From 43b01b323657746ff88c6a49dc8a056e801470b3 Mon Sep 17 00:00:00 2001
From: Simon Duquennoy <simonduq@sics.se>
Date: Sat, 23 Apr 2016 00:13:59 +0200
Subject: [PATCH] RPL: if the best parent is not fresh, use the best fresh
 instead and utilize urgent probing to update link estimates

---
 core/net/rpl/rpl-dag.c | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/core/net/rpl/rpl-dag.c b/core/net/rpl/rpl-dag.c
index a0f01caaf..c0a616b9d 100644
--- a/core/net/rpl/rpl-dag.c
+++ b/core/net/rpl/rpl-dag.c
@@ -832,7 +832,7 @@ rpl_select_dag(rpl_instance_t *instance, rpl_parent_t *p)
 }
 /*---------------------------------------------------------------------------*/
 static rpl_parent_t *
-best_parent(rpl_dag_t *dag)
+best_parent(rpl_dag_t *dag, int fresh_only)
 {
   rpl_parent_t *p;
   rpl_of_t *of;
@@ -851,6 +851,11 @@ best_parent(rpl_dag_t *dag)
       continue;
     }
 
+    if(fresh_only && !rpl_parent_is_fresh(p)) {
+      /* Filter out non-fresh parents if fresh_only is set */
+      continue;
+    }
+
 #ifndef UIP_CONF_ND6_SEND_NA
     {
     uip_ds6_nbr_t *nbr = rpl_get_nbr(p);
@@ -871,13 +876,23 @@ best_parent(rpl_dag_t *dag)
 rpl_parent_t *
 rpl_select_parent(rpl_dag_t *dag)
 {
-  rpl_parent_t *best = best_parent(dag);
+  /* Look for best parent (regardless of freshness) */
+  rpl_parent_t *best = best_parent(dag, 0);
 
   if(best != NULL) {
     if(rpl_parent_is_fresh(best)) {
       rpl_set_preferred_parent(dag, best);
       dag->rank = rpl_rank_via_parent(dag->preferred_parent);
     } else {
+      /* The best is not fresh. Look for the best fresh now. */
+      rpl_parent_t *best_fresh = best_parent(dag, 1);
+      if(best_fresh == NULL) {
+        /* No fresh parent around, use best (non-fresh) */
+        rpl_set_preferred_parent(dag, best);
+      } else {
+        /* Use best fresh */
+        rpl_set_preferred_parent(dag, best_fresh);
+      }
 #if RPL_WITH_PROBING
       /* Probe the new best parent shortly in order to get a fresh estimate */
       dag->instance->urgent_probing_target = best;