By Steve F., March 23, 2026

1. How Do Alarm Panels Work?

An alarm panel is the core component of an alarm system. On one side, it connects to various sensors (such as fire or intrusion detectors) via a two-wire bus. On the other side, it connects to the PSTN network through a telephone interface, enabling communication with a receiver.

The receiver is typically deployed at a remote monitoring center (monitoring company). Its primary functions include:

• Receiving alarm signals from alarm panels
• Performing supervisory tasks such as periodic check-ins (“polling”)

A receiver can handle connections from multiple alarm panels and usually provides computer interfaces to forward alarm data to systems such as Fire Monitoring Systems (FMS). A typical example is the Conettix series from Bosch.

2. What Protocols Are Used Between Alarm Panels and Receivers?

Over decades of development, more than a dozen communication protocols have emerged between alarm panels and receivers. These protocols were originally introduced by different manufacturers and later became widely adopted across the industry.

All these protocols are designed to operate over the PSTN network. Technically, they can be categorized into three main types:

1. Pulse-Based Protocols

These protocols transmit information using tone bursts (pulse signaling). Example: “3+1 Standard 1900 Hz Carrier, 1400 Hz ACK.”

2. DTMF-Based Protocols

These use Dual-Tone Multi-Frequency (DTMF) signaling. The most widely used protocol today is Contact ID, which falls into this category.

3. FSK-Based Protocols

These rely on Bell 103 Frequency Shift Keying (FSK). Examples include BFSK and Modem II.

3. Key Challenges of POTS Replacement in Alarm Applications

As described above, all alarm communication protocols were originally designed for transmission over PSTN networks. Decades of real-world deployment have proven that they can operate reliably in that environment, supporting millions of alarm panel connections.

However, these protocols inherently depend on key characteristics of PSTN networks:

• Low latency
• Synchronized transmission (no jitter)

This dependency becomes a major challenge when migrating to IP-based networks.

Example: Handshake-Based Protocol Detection

In many systems, receivers automatically detect the protocol used by an alarm panel through handshake tones.

For example:

• Contact ID handshake:

o100 ms at 1400 Hz, 100 ms silence, 100 ms at 2300 Hz

• Pulse-based protocols:

o Typically a continuous 1400 Hz or 2300 Hz tone lasting more than 500 ms

After call established, the receiver sends different handshake tones and determines the protocol based on the panel’s response.

However, this process requires precise timing control. While PSTN networks naturally support such precision, VoIP networks are facing:

• Jitter
• Packet loss
• Variable latency

These factors disrupt timing-sensitive signaling, leading to communication failures. This is one of the primary reasons why alarm panels often fail when connected via standard VoIP solutions.

Alarm protocols are also highly sensitive to latency. Traditional VoIP approaches—such as increasing jitter buffer size to compensate for instability—do not work well in this scenario, as they introduce additional delay that further disrupts protocol timing.

4. Vola’s Solution for Alarm Panel Connectivity

4.1 A General Solution: V.152 + SBC

The International Telecommunication Union (ITU) defined the V.152 standard to enable Voice Band Data (VBD) transmission over VoIP networks.

However, due to:

• Limited demand (VBD represents a small portion of traffic)
• Implementation complexity

most UC platforms have chosen not to support V.152.

Vola’s POTS replacement CPE devices—including PR08-Pro, LM150, PR12, and PR18—fully support V.152. Combined with the Vola POTS Media SBC, they enable seamless conversion between V.152 and standard G.711, allowing interoperability with mainstream UC platforms such as:

• Netsapiens
• MetaSwitch
• Alianza
• FreeSWITCH

Based on both theoretical analysis and lab testing, Under Vola lab network conditions of total latency (fixed + jitter) < 300 ms and Packet loss < 3%, our solution can achieve: 99.99% communication success rate. This makes it a practical and scalable solution for MSP deployments.

4.2 Enhanced Feature: Contact ID Overriding

Beyond standard protocol support, Vola’s solution provides advanced override capabilities, including:

• Dialed number overriding
• Contact ID Account Number overriding

This is especially useful in retrofit scenarios. MSPs can:

• Redirect calls to a new monitoring center
• Modify account identifiers without changing the alarm panel configuration

As a result, deployment becomes significantly faster and more flexible.

4.3 Moving to IP-Based Communication: IP Communicator

With the evolution of monitoring infrastructure, many monitoring centers are transitioning to IP-based receivers.

Vola CPE devices support an IP Communicator mode, enabling direct IP reporting to alarm monitoring platforms.

When operating in IP Communicator mode:

• PSTN-based protocols are confined to:

o Alarm Panel ↔ Vola CPE

• They are not transmitted over VoIP networks, eliminating:

o Jitter issues

o Packet loss impact

o Latency sensitivity

• The CPE converts signals into IP-based reporting for transmission to the monitoring center

This approach completely avoids VoIP-related instability.

4.4 Event Logging in VolaCloud

When operating in IP Communicator mode, alarm data is processed, formatted, and forwarded through the VolaCloud platform.

Additionally, the CPE’s event logging function records alarm activities, enabling:

• Service quality monitoring
• Troubleshooting and diagnostics
• Historical event tracking

This provides MSPs with better visibility and operational control.

5. Summary: Which Solution Is Right for Your Service?

For most UC service providers:

The V.152 + SBC solution is the most practical choice

• Fast integration (within days)
• No need to modify existing systems
• Reliable POTS replacement capability

However, in challenging network environments—such as:

• Jitter > 500 ms
• Packet loss > 5%
• Frequent connectivity interruptions

The IP Communicator solution is the better option, it eliminates dependency on VoIP transmission quality and ensures maximum reliability for critical alarm communications.

PSTN is fading. But your customers’ alarm systems still speak its language.

Contact ID, pulse-based protocols, FSK—they were all built for the precision of analog phone lines. Every handshake, every timing window, every tone matters.

Now try running that over VoIP.