diff --git a/usrsctplib/netinet/sctp_callout.c b/usrsctplib/netinet/sctp_callout.c
new file mode 100755
index 0000000..c9e467a
--- /dev/null
+++ b/usrsctplib/netinet/sctp_callout.c
@@ -0,0 +1,224 @@
+/*-
+ * 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:
+ *
+ * a) Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ *
+ * b) 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.
+ *
+ * c) Neither the name of Cisco Systems, Inc. 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 COPYRIGHT HOLDERS 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 COPYRIGHT OWNER 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.
+ */
+
+#if defined(__Userspace__)
+#include <sys/types.h>
+#if !defined (__Userspace_os_Windows)
+#include <sys/wait.h>
+#include <unistd.h>
+#include <pthread.h>
+#endif
+#if defined(__Userspace_os_NaCl)
+#include <sys/select.h>
+#endif
+#include <stdlib.h>
+#include <string.h>
+#include <stdio.h>
+#include <errno.h>
+#include <netinet/sctp_sysctl.h>
+#include <netinet/sctp_pcb.h>
+#else
+#include <netinet/sctp_os.h>
+#include <netinet/sctp_callout.h>
+#include <netinet/sctp_pcb.h>
+#endif
+
+/*
+ * Callout/Timer routines for OS that doesn't have them
+ */
+#if defined(__APPLE__) || defined(__Userspace__)
+static int ticks = 0;
+#else
+extern int ticks;
+#endif
+
+int sctp_get_tick_count(void) {
+	int ret;
+
+	SCTP_TIMERQ_LOCK();
+	ret = ticks;
+	SCTP_TIMERQ_UNLOCK();
+	return ret;
+}
+
+/*
+ * SCTP_TIMERQ_LOCK protects:
+ * - SCTP_BASE_INFO(callqueue)
+ * - sctp_os_timer_next: next timer to check
+ */
+static sctp_os_timer_t *sctp_os_timer_next = NULL;
+
+void
+sctp_os_timer_init(sctp_os_timer_t *c)
+{
+	bzero(c, sizeof(*c));
+}
+
+void
+sctp_os_timer_start(sctp_os_timer_t *c, int to_ticks, void (*ftn) (void *),
+                    void *arg)
+{
+	/* paranoia */
+	if ((c == NULL) || (ftn == NULL))
+	    return;
+
+	SCTP_TIMERQ_LOCK();
+	/* check to see if we're rescheduling a timer */
+	if (c->c_flags & SCTP_CALLOUT_PENDING) {
+		if (c == sctp_os_timer_next) {
+			sctp_os_timer_next = TAILQ_NEXT(c, tqe);
+		}
+		TAILQ_REMOVE(&SCTP_BASE_INFO(callqueue), c, tqe);
+		/*
+		 * part of the normal "stop a pending callout" process
+		 * is to clear the CALLOUT_ACTIVE and CALLOUT_PENDING
+		 * flags.  We don't bother since we are setting these
+		 * below and we still hold the lock.
+		 */
+	}
+
+	/*
+	 * We could unlock/splx here and lock/spl at the TAILQ_INSERT_TAIL,
+	 * but there's no point since doing this setup doesn't take much time.
+	 */
+	if (to_ticks <= 0)
+		to_ticks = 1;
+
+	c->c_arg = arg;
+	c->c_flags = (SCTP_CALLOUT_ACTIVE | SCTP_CALLOUT_PENDING);
+	c->c_func = ftn;
+	c->c_time = ticks + to_ticks;
+	TAILQ_INSERT_TAIL(&SCTP_BASE_INFO(callqueue), c, tqe);
+	SCTP_TIMERQ_UNLOCK();
+}
+
+int
+sctp_os_timer_stop(sctp_os_timer_t *c)
+{
+	SCTP_TIMERQ_LOCK();
+	/*
+	 * Don't attempt to delete a callout that's not on the queue.
+	 */
+	if (!(c->c_flags & SCTP_CALLOUT_PENDING)) {
+		c->c_flags &= ~SCTP_CALLOUT_ACTIVE;
+		SCTP_TIMERQ_UNLOCK();
+		return (0);
+	}
+	c->c_flags &= ~(SCTP_CALLOUT_ACTIVE | SCTP_CALLOUT_PENDING);
+	if (c == sctp_os_timer_next) {
+		sctp_os_timer_next = TAILQ_NEXT(c, tqe);
+	}
+	TAILQ_REMOVE(&SCTP_BASE_INFO(callqueue), c, tqe);
+	SCTP_TIMERQ_UNLOCK();
+	return (1);
+}
+
+void
+sctp_handle_tick(unsigned int delta)
+{
+	sctp_os_timer_t *c;
+	void (*c_func)(void *);
+	void *c_arg;
+
+	SCTP_TIMERQ_LOCK();
+	/* update our tick count */
+	ticks += delta;
+	c = TAILQ_FIRST(&SCTP_BASE_INFO(callqueue));
+	while (c) {
+		if (c->c_time <= ticks) {
+			sctp_os_timer_next = TAILQ_NEXT(c, tqe);
+			TAILQ_REMOVE(&SCTP_BASE_INFO(callqueue), c, tqe);
+			c_func = c->c_func;
+			c_arg = c->c_arg;
+			c->c_flags &= ~SCTP_CALLOUT_PENDING;
+			SCTP_TIMERQ_UNLOCK();
+			c_func(c_arg);
+			SCTP_TIMERQ_LOCK();
+			c = sctp_os_timer_next;
+		} else {
+			c = TAILQ_NEXT(c, tqe);
+		}
+	}
+	sctp_os_timer_next = NULL;
+	SCTP_TIMERQ_UNLOCK();
+}
+
+#if defined(__APPLE__)
+void
+sctp_timeout(void *arg SCTP_UNUSED)
+{
+	sctp_handle_tick(SCTP_BASE_VAR(sctp_main_timer_ticks));
+	sctp_start_main_timer();
+}
+#endif
+
+#if defined(__Userspace__)
+#define TIMEOUT_INTERVAL 10
+
+void *
+user_sctp_timer_iterate(void *arg)
+{
+	sctp_userspace_set_threadname("SCTP timer");
+	for (;;) {
+#if defined (__Userspace_os_Windows)
+		Sleep(TIMEOUT_INTERVAL);
+#else
+		struct timeval timeout;
+
+		timeout.tv_sec  = 0;
+		timeout.tv_usec = 1000 * TIMEOUT_INTERVAL;
+		select(0, NULL, NULL, NULL, &timeout);
+#endif
+		if (SCTP_BASE_VAR(timer_thread_should_exit)) {
+			break;
+		}
+		sctp_handle_tick(MSEC_TO_TICKS(TIMEOUT_INTERVAL));
+	}
+	return (NULL);
+}
+
+void
+sctp_start_timer(void)
+{
+	/*
+	 * No need to do SCTP_TIMERQ_LOCK_INIT();
+	 * here, it is being done in sctp_pcb_init()
+	 */
+	int rc;
+
+	rc = sctp_userspace_thread_create(&SCTP_BASE_VAR(timer_thread), user_sctp_timer_iterate);
+	if (rc) {
+		SCTP_PRINTF("ERROR; return code from sctp_thread_create() is %d\n", rc);
+	}
+}
+
+#endif