Increase STUN RTOs

webrtc/p2p/base/stunrequest.cc

 /*
  *  Copyright 2004 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
 #include "webrtc/p2p/base/stunrequest.h"
 
 #include <algorithm>
 #include <memory>
 
 #include "webrtc/base/checks.h"
 #include "webrtc/base/helpers.h"
 #include "webrtc/base/logging.h"
 #include "webrtc/base/stringencode.h"
 
 namespace cricket {
 
 const uint32_t MSG_STUN_SEND = 1;
 
-const int MAX_SENDS = 9;
-const int DELAY_UNIT = 100;  // 100 milliseconds
-const int DELAY_MAX_FACTOR = 16;
+// RFC 5389 says SHOULD be 500ms.
+// For years, this was 100ms, but for networks that
+// experience moments of high RTT (such as 2G networks), this doesn't
+// work well.
+const int STUN_INITIAL_RTO = 250;  // milliseconds
+
+// The timeout doubles each retransmission, up to this many times
+// RFC 5389 says SHOULD retransmit 7 times.
+// This has been 8 for years (not sure why).
+const int STUN_MAX_RETRANSMISSIONS = 8;  // Total sends: 9
+
+// We also cap the doubling, even though the standard doesn't say to.
+// This has been 1.6 seconds for years, but for networks that
+// experience moments of high RTT (such as 2G networks), this doesn't
+// work well.
+const int STUN_MAX_RTO = 8000;  // milliseconds, or 5 doublings
 
 StunRequestManager::StunRequestManager(rtc::Thread* thread)
     : thread_(thread) {
 }
 
 StunRequestManager::~StunRequestManager() {
   while (requests_.begin() != requests_.end()) {
     StunRequest *request = requests_.begin()->second;
     requests_.erase(requests_.begin());
     delete request;
@@ skipping 181 matching lines @@
   msg_->Write(&buf);
   manager_->SignalSendPacket(buf.Data(), buf.Length(), this);
 
   OnSent();
   manager_->thread_->PostDelayed(RTC_FROM_HERE, resend_delay(), this,
                                  MSG_STUN_SEND, NULL);
 }
 
 void StunRequest::OnSent() {
   count_ += 1;
-  if (count_ == MAX_SENDS) {
+  int retransmissions = (count_ - 1);
+  if (retransmissions >= STUN_MAX_RETRANSMISSIONS) {
     timeout_ = true;
   }
   LOG(LS_VERBOSE) << "Sent STUN request " << count_
                   << "; resend delay = " << resend_delay();
 }
 
 int StunRequest::resend_delay() {
   if (count_ == 0) {
     return 0;
   }
-  return DELAY_UNIT * std::min(1 << (count_-1), DELAY_MAX_FACTOR);
+  int retransmissions = (count_ - 1);
+  int rto = STUN_INITIAL_RTO << retransmissions;
+  return std::min(rto, STUN_MAX_RTO);
 }
 
 }  // namespace cricket