VoIP Quality of Service

There seems to be a common misconception that bandwidth is the key factor in determining the quality of voice over a network. In reality, this is not true. It’s, of course, important to have enough bandwidth for your VoIP needs, but there are other important qualities of your Internet connection that affect VoIP QoS — packet loss, latency, and jitter.

The Internet works by breaking up all data into small groups called packets. Occasionally, some of these packets are lost in the network and don’t reach the far-end. This is called packet loss and results in degradation to the quality of your phone call. Ideally, you would want packet loss to be 0% (or at least under 1%), however, it’s possible for you to experience acceptable VoIP quality with packet loss as high as 5%.

Latency is the amount of time it takes data packets to travel through travel through the network. For most calls in North America, latency is very low (less than 100-150ms even on the public Internet). This is excellent and makes for good quality calls. On the other hand, calls to overseas numbers may have latency in the 250-350ms range or sometimes higher. At these levels of latency, the quality of the call is affected. The callers will start to notice the delay. Fortunately, most overseas callers have been conditioned to expect this type of delay and are comfortable with it.

Jitter is the variation in the inter-arrival time between packets. In other words, jitter is the consistency of the network — is it consistently feeding packets to the far end? The jitter of less than 20ms is usually expected for good quality connections. When jitter is high, it means that some packets have higher latency than others. This may cause the packets to arrive too late and be discarded by the other end of your phone call.

VoIP sometimes gets a bad rep because of data packet delays, which lessen audio and video quality. The effect of packet delays to VoIP quality varies – and there will always be packet delays.

Delays are natural occurrences in telecommunications, even traditional communications. After all, voice and data travel through a series of systems: from satellites to landlines, or from servers to landlines to your digital phone. The difference between one service and another is the amount of delay. And delay has a direct effect on the quality of communications.

Good network service is able to minimize the effects of delay on your VoIP quality. Effects are negligible, imperceptible even. You experience continuous good quality talk and video reception. This is VoIP at its best.

Sometimes, however, you may experience packet delays, which translates to increased latency in your network and VoIP systems. Latency is defined as the time it takes for packets to travel from one point to another. Increased latency can cause dips in VoIP quality, which is perceptible to the users as low audio and video quality, echo, feedback and pauses.

Latency issues can be addressed by either the user or the network manager, depending on the severity and cause of packet delays.

Causes of Packet Delays

Packet delays in VoIP are normal up to a certain point. These should never affect how parties talk to each other or see each other on video. VoIP technology is made to overcome normal delays and deliver quality connections, comparable (or even better) to wireline communications.

Packet delays – latency – have two main causes: network connections and end systems.

In a network delay, traffic congestion and connection quality are the root causes of network quality dips. It could be that you are connecting to your network during peak hours. It could also be that your connection is not powerful enough for VoIP. Delays here vary from a minimal ten milliseconds to huge delays reaching thousands of milliseconds.

In end system delays, data handling causes latency problems. Data necessarily goes through encoding, decoding and jitter buffer, which can take longer than normal because of certain conditions. For instance, if there is network delay, jitter buffer time increases too as this stage is supposed to remove gaps between data packets.

With packet delays, the quality of VoIP naturally decreases. At a certain level, it can get too much that it diminishes benefits from VoIP communications.

Troubleshooting Packet Delays

As end users, there are some things you can do to circumvent issues with packet delays. The first thing to do here is to sign up with a VoIP Quality Monitoring service, such as VoIP Spear, to help determine if the cause of your decreased VoIP quality is indeed packet delay or latency. The service enables you to determine VoIP issues and causes, which can then be addressed either by you or your service provider.

Here are some troubleshooting measures you can take on the user’s end:

  1. Cut down the systems in the flow of data: Before packets get to you, it p ... through switches, servers, and wirelines. You may be connecting to the network via Wi-Fi. Try to connect directly to the router or switch.
  2. Damage in the hardware you use also worsens packet delays. Make sure that your system’s A-OK.
  3. Sometimes, you just need to renew connections in order to fix delays. Do a power cycle and see if it works.
  4. Try to dedicate bandwidth to VoIP by shutting down other applications that may use up bandwidth.

Set your QoS settings to prioritize voice. Most new routers allow this through their software.

Material contributed by Henry Fernandes of VoIP Spear