1 Introduction to ENUM Technical and operational aspects Marco Bernardi NeuStar, Inc

2 Contents Convergence between IP and E.164 based networks Introduction to DNS ENUM technical aspects ENUM architectural/operational aspects ENUM alternative implementations

3 ENUM in the context of convergence (I) ENUM is an enabler of the convergence process between E.164 based networks (PSTN, GSM, ect.) and IP based networks providing interoperability between different naming/addressing schemes across different networks ENUM offers the possibility to have a single contact point (E.164 number) for different services across different networks 1.2 Billion telephone numbers worldwide PSTN, GSM.. Internet Networks 350 Million Internet users worldwide ENUM

4 ENUM in the context of convergence (II) ENUM is…. –A “bearer capability” that allows the mapping an E.164 number into a set of IP terminations and associated protocols by using DNS technology ENUM is not …. –A telecommunication service/application –A carrier selection mechanism –A directory service –A threat/replacement of existing E.164 numbering plans

5 Introduction to Domain Name System (DNS) DNS is the mechanism that allows to translate “user-friendly” names (e.g. neustar.biz) into “network oriented” addresses (e.g ) and vice versa –Address and name have different functions. An address is a locator and name is an identifier DNS is a world-wide distributed, scalable, reliable, dynamic database –Data are stored locally but can be retrieved globally –Domain name (neustar.biz, e164.arpa) is the “key” to retrieve data DNS is composed of three main elements –Domain name space –Name servers –Resolvers

6 The Domain Namespace (I) The namespace is the “skeleton” of DNS database –An inverted tree with the root node at the top –Each node has a label. The root has an “empty” label A domain name is the sequence of labels from a node to the root separated by “.” – A domain name is unique and identifies the position of the correspondent node in the namespace trial.enum.neustar.biz

7 Domain Namespace (II) A subdomain is a portion of a domain –Ex: enum.neustar.biz is a subdomain of neustar.biz A domain can be split in a number of administrative independent subdomains called zones –Delegation is the process to create zones that is a mechanism to decentralize control Below neustar.biz there are two (child) zones: enum.neustar.biz (orange) and us.neustar.biz (green)

8 Name Servers and resolvers (I) Name resolution is a server/client mechanism to find data in the DNS Name server is the “server half” of the mechanism. The resolver is the “client half” Name server is a program storing information about a zone (zone file) –The name server that stores a complete zone is “authoritative for” the zone –More than one name server are authoritative for the same zone redundancy and robustness –In addition to authoritative name servers there are also caching name servers that store only part of zone file data

9 Name servers and resolvers (II) Resolver is a program running on a host that queries from information A name server receives a query from a resolver and looks for the answer –1) search starts from authoritative data and then its cache –2) if the name server doesn’t have the requested data and is not authoritative for that domain, the request is passed to other name servers with a recursion process Only a single branch of the DNS tree can be searched (it’s branch the domain name belongs to). It’s NOT a directory service

10 What’s ENUM (I) E.164 numbers because… –They have been used for years in telephony, are authoritatively managed and well accepted by users –Other numbers/identifiers (E.212, car number plate) could be used as entries for DNS look up but it’s not ENUM DNS because…. –It’s available, global, cheap, reliable, scalable ENUM is about E.164 numbers into DNS by using a single, authoritative structured domain - e164.arpa

11 What’s ENUM (II) A single, authoritative structured domain because… –It’s crucial to ensure the integrity of the E.164 numbering plan –It’s vital to protect customers from traffic hijacking and privacy violation –DNS is not a directory service. Consistency of the information retrieved by DNS look up (the same information irrespective of the location of the DNS query) E164.arpa because…. –.arpa is the TLD designated by the IAB for Internet Infrastructure issues e.g. in-addr.arpa (reverse IP address look up) –.arpa is available today, well managed, stable and secure with operational environment under IAB/IETF supervision

12 ENUM technical description (I) ENUM is a protocol defined in IETF RFC 2916 that allows –Mapping of a E.164 number into a fully qualified domain name belonging to a single, authoritative and structured subdomain (e164.arpa) –Retrieval of URIs in DNS by using E.164 fully qualified domain name as entry Mapping E.164 “international” number into DNS –Remove all characters with exception of the digits (e.g. +) –Insert a “.” between each digit –Reverse the order of the digits and append.e164.arpa to the end –Example  e164.arpa

13 ENUM technical description (II) NAPTR Records –NAPTR Records are DNS resource records (defined in IETF RFC 2915) that indicate the protocols/services associated to the E.164 domain name –One or more URIs as result of the DNS look up. Order and preferences can be indicated –Example $ORIGIN e164.arpa. IN NAPTR "u" "sip+E2U" IN NAPTR "u" "mailto+E2U"

14 ENUM architecture (I) ENUM is a based on a layered architecture to follow DNS hierarchy and ensure proper competition Three layers: Tier0, Tier1 and Tier2 Tier0 functions <> Administration and technical management of ENUM domain –Tier 0 Registry is an international registry containing pointers to authoritative national registries (Tier1 Registries) Tier1 functions <> Management and operation of ENUM in the country (or portion of it) identified by a Country Code –Tier1 Registry is a national registry containing pointers to authoritative name servers where NAPTR records are stored (Tier2 Registries)

15 ENUM architecture (II) Tier2 functions<> Provision of ENUM service –Tier2 Registry stores the NAPTR records associated to an E.164 number –Tier2 Registrar is the commercial interface with the ENUM subscriber and it is involved in the validation process (E.164 number, user identity) Tier0 and Tier1 are natural monopolies, Tier2 is open to competition How Tier1 and Tier2 functions are implemented is a national matter

16 Tier0 Registry e164.arpa Tier 1 Registry CC.e164.arpa DNS zone delegation for individual number serviced by Tier2 Registry DNS zone delegation for CC end user Tier 2 Registrar CC.e164.arpa Tier 2 Registry CC.e164.arpa Tier 2 Registry Tier 2 Registrar ENUM architecture (III) Tier0 Tier1 Tier2 end user DNS delegation ENUM Interaction It’s not a business model

17 ENUM Alternative implementations (I) Ongoing discussions between ITU and IAB/IETF to agree upon the “ENUM TLD” and delegation model –Crucial that ENUM implementations follow the ITU/IAB/IETF agreement Today ENUM-like alternative implementations are already available –Creation of multiple conflicting trees (e164.com, e164.net,..) Threats/challenges posed by multiple conflicting trees –Integrity of E.164 numbering plans –Lack of consistency of data in ENUM databases –Search in multiple branches –Lack of common rules to protect E.164 customers and network operators’ rights Privacy, data protection, QoS, traffic hijacking

18 ENUM Alternative implementations (II) Multiple conflicting ENUM trees must not encouraged ENUM developments cannot be only left to market forces Set of rules in order to ensure that competition and customer choice take place at the appropriate level (Tier2) without negatively affecting existing E.164 and IP based services and naming/addressing resources

19 ARPAAdvanced Research Project Administration DNSDomain Name Server ENUMElectronic NUMbering IABInternet Architecture Board IETFInternet Engineering Task Force IPInternet Protocol ITUInternational Telecommunication Union NAPTRNaming Authority Pointer Record in a DNS RFCRequest For Comments PSTNPublic Switched Telephone Network SIPSession Initiation Protocol TLDTop Level Domain URIUniform Resource Identifier Acronyms

20 Introduction to NeuStar NeuStar is the leading provider of database, clearinghouse and registry services that enable network operators and service providers to interoperate NeuStar is a neutral trusted third party NeuStar main areas –Registry services:.biz,.us, North American Numbering Plan, Numbering Pooling, ETNS –US Local Number Portability Administration (NPAC) –Convergence IP and PSTN: ENUM –OSS clearinghouse services: Care

21 Questions ?