Connecting VOIP to the PSTN and Cellular networks

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ENUM - The bridge between the switched telephony network and the Internet

ENUM RFC 3761 is a protocol the uses the Internet DNS system to translate E.164 (i.e. ordinary) telephone numbers into IP addressing schemes (like SIP, H323 or Email). RFC 3761 has replaced the former RFC 2916 in May 2004.

Current ENUM deployment status in various countries

ENUM Progress Matrix maintained by RIPE ENUM working group

Applicable RFCs

RFC 2915 : NAPTR RR
RFC 2916 : ENUM Protocol (obsolete)
RFC 3761 : ENUM Protocol (obsoletes RFC 2916)
RFC 3762 : Usage of H323 addresses in ENUM Protocol
RFC 3764 : Usage of SIP addresses in ENUM Protocol
RFC 3026 : Berlin Liaison Statement
RFC 2870 : Root Name Server Operational Requirements

ENUM is already supported by SIP Proxies like SER or SNOM 4S, VoIP gateways like Asterisk , Cisco) and SIP phones (SNOM 200).

From the RFC abstract:

This document discusses the use of the Domain Name System (DNS) for storage of E.164 numbers. More specifically, how DNS can be used for identifying available services connected to one E.164 number.

Routing of the actual connection using the service selected using these methods is not discussed.

In short, a server with ENUM support will lookup a dialled telephone number in DNS to see if there's alternate ways to set up the call instead of just calling out on the PSTN telephone line. ENUM may contain a reference to a SIP URL ? , a telephone number to dial, a web page or an e-mail address.

Enum uses DNS NAPTR resource records.

News

The lastest ENUM plugtest was held 30 May - 3 June 2005, the first at ETSI was in Nov-Dec 2004 http://www.etsi.org/plugtests/ENUM.htm

Software support

PowerDNS supports NAPTR and many (custom even!) back-ends.
Bind from ISC , version 9. Please note that earlier versions of bind might give you trouble with wildcard records in ENUM.
AG Projects Managed DNS platform has web management interface for DNS NAPTR and SRV records
Sentiro's ENUM lookup webpage - Lookup ENUM records worldwide (UK)
Alex Mayrhofer's ENUM lookup webpage - Lookup ENUM records worldwide (Austria)
Adrian Georgescu's Managed DNS lookup webpage - (NL)
The Voice Peering Fabric
ENUM PUA (Personal User Agent) prototype source code released under an Open Source BSD Licence http://www.internetnz.net.nz/public/enum

Organizations involved with ENUM

RIPE - Tier 0 administrator for "official" e164.arpa ENUM top level domain
ITU-T TSB - International Telecommunication Union
ETSI - European Telecommunications Standards Institute

Articles

IEEE - Carriers and Users Prepare to Midwife ENUM
Lightreading - Carrier ENUM Gains Ground
Article at www.SIPCenter.com by Adrian Georgescu http://www.sipcenter.com/sip.nsf/html/ENUM+on+its+way+to+maturity
Article in NWfusion.com http://www.nwfusion.com/news/2001/0430enum.html

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