# Notify hold

The notify hold operation notifies a remote user of a call hold operation involving the user. Notify hold is available in an ETS 300 configuration and in a Q.SIG configuration.

## Notify hold (ETS 300)

In an ETS 300 configuration, the stack performs this operation to notify the application when the remote equipment has changed the auxiliary state of a local subscriber to the on hold state. An acu_ss_notify_hold_invoke extended data structure is sent to the application in an ACU indication message.

## Notify hold (Q.SIG)

In a Q.SIG configuration, the application at one node performs this operation to notify the application on a remote node when a call from the remote node is on hold. To do so, it sends an acu_ss_notify_hold_invoke extended data structure to the location in an ACU request message.

The following illustrations show the message types interchanged between the stack and a Q.SIG application when notify hold is invoked from the perspectives of the local node and the remote node:

Local notify hold

Remote notify hold