diff --git a/include/nuttx/mm/iob.h b/include/nuttx/mm/iob.h
index 86150e9cf8..e47f4b55d5 100644
--- a/include/nuttx/mm/iob.h
+++ b/include/nuttx/mm/iob.h
@@ -195,7 +195,17 @@ FAR struct iob_s *iob_tryalloc(bool throttled);
  *
  ****************************************************************************/
 
-int iob_navail(void);
+int iob_navail(bool throttled);
+
+/****************************************************************************
+ * Name: iob_quentry_navail
+ *
+ * Description:
+ *   Return the number of available IOB chains.
+ *
+ ****************************************************************************/
+
+int iob_quentry_navail(void);
 
 /****************************************************************************
  * Name: iob_free
diff --git a/mm/iob/iob_free.c b/mm/iob/iob_free.c
index b422bdd0ed..b29dafe610 100644
--- a/mm/iob/iob_free.c
+++ b/mm/iob/iob_free.c
@@ -39,6 +39,7 @@
 
 #include <nuttx/config.h>
 
+#include <stdbool.h>
 #include <semaphore.h>
 #include <assert.h>
 #include <debug.h>
@@ -148,7 +149,7 @@ FAR struct iob_s *iob_free(FAR struct iob_s *iob)
    * for an IOB.
    */
 
-  if (iob_navail() > 0)
+  if (iob_navail(false) > 0)
     {
       /* Signal any threads that have requested a signal notification
        * when an IOB becomes available.
diff --git a/mm/iob/iob_navail.c b/mm/iob/iob_navail.c
index 7a14e5533f..4f41cadfe7 100644
--- a/mm/iob/iob_navail.c
+++ b/mm/iob/iob_navail.c
@@ -39,6 +39,8 @@
 
 #include <nuttx/config.h>
 
+#include <stdbool.h>
+
 #include <nuttx/semaphore.h>
 #include <nuttx/mm/iob.h>
 
@@ -56,17 +58,62 @@
  *
  ****************************************************************************/
 
-int iob_navail(void)
+int iob_navail(bool throttled)
 {
   int navail = 0;
   int ret;
 
-#if CONFIG_IOB_NCHAINS > 0
-  ret = nxsem_getvalue(&g_qentry_sem, &navail);
+#if CONFIG_IOB_NBUFFERS > 0
+  /* Get the value of the IOB counting semaphores */
+
+  ret = nxsem_getvalue(&g_iob_sem, &navail);
   if (ret >= 0)
     {
       ret = navail;
+
+#if CONFIG_IOB_THROTTLE > 0
+      /* Subtract the throttle value is so requested */
+
+      if (throttled)
+        {
+          ret -= CONFIG_IOB_THROTTLE;
+          if (ret < 0)
+            {
+              ret = 0;
+            }
+        }
+#endif
     }
+
+#else
+  ret = navail;
+#endif
+
+  return ret;
+}
+
+/****************************************************************************
+ * Name: iob_quentry_navail
+ *
+ * Description:
+ *   Return the number of available IOB chains.
+ *
+ ****************************************************************************/
+
+int iob_quentry_navail(void)
+{
+  int navail = 0;
+  int ret;
+
+#if CONFIG_IOB_NCHAINS > 0
+  /* Get the value of the IOB chain qentry counting semaphores */
+
+  ret = nxsem_getvalue(&g_qentry_sem, &navail);
+  if (ret >= 0)
+    {
+      ret = navail;
+    }
+
 #else
   ret = navail;
 #endif
diff --git a/mm/iob/iob_notifier.c b/mm/iob/iob_notifier.c
index 397eb4f04e..c914a644f5 100644
--- a/mm/iob/iob_notifier.c
+++ b/mm/iob/iob_notifier.c
@@ -86,9 +86,11 @@ int iob_notifier_setup(int qid, worker_t worker, FAR void *arg)
 
   /* If there are already free IOBs, then return zero without setting up the
    * notification.
+   *
+   * REVISIT: The 'throttled' argument should not always be 'false'.
    */
 
-  if (iob_navail() > 0)
+  if (iob_navail(false) > 0)
     {
       return 0;
     }
diff --git a/net/tcp/tcp_recvwindow.c b/net/tcp/tcp_recvwindow.c
index 4929e797ee..7123001c18 100644
--- a/net/tcp/tcp_recvwindow.c
+++ b/net/tcp/tcp_recvwindow.c
@@ -40,6 +40,7 @@
 #include <nuttx/config.h>
 
 #include <stdint.h>
+#incldue <stdbool.h>
 #include <debug.h>
 
 #include <net/if.h>
@@ -109,7 +110,7 @@ uint16_t tcp_get_recvwindow(FAR struct net_driver_s *dev)
    * availability.
    */
 
-  navail = iob_navail();
+  navail = iob_navail(true);
 
   /* Are the read-ahead allocations throttled?  If so, then not all of these
    * IOBs are available for read-ahead buffering.