Call Quality

While many internet service providers will advertise peak download speeds, it is important to find business class internet access that offers a guaranteed sustained download and upload speed with some form of service-level agreement, when considering VoIP applications. 

• Your best option is always business class fiber-optic-based internet access.
• The next best option is a business class cable.
• If the only option is a business class DSL internet access, you should ensure the speeds are adequate for your usage.
• Consumer-grade residential internet access should never be used for more than 1 or 2 phones.
• Wireless internet access should never be used at all because the quality of the connection is inadequate for VoIP applications.

For an example of some real world bandwidth needs, see the table below

Unlike traditional phone calls, VoIP calls are broken into small packets of information. These packets are sent out over IP networks, each often finding its own route to the destination. The packets are reassembled at the destination to reproduce the original voice. Because the destination is your home or office, your local network, your internet connection, and network devices all contribute to overall call quality.

The three most common factors that affect call quality are Jitter, Latency, and Packet Loss.

Though it may sound like a dance move, jitter actually measures the variation in the arrival time of individual packets, as they make their way along various routes over the Internet. Jitter can be caused by Internet congestion, timing drift, or Internet route changes. Jitter is measured in milliseconds (ms) or thousandths of a second. Jitter greater than 50ms can result in packet loss and degraded voice quality.

Latency is the time it takes a voice packet to reach its destination; it is measured in milliseconds (ms)—thousandths of a second. Latency of 150ms is barely noticeable and generally acceptable. Latency higher than 150ms adversely affects VoIP Quality of Service (QoS), while latency higher than 300ms is generally unacceptable.

Packets are sent over the Internet and reassembled at their destination. Packet loss occurs when some packets are dropped by congested network routers or switches, or are discarded by the jitter buffer. If you miss one out of every 10 words, or 10 words all at once, chances are you won’t understand the conversation.

Quality of Service (QoS) is a form of network traffic management that prioritizes certain types of data by delaying/slowing other data packets. This helps the more important packets reach their destination with less delay. The service with the higher priority gets to pass through the router first, thereby lowering the delay that it might experience without QoS.

By setting up QoS for VoIP, you can help correct choppy audio or other call quality problems.

The most common form of QoS in home or small business routers and firewalls is through QoS tagging.  A tag is attached to each data packet indicating its priority level; high to medium to low or critical, important or best-effort. Depending on the router model, the tagging is done at the router's Ethernet port, the endpoint MAC address, or based upon the TCP or UDP port.

If you are like most small businesses, you likely have one Internet connection at your office which is shared for email, web browsing, VoIP calls, application backups, and perhaps even monitoring your security system and/or other business systems (such as point-of-sale system). Implementing Quality of Service (QoS) on your network edge devices (router or firewall) will help minimize the impact of using shared internet access on your VoIP phone call quality. Without QoS, call quality will be inconsistent and poor at best. It is highly recommended that you enable whatever form of traffic shaping is possible with your device.