Reliable-state-machines-(concept).md

@@ -20,7 +20,8 @@ The basic hexabus packet header after this addition then looks like this:
 ```
 The `HX0D` prefix field, the `type` field and the `flags` field retain their original meaning. While the original packet format did not define any flags, the new format defines one flag:
 ```
-WANT_ACK (0x01): sending node requires acknowledgement from recipients
+WANT_ACK (0x01): sending node requires acknowledgement from recipients in any case
+WANT_UL_ACK (0x02): upper layer decides if there is an ACK to be sent, e.g. if the packet is relevant for the state machine.
 ``` 
 
 The packet footer remains unmodified and contains only a two-byte CRC of the packet, calculated with the CRC field set to `0`.