1. ENUM Technical issues / DNS
Patrik Fältström Area Director, Applications Area, IETF

2. Agenda Background Problem we want to solve Technical solution
Conclusion

3. Background
ENUM 3

4. The Domain Name System It is a distributed database It is a protocol
Often the two get mixed up

5. DNS as distributed database
Central server,
“root server”
Server for
“com”
Server for
“se”
Local
resolver
Client
Server for
“jp”

6. Recursion Root-server Query a.paf.se? Ask “se”! Server “se” Query
Ask “paf.se”!
Query
a.paf.se?
Query
a.paf.se?
Local
resolver
Server
“paf.se”

7. Domains and zones "root" se a c b ns ns ns zone "a.se." domain "a.se."
domain/zone "b.a.se." b ns ns ns

8. Delegations Root server ns.nic-se.se se. IN NS ns.nic-se.se
ns.nic-se.se. IN A
ns.nic-se.se
ns.se. IN NS ns.nic-se.se.
a.se. IN NS ns.a.se.
c.se. IN NS ns.c.se.
ns.nic-se.se. IN A
ns.a.se. IN A
ns.c.se. IN A
ns.a.se
a.se. IN NS ns.c.se.
b.a.se. IN NS ns.b.se.
ns.a.se. IN A
ns.b.se. IN A
ns.c.se.
c.se. IN NS ns.c.se.
ns.c.se. IN A
ns.b.a.se.
b.a.se. IN N S ns.b.a.se.
ns.b.a.se. IN A

9. E.164 numbers
Allocation at CC level by the ITU, SG2/WP1/2 (from an IETF perspective)
E.164 provides the number structure and functionality of numbers used for international public
telecommunicationsHierarchically allocated

10. Structure of E.164 Structure to use for geographic areas CC NDC SN
1-3 digits
N digits
Max (15-N) digits
National (significant) number
International public telecommunication
Number for geographical areas

11. Problem we want to solve
ENUM 11

12. Problem statements 1(2)
How do network elements find services on the Internet if you only have a telephone (E.164) number?
How can subscribers (as opposed to carriers) define their preferences for incoming communications?
How can we (IETF/ITU) enable new services while enabling competition, consumer choice and consumer protection?

13. Problem statements 2(2)
How can consumers, carriers and new players have equal access to these new opportunities?
How do we (IETF/ITU) make this simple and easy to use without reinventing the wheel?

14. Technical solution
ENUM 14

15. Solution in short
Put telephone numbers* in the global domain name system, DNS
ENUM Working Group created to solve the problem of using the DNS for:
Domainname in
[Numbers reformatted as domain names]
URI out
[mailto, sip, tel, http or other URI scheme]
Solution was to use NAPTR records
* Maybe not in the original E.164 format

16. Example
$ORIGIN e164.arpa. IN NAPTR "U" "sip+E2U" IN NAPTR "U" "ldap+E2U"

17. Why DNS?
It’s there
It works… It’s global… It scales… It’s fast… It’s open…
Grandfather existing DNS delegation mechanisms, which looks like delegation in E.164 world
ENUM enabled DNS provides a low cost, shared SCP-like infrastructure for IP infrastructure
ENUM facilitates PSTN/IP convergence

18. Step 1
Take an E.164 number and create a fully qualified domain name in a single highly defined and structured domain
e164.arpa.
The input to the
NAPTR algorithm

19. Step 1 Explanation
Each digit becomes a definable and distributed “zone” in DNS terms
Delegation can (doesn’t 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 nameservers for NAPTR/service resource records (RR’s)

20. Step 2 Lookup NAPTR RR’s in DNS, and apply NAPTR/ENUM algorithm
e164.arpa.
!^+46(.*)$!ldap://ldap.telco.se/cn=0\1!
Use rewrite rules using regular expressions which operate on the E.164 number ( )

21. Regular expressions
For ENUM, the NAPTR regexp field may yield an (unchanged) URL
!<regexp>!<string>!
“Match <regexp> on original E.164, and apply rewrite rule <string>”
^ - Match beginning
$ - Match end
. - Match any character
.* - Match any number of any character
() - Grouping, \n in <string> is replaced with group number ‘n’ in <regexp>

22. Step 2 in detail $ORIGIN 4.3.2.1.7.9.8.6.4.e164.arpa.
IN NAPTR “U” “mailto+E2U”
IN NAPTR “U” “ldap+E2U” “!^+46(.*)$!ldap://ldap.telco.se/cn=0\1”
Note that no line break should be in the records

23. ENUM DNS Hierarchy Alternative 2 Alternative 1 e164.arpa 6.4.e164.arpa

24. +46-8-976123 ns.ripe.net e164.arpa. IN NS ns.ripe.net.
6.4.e164.arpa. IN NS ns.e164.se.
ns.ns.e164.se. IN A
Root server
e164.arpa. IN NS. ns.ripe.net
ns.ripe.net. IN A
ns.e164.se
6.4.e164.arpa IN NS ns.e164.se.
e164.se. IN NS e164.telco.se.
e164.telia.se. IN A
e164.telco.se.
e164.se. IN NS e164.telco.se.
e164.arpa. IN NS ns.eservice.net.
ns.eservice.net.
e164.arpa. IN NS eservice.net.
e164.arpa. IN NAPTR …….

25. DNS Hierarchy Strictly delegated
One authoritative server for each name, and only one
Have led to the registry/registrar model
One responsible registry, but many registrars which talk with customers

26. Verisign Global Registry
Registry/registrar
Root server
Server for .com
Verisign Global Registry
Registrars for .com
Today 77
Registrar for .com
Network Solutions
Active ISP
interQ Incorporated
Server for .se
NIC-SE AB
Registrar for .se
Tele2
Registrars for .se
Today 227

27. Conclusion
ENUM 27

28. ENUM example flow/usage
DNS-Server
Query
e164.arpa?
Response
“Call setup”
Dial
Sip
Sip proxy
Sip proxy

29. ENUM and VoIP ENUM allows VoIP proxies and servers to find each other
Intra and inter domain call setup
Only for declaring ability to accept certain applications
ENUM is an opt-in system (also on country code level)

30. ENUM in Universal Messaging
IETF Voice Profile for Internet Mail
ENUM enables carrier and enterprise voice mail systems to find each other, interoperate and exchange messages
Linkage to directory gives access to “spoken name” as well as authenticated access to sensitive information (privacy)

31. ENUM in Internet Fax IETF RFC 2305 / ITU-T Rec. T.37
ENUM enables internet aware fax machines to find each other, interoperate and exchange messages

32. Detailed example of Fax
Person X wants to send a fax to Person Y; she knows Y's E.164 number.
Person Y has many IP applications tied to her own (Y's) E.164 number.
Device C became responsible for delivering the fax. Device C is Internet Aware, is ENUM-enhanced, can do SMTP and SIP, but can't do H.323 yet.
Device C does a DNS query on the E.164 number. Device C discovers from the response that Person Y prefers real-time to store-and-forward fax delivery, likes SIP and H.323 equally, and has SMTP, too.
Device C tries SIP first. If SIP fails, Device C does not try H.323. Instead, Device C then tries SMTP.
Note: Device C uses ENUM in its application selection logic. ENUM is an enabler and not the same sort of thing as SMTP, SIP, H.323, voice/fax/data, etc.

33. From RFC 2916 4. IANA Considerations
This memo requests that the IANA delegate the E164.ARPA domain following instructions to be provided by the IAB. Names within this zone are to be delegated to parties according to the ITU recommendation E.164. The names allocated should be hierarchic in accordance with ITU Recommendation E.164, and the codes should assigned in accordance with that Recommendation.
Delegations in the zone e164.arpa (not delegations in delegated domains of e164.arpa) should be done after Expert Review, and the IESG will appoint a designated expert.

34. Status as of Jan 10, 2001 (done) Base spec published as RFC 2916
e164.arpa delegated to RIPE-NCC
ITU SG2/WP1/2 liaison statement:
Member state can inform ITU on entry of numbers in DNS, provision of E.164 information

35. Status as of Jan 10, 2001 (not done)
Delegation of domains below e164.arpa to managing entities that are appointed by member states
National issues

36. Resources NAPTR Resource Records (RFC 2915)
ENUM Specification (RFC 2916)
Liaison Statement (RFC 3026)
IAB on need for unique root (RFC 2826)
IAB Statement on ARPA
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