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ENUM Technical issues / DNS

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Presentation on theme: "ENUM Technical issues / DNS"— Presentation transcript:

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

2 Agenda Background Problem we want to solve Technical solution

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 Ask “se”! Server “se” Query
Ask “”! Query Query Local resolver Server “”

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

8 Delegations Root server se. IN NS IN A IN NS IN NS IN NS IN A IN A IN A IN NS IN NS IN A IN A IN NS IN A IN N S 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

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 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 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 !^+46(.*)$!ldap://\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 $ORIGIN
IN NAPTR “U” “mailto+E2U” IN NAPTR “U” “ldap+E2U” “!^+46(.*)$!ldap://\1” Note that no line break should be in the records

23 ENUM DNS Hierarchy Alternative 2 Alternative 1

24 +46-8-976123 IN NS IN NS IN A Root server IN NS. IN A IN NS IN NS IN A IN NS IN NS IN NS 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 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 (not delegations in delegated domains of 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 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 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 My address:

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