Non POTS service with Life Safety Systems

[jschwindler]

Greetings all,

I am a Fire Alarm contractor in Florida and have run into a situation that I hope someone with expertise in telephony can weigh in on. I have a large customer with over 240 separate fire alarm systems currently being remotely monitored via POTS lines (2 lines for each panel). The end user is attempting to save costs by moving to a Centrex system, and has requested that we come out to reprogram all of the panels to dial a "9". This was approved by the local AHJ as code compliant (based on the PBX being virtual and not located at the protected facility), with verification that the new Centrex lines being provided are still analog lines.

We have converted about a third of the systems, and are seeing a substantial increase in "Did not Test" signals, and phone line troubles. My suspicion is that the Centrex system is actually utilizing a digital line with an analog converter.

The following is a copy of an explanation I previously provided to a customer with guidance from a Fire Alarm System Engineer with Silent Knight (fire alarm manufacturer). I am not sure it applies until we get absolute confirmation from AT&T that this is not the case in our scenario:

Below is a brief synopsis of the issues we are currently seeing with (other) customers that are switching from a POTS (Plain Old Telephone Service) phone lines provided by a PSTN (Public Switched Telephone Network), to a digital phone line converted to analog over a cable/fiber network.

As a technology, analog is the process of taking an audio or video signal (in most cases, the human voice) and translating it into electronic pulses. Digital on the other hand is breaking the signal into a binary format where the audio or video data is represented by a series of "1"s and "0"s called packets. These packets are then numbered, packaged, and sent over the network to a remote machine that receives the packets. Since the Internet routes packets one at a time, some of these packets may be delayed for various amounts of time or even lost in transmission. The remote/local machines are tasked with the job of taking these packets, sorting them, and re-creating the original voice or tone. They do this by assembling the packets as they come in, and waiting some predetermined amount of time to play back the packets. Any packets that come in AFTER they should have been worked into the voice/tone stream are discarded (thrown away), because they are useless - the need for them has already passed by. Any packets that never make it at all are called "Lost" packets. This is one area in which we are having trouble. When we experience connectivity issues such as; lag time due to high internet traffic, or local Ethernet traffic, these lost packets being transmitted to the central station receiver are being ignored. If the central station receiver receives incomplete signals, they are discarded. The signal that was just “discarded”, may have been the smoke detector alarm that the panel was trying to send to the receiver delaying or prohibiting the fire department from being dispatched at all. This result is obviously not optimal for a life safety system.


Sorry for the long post, but I am hoping that I can get some opinions on the subject so I can take the appropriate corrective action.

 

[mforrence]

In my view, converting to "digital" (TDM or time division multiplexing) is not your issue. It is WAY more likely that it is being converted to IP (internet protocol). If it is being routed over the true internet (vs a private network), success will be a crap shoot. It happens that I read some of the recent regs and found that, if the equipment is supplied and supported by the LEC, it is generally approved. As time goes on, this issue will only get worse. Couple of things you can do:
1. Slow the modems down. 9600 baud, 4800 baud, etc. Slower is better.
2. Start planning on an IP-based communication solution. This is what this sized customer should consider anyway - IP primary with cellular or dialup backup.

In the land of IP, faxes and modems are going to become less reliable. Start planning now.
Good luck.

 

[allworxguy]

There are digital and analog Centrex lines. The Centex system internally is digital using PCM (pulse code modulation) to convert A/D and D/A. It reliable transmission medium. However there can be signal loss in the A/D D/A translation. This might be your problem. The UARTS are designed for voice not data.

Internet uses TCP/IP. A voice signal is sent using a protocol such as UDP (User Datagram Protocol). This is an unreliable transmission protocol for the reasons you mentioned as UDP is connectless send and forget protocol.

Connection-oriented connections setup a handshke to insure reception and retransmission if packets sre corrupted or fails to reach the destination.



Marv ccna

http://www.telemarv.ca

Sales, Installation & Service for Norstar, BCM, Samsung & Allworx Serving Ottawa and Eastern Ontario since 1990

 

[jschwindler]

Thank you for the prompt and insightful responses! The Centrex service is being provided to the customer by AT&T. Is there a testing method I can self perform, or specific question I can pose to AT&T to definitivly determine if the new lines are truly analog only as opposed to converted or emulated DTM, IP or other?

 

[mforrence]

There is really no self-test for this situation. A physical site survey may tell the tale - if the "POTS" lines go to a piece of electronics on site, that then has an Ethernet connection, you know it's likely IP. If it goes to a piece of electronics that has a T1 connection, it is likely digital/TDM. Google electronics make/model to get more info. It it goes to a classic NID and out on copper, then who knows. You could ask AT&T what the underlying network is...

In the end, you may not have an option. Slowing modems will result in better success rate.

 

[jschwindler]

Since this is a "virtual" PBX, there is no equipment on site to investigate. It sounds like I will have to wait on AT&T to provide me with confirmation of the medium. Thanks again for the help.

 

[libellis]

You might also try programming a pause between the "9" and the rest of the number in the modem dialing string to be sure the Centrex system interprets this as an outside call and not an internal Centrex system extension. A pause (generally 1 second) is usually represented by a comma in the modem dialing string, although your modems might be different. You can use multiple commas, but that's not likely required - a one second delay should be far more than adequate.

 

[libellis]

One clarification. The delay helps to make sure that there is time for the Centrex system to interpret the "9" as meaning that an outside call has been dialed without losing the first digit after the "9" and ending up with an incomplete number that then fails. This is the reason rather than what I said about it being interpreted as an internal Centrex extension (which would happen if the "9" was omitted and the system had been setup with internal extensions).

 

[sbcsu]

Quote: I have a large customer with over 240 separate fire alarm systems currently being remotely monitored via POTS lines

Surely in this age those alarm systems can be connected either by IP to the control center or you can install a local PBX for them.

 

[libellis]

Forgot to mention the most obvious. If there are sites that don't work at all (as opposed to intermittently working), presumably someone has checked to be sure the lines were in fact converted to dial "9". Very common for the Telco to miss something.

 

[Westi]

Seeing all those posts I see it is full of good information. Converting to IP is one of them but it may be that the local laws that have not caught up with the technology and so analog has to be used until they wake up.


Joe W.

FHandw, ACSS (SME)


"This is the end of the world, make sure to buy your T-shirt before it is too late"
Original expression of my daughter

 

[donb01]

Something or other has to be providing you with the "analog" lines. In my experience, to save acutal cable pairs, AT&T has a tendency to use "PairGain" equipment where they will mux 6 lines over a single pair or two and get 6 individual lines out the other end. If they are not physically doing it at your site they may be doing it in a hand hole or someplace outside your site. In my experience with alarm systems, they Do Not like PairGain - the lines need to be traditional TDM lines with stable voltage on them, and the voltage fluctuations that seem to come from the PairGain units seem to cause the security/fire system to think there is a momentary drop in the line, which is enough to kick off a trouble that goes away once a user shuts it up - typically by keying in their disarm code twice in the case of Ademco and Simplex. I provide analog lines from my PBX in some buildings, but in most of them I tie them into loop start trunks via RJ31x before they go into the PBX or I put them in front of fax machines or credit card terminals on traditional 1MB lines. It AT&T is splitting lines to save cost that is a likely cause of your problems. Generally if you are being provided with an "analog" signal I haven't had too many problems with that - even in the cases where I have had a fractional T1 coming into the building and plugged into an appliance that gives out "analog" lines. The alarm systems generally monitor line voltage, and they are usually set up to "phone home" on occasion. If either of those fails it will trigger a trouble.

 

[BTBZ]

Use alarm net radio cellular will meet your connection don't require two phone line

 

[nessman]

What does local code say on the matter. Some local jurisdictions may have fire code that specifies POTS (and only POTS) as your primary then PBX/cell/VoIP/morse code/smoke signals (ha!) as your secondary.