Checklist for ensuring good quality business VoIP calls


There are many cost and operational advantages associated with using Voice over Internet Protocol (VoIP) to route your business phone calls over the internet.

However, these are only advantages if VoIP call quality is at least as good as that experienced on legacy analogue and ISDN lines.

To ensure good quality VoIP calls it is essential that VoIP data packets are routed between your desk-phone (or office phone system) and your VoIP Service Provider with minimum delay and without any dropped data packets.

This is a significant network design and implementation challenge since most internet connections are optimised for applications such as web browsing and email where delays and dropped packets are not a significant problem.

At Premitel we have the expertise and experience to address this challenge and ensure the delivery of business VoIP phone systems with the best possible call quality.

If you are experiencing any VoIP call quality problems, or if you are about to implement a VoIP phone system in your business, then you should get in touch with Premitel for a no-obligation consultation.

Our underlying approach to the design and implementation of business VoIP phone systems is to follow the six point checklist below and ensure that we can answer YES to each question in the checklist.

1. Does your VoIP Service Provider and your Internet Service Provider have a peering arrangement?

The first thing to be aware of before deploying a VoIP solution is the importance of choosing a VoIP Service Provider and an Internet Service Provider that have a “peering” arrangement.

A “peering” arrangement would mean that your VoIP Service Provider’s servers are connected directly to your Internet Service Provider’s servers, probably in the same data centre.

If there is no “peering” arrangement then your VoIP data packets would have to be routed via the general internet before they reach your VoIP Service Provider.

This could be a problem because once VoIP data packets are being routed across the general internet they are likely to be treated like all other data packets and be subject to delays and interference that would vary depending on the volume of general internet traffic and the quality of the connections hops.

2. Does your Internet Service Provider give priority to VoIP traffic?

A peering arrangement between your Internet Service Provider and your VoIP Service Provider is of limited value unless your Internet Service Provider gives priority to VoIP data traffic on its own network.

If this is not the case then your VoIP traffic would be mixed-up with their other general internet traffic on their backbone network. Your VoIP data packets would then be affected by any internet congestion on your Internet Service Provider’s network.

One way of ensuring priority for VoIP data packets is for you to to rent a leased line internet connection from your Internet Service Provider that would be used solely for VoIP. However, that is not a cost-effective option for many businesses.

A better option is that your Internet Service Provider (somehow) identifies VoIP data packets and then gives those data packets priority when being routed across their network to your (peered) VoIP Service Provider.

This can be achieved by configuring your VoIP equipment so that Quality of Service (QoS) tags are attached to VoIP data packets.

Your Internet Service Provider must then recognise these QoS tags and give data packets with the appropriate tag value the highest priority when being routed across their network.

Fortunately, there is a standard for QoS tagging known as DSCP that is supported by most VoIP equipment.

You therefore need to establish if your your Internet Service Provider also supports DSCP QoS tagging and then establish what the tag values should be to ensure that VoIP data packets are given the required priority.

3. Is your internet connection of sufficient capacity and quality to support VoIP traffic?

Most internet connections are asynchronous.

In other words the transmit and receive capacities (ie bandwidth) are different, with the receive capacity usually significantly higher than the transmit capacity.

Asynchronous internet connections are ideal for general web browsing and streaming services in which the amount of data downloaded usually exceeds significantly the amount of data uploaded.

However, VoIP traffic is synchronous.

In other words an equal amount of capacity is required for both transmission and reception. This means that the transmit bandwidth of your internet connection has to be considered carefully.

The transmit bandwidth is usually significantly lower than the receive bandwidth and is typically the limiting factor in determining how many simultaneous VoIP calls can be supported by an asynchronous internet connection.

One point to note when considering internet capacity is that the bandwidth required by a single VoIP call is relatively low at less than 100 Kbps. In other words 10 x simultaneous VoIP calls require only 1 Mbps of bandwidth.

The two factors that affect the quality of your internet connection are latency and jitter

Latency is a measure of end-to-end packet delay and has been addressed to a large extent by the QoS and peering requirements discussed above.

Jitter is best described as interference that would cause errors in the data packets which would result in the packets being dropped or being unintelligible to the receiving equipment. A high number of data packet errors would cause a stuttering VoIP conversation.

The best way to avoid jitter is to have a business quality internet connection from an Internet Service Provider that takes specific measures to minimise jitter and other causes of data packet errors.

Unfortunately, this usually means that you will have to pay a bit more for your internet connection.

4. Have your VoIP phones (or phone system) been configured to attach DSCP QoS tags to VoIP calls?

An obvious pre-requisite for this is that your VoIP phones (or phone system) must be able to support DSCP QoS tagging.

Fortunately most new VoIP phones support QoS DSCP tagging, but it is worth checking if it is not explicitly stated in the specification of your phones.

It is also the case that the default QoS DSCP tag values in most new VoIP phones have usually been set to the highest priority values.

Nevertheless, you should confirm this and if necessary make the required changes to the QoS tags. You should also confirm that your QoS tags match your Internet Service Provider’s VoIP QoS tagging criteria.

5. Has your router been configured to give priority to VoIP traffic before it is passed to your Internet Service Provider?

There are several ways in which a router can be configured to give priority to VoIP traffic on the connection between your premises and your Internet Service Provider’s equipment at your local telephone exchange.

The router could use QoS DSCP tags discussed above, but it is usually simpler and just as effective to prioritise traffic according to IP addresses.

This requires that the IP address of each VoIP phone is known and may also require that the router and the network switches are capable of assigning different types of traffic to specific Virtual Local Area Network (VLAN) IP subnets.

6. Have your network switches been configured to give priority to VoIP traffic within your local network?

The issue of giving priority to VoIP traffic within your local area network is not usually a significant problem due to the relatively large capacity in most local area network (ie 100+ Mbps) and also the very low latency times that are inherent in local area networks.

Nevertheless, it is good practice to ensure that you deploy network switches that can prioritise VoIP traffic within your local area network just in case there is some network overload issues caused by a malfunction or malware.

One point to note is that network switches do not use DSCP QoS tagging discussed above. Instead they use their own proprietary methods or the 802.1P QoS standard for network switches.

If you ask Premitel to assist with your VoIP deployment we would ensure that you could answer YES to all of the above questions.

Get in touch with Premitel if you have a specific requirement or if you wish to discuss how your business could make better and more cost-effective use of its existing telecommunications and internet infrastructure and services.