The VoIP Peering Puzzle�Part 16: Voice Peering Fabric ENUM Registry

The Voice Peering Fabric (VPF), operated by Stealth Communications, Inc. ( , opened in New York City in 2003, and since that time has continued in its leadership as one of the world’s most widely recognized VoIP peering exchanges.

The VPF is built as a distributed private Ethernet network, with points of presence (POPs) in nine major cities across the United States, plus a facility in London, England. By providing a Layer 2 transport service, the VPF can transparently support all higher layer VoIP protocols, including IAX (Inter-Asterisk Exchange), which is used to connect Asterisk servers; SIP (the Session Initiation Protocol), MGCP (the Media Gateway Control Protocol); and H.323.

The VPF service provides an environment in which members can directly connect to one another and economically exchange traffic, thus avoiding unnecessary delays and relays of their transmitted information. Over 100 organizations are members of the VPF, representing carriers, enterprises, and government organizations. Members include AT&T Wholesale, China Telecom, Galaxy Multimedia, IDT Corporation, INFONXX, Massachusetts Institute of Technology, Net2Phone, Packet8, SNET DG, SunRocket, Telecom New Zealand, Transaction Network Services, VeriSign, XO Communications, Yale University, and many others.

The VPF provides many different services to its members, including a Minutes Market, which allows members to buy and sell origination and termination services among each other; an Application Service Provider (ASP) Market, which connects to ASPs for services such as Caller Name (CNAM), Directory Assistance (411), International Code Database (ICDB), and Local Number Portability (LNP) applications—plus an ENUM Registry. This registry is based upon the IETF’s ENUM standard, RFC 3761 (see

The VPF ENUM Registry is a free service provided to members, which resides within the VPF network. The registry is configured as a multi-lateral peering system, thus enabling all registry members to send and receive calls among one another, in peer-to-peer fashion, directly across the VPF Layer 2 Ethernet Fabric. This architecture makes for a secure, high-service-quality environment in which organizations can exchange communications traffic at a performance consistent level. Moreover, the VPF’s ENUM Registry architecture lets rich multimedia applications run at Layer 2, bypassing the public Internet and PSTN. There are no fees for registering numbers, querying the registry, or terminating calls.

The VPF ENUM Registry was the first production ENUM service in the world. It holds over 23 million unique numbers and processes over 1.2 billion minutes annually. The ENUM Registry in each registry server can process just over 150,000 queries (transactions) per second, timed at less than two milliseconds from query to response. On its website, the VPF keeps a daily running total of the calls completed using the ENUM Registry. At the time of this writing, the system had connected well over 770,000 on the previous day. (See

The VPF’s ENUM Registry is a custom-written application developed in house, with a fully distributed database array located at each VPF POP. That is, all of these local databases contain the same exact information—similar to that of the root nameservers used within the Internet’s Domain Name Service, or DNS. The distributed architecture enables VPF Members to query the database that is local to them, thus keeping query and call setup times to a minimum.

When a user dials a call from an IP telephone, a query is sent via their carrier to the ENUM Registry. If the VPF registry contains the required routing information, then a call is established through the VPF network from calling party’s carrier or enterprise, to the destination carrier or enterprise—and ultimately to the destination IP telephone. If the routing information is not in the database, then the call is sent to a selected termination carrier, via the VPF Minutes Market or a PSTN connection.

More importantly, the ENUM Registry supports a wide range of applications. Telephone numbers in the registry can be mapped to SIP/H.323 addresses to support traditional audio telephone calls—plus Multimedia Message Service/Short Message Service (MMS/SMS) messaging, SIP video, and the emerging Telepresence devices and applications. Telepresence is a set of technologies that allows a person to feel as if they are present in a location other than where they presently reside. This technology may include sensory input (vision, hearing, etc.), plus the user’s position and movements. Entertainment applications, which build on the IMAX theatre model, are obvious, but more advanced applications, including hazardous environment operations such as bomb disposal, undersea work, remote pipeline inspection, remote surgery, and education have also been proposed (see

Further details on the VPF’s ENUM Registry are available at Our next tutorial will begin our investigation of another key element in the VoIP peering puzzle—SIP trunking.

Copyright Acknowledgement: © 2007 DigiNet Corporation ®, All Rights Reserved

Author’s Biography
Mark A. Miller, P.E. is President of DigiNet Corporation®, a Denver-based consulting engineering firm. He is the author of many books on networking technologies, including Voice over IP Technologies, and Internet Technologies Handbook, both published by John Wiley & Sons.

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