Poor voice quality—we’ve all experienced it before. Dealing with the occasional dropped call is no fun. What is causing these call quality issues?
Understanding the Two Pathways of a SIP Call:
When connecting a phone call, there are actually two channels established for the same call - signaling and media. Signaling handles the establishment and termination of the call. When a call is initiated, the phone sends a request to the provider who then reaches out to the destination number and informs them that there is a call trying to get through by ringing their phone. Once the call is connected the Media channel is established allowing the flow of audio or audio + video packets.
The channels pathway are independent and may travel completely different routes, unlike signaling, there is no guarantee that the media channel will go through your carrier at all. In fact, it is often the case that VoIP providers use what is known as media-bypass. Media bypass is when the carrier establishes the call and then removes itself from the media pathway. In these conditions, the two end-users on the call are sending the audio directly to one another over the Internet. The opposite method is called Media Proxy, where the carrier remains in the media path for the duration of the call.
Examining Issues with Media-Bypass and Media-Proxy:
If your carrier uses media-bypass, then you are sending audio directly to the person on the other end of the phone call. This means that your voice traffic pathway is entirely over the public internet and your carrier cannot do anything to improve your audio quality once the call is sent. The audio quality issues you experience are most likely caused by the delay between sending the traffic out your local internet connection and it arriving at the receiving party’s local connection. Similar to the transportation network, the speed of travel on the Internet is largely impacted by how much traffic there it is at a given time. With media-bypass, you are left on your own to travel the public internet to get your audio from end-to-end on a call.
To improve on your poor voice quality, you can try getting a dedicated connection from your Internet service provider; however, your calls will still go out to the public internet. The longer your calls have to travel on the Internet to get to their destination, the more susceptible you will be to audio issues.
If your carrier uses media-proxy, the calling party sends the audio to the carrier who then sends it to the receiving party. Depending on the situation, this can improve or damage call quality. If you were calling someone nearby, you might be better off sending the audio directly to them. Your carrier might be farther away than the person you are calling. Therefore it would be quicker to send the audio direct rather than send it to your carrier and have them send it back to the person you are calling. There are cases in which the audio quality suffers for exactly this reason. Inefficient routing over the Internet from sending media to your carrier and back to the end-user that was already nearby. However, there can also be significant quality benefits when your carrier anchors media.
A carrier with a sophisticated network can leverage their own network infrastructure to eliminate time spent traveling on the public internet. For example, if you were calling from one side of the country to the other, you wouldn’t want to ride the public internet the whole way there, which is exactly what happens in media-bypass. Instead, you could send the audio to your carrier that is much closer than your call’s destination. Your carrier would then send your media across their own private fiber (like having a private highway lane all to yourself during rush hour) and avoid the public Internet for the majority of the pathway. The greater your carrier’s network, the less time you spend on the public Internet and the better potential call quality.
Another great benefit of media-proxy is NAT traversal. If either or both of the endpoints of a call are behind NAT then there are more chances for the establishment of the audio channel to fail. Having a carrier in the middle handling the media channel and using NAT traversal mechanisms will ensure that there will be no issues with the call.
The Internet is an amazing network for communications; however, it does have limitations. Just like the transportation system, traffic impacts the quality and time required for traveling. In order to have a meaningful conversation, you need to be able to hear each other clearly and immediately - no delays. The best way to eliminate delays and poor voice quality is to avoid the public Internet wherever possible. If your carrier lacks the private network to deliver your calls, then you’ll want to make sure you are going directly to your called destination (media-bypass) to ensure you are not making an unnecessary extra stop along the way. If your carrier has a network you can leverage, you will likely benefit from having them anchor the media and using private fiber when possible.
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