Methods of Security System Alert Transmission

Monitored alarm systems transmit signal from the protected premise to the Central Monitoring Station (CS) over some form (or combination of forms) of signal transport system. There are six types of signal transport systems: 

  • POTS – plain old telephone system. This system consists of a wire running from the telephone central office (TELCO) to the protected premise. Customer gets dial tone at the premise from the TELCO and all switching, dialing and processing of the call is done at the TELCO. The signal is transported from the TELCO  to the CS over the TELCO network.
  • VOIP – DSL – Customer has a VOIP modem that is connected to the Customer’s DSL broadband connection. This modem generates a dial tone and converts the phone dialing to internet protocol and accesses the TELCO over the internet to place the call. The actual alarm signal communication is converted to message packets and sent to the TELCO through the internet where it is reassembled and routed to the CS over the TELCO network. The signal is carried from the protected premise to the TELCO over the telephone wire.
  • VOIP – Cable - Customer has a VOIP modem that is connected to the Customer’s cable broadband connection. This modem generates a dial tone and converts the phone dialing to internet protocol and accesses the Cable central office (CCO) over the cable network to place the call. The actual alarm signal communication is converted to message packets and sent to the CCO through the cable network where it is reassembled and routed to the CS over the TELCO network. The signal is carried from the protected premise to the CCO over the cable wire.
  • Cellular – This system consists of a cellular module that attaches to the alarm control panel. The cellular module transmits the alarm signal to a cellular network alarm provider over the cellular network. The provider retransmits the signal to the CS over the TELCO network. The signal is carried from the protected premise to the cellular network alarm provider over the cellular network (wireless)
  • Internet – The system consists of an internet module that is connected to the alarm control panel. The internet module connects to the customer broadband and transmits the alarm signal via the internet to the CS. . The signal is carried from the protected premise to the CS over the internet. (multiple combinations of wireless and wire or cable)
  • Radio - The system consists of a radio module that is connected to the alarm control panel. The radio transmits the alarm signal via the radio network to the CS. The alarm signal is carried from the protected premise to the CS over the radio network (wireless)

All alarm control panels have built in communicators that can transmit alarm signal over a dial tone network, using an analog tone sequence.  Transmission alternatives 1, 2 and 3 all operate as a dial tone networks but as technology changes from an analog to a digital environment problems can occur. Currently POTS line use analog technology and the signal is unadulterated from the alarm panel to the CS. VOIP – Cable changes the signal from analog to digital. Cable companies have agreed to a single protocol that does not compress the signal (at this time) This uncompressed digital signal appears to work seamlessly in the transmission of the alarm signal between the protected premise and the CS. VOIP - DSL converts the alarm signal from analog to digital and the various DSL providers have not agreed on protocol  standard for VOIP transmissions. Some DSL companies don’t compress but others compress 4, 8, 16, 32 or 64 times. As technology advances and competition for broadband bandwidth increases there is no reason to believe that all the dial tone providers will not convert to some form of compressed digital transmission for all their voice phone transmissions. The alarm signal transmission using a compressed digital signal is not 100 percent reliable as an alarm transmission method. It is also not absolute, meaning a signal might get through sometimes and not other times. This is because the current alarm signaling receivers that use the dial tone network were designed to an analog specification.

Transmission methods 4, 5 and 6, were designed in a digital world but require additional equipment to function. Because most people still have a premise dial tone phone line, often times they will use a combination of transmission methods to increase the surety and reliability of the alarm transmission. When multiple technologies are used in the transmission of the alarm signal they are used in two ways: 
  • Backup – The second technology is used in the event that the first technology equipment has failed or the transmission path has failed.
  • Redundant – Both technologies are used to transmit an alarm signal to the CS.



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