Defining prefixes to use with Pexip's BYOC

To use Pexip's "Bring your own carrier" (BYOC) you need to decide how many phone numbers to purchase from your chosen telephony carrier and which prefixes you may want to associate with those phone numbers.

This guide provides help on defining prefixes. For help deciding how many phone numbers to have, see Choosing phone numbers to use with Pexip's BYOC, and for a general introduction to BYOC, see Pexip's "Bring your own carrier" (BYOC) — using your VTC system to dial out to PSTN.

What is a prefix?

With Pexip’s BYOC you can buy multiple phone numbers (from one or more carriers) and specify which source phone numbers to use for different PSTN destinations. For each source phone number you buy there's a corresponding rule defined in Pexip containing a unique prefix value specified by you. The prefix is entered at the front of the dial string when a user places a call and is used to apply the correct rule within Pexip which targets the carrier and source phone number to use for the call. You can configure whether or not the prefix is passed to the carrier as part of the dial string.

In most cases the prefix is part of the dial string entered by a video endpoint user when they place a call to a PSTN destination via Pexip's BYOC. The exception is if a macro is used on Cisco devices, in which case the string that is entered by the user is transformed by the macro and the macro inserts the prefix. Either way the Pexip Service must receive the prefix so that it can apply the correct routing rules for the call.

Using prefixes to control calls

Prefixes are defined by you, the company administrator responsible for setting up BYOC for your organization. They form part of the information required by your partner when creating your BYOC configuration in Pexip. Prefixes enable you to have control over which phone numbers are used for which calls, and which PSTN destinations — regions, country codes, area codes, or specific phone numbers — can be reached. For example:

  • You may decide you need only one prefix for all the calls your users make. You could buy a phone number capable of international calls, define a single rule and prefix, and your users could make calls anywhere in the world using that one prefix.
  • You may want to buy different phone numbers for local, national or international calls. In this case, you can use prefixes to ensure that all calls made to a specific region or country use the phone number you bought for that purpose.
  • You may decide to buy one international number but have multiple prefixes to determine which regions, countries, area codes, or phone numbers can be dialed.

Defining a prefix

You need at least one prefix per source phone number. Whether you have more than one prefix for the same source phone number depends on whether you want to limit the PSTN destinations that can be dialed using this phone number.

When defining a prefix, you need to consider the prefix value itself and whether the prefix needs to be stripped from the dial string before it is sent to the carrier. Note that different carriers may have different requirements when it comes to the dial string they receive.

  • A Prefix must meet one of the following criteria:

    • consist of one or more digits, or

    • consist of the + character on its own, or

    • start with the + character followed by one or more digits.

  • A prefix must be unique within your company. When a call is placed, the dial string is compared against the full list of prefixes for your company, and the Prefix with the most matching characters is used. For example, if you have two rules — one with prefix +4 and another with prefix +44 — then if a call is placed using the dial string +44 1234 123456 the +44 prefix and related rule are used.

  • You can decide whether to strip the prefix or not before it is sent to the carrier.

    • Strip prefix = no: the prefix can be used to limit which PSTN numbers can be dialed.
    • Strip prefix = yes: the prefix may be used to shorten dial strings in some circumstances, provided your carrier can accept dial strings without the country code, for example.

If you have Microsoft Teams CVI, Teams Room, or Google Meet interoperability, and endpoints that register to the same domain as used for Teams / Google Meet, then you cannot use a digit as a dial prefix (note that directly registered endpoints can use just the numerical conference ID for this type of call). It must be the non-digit + character (otherwise it will lead to a dial plan clash and calls will fail). Note that if you have Cisco endpoints you can use a macro to transform what your users dial to include a prefix that matches what is configured on the Pexip Service.

Limiting which PSTN destinations can be dialed

You can use prefixes to limit which countries, which area codes and also which phone numbers can be called by using Strip prefix = no. This means the carrier receives exactly what the user entered at the video endpoint when they placed the call. Therefore the prefix you define must start with '+' and what follows must be valid too, although you can define just a country code, or both country code and area code, or a full phone number.

For example, if you bought one UK number capable of dialing anywhere in the world, you could limit calls to specific countries, area codes or phone numbers by defining a rule with a unique prefix for each country/region/phone number that you want your users to be able to dial out to. For each of those rules, you would set Strip prefix = no which means that the string entered by the video endpoint user must be a valid international phone number.

For example, if you defined four rules with prefix values +3, +4, +6, and +44 1234 123456 respectively, your users would only be able to call:

  • numbers in Europe (beginning +3 and +4)
  • numbers in Asia and Oceania (starting with +6), and
  • the specific phone number +44 1234 123456.

Calls to other destinations would not work. For example, a call to +1 555 nnnnnn would fail.