Circuit To Packet Migration: IP Telephony
Adoption Is Up
BY JON KENTON
Even amidst the turmoil the telecommunications industry finds itself in,
industry pundits are still expounding the benefits of packet telephony.
Forecasts may be down, but it appears that longer term, there has merely
been a phase shift in the adoption rate. The trend, begun over the last few
years, to migrate away from the circuit switched environment towards the
more open world of IP telephony continues. Why are the carrier and
enterprise community alike adopting this technology and what benefits does
it bring? Perhaps the answer can best be summed up by the acronym, WIIFM:
Whatï¿½s In It For Me?
Circuit switching was the technology implemented for telecommunications
networks many years ago. Voice telephony was (and predominantly still is)
essentially based on creating a physical path (or circuit) between two
handsets by closing a series of relays or switches. Todayï¿½s high-speed
digital switches are based on the same circuit principals as the original
switchboards with their manual operators who used patch cords to
interconnect two parties. They do however manage many orders of magnitude
more calls and with switch times measured in milliseconds. There may be no
operator to relay the gossip anymore but the sole purpose of existence
remains the same, switching voice circuits,
Although data communications have been around for 40+ years it was the
advent of the Internet that created the most dramatic changes in our
telecommunications infrastructure. The limitations and issues related to
transmitting data using circuit-switched equipment lead to the rapid
adoption and deployment of packet-based networking infrastructure across the
carrier and enterprise worlds.
But why the different networks? A circuit switched network, as mentioned
earlier, creates what is essentially a physical link between the two
endpoints. Itï¿½s really like having the two phones directly connected
together; the circuit is dedicated to that call alone whether anybody is
speaking or not.
In contrast, a packet-based network does not tie up dedicated bandwidth
for one call alone, it uses only what it needs, when it needs it. Multiple
calls are transmitted over a single ATM or IP network, sharing and
optimizing resources. In most conversations people are only speaking 50
percent of the time. With a dedicated circuit this 50 percent of ï¿½nothingï¿½
is sent along with the actual voice. In a VoIP environment, Voice Activity
Detection (VAD) takes place prior to compression and packetization so wasted
packets of silence are not transmitted. The packets, once inside the
network, can take different routes to their destination. This allows for
redundancy or traffic buildup issues to be solved through flexible routing.
The equipment that makes up Packet Voice infrastructure separates the
control and bearer traffic into different elements. The voice traffic itself
is converted from circuit to packet using a Media Gateway while the Media
Gateway Controller (often called the softswitch) is the control element that
manages the traffic flow. A number of different gateway classifications have
been defined. Three primary elements are enterprise, access, and trunking
Enterprise gateways are typically for installation within an
organizationï¿½s private infrastructure. They would interconnect a corporate
intranet and the PBXs at both the HQ and branch offices, IP phones could
also be directly connected to such devices. This would allow for voice
traffic for frequent intracompany conversations to be carried over existing,
owned, data infrastructure rather than that of the local or international
carriers the company uses for regular telephone connections.
Access gateways are installed at the edge of the network and provide
traditional analog or primary rate (PRI) line interfaces to a voice over
packet (VoP) network. The inverse function is also applicable in VoB (voice
over broadband) applications where the phone call is digitally encoded
before entering the access network and needs routing via conventional
telephony once inside the network.
Trunking gateways interface between the telephone network and a VoP
network at the core. Such gateways are responsible for bulk conversion and
typically manage a large number of digital virtual circuits.
Overall the next generation packet based systems are very efficient and
the separation of the control and bearer planes allows for much flexibility.
The network becomes highly extensible with individual elements designed
specifically to fit snugly, matching the application requirements needed at
distinct points in the infrastructure.
So we now know about the differences between circuit and packet
telephony, but what are the realizable benefits of implementing packet-based
architectures. Whatï¿½s in it for me?
Depending on whether one is a service provider or enterprise the details
are distinctly different but the perspectives are very similar. Collectively
the benefits fall into two primary categories:
ï¿½ Reductions in operational costs.
ï¿½ New and improved services.
A recent report from Dittberner Associates, Inc., clearly substantiates
this. Dittberner surveyed a number of ILECs and CLECs across the United
States and Europe with a view to understanding their plans and directions
for implementation of next-generation networks. When asked to rank whatï¿½s
driving them towards adoption of the new technologies the top answers were:
1. Operational Costs.
2. Available Services from NGN Equipment.
4. Ability to Offer Bundled Services.
Letï¿½s first examine how utilizing packet-based telephony impacts costs.
For any small to medium-sized enterprise, especially those with many
widespread satellite offices, the reduction or elimination of interoffice
phone charges is one of the primary attractions. By utilizing spare
bandwidth from data connections to carry remote office voice traffic a
significant reduction in long-distance and/or international charges can be
Service providers and enterprises alike can reap significant savings due
to the reduction in support and ownership costs. This is possible, as only
one data network is required to manage voice and data combined. Reducing
equipment count not only saves on capital costs, but ongoing utility charges
such as air-conditioning and electricity.
There are also tremendous potential savings to be realized in reducing
manpower support costs. VoIP gateways are essentially network routers and as
such could be supported by regular IT or networking staff -- specialized PBX
or voice switching staff wouldnï¿½t be required. Many enterprises use outside
services to manage their PBX infrastructure; multiplied by numerous branch
offices the cost of such services can add up rather quickly. Service
organizations often charge for adding or moving extensions, but provisioning
a new IP phone is similar to adding a computer on the network, a few mouse
clicks and youï¿½re done.
The aggregation of all traffic into a single network has the effect of
significantly increasing overall efficiencies. Using packet-based, IP or ATM
streams to replace those fixed 64K circuits (especially in provider trunk
circuits) can create bandwidth savings in the region of 20-30 percent,
possibly more if using high levels of compression. The choice is then
whether to realize cost savings by reducing bandwidth or fill that increased
capacity with paying subscribers. Either way it generates cash to the bottom
The ability to introduce new capabilities to the enterprise or new
subscriber services (for carriers) is another commonly discussed benefit of
packet voice technologies.
The benefits of migrating to IP telephony are numerous. For many
companies these potential cost savings and new capabilities are within reach
and can aid their campaigns for increased competitiveness. One distinct
advantage of packet-based technologies is the ability to install slowly,
then upgrade and extend over time. Coexistence is easily made possible while
migration plans are created and implemented. Ultimately the efficiency and
cost management trends continue downward and with carriers searching for
that next killer service application the answers lay within the packet
Jon Kenton is product marketing manager at Motorola Computer Group.
Motorola Computer Group is a business unit of the Motorola Integrated
Electronic Systems Sector (IESS). It is a leading supplier of embedded
computing platforms for equipment manufacturers in telecommunications,
military and aerospace, medical equipment and industrial automation, with
core competencies in services and training, design, manufacturing, and
systems integration capabilities. For more information visit
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