AMSG Command

Command

AMSG -- Enter APRS Messaging mode.

Synopsis

AM[sg] <portnum>

Description

The AMSG command switches the user's session into APRS messaging mode, enabling him to exchange messages and bulletins with APRS and UI-View users.

The <portnum> argument specifies the radio port upon which traffic will be sent and received. e.g. "AM 13" will use port 13.

Within messaging mode, all commands begin with a forward slash (/), and anything else is treated as message text for transmission. The commands are as follows:

        /A[nnouncements]    Show announcements
        /B[ulletins]        Show bulletins
        /C[ancel] [#]       List / cancel unacked message(s)
        /D[irects]          Show directly heard stations
        /H[elp] [cmd]       Display command help
        /Monitor [on|off]   Query / set traffic Monitor mode
        /Q[uit]             Quit (exit)
        /T[arget] [call]    Query / set target for msg
        /U[iview] [on|off]  Query / set UI-View mode
        /V[ia] [digis]      Query / set digipeater path
        /X                  Exit

Only the first letter of each command needs to be supplied. A few are worthy of further explanation....

The /D command shows a list of all the stations heard directly, i.e. not via digipeaters or 3rd party networks.

Before any type of message or query can be sent, the user must specify a "target" address, using "/T [call]". For messages, the target will be a callsign. For bulletins the target should be BLN#*, where "#" represents a single digit, and "*" represents the bulletin category of up to 5 characters. Announcements use the same format as bulletins, except that "#" represents a non-digit. Attempting to send a message without first defining a target will result in an error response. The target remains in force until a new target is specified. The current target can be displayed by entering "/T" alone, or cleared by entering an invalid target, e.g. "/T .".

Outgoing messages and bulletins are re-transmitted at intervals until either an acknowledgement is received, or too many retries have taken place. Bulletins are re-transmitted every 20 minutes for 4 hours, whilst announcements are re- transmitted every hour for 4 days. Messages are initially re- transmitted after 10 seconds, then the interval doubles with each re-send. When the interval exceeds approximately 1.5 hours, the message is expired and re-transmission ceases. The "cancel" command allows the re-transmission of outgoing messages and bulletins to be cancelled at any time before expiry.

The /M (Monitor) command allows other APRS and UI-View message traffic on the channel to be watched. The default is "off". Entering /M by itself shows the current state.

The /U (Ui-View mode) command sets the type of outgoing message to be used. The default is "off", which means that all outgoing messages will be in APRS format. If turned "on", outgoing messages will be in "UI-View" format. In either mode, both types of message can be received. UI-View messages will display with a tilde (~) between the message and its ID, whereas APRS-format messages will display with a curly opening bracket ({) if a message ID was supplied. In UI-View mode, "\<decimal>" will send a UIVIEW message whose text portion contains a single byte of value <decimal>, e.g. "\254" will send a PING request.

/Q (quit) and /X (exit) are identical in function, exiting message mode and returning the user to the router's main command prompt.

The /V (via) command sets the digipeater path for outgoing messages, or if used by itself displays the currently set path. The path defaults to the port APRSPATH specified in XROUTER.CFG. In APRS mode, the destination call is fixed at APZ###, where ### is the 3 digit Xrouter version number, whereas in UI-View mode the destination call is set by the /Target command.

The /H (help) command is used to display help for the messaging commands. If no argument is supplied, a very brief (low bandwidth) command resume is displayed. If the help files are installed, "/H *" will list the help available, and "/H <cmd>" can be used to obtain more detailed help for <cmd>, e.g. "/H /V". Note that the leading slash of the argument is ignored, so "/H V" is equally valid.

Notes

If Xrouter receives an APRS message whose target address is a user currently logged into the APRS messaging shell, the message is delivered to the user and, if there was a message ID, an acknowledgement is sent. Each re-send of the message is acknowledged, because a re-send probably indicates that the sender didn't receive the previous ack.

If the same message is received twice within 30 seconds, the second copy is ignored. This helps to eliminate duplicates received via different digipeater routes.

Expired messages are retained for 1 day before being deleted. During this interval they will be reactivated if a "?APRSM" query is received from the target station. Outgoing bulletins and announcements are not retained after expiry. Incoming bulletins are retained for 4 hours after last received, and incoming announcements are retained for 4 days after last received.

The APRS spec limits the maximum message length to 67 characters. Because a message ID of up to 6 characters is appended to the message, Xrouter splits messages longer than 61 characters into separate messages no longer than 61 characters (excluding ID) each.

All APRS facilities are an ongoing experiment and may be liable to change as development continues. The so-called "APRS Protocol Reference" is rather fuzzy in places!

Availability

The messaging shell is available to all users, but guests can't send messages.