The recipe for an efficient SIP Trunk is obviously to find the perfect balance between quality and price. 

In order to guarantee a good quality/price relationship, we believe that there are 3 variables: capacity, quality and cost.

Capacity:

Fixed telephony providers generally offer fixed telephony offer by channel. A channel is the smallest unit of fixed telephony, as it can only handle one call at a time. Try to estimate the number of clients and the call volume of your service. That will give you the required number of channels.

Many providers will therefore propose an offer per channel. They are those who often also provide your telephones, your servers or your office applications. If your requirements are bigger and you are looking for a more sizeable/scalable offer, then you will need to by per “SIP trunk” and not per channel.

Thus, at the other end of the market, some providers offer you with a unlimited channels. Here, you buy the ability to access one (or more) SIP trunks. This means that you no longer need to worry about your infrastructure ability to absorb the number of clients on your network or their call volume. Your offer will automatically scale up. This format better suits IT integrators or access providers, who need to construct a fixed offer of greater size.

There do exist other indicators of capacity, which are more specific. For example, CAPS (call attempts per second), yet they are oriented towards specific businesses, such as call centers.

Quality:

Fixed telephony service quality revolves around routing reliability, above all. You cannot afford for calls to be cut off right in the middle of a conversation!

Your provider’s main role is therefore to guarantee that the routes used for the calls are reliable. This requires a certain technical “durability”. If a route or a server goes down, the provider must have considered a back-up one, which is what is called redundancy. So check the provider’s ability to provide quality routes, as well as its redundancy scenarios.

Finally, the availability of its customer service tam is essential. First of all to cope with certain client issues: number management, legal matters, etc.

Cost:

Of course, capacity and quality are the main factors influencing the cost per minute offered by a provider. However, beware that the SIP trunk costs are complex. Do not only look at the rate for your home country. Look at  the purchasing costs from your abroad calls and other un-usual usages. What are the tariffs for calling cellphones? Does your provider apply local tariffs in countries other than yours? Which countries are your clients likely to call?

Be aware that, for international calls, certain providers are going to search for low purchase prices at source by contracting with local historical operators (which is called a direct interconnection). Others, however, will only buy from wholesalers, who themselves have already bought second-hand.