clarify framing

Co-authored-by: bit-aloo <[email protected]>

Author: plebhash

03-Protocol-Overview.md

@@ -96,11 +96,22 @@ The message framing is outlined below:
 
 | Field Name  | Type | Description                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
 | -------------- | ----------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
-| extension_type | U16         | Unique identifier of the extension describing this protocol message. <br>Least significant bit (i.e.bit 15, 0-indexed, aka channel_msg) indicates a message which is specific to a channel, whereas if the most significant bit is unset, the message is to be interpreted by the immediate receiving device. <br>Note that the channel_msg bit is ignored in the extension lookup, i.e.an extension_type of 0x8ABC is for the same "extension" as 0x0ABC. <br>If the channel_msg bit is set, the first four bytes of the payload field is a U32 representing the channel_id this message is destined for (these bytes are repeated in the message framing descriptions below). <br>Note that for the Job Declaration and Template Distribution Protocols the channel_msg bit is always unset. |
-| msg_type       | U8          | Unique identifier of the extension describing this protocol message                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
+| extension_type | U16         | Unique identifier of the extension associated with this protocol message                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
+| msg_type       | U8          | Unique identifier of this protocol message                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
 | msg_length     | U24         | Length of the protocol message, not including this header                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
 | payload        | BYTES       | Message-specific payload of length msg_length. If the MSB in extension_type (the channel_msg bit) is set the first four bytes are defined as a U32 "channel_id", though this definition is repeated in the message definitions below and these 4 bytes are included in msg_length.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
 
+### 3.2.1 Routing Frames over Channels
+
+Some bits of the `extension_type` field can also be repurposed for signaling on how the frame should be handled across channels.
+
+The least significant bit of `extension_type` (i.e., bit 15, 0-indexed, also known as `channel_msg`) indicates a message which is specific to a channel, whereas if the most significant bit is unset, the message is to be interpreted by the immediate receiving device. 
+
+Note that the `channel_msg` bit is ignored in the extension lookup, i.e., an `extension_type` of `0x8ABC` is for the same "extension" as `0x0ABC`. 
+
+If the `channel_msg` bit is set, the first four bytes of the payload field is a `U32` representing the `channel_id` this message is destined for (these bytes are repeated in the message framing descriptions below).
+
+Note that for the Job Declaration and Template Distribution Protocols the `channel_msg` bit is always unset.
 
 ## 3.3 Reconnecting Downstream Nodes