Latency

Latency is the delay between an action being performed and the resulting information, voice or data being received by another user or system.

In two-way radio communications, latency is particularly noticeable as a delay between pressing the Push-to-Talk (PTT)Push-to-Talk (PTT) is the button or control used to activate a two-way radio's transmitter. Press it to speak and release it to listen. button and the other user hearing the transmissionTransmission is the process of sending voice, data or signalling from a radio using a radio-frequency signal to another radio, repeater or communication system..

Latency can occur within the radio equipment itself, the radio networkA Network is a connected system of radios, equipment and infrastructure that allows users to communicate across a defined area. Radio networks can range from simple radio-to-radio systems to large multi-site networks., repeaters, IP connections or software platforms.

What causes latency?

Latency can be introduced at different points within a communication system, including:

• Radio processing
• Digital voice processing
• Repeaters
• IP networks
• Mobile networks
• Internet connections
• Cloud platforms
• Dispatch systems
• Communication gateways

The amount of latency depends on the technology and the way the complete system is configured.

Latency in analogue radio

Traditional analogue radioAnalogue radio uses continuously varying radio signals to transmit voice communication. It remains widely used for reliable two-way communication across business, industry, events, security and other applications. can provide very low communication latency because the voice signal is transmitted with relatively little processing.

In a simple radio-to-radio system, the delay can be extremely small.

Latency in digital radio

Digital radios process voice before transmitting it.

The voice is converted into digital information, transmitted and then converted back into audio at the receiving radio.

This processing introduces some latency.

Modern professional digital radio systems are designed to keep this delay low enough for normal two-way communication.

Latency and DMR

DMR (Digital Mobile RadioA Mobile Radio is a two-way radio designed to be installed in a vehicle. It normally uses the vehicle's power supply and an external antenna to provide reliable communication while travelling or working in the field.) systems introduce some processing delay because voice is digitally encoded and decoded.

A typical communication path may be:

Radio → RepeaterA Repeater receives a two-way radio transmission and retransmits it, usually from an elevated location, to extend the coverage and reliability of a radio communication system. → Radio

Each stage can contribute a small amount of processing or transmission delay.

For normal DMR voice communication, this delay is generally short enough that users can communicate naturally.

Latency and repeaters

A Repeater receives a radio transmission and retransmits it.

The processing required by the repeater can introduce a small delay between the original transmission and the retransmitted signal.

This is normally small and is not usually noticeable during everyday radio use.

Latency and IP Site Connect

Latency becomes more significant when radio sites are connected using an IP network.

For example:

Radio → Repeater → IP Network → Repeater → Radio

The IP network introduces additional transmission and processing time.

Network distance, routing and congestion can all affect latency.

Latency and IP networks

An IP network does not necessarily provide a fixed transmission time.

Latency can vary according to:

• Network distance
• Routing
• Congestion
• Connection type
• Network quality
• Packet loss
• Network equipment

A stable, well-designed network can provide predictable performance.

Latency and the internet

When radio communications are carried across the internet, the transmission may travel through multiple networks before reaching its destination.

This can introduce additional latency compared with a local radio systemA Radio System is a complete communication solution comprising two-way radios and, where required, equipment such as repeaters, antennas, base stations, mobile radios and network infrastructure..

Internet-based radio systems therefore need suitable network connectivity for reliable real-time communication.

Latency and Cloud Dispatch

Cloud DispatchCloud Dispatch is a cloud-based radio management and communication system that allows authorised dispatchers to communicate with, monitor and manage two-way radio users through an internet-connected platform. systems can introduce additional latency because communications may pass through cloud infrastructureRadio infrastructure is the equipment and supporting systems behind a professional two-way radio network, including repeaters, antennas, base stations, network connections, power systems and dispatch equipment..

For example:

Radio → Network → Cloud Platform → Network → Radio

The additional processing and network connections can create a delay.

The effect depends on the particular platform and network.

Latency and Push-to-Talk

Latency can be noticed most easily during Push-to-Talk (PTT) operation.

A user presses PTT and begins speaking, but the receiving user may not hear the audio immediately.

A short delay is normal in many digital and network-connected systems.

PTT delay

The time between pressing the PTT button and the communication channelA two-way radio channel is a programmed set of communication settings, typically including frequency and signalling, that allows compatible radios to communicate with one another. becoming available is sometimes referred to as PTT Access Time or Call Setup Time.

This is related to latency but is not exactly the same thing.

Latency generally refers to delay during communication, while call setup time describes how long it takes to establish the communication path.

Latency and voice communications

Low latency is desirable for natural two-way conversations.

If latency becomes excessive, users can experience:

• People talking over each other
• Delayed responses
• Difficulty judging when another person has finished speaking
• Awkward pauses
• Reduced conversational flow

This can become particularly noticeable in operational environments where rapid communication is important.

Latency and group calls

In a Group Call, the communication may need to be distributed to several radios or sites.

If the system uses multiple networked components, the overall communication path can introduce additional delay.

The system should be designed to provide consistent performance across the required coverageRadio Coverage is the geographical area in which a two-way radio system can provide reliable communication. Coverage depends on the radios, antennas, frequency, terrain, buildings and system infrastructure. area.

Latency and multi-site radio

Multi-site radio systems can have more latency than a simple local radio system because communications may travel through additional infrastructure.

For example:

Radio → Site A Repeater → IP Network → Site B Repeater → Radio

The additional network connection can increase the overall delay.

Latency and PoC

Push-to-Talk over Cellular (PoC)Push-to-Talk over Cellular (PoC) provides radio-style push-to-talk communication over cellular or IP networks, allowing users to communicate across wide areas where suitable network connectivity is available. systems use cellular or IP networks rather than traditional dedicated radio channels.

Because communication passes through network infrastructure and often cloud servers, PoC systems can have more latency than a simple direct radio transmission.

The actual delay depends on network conditions and the platform being used.

Latency and hybrid communication

Hybrid CommunicationHybrid Communication combines two or more communication technologies, such as two-way radio, DMR, cellular, Wi-Fi or IP networks, allowing different systems or users to communicate through a common platform. systems can connect different communication technologies.

For example:

DMR Radio → Gateway → Cellular Network → PoC User

Each additional system or network component can introduce latency.

This is one reason why the communication path should be considered when designing an interoperable system.

Latency and gateways

A Gateway connects different communication systems.

A gateway may need to receive, process and retransmit or convert communications between technologies.

This processing can introduce additional latency.

Latency and network quality

Low latency is not the only requirement for reliable networked radio communication.

Other factors include:

• Packet loss
• Jitter
• Connection stability
• Bandwidth
• Network availability

A network with low average latency but significant packet loss or instability may still provide poor communication performance.

Latency and jitter

Jitter is variation in packet arrival times.

Latency describes the delay, while jitter describes how much that delay changes.

For real-time voice communication, both can affect the quality and natural flow of a conversation.

Latency and packet loss

Packet loss occurs when some transmitted data does not reach its destination.

In a digital voice system, packet loss can result in:

• Broken audio
• Missing sections of speech
• Distortion
• Reduced intelligibility

Packet loss and latency can therefore both affect the performance of an IP-based radio system.

Latency and coverage

Latency and radio coverage are separate issues.

Poor Coverage means the radio signal may be too weak or unavailable.

Latency means the communication is delayed.

A system can therefore have excellent coverage but still experience excessive latency if communications rely on a slow or unstable network.

Latency and dead spots

A Dead SpotA Dead Spot is an area where two-way radio communication is weak, unreliable or unavailable. Dead spots can be caused by buildings, terrain, distance, interference or inadequate radio coverage. is an area where radio coverage is unavailable or unreliable.

A dead spot is not the same as latency.

Adding network infrastructure may reduce latency in some systems, but it will not automatically resolve an RF coverage dead spot.

Latency and emergency calls

Latency is particularly important for emergency communications.

When an Emergency CallAn Emergency Call is a priority two-way radio function that allows a user to quickly request assistance and, on supported systems, establish an urgent voice communication with a dispatcher or control room. or emergency alert is initiated, users need the alert to reach the intended recipients quickly and reliably.

Networked emergency communication systems should therefore be tested under realistic operating conditions.

Latency and emergency alerts

Emergency alerts may follow a different communication path from ordinary voice traffic.

For example:

Emergency ButtonAn Emergency Button is a dedicated two-way radio control that allows users to quickly send an emergency alert to a dispatcher, control room or authorised radio users. → Radio → Repeater → Network → Dispatch

Each stage can introduce some delay.

The expected response time should be considered when designing and testing the system.

Latency and call recording

Call RecordingCall Recording is a two-way radio feature or system function that captures and stores radio communications for later playback, review, incident investigation or record keeping. systems can introduce additional processing when communications are captured, stored or transmitted.

The recording process should not unnecessarily interfere with the real-time communication path.

The exact architecture depends on the recording system.

Latency and GPS

GPS information is generally separate from voice latency.

However, when GPS data is transmitted through a network to a dispatch or management platform, there can be a delay between the radio’s actual position and the position displayed by the software.

This is sometimes referred to as location-update latency.

Latency and job tracking

In a Job TrackingJob Tracking is the process of monitoring the progress, status and, where supported, location of a job or field worker from assignment through to completion, often using GPS, radio and dispatch systems. system, latency can affect how quickly job status or location information appears in the control system.

For example, a worker may update a job as complete, but the dispatcher may not see the update immediately if it has to travel through a network or cloud platform.

Latency and cloud management

Cloud ManagementCloud Management uses an online platform to remotely manage and monitor compatible two-way radios, users, devices and communication settings from a central location. platforms can introduce delays when configuration or status information is transmitted between radios and remote servers.

This is generally different from voice latency because management traffic does not normally need to be delivered in real time.

Measuring latency

Latency can be measured by determining the time between a transmission being sent and the corresponding information being received.

Network engineers may measure latency using tools such as:

• Ping
• Network monitoring
• Packet analysis
• System diagnostics

Radio manufacturers and system suppliers may also have specific methods for measuring communication delay.

Acceptable latency

There is no single latency value that is appropriate for every radio system.

The acceptable level depends on:

• Radio technology
• Network architecture
• Number of sites
• Communication type
• Operational requirements
• Whether communications are safety-critical

A local radio system may have very different latency characteristics from a cloud-connected multi-site system.

Reducing latency

Latency can sometimes be reduced by:

• Improving network connectivity
• Reducing unnecessary network routing
• Using suitable IP connections
• Improving network reliability
• Selecting appropriately designed radio infrastructure
• Optimising cloud or dispatch architecture
• Reducing unnecessary gateway stages

The best solution depends on where the delay is being introduced.

Latency and system design

When designing a professional radio system, the complete communication path should be considered.

For example:

Radio → Repeater → Network → Repeater → Radio

If the system includes dispatch or cloud services:

Radio → Repeater → Network → Cloud → Network → Dispatch / Radio

Each additional stage can potentially affect latency.

Latency and radio hire

For Radio HireRadio Hire is the temporary rental of two-way radios and related communication equipment for events, projects and operational requirements, providing professional communication without purchasing the equipment., latency is generally most relevant when the hired system uses repeaters, IP site linking, cloud services or other network-connected infrastructure.

A straightforward local radio system may have very little noticeable delay.

For larger temporary operations, the complete communication architecture should be tested before deployment.

Latency and DCS

DCS can design professional radio systems with communication latency appropriate to the application.

Where systems incorporate repeaters, IP Site ConnectIP Site Connect links compatible DMR radio sites using an IP network, allowing selected radio communications to be shared between separate buildings, facilities or geographical locations., dispatch platforms or other networked infrastructure, the complete communication path can be considered when planning the system.

For operationally critical communications, network performance and latency should be tested as part of system commissioning.