# Transmit Allow Timer

By default, the SRS-3 will automatically key up and transmit all frames that are routed for transmission on the space link interface. This default behavior can be changed using the `tx.allow.always` (default `true`) and `tx.allow.time` (default 0) properties.

Each second, `tx.allow.time` is decremented if its value is greater than 0. Before each transmission of a frame (normal or idle), the SRS-3 will check these properties and only allow the transmission if either `tx.allow.always` is `true` or `tx.allow.time` is greater than 0. If neither of these conditions are met, the frame is dropped.

To always boot in an inhibited state, the `tx.allow.always` property can be saved with a value of `false` in the boot and/or fallback stores. In the beginning of a pass, `tx.allow.time` can then be set to a value greater than 0 to allow transmissions during the pass. The figure below illustrates how the time can for example be set once in the beginning of a pass, or set periodically during the pass, similar to a watchdog timer. The `tx.allow.time` can always be set to 0 to disable the transmission as soon as possible.

The `tx.allow.time` can not be stored and will always initialize to 0 on startup.