From f27a3c7b2a1a3ab413a0bc89369b7bbcb3f9a1de Mon Sep 17 00:00:00 2001
From: suveshpratapa <66088488+suveshpratapa@users.noreply.github.com>
Date: Wed, 16 Jun 2021 16:02:00 -0400
Subject: [PATCH] [mesh-forwarder] calculate PAN ID compression according to
 802.15.4-2015 (#6739)

---
 src/core/thread/mesh_forwarder.cpp | 27 +++++++++++++++++++++++++--
 1 file changed, 25 insertions(+), 2 deletions(-)

diff --git a/src/core/thread/mesh_forwarder.cpp b/src/core/thread/mesh_forwarder.cpp
index 53aa1ac99..7711a0947 100644
--- a/src/core/thread/mesh_forwarder.cpp
+++ b/src/core/thread/mesh_forwarder.cpp
@@ -666,9 +666,32 @@ start:
         break;
     }
 
-    if (dstpan == Get<Mac::Mac>().GetPanId())
+    // Handle special case in 15.4-2015:
+    //  Dest Address: Extended
+    //  Source Address: Extended
+    //  Dest PanId: Present
+    //  Src Panid: Not Present
+    //  Pan ID Compression: 0
+    if (dstpan == Get<Mac::Mac>().GetPanId() &&
+        ((fcf & Mac::Frame::kFcfFrameVersionMask) == Mac::Frame::kFcfFrameVersion2006 ||
+         (fcf & Mac::Frame::kFcfDstAddrMask) != Mac::Frame::kFcfDstAddrExt ||
+         (fcf & Mac::Frame::kFcfSrcAddrMask) != Mac::Frame::kFcfSrcAddrExt))
     {
-        fcf |= Mac::Frame::kFcfPanidCompression;
+#if OPENTHREAD_CONFIG_MAC_HEADER_IE_SUPPORT
+        // Handle a special case in IEEE 802.15.4-2015, when Pan ID Compression is 0, but Src Pan ID is not present:
+        //  Dest Address:       Extended
+        //  Src Address:        Extended
+        //  Dest Pan ID:        Present
+        //  Src Pan ID:         Not Present
+        //  Pan ID Compression: 0
+
+        if ((fcf & Mac::Frame::kFcfFrameVersionMask) != Mac::Frame::kFcfFrameVersion2015 ||
+            (fcf & Mac::Frame::kFcfDstAddrMask) != Mac::Frame::kFcfDstAddrExt ||
+            (fcf & Mac::Frame::kFcfSrcAddrMask) != Mac::Frame::kFcfSrcAddrExt)
+#endif
+        {
+            fcf |= Mac::Frame::kFcfPanidCompression;
+        }
     }
 
     aFrame.InitMacHeader(fcf, secCtl);