The GSM network is subject to delays in the voice transmissions which may cause problems in dialing to Central Monitoring Stations which expect very tight limits on the delays between signalling tones.
Depending on the GSM Network traffic, the network may introduce delays in the signal sent to the Central Monitoring Station Receiver which may cause the signal to be rejected. The UCM/GSM will redial in such situations but it is not guaranteed that it would succeed. The number of redials should be increased to 10 or more.
For this reason the UCM/GSM should not be relied on as the main purpose of dialing to a CMS Receiver