BS 8521:2009 pdf download – Specification for dual-tone multi-frequency (DTMF) signalling protocol for social alarm systems
5 Communication
5.1 Session initiation Following completion of call set‑up signalling, the local unit and controller shall send an enquiry tone to the line to indicate that automatic equipment is using the line. When the ARC detects ringing current, it shall loop the line and shall send a data request tone to the local unit and controller. If no data request tone is detected by the local unit and controller, it shall disconnect from the network.
A received tone shall be interpreted as a data request tone by the local unit and controller only if its duration is not less than 500 ms. When the local unit and controller detects the data request tone, it shall cease to send the enquiry tone and shall wait until the end of the data request tone; after a delay of (80 ± 5) ms the local unit and controller shall then send an alarm transmission message to the ARC. If no acknowledge tone or start of data transmission is received by the ARC within (600 ± 30) ms of the end of a data request tone, the ARC shall send a further data request tone. This shall be repeated up to four times, after which the ARC shall disconnect from the network if no acknowledge or start of data transmission is received by the ARC within (600 ± 30) ms of the end of the fourth data request tone. If an acknowledge tone or start of data transmission is received by the ARC within (600 ± 30) ms of the end of a data request tone, the ARC shall cease to send the data request tone and shall wait to receive a valid data transmission. If a valid data transmission is not received by the ARC within 25 s from the end of the transmission of the originating data request tone, it shall disconnect from the network.
If no acknowledge tone is received by the local unit and controller within (600 ± 30) ms of the end of an alarm transmission message, the local unit and controller shall send a further alarm transmission message. This shall be repeated up to four times, after which the local unit and controller shall disconnect from the network if no acknowledge tone is received by the local unit and controller within (600 ± 30) ms of the end of the fourth alarm transmission message. Any redial or reconnection attempts shall be made in accordance with BS EN 50134‑3.
5.2 Alarm transmission message format
The message sent by the local unit and controller to the ARC shall consist of the sequence: A CC TT GGGGGGGG RRRR EEE LL P SS XX # where: A and # are the message string start and stop delimiters; CC is the two‑digit system configuration, to indicate the type of equipment (see Table 2);
TT is the two‑digit system type assignment, to indicate to the ARC whether the local unit and controller is using the standard protocol or a proprietary variant (see Table 3); GGGGGGGG is the eight‑digit controller identification field, to uniquely define the identity of the specific site/installation;
NOTE 1 This is right-justified, padded with leading zeros (i.e. zero is transmitted as DTMF0). RRRR is the four‑digit local unit identification field, to uniquely define the identity of the local unit within the installation;
NOTE 2 This is right-justified, padded with leading zeros (i.e. zero is transmitted as DTMF0).
NOTE 3 In grouped equipment, the controller has the reserved identity of0000.
NOTE 4 For a combined local unit and controller, the unique identity ofthat specific unit is given by the combined twelve digits ofboth the local unit and controller and local unit fields as a single entity. This is right-justified, padded with leading zeros (i.e. zero is transmitted as DTMF0). EEE is the three‑digit event code, to define the nature of the alarm (see Table 4); LL is the two‑digit location information field, to allow detailed locations of alarm events to be indicated (see Table 5);
P is the single‑digit priority field, to indicate that a priority over other alarms has been assigned to this event (see Table 6); SS is the two‑digit status code, to indicate the status of the local unit (see Table 7); XX is the two‑digit checksum (see 5.3). NOTE 5 An example ofan alarm transmission protocol is shown diagrammatically in Figure 1.