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AusRegistry International gratefully acknowledges NeuStar®, Inc. (www.neustar.biz) for their
assistance with ENUM FAQs.
What ENUM numbers can I register?
The ACMA has issued numbers in the following range: 0590 000 000 to
0590 099 999. This range may be extended by the ACMA if required
during the course of the trial.
What is ENUM?
ENUM is the mapping of telephone numbers to domain names using
Domain Name System (DNS) based architecture, in order to help
facilitate such services as Voice over IP (VoIP). It allows network
elements to find services on the Internet using only a telephone
number. ENUM is simply the convergence of Public Switched Telephone
Networks (PSTN) to Internet Protocol (IP) Networks.
It is also the title of RFC 2916, the approved protocol document
that discusses the use of DNS for the storage of E.164 numbers and
the available services connected to an E.164 number.
ENUM does not change the Numbering Plan and does not change
telephony numbering or its administration in any way. ENUM will not
drain already scarce numbering resources because it uses existing
numbers.
What is E.164?
The International Telecommunications Union (ITU) is a global
organisation where governments and the private sector come together
to coordinate global telecom networks and services. The ITU
administered E.164 as the international telephone numbering plan,
the structure of which is described in the ITU document “E.164.”
Country codes are issued by the ITU, however local
telecommunications regulatory bodies within each country administers
its own telephone numbers. An example of a fully qualified E.164
number includes that telephone number’s country code, area code and
the phone number. For example the phone number 9777 1234 in
Melbourne Australia would be +61 3 9777 1234.
E.164 is an existing global numbering system and is therefore
appropriate for use by ENUM.
What are the main benefits of ENUM for
subscribers?
The benefit of ENUM is allowing internet users the ability to
communicate with other people via a range of services when the
caller knows only the telephone number of that person or only has
access to a telephone keypad.
Internet services and resources can be accessed by end users with IP
telephones, ordinary telephones connected to the Internet and other
numeric input Internet connected devices.
ENUM allows an end user to choose how they wish to be contacted,
giving them greater control.
Who could use ENUM?
Aside from accredited Registrars, ENUM can be used by individuals,
businesses, government agencies etc.
How is ENUM going to work for the average end user?
What will it look like?
The mechanics of ENUM when a call is made from one person to another
are virtually invisible. A person making a call to another person
where for instance, both are using IP phones, would appear as if it
were being made over the regular PSTN. The caller would however have
to specify the ENUM service they wish to use.
What kinds of applications could use ENUM?
The core applications ENUM will focus on are Voice over IP (VoIP)
and Voice Profile for Internet e-mail (VPIM). The goal of the VoIP
industry is to be able to make simple and high-quality voice calls
using IP networks. The VPIM industry wants to develop voice mail
systems that can exchange messages over IP networks. ENUM’s
applications will most certainly reach beyond VoIP and VPIM to such
services as internet fax and Instant Messaging.
How does ENUM work?
A telephone number, once entered, is translated into an Internet
address. The following steps explain the process:
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1. |
The number entered is translated into a full qualified E.164
number, as described earlier. Example 9777-1234 is translated to
+61-3-9777-1234 (Melbourne, Australia). |
|
2. |
The number is reduced to digits only. Example: 61397771234 |
|
3. |
The digits are re-ordered back to front. Example: 43217779361 |
|
4. |
Dots are placed between each digit. Example:
4.3.2.1.7.7.7.9.3.1.6 |
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5. |
The domain "e164.arpa" is added to the end. Example:
4.3.2.1.7.7.7.9.3.0.1.6.e164.arpa |
A DNS query is then issued on this domain and
once the authoritative name server is found, ENUM retrieves relevant
NAPTR Resource records and will perform according to the user's
registered services for that number.
What is .arpa, and why is it the top level domain for ENUM? Why
not create a new top-level domain specifically for ENUM?
E164.arpa has been proposed as the DNS domain for use with ENUM.
This designation may change as a result of ongoing discussions
between the ITU, the IETF, and other international organisations
involved with ENUM. In the event that the international community
chooses a different ENUM domain, the structures discussed here and
in IETF RFC 2916 will apply to that new designated domain. The .arpa
domain has been designated for Internet infrastructure purposes. It
is managed by the Internet Assigned Numbers Authority (IANA) in
cooperation with the Internet technical community under the guidance
of the Internet Architecture Board (IAB). A new top-level domain
(e.g., .e164) was not created because ENUM is an infrastructure
application appropriate for designation within the previously
established .arpa domain. ENUM is considered appropriate as an
infrastructure application because it provides a set of DNS-based
resource directories, referenced by phone number, for use by various
ENUM-enabled application clients (such as telephones, SIP servers,
and voice messaging systems).
Why is the number reversed?
DNS, when reading a domain name, will first search for the top level
domain (being .arpa), then the second level domain (being e.164). It
then searches for the country code, area code and phone number.
Why are there dots between the numbers?
Each dot separates the number into administrative domains, or zones.
This allows for delegation of authority at various points along the
name and eliminates the requirement for clients to know individual
delegation schemes to know where to put the dots.
Will ENUM telephone routing confuse the PSTN routing system?
ENUM will not affect application level functions such as call
routing and signalling. ENUM facilitates the discovery of resources
associated with a telephone number and does not impact how
applications operate.
It is important to note that ENUM will not change the existing
right-to-use rules and principles for telephone numbers. ENUM is
intended to facilitate applications using telephone numbers as
subscriber names, not to change how telephone numbers are
administered.
How will the e164.arpa domain be organised?
One convenient way of doing this would be to delegate according to
the 243 country codes designated by the ITU. It is important to
understand, however, that delegation in DNS can occur at any digit
or zone domain in DNS terms.
For example, within the root e164.arpa, there would be:
An NS listing for .1.e164.arpa - representing the country code (1)
of the North American Numbering Plan (US, Canada, and several
Caribbean countries).
An NS listing for .4.4.e164.arpa -
representing the country code (44) of the UK.
An NS listing
for .6.4.e164.arpa - representing the country code (46) of
Sweden,
An NS listing for .1.8.e164.arpa - representing the country code
(81) of Japan, and
An NS listing for .8.5.3.e164.arpa - representing
the country code (358) of Finland.
At the national TN/NS level, further NS delegation [DNAME, CNAME,
PTR] can occur to enterprises, TN/NS application service providers,
carriers, and even individuals who have DNS servers in their homes.
Why use DNS?
The beauty of DNS is that it exists already and is a global,
efficient, open and scalable system. Using DNS for ENUM also
provides a low cost solution.
What is the effect of e164.arpa deployment on the global DNS
system?
This is going to require research, such as the effect of "wrong
dials" on the root of e164. That is, caller specification of a wrong
number can result in many additional queries to the e164.arpa root.
Additional work will be necessary in advising ENUM applications such
things as the level of data caching necessary in order to relieve
stress, suppress escalating of poorly formed queries, mis-dials, or
cache misses on the root structure. For telephony applications,
performance and load engineering is critical, as query volumes from
small to medium sized cities alone can easily reach many thousands
per second. Response times, as well as transaction loads, must be
carefully considered. Conventional DNS caching is of significantly
reduced value in ENUM due to the huge size of the name space and
relatively even distribution of queries into the space over
arbitrary time intervals. Unlike conventional DNS queries, call
volumes are not highly concentrated into a popular small subset of
the number space.
What are SRV and NAPTR Records?
SRV and NAPTR are DNS Resource Records that contain information
about resources, services, and applications associated with a
specific phone number.
What happens if a user dials a number that cannot be resolved by
DNS?
Where a number cannot be resolved by DNS, a 404-Not Found error
message is returned to the device or program initiating the call.
The 404-Not Found error message is displayed in the case of a web
browser. With IP telephones, the call will be diverted to the PSTN
and connected the traditional way.
What happens if a user dials an emergency number
(e.g. 000 in Australia)?
Emergency numbers are not considered part of the E.164 and ENUM
services. Dialled emergency numbers will be connected, for example
by an IP phone, via the PSTN.
What protocol does ENUM use for Internet Telephony?
ENUM itself is "protocol agnostic" because it is application
agnostic. It does not specify what applications a particular number
is associated with, but instead provides a unified way of
discovering resources associated with it. It can, for example, work
with either H.323 or SIP.
What can be said about the scepticism around VoIP?
VoIP will most certainly become a reality in the near future, where
internet telephony is fully integrated with traditional telephony,
on a global scale. Although in its early stages, VoIP is always
evolving and improving. It should be remembered however that ENUM is
not intended to facilitate VoIP solely – it is intended to work with
a number of applications.
What is SIP? How does ENUM relate to SIP?
SIP is the abbreviation of Session Initiation Protocol. SIP is the
initiator of interactive communications sessions between users. It
also terminates those sessions and modifies sessions. With ENUM, SIP
can be used to initiate attempts to multiple locations to find the
user receiving the call.
Could ENUM be used to provide telephone number portability?
ENUM is not intended for this use, although it may have a place in
countries that do not have a centralised database administration.
There are implications and limitations in using ENUM in this way
ENUM is a shared resource discovery service, not an industry
provisioning service. Countries that deploy number portability have
telephone service providers that are generally required to comply
with regulatory/industry processes and procedures regardless of the
underlying technology they employ for telephony service delivery.
It’s important to highlight that ENUM will need to be deployed
consistent with applicable national requirements. It does not create
an alternate numbering system with its own set of rules and
policies.
How is the user of a number authenticated?
Users could be corporations, individuals, government agencies,
military organisations, and hosts of other non-individual users.
Service providers typically assign large blocks of numbers to these
entities. The telecom manager within these entities then assigns
numbers to users, so even the service providers cannot identify the
users for a large portion of the allocated numbers. This is an
unresolved issue but one that must be resolved prior to deploying a
robust and secure ENUM service. It is likely that the service
provider that allocated the number(s) to the user will be involved
in the process of authentication.
What about private numbering plans within a company?
The ENUM protocol can be used in private numbering plans the same
way it can be used in the public E.164 numbering plan. The Internet
Telephony gateway or proxy needs some intelligence to "decode" a
particular dialling string and then decide how to look up resources
for that particular number. Instead of looking for resources in
e164.arpa, the gateway or proxy would look for SRV or NAPTR records
for private numbers under some other structure, such as
e164.bigcompany.com.
Are users going to have to pay to have their telephone numbers
ENUM-provisioned?
Probably yes, but most likely the costs will be indirectly recovered
through the underlying prices for ENUM-enabled services that
subscribers pay. This is a DNS-based system, and someone must pay to
have a domain name registered in DNS. Listing telephone numbers will
be no different. Whether the cost will be charged directly to the
subscriber or will be an indirect charge as part of some larger
services will depend on those offering the services.
It is important to remember that a user does not have to have ENUM
list his phone number. ENUM would be a subscriber-controlled
"opt-in" system to "announce," over the Internet, the availability
of a particular telephone number to accept service sessions and how
to manage those sessions as a result of having subscribed to an ENUM-enabled
service. If a customer does not have an Internet telephony device or
service, the associated phone number will likely not be listed. On
the other hand, subscribers may not necessarily be aware that they
have subscribed to such a service, and have had ENUM provisioned for
that service by their service provider on their behalf.
Are users going to have control over how this system is used with
their phone numbers?
Ultimately yes. To reiterate, the first principle in the creation
and operation of a global ENUM service is that phone number
subscribers or their designated representatives are the ultimate
decision makers on how a DNS record for a phone number is to be
provisioned.
How will the rights of telephone number subscribers be protected?
This is an essential question that must be resolved, but a clear
statement of policy protecting subscribers should be part of any
ENUM system charter. A simple answer is by respecting existing
regulatory and business rules regarding number administration,
slamming, non-reliance, etc. Only by replicating or re-implementing
ENUM analogs to the existing rules of the road will we avoid a wide
range of serious administrative, operational, and political
conflicts.
How are you going to prevent "slamming" or "hijacking"?
Slamming, or the involuntary transfer of service provider, must be
avoided in any ENUM system. However, it is a serious problem in the
PSTN and we must be careful not to expect more from Internet
services than we are able to guarantee elsewhere. Note that
anti-slamming fundamentally requires a neutral third party solution.
The US industry is grappling with this issue on long distance right
now. It was solved on number portability from the outset.
Authenticated subscriber access is not a total solution, because if
subscribers disconnect their telephony service, they lose rights to
the phone number. Consequently, some combination of originator
authentication as well as telephone number rights validation, using
new and existing validation sources, can be used to solve the
problem, depending on the level of standard required.
Are there any examples of global namespace delegation that should
be considered as models?
The closest technical equivalent is in-addr.arpa. That domain
provides a reverse mapping from IP address to domain name. It is
used as part of the Internet infrastructure operation to help
authenticate an IP address and identify the operator associated with
an IP address. It is not seen directly by users. The same is true
for e164.arpa. It will be for operational infrastructure, rather
than for direct access by end users.
As with e164.arpa, in-addr.arpa, allocations are hierarchical
according to the infrastructure administrative structure. For in-addr.arpa,
the hierarchy uses the "CIDR" address allocation hierarchy. For
e164.arpa, the hierarchy will be based on the ITU E.164
recommendation.
What will be the effort to administer the root of the e164.arpa
namespace?
Any solution ought to require little or no work on the part of the
e164.arpa root administrator. Optimally the root of e164.arpa should
contain a small listing of all of the national ENUM top-level
country code name servers.
Who can administer the ENUM registry in the near-term?
ENUM is approaching the stage where the industry will want to start
interoperability testing, and they will want to test using the
e164.arpa domain. The interoperability test would have the same
principles that current ones do; that is, no charge, sharing of
information, etc. One method of enabling the registry would be to
develop an RFC that defines the interim delegation principles for
IANA as well as principles for the transition to the permanent
registry.
What can be done in the long term?
There will need to be a formal effort to define and establish the
structure for this activity. An example of the charter for that
effort would be:
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1. |
Define the global ENUM Service. |
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2. |
Perform the task of certifying organisations to IANA that wish
to operate national TN/NS once they have been nominated by their
respective nation states. A simple letter could be sent to
appropriate national authorities asking them how they wish to
proceed or if they even want to participate. |
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3. |
Coordinate technical standards for the operation of ENUM service
in cooperation with the IETF. |
|
4. |
Establish guidelines and policies, which national TN/NS
administrators operate. |
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5. |
Promote
public policy on how ENUM resources should be used. |
Oversight for this activity should comprise
several constituencies, such as:
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1. |
The potential ENUM user community, |
|
2. |
The potential ENUM provider community, |
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3. |
National governments, at least as an advisory, and |
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4. |
IAB-IESG representatives. |
Who will administer the national telephone
number name servers?
There are many competent companies or organisations that can operate
these servers. A number of companies have already come forward to
express their interest in running these servers, initially free of
charge and on an experimental basis, until such time as consensus
can be reached on how this system is to ultimately organise.
There are a number of regulatory constraints in various countries
that might apply to the ENUM administrator, name service operators,
and delegation policies below the national level. For example, where
local telephony service competition and number portability are being
deployed in a country, it is not unusual that a neutral third party
is required to provide master database administration services, and
a requirement for anti-slamming and non-reliance on competing
carriers for routing or resolution functions. |
