A user receiving a SETUP message shall perform compatibility checking before responding to that SETUP message. Any reference to user in 5.2.3 through 5.2.7 implicitly refers to a compatible user equipment. Annex B defines compatibility checking to be performed by users upon receiving a SETUP message.
When the SETUP message is delivered via a broadcast data link, an incompatible user shall either:
a) ignore the incoming call; or
b) respond by sending a RELEASE COMPLETE message with cause No. 88, incompatible destination, and enter the Null state. The network processes this RELEASE COMPLETE message in accordance with 5.2.5.3.
When the SETUP message is delivered via point-to-point data link, an incompatible user shall respond with RELEASECOMPLETE message with cause No. 88, incompatible destination, and enter the Null state. The network shall process this RELEASE COMPLETE message in accordance with 5.2.5.3.