diff --git a/pc/jsep_transport_controller.cc b/pc/jsep_transport_controller.cc
index 542dae4..0ded1de 100644
--- a/pc/jsep_transport_controller.cc
+++ b/pc/jsep_transport_controller.cc
@@ -105,10 +105,8 @@
 JsepTransportController::~JsepTransportController() {
   // Channel destructors may try to send packets, so this needs to happen on
   // the network thread.
-  network_thread_->Invoke<void>(RTC_FROM_HERE, [this] {
-    RTC_DCHECK_RUN_ON(network_thread_);
-    DestroyAllJsepTransports_n();
-  });
+  RTC_DCHECK_RUN_ON(network_thread_);
+  DestroyAllJsepTransports_n();
 }
 
 RTCError JsepTransportController::SetLocalDescription(
@@ -145,6 +143,7 @@
 
 RtpTransportInternal* JsepTransportController::GetRtpTransport(
     const std::string& mid) const {
+  RTC_DCHECK_RUN_ON(network_thread_);
   auto jsep_transport = GetJsepTransportForMid(mid);
   if (!jsep_transport) {
     return nullptr;
@@ -154,6 +153,7 @@
 
 DataChannelTransportInterface* JsepTransportController::GetDataChannelTransport(
     const std::string& mid) const {
+  RTC_DCHECK_RUN_ON(network_thread_);
   auto jsep_transport = GetJsepTransportForMid(mid);
   if (!jsep_transport) {
     return nullptr;
@@ -163,6 +163,7 @@
 
 cricket::DtlsTransportInternal* JsepTransportController::GetDtlsTransport(
     const std::string& mid) {
+  RTC_DCHECK_RUN_ON(network_thread_);
   auto jsep_transport = GetJsepTransportForMid(mid);
   if (!jsep_transport) {
     return nullptr;
@@ -172,6 +173,7 @@
 
 const cricket::DtlsTransportInternal*
 JsepTransportController::GetRtcpDtlsTransport(const std::string& mid) const {
+  RTC_DCHECK_RUN_ON(network_thread_);
   auto jsep_transport = GetJsepTransportForMid(mid);
   if (!jsep_transport) {
     return nullptr;
@@ -181,6 +183,7 @@
 
 rtc::scoped_refptr<webrtc::DtlsTransport>
 JsepTransportController::LookupDtlsTransportByMid(const std::string& mid) {
+  RTC_DCHECK_RUN_ON(network_thread_);
   auto jsep_transport = GetJsepTransportForMid(mid);
   if (!jsep_transport) {
     return nullptr;
@@ -190,6 +193,7 @@
 
 rtc::scoped_refptr<SctpTransport> JsepTransportController::GetSctpTransport(
     const std::string& mid) const {
+  RTC_DCHECK_RUN_ON(network_thread_);
   auto jsep_transport = GetJsepTransportForMid(mid);
   if (!jsep_transport) {
     return nullptr;
@@ -236,11 +240,16 @@
 
 absl::optional<rtc::SSLRole> JsepTransportController::GetDtlsRole(
     const std::string& mid) const {
+  // TODO(tommi): Remove this hop. Currently it's called from the signaling
+  // thread during negotiations, potentially multiple times.
+  // WebRtcSessionDescriptionFactory::InternalCreateAnswer is one example.
   if (!network_thread_->IsCurrent()) {
     return network_thread_->Invoke<absl::optional<rtc::SSLRole>>(
         RTC_FROM_HERE, [&] { return GetDtlsRole(mid); });
   }
 
+  RTC_DCHECK_RUN_ON(network_thread_);
+
   const cricket::JsepTransport* t = GetJsepTransportForMid(mid);
   if (!t) {
     return absl::optional<rtc::SSLRole>();
@@ -846,24 +855,34 @@
 bool JsepTransportController::SetTransportForMid(
     const std::string& mid,
     cricket::JsepTransport* jsep_transport) {
-  RTC_DCHECK(jsep_transport);
-  if (mid_to_transport_[mid] == jsep_transport) {
-    return true;
-  }
   RTC_DCHECK_RUN_ON(network_thread_);
+  RTC_DCHECK(jsep_transport);
+
+  auto it = mid_to_transport_.find(mid);
+  if (it != mid_to_transport_.end() && it->second == jsep_transport)
+    return true;
+
   pending_mids_.push_back(mid);
-  mid_to_transport_[mid] = jsep_transport;
+
+  if (it == mid_to_transport_.end()) {
+    mid_to_transport_.insert(std::make_pair(mid, jsep_transport));
+  } else {
+    it->second = jsep_transport;
+  }
+
   return config_.transport_observer->OnTransportChanged(
       mid, jsep_transport->rtp_transport(), jsep_transport->RtpDtlsTransport(),
       jsep_transport->data_channel_transport());
 }
 
 void JsepTransportController::RemoveTransportForMid(const std::string& mid) {
+  RTC_DCHECK_RUN_ON(network_thread_);
   bool ret = config_.transport_observer->OnTransportChanged(mid, nullptr,
                                                             nullptr, nullptr);
   // Calling OnTransportChanged with nullptr should always succeed, since it is
   // only expected to fail when adding media to a transport (not removing).
   RTC_DCHECK(ret);
+
   mid_to_transport_.erase(mid);
 }
 
diff --git a/pc/jsep_transport_controller.h b/pc/jsep_transport_controller.h
index 506a418..59d66a2 100644
--- a/pc/jsep_transport_controller.h
+++ b/pc/jsep_transport_controller.h
@@ -363,8 +363,9 @@
   // transports are bundled on (In current implementation, it is the first
   // content in the BUNDLE group).
   const cricket::JsepTransport* GetJsepTransportForMid(
-      const std::string& mid) const;
-  cricket::JsepTransport* GetJsepTransportForMid(const std::string& mid);
+      const std::string& mid) const RTC_RUN_ON(network_thread_);
+  cricket::JsepTransport* GetJsepTransportForMid(const std::string& mid)
+      RTC_RUN_ON(network_thread_);
 
   // Get the JsepTransport without considering the BUNDLE group. Return nullptr
   // if the JsepTransport is destroyed.
@@ -460,7 +461,8 @@
       jsep_transports_by_name_ RTC_GUARDED_BY(network_thread_);
   // This keeps track of the mapping between media section
   // (BaseChannel/SctpTransport) and the JsepTransport underneath.
-  std::map<std::string, cricket::JsepTransport*> mid_to_transport_;
+  std::map<std::string, cricket::JsepTransport*> mid_to_transport_
+      RTC_GUARDED_BY(network_thread_);
   // Keep track of mids that have been mapped to transports. Used for rollback.
   std::vector<std::string> pending_mids_ RTC_GUARDED_BY(network_thread_);
   // Aggregate states for Transports.
diff --git a/pc/jsep_transport_controller_unittest.cc b/pc/jsep_transport_controller_unittest.cc
index 5361f90..9efa205 100644
--- a/pc/jsep_transport_controller_unittest.cc
+++ b/pc/jsep_transport_controller_unittest.cc
@@ -904,6 +904,9 @@
   EXPECT_EQ(2, candidates_signal_count_);
 
   EXPECT_TRUE(!signaled_on_non_signaling_thread_);
+
+  network_thread_->Invoke<void>(RTC_FROM_HERE,
+                                [&] { transport_controller_.reset(); });
 }
 
 // Test that if the TransportController was created with the
diff --git a/pc/peer_connection.cc b/pc/peer_connection.cc
index 406c44d..087cffc 100644
--- a/pc/peer_connection.cc
+++ b/pc/peer_connection.cc
@@ -489,12 +489,17 @@
 
     sdp_handler_->ResetSessionDescFactory();
   }
-  transport_controller_.reset();
 
-  // port_allocator_ lives on the network thread and should be destroyed there.
+  // port_allocator_ and transport_controller_ live on the network thread and
+  // should be destroyed there.
   network_thread()->Invoke<void>(RTC_FROM_HERE, [this] {
     RTC_DCHECK_RUN_ON(network_thread());
+    transport_controller_.reset();
     port_allocator_.reset();
+    if (network_thread_safety_) {
+      network_thread_safety_->SetNotAlive();
+      network_thread_safety_ = nullptr;
+    }
   });
   // call_ and event_log_ must be destroyed on the worker thread.
   worker_thread()->Invoke<void>(RTC_FROM_HERE, [this] {
@@ -527,13 +532,15 @@
   }
 
   // The port allocator lives on the network thread and should be initialized
-  // there.
+  // there. Also set up the task safety flag for canceling pending tasks on
+  // the network thread when closing.
   // TODO(bugs.webrtc.org/12427): See if we can piggyback on this call and
   // initialize all the |transport_controller_->Subscribe*| calls below on the
   // network thread via this invoke.
   const auto pa_result =
       network_thread()->Invoke<InitializePortAllocatorResult>(
           RTC_FROM_HERE, [this, &stun_servers, &turn_servers, &configuration] {
+            network_thread_safety_ = PendingTaskSafetyFlag::Create();
             return InitializePortAllocator_n(stun_servers, turn_servers,
                                              configuration);
           });
@@ -832,6 +839,16 @@
   return AddTransceiver(track, RtpTransceiverInit());
 }
 
+RtpTransportInternal* PeerConnection::GetRtpTransport(const std::string& mid) {
+  RTC_DCHECK_RUN_ON(signaling_thread());
+  return network_thread()->Invoke<RtpTransportInternal*>(
+      RTC_FROM_HERE, [this, &mid] {
+        auto rtp_transport = transport_controller_->GetRtpTransport(mid);
+        RTC_DCHECK(rtp_transport);
+        return rtp_transport;
+      });
+}
+
 RTCErrorOr<rtc::scoped_refptr<RtpTransceiverInterface>>
 PeerConnection::AddTransceiver(
     rtc::scoped_refptr<MediaStreamTrackInterface> track,
@@ -1588,11 +1605,11 @@
 
 rtc::scoped_refptr<SctpTransportInterface> PeerConnection::GetSctpTransport()
     const {
-  RTC_DCHECK_RUN_ON(signaling_thread());
-  if (!sctp_mid_s_) {
+  RTC_DCHECK_RUN_ON(network_thread());
+  if (!sctp_mid_n_)
     return nullptr;
-  }
-  return transport_controller_->GetSctpTransport(*sctp_mid_s_);
+
+  return transport_controller_->GetSctpTransport(*sctp_mid_n_);
 }
 
 const SessionDescriptionInterface* PeerConnection::local_description() const {
@@ -1673,11 +1690,16 @@
   // WebRTC session description factory, the session description factory would
   // call the transport controller.
   sdp_handler_->ResetSessionDescFactory();
-  transport_controller_.reset();
   rtp_manager_->Close();
 
-  network_thread()->Invoke<void>(
-      RTC_FROM_HERE, [this] { port_allocator_->DiscardCandidatePool(); });
+  network_thread()->Invoke<void>(RTC_FROM_HERE, [this] {
+    transport_controller_.reset();
+    port_allocator_->DiscardCandidatePool();
+    if (network_thread_safety_) {
+      network_thread_safety_->SetNotAlive();
+      network_thread_safety_ = nullptr;
+    }
+  });
 
   worker_thread()->Invoke<void>(RTC_FROM_HERE, [this] {
     RTC_DCHECK_RUN_ON(worker_thread());
@@ -1831,6 +1853,17 @@
   }
 }
 
+void PeerConnection::SetSctpDataMid(const std::string& mid) {
+  RTC_DCHECK_RUN_ON(signaling_thread());
+  sctp_mid_s_ = mid;
+}
+
+void PeerConnection::ResetSctpDataMid() {
+  RTC_DCHECK_RUN_ON(signaling_thread());
+  sctp_mid_s_.reset();
+  sctp_transport_name_s_.clear();
+}
+
 void PeerConnection::OnSctpDataChannelClosed(DataChannelInterface* channel) {
   // Since data_channel_controller doesn't do signals, this
   // signal is relayed here.
@@ -2044,13 +2077,8 @@
 
 absl::optional<std::string> PeerConnection::sctp_transport_name() const {
   RTC_DCHECK_RUN_ON(signaling_thread());
-  if (sctp_mid_s_ && transport_controller_) {
-    auto dtls_transport = transport_controller_->GetDtlsTransport(*sctp_mid_s_);
-    if (dtls_transport) {
-      return dtls_transport->transport_name();
-    }
-    return absl::optional<std::string>();
-  }
+  if (sctp_mid_s_ && transport_controller_)
+    return sctp_transport_name_s_;
   return absl::optional<std::string>();
 }
 
@@ -2289,6 +2317,15 @@
   data_channel_controller_.set_data_channel_transport(transport);
   data_channel_controller_.SetupDataChannelTransport_n();
   sctp_mid_n_ = mid;
+  auto dtls_transport = transport_controller_->GetDtlsTransport(mid);
+  if (dtls_transport) {
+    signaling_thread()->PostTask(
+        ToQueuedTask(signaling_thread_safety_.flag(),
+                     [this, name = dtls_transport->transport_name()] {
+                       RTC_DCHECK_RUN_ON(signaling_thread());
+                       sctp_transport_name_s_ = std::move(name);
+                     }));
+  }
 
   // Note: setting the data sink and checking initial state must be done last,
   // after setting up the data channel.  Setting the data sink may trigger
@@ -2633,9 +2670,19 @@
   if (base_channel) {
     ret = base_channel->SetRtpTransport(rtp_transport);
   }
+
   if (mid == sctp_mid_n_) {
     data_channel_controller_.OnTransportChanged(data_channel_transport);
+    if (dtls_transport) {
+      signaling_thread()->PostTask(ToQueuedTask(
+          signaling_thread_safety_.flag(),
+          [this, name = dtls_transport->internal()->transport_name()] {
+            RTC_DCHECK_RUN_ON(signaling_thread());
+            sctp_transport_name_s_ = std::move(name);
+          }));
+    }
   }
+
   return ret;
 }
 
@@ -2645,6 +2692,23 @@
   return observer_;
 }
 
+void PeerConnection::StartSctpTransport(int local_port,
+                                        int remote_port,
+                                        int max_message_size) {
+  RTC_DCHECK_RUN_ON(signaling_thread());
+  if (!sctp_mid_s_)
+    return;
+
+  network_thread()->PostTask(ToQueuedTask(
+      network_thread_safety_,
+      [this, mid = *sctp_mid_s_, local_port, remote_port, max_message_size] {
+        rtc::scoped_refptr<SctpTransport> sctp_transport =
+            transport_controller()->GetSctpTransport(mid);
+        if (sctp_transport)
+          sctp_transport->Start(local_port, remote_port, max_message_size);
+      }));
+}
+
 CryptoOptions PeerConnection::GetCryptoOptions() {
   RTC_DCHECK_RUN_ON(signaling_thread());
   // TODO(bugs.webrtc.org/9891) - Remove PeerConnectionFactory::CryptoOptions
diff --git a/pc/peer_connection.h b/pc/peer_connection.h
index 4bab90a..92e33d2 100644
--- a/pc/peer_connection.h
+++ b/pc/peer_connection.h
@@ -404,14 +404,15 @@
   // channels are configured this will return nullopt.
   absl::optional<std::string> GetDataMid() const;
 
-  void SetSctpDataMid(const std::string& mid) {
-    RTC_DCHECK_RUN_ON(signaling_thread());
-    sctp_mid_s_ = mid;
-  }
-  void ResetSctpDataMid() {
-    RTC_DCHECK_RUN_ON(signaling_thread());
-    sctp_mid_s_.reset();
-  }
+  void SetSctpDataMid(const std::string& mid);
+
+  void ResetSctpDataMid();
+
+  // Asynchronously calls SctpTransport::Start() on the network thread for
+  // |sctp_mid()| if set. Called as part of setting the local description.
+  void StartSctpTransport(int local_port,
+                          int remote_port,
+                          int max_message_size);
 
   // Returns the CryptoOptions for this PeerConnection. This will always
   // return the RTCConfiguration.crypto_options if set and will only default
@@ -427,12 +428,7 @@
       bool fire_callback = true);
 
   // Returns rtp transport, result can not be nullptr.
-  RtpTransportInternal* GetRtpTransport(const std::string& mid) {
-    RTC_DCHECK_RUN_ON(signaling_thread());
-    auto rtp_transport = transport_controller_->GetRtpTransport(mid);
-    RTC_DCHECK(rtp_transport);
-    return rtp_transport;
-  }
+  RtpTransportInternal* GetRtpTransport(const std::string& mid);
 
   // Returns true if SRTP (either using DTLS-SRTP or SDES) is required by
   // this session.
@@ -648,6 +644,8 @@
   // The unique_ptr belongs to the worker thread, but the Call object manages
   // its own thread safety.
   std::unique_ptr<Call> call_ RTC_GUARDED_BY(worker_thread());
+  ScopedTaskSafety signaling_thread_safety_;
+  rtc::scoped_refptr<PendingTaskSafetyFlag> network_thread_safety_;
   std::unique_ptr<ScopedTaskSafety> call_safety_
       RTC_GUARDED_BY(worker_thread());
 
@@ -677,6 +675,7 @@
   // thread, but applied first on the networking thread via an invoke().
   absl::optional<std::string> sctp_mid_s_ RTC_GUARDED_BY(signaling_thread());
   absl::optional<std::string> sctp_mid_n_ RTC_GUARDED_BY(network_thread());
+  std::string sctp_transport_name_s_ RTC_GUARDED_BY(signaling_thread());
 
   // The machinery for handling offers and answers. Const after initialization.
   std::unique_ptr<SdpOfferAnswerHandler> sdp_handler_
diff --git a/pc/peer_connection_factory.cc b/pc/peer_connection_factory.cc
index c65b2f5..a8d64fa 100644
--- a/pc/peer_connection_factory.cc
+++ b/pc/peer_connection_factory.cc
@@ -265,8 +265,15 @@
   if (!result.ok()) {
     return result.MoveError();
   }
+  // We configure the proxy with a pointer to the network thread for methods
+  // that need to be invoked there rather than on the signaling thread.
+  // Internally, the proxy object has a member variable named |worker_thread_|
+  // which will point to the network thread (and not the factory's
+  // worker_thread()).  All such methods have thread checks though, so the code
+  // should still be clear (outside of macro expansion).
   rtc::scoped_refptr<PeerConnectionInterface> result_proxy =
-      PeerConnectionProxy::Create(signaling_thread(), result.MoveValue());
+      PeerConnectionProxy::Create(signaling_thread(), network_thread(),
+                                  result.MoveValue());
   return result_proxy;
 }
 
diff --git a/pc/peer_connection_integrationtest.cc b/pc/peer_connection_integrationtest.cc
index 4a25619..4ed92ad 100644
--- a/pc/peer_connection_integrationtest.cc
+++ b/pc/peer_connection_integrationtest.cc
@@ -5969,9 +5969,11 @@
   callee()->AddAudioVideoTracks();
   caller()->CreateAndSetAndSignalOffer();
   ASSERT_TRUE_WAIT(SignalingStateStable(), kDefaultTimeout);
-  ASSERT_EQ_WAIT(SctpTransportState::kConnected,
-                 caller()->pc()->GetSctpTransport()->Information().state(),
-                 kDefaultTimeout);
+  network_thread()->Invoke<void>(RTC_FROM_HERE, [this] {
+    ASSERT_EQ_WAIT(SctpTransportState::kConnected,
+                   caller()->pc()->GetSctpTransport()->Information().state(),
+                   kDefaultTimeout);
+  });
   ASSERT_TRUE_WAIT(callee()->data_channel(), kDefaultTimeout);
   ASSERT_TRUE_WAIT(callee()->data_observer()->IsOpen(), kDefaultTimeout);
 }
diff --git a/pc/sctp_transport.cc b/pc/sctp_transport.cc
index f3e40b8..bb579af 100644
--- a/pc/sctp_transport.cc
+++ b/pc/sctp_transport.cc
@@ -45,7 +45,15 @@
 }
 
 SctpTransportInformation SctpTransport::Information() const {
-  MutexLock lock(&lock_);
+  // TODO(tommi): Update PeerConnection::GetSctpTransport to hand out a proxy
+  // to the transport so that we can be sure that methods get called on the
+  // expected thread. Chromium currently calls this method from
+  // TransceiverStateSurfacer.
+  if (!owner_thread_->IsCurrent()) {
+    return owner_thread_->Invoke<SctpTransportInformation>(
+        RTC_FROM_HERE, [this] { return Information(); });
+  }
+  RTC_DCHECK_RUN_ON(owner_thread_);
   return info_;
 }
 
@@ -71,103 +79,78 @@
 void SctpTransport::Clear() {
   RTC_DCHECK_RUN_ON(owner_thread_);
   RTC_DCHECK(internal());
-  {
-    MutexLock lock(&lock_);
-    // Note that we delete internal_sctp_transport_, but
-    // only drop the reference to dtls_transport_.
-    dtls_transport_ = nullptr;
-    internal_sctp_transport_ = nullptr;
-  }
+  // Note that we delete internal_sctp_transport_, but
+  // only drop the reference to dtls_transport_.
+  dtls_transport_ = nullptr;
+  internal_sctp_transport_ = nullptr;
   UpdateInformation(SctpTransportState::kClosed);
 }
 
 void SctpTransport::SetDtlsTransport(
     rtc::scoped_refptr<DtlsTransport> transport) {
   RTC_DCHECK_RUN_ON(owner_thread_);
-  SctpTransportState next_state;
-  {
-    MutexLock lock(&lock_);
-    next_state = info_.state();
-    dtls_transport_ = transport;
-    if (internal_sctp_transport_) {
-      if (transport) {
-        internal_sctp_transport_->SetDtlsTransport(transport->internal());
-        transport->internal()->SignalDtlsState.connect(
-            this, &SctpTransport::OnDtlsStateChange);
-        if (info_.state() == SctpTransportState::kNew) {
-          next_state = SctpTransportState::kConnecting;
-        }
-      } else {
-        internal_sctp_transport_->SetDtlsTransport(nullptr);
+  SctpTransportState next_state = info_.state();
+  dtls_transport_ = transport;
+  if (internal_sctp_transport_) {
+    if (transport) {
+      internal_sctp_transport_->SetDtlsTransport(transport->internal());
+      transport->internal()->SignalDtlsState.connect(
+          this, &SctpTransport::OnDtlsStateChange);
+      if (info_.state() == SctpTransportState::kNew) {
+        next_state = SctpTransportState::kConnecting;
       }
+    } else {
+      internal_sctp_transport_->SetDtlsTransport(nullptr);
     }
   }
+
   UpdateInformation(next_state);
 }
 
 void SctpTransport::Start(int local_port,
                           int remote_port,
                           int max_message_size) {
-  {
-    MutexLock lock(&lock_);
-    // Record max message size on calling thread.
-    info_ = SctpTransportInformation(info_.state(), info_.dtls_transport(),
-                                     max_message_size, info_.MaxChannels());
-  }
-  if (owner_thread_->IsCurrent()) {
-    if (!internal()->Start(local_port, remote_port, max_message_size)) {
-      RTC_LOG(LS_ERROR) << "Failed to push down SCTP parameters, closing.";
-      UpdateInformation(SctpTransportState::kClosed);
-    }
-  } else {
-    owner_thread_->Invoke<void>(
-        RTC_FROM_HERE, [this, local_port, remote_port, max_message_size] {
-          Start(local_port, remote_port, max_message_size);
-        });
+  RTC_DCHECK_RUN_ON(owner_thread_);
+  info_ = SctpTransportInformation(info_.state(), info_.dtls_transport(),
+                                   max_message_size, info_.MaxChannels());
+
+  if (!internal()->Start(local_port, remote_port, max_message_size)) {
+    RTC_LOG(LS_ERROR) << "Failed to push down SCTP parameters, closing.";
+    UpdateInformation(SctpTransportState::kClosed);
   }
 }
 
 void SctpTransport::UpdateInformation(SctpTransportState state) {
   RTC_DCHECK_RUN_ON(owner_thread_);
-  bool must_send_update;
-  SctpTransportInformation info_copy(SctpTransportState::kNew);
-  {
-    MutexLock lock(&lock_);
-    must_send_update = (state != info_.state());
-    // TODO(https://bugs.webrtc.org/10358): Update max channels from internal
-    // SCTP transport when available.
-    if (internal_sctp_transport_) {
-      info_ = SctpTransportInformation(
-          state, dtls_transport_, info_.MaxMessageSize(), info_.MaxChannels());
-    } else {
-      info_ = SctpTransportInformation(
-          state, dtls_transport_, info_.MaxMessageSize(), info_.MaxChannels());
-    }
-    if (observer_ && must_send_update) {
-      info_copy = info_;
-    }
+  bool must_send_update = (state != info_.state());
+  // TODO(https://bugs.webrtc.org/10358): Update max channels from internal
+  // SCTP transport when available.
+  if (internal_sctp_transport_) {
+    info_ = SctpTransportInformation(
+        state, dtls_transport_, info_.MaxMessageSize(), info_.MaxChannels());
+  } else {
+    info_ = SctpTransportInformation(
+        state, dtls_transport_, info_.MaxMessageSize(), info_.MaxChannels());
   }
-  // We call the observer without holding the lock.
+
   if (observer_ && must_send_update) {
-    observer_->OnStateChange(info_copy);
+    observer_->OnStateChange(info_);
   }
 }
 
 void SctpTransport::OnAssociationChangeCommunicationUp() {
   RTC_DCHECK_RUN_ON(owner_thread_);
-  {
-    MutexLock lock(&lock_);
-    RTC_DCHECK(internal_sctp_transport_);
-    if (internal_sctp_transport_->max_outbound_streams() &&
-        internal_sctp_transport_->max_inbound_streams()) {
-      int max_channels =
-          std::min(*(internal_sctp_transport_->max_outbound_streams()),
-                   *(internal_sctp_transport_->max_inbound_streams()));
-      // Record max channels.
-      info_ = SctpTransportInformation(info_.state(), info_.dtls_transport(),
-                                       info_.MaxMessageSize(), max_channels);
-    }
+  RTC_DCHECK(internal_sctp_transport_);
+  if (internal_sctp_transport_->max_outbound_streams() &&
+      internal_sctp_transport_->max_inbound_streams()) {
+    int max_channels =
+        std::min(*(internal_sctp_transport_->max_outbound_streams()),
+                 *(internal_sctp_transport_->max_inbound_streams()));
+    // Record max channels.
+    info_ = SctpTransportInformation(info_.state(), info_.dtls_transport(),
+                                     info_.MaxMessageSize(), max_channels);
   }
+
   UpdateInformation(SctpTransportState::kConnected);
 }
 
diff --git a/pc/sctp_transport.h b/pc/sctp_transport.h
index d916a00..4bb4274 100644
--- a/pc/sctp_transport.h
+++ b/pc/sctp_transport.h
@@ -20,7 +20,6 @@
 #include "media/sctp/sctp_transport_internal.h"
 #include "p2p/base/dtls_transport_internal.h"
 #include "pc/dtls_transport.h"
-#include "rtc_base/synchronization/mutex.h"
 #include "rtc_base/third_party/sigslot/sigslot.h"
 #include "rtc_base/thread.h"
 #include "rtc_base/thread_annotations.h"
@@ -54,12 +53,12 @@
   // internal() to be functions on the webrtc::SctpTransport interface,
   // and make the internal() function private.
   cricket::SctpTransportInternal* internal() {
-    MutexLock lock(&lock_);
+    RTC_DCHECK_RUN_ON(owner_thread_);
     return internal_sctp_transport_.get();
   }
 
   const cricket::SctpTransportInternal* internal() const {
-    MutexLock lock(&lock_);
+    RTC_DCHECK_RUN_ON(owner_thread_);
     return internal_sctp_transport_.get();
   }
 
@@ -75,15 +74,12 @@
   void OnDtlsStateChange(cricket::DtlsTransportInternal* transport,
                          cricket::DtlsTransportState state);
 
-  // Note - owner_thread never changes, but can't be const if we do
-  // Invoke() on it.
-  rtc::Thread* owner_thread_;
-  mutable Mutex lock_;
-  // Variables accessible off-thread, guarded by lock_
-  SctpTransportInformation info_ RTC_GUARDED_BY(lock_);
+  // NOTE: |owner_thread_| is the thread that the SctpTransport object is
+  // constructed on. In the context of PeerConnection, it's the network thread.
+  rtc::Thread* const owner_thread_;
+  SctpTransportInformation info_ RTC_GUARDED_BY(owner_thread_);
   std::unique_ptr<cricket::SctpTransportInternal> internal_sctp_transport_
-      RTC_GUARDED_BY(lock_);
-  // Variables only accessed on-thread
+      RTC_GUARDED_BY(owner_thread_);
   SctpTransportObserverInterface* observer_ RTC_GUARDED_BY(owner_thread_) =
       nullptr;
   rtc::scoped_refptr<DtlsTransport> dtls_transport_
diff --git a/pc/sdp_offer_answer.cc b/pc/sdp_offer_answer.cc
index 4dd5b6f..9fa4188 100644
--- a/pc/sdp_offer_answer.cc
+++ b/pc/sdp_offer_answer.cc
@@ -729,6 +729,21 @@
   return true;
 }
 
+rtc::scoped_refptr<webrtc::DtlsTransport> LookupDtlsTransportByMid(
+    rtc::Thread* network_thread,
+    JsepTransportController* controller,
+    const std::string& mid) {
+  // TODO(tommi): Can we post this (and associated operations where this
+  // function is called) to the network thread and avoid this Invoke?
+  // We might be able to simplify a few things if we set the transport on
+  // the network thread and then update the implementation to check that
+  // the set_ and relevant get methods are always called on the network
+  // thread (we'll need to update proxy maps).
+  return network_thread->Invoke<rtc::scoped_refptr<webrtc::DtlsTransport>>(
+      RTC_FROM_HERE,
+      [controller, &mid] { return controller->LookupDtlsTransportByMid(mid); });
+}
+
 }  // namespace
 
 // Used by parameterless SetLocalDescription() to create an offer or answer.
@@ -1308,8 +1323,8 @@
       // Note that code paths that don't set MID won't be able to use
       // information about DTLS transports.
       if (transceiver->mid()) {
-        auto dtls_transport = transport_controller()->LookupDtlsTransportByMid(
-            *transceiver->mid());
+        auto dtls_transport = LookupDtlsTransportByMid(
+            pc_->network_thread(), transport_controller(), *transceiver->mid());
         transceiver->internal()->sender_internal()->set_transport(
             dtls_transport);
         transceiver->internal()->receiver_internal()->set_transport(
@@ -1725,9 +1740,9 @@
         transceiver->internal()->set_current_direction(local_direction);
         // 2.2.8.1.11.[3-6]: Set the transport internal slots.
         if (transceiver->mid()) {
-          auto dtls_transport =
-              transport_controller()->LookupDtlsTransportByMid(
-                  *transceiver->mid());
+          auto dtls_transport = LookupDtlsTransportByMid(pc_->network_thread(),
+                                                         transport_controller(),
+                                                         *transceiver->mid());
           transceiver->internal()->sender_internal()->set_transport(
               dtls_transport);
           transceiver->internal()->receiver_internal()->set_transport(
@@ -4276,13 +4291,11 @@
   // Need complete offer/answer with an SCTP m= section before starting SCTP,
   // according to https://tools.ietf.org/html/draft-ietf-mmusic-sctp-sdp-19
   if (pc_->sctp_mid() && local_description() && remote_description()) {
-    rtc::scoped_refptr<SctpTransport> sctp_transport =
-        transport_controller()->GetSctpTransport(*(pc_->sctp_mid()));
     auto local_sctp_description = cricket::GetFirstSctpDataContentDescription(
         local_description()->description());
     auto remote_sctp_description = cricket::GetFirstSctpDataContentDescription(
         remote_description()->description());
-    if (sctp_transport && local_sctp_description && remote_sctp_description) {
+    if (local_sctp_description && remote_sctp_description) {
       int max_message_size;
       // A remote max message size of zero means "any size supported".
       // We configure the connection with our own max message size.
@@ -4293,8 +4306,9 @@
             std::min(local_sctp_description->max_message_size(),
                      remote_sctp_description->max_message_size());
       }
-      sctp_transport->Start(local_sctp_description->port(),
-                            remote_sctp_description->port(), max_message_size);
+      pc_->StartSctpTransport(local_sctp_description->port(),
+                              remote_sctp_description->port(),
+                              max_message_size);
     }
   }
 
@@ -4520,8 +4534,16 @@
     return false;
   }
 
-  std::string transport_name = GetTransportName(result.value()->name);
-  return !transport_name.empty();
+  bool has_transport = false;
+  cricket::ChannelInterface* channel = pc_->GetChannel(result.value()->name);
+  if (channel) {
+    has_transport = !channel->transport_name().empty();
+  } else if (data_channel_controller()->data_channel_transport()) {
+    auto sctp_mid = pc_->sctp_mid();
+    RTC_DCHECK(sctp_mid);
+    has_transport = (result.value()->name == *sctp_mid);
+  }
+  return has_transport;
 }
 
 void SdpOfferAnswerHandler::ReportRemoteIceCandidateAdded(
@@ -4644,6 +4666,7 @@
 cricket::VideoChannel* SdpOfferAnswerHandler::CreateVideoChannel(
     const std::string& mid) {
   RTC_DCHECK_RUN_ON(signaling_thread());
+  // NOTE: This involves a non-ideal hop (Invoke) over to the network thread.
   RtpTransportInternal* rtp_transport = pc_->GetRtpTransport(mid);
 
   // TODO(bugs.webrtc.org/11992): CreateVideoChannel internally switches to the