This section is included to highlight the differences between common channel and exchange data link signaling protocols.
When using an exchange data link protocol, a near end hang-up can also signify the completion of an earlier call transfer request (see Call transfer model).
If the exchange data link signaling process has registered with transfer capability(see SL_SIGPROC_CAPABILITY_TRANSFER), the signaling process will receive an SL_CALL_TERMINATE_REQ on near end hang-up. The exchange data link signaling process should use this as an indication that it should complete an earlier transfer request if there is one outstanding. An SL_CALL_TERMINATE_CNF should be returned when the transfer has completed. If the transfer request can be completed by allowing the CAS signaling to perform a hang-up, then the signaling process can return the SL_CALL_TERMINATE_CNF immediately with a reply code of SL_REPLY_SUCCESS.
If there is no outstanding transfer request, the SL_CALL_TERMINATE_CNF can be returned immediately with a reply code of SL_REPLY_SUCCESS.