ENUM Primer

1
ENUM Primer

• November 4, 2004
• Tom McGarry - NeuStar
• tom.mcgarry_at_neustar.biz

2
ENUM Primer

• What is ENUM?
• How is ENUM used in telecommunications?
• What is the current status of ENUM?

3
What is ENUM?

• ENUM is an IETF Standard that defines a process
  for representing an E.164 telephone number as an
  Internet address, using the e164.arpa domain in
  the Internets domain name system.
• This definition raises some more questions
• What is an IETF Standard?
• What is an E.164 telephone number?
• What is the domain name system and how does it
  work?
• What is an Internet address?
• What is the e164.arpa domain?
• What is the process that represents an E.164 TN
  as an Internet address?

4
What is an IETF standard?

• The Internet Engineering Task Force (IETF) is a
  standards body that has defined most of the
  protocols that support the Internet including
• TCP/IP
• DNS
• Email
• The oversight body of the IETF is the Internet
  Architecture Board (IAB), a group of individuals
  elected by the IETF participants.

5
What is an E.164 telephone number?

• E.164 is an industry standard developed and
  maintained by the International
  Telecommunications Union (ITU) that defines a
  global standard for the structure of a telephone
  number (TN).
• All US TNs conform to the E.164 standard, for
  example 1 202 555 1212 and 1 800 325 3535
• The ITU administers telephone number country
  codes among sovereign nations.
• For example, the country code 1 is assigned to
  the US and country code 44 is assigned to the
  UK.
• Each country determines their own policies with
  regard to administering numbers within their
  country (i.e., country code), as long as they
  adhere to the E.164 standard.
• The E.164 standard combined with the ITU
  administration of country codes ensures that ALL
  E.164 TNs are globally unique.
• The fact that each country has a unique country
  code and administers its own TNs within that
  country code is a very important aspect of the
  ENUM architecture.

6
What is the domain name system?

• The domain name system (DNS) is an Internet
  service that translates domain names into IP
  addresses. The IP addresses are addresses of
  servers which provide applications such as web
  pages and email.
• Because domain names are alphabetic, they're
  easier to remember. The Internet however, is
  really based on IP address. Every time you use a
  domain name, therefore, a DNS service must
  translate the name into the corresponding IP
  address.
• For example, the domain name example.com might
  translate to IP address 198.105.232.4.
• Domain names are used to locate servers and
  access services on the internet.

7
How does the DNS work?
The DNS is a distributed database. Individual
zones can be locally controlled. In the example
provided ICANN manages the Root zone, NeuStar
has been contracted by ICANN to manage the .biz
zone, and NeuStar as the registrant of
neustar.biz manages that zone. All of the
zones at the top level are managed by an entity
called a registry. For example NeuStar is the
registry for .biz and VeriSign is the registry
for .com. Each node in the DNS hierarchy is
designated by a domain name. In the example
provided the node identified as neustar has the
domain name neustar.biz. The node identified as
nanpa has the domain name nanpa.neustar.biz.
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How does the DNS work?
Even though each zone can be locally controlled
the data is available across the entire network
through a client-server architecture.
Nameservers constitute the server half of the
architecture. The zone managers provide
nameservers for their zones. Clients called
resolvers query the nameservers for information
about the zone. Web browsers and email servers
have resolvers built-in for this purpose. DNS
queries are recursive. The nameserver always
responds to the resolver as opposed to
forwarding the resolvers query to the next
level.
9
How does the DNS work?

• Domain name registries
• Registries are responsible for managing top level
  domains (zone). This concept is also applied to
  other levels within the DNS such as co.uk, and
  fed.us, but is required at the top level.
• Registries typically have the following
  responsibilities
• Maintain authoritative database for the zone
• Provide a Whois
• Provide a registrar interface
• Update and publish the zone file
• Operate the nameservers
• Registrars act as an interface between the
  registrants, i.e., the consumers that register
  domain names, and the registry. They are the
  retail channel for domain names.

10
How does the DNS work?
An example of a resolver using the the DNS and
the domain name acme.biz to view a webpage.
11
What is an Internet address?

• An Internet address is called a Uniform Resource
  Identifier (URI). Some examples of URIs
• http//www.fcc.gov/ is the URI for the FCCs
  website.
• The protocol is identified on the left side of
  the colon (). In this case its http - hyper
  text transport protocol - the protocol used to
  display websites
• To the right of the colon () is the name of the
  address - www.fcc.gov
• mail tojoe.smith_at_fcc.gov is the URI for Joe
  Smiths email box at the FCC.
• The protocol which designates email is - mail to
• The name for this particular email box is -
  joe.smith_at_fcc.gov
• Notice that one domain name - fcc.gov - can be
  used for multiple services e,g, websites and
  email

12
What is the e164.arpa domain?

• e164.arpa is a second level domain that was
  designated specifically for providing ENUM
  service.
• The Internet Architecture Board (IAB) is
  responsible for the e164.arpa domain.
• The IAB has outsourced the registry operations to
  an organization called RIPE, i.e., RIPE runs the
  technical operations for the domain
• Telephone number country codes will be delegated
  from this domain
• For example, country code 1 will become the
  domain 1.e164.arpa
• Since it is the ITU that administers country
  codes, they have a role in the delegation
  process

13
What is the process that represents an E.164 TN
as an Internet address?

• There are a few steps in the process of
  representing an E.164 TN as an Internet address
• First the TN must be turned into an ENUM domain
  name
• TN 1 202-555-1212 becomes domain name
  2.1.2.1.5.5.5.2.0.2.1.e164.arpa
• Second the domain name must be registered in an
  ENUM registry
• This process is similar to registering a .com or
  .org domain name
• Then resolvers query the DNS to get the Internet
  address
• For example a resolover looking for the Internet
  address for TN 1 202-555-1212 will query the
  DNS, using the ENUM domain name,
  2.1.2.1.5.5.5.2.0.2.1.e164.arpa

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What is the process that represents an E.164 TN
as an Internet address?

• The VoIP user on the bottom left dials 1
  202-555-1212 to call the VoIP user on the bottom
  right.
• The users resolver creates an ENUM domain name
  from the TN and queries the DNS.
• The DNS will return the Internet address (VoIP
  server) of the VoIP user.
• A call is established between the two VoIP
  users.
• The Internet address is hosted in the Tier 2
  service providers DNS servers.
• The Tier 2 service provider will register the
  ENUM domain name with the Tier 1 registry.
• The Tier 1 registry manages the ENUM domain names
  within a country code.
• The Tier 1 points the resolver to the Tier 2 to
  retrieve the Internet address.

15
How is ENUM used in telecommunications?

• While ENUM can be used for multiple applications,
  such as email, instant messaging and websites it
  is primarily being considered for voice (VoIP)
• ENUM can be used for PSTN-gtVoIP and VoIP-gtVoIP
  calling
• ENUM will accelerate the migration of voice
  traffic from the PSTN to the Internet
• Today VoIP-gtVoIP calls are typically routed
  through the PSTN
• Calls go VoIP-gtPSTN-gtVoIP, which is less
  efficient than VoIP-gtVoIP
• VoIP-related services that require end-to-end IP
  connectivity will be lost in such a call
• ENUM provides a scalable solution for maintaining
  end-to-end IP connectivity for VoIP-gtVoIP calls

16
VoIP Call Processing With ENUM PSTN to VoIP
2.1.2.1.5.5.5.2.0.2.1.e164.arpa
sally.smith_at_voip.net
DNS
2.1.2.1.5.5.5.2.0.2.1.e164.arpa
sally.smith_at_voip.net
sally.smith_at_voip.net
LEC Switch
Caller dials 1 202-555-1212
The PSTN routes the call to the VoIP
service provider.
The Gateway converts the telephone number into
an ENUM domain name and queries the DNS.
The DNS responds with the Internet address of
the user. The VoIP service provider will
use the Internet address to complete the
call to the VoIP phone.
The caller dials the phone number. The
callers local service provider routes the
call to the PSTN.
17
VoIP Call Processing With ENUM VoIP to VoIP
DNS
2.1.2.1.5.5.5.2.0.2.1.e164.arpa
sally.smith_at_voip.net
Internet
Caller dials 1 202-555-1212
The Internet routes the call to the VoIP
service provider.
The caller dials the telephone number. The
callers VoIP service provider converts the
telephone number into an ENUM domain name
and launches a query to the DNS. The DNS
responds with the Internet address of the
user. The VoIP switch routes the call to the
Internet.
The VoIP service provider completes the
call to the user.
18
What is the current status of ENUM?

• Many countries are evaluating the process for
  deploying ENUM
• ENUM deployment decisions include
• Developing a process for establishing a Tier 1
  registry
• Developing policies with regard to registering an
  ENUM domain name in Tier 1
• Developing policies with regard to registering an
  Internet address in Tier 2
• Austria is the only country that has deployed
  ENUM
• The US ENUM Forum has been evaluating deployment
  policies and practices for ENUM in the US
• A Limited Liability Corporation (LLC) has been
  established within the US for the purposes of
  selecting a Tier 1 registry
• Because country code 1 is a national asset the
  US Government will have a role in the selection
  process, if the LLC progresses to the stage of
  selecting a Tier 1

19
Limits of ENUM

• DNS is very different than the PSTNs intelligent
  network infrastructure
• Anyone can query the DNS
• Vulnerable to privacy abuses users can mine
  the DNS acquiring all available records
• Every query to the DNS gets the same answer no
  authentication or authorization of query
  originator
• For the most part the DNS is not secure digital
  signatures and encryption has not been widely
  deployed

20
Limits of ENUM

• The authority of an ENUM record is unclear
• The consumer must opt-in to ENUM service
  because the DNS is public, i.e., publicly
  available consumer information
• How do you ensure that ENUM is available for all
  potential application providers, e.g., AOL for
  instant messaging, Vonage for voice, Google for
  email, etc.
• What is the authority of the telco assigned the
  numbering resource by NANPA/PA?
• Can the telco provision the Tier 1 record?
• If so, can the consumer override the telcos Tier
  1 record?
• Does the telco have preference over other
  application providers?
• There are no provisions within ENUM to
  synchronize with existing numbering
  infrastructure NANPA, LERG, Pooling
  Administration, NPAC
• Potential impact on the integrity of numbering in
  a converged world, i.e., two networks, PSTN and
  Internet, sharing one namespace - the NANP

21
Alternatives to ENUM

• Private ENUM is a service that utilizes ENUM
  technology but in a domain other than e164.arpa
• Private ENUM typically creates a closed user
  group in a restricted domain to avoid many of the
  limitations of public ENUM (i.e., ENUM in the
  e164.arpa domain)
• Recently there is an effort to address the
  specific needs of telecom carriers within public
  ENUM. This effort is called carrier ENUM.
• Examples of private ENUM deployments
• The wireless standards organization 3GPP has
  recommended private ENUM for interoperability
  between home and roaming networks
• US wireless carriers use private ENUM to enable
  intercarrier routing of MMS messages (MMS routing
  requires end-to-end IP connectivity)

22
ENUM Summary

• ENUM is an IETF Standard that defines a process
  for representing an E.164 telephone number as an
  Internet address, using the e164.arpa domain in
  the Internets domain name system.
• ENUM provides a capability to integrate VoIP into
  the PSTN
• ENUM is still in the process of being defined and
  deployed
• Consumer privacy
• Authority over ENUM records
• Maintaining the integrity of numbering in a
  converged world
• Carrier ENUM
• Private ENUM is being adopted and implemented