IGate Details


Gating Criteria

The following is the basic criteria for what an IGate gates to/from RF.

Gate all packets heard on RF to the Internet EXCEPT if any of the following are true:

  1. (AX.25 RF) The packet does not have a control field of 0x03 or a PID of 0xf0.
  2. The TNC has PASSALL turned on.
  3. 3rd-party packets (data type } ) with TCPIP or TCPXX in the 3rd party header.
    3rd-party packets without TCPXX or TCPIP mnust have the RF header and the 3rd party data type stripped before passing to APRS-IS.
  4. generic queries (data type ? ).
  5. packets with TCPIP, TCPXX, NOGATE, or RFONLY in the header (last 2 are optional).

Gate message packets and associated posits to RF if all of the following are true:

  1. the receiving station has been heard within range within a predefined time period (range defined as digi hops, distance, or both).
  2. the sending station has not been heard via RF within a predefined time period (packets gated from the Internet by other stations are excluded from this test).
  3. the sending station does not have TCPXX, NOGATE, or RFONLY in the header.
  4. the receiving station has not been heard via the Internet within a predefined time period.
    A station is said to be heard via the Internet if packets from the station contain TCPIP* or TCPXX* in the header or if gated (3rd-party) packets are seen on RF gated by the station and containing TCPIP or TCPXX in the 3rd-party header (in other words, the station is seen on RF as being an IGate).

Gate all packets to RF based on criteria set by the sysop (such as callsign, object name, etc.).

Paths

IGates must not modify paths of packets gated to APRS-IS except to append ,qAR,IGATECALL (IGATECALL = the callsign-SSID of the IGate). qAO should be used instead of qAR if the IGate is receive-only (cannot transmit). Packets containing TCPIP or TCPXX in the header or 3rd-party header should not be gated to APRS-IS (see above).

IGates must use the 3rd-party format on RF of 

IGATECALL>APRS,GATEPATH:}FROMCALL>TOCALL,TCPIP,IGATECALL*:original packet data
where GATEPATH is the path that the gated packet is to follow on RF. This format will allow IGates to prevent gating the packet back to APRS-IS. The format of the 3rd party path (TCPIP,IGATECALL*) is mandatory; APRS-IS paths MUST be removed before gating to RF.

q constructs must never appear on RF.
The I construct must never appear on RF.
Except for within gated packets, TCPIP and TCPXX must not be used on RF.