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VoIP monitoring problems
To illustrate, in several tests problems have been reported that the tones intended for the central monitoring station receivers do not reliably propagate over some VoIP channels. Sometimes these transmission failures are the result of protocol conflicts, while other times they result from distortion of signals on the lines.
Some companies have tested panels using different VoIP applications and have reported marginal results. Some formats do not function at all, while others had to resend multiple times in order to be successful. VoIP varies its compression based upon the available bandwidth. These problems will adversely affect VoIP conversion by alarm system owners since failure of these systems could result in loss of life and property. This opens the possibility of substantial liability. Some operations have tried to solve the problem using an IP-based system with long-range radio backup. Most of these setups made no provision for battery backup or 24 hours of standby.
While the standards for transmission of security signals to off-site locations are primarily specified by industry groups, the standards for the transmission of fire alarms and their supervisory signals are subject to legal enforcement. In particular, the NFPA 72 National Fire Alarm Code does not prohibit transmission means other than POTS – an acronym for “plain-old telephone system – but whatever method is chosen must be compliant with NFPA 72 standards. These compliance issues will necessitate the industry to take a slow, cautious approach to the use of VoIP as an alternative to POTS in conventional panels using Digital Alarm Communicator Transmitter or DACT-based communications.
Data on DACT
NFPA 72 Section 5-5.2 requires a DACT to be connected to two independent means of communications to a supervising station, the first of which must be a telephone line. The telephone line must be a loop start line, and may not be a ground start line commonly found on a Private Branch Exchange (PBX). Loop start telephone lines always have voltage present and therefore can be monitored for integrity. The second method of communication may be a cellular telephone, active multiplex, derived local channel, one-way private microwave, one-way RF or two-way RF.
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