1. Introduction

Since version 0.3.0, D-RATS has supported automatic message forwarding as a mechanism to bridge stations in a simplex network or even stations across different RF domains.  Version 0.3.1 brought many fixes and improvements to this function and thus it is recommended that readers of this document use 0.3.1 at a minimum.

In the default and common case, D-RATS will forward a message only once, which means it will only automatically route a message from the source to the destination through a single intermediate station.  With some configuration it will do much more than this, but even the simple case is extremely useful in many practical scenarios.  In a situation requiring establishment of a quick message-passing network on simplex, this functionality will help weak stations get messages into and out of the area without any complex configuration.

NOTE: It is not recommended to have automatic message forwarding enabled on a shared Voice/Data frequency.  You will inevitably interfere with voice communication and the data communication is unlikely to be successful.  Please don't do it.

2. Addressing a Message

In order for D-RATS to properly decide on an action to take on a new message, the Routing Information block at the top of a message must be filled in.  The Source Callsign is fixed to that which D-RATS is currently configured for and is not editble in the form dialog.  The Destination Callsign field is the important piece of information which tells any D-RATS instance along the message path where the form ultimately needs to go.  The destination callsign must match the final station's configuration exactly.  If you put "W1AW" and the station is configured for "W1AW-1" or "W1AW   H" the message will not be automatically routable to the appropriate destination.

2.1. Internet Addressing

If you put an internet email address in the destination callsign field, D-RATS will attempt to forward the email via the current outgoing mail server, if so configured.  Similarly, even if the local station is not configured for or capable of doing internet email, you can address a message as such as then send it manually to another station that does have that capability.  When the message arrives at a station that can deliver it to the internet, it will be sent.

Similarly, a station that is configured to poll an internet mail server for incoming messages will convert any received into forms and place them in the Outbox.  If appropriate routing information was extracted from the message then the message router will attempt to initiate a form transfer to deliver the message received by email to the appropriate RF station.

3. Enabling Automatic Forwarding

In the Preferences dialog, under Messages there is an option to Automatically Forward Messages.  In order for D-RATS to act autonomously on messages, you must enable this feature.  The Queue Flush Interval controls how often D-RATS checks the Outbox for messages that need to be sent.  This should be set to a reasonably short interval such that messages do not take too long to move through the system, but long enough to leave at least some time between message transfers for radios to cool and stations to break in if necessary.  Something on the order of 30 to 60 seconds is probably reasonable for dedicated data-only networks.

4. Behavior of the Message Routing Logic

Once automatic forwarding is enabled, the message routing logic will check the Outbox for new messages that are destined for other stations periodically according to the queue flush interval.  New messages that you originate from your station are automatically placed here and will be picked up and sent if they are destined for another station.  Messages received by your station are examined and placed either in the Inbox (if they are destined for you) or the Outbox (if they are destined for another station).

The message router determines if it can send a message to another station based on whether that station has been heard (and thus whether or not it shows up in the Stations side-bar).  If you receive a message destined for a station that has not yet been heard, D-RATS will leave it in the Outbox.  If you know that the message can be delivered to the destination through another station, you can manually send the form to that station and let it handle it.  Alternately, the message can remain queued in your Outbox until the destination station is heard.

Consider the scenario where the destination Station B for a message has not been heard and the message is being queued at Station A.  When Station B comes on frequency, if it pings Station A, then it will be "heard" and will thus trigger the router at Station A to send the message on.

5. Multiple Ports

Since version 0.3.0, D-RATS has had the ability to connect multiple devices simultaneously.  This includes D-STAR radios, TNCs, DVDongles, and network proxies.  The message router is aware of all the currently-configured ports and knows which stations have been heard on which ports.  That means that you can (for example) have a station with a 2-meter D-STAR radio and a 440 MHz D-STAR radio connected at the same time to bridge between two RF domains.  If a user on the 440 MHz system has a message for a user on the 2-meter system, she may send that message (addressed to the 2-meter user) to the station with both links.  The intermediate station will ensure that the message is sent out on the 2-meter frequency because it knows that the destination user has been heard on the 2-meter path and not the 440MHz path.

If possible, the use of mutliple ports to segment a message routing domain is desirable.  If two stations have heard each other, even just from a small chat packet, they will try to exchange messages and may fail if their signal is too marginal.  Thus, keeping extremely weak stations off on another frequency will help by keeping all traffic flowing through a known-good station.  Further, the use of a 2-meter radio to make a long-haul connection to a distant user is likely to be more effective than that user attempting to participate in a 440MHz local area simplex net.

6. Static Message Routing Tables

In addition to D-RATS attempting to automatically determine how to send a message based on its list of heard stations, you can also give it a static routing table by which to make those decisions.  In the scenario mentioned above where all traffic for a distant station should go through a gateway machine, a static routing table entry on the non-gateway stations will ensure that they automatically direct traffic to the gateway when appropriate.

TBD: Document the location and format of the routing table