cloud SIP trunkingLow cost and flexibility are the primary reasons that more and more companies are moving away from traditional PRI telephone lines and to cloud SIP trunking for their communications needs.  Cloud SIP trunking is an excellent choice for most businesses, but some planning ahead is required and there are some infrastructure considerations that should be addressed.  Here are a few things to think about to make sure you are ready to take full advantage of your SIP trunks.

How Many Concurrent Calls Do You Need to Support?

The number of anticipated concurrent calls is important in determining how many SIP channels you will need as well as the required Internet bandwidth.  Keep in mind that the number of concurrent calls is not usually the same as the number of employees or DID numbers, in fact, for most companies it is far fewer. An average business has a ratio of about 3:1 or 4:1 employees to concurrent calls.  Meaning a 30 person company might have 10 concurrent calls.  Every business is different, however and those with call centers or other high volume calling operations might have a 1.5:1 or a 2:1 ratio.  Each SIP channel supports one call, so you need to purchase enough SIP channels to ensure there is one available channel for each concurrent call during peak calling times.

Is Your Internet Bandwidth Sufficient to Support Cloud SIP Trunking?

The amount of bandwidth necessary to support SIP trunking depends on the voice codec used by the SIP provider.  SIP.US uses the G.711 voice codec which consumes 85kbps of bandwidth per call.  So we can determine, for example that a DSL connection of 512kbps will support 6 simultaneous calls by dividing 512 by 85.  (This is a very low end example, most broadband Internet connections these days are much faster and can support many more calls.)

You’ll want to base your calculations on the actual bandwidth at your location, not on the capacity claims of your ISP, which can vary from actual results.  In order to measure Internet bandwidth, run a speed test from a computer that utilizes the Internet connection to be tested.  In order to get the most accurate measurement, it is best to run the test during off-peak hours when the Internet connection is not being utilized.  There are many speed tests available online, one example is

Is Your PBX SIP-Enabled?

You can utilize cloud SIP trunking whether or not your PBX is SIP enabled, but if it is not, you will need a special device, so it is important to know.   Most new PBX systems are SIP enabled, so if you’ve purchased yours recently, it very likely is.  If it is older, there are several ways to check and see if your PBX is SIP-enabled.  First, if your PBX has a data jack or Ethernet jack on the back, it is probably SIP-capable.  Older PBX or key systems have only analog lines, so if your system does not have a data jack or Ethernet jack it is probably not SIP enabled.  If your PBX has a data jack and you are still unsure if it’s SIP-capable, conslut the user manual.  If the system is SIP ready, there will be  a section on ‘configuring a SIP Trunk’ or it will be mentioned in the specifications section, typically located at the end of the manual.  Look for words like SIP or SIP-enabled IP calling.

If your PBX is not SIP-enabled, you can still use what is called an ATA (analog telephone adapter) that will convert SIP to analog.  The ATA acts as a gateway to your legacy PBX and allows you to use cloud SIP trunks.  There are a variety of ATAs in the market and they come in a variety of sizes, from single port all the way up to 24 analog ports.

The infrastructure required for SIP trunking is not complex, but taking these factors into consideration early in your planning process will help you make the transition to cloud SIP trunking a smooth one.


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