Ping connections with the fast rate until each connection is pinged at least three times.

webrtc/p2p/base/p2ptransportchannel.cc

Index: webrtc/p2p/base/p2ptransportchannel.cc
diff --git a/webrtc/p2p/base/p2ptransportchannel.cc b/webrtc/p2p/base/p2ptransportchannel.cc
index 92bec6f8970a95878fcb5fe3ed20cb7ed43c1603..fd962d549769a262d717f7f14d276629a24cf927 100644
--- a/webrtc/p2p/base/p2ptransportchannel.cc
+++ b/webrtc/p2p/base/p2ptransportchannel.cc
@@ -1302,9 +1302,15 @@ void P2PTransportChannel::OnCheckAndPing() {
   // Make sure the states of the connections are up-to-date (since this affects
   // which ones are pingable).
   UpdateConnectionStates();
-  // When the best connection is either not receiving or not writable,
-  // switch to weak ping interval.
-  int ping_interval = weak() ? weak_ping_interval_ : STRONG_PING_INTERVAL;
+  // When the best connection is receiving and writable, and all connections
+  // have been pinged sufficiently, switch to strong (longer) ping interval.
+  bool all_connections_pinged_sufficiently = std::all_of(
+      connections_.begin(), connections_.end(), [](Connection* conn) {
+        return !conn->active() || conn->num_pings_sent() >= kMinNumPingsSent;
+      });
+  int ping_interval = (all_connections_pinged_sufficiently && !weak())
+                          ? STRONG_PING_INTERVAL

[pthatcher1, 2016/05/25 17:29:13]

This might be more clear as :

bool need_more_pings_at_weak_interval = std::any_of(...,
  return conn->active() && conn->num_pings_sent() <
MIN_PINGS_AT_WEAK_INTERVAL));

int ping_interval = (weak() || need_more_pings_at_weak_interval) ?
weak_ping_interval_ : STRONG_PING_INTERVAL;

[honghaiz3, 2016/05/25 18:40:02]

Done.

+                          : weak_ping_interval_;
   if (rtc::TimeMillis() >= last_ping_sent_ms_ + ping_interval) {
     Connection* conn = FindNextPingableConnection();
     if (conn) {