What in the World does QoS have to do with VoIP?

Learn why establishing QoS is critical for your phone system to operate properly.

Dylan Conkle
September 12, 2017

Ring, Ring! That's the sound of a client calling with voice quality issues. Customers may be frustrated with their phones and with you for recommending them. There is just one question you need to ask yourself, "Did I set up Quality of Service (QoS) on the firewall?"

What's QoS? Think about a busy highway. QoS would be a lane that would allow emergency traffic to always get through no matter how congested the roadway. In looking at a client's network, once they start getting close to using all of their bandwidth, the firewall tags voice packets as emergency vehicles that take priority over other data on the network. Establishing QoS is necessary in ensuring your customer is a happy VoIP customer, but there is another proactive measure you can also take. Enter Bandwidth Management (BWM).

What's Bandwidth Management? BWM allocates and guarantees bandwidth for certain protocols such as SIP and VoIP related RTP(Real-time Transport Protocol). Putting the highway image aside, let's think of bandwidth like a pizza. BWM allocates and guarantees that VoIP can have a certain slice. All other network activity gets what's left over.

So the question is, how much bandwidth does VoIP require? The general rule of thumb is that each call will use 75 kbps concurrently. Multiply 75 by the number of phones they have to get the bandwidth needed to sufficiently support the client's phone needs. This is usually an overestimate because typically, all users aren't on the phone at the same time. Using this formula ensures that there is plenty of bandwidth available for their VoIP system.

While establishing QoS and BWM is important, it's just as important to note that there has to be a dependable network connection coming from the ISP and the appropriate bandwidth to serve the customer's needs. Cytracom performs preemptive testing on the clients' network prior to them becoming a customer. We want to ensure that they are VoIP ready. Simply send in an IP address to and request a network monitor for all prospective clients.

QoS, BWM, and a stable network connection are all part of a successful VoIP deployment. Cytracom and Cytracom partners working together bring a quality VoIP solution to clients nationwide. For help articles covering this topic and many others, visit