Why a network without QoS is insufficient
A classic computer network sends all packets in the same way, regardless of whether it is a voice call, file download or video stream. For email or web browsing this does not matter: a delayed packet is simply delivered a little later.
Voice works differently. Packets must arrive regularly and with minimal delay; otherwise, the voice call will crackle or drop. A network without QoS treats all packets equally during congestion, so a call suffers even when the issue is caused by a completely different application.
How QoS works in practice
QoS classifies network traffic into priority classes. Voice packets receive the highest priority during transmission on the local network (LAN) and at the edge router towards the internet. The DSCP (Differentiated Services Code Point) standard is most commonly used for packet marking - the EF (Expedited Forwarding) value identifies traffic requiring low latency.
In practice, you configure QoS on the router or switch. You assign voice traffic to a priority queue and optionally reserve part of the bandwidth for it. Modern enterprise routers support this configuration; consumer devices usually lack it or offer only limited options.
QoS and Cloud Central Station: What to Configure on Your Side
The cloud-based PBX is located on the provider's side, where QoS is already resolved. However, issues may arise in your local network and internet connection. If data backups or video conferences are running simultaneously at your company, these activities can degrade call quality without QoS.
Basic steps to ensure quality:
- Configure your router to prioritise SIP and RTP traffic (voice packets).
- Segregate voice devices onto a separate VLAN if your switch supports this feature.
- Check whether your internet provider offers service with guaranteed bandwidth for VoIP.
At virtualni-ustredna.cz we will advise you on the network settings we recommend for your type of connection when setting up.
How to verify that QoS is working
The simplest test is to make a call while simultaneously starting a large download or backup. If the call remains clear, QoS is working. If it deteriorates, the issue lies either in the priority settings or in insufficient line bandwidth.
For more detailed diagnostics, tools for measuring latency and jitter or specialised applications for monitoring VoIP quality are used. These values will precisely show where the problem originates and whether it concerns the local network or the internet connection.
Frequently Asked Questions
Do I need to configure QoS for the cloud PBX as well?
On the side of the cloud central station provider, QoS is ensured. You should configure QoS in your local network and on the router, especially if the company transfers large volumes of data simultaneously with calls.
What happens if I do not configure QoS?
In most situations, calls work without problems. Issues arise when the network is overloaded, for example during data backup or mass downloads. Without QoS, voice packets suffer like all other traffic and call quality deteriorates.
Do I need special hardware for QoS?
Basic QoS is handled by most business routers. If your network is segmented into VLANs, you also need a switch that supports 802.1p prioritisation. Consumer routers either do not support QoS or offer it only in a limited form.