Melissa Swartz | BCStrategies Views | April 1, 2016 defines a pitfall as “a lightly covered and unnoticeable pit prepared as a trap for people or animals,” and as “any trap or danger for the unwary.”

We all want to avoid that stuff. Here are five areas where you can run into trouble when implementing SIP trunking.


Yes, SIP is a standard. However, there is only a part that everyone agrees to; beyond that, it is often customized by various manufacturers. SIP devices are not necessarily interchangeable. So if you are installing SIP trunking, you must make sure that your SIP trunking provider is compatible with your telephony system AND your session border controller (SBC—more on this later).

Your SIP provider should be able to provide you with certification of compatibility with your telephony system and SBC, as well as best practices for configuration. If they can’t provide this information, consider this a red flag.

Avoid configuration pitfalls by requiring your SIP provider to supply links to the systems and SBCs for which they have certified compatibility, as well as best practices for configuration.


There is a lot of variety in how SIP trunks are priced. Some providers charge by the number of concurrent call paths, or sessions. Others are strictly usage based. All of them charge for long distance calls, but some include bundles of minutes with the monthly cost, so you only pay for the usage that exceeds the minutes in the bundle. Many of them charge for local calls. Most organizations don’t track local usage, so it’s hard to know how that will impact your total cost. The best way to avoid surprises is to know what your usage is and do the math when you are comparing offers. If you don’t know how many local minutes you are using, make an assumption. Is it twice as much as your long distance? Four times as much? Run a couple of scenarios if you need to. But don’t trust the vendor’s projections. They don’t know your environment like you do.

In addition, you need to read the contracts. There are many costs hidden in contracts that are not on the pricing pages. For example, we saw a contract recently where the carrier charges $75 for every call to 911. That can get expensive quickly. Another common charge is for excessive short calls, which are typically calls under 15 seconds. If that type of call makes up too large a percentage of your usage, additional charges apply. This is typically meant to address outbound telemarketers and doesn’t impact other types of businesses.

Finally, there are major differences in pricing for backup and redundancy. We have a client who has a primary and a backup data center, and was planning on running SIP trunks to both sites. In their environment, the only time there would be traffic at the backup site would be during an outage of some sort. They wanted 200 sessions at the primary site, and the ability to support 200 sessions at the backup site when needed. Some carriers proposed services that only charged for the use of the 200 sessions, since they would only be using one site or the other. Others charged for 400 sessions because there were two sites with 200 sessions each. Others offered options for bursting to accommodate higher usage when needed.

To avoid the pricing pitfalls, you need to:

  • Know how much usage you have (both local and long distance), and understand how the services will be priced.
  • Look at the contract to find hidden charges such as 911 calling or possibly short calls.
  • Understand how options for backup or redundancy are priced and make sure that you are analyzing all of the costs.


You have to have a way for SIP trunks to reach your network. There are two main options:

  1. A private connection such as MPLS. Some clients have added a connection to the SIP trunk provider, or have had the SIP trunks come in over an existing MPLS connection when the carrier was the same for both.
  2. OTT or Over The Top services where SIP trunks come in over an existing connection such as your internet.

Of course, there can be costs for these services if you have to increase bandwidth or add a new location to your network, and those need to be factored into your pricing analysis.

However, there are other considerations as well:

  • If you are using an OTT connection, you will lose QoS once your calls hit the public internet. This can result in poor call quality, since the priority markings don’t stay with the call. If you have a private connection, you can still have call quality issues but normally you can work with the carrier to get the issues resolved.
  • Are you on the same carrier the entire route, or is there another provider for the last mile? Adding another provider into the mix can create delays when there are problems with the service. When you are buying the service, the sales person tells you, “We are one of ABC Company’s biggest customers, and when we have an issue they jump to fix it.” After you have the service, and you have a problem, they say, “It’s not our fault. It’s a problem with ABC Company and they aren’t getting it fixed.”
  • Depending on how the services reach you, there may be different equipment needed on your end. Are they bringing you fiber, Ethernet, or bonded T-1s? You may need to buy some gear to support a different type of connection. If you are getting bonded T-1s, ask the provider how they will alert you if one of the T-1s is lost. We had a client who was getting a lot of complaints about slow service and finally figured out that one of their bonded T-1s was down. It took some digging to figure out the cause.
  • Installation intervals are typically longer for private connections if you can’t use an existing one. We are routinely seeing it take 90 days to install new MPLS connections.
  • Number porting can be unpredictable. We’ve seen it go very well, and we have seen nightmares. In some rural locations, numbers may not even be able to be ported. We’ve run into this three times in the past year. The process can be frustrating and create delays; in fact, I wrote an article about it for NoJitter.

To avoid pitfalls due to facilities, be sure you understand:

  • How your provider will be bringing the services to you
  • Whether there is a different last mile provider involved
  • What the physical handoff will be
  • How long it will take to get services and port numbers
  • Then add more time into your project time line to account for unexpected delays. If you don’t have the delays, it will give you extra time for testing.

In the next article in this series, I’ll examine pitfalls that occur in configuration and failover of SIP trunking.

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