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Three Major Factors Affecting VoIP Call Quality

|  4 min
In this article

Voice over Internet Protocol technology has been used for voice communications for about a decade. Until fairly recently, reliability and quality issues had a negative effect on the reputation of these systems, particularly as users compared the service to the impeccable clarity they were accustomed to on their landline phones.

These dark days are gone and improvements in quality have been huge. Nevertheless, it remains likely that anyone who regularly uses a VoIP phone service has experienced some instances of poor call quality. The good news is that the reasons behind these quality issues are generally quite easy to diagnose and put right. A good service provider will help you to get to the bottom of any problems you are experiencing and ensure that they don’t become on-going issues once they have been fixed. If this is not the case, you should be looking for a different service provider!

This article takes a look at some of the main factors that can affect voice quality, common problems experienced by VoIP users and what can be done to resolve them.

A sub-standard internet connection

Your own internet connection and particularly the bandwidth available are always the main factors affecting voice quality. One would never expect to be able to get a good VoIP service with a dial-up connection, but most broadband connections should work well provided that they are not shared with too many different communications applications. However, as most ISPs are optimised for web surfing rather than the settings required to achieve high-quality voice calls, an internet connection that is good for most uses may still give a poor call quality. The transmission of voice packets needs different internet protocol settings to those that may be provided as standard. A business class high-speed connection will provide the best experience.


The VoIP equipment that you use will have a significant impact on the voice call quality you can achieve. You need to invest in the right IP phone or ATA / router. The frequency of your IP phone can also cause interference, with lower frequency options (eg 2.4 GHz) often performing better than higher frequency. For ATA / routers you need to consider the codecs supported (compression technologies), echo cancellation and firewall / security support.

An inadequate router is a very common problem. Lots of small businesses tend to use their internet connection for both data and voice, which only works well if your router can prioritise for VoIP traffic. If this is not the case, it would only take another user to download a larger than average file to degrade your call quality. Specialised VoIP routers are a relatively inexpensive piece of equipment and will generally solve this problem when used in a properly configured internal network.

Latency and Jitter

Latency, or VoIP delay, is the length of time taken for speech to leave the mouth of the speaker and reach the ear of the listener. It can sound like an echo and is caused by three types of delay:

1. Propagation: this delay is so small as to be barely perceptible and is the time taken for data to be transmitted through the network cables at the speed of light. If the distance travelled for an intercontinental call was half way around the world, the propagation delay would be approximately seventy milliseconds.

2. Handling: delays caused by devices in the network.

3. Queuing delays: these are delays caused when packets are put in a queue when the number sent is greater than the interface can handle in a given time period.

Jitter, which is a measure of the change in latency over time in a network, is a very common problem in connectionless or packet-switched networks. This is because the voice packets that carry information between the sender and receiver all travel via different paths and arrive in a different order from that in which they started out. This can cause scrambled and poor quality audio and can be fixed by using jitter buffers which store packets as they arrive in order to reduce delay variations and discard them if they arrive too late.

Both latency and jitter can be improved by making sure that VoIP calls are correctly prioritised, which will be the case for a business quality VoIP service. Techniques used for prioritising traffic include bandwidth reservation, multi-protocol label switching and policy-based network management.

You would expect all of the factors described above to be taken care of if you are paying for a business quality voice over IP service, such as those from IDT Express. There may still be other factors that can come into play, such as static and distortions caused by weather conditions or electrical feedback caused by the positioning of your hardware, for example, if you place your ATA too close to your broadband router. In general, however, you should expect to enjoy a high-quality voice experience.

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