diff --git a/srtcore/common.cpp b/srtcore/common.cpp
index 27dbe89d1..5236df454 100644
--- a/srtcore/common.cpp
+++ b/srtcore/common.cpp
@@ -438,7 +438,8 @@ std::string TransmissionEventStr(ETransmissionEvent ev)
         "checktimer",
         "send",
         "receive",
-        "custom"
+        "custom",
+        "sync"
     };
 
     size_t vals_size = Size(vals);
diff --git a/srtcore/common.h b/srtcore/common.h
index 60a884f5c..13fee4a84 100644
--- a/srtcore/common.h
+++ b/srtcore/common.h
@@ -290,6 +290,7 @@ enum ETransmissionEvent
     TEV_SEND,       // --> When the packet is scheduled for sending - older CCC::onPktSent
     TEV_RECEIVE,    // --> When a data packet was received - older CCC::onPktReceived
     TEV_CUSTOM,     // --> probably dead call - older CCC::processCustomMsg
+    TEV_SYNC,       // --> Backup group. When rate estimation is derived from an active member, and update is needed.
 
     TEV_E_SIZE
 };
diff --git a/srtcore/core.cpp b/srtcore/core.cpp
index 7ec8cb767..135744d8a 100644
--- a/srtcore/core.cpp
+++ b/srtcore/core.cpp
@@ -7551,7 +7551,7 @@ bool srt::CUDT::updateCC(ETransmissionEvent evt, const EventVariant arg)
 
     // This part is also required only by LiveCC, however not
     // moved there due to that it needs access to CSndBuffer.
-    if (evt == TEV_ACK || evt == TEV_LOSSREPORT || evt == TEV_CHECKTIMER)
+    if (evt == TEV_ACK || evt == TEV_LOSSREPORT || evt == TEV_CHECKTIMER || evt == TEV_SYNC)
     {
         // Specific part done when MaxBW is set to 0 (auto) and InputBW is 0.
         // This requests internal input rate sampling.
diff --git a/srtcore/core.h b/srtcore/core.h
index 7c2532560..8fc1b8f62 100644
--- a/srtcore/core.h
+++ b/srtcore/core.h
@@ -728,6 +728,22 @@ class CUDT
     static loss_seqs_t defaultPacketArrival(void* vself, CPacket& pkt);
     static loss_seqs_t groupPacketArrival(void* vself, CPacket& pkt);
 
+    CRateEstimator getRateEstimator() const
+    {
+        if (!m_pSndBuffer)
+            return CRateEstimator();
+        return m_pSndBuffer->getRateEstimator();
+    }
+
+    void setRateEstimator(const CRateEstimator& rate)
+    {
+        if (!m_pSndBuffer)
+            return;
+
+        m_pSndBuffer->setRateEstimator(rate);
+        updateCC(TEV_SYNC, EventVariant(0));
+    }
+
 
 private: // Identification
     CUDTSocket* const   m_parent;                       // Temporary, until the CUDTSocket class is merged with CUDT
diff --git a/srtcore/group.cpp b/srtcore/group.cpp
index aa562da5c..db50b3ec2 100644
--- a/srtcore/group.cpp
+++ b/srtcore/group.cpp
@@ -3525,8 +3525,8 @@ size_t CUDTGroup::sendBackup_TryActivateStandbyIfNeeded(
         return 0;
     }
 
-    const unsigned num_stable = w_sendBackupCtx.countMembersByState(BKUPST_ACTIVE_FRESH);
-    const unsigned num_fresh  = w_sendBackupCtx.countMembersByState(BKUPST_ACTIVE_STABLE);
+    const unsigned num_stable = w_sendBackupCtx.countMembersByState(BKUPST_ACTIVE_STABLE);
+    const unsigned num_fresh  = w_sendBackupCtx.countMembersByState(BKUPST_ACTIVE_FRESH);
 
     if (num_stable + num_fresh == 0)
     {
@@ -3571,6 +3571,10 @@ size_t CUDTGroup::sendBackup_TryActivateStandbyIfNeeded(
 
         try
         {
+            CUDT& cudt = d->ps->core();
+            // Take source rate estimation from an active member (needed for the input rate estimation mode).
+            cudt.setRateEstimator(w_sendBackupCtx.getRateEstimate());
+
             // TODO: At this point all packets that could be sent
             // are located in m_SenderBuffer. So maybe just use sendBackupRexmit()?
             if (w_curseq == SRT_SEQNO_NONE)
@@ -3582,7 +3586,7 @@ size_t CUDTGroup::sendBackup_TryActivateStandbyIfNeeded(
                 HLOGC(gslog.Debug,
                     log << "grp/sendBackup: ... trying @" << d->id << " - sending the VERY FIRST message");
 
-                stat = d->ps->core().sendmsg2(buf, len, (w_mc));
+                stat = cudt.sendmsg2(buf, len, (w_mc));
                 if (stat != -1)
                 {
                     // This will be no longer used, but let it stay here.
@@ -3599,7 +3603,7 @@ size_t CUDTGroup::sendBackup_TryActivateStandbyIfNeeded(
                     << " collected messages...");
                 // Note: this will set the currently required packet
                 // because it has been just freshly added to the sender buffer
-                stat = sendBackupRexmit(d->ps->core(), (w_mc));
+                stat = sendBackupRexmit(cudt, (w_mc));
             }
             ++num_activated;
         }
@@ -4384,6 +4388,9 @@ int CUDTGroup::sendBackup_SendOverActive(const char* buf, int len, SRT_MSGCTRL&
         {
             ++w_nsuccessful;
             w_maxActiveWeight = max(w_maxActiveWeight, d->weight);
+
+            if (u.m_pSndBuffer)
+                w_sendBackupCtx.setRateEstimate(u.m_pSndBuffer->getRateEstimator());
         }
         else if (erc == SRT_EASYNCSND)
         {
diff --git a/srtcore/group_backup.h b/srtcore/group_backup.h
index 760ccfbe4..790cf55ed 100644
--- a/srtcore/group_backup.h
+++ b/srtcore/group_backup.h
@@ -110,11 +110,16 @@ namespace groups
 
         std::string printMembers() const;
 
+        void setRateEstimate(const CRateEstimator& rate) { m_rateEstimate = rate; }
+
+        const CRateEstimator& getRateEstimate() const { return m_rateEstimate; }
+
     private:
         std::vector<BackupMemberStateEntry> m_memberStates; // TODO: consider std::map here?
         unsigned m_stateCounter[BKUPST_E_SIZE];
         uint16_t m_activeMaxWeight;
         uint16_t m_standbyMaxWeight;
+        CRateEstimator m_rateEstimate; // The rate estimator state of the active link to copy to a backup on activation.
     };
 
 } // namespace groups