A communication device adapted for communicating with a network in a wireless communication system, comprising: a storage unit for storing instructions of: establishing a plurality of bearer contexts with the network; initiating a data transmission associated with a first bearer context of the plurality of bearer contexts; transmitting a first Non Access stratum, NAS, request message comprising only one first bearer identity for the first bearer context to the network in response to the initiation when the network supports a Cellular Internet of Thing, CIoT, optimization; receiving a first radio resource control, RRC, message configuring only one data radio bearer, DRB, for the first bearer context from the network, after transmitting the first NAS request message; transmitting a second NAS request message not comprising any bearer identity for the first bearer context to the network in response to the initiation when the network does not support the CIoT optimization; and receiving a second RRC message configuring a plurality of DRBs for the plurality of bearer contexts from the network, after transmitting the second NAS request message; and a processing circuit, coupled to the storage unit, configured to execute the instructions stored in the storage unit. a storage unit for storing instructions of: establishing a plurality of bearer contexts with the network; initiating a data transmission associated with a first bearer context of the plurality of bearer contexts; transmitting a first Non Access stratum, NAS, request message comprising only one first bearer identity for the first bearer context to the network in response to the initiation when the network supports a Cellular Internet of Thing, CIoT, optimization; receiving a first radio resource control, RRC, message configuring only one data radio bearer, DRB, for the first bearer context from the network, after transmitting the first NAS request message; transmitting a second NAS request message not comprising any bearer identity for the first bearer context to the network in response to the initiation when the network does not support the CIoT optimization; and receiving a second RRC message configuring a plurality of DRBs for the plurality of bearer contexts from the network, after transmitting the second NAS request message; and establishing a plurality of bearer contexts with the network; initiating a data transmission associated with a first bearer context of the plurality of bearer contexts; transmitting a first Non Access stratum, NAS, request message comprising only one first bearer identity for the first bearer context to the network in response to the initiation when the network supports a Cellular Internet of Thing, CIoT, optimization; receiving a first radio resource control, RRC, message configuring only one data radio bearer, DRB, for the first bearer context from the network, after transmitting the first NAS request message; transmitting a second NAS request message not comprising any bearer identity for the first bearer context to the network in response to the initiation when the network does not support the CIoT optimization; and receiving a second RRC message configuring a plurality of DRBs for the plurality of bearer contexts from the network, after transmitting the second NAS request message; and a processing circuit, coupled to the storage unit, configured to execute the instructions stored in the storage unit.