Understanding ENUM

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Understanding ENUMCurrent Status

• Kmccandless_at_illuminet.com

Network Planning August 21, 2001
2
ACRONYMS
A Record (A host Address) ARPA (Advanced
Research Project Administration) DNS (Domain
Name Server) E.164 (ITU telephone numbering
plan) IETF (Internet Engineering Task
Force) ITU (International Telecommunication
Union) MGC (Media Gateway Controller) NAPTR (Nam
ing Authority Pointer Record in a
DNS) NS (Authoritative Name Server, DNS
record) RTP (Real-Time Transport
Protocol) SG (Signaling Gateway) SGA (Study
Group A of the International Telecommunication
Advisory Committee, US
policy and regulatory aspects
telecommunications services.) SIP (Session
Initiation Protocol) URI (Uniform Resource
Identifiers)
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DNS Hierarchy
This slide is from draft 4 of the Ad-Hoc Study
Group A report on ENUM
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TIER 0, I, II
Tier 0
Directs the DNS query to the controlling country
based on country code. This is done by
providing the NS record of Tier I.
e164.arpa
Tier I
Tier I directs the DNS query to the customer Tier
II provider. The NS record is provided for the
subscribers telephone number.
1.e164.arpa
Tier II
DNS service that stores a list of service
specific internet addresses in the form of URIs
in a DNS resource record called NAPTR. TIER II
will return the full list of Internet addresses
associated with the E.164 number being
queried. IN NAPTR 10 10 "u" "sipE2U"
!.!sipkmccandless_at_illuminet.com! IN NAPTR
10 10 "u" "mailtoE2U" !.!mailtokmccandless_at_i
lluminet.com! IN NAPTR 10 10 "u" faxE2U"
!.!mailtofaxmachine5_at_illuminet.com! IN
NAPTR 10 10 "u" printE2U" !.!mailtoprint
er03_at_illuminet.com! IN NAPTR 10 10 "u" "telE2U"
!.!tel[phone]!
.1.e164.arpa
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Example
Requestor types into their browser a E.164
number 19135551212 The requestors software
converts the phone number With country code into
a ENUM ready number. 2.1.2.1.5.5.5.3.1.9.1.e164.ar
pa
Requestor
.
The Root Node
The root node is the root server that directs
queries to the appropriate zone. .arpa, .com,
.org, etc
Tier 0 database will direct the request to the
North American Tier I database(s) based on the
country code of 1. (Assumes specific model for
Tier I.)
e164.arpa
Tier 0
1.e164.arpa
The Tier I database, for country code 1, could be
two sub-tiers one sub-tier to receive country
code 1 and the other to segment the NPAs within
North America. The NPAs could be grouped
by individual countries within North America.
Tier I
.1.e164.arpa
The Tier II database will return to the
requesting computer the list of service specific
addresses (URIs) associated with the queried
number.
Tier II
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Example Continued
.
FAX
e164.arpa
In this continued example, a requesting
computer can deliver information to several
devices just by knowing a phone number. This
could be a number from a business card. Now the
user can send information to a business associate
based on the options returned by the query.
1.e164.arpa
.1.e164.arpa
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TIER 0 II DATABASES

• Tier 0
• Only one database controlled by RIPE NCC and ITU
  (policy only)
• Contains participating country codes.
• Tier I
• Within North America there could be several Tier
  1 databases.
• There would have to be a delegation process from
  the North Americancountry code of 1 to a NPA
  sub-database. The NPAs could be grouped by
  individual countries in North America.
• Contains the fully qualified E.164 numbers and
  pointers to Tier II provider for the subscribers
  URIs.
• Tier II
• Competitive with many Tier II providers
• Hosting the subscribers URIs

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Countries Covered by the North American Code of 1
(One)
United States Canada Jamaica Bahamas Grenada Barba
dos Barbuda Antigua St. Kitts Nevis St.
Lucia St. Vincent the Grenadines Dominica Trinid
ad Tobago Dominican Republic Anguilla Bermuda Br
itish Virgin Islands Cayman Islands Commonwealth
of the Northern Mariana Islands Guam Montserrat Pu
erto Rico Turks Caicos Islands US Virgin Islands
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Problem

• More then one Country under the 1 code for North
  America
• Who will administer the Tier I database for North
  America?
• What happens if one of the other countries within
  North America respond to the ITU before the
  United States and are granted provisioning rights
  to the North American Code of 1?
• Do we want to be involved with all the other
  Countries in North America for ENUM deployment?

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A Better Approach
.e164.arpa
Tier 0 (Containing list of country codes)
Tier I for North America (Containing NPA
pointers for each country that is a subset of the
1 code)
1.e164.arpa
.1.e164.arpa Barbados NPA
.1.e164.arpa ETC
..
.1.e164.arpa United States NPAs
.1.e164.arpa Dominica NPA
.1.e164.arpa Jamaica NPA
.1.e164.arpa Barbuda Antigua NPA
.1.e164.arpa Grenada NPA
.1.e164.arpa Canada NPAs
Tier I(subset) would allow each country in
North America to manage their own Tier I
equivalent database.
Any Tier II Provider
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A Better Approach

• Allows each country in North America to maintain
  their own Tier I equivalent database.
• Reflects the fact that the United States is not
  the only entity within the 1 (one) code.
• Once routed to the individual country Tier I
  database, the subscribers phone number and not
  the NPA will determine the Tier II provider for
  NAPTER records.

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ENUM enables PSTN to SIP calls
ENUM Server
ENUM 21215553191.e164.arpa
Signaling Gateway
STP
4
5
Invite 3
Proxy Server A
MGC
SIP UserB_at_illuminet.com
Invite 19135551212From 12025551212
Invite 6
User A
Proxy Server B

1
2
MediaGateway
SSP
Invite 7
Invite SIP UserB_at_illuminet.comFrom
12025551212
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User B

• In this example, User A attempts to contact User
  B who is on a VoIP network and uses a SIP phone.
• User A dials the global E.164 number for User B.
• The SSP sends an IAM message via SS7 to a SG
  (which is part of the Media Gateway Controller /
  Media Gateway).
• The Media Gateway Controller sends an invite
  message to the nearest Proxy Server.
• Proxy Server A does not know User B address
  therefore it contacts an ENUM Server.
• The ENUM Server returns the address of User B.
• Proxy A sends invite message to User Bs Proxy
  Server B
• Proxy Server B passes the invite to User B
• If User B accepts the call, there is a two-way
  RTP path established between User B and the Media
  Gateway controller. A two-way path is also
  established between the Media Gateway and User A.
  At this point User A is able to communicate with
  User B.

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Competitive Model Advantages Disadvantages

• Advantages
• Any DNS provider can set up ENUM like structure
  in any Top Level Domain.
• The DNS provider could provide all Tiers, 0 II,
  and possibly root.
• Provide Registrar Functions
• Provide Register Functions
• Can offer ENUM services outside of the United
  States.
• Disadvantages
• Will require clients and non-client to have
  resolver software.
• Performance issues are a concern for clients and
  none clients
• Major performance concerns for VoIP providers
  when ENUM is used as a location server.
• Not compliant with RFC2916 from the IETF.
• Not supported by the ITU-T Study Group 2.

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Status on ENUM

• US Department of State Ad-Hoc Study Group A on
  ENUM
• Completed recommendation to Department of State.
• Document Released on July 6.
• Presentation given to Study Group A on July 31.
• Recommendations
• Recommendation for US participation in ENUM.
• Provides guidance to respond to ITU.
• Use the single zone per RFC 2916 (.arpa).
• Understand that there will be competitive models
  deployed.
• ENUM is an Opt In service.
• Privacy Protection is a high priority.
• Scheduled Events
• August 27 First face-to-face meeting of the new
  ENUM Forum
• Agree to forum principles and procedures
• Agree to work plan
• Pick leaders for the 5 proposed subcommittees.
• September 4 Next Study Group 2 ITU-T meeting.