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VoIP offers tremendous opportunities that cable operators, telcos
and others are rushing to address. As you build out VoIP offerings,
it is important to keep the broader context of next-generation communication
services in mind � because VoIP is just the beginning.
Once you free voice traffic from the PSTN telephone lines and integrate
it with IP-based traffic, the possibilities for converged communication
services are enormous. As you make decisions about VoIP
infrastructure, keep an eye on the long-term objectives.
ENUM (from TElephone NUmber
Mapping, but also called �Electronic
NUMbering�) is a prime example of a
technology that has both immediate
applications and long-term potential in
carrier networks. Many carriers today
are making ENUM decisions based on
immediate needs for VoIP peering �
interconnecting VoIP calls between
networks over IP networks. Initially
defined by the IETF as enabling a
global, publicly-available database of
phone numbers, ENUM is now being
widely adopted as a mechanism to
facilitate VoIP peering. While public
ENUM efforts are still underway
around the globe, carrier ENUM (or
private ENUM) implementations are
solving immediate business needs. As
with many technologies, the potential
uses of ENUM exceed the originating
vision.
ENUM connects E164 phone numbers
to URIs (and hence IP addresses),
enabling efficient routing of voice
traffic over IP networks. Today carriers
are deploying ENUM to route
calls between VoIP networks, enabling
end-to-end IP connectivity for VoIP
calls. VoIP peering is essential for carriers
that want to maintain the cost
benefits of VoIP (bypassing the
PSTN) and offer new, next-generation
services, such as automatically switching
into video conferencing mode
when both endpoints have the capability
to do so.
ENUM�s potential is much greater
than simply directing VoIP calls.
ENUM can connect all kinds of nextgeneration
services to a phone number
� allowing subscribers to use a single
number for a wide range of communication
services. ENUM directories can
contain preference ordering, optimal
routing information, and can serve as
broader IP-application Routing
Directories (IPRDs).
What this means for providers
deploying VoIP services today is as
follows:
� There isn�t one right way to deploy
ENUM; there are many ways to
derive value from the technology.
� You can phase-in ENUM and VoIP
peering, starting with a limited
scope to address an immediate
problem and adding subscribers and
levels of information over time.
� Whatever approach you take, consider
future scalability and service
integration as you implement
ENUM directories.
We�ll briefly discuss several areas that
ENUM can address today.
Softswitch Interconnectivity
For networks employing softswitch
equipment from different vendors,
ENUM can be used to centralize routing
information, rather than maintaining
and updating routing tables on all
softswitches. In this function, ENUM
simplifies the management of in-network
routing data. In a sense, ENUM
becomes a standard for sharing interconnectivity
information between
softswitches.
Intracarrier Peering
A single carrier environment may
have multiple VoIP �islands� within
their network � for example, VoIP
offerings for different regional subscriber
groups, or for business/consumer
users. Often in such situations there is
no mechanism for exchanging routing
information across the islands and so
calls between the VoIP islands use the
PSTN.
Routing VoIP-to-VoIP calls over the
PSTN degrades call quality (with voice
transcoding required at the gateways
between IP and PSTN), and imposes
telecommunications costs. Additionally,
extra features that rely on IP networks
will not have corollary features in the
PSTN. ENUM is a great solution to
this problem because it creates a standards-
based repository of call routing
data. In this �intracarrier peering� situation,
the data within the ENUM
directory is the carrier�s own subscriber
data. The carrier can use this information
to route the data entirely over IP
networks for optimal efficiency and
functionality.
Inter carrier Peering, or Connecting VoIP Calls between Carriers
Carriers offering VoIP services face
similar issues when routing VoIP calls
out of their networks to other carriers�
subscribers. The advantages of end-toend
IP connectivity include reduced
costs, consistent quality of service without
transcoding, and the ability to support
new, IP-based features. Many carriers
are entering into VoIP peering agreements
with other carriers to exchange
subscriber information, supporting
direct IP connections with partner VoIP
networks.
In addition to the obvious requirements
for scalability and performance,
reliable and secure provisioning of the
ENUM directory is a key consideration.
The directory may accept information
and updates from multiple sources,
including internal subscriber data, partner
data, and possibly service bureau
data. Provisioning interfaces and performance
during updates are both critical
factors to consider for an ENUM
directory in this role.
Least-Cost Routing
The ENUM protocol is currently
being extended to reduce call placement
costs through �enumservices� definitions
that provide PSTN routing information
traditionally available on telephony networks.
Using data in these service-specific
fields, carriers can avoid unnecessary
SS7 dips and reduce the cost of call
placement.
For example, for routing calls to a
destination, it is possible to directly host
the number portability data locally in
the ENUM database rather than require
the services from an SCP. Using the
enumservices type E2U+pstn:tel in the
ENUM record, the querying switch can
receive the associated routing number
that should be used for the call. This
allows the call to be routed directly to
the destination central office without
requiring an external number portability
dip, or routing the call to the PSTN for
resolution.
Other cost-saving features of
ENUM include encoding the closest
gateway to the destination (�far end
hop off �) or the least-expensive market
to reduce the cost of the PSTN �hop�
for the call. In other words, the
ENUM directory may provide the
information to optimize the call routing
through a combination of IP and
PSTN networks.
Optimal routing information changes
frequently. Over time, the ENUM
directory will become a dynamic repository
for routing information, offering
arbitrage between routes as the cost and
availability of routes change continuously.
The ENUM server will eventually
include logic that allows the call to take
the most efficient route, depending on
time of day, network congestion, business
rules, etc.
Beyond Voice: IP-Application Routing Directories
At its core, ENUM directories offer
routing information for services connected
with a phone number. These
services may easily extend beyond traditional
voice traffic to include fax, video
conferencing, gaming, and a large range
of next-generation services. At
Nominum (News - Alert), we refer to this role as an
IP-application Routing Directory
(IPRD). In this capacity, ENUM plays
an essential role in next-generation networks.
Why use ENUM for this role? The
very attributes that make it a good
choice for the applications described
above also contribute to its broader utility
as an IPRD. As a standards-based
technology, ENUM provides interoperability
in heterogeneous networks and
between diverse networks. It leverages
the proven, highly scalable Domain
Name System (DNS) protocol, which
has served to direct traffic on the
Internet for decades. It is inherently
extensible to support a wide variety of
services and types of information.
Functioning in this capacity, ENUM
directories will be integrated with a wide
variety of applications and network elements.
High performance interfaces for
querying, provisioning, and administration
will be essential. As converged networks
are deployed, ENUM-based
directories will expand with local in-network
copies of many types of session
routing information, such as number
portability information or CNAM data
replicated from SS7 databases or service
bureaus. This data will be combined
with powerful routing logic to provide a
critical function in these environments,
connecting multimedia sessions in the
most efficient way.
Steps to Take Today
If you are using or deploying ENUM
for any of the issues described above,
keep the long-term benefits in mind. In
summary:
1. Treat the ENUM directory as the
essential network element it is � with
the reliability and availability necessary
for telephony-grade traffic.
2. Think big � beyond your initial
trial to the larger potential uses of
ENUM. Some providers start their
ENUM trials using open-source DNS
software, either to save money or
because it is what they are familiar with.
These general-purpose servers were not
designed with the scalable performance
or capacity to handle the large (and different)
data volumes of ENUM. Most
of these trials quickly encounter the limits
of the open-source software.
3. For long-term cost of ownership,
insist on adherence to industry standards
and carrier-grade manageability.
The ENUM directory server should fit
smoothly into existing element and network
management processes rather than
adding to management complexity.
4. Work with providers who share the
long-term vision for ENUM, with a
roadmap for future applications and
close partnerships with softswitch vendors,
to support the full potential benefits
of ENUM. IT
Chris Risley is CEO of Nominum. For more
information, please visit the company online
at www.nominium.com.
If you are interested in purchasing reprints of this article (in either print or PDF format), please visit Reprint Management Services online at www.reprintbuyer.com or contact a representative via e-mail at [email protected] or by phone at 800-290-5460.
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