Datagram Transport Integration

- Implement datagram transport adaptor, which wraps datagram transport in DtlsTransportInternal. Datagram adaptor owns both ICE and Datagram Transports.
- Implement setup of datagram transport based on RTCConfiguration flag use_datagram_transport. This is very similar to MediaTransport setup with the exception that we create DTLS datagram adaptor.
- Propagate maximum datagram size to video encoder via MediaTransportConfig.

TODO: Currently this CL can only be tested in downstream projects. Once we add fake datagram transport, we will be able to implement unit tests similar to loopback media transport.

Bug: webrtc:9719
Change-Id: I4fa4a5725598dfee5da4f0f374269a7e289d48ed
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/138100
Commit-Queue: Anton Sukhanov <sukhanov@webrtc.org>
Reviewed-by: Bjorn Mellem <mellem@webrtc.org>
Reviewed-by: Steve Anton <steveanton@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#28047}
diff --git a/pc/jsep_transport.cc b/pc/jsep_transport.cc
index f82cf2a..26311d1 100644
--- a/pc/jsep_transport.cc
+++ b/pc/jsep_transport.cc
@@ -116,6 +116,7 @@
               : nullptr),
       media_transport_(std::move(media_transport)) {
   RTC_DCHECK(rtp_dtls_transport_);
+  RTC_DCHECK(!datagram_transport() || !media_transport_);
   // Verify the "only one out of these three can be set" invariant.
   if (unencrypted_rtp_transport_) {
     RTC_DCHECK(!sdes_transport);
@@ -135,12 +136,13 @@
 }
 
 JsepTransport::~JsepTransport() {
+  // Disconnect media transport state callbacks and  make sure we delete media
+  // transports before ICE.
   if (media_transport_) {
     media_transport_->SetMediaTransportStateCallback(nullptr);
-
-    // Make sure we delete media transport before ICE.
     media_transport_.reset();
   }
+
   // Clear all DtlsTransports. There may be pointers to these from
   // other places, so we can't assume they'll be deleted by the destructor.
   rtp_dtls_transport_->Clear();
@@ -717,5 +719,4 @@
   }
   SignalMediaTransportStateChanged();
 }
-
 }  // namespace cricket
diff --git a/pc/jsep_transport.h b/pc/jsep_transport.h
index 0f31403..fce21be 100644
--- a/pc/jsep_transport.h
+++ b/pc/jsep_transport.h
@@ -217,6 +217,12 @@
     return media_transport_.get();
   }
 
+  // Returns datagram transport, if available.
+  webrtc::DatagramTransportInterface* datagram_transport() const {
+    rtc::CritScope scope(&accessor_lock_);
+    return rtp_dtls_transport_->internal()->datagram_transport();
+  }
+
   // Returns the latest media transport state.
   webrtc::MediaTransportState media_transport_state() const {
     rtc::CritScope scope(&accessor_lock_);
@@ -332,6 +338,10 @@
 
   // If |media_transport_| is provided, this variable represents the state of
   // media transport.
+  //
+  // NOTE: datagram transport state is handled by DatagramDtlsAdaptor, because
+  // DatagramDtlsAdaptor owns DatagramTransport. This state only represents
+  // media transport.
   webrtc::MediaTransportState media_transport_state_
       RTC_GUARDED_BY(accessor_lock_) = webrtc::MediaTransportState::kPending;
 
diff --git a/pc/jsep_transport_controller.cc b/pc/jsep_transport_controller.cc
index fd9551a..55f1d1c 100644
--- a/pc/jsep_transport_controller.cc
+++ b/pc/jsep_transport_controller.cc
@@ -15,6 +15,9 @@
 
 #include "absl/algorithm/container.h"
 #include "absl/memory/memory.h"
+#include "api/datagram_transport_interface.h"
+#include "api/media_transport_interface.h"
+#include "p2p/base/datagram_dtls_adaptor.h"
 #include "p2p/base/ice_transport_internal.h"
 #include "p2p/base/no_op_dtls_transport.h"
 #include "p2p/base/port.h"
@@ -136,12 +139,42 @@
   return jsep_transport->rtp_transport();
 }
 
-MediaTransportInterface* JsepTransportController::GetMediaTransport(
+MediaTransportConfig JsepTransportController::GetMediaTransportConfig(
     const std::string& mid) const {
   auto jsep_transport = GetJsepTransportForMid(mid);
   if (!jsep_transport) {
+    return MediaTransportConfig();
+  }
+
+  MediaTransportInterface* media_transport = nullptr;
+  if (config_.use_media_transport_for_media) {
+    media_transport = jsep_transport->media_transport();
+  }
+
+  DatagramTransportInterface* datagram_transport =
+      jsep_transport->datagram_transport();
+
+  // Media transport and datagram transports can not be used together.
+  RTC_DCHECK(!media_transport || !datagram_transport);
+
+  if (media_transport) {
+    return MediaTransportConfig(media_transport);
+  } else if (datagram_transport) {
+    return MediaTransportConfig(
+        /*rtp_max_packet_size=*/datagram_transport->GetLargestDatagramSize());
+  } else {
+    return MediaTransportConfig();
+  }
+}
+
+MediaTransportInterface*
+JsepTransportController::GetMediaTransportForDataChannel(
+    const std::string& mid) const {
+  auto jsep_transport = GetJsepTransportForMid(mid);
+  if (!jsep_transport || !config_.use_media_transport_for_data_channels) {
     return nullptr;
   }
+
   return jsep_transport->media_transport();
 }
 
@@ -403,7 +436,8 @@
 
 void JsepTransportController::SetMediaTransportSettings(
     bool use_media_transport_for_media,
-    bool use_media_transport_for_data_channels) {
+    bool use_media_transport_for_data_channels,
+    bool use_datagram_transport) {
   RTC_DCHECK(use_media_transport_for_media ==
                  config_.use_media_transport_for_media ||
              jsep_transports_by_name_.empty())
@@ -419,6 +453,7 @@
   config_.use_media_transport_for_media = use_media_transport_for_media;
   config_.use_media_transport_for_data_channels =
       use_media_transport_for_data_channels;
+  config_.use_datagram_transport = use_datagram_transport;
 }
 
 std::unique_ptr<cricket::IceTransportInternal>
@@ -439,16 +474,25 @@
 
 std::unique_ptr<cricket::DtlsTransportInternal>
 JsepTransportController::CreateDtlsTransport(
-    std::unique_ptr<cricket::IceTransportInternal> ice) {
+    std::unique_ptr<cricket::IceTransportInternal> ice,
+    std::unique_ptr<DatagramTransportInterface> datagram_transport) {
   RTC_DCHECK(network_thread_->IsCurrent());
 
   std::unique_ptr<cricket::DtlsTransportInternal> dtls;
-  // If media transport is used for both media and data channels,
-  // then we don't need to create DTLS.
-  // Otherwise, DTLS is still created.
-  if (config_.media_transport_factory &&
-      config_.use_media_transport_for_media &&
-      config_.use_media_transport_for_data_channels) {
+
+  if (datagram_transport) {
+    RTC_DCHECK(config_.use_datagram_transport);
+
+    // Create DTLS wrapper around DatagramTransportInterface.
+    dtls = absl::make_unique<cricket::DatagramDtlsAdaptor>(
+        std::move(ice), std::move(datagram_transport), config_.crypto_options,
+        config_.event_log);
+  } else if (config_.media_transport_factory &&
+             config_.use_media_transport_for_media &&
+             config_.use_media_transport_for_data_channels) {
+    // If media transport is used for both media and data channels,
+    // then we don't need to create DTLS.
+    // Otherwise, DTLS is still created.
     dtls = absl::make_unique<cricket::NoOpDtlsTransport>(
         std::move(ice), config_.crypto_options);
   } else if (config_.external_transport_factory) {
@@ -1024,6 +1068,72 @@
   return media_transport_result.MoveValue();
 }
 
+// TODO(sukhanov): Refactor to avoid code duplication for Media and Datagram
+// transports setup.
+std::unique_ptr<webrtc::DatagramTransportInterface>
+JsepTransportController::MaybeCreateDatagramTransport(
+    const cricket::ContentInfo& content_info,
+    const cricket::SessionDescription& description,
+    bool local) {
+  if (config_.media_transport_factory == nullptr) {
+    return nullptr;
+  }
+
+  if (!config_.use_datagram_transport) {
+    return nullptr;
+  }
+
+  // Caller (offerer) datagram transport.
+  if (local) {
+    if (offer_datagram_transport_) {
+      RTC_LOG(LS_INFO) << "Offered datagram transport has now been activated.";
+      return std::move(offer_datagram_transport_);
+    } else {
+      RTC_LOG(LS_INFO)
+          << "Not returning datagram transport. Either SDES wasn't enabled, or "
+             "datagram transport didn't return an offer earlier.";
+      return nullptr;
+    }
+  }
+
+  // Remote offer. If no x-mt lines, do not create datagram transport.
+  if (description.MediaTransportSettings().empty()) {
+    return nullptr;
+  }
+
+  // When bundle is enabled, two JsepTransports are created, and then
+  // the second transport is destroyed (right away).
+  // For datagram transport, we don't want to create the second
+  // datagram transport in the first place.
+  RTC_LOG(LS_INFO) << "Returning new, client datagram transport.";
+
+  RTC_DCHECK(!local)
+      << "If datagram transport is used, you must call "
+         "GenerateOrGetLastMediaTransportOffer before SetLocalDescription. You "
+         "also must use kRtcpMuxPolicyRequire and kBundlePolicyMaxBundle with "
+         "datagram transport.";
+  MediaTransportSettings settings;
+  settings.is_caller = local;
+  settings.event_log = config_.event_log;
+
+  // Assume there is only one media transport (or if more, use the first one).
+  if (!local && !description.MediaTransportSettings().empty() &&
+      config_.media_transport_factory->GetTransportName() ==
+          description.MediaTransportSettings()[0].transport_name) {
+    settings.remote_transport_parameters =
+        description.MediaTransportSettings()[0].transport_setting;
+  }
+
+  auto datagram_transport_result =
+      config_.media_transport_factory->CreateDatagramTransport(network_thread_,
+                                                               settings);
+
+  // TODO(sukhanov): Proper error handling.
+  RTC_CHECK(datagram_transport_result.ok());
+
+  return datagram_transport_result.MoveValue();
+}
+
 RTCError JsepTransportController::MaybeCreateJsepTransport(
     bool local,
     const cricket::ContentInfo& content_info,
@@ -1052,8 +1162,15 @@
     media_transport->Connect(ice.get());
   }
 
+  std::unique_ptr<DatagramTransportInterface> datagram_transport =
+      MaybeCreateDatagramTransport(content_info, description, local);
+  if (datagram_transport) {
+    datagram_transport_created_once_ = true;
+    datagram_transport->Connect(ice.get());
+  }
+
   std::unique_ptr<cricket::DtlsTransportInternal> rtp_dtls_transport =
-      CreateDtlsTransport(std::move(ice));
+      CreateDtlsTransport(std::move(ice), std::move(datagram_transport));
 
   std::unique_ptr<cricket::DtlsTransportInternal> rtcp_dtls_transport;
   std::unique_ptr<RtpTransport> unencrypted_rtp_transport;
@@ -1064,19 +1181,36 @@
           PeerConnectionInterface::kRtcpMuxPolicyRequire &&
       content_info.type == cricket::MediaProtocolType::kRtp) {
     RTC_DCHECK(media_transport == nullptr);
+    RTC_DCHECK(datagram_transport == nullptr);
     rtcp_dtls_transport = CreateDtlsTransport(
-        CreateIceTransport(content_info.name, /*rtcp=*/true));
+        CreateIceTransport(content_info.name, /*rtcp=*/true),
+        /*datagram_transport=*/nullptr);
   }
 
-  // TODO(sukhanov): Do not create RTP/RTCP transports if media transport is
-  // used, and remove the no-op dtls transport when that's done.
-  if (config_.disable_encryption) {
+  if (datagram_transport) {
+    // TODO(sukhanov): We use unencrypted RTP transport over DatagramTransport,
+    // because MediaTransport encrypts. In the future we may want to
+    // implement our own version of RtpTransport over MediaTransport, because
+    // it will give us more control over things like:
+    // - Fusing
+    // - Rtp header compression
+    // - Handling Rtcp feedback.
+    RTC_LOG(LS_INFO) << "Creating UnencryptedRtpTransport, because datagram "
+                        "transport is used.";
+    RTC_DCHECK(!rtcp_dtls_transport);
+    unencrypted_rtp_transport = CreateUnencryptedRtpTransport(
+        content_info.name, rtp_dtls_transport.get(), rtcp_dtls_transport.get());
+  } else if (config_.disable_encryption) {
+    RTC_LOG(LS_INFO)
+        << "Creating UnencryptedRtpTransport, becayse encryption is disabled.";
     unencrypted_rtp_transport = CreateUnencryptedRtpTransport(
         content_info.name, rtp_dtls_transport.get(), rtcp_dtls_transport.get());
   } else if (!content_desc->cryptos().empty()) {
     sdes_transport = CreateSdesTransport(
         content_info.name, rtp_dtls_transport.get(), rtcp_dtls_transport.get());
+    RTC_LOG(LS_INFO) << "Creating SdesTransport.";
   } else {
+    RTC_LOG(LS_INFO) << "Creating DtlsSrtpTransport.";
     dtls_srtp_transport = CreateDtlsSrtpTransport(
         content_info.name, rtp_dtls_transport.get(), rtcp_dtls_transport.get());
   }
@@ -1087,6 +1221,7 @@
           std::move(sdes_transport), std::move(dtls_srtp_transport),
           std::move(rtp_dtls_transport), std::move(rtcp_dtls_transport),
           std::move(media_transport));
+
   jsep_transport->SignalRtcpMuxActive.connect(
       this, &JsepTransportController::UpdateAggregateStates_n);
   jsep_transport->SignalMediaTransportStateChanged.connect(
@@ -1508,20 +1643,25 @@
 
 absl::optional<cricket::SessionDescription::MediaTransportSetting>
 JsepTransportController::GenerateOrGetLastMediaTransportOffer() {
-  if (media_transport_created_once_) {
+  if (media_transport_created_once_ || datagram_transport_created_once_) {
     RTC_LOG(LS_INFO) << "Not regenerating media transport for the new offer in "
                         "existing session.";
     return media_transport_offer_settings_;
   }
 
   RTC_LOG(LS_INFO) << "Generating media transport offer!";
+
+  absl::optional<std::string> transport_parameters;
+
   // Check that media transport is supposed to be used.
+  // Note that ICE is not available when media transport is created. It will
+  // only be available in 'Connect'. This may be a potential server config, if
+  // we decide to use this peer connection as a caller, not as a callee.
+  // TODO(sukhanov): Avoid code duplication with CreateMedia/MediaTransport.
   if (config_.use_media_transport_for_media ||
       config_.use_media_transport_for_data_channels) {
     RTC_DCHECK(config_.media_transport_factory != nullptr);
-    // ICE is not available when media transport is created. It will only be
-    // available in 'Connect'. This may be a potential server config, if we
-    // decide to use this peer connection as a caller, not as a callee.
+    RTC_DCHECK(!config_.use_datagram_transport);
     webrtc::MediaTransportSettings settings;
     settings.is_caller = true;
     settings.pre_shared_key = rtc::CreateRandomString(32);
@@ -1532,19 +1672,37 @@
 
     if (media_transport_or_error.ok()) {
       offer_media_transport_ = std::move(media_transport_or_error.value());
+      transport_parameters =
+          offer_media_transport_->GetTransportParametersOffer();
     } else {
       RTC_LOG(LS_INFO) << "Unable to create media transport, error="
                        << media_transport_or_error.error().message();
     }
+  } else if (config_.use_datagram_transport) {
+    webrtc::MediaTransportSettings settings;
+    settings.is_caller = true;
+    settings.pre_shared_key = rtc::CreateRandomString(32);
+    settings.event_log = config_.event_log;
+    auto datagram_transport_or_error =
+        config_.media_transport_factory->CreateDatagramTransport(
+            network_thread_, settings);
+
+    if (datagram_transport_or_error.ok()) {
+      offer_datagram_transport_ =
+          std::move(datagram_transport_or_error.value());
+      transport_parameters =
+          offer_datagram_transport_->GetTransportParametersOffer();
+    } else {
+      RTC_LOG(LS_INFO) << "Unable to create media transport, error="
+                       << datagram_transport_or_error.error().message();
+    }
   }
 
-  if (!offer_media_transport_) {
-    RTC_LOG(LS_INFO) << "Media transport doesn't exist";
+  if (!offer_media_transport_ && !offer_datagram_transport_) {
+    RTC_LOG(LS_INFO) << "Media and data transports do not exist";
     return absl::nullopt;
   }
 
-  absl::optional<std::string> transport_parameters =
-      offer_media_transport_->GetTransportParametersOffer();
   if (!transport_parameters) {
     RTC_LOG(LS_INFO) << "Media transport didn't generate the offer";
     // Media transport didn't generate the offer, and is not supposed to be
diff --git a/pc/jsep_transport_controller.h b/pc/jsep_transport_controller.h
index fff08d1..a79817c 100644
--- a/pc/jsep_transport_controller.h
+++ b/pc/jsep_transport_controller.h
@@ -19,6 +19,7 @@
 
 #include "api/candidate.h"
 #include "api/crypto/crypto_options.h"
+#include "api/media_transport_config.h"
 #include "api/media_transport_interface.h"
 #include "api/peer_connection_interface.h"
 #include "logging/rtc_event_log/rtc_event_log.h"
@@ -93,6 +94,9 @@
     // MediaTransportFactory is provided.
     bool use_rtp_media_transport = false;
 
+    // Use encrypted datagram transport to send packets.
+    bool use_datagram_transport = false;
+
     // Optional media transport factory (experimental). If provided it will be
     // used to create media_transport (as long as either
     // |use_media_transport_for_media| or
@@ -133,7 +137,16 @@
   rtc::scoped_refptr<webrtc::DtlsTransport> LookupDtlsTransportByMid(
       const std::string& mid);
 
-  MediaTransportInterface* GetMediaTransport(const std::string& mid) const;
+  MediaTransportConfig GetMediaTransportConfig(const std::string& mid) const;
+
+  MediaTransportInterface* GetMediaTransportForDataChannel(
+      const std::string& mid) const;
+
+  // TODO(sukhanov): Deprecate, return only config.
+  MediaTransportInterface* GetMediaTransport(const std::string& mid) const {
+    return GetMediaTransportConfig(mid).media_transport;
+  }
+
   MediaTransportState GetMediaTransportState(const std::string& mid) const;
 
   /*********************
@@ -190,7 +203,8 @@
   // you did not call 'GetMediaTransport' or 'MaybeCreateJsepTransport'. Once
   // Jsep transport is created, you can't change this setting.
   void SetMediaTransportSettings(bool use_media_transport_for_media,
-                                 bool use_media_transport_for_data_channels);
+                                 bool use_media_transport_for_data_channels,
+                                 bool use_datagram_transport);
 
   // If media transport is present enabled and supported,
   // when this method is called, it creates a media transport and generates its
@@ -308,6 +322,17 @@
       const cricket::ContentInfo& content_info,
       const cricket::SessionDescription& description,
       bool local);
+
+  // Creates datagram transport if config wants to use it, and a=x-mt line is
+  // present for the current media transport. Returned
+  // DatagramTransportInterface is not connected, and must be connected to ICE.
+  // You must call |GenerateOrGetLastMediaTransportOffer| on the caller before
+  // calling MaybeCreateDatagramTransport.
+  std::unique_ptr<webrtc::DatagramTransportInterface>
+  MaybeCreateDatagramTransport(const cricket::ContentInfo& content_info,
+                               const cricket::SessionDescription& description,
+                               bool local);
+
   void MaybeDestroyJsepTransport(const std::string& mid);
   void DestroyAllJsepTransports_n();
 
@@ -320,7 +345,8 @@
       bool local);
 
   std::unique_ptr<cricket::DtlsTransportInternal> CreateDtlsTransport(
-      std::unique_ptr<cricket::IceTransportInternal> ice);
+      std::unique_ptr<cricket::IceTransportInternal> ice,
+      std::unique_ptr<DatagramTransportInterface> datagram_transport);
   std::unique_ptr<cricket::IceTransportInternal> CreateIceTransport(
       const std::string transport_name,
       bool rtcp);
@@ -399,6 +425,22 @@
   absl::optional<cricket::SessionDescription::MediaTransportSetting>
       media_transport_offer_settings_;
 
+  // Early on in the call we don't know if datagram transport is going to be
+  // used, but we need to get the server-supported parameters to add to an SDP.
+  // This server datagram transport will be promoted to the used datagram
+  // transport after the local description is set, and the ownership will be
+  // transferred to the actual JsepTransport. This "offer" datagram transport is
+  // not created if it's done on the party that provides answer. This offer
+  // datagram transport is only created once at the beginning of the connection,
+  // and never again.
+  std::unique_ptr<DatagramTransportInterface> offer_datagram_transport_ =
+      nullptr;
+
+  // Contains the offer of the |offer_datagram_transport_|, in case if it needs
+  // to be repeated.
+  absl::optional<cricket::SessionDescription::MediaTransportSetting>
+      datagram_transport_offer_settings_;
+
   // When the new offer is regenerated (due to upgrade), we don't want to
   // re-create media transport. New streams might be created; but media
   // transport stays the same. This flag prevents re-creation of the transport
@@ -411,6 +453,7 @@
   // recreate the Offer (e.g. after adding streams in Plan B), and so we want to
   // prevent recreation of the media transport when that happens.
   bool media_transport_created_once_ = false;
+  bool datagram_transport_created_once_ = false;
 
   const cricket::SessionDescription* local_desc_ = nullptr;
   const cricket::SessionDescription* remote_desc_ = nullptr;
diff --git a/pc/jsep_transport_controller_unittest.cc b/pc/jsep_transport_controller_unittest.cc
index c0927b9d..346168d 100644
--- a/pc/jsep_transport_controller_unittest.cc
+++ b/pc/jsep_transport_controller_unittest.cc
@@ -442,7 +442,7 @@
                   .ok());
 
   FakeMediaTransport* media_transport = static_cast<FakeMediaTransport*>(
-      transport_controller_->GetMediaTransport(kAudioMid1));
+      transport_controller_->GetMediaTransportForDataChannel(kAudioMid1));
 
   ASSERT_NE(nullptr, media_transport);
 
@@ -451,7 +451,8 @@
   EXPECT_TRUE(media_transport->pre_shared_key().has_value());
 
   // Return nullptr for non-existing mids.
-  EXPECT_EQ(nullptr, transport_controller_->GetMediaTransport(kVideoMid2));
+  EXPECT_EQ(nullptr,
+            transport_controller_->GetMediaTransportForDataChannel(kVideoMid2));
 
   EXPECT_EQ(cricket::ICE_CANDIDATE_COMPONENT_RTP,
             transport_controller_->GetDtlsTransport(kAudioMid1)->component())
@@ -563,8 +564,6 @@
   EXPECT_EQ(absl::nullopt, media_transport->settings().pre_shared_key);
   EXPECT_TRUE(media_transport->is_connected());
 
-  EXPECT_EQ("fake-remote-settings",
-            media_transport->remote_transport_parameters());
   // Return nullptr for non-existing mids.
   EXPECT_EQ(nullptr, transport_controller_->GetMediaTransport(kVideoMid2));
 
diff --git a/pc/peer_connection.cc b/pc/peer_connection.cc
index ca66a09..14c8683 100644
--- a/pc/peer_connection.cc
+++ b/pc/peer_connection.cc
@@ -764,6 +764,7 @@
     bool active_reset_srtp_params;
     bool use_media_transport;
     bool use_media_transport_for_data_channels;
+    bool use_datagram_transport;
     absl::optional<CryptoOptions> crypto_options;
     bool offer_extmap_allow_mixed;
   };
@@ -822,6 +823,7 @@
          use_media_transport == o.use_media_transport &&
          use_media_transport_for_data_channels ==
              o.use_media_transport_for_data_channels &&
+         use_datagram_transport == o.use_datagram_transport &&
          crypto_options == o.crypto_options &&
          offer_extmap_allow_mixed == o.offer_extmap_allow_mixed;
 }
@@ -1021,7 +1023,8 @@
 #endif
   config.active_reset_srtp_params = configuration.active_reset_srtp_params;
 
-  if (configuration.use_media_transport ||
+  if (configuration.use_datagram_transport ||
+      configuration.use_media_transport ||
       configuration.use_media_transport_for_data_channels) {
     if (!factory_->media_transport_factory()) {
       RTC_DCHECK(false)
@@ -1051,6 +1054,7 @@
     config.use_media_transport_for_media = configuration.use_media_transport;
     config.use_media_transport_for_data_channels =
         configuration.use_media_transport_for_data_channels;
+    config.use_datagram_transport = configuration.use_datagram_transport;
     config.media_transport_factory = factory_->media_transport_factory();
   }
 
@@ -3412,8 +3416,23 @@
     return SafeSetError(RTCErrorType::INVALID_MODIFICATION, error);
   }
 
+  if (local_description() && configuration.use_datagram_transport !=
+                                 configuration_.use_datagram_transport) {
+    RTC_LOG(LS_ERROR) << "Can't change use_datagram_transport "
+                         "after calling SetLocalDescription.";
+    return SafeSetError(RTCErrorType::INVALID_MODIFICATION, error);
+  }
+
+  if (remote_description() && configuration.use_datagram_transport !=
+                                  configuration_.use_datagram_transport) {
+    RTC_LOG(LS_ERROR) << "Can't change use_datagram_transport "
+                         "after calling SetRemoteDescription.";
+    return SafeSetError(RTCErrorType::INVALID_MODIFICATION, error);
+  }
+
   if (configuration.use_media_transport_for_data_channels ||
-      configuration.use_media_transport) {
+      configuration.use_media_transport ||
+      configuration.use_datagram_transport) {
     RTC_CHECK(configuration.bundle_policy == kBundlePolicyMaxBundle)
         << "Media transport requires MaxBundle policy.";
   }
@@ -3506,7 +3525,8 @@
   transport_controller_->SetIceConfig(ParseIceConfig(modified_config));
   transport_controller_->SetMediaTransportSettings(
       modified_config.use_media_transport,
-      modified_config.use_media_transport_for_data_channels);
+      modified_config.use_media_transport_for_data_channels,
+      modified_config.use_datagram_transport);
 
   if (configuration_.active_reset_srtp_params !=
       modified_config.active_reset_srtp_params) {
@@ -6317,15 +6337,13 @@
 cricket::VoiceChannel* PeerConnection::CreateVoiceChannel(
     const std::string& mid) {
   RtpTransportInternal* rtp_transport = GetRtpTransport(mid);
-  MediaTransportInterface* media_transport = nullptr;
-  if (configuration_.use_media_transport) {
-    media_transport = GetMediaTransport(mid);
-  }
+  MediaTransportConfig media_transport_config =
+      transport_controller_->GetMediaTransportConfig(mid);
 
   cricket::VoiceChannel* voice_channel = channel_manager()->CreateVoiceChannel(
       call_ptr_, configuration_.media_config, rtp_transport,
-      MediaTransportConfig(media_transport), signaling_thread(), mid,
-      SrtpRequired(), GetCryptoOptions(), &ssrc_generator_, audio_options_);
+      media_transport_config, signaling_thread(), mid, SrtpRequired(),
+      GetCryptoOptions(), &ssrc_generator_, audio_options_);
   if (!voice_channel) {
     return nullptr;
   }
@@ -6342,15 +6360,13 @@
 cricket::VideoChannel* PeerConnection::CreateVideoChannel(
     const std::string& mid) {
   RtpTransportInternal* rtp_transport = GetRtpTransport(mid);
-  MediaTransportInterface* media_transport = nullptr;
-  if (configuration_.use_media_transport) {
-    media_transport = GetMediaTransport(mid);
-  }
+  MediaTransportConfig media_transport_config =
+      transport_controller_->GetMediaTransportConfig(mid);
 
   cricket::VideoChannel* video_channel = channel_manager()->CreateVideoChannel(
       call_ptr_, configuration_.media_config, rtp_transport,
-      MediaTransportConfig(media_transport), signaling_thread(), mid,
-      SrtpRequired(), GetCryptoOptions(), &ssrc_generator_, video_options_,
+      media_transport_config, signaling_thread(), mid, SrtpRequired(),
+      GetCryptoOptions(), &ssrc_generator_, video_options_,
       video_bitrate_allocator_factory_.get());
   if (!video_channel) {
     return nullptr;
@@ -6529,7 +6545,8 @@
 
 bool PeerConnection::SetupMediaTransportForDataChannels_n(
     const std::string& mid) {
-  media_transport_ = transport_controller_->GetMediaTransport(mid);
+  media_transport_ =
+      transport_controller_->GetMediaTransportForDataChannel(mid);
   if (!media_transport_) {
     RTC_LOG(LS_ERROR)
         << "Media transport is not available for data channels, mid=" << mid;
@@ -6886,8 +6903,9 @@
 }
 
 bool PeerConnection::SrtpRequired() const {
-  return dtls_enabled_ ||
-         webrtc_session_desc_factory_->SdesPolicy() == cricket::SEC_REQUIRED;
+  return !configuration_.use_datagram_transport &&
+         (dtls_enabled_ ||
+          webrtc_session_desc_factory_->SdesPolicy() == cricket::SEC_REQUIRED);
 }
 
 void PeerConnection::OnTransportControllerGatheringState(
diff --git a/pc/peer_connection.h b/pc/peer_connection.h
index d9c625c..7287b7c 100644
--- a/pc/peer_connection.h
+++ b/pc/peer_connection.h
@@ -1079,22 +1079,6 @@
     return rtp_transport;
   }
 
-  // Returns media transport, if PeerConnection was created with configuration
-  // to use media transport. Otherwise returns nullptr.
-  MediaTransportInterface* GetMediaTransport(const std::string& mid)
-      RTC_RUN_ON(signaling_thread()) {
-    auto media_transport = transport_controller_->GetMediaTransport(mid);
-    RTC_DCHECK((configuration_.use_media_transport ||
-                configuration_.use_media_transport_for_data_channels) ==
-               (media_transport != nullptr))
-        << "configuration_.use_media_transport="
-        << configuration_.use_media_transport
-        << ", configuration_.use_media_transport_for_data_channels="
-        << configuration_.use_media_transport_for_data_channels
-        << ", (media_transport != nullptr)=" << (media_transport != nullptr);
-    return media_transport;
-  }
-
   void UpdateNegotiationNeeded();
   bool CheckIfNegotiationIsNeeded();