AS5300 are gateways and they are reponsible for
disconnecting calls made or received. The DRQ is used to inform the gatekeeper
that the call has been disconnect and a DCF is sent back to the gateway
resulting in proper house cleaning of the terminated call.
Gateways do not recognise DRQ as they are issuers not responders to DRQ.
The functionality you're looking for is available in mgcp controlled gateways by CAll-AGENTS, where you
can issue a DLCX and have the Gateway terminate the call.