Question: In a Public Land Mobile Network (PLMN), what happens when a User Equipment (UE) supporting one teleservice standard (but not another, more advanced one) receives a call setup for the more advanced standard, and the network supports this advanced standard?
Option 1: The call is automatically set up as the lesser-supported standard without negotiation.
Option 2: The UE rejects the call due to incompatible service subscription.
Option 3: The network negotiates the call from the more advanced standard to the lesser-supported one according to adaptation rules, and if unsuccessful, releases the call.
Option 4: The UE is upgraded temporarily to support the more advanced standard for the duration of the call.
Explanation: This correct answer reflects the requirement for backward compatibility and negotiation between different teleservices. Since a subscription for an advanced service often includes lesser ones, and to allow flexibility between devices supporting either, the network attempts to adapt the call from the advanced to the lesser-supported service if direct support is lacking, following predefined adaptation rules. If this adaptation fails, the call is terminated to maintain service integrity.