From eabfc6f5e270503607dac0b7dd53ef9d9edf1b08 Mon Sep 17 00:00:00 2001
From: Nicola Baldo <nbaldo@cttc.es>
Date: Thu, 28 Mar 2013 13:44:27 +0100
Subject: [PATCH] safer RLC overhead estimation for SRB1

---
 src/lte/model/lte-ue-mac.cc          | 23 +++++++++++++++++++----
 src/lte/model/pf-ff-mac-scheduler.cc | 21 +++++++++++++++++----
 src/lte/model/rr-ff-mac-scheduler.cc | 21 +++++++++++++++++----
 3 files changed, 53 insertions(+), 12 deletions(-)

diff --git a/src/lte/model/lte-ue-mac.cc b/src/lte/model/lte-ue-mac.cc
index e086393ab..0e27a7e2d 100644
--- a/src/lte/model/lte-ue-mac.cc
+++ b/src/lte/model/lte-ue-mac.cc
@@ -633,11 +633,26 @@ LteUeMac::DoReceiveLteControlMessage (Ptr<LteControlMessage> msg)
                             }
                           else if ((*itBsr).second.txQueueSize > 0)
                             {
-                              NS_LOG_DEBUG (this << " serve tx DATA, bytes " << bytesForThisLc);
-                              (*it).second.macSapUser->NotifyTxOpportunity (bytesForThisLc, 0, 0);
-                              if ((*itBsr).second.txQueueSize >= bytesForThisLc - 2)
+                              uint16_t lcid = (*it).first;
+                              uint32_t rlcOverhead;
+                              if (lcid == 1)
                                 {
-                                  (*itBsr).second.txQueueSize -= bytesForThisLc - 2;
+                                  // for SRB1 (using RLC AM) it's better to
+                                  // overestimate RLC overhead rather than
+                                  // underestimate it and risk unneeded
+                                  // segmentation which increases delay 
+                                  rlcOverhead = 4;                                  
+                                }
+                              else
+                                {
+                                  // minimum RLC overhead due to header
+                                  rlcOverhead = 2;
+                                }
+                              NS_LOG_DEBUG (this << " serve tx DATA, bytes " << bytesForThisLc << ", RLC overhead " << rlcOverhead);
+                              (*it).second.macSapUser->NotifyTxOpportunity (bytesForThisLc, 0, 0);
+                              if ((*itBsr).second.txQueueSize >= bytesForThisLc - rlcOverhead)
+                                {
+                                  (*itBsr).second.txQueueSize -= bytesForThisLc - rlcOverhead;
                                 }
                               else
                                 {
diff --git a/src/lte/model/pf-ff-mac-scheduler.cc b/src/lte/model/pf-ff-mac-scheduler.cc
index 9790c4398..36811be45 100644
--- a/src/lte/model/pf-ff-mac-scheduler.cc
+++ b/src/lte/model/pf-ff-mac-scheduler.cc
@@ -2058,15 +2058,28 @@ PfFfMacScheduler::UpdateDlRlcBufferInfo (uint16_t rnti, uint8_t lcid, uint16_t s
         }
       else if ((*it).second.m_rlcTransmissionQueueSize > 0)
         {
+          uint32_t rlcOverhead;
+          if (lcid == 1)
+            {
+              // for SRB1 (using RLC AM) it's better to
+              // overestimate RLC overhead rather than
+              // underestimate it and risk unneeded
+              // segmentation which increases delay 
+              rlcOverhead = 4;                                  
+            }
+          else
+            {
+              // minimum RLC overhead due to header
+              rlcOverhead = 2;
+            }
           // update transmission queue
-          if ((*it).second.m_rlcTransmissionQueueSize <= size)
+          if ((*it).second.m_rlcTransmissionQueueSize <= size - rlcOverhead)
             {
               (*it).second.m_rlcTransmissionQueueSize = 0;
             }
           else
-            {
-              size -= 2; // remove minimun RLC overhead due to header
-              (*it).second.m_rlcTransmissionQueueSize -= size;
+            {                    
+              (*it).second.m_rlcTransmissionQueueSize -= size - rlcOverhead;
             }
         }
     }
diff --git a/src/lte/model/rr-ff-mac-scheduler.cc b/src/lte/model/rr-ff-mac-scheduler.cc
index 53173776f..3da530881 100644
--- a/src/lte/model/rr-ff-mac-scheduler.cc
+++ b/src/lte/model/rr-ff-mac-scheduler.cc
@@ -1840,15 +1840,28 @@ RrFfMacScheduler::UpdateDlRlcBufferInfo (uint16_t rnti, uint8_t lcid, uint16_t s
               }
             else if ((*it).m_rlcTransmissionQueueSize > 0)
               {
+                uint32_t rlcOverhead;
+                if (lcid == 1)
+                  {
+                    // for SRB1 (using RLC AM) it's better to
+                    // overestimate RLC overhead rather than
+                    // underestimate it and risk unneeded
+                    // segmentation which increases delay 
+                    rlcOverhead = 4;                                  
+                  }
+                else
+                  {
+                    // minimum RLC overhead due to header
+                    rlcOverhead = 2;
+                  }
                 // update transmission queue
-                if ((*it).m_rlcTransmissionQueueSize <= size)
+                if ((*it).m_rlcTransmissionQueueSize <= size - rlcOverhead)
                   {
                     (*it).m_rlcTransmissionQueueSize = 0;
                   }
                 else
-                  {
-                    size -= 2; // remove minimun RLC overhead due to header
-                    (*it).m_rlcTransmissionQueueSize -= size;
+                  {                    
+                    (*it).m_rlcTransmissionQueueSize -= size - rlcOverhead;
                   }
               }
           return;