---

Messages which are processed by the annunciation equipment, cannot be lost as the annunciation equipment acknowledges and secures every message passed by the receiving centre transceiver (as per 4.3.1 and 3.10 of CLC/TS 50136-4).

Conversely, messages which are received from a supervised premises transceiver by a receiving centre transceiver, may not be secured before they are acknowledged (as per 6.4.2 of EN 50136-1-1 and 5.5 of EN 50136-2-1).

Possibilities are given to the supervised premises transceivers, to generate through local output, information back to the associated alarm systems, in case messages can not be sent:

• acknowledgement from the receiving centre transceiver not received;

• transmission network not available;

• secondary alarm receiving centre not available as specified in 5.3.6 of EN 50136-2-3, 5.3.6 of EN 50136-2-4, 4.2 of EN 50136-2-2.

As the receiving centre transceiver may loose messages (e.g. in case of power failure, ...) and considering that the annunciation equipment secures all messages that are acknowledged, those considerations should be taken in account to prevent the alarm transmission system from loosing messages.

A so called dead man feature may be used in alarm receiving centres to monitor the availability of the operator in charge of processing the information presented by the annunciation equipment. This function may be programmed within the annunciation equipment through

• programming a maximum time during which no action is made by the operator,

• in case the time is exceeded, generating a local information or activating the alert indication or sending an alarm to a secondary alarm receiving centre.

5 Application of alarm transmission systems

Intruder and hold-up alarms can be divided into several applications which may relate to the level of risk.

Intruder alarm systems are graded normally on the level of risk; this grading also takes into account the alarm transmission system (see EN 50131-1 and CLC/TS 50131-7). When selecting an alarm transmission system for intruder alarm applications, consideration should be given to the following criteria.

• Transmission time (see Table 1 of Annex B) The following parameters should be analysed :

• the time it takes for an intruder to penetrate the supervised premises;

• the physical resistance of the supervised premises;

• the time it takes for the alarm system to detect the intrusion;

• the time it takes for an intruder to fulfil its thief when inside the premises;

• the average response time from the intervention forces.

NOTE For hold-up alarms, used to protect lives in case of emergency, special attention should be paid to enable a short transmission time

• Fault reporting time (see Table 3 of Annex B)

" It is desirable in any alarm transmission system to select the shortest reporting time if possible.

However, commercial considerations (e.g. due to the cost of every call initiated on the switched telephone network), may lead to find a cost I performance compromise. Attention should be drawn to the fact that, the longer the reporting time, the longer the alarm transmission system which may presumably be faulty, will remain unavailable.

• Availability (see Table 4 of Annex B)

■ It is desirable in any alarm transmission system to reach the highest level of availability, as the aim of the alarm transmission system is to be substituted to local warnings.

The combined use of secondary paths or alarm receiving centres as redundant equipment may be required if a high level of availability is necessary.

• Signalling security

■ The minimum requirements which can be used to access the level of signalling security (substitution security and information security) are found in EN 50131-1.

The selection of the type and performance of an alarm transmission system to be used in fire alarms applications should take into account the fact that response time is crucial and lives may be in danger.

Therefore, special consideration should be given to transmission time and availability criterias. Reference should be made to the relevant fire standards (series EN 54) to select the appropriate grades of the alarm transmission system.

In social alarm applications, the service is often given remotely, through two way speech communication initialised after a triggering device generated an alarm transmission.

When selecting the alarm transmission system, the quality of the voice transmission through the transmission network, is an essential criteria to be considered.

Reference should be made to the series of standards EN 50134, concerning social alarms, and particularly to CLC/TS 50134-7.

Typical access control alarms which may need to be transmitted through an alarm transmission system, relate to unauthorised access, time zone limits exceeded, system failure...

Some access control systems may also generate intrusion alarm. In that case the relevant applicable standards (EN 50131 series for intrusion, EN 50133 series for access control) should be used as guides to select the appropriate alarm transmission system.

When pictures are to be transmitted through an alarm transmission system, the ratio between the quality of the image and the transmission time should be considered, depending on the remote interpretation which is to be made (e.g. identification of intruders, alarm verification,...).

When a CCTV is to be remotely controlled through an alarm transmission system, attention shall be paid on the load of information to be sent.

Therefore, the alarm transmission system (including the transmission network), should be adequately chosen to support a potentially important flood of information. Reference should be made to the EN 50132 CCTV surveillance systems for use in security applications, to evaluate those criterias.

Other applications may be, technical alarms which generally relate to equipment failures, to physical values over preset limits, etc...

However, the level of risk may vary significantly from one to another type of technical alarms (e.g., temperature gauge in fridge, elevators failures, cooling systems in nuclear plants,...).

Therefore the performance needs of the alarm transmission system should be selected accordingly.

When existing, the standards which apply to other applications, should be consulted.

An alarm transmission system may be used for multiple applications, which can be combinations of the applications described in 5.1 to 5.6.

Should all applications be known when selecting the alarm transmission system, the most severe criterias of performance should apply.

If other applications are to be added to an existing alarm transmission system, a re-evaluation of the criterias should be made, to ensure that it still complies.

In any case the prioritisation of the alarm transmission and presentation of information, is an important factor to be considered, which may lead, in case of difficulty to achieve it, to select more than one alarm transmission system (e.g. by using different annunciation equipment or receiving centre transceivers in the alarm receiving centre, different supervised premises transceivers in the premises to be protected).

In all cases, consideration should be taken to avoid delaying the transmission of alarm messages

Applications which can use the alarm transmission system for an extended period of time, which would result in restricting the use for others application are: CCTV (long transmission time when motion pictures are transmitted), social alarms (speech conversations between the operator of the alarm receiving centre and the user at risk) ... The effect of that should therefore be considered in other applications.

6 Installation and connection of alarm transmission equipment

When connected to an associated alarm system, it would be necessary to prevent the loss of alarm messages. The means that is provided in case of failure to send the alarm message (see EN 50136-2-2/2-3/2-4)) should be used in an appropriate way to enable the alarm system reacting accordingly (e.g. by keeping a record of the alarm, by activating other warnings, or other means of notification,...).

The use of other transmission devices connected on the same line (e.g. fax machine, modem,...) may randomly prevent the supervised premises transceiver from transmitting.

The supervised premises transceiver should be connected in first order to line (nearest to the telephone exchange) to avoid interference or interruption from other equipment on the same line.

The message acknowledgement signal which is provided (see CLC/TS 50136-4, subclause 3.9) by the annunciation equipment should be systematically sent back to the receiving centre transceiver, when this transceiver can process that information, as it is the only guarantee that a message is properly secured within an alarm receiving centre

.

Figure 1 from EN 50136-1-1

Annex A

Supervised premises

Alarm receiving centre

Alarm transmission system

Figure 1

Annex В

Tables from EN 50136-1-1

Table 1

Table 2

Table 3

Table 4

Signalling security

• Substitution security

SO : No measures

S1 : Measures to detect substitution of the supervised premises transceiver by addition of an identity or address in all messages transmitted on the alarm transmission path.

S 2: Measures to detect substitution of the supervised premises transceiver by

1. encryption of an identity or address in all messages transmitted on the alarm transmission path, or

2. authentication of the supervised premised transceiver by the addition of a different and unreveamed code for each connected transceiver, or

3. another measure as specified by the manufacturer

• Information security

IO : No measures

11. : Measures to prevent unauthorised reading of the information transmitted

12. : Measures to prevent unauthorised modification of the information transmitted

ІЗ : Measures to prevent unauthorised reading and unauthorised modification of the information transmitted

1 This part is published as a Technical Specification.