BT's 21st Century Network (21CN) is not analogue like your existing BT landline. It is digital and uses IP (Internet Protocol) as its base protocol. On top of that, it uses the Session Initiation Protocol (SIP) which is the same protocol used by 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 VoIP networks.
Alarm Monitoring with Digicoms over 21CN
21CN Problems with Digital Communicators
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, their 21CN Trials document seems to contradict that view, which has led to a lot of confusion within the 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 publishes a 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 will work on BT�s 21CN network". That kind of says it all really !