# Presentation: 683178

## ENUM Primer

- November 4, 2004
- Tom McGarry - NeuStar
- tom.mcgarry@neustar.biz

## ENUM Primer

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

## 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 Internet’s* ***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?

## 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.

## 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.*_

## 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.

## 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.

## 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
- resolver’s query to the next level.

## 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.

## How does the DNS work?

- An example of a resolver using the the DNS and the domain name acme.biz
- to view a webpage.

## 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 FCC’s website.
- The protocol is identified on the left side of the colon (:).  In this case it’s 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 to:joe.smith@fcc.gov is the URI for Joe Smith’s email box at the FCC.
- The protocol which designates email is - mail to
- The name for this particular email box is - joe.smith@fcc.gov
- Notice that one domain name - fcc.gov - can be used for multiple services; e,g, websites and email

## 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

## 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

## 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 user’s 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 provider’s 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.

## 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->VoIP and VoIP->VoIP calling
- ENUM will accelerate the migration of voice traffic from the PSTN to the Internet
- Today VoIP->VoIP calls are typically routed through the PSTN:
- Calls go VoIP->PSTN->VoIP, which is less efficient than VoIP->VoIP
- 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->VoIP calls

## VoIP Call Processing With ENUM – PSTN to VoIP

- •  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.

- LEC
- Switch

- Caller dials
- +1 202-555-1212

- 2.1.2.1.5.5.5.2.0.2.1.e164.arpa =
- sally.smith@voip.net

- sally.smith@voip.net

- •  The caller dials the phone number.
- •  The caller’s local service provider routes
-     the call to the PSTN.

**DNS**

- 2.1.2.1.5.5.5.2.0.2.1.e164.arpa

- sally.smith@voip.net

## VoIP Call Processing With ENUM – VoIP to VoIP

- •  The Internet routes the call to the
-     VoIP service provider.

**DNS**

- Internet

- •  The caller dials the telephone number.
- •  The caller’s 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.

- Caller dials
- +1 202-555-1212

- 2.1.2.1.5.5.5.2.0.2.1.e164.arpa =
- sally.smith@voip.net

## 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

## Limits of ENUM

- DNS is very different than the PSTN’s 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

## 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 telco’s 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

## 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)

## 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 Internet’s* ***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