add "Ligtning Messages" section

communications_protocol.asciidoc

@@ -13,6 +13,21 @@ If you want to learn more we suggest you check out http://www.noiseprotocol.org/
 
 === Ligtning Messages
 
+Each Ligtning Message contains 2 bytes indicating the *type* of message, and a variable-length *payload*.
+A *payload* needs to be interpreted according the *type*.
+
+A Ligtning Message falls into one of the following groups:
+
+[cols="3,3,10",options="header"]
+|=======
+| Group | Type | Description
+| Setup & Control | 0~31 | Messages related to connection setup, control, supported features, and error reporting
+| Channel | 32~127 | Messages related to setup and close channels
+| Commitment | 128~255 | Messages related to updating the current commitment transaction
+| Routing | 256~511 | Messages related to node and channel announcements, or active route explorations
+| Custom | 32768~65535 | Experimental or custom messages
+|=======
+
 === Opening a Payment channel
 
 === forwarding, making and receiving a payment