FAQ

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What is ENUM?

ENUM is an internet database in which phone number holders publish information on how others can call their phone number over the internet. You will find more information on this site.

Why are ENUM domains registered through CZ.NIC?

ENUM is a global system under which each country has an administrator of the register of numbers with the national prefix. CZ.NIC administers the ENUM register for numbers in the Czech Republic (numbers with 420 as the international prefix). The actual registration of domains is done through “registrars”. Registrars have access to the register and allow their customers register and manage their phone numbers.

What do I need to call through ENUM?

To use ENUM, you need a phone capable of making calls over the internet, called an IP phone, and an internet connection. You will also need to make a query about the called number in the ENUM database. The query can be made either right at the telephone set, at a PBX or at a telecom operator’s exchange. You will find more information on this site.

What do I need to be called by others through ENUM?

To be called by others through ENUM, you need a phone capable of receiving a call over the internet (with the appropriate VoIP telecommunication service) and a phone number with a registered ENUM domain. You will find more information on registering a domain on this site.

What is validation?

Validation is making sure that an ENUM domain registration applicant is the holder of the phone number to be registered. Each number then has to be revalidated at least once in six months to make sure the telecom operator has not assigned the phone number returned by the old customer to a new customer whose call routing would be affected by the old settings.

How is the validation done?

In practice, validation is most often done in three ways. The first way is using a one-time password sent to the number to be registered via SMS or read out by an automatic machine during a call, which is entered by the user in the registration form. The second option is presenting the operator’s bill showing the phone number and its holder. And the third way used in practice is presenting an agreement that states the phone number and its holder or otherwise documents the relation between the number and the holder.

Why is it that I can register a domain for a whole year (or even more) but validation is only valid for six months?

Six months is the time given by an unwritten rule agreed by telecom operators. After that time, a number returned by a former customer can be “recycled” for another customer. The new customer could be affected by the old customer’s settings and their calls could be routed incorrectly.

What is the difference between an operator and a registrar?

An operator provides the user with a telecommunication service and, as part of it, with a phone number and SIP address. The user will then need a registrar when they register their number in ENUM. In practice, it is not uncommon that one entity is an operator and a registrar at the same time.

Can anybody else register my phone number in ENUM?

No, a number in ENUM must always be registered by its holder. However, you as the holder can authorize somebody else to perform the registration process, arranging everything for you. This is used, for example, by telecom operators that register numbers in ENUM as part of their telecommunication service. You can find a list of them on this site.

What is SIP?

SIP is a protocol for voice transmission over the internet. It defines how the caller connects to the called party and how the call audio data is transmitted over the internet. SIP is related to ENUM in that for their numbers registered in ENUM, users enter the SIP address of their phone with the appropriate phone number in the DNS. You can find more information about the SIP protocol e.g. in Wikipedia.

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