Bug 2272 - SixLowPan NetDevice can not send uncompressed packets larger than 802.15.4 MTU

RELEASE_NOTES

@@ -82,6 +82,7 @@ Bugs fixed
 - Bug 2257 - Ipv[4,6]InterfaceContainer::Add are not consistent
 - Bug 2259 - GSL not successfully enabled for Wi-Fi DSSS error rate model
 - Bug 2267 - Wrong channel bandwidth value in pcap files
+- Bug 2272 - SixLowPan NetDevice can not send uncompressed packets larger than 802.15.4 MTU
 
 Known issues
 ------------

src/sixlowpan/doc/sixlowpan.rst

@@ -62,8 +62,8 @@ The attributes are:
 The CompressionThreshold attribute is similar to Contiki's SICSLOWPAN_CONF_MIN_MAC_PAYLOAD
 option. If a compressed packet size is less than the threshold, the uncompressed version is
 used (plus one byte for the correct dispatch header).
-This option is useful only when a MAC with specific requirement for minimum frame size is 
-used (e.g., ContikiMAC).
+This option is useful when a MAC requires a minimum frame size (e.g., ContikiMAC) and the 
+compression would violate the requirement.
 
 The last two attributes are needed to use the module with a NetDevice other than 802.15.4, as
 neither IANA or IEEE did reserve an EtherType for 6LoWPAN. As a consequence there might be a

src/sixlowpan/model/sixlowpan-net-device.cc

@@ -437,13 +437,25 @@ bool SixLowPanNetDevice::DoSend (Ptr<Packet> packet,
       protocolNumber = m_etherType;
     }
 
-  if (m_useIphc)
+  if (origPacketSize > m_compressionThreshold)
     {
-      origHdrSize += CompressLowPanIphc (packet, m_netDevice->GetAddress (), dest);
+      if (m_useIphc)
+        {
+          NS_LOG_LOGIC ("Compressing packet using IPHC");
+          origHdrSize += CompressLowPanIphc (packet, m_netDevice->GetAddress (), dest);
+        }
+      else
+        {
+          NS_LOG_LOGIC ("Compressing packet using HC1");
+          origHdrSize += CompressLowPanHc1 (packet, m_netDevice->GetAddress (), dest);
+        }
     }
   else
     {
-      origHdrSize += CompressLowPanHc1 (packet, m_netDevice->GetAddress (), dest);
+      NS_LOG_LOGIC ("Compressed packet too short, using uncompressed one");
+      packet = origPacket;
+      SixLowPanIpv6 ipv6UncompressedHdr;
+      packet->AddHeader (ipv6UncompressedHdr);
     }
 
   if ( packet->GetSize () > m_netDevice->GetMtu () )
@@ -471,14 +483,6 @@ bool SixLowPanNetDevice::DoSend (Ptr<Packet> packet,
     }
   else
     {
-      if (packet->GetSize () < m_compressionThreshold)
-        {
-          NS_LOG_LOGIC ("Compressed packet too short, using uncompressed one");
-          packet = origPacket;
-          SixLowPanIpv6 ipv6UncompressedHdr;
-          packet->AddHeader (ipv6UncompressedHdr);
-        }
-
       m_txTrace (packet, m_node->GetObject<SixLowPanNetDevice> (), GetIfIndex ());
       if (doSendFrom)
         {