Method and apparatus for providing application service between a first protocol and a second protocol

Application service is provided for a subscriber unit (SU), employing a first protocol, in a communication network employing a second protocol. The method includes receiving a CAI OTAR message from the SU. The CAI OTAR message includes at least a key management message (KMM) and a CAI header of the SU. The method then includes determining that the first protocol employed by the SU is different from the second protocol associated with the communication network based on the received CAI OTAR message. The method further includes creating a key management message (KMM) preamble, associated with the second protocol, based on at least one of the CAI header and configuration information of the SU, and creating a data link independent (DLI) OTAR message associated with the second protocol. The DLI OTAR message includes the received KMM. The method finally includes encapsulating the DLI OTAR message with the created KMM preamble, and sending the encapsulated DLI OTAR message to a key management facility (KMF) unit operating at a second protocol.