VoIP troubleshooting with PRTG

The QoS (Quality of Service) Round Trip sensor monitors parameters regarding the quality of a network connection between two probes. It can show the following:

• Average, minimum, and maximum jitter
• Average, minimum, and maximum packet delay variation
• Average, minimum, and maximum round trip time (RTT)
• Corrupted, duplicated, lost, and out-of-sequence packets
• The MOS

The SIP Options Ping sensor monitors the connectivity to a Session Initiation Protocol (SIP) server using SIP options "ping". The sensor sends auth and options requests to the SIP server. It can show the following:

• Response code
• Response time

The SNMP Cisco CBQoS sensor monitors network parameters using Cisco's Class Based Quality of Service (CBQoS). It can show the following:

• Current and maximum queue depth
• Number of drop packets (without buffer)
• Drop size
• Pre-policy and post-policy size

Number of pre-policy packets

VoIP (Voice over Internet Protocol) connections can experience a variety of issues that affect call quality, reliability, or the ability to connect. Some common VoIP connection issues that often require troubleshooting include:

• Poor call quality like choppy audio, echoes, or delays
• Calls that suddenly drop or disconnect
• One party can hear the other, but the reverse is not true
• VoIP phone shows no dial tone or cannot make/receive calls
• Hearing an echo of your own voice during the call
• Long pauses between when someone speaks and the other person hears them
• VoIP phone doesn't turn on, freezes, or frequently reboots

Depending on the issue you have with VoIP, you can take different measures to troubleshoot your VoIP system. Here are some examples:

Poor call quality

• Ensure sufficient bandwidth (especially if multiple devices are sharing the network)
• Prioritize VoIP traffic using Quality of Service (QoS) settings on the router
• Use a wired connection instead of Wi-Fi for better stability
• Test for packet loss or jitter using network analysis tools

Dropped calls

• Check for internet connection issues or switch to a more stable network
• Update router firmware and check router settings for VoIP traffic prioritization
• Check if the VoIP provider is experiencing an outage

Echo

• Use a headset instead of speakers to reduce acoustic echo
• Test for high latency on the network, which may be contributing to the echo
• Ensure the audio devices on both ends are properly configured and not causing feedback

Inability to make or receive calls

• Restart the VoIP device and router to reset the connection
• Ensure that the device is properly configured with the correct SIP server settings
• Check DNS settings and ensure that VoIP traffic is not being blocked by the firewall

Use VoIP monitoring tools like Paessler PRTG to keep an eye on different parameters that can affect network quality, for example:

• Test your internet connection to check your upload and download speeds
• Check for bandwidth usage of other devices that can affect VoIP calls
• Monitor jitter, latency packet loss, and MOS in your network
• Check router and firewall settings that might block VoIP traffic, including NAT rules or closed ports
• Test for overall network congestions

In PRTG, “sensors” are the basic monitoring elements. One sensor usually monitors one measured value in your network, for example the traffic of a switch port, the CPU load of a server, or the free space on a disk drive.

On average, you need about 5-10 sensors per device or one sensor per switch port.