet/sctp_callout.h
@@ -0,0 +1,109 @@
+/*-
+ * Copyright (c) 2001-2007, by Cisco Systems, Inc. All rights reserved.
+ * Copyright (c) 2008-2012, by Randall Stewart. All rights reserved.
+ * Copyright (c) 2008-2012, by Michael Tuexen. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the project nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#ifdef __FreeBSD__
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+#endif
+
+#ifndef _NETINET_SCTP_CALLOUT_
+#define _NETINET_SCTP_CALLOUT_
+
+/*
+ * NOTE: the following MACROS are required for locking the callout
+ * queue along with a lock/mutex in the OS specific headers and
+ * implementation files::
+ * - SCTP_TIMERQ_LOCK()
+ * - SCTP_TIMERQ_UNLOCK()
+ * - SCTP_TIMERQ_LOCK_INIT()
+ * - SCTP_TIMERQ_LOCK_DESTROY()
+ */
+
+#define _SCTP_NEEDS_CALLOUT_ 1
+
+#define SCTP_TICKS_PER_FASTTIMO 20	/* called about every 20ms */
+
+#if defined(__Userspace__)
+#if defined(__Userspace_os_Windows)
+#define SCTP_TIMERQ_LOCK()          EnterCriticalSection(&SCTP_BASE_VAR(timer_mtx))
+#define SCTP_TIMERQ_UNLOCK()        LeaveCriticalSection(&SCTP_BASE_VAR(timer_mtx))
+#define SCTP_TIMERQ_LOCK_INIT()     InitializeCriticalSection(&SCTP_BASE_VAR(timer_mtx))
+#define SCTP_TIMERQ_LOCK_DESTROY()  DeleteCriticalSection(&SCTP_BASE_VAR(timer_mtx))
+#else
+#ifdef INVARIANTS
+#define SCTP_TIMERQ_LOCK()          KASSERT(pthread_mutex_lock(&SCTP_BASE_VAR(timer_mtx)) == 0, ("%s: timer_mtx already locked", __func__))
+#define SCTP_TIMERQ_UNLOCK()        KASSERT(pthread_mutex_unlock(&SCTP_BASE_VAR(timer_mtx)) == 0, ("%s: timer_mtx not locked", __func__))
+#else
+#define SCTP_TIMERQ_LOCK()          (void)pthread_mutex_lock(&SCTP_BASE_VAR(timer_mtx))
+#define SCTP_TIMERQ_UNLOCK()        (void)pthread_mutex_unlock(&SCTP_BASE_VAR(timer_mtx))
+#endif
+#define SCTP_TIMERQ_LOCK_INIT()     (void)pthread_mutex_init(&SCTP_BASE_VAR(timer_mtx), &SCTP_BASE_VAR(mtx_attr))
+#define SCTP_TIMERQ_LOCK_DESTROY()  (void)pthread_mutex_destroy(&SCTP_BASE_VAR(timer_mtx))
+#endif
+#endif
+
+int sctp_get_tick_count(void);
+
+TAILQ_HEAD(calloutlist, sctp_callout);
+
+struct sctp_callout {
+	TAILQ_ENTRY(sctp_callout) tqe;
+	int c_time;		/* ticks to the event */
+	void *c_arg;		/* function argument */
+	void (*c_func)(void *);	/* function to call */
+	int c_flags;		/* state of this entry */
+};
+typedef struct sctp_callout sctp_os_timer_t;
+
+#define	SCTP_CALLOUT_ACTIVE	0x0002	/* callout is currently active */
+#define	SCTP_CALLOUT_PENDING	0x0004	/* callout is waiting for timeout */
+
+void sctp_os_timer_init(sctp_os_timer_t *tmr);
+void sctp_os_timer_start(sctp_os_timer_t *, int, void (*)(void *), void *);
+int sctp_os_timer_stop(sctp_os_timer_t *);
+void sctp_handle_tick(unsigned int);
+
+#define SCTP_OS_TIMER_INIT	sctp_os_timer_init
+#define SCTP_OS_TIMER_START	sctp_os_timer_start
+#define SCTP_OS_TIMER_STOP	sctp_os_timer_stop
+/* MT FIXME: Is the following correct? */
+#define SCTP_OS_TIMER_STOP_DRAIN SCTP_OS_TIMER_STOP
+#define	SCTP_OS_TIMER_PENDING(tmr) ((tmr)->c_flags & SCTP_CALLOUT_PENDING)
+#define	SCTP_OS_TIMER_ACTIVE(tmr) ((tmr)->c_flags & SCTP_CALLOUT_ACTIVE)
+#define	SCTP_OS_TIMER_DEACTIVATE(tmr) ((tmr)->c_flags &= ~SCTP_CALLOUT_ACTIVE)
+
+#if defined(__Userspace__)
+void sctp_start_timer(void);
+#endif
+#if defined(__APPLE__)
+void sctp_timeout(void *);
+#endif
+
+#endif