diff --git a/DRAMSys/library/src/simulation/Arbiter.cpp b/DRAMSys/library/src/simulation/Arbiter.cpp
index 68f77dcc..e1f7e0af 100644
--- a/DRAMSys/library/src/simulation/Arbiter.cpp
+++ b/DRAMSys/library/src/simulation/Arbiter.cpp
@@ -257,27 +257,27 @@ void ArbiterFifo::peqCallback(tlm_generic_payload &cbPayload, const tlm_phase &c
                 nextThreadPayloadIDToAppend[threadId]++, nextChannelPayloadIDToAppend[channelId]++);
         activeTransactions[threadId]++;
 
-        if (activeTransactions[threadId] < maxActiveTransactions)
+        if (activeTransactions[threadId] <= maxActiveTransactions)
         {
             tlm_phase tPhase = END_REQ;
             sc_time tDelay = SC_ZERO_TIME;
             tSocket[static_cast<int>(threadId)]->nb_transport_bw(cbPayload, tPhase, tDelay);
+            pendingRequests[channelId].push(&cbPayload);
         }
         else
         {
             outstandingEndReq[threadId] = &cbPayload;
         }
 
-        pendingRequests[channelId].push(&cbPayload); // TODO: wrong, only insert when END_REQ has been sent
-
-        if (!channelIsBusy[channelId])
+        if (!channelIsBusy[channelId]) // TODO: only required if pendingRequests was empty?
         {
             channelIsBusy[channelId] = true;
 
             tlm_generic_payload *tPayload = pendingRequests[channelId].front();
             pendingRequests[channelId].pop();
             tlm_phase tPhase = BEGIN_REQ;
-            sc_time tDelay = tCK; // TODO: SC_ZERO_TIME
+            // TODO: what if END_REQ was in the same cycle?
+            sc_time tDelay = SC_ZERO_TIME;
 
             iSocket[static_cast<int>(channelId)]->nb_transport_fw(*tPayload, tPhase, tDelay);
         }
@@ -315,26 +315,28 @@ void ArbiterFifo::peqCallback(tlm_generic_payload &cbPayload, const tlm_phase &c
             tlm_generic_payload *tPayload = pendingResponses[threadId].front();
             pendingResponses[threadId].pop();
             tlm_phase tPhase = BEGIN_RESP;
-            sc_time tDelay = tCK;
+            // TODO: what if one BEGIN_RESP has already been sent in this cycle?
+            sc_time tDelay = SC_ZERO_TIME;
 
             tlm_sync_enum returnValue = tSocket[static_cast<int>(threadId)]->nb_transport_bw(*tPayload, tPhase, tDelay);
             if (returnValue == TLM_UPDATED)
                 payloadEventQueue.notify(*tPayload, tPhase, tDelay);
-
-            if (activeTransactions[threadId] == maxActiveTransactions)
-            {
-                tlm_phase tPhase = END_REQ;
-                sc_time tDelay = SC_ZERO_TIME;
-                tPayload = outstandingEndReq[threadId];
-                tSocket[static_cast<int>(threadId)]->nb_transport_bw(*tPayload, tPhase, tDelay);
-            }
-
-            activeTransactions[threadId]--;
         }
     }
     else if (cbPhase == END_RESP) // from initiator
     {
         cbPayload.release();
+        activeTransactions[threadId]--;
+
+        if (activeTransactions[threadId] == maxActiveTransactions)
+        {
+            tlm_phase tPhase = END_REQ;
+            sc_time tDelay = SC_ZERO_TIME;
+            tlm_generic_payload *tPayload = outstandingEndReq[threadId];
+            tSocket[static_cast<int>(threadId)]->nb_transport_bw(*tPayload, tPhase, tDelay);
+            unsigned int tChannelId = DramExtension::getExtension(tPayload).getChannel().ID();
+            pendingRequests[tChannelId].push(tPayload);
+        }
 
         if (!pendingResponses[threadId].empty())
         {
@@ -345,16 +347,6 @@ void ArbiterFifo::peqCallback(tlm_generic_payload &cbPayload, const tlm_phase &c
             tlm_sync_enum returnValue = tSocket[static_cast<int>(threadId)]->nb_transport_bw(*tPayload, tPhase, tDelay);
             if (returnValue == TLM_UPDATED)
                 payloadEventQueue.notify(*tPayload, tPhase, tDelay);
-
-            if (activeTransactions[threadId] == maxActiveTransactions)
-            {
-                tlm_phase tPhase = END_REQ;
-                sc_time tDelay = SC_ZERO_TIME;
-                tPayload = outstandingEndReq[threadId];
-                tSocket[static_cast<int>(threadId)]->nb_transport_bw(*tPayload, tPhase, tDelay);
-            }
-
-            activeTransactions[threadId]--;
         }
         else
         {
@@ -377,27 +369,27 @@ void ArbiterReorder::peqCallback(tlm_generic_payload &cbPayload, const tlm_phase
                 nextThreadPayloadIDToAppend[threadId]++, nextChannelPayloadIDToAppend[channelId]++);
         activeTransactions[threadId]++;
 
-        if (activeTransactions[threadId] < maxActiveTransactions)
+        if (activeTransactions[threadId] <= maxActiveTransactions)
         {
             tlm_phase tPhase = END_REQ;
             sc_time tDelay = SC_ZERO_TIME;
             tSocket[static_cast<int>(threadId)]->nb_transport_bw(cbPayload, tPhase, tDelay);
+            pendingRequests[channelId].push(&cbPayload);
         }
         else
         {
             outstandingEndReq[threadId] = &cbPayload;
         }
 
-        pendingRequests[channelId].push(&cbPayload);
-
-        if (!channelIsBusy[channelId])
+        if (!channelIsBusy[channelId]) // TODO: only required if pendingRequests was empty?
         {
             channelIsBusy[channelId] = true;
 
             tlm_generic_payload *tPayload = pendingRequests[channelId].front();
             pendingRequests[channelId].pop();
             tlm_phase tPhase = BEGIN_REQ;
-            sc_time tDelay = tCK;
+            // TODO: what if END_REQ was in the same cycle?
+            sc_time tDelay = SC_ZERO_TIME;
 
             iSocket[static_cast<int>(channelId)]->nb_transport_fw(*tPayload, tPhase, tDelay);
         }
@@ -439,26 +431,29 @@ void ArbiterReorder::peqCallback(tlm_generic_payload &cbPayload, const tlm_phase
                 threadIsBusy[threadId] = true;
 
                 tlm_phase tPhase = BEGIN_RESP;
-                sc_time tDelay = tCK;
+                // TODO: what if one BEGIN_RESP has already been sent in this cycle?
+                sc_time tDelay = SC_ZERO_TIME;
+
                 tlm_sync_enum returnValue = tSocket[static_cast<int>(threadId)]->nb_transport_bw(*tPayload, tPhase, tDelay);
                 if (returnValue == TLM_UPDATED)
                     payloadEventQueue.notify(*tPayload, tPhase, tDelay);
-
-                if (activeTransactions[threadId] == maxActiveTransactions)
-                {
-                    tlm_phase tPhase = END_REQ;
-                    sc_time tDelay = SC_ZERO_TIME;
-                    tPayload = outstandingEndReq[threadId];
-                    tSocket[static_cast<int>(threadId)]->nb_transport_bw(*tPayload, tPhase, tDelay);
-                }
-
-                activeTransactions[threadId]--;
             }
         }
     }
     else if (cbPhase == END_RESP) // from initiator
     {
         cbPayload.release();
+        activeTransactions[threadId]--;
+
+        if (activeTransactions[threadId] == maxActiveTransactions)
+        {
+            tlm_phase tPhase = END_REQ;
+            sc_time tDelay = SC_ZERO_TIME;
+            tlm_generic_payload *tPayload = outstandingEndReq[threadId];
+            tSocket[static_cast<int>(threadId)]->nb_transport_bw(*tPayload, tPhase, tDelay);
+            unsigned int tChannelId = DramExtension::getExtension(tPayload).getChannel().ID();
+            pendingRequests[tChannelId].push(tPayload);
+        }
 
         tlm_generic_payload *tPayload = *pendingResponses[threadId].begin();
 
@@ -467,22 +462,11 @@ void ArbiterReorder::peqCallback(tlm_generic_payload &cbPayload, const tlm_phase
         {
             nextThreadPayloadIDToReturn[threadId]++;
             pendingResponses[threadId].erase(pendingResponses[threadId].begin());
-
             tlm_phase tPhase = BEGIN_RESP;
             sc_time tDelay = tCK;
             tlm_sync_enum returnValue = tSocket[static_cast<int>(threadId)]->nb_transport_bw(*tPayload, tPhase, tDelay);
             if (returnValue == TLM_UPDATED)
                 payloadEventQueue.notify(*tPayload, tPhase, tDelay);
-
-            if (activeTransactions[threadId] == maxActiveTransactions)
-            {
-                tlm_phase tPhase = END_REQ;
-                sc_time tDelay = SC_ZERO_TIME;
-                tPayload = outstandingEndReq[threadId];
-                tSocket[static_cast<int>(threadId)]->nb_transport_bw(*tPayload, tPhase, tDelay);
-            }
-
-            activeTransactions[threadId]--;
         }
         else
         {