04.563GPPGSM Cordless Telephony System (CTS), (Phase 1) CTS Radio Interface Layer 3 SpecificationTS
This section describes the call control (CC) protocol, which is one of the protocols of the Connection Management (CM) sublayer (see GSM 04.07).
As a general rule, the CC protocol on the CTS radio interface Um* is the same as the one used in the GSM radio interface Um. However, several specific procedures are introduced: the hook flash procedure and the internal call procedure.
6.2 Hook flash procedure
The hook flash is used for the control of some fixed-line supplementary services, associated with DTMF tones.
The mobile station shall be capable of transmitting hook flash request with the same conditions as the ones required for DTMF transmission but only on the Um* interface. The hook flash itself is generated by the CTS-FP on the fixed line. As a general rule, the hook flash procedure is the same procedure as the one used to perform DTMF transmission except that a specific keypad value is used. The DTMF protocol control procedure is defined in GSM 04.08.
6.2.1 Hook flash request by the mobile station
A user may cause a hook flash to be generated e.g. by depression of a key in the mobile station. The relevant action is interpreted by the mobile station as a requirement for a hook flash to be sent in a START DTMF message on an established FACCH.
6.2.2 Hook flash response by the fixed part
Upon receiving the START DTMF message indicating "hook flash", the fixed part shall generate a hook flash on the fixed line and shall return a START DTMF ACKNOWLEDGE message to the mobile station indicating successful initiation of the procedure.
If the fixed line can not accept the hook flash (e.g.; ISDN), a START DTMF REJECT message shall be sent to the mobile station.
6.2.3 Stop hook flash request by the mobile station
When the user indicates that the hook flash generation should cease e.g. by releasing the key the mobile station will send a STOP DTMF message to the fixed part.
6.2.4 Stop hook flash response by fixed part
After receiving the STOP DTMF message the fixed part returns a STOP DTMF ACKNOWLEDGE message to the mobile station when it has finished to generate the hook flash on the fixed line.
NOTE 1: The Fixed Part may implement the time limit option where the hook flash duration is controlled by the Fixed Part irrespective of the receipt of a stop hook flash request from the mobile station. The maximum duration of the hook flash to be generated on the fixed line is outside the scope of the present document and may be determined by specific regulations.
NOTE 2: The Fixed Part shall ensure that the minimum length of hook flash and minimum gap between hook flash and tones according to specific regulations are fulfilled.
6.3 Internal call procedure
To perform a internal call, the same procedure as the one used to perform a normal call shall be used except that the internal numbering plan is used.