Steve Nutt

21CN and your Intruder Alarm

If you have a monitored alarm system over a British Telecom landline then you should understand the consequences of sending signals over the new 21CN network.

21CN is not analogue like your existing BT landline, rather it is digital and uses an Internet Protocol (IP) as its base protocol. On top of that, it uses the Session Initiation Protocol (SIP) which is the same protocol used by most Voice over IP network providers. It stands to reason that the 21CN network will suffer many of the same issues as alarm systems have suffered for many years attempting to send signals over networks of 3rd party VoIP providers.

Unfortunately, most Alarm Companies are holding back to find out just how much their Customers systems will be affected by 21CN. As BT explain in their 21CN Trials document, the problem is not just with their new network. Carrier Pre-Select and local loop unbundling means that an increasing number of core networks from other Telco’s that are used for the transmission of alarm signals will be VoIP (Voice over Internet Protocol) - often without the knowledge of the Alarm Installation Company or the Customer.

History has proven that alarm panel modems and digital communicators are unable to reliably transmit their signals over a VoIP network. 21CN may allow consistent results early on, but will start to suffer more as time goes by as increasing numbers of users put the network under load. As a large number of Customers already have an Internet connection available, it makes sense to tackle the issue now rather than wait for costly failures in communication.

One problem is that BT will not acknowledge the fact that there are likely to be many issues in the area of alarm monitoring, however, other 21CN documents seem to contradict that view, which has led to a lot of confusion within the security alarm industry.

In 2007 BT told us there would be no problems with alarms signalling over 21CN. In 2008 we were told "The systems will be 'groomed out' of the 21CN Cardiff trial as a result of work undertaken by the British Security Industry Association."

In April 2009 BSIA published the BT 21CN test plan. The test plan has been put together after almost two years of development by the BSIA and its members including extensive testing of systems on the 21st Century Network at BT's facilities at Adastral Park and Swansea. The main causes for concern were:

Echo cancellation always used unless high-speed fax or modems are detected

Audio path discontinuities will occur when jitter buffer lengths change, either during a voice call or when modems or faxes are detected

Potential increase to round trip delay

The test plan goes on to state "Please note: Any results obtained from testing will not guarantee that CPE (customer premises equipment) will work on BT’s 21CN network".

So, with information like that from BT and your Alarm Company with their head in the sand, you would be well advised to do your own research and seek out Alarm Companies and Monitoring Centres that take the issue a little more seriously.

Article Tags: Test Plan

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