Demise of the Public Switched Telephone Network
For decades, PSTN has been the chosen communication platform for the transmission of alarm signals. Today, many are predicting its days are numbered. Two transmission paths have emerged as the preferred methods of communication between an alarm panel and Monitoring Centre – IP (the Internet) and GSM. This article will examine the pros and cons of each.
GSM Wireless Networks
In todays high tech world, almost everybody owns a mobile phone. The perception is that GSM networks are very reliable and rarely suffer from network outages. This makes GSM a viable platform for alarm communications and three different technologies can be employed for signal transmission – SMS, Voice and Data. The reliability of SMS varies greatly from country to country and delays in message delivery rule it out from being considered a serious option in countries where messages can often be delayed for many hours. In countries that do not experience such delays, SMS can be a good low cost method of alarm communication, however, it is often not popular with alarm monitoring companies as it opens up the possibility of self monitoring where messages can be sent directly to the end users mobile phone.
The use of a GSM Dialer/Communicator allows an alarm panel modem to dial out and make a phone call to the Monitoring Centre over the GSM network. When a conventional analogue alarm receiver answers the call, an audio/voice channel is opened up and the alarm panel can communicate with the receiver just as it would over a PSTN line. This technology benefits from being alarm protocol independent and industry
experts claim a transmission success rate of somewhere between 80% and 100%.
PROS: Both SMS and Voice benefit from low equipment costs and low network rates.
CONS: SMS and Voice technologies do not allow for the cost efficient supervision of a connection to the Monitoring Centre and often the first anyone gets to know about sabotage or network failure is when a scheduled signal, or worse, an emergency signal fails to arrive.
GPRS Wireless Networks
The use of a GPRS data plan overcomes this problem and allows constant supervision of the connection between the protected premises and the Monitoring Centre. A GPRS device uses the GSM network to achieve an ‘always on’ wireless connection to the Internet. Once connected, it can communicate using Internet Protocols (IP) just like any other Internet enabled device. This allows the sending of regular heartbeats to the monitoring server so that any equipment failure, sabotage or loss of network can be detected within seconds.
GPRS devices do not support audio/voice communications, so any alarm signals using standard protocols such as ademco Contact ID or Fast Format have to be converted from analogue to digital within the device itself. This is referred to as Dialer Capture. GPRS enabled devices are more expensive than SMS and Voice devices and the cost of data plans vary widely from country to country. Asian countries tend to have very reasonable rates whereas rates in North America are very restrictive.
CONS: All of the GSM technologies are vulnerable to sabotage from a GSM Jammer which can be
used to prevent devices from connecting to the network.
IP Networks (the Internet)
Due to the widespread availability of the Internet, a large number of consumers are turning to voice over IP for voice service. For the continuity of clear telephone calls from human to human its a simple case of unplugging your analogue telephone handset from the PSTN line and plugging it into an analogue terminal adapter to make and receive calls over the Internet. The human ear is very forgiving and even though delays and echo in voice conversations can sometimes be off-putting, both parties are usually able to understand each other.
Unfortunately, this is not the case with alarm communications. Somewhere between converting analogue into digital, traveling over the wire and converting digital back to analogue, things like noise and latency are introduced and along with other problems with VoIP networks, can cause alarm communications to fail.
An in depth knowledge of alarm panel protocols, alarm receivers and Internet protocols has made it possible for some solutions providers to allow the use of regular low cost ‘off the shelf’ VoIP ATAs for the reliable transmission of alarm signals over the Internet. This obviously provides huge cost benefits to both installers and end users as devices can be sourced locally and existing Internet connections can be utilized as the transmission path.
