ENUM Tutorial

1
ENUM Tutorial

• Slides by
• Steven D. Lind, ATT
• Jim McEachern

2
Disclaimer

• Heavily borrowed from
• Patrik Faltströms IETF presentation to February
  2002 ITU Workshop on ENUM
• ATT/ENUM Forum presentation to December 2002 SG2
  meeting

3
Assumption

• Use of standard telephone numbers is not going
  away
• PSTN/analog terminals are going to be around
• IP phones use 12-button keypad
• Globally unique identifier that has established
  familiarity with end users

4
Problem statements

• How do network elements (gateways, SIP servers
  etc) find services on the Internet if you only
  have a telephone (E.164) number?
• How can subscribers define their preferences for
  incoming communications?

5
More Problem Statements

• How do you address an IP-based voice terminal
  from the PSTN?
• For a call that starts out as VoIP, how do you
  know to keep the call on the IP-plane (as opposed
  to the PSTN) for a dialed telephone number if the
  customer is not yours?

6
Today, Many Addresses
tel[phone]
mailtopaf_at_example.com
tel[phone]
sippaf_at_example.com
7
With ENUM, Only One
tel[phone]
mailtopaf_at_example.com
ENUM
tel[phone]
tel[phone]
sippaf_at_example.com
Give this number to friends 46-8-971234
8
Solution in short

• Put domain names derived from telephone numbers
  in the global domain name system, DNS
• IETF ENUM Working Group created to solve the
  problem of using the DNS for
• domain name in
• Numbers re-formatted as domain names
• URI out
• mailto, sip, tel, http or other URI scheme
• Solution NAPTR records
• Use the URIs for the communication

9
ENUM in a nutshell

• take phone number

46-8-6859131

• turn into domain name

1.3.1.9.5.8.6.8.6.4.e164.arpa.

• ask the DNS

mailtopaf_at_cisco.com

• return list of URIs

sippaf_at_cisco.com
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Step 1

• Take an E.164 number and create a fully qualified
  domain name in a single highly defined and
  structured domain
• 46-8-971234
• 468971234
• 4.3.2.1.7.9.8.6.4.e164.arpa.

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Step 1 - Explanation

• Each digit can become a definable and distributed
  zone in DNS terms
• Delegation can (doesnt have to) happen at every
  digit, including at last digit
• Zones such as country codes, area codes or
  primary delegated blocks of numbers can be
  delegated as well as individual numbers
• DNS defines authoritative name servers for
  NAPTR/service resource records

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Step 2

• Lookup NAPTR RRs in DNS, and apply NAPTR/ENUM
  algorithm
• 4.3.2.1.7.9.8.6.4.e164.arpa.
• !.!mailtospam_at_paf.se!
• !46(.)!ldap//ldap.telco.se/cn0\1!
• Use rewrite rules using regular expressions which
  operate on the E.164 number (468971234)

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Regular Expressions

• For ENUM, the NAPTR regexp field may yield an
  (unchanged) URL
• !!!
• Match on original E.164, and apply
  rewrite rule

- Match beginning - Match end . - Match
any character . - Match any number of any
character () - Grouping, \n in is
replaced with group number n in
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Step 2 in detail

• ORIGIN 4.3.2.1.7.9.8.6.4.e164.arpa.
• IN NAPTR 10 10 U mailtoE2U
  !.!mailtospam_at_paf.se!
• IN NAPTR 20 10 U ldapE2U
  !46(.)!ldap//ldap.telco.se/cn0\1
• Note that no line break should be in the records

15
ENUMEnabledApplications
DomainNameSystem
Provisioning
Authentication ValidationEntities
Tier 0
Registrar
Registry
Tier 1

• voice
• fax
• messaging presence
• email
• web pages

ApplicationServiceProvider
Tier 2
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The Public ENUM Infrastructure
e164.arpa
Tier 0 (Country Code Registry)
ORIGIN e164.arpa. 3.7.9.1 IN NS
nsnanp.enum.com . 4.4 IN NS sweden_enum.com .

Tier 1 (Telephone Number Registry)
ORIGIN 3.7.9.1.e164.arpa. 7.9.7.6.6.3.2 IN NS
e164.att.net . 8.9.7.6.6.3.2 IN NS e164.xyz.com
.
Tier 2 (Application Information)
ORIGIN 7.9.7.6.6.3.2.3.7.9.1.e164.arpa. IN
NAPTR 100 10 "u" "sipE2U" "!.!sip19732366797_at_
att.net!" .
International Implementation worked in IETF and
ITU-T
National Implementation worked in ENUM Forum (US)
17
Important Aspects of ENUM

• Access
• Public DNS (e164.arpa) or Private?
• Content
• User URI (AoR) or Interconnection URI?
• Control of content
• End user opt-in control, or carrier control?
• Routing decision
• originating end user, terminating end user, or
  carrier?

18
ENUM for Dummies
User ENUM
Infrastructure ENUM
Public (e164.arpa)
Private ENUM
Infrastructure ENUM?
Private
User URI
Interconnect URI
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Who is in Control?
User ENUM
Infrastructure ENUM
End User opt-in
Public (e164.arpa)
Private ENUM
Infrastructure ENUM?
Carrier Control
Private
User URI
Interconnect URI
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User ENUM (SIP) Call Flow
ENUM Global Directory (DNS) Equates
1-202-555-1234 to sipname_at_domain.com to enable
Voice over IP using SIP
3. DNS returns NAPTR record containing SIP URL
2. Calling party proxy UAC queries DNS for
location of end point
1. The caller simply dials the persons normal
telephone number
4. Calling party UA connects the call
ENUM typically illustrated like this, but
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Infrastructure ENUM
I-ENUM
SIP Client B
SIP Client A
Carrier B
Carrier A
Infrastructure ENUM identifies interconnect point
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IMS - Private ENUM
I-ENUM
P-ENUM
SIP Client B
SIP Client A
Carrier B
Carrier A
Private ENUM Translates E.164 - to - URI
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Enterprise ENUM
Internal translation from E.164 to SIP URI
SIP Client B
ENUM
ENUM
1
2
3
SIP Client C
SIP Client A
Carrier B
Carrier A
Enterprise ENUM can take many forms