Harmonizing Carrier-Grade And
BY KONSTANTIN NIKASHOV
Today, as the enterprise IP telephony market gains momentum, migration to IP
telephony is no longer a question of ï¿½ifï¿½ but rather a question of ï¿½whenï¿½
for most businesses. Toll-free long-distance between office locations, fast
and easy connection of remote and SOHO workers, a full set of
business-critical features, and ready scalability are but a few compelling
advantages of voice and data convergence. Todayï¿½s IP PBX technologies ensure
fault-proof operation of IP-based phone systems within the enterprise
network. However, interconnection of multivendor IP PBXs with service
provider networks still remains a challenge. Protocol inconsistencies,
incompatibility, and the lack of quality and reliability are just some of
the issues that make deployment of IP PBX systems a disheartening venture
and hinder widespread adoption of IP telephony.
Incompatibility Is Historical
Today we speak about carrier-grade and enterprise VoIP technologies. This is
not a purely functional distinction since historically two kinds of urges
pushed development in this field: the needs of carriers and those of
enterprises. Essentially, it means that VoIP technology vendors focus on two
separate customer groups and deliver solutions targeted either at carriers
Traditionally IP PBX vendors have taken good care to make sure that their
systems are off-the-shelf interoperable with the end-user equipment, be it
IP phones, softphones, or legacy desktop phone sets. But both gateway and IP
PBX manufacturers have done little if anything to secure that carrier and
enterprise networks interoperate well with each other.
Compatibility of an IP PBX with a handset is good enough as long as the call
doesnï¿½t leave the office network. But as soon as you want to talk to someone
located outside, interoperability of the IP PBX with your service providerï¿½s
gateway becomes an issue of primary significance. Imagine you have received
a call from an important customer, and are transferring it to the sales
team. Once youï¿½ve pushed the transfer button, the signal from your office
phone goes to the IP PBX, which needs to exchange a whole bunch of signaling
messages with the carrierï¿½s gateway in order to make the transfer happen.
And thereï¿½s the rub! The carrierï¿½s gateway may not be able to interpret all
the messages correctly, and can therefore close the connection. No need to
describe how your very valued customer will feel when they learn that their
call is rejected.
Because the IP telephony industry is still young, interoperability between
carrier and enterprise networks has not received any special attention until
very recently. Now that IP PBX deployments are predicted to outnumber the
sales of legacy telephony systems, this issue has finally come into focus,
and is getting really topical.
Choosing The (Right) Scenario
To ensure interworking between their network and customer-premises IP PBXs,
service providers can opt for one of the following types of connection:
1. They may choose to connect their customerï¿½s IP PBX directly through IP
links (for example, via a DSL modem)
2. They may use a softswitch or
3. An application layer gateway (ALG).
Naturally enough, each of the above solutions has its pros and cons
(weaknesses and strengths).
Connection of your IP PBX through a PRI interface to an IP network is the
simplest yet most expensive way in terms of both capital expense and
maintenance, and ï¿½ perhaps more importantly ï¿½ cannot efficiently manage
media flows or guarantee QoS. To enable a PRI connection, enterprises need
to purchase and maintain a gateway, which unreasonably drives up the cost of
the phone system.
Another drawback of this solution is absence of QoS control, yet another
stumbling block of converged communications. In this scenario, the call
begins at the enterprise as VoIP, is converted to TDM and then back to IP
through a customer-premises gateway. These multiple conversions of voice
information have a very negative impact on QoS. However, they can be avoided
by using IP-to-IP configurations, as in the two scenarios that follow.
The softswitch technology is one of the options. Deployed at the carrierï¿½s
premises, a softswitch controls multiple PBXs and thus requires no capital
investment on the part of the customer for QoS management and control of
media flows. However, a big deterrent to this scenario is the fact that
there exists no protocol to handle data exchange between IP PBX and
Another option is the use of an application layer gateway (ALG). Basically,
an ALG is a software solution that enables the critical softswitch functions
such as routing, QoS assurance, and security protection, and performs
protocol repair by fixing inconsistencies between a diversity of protocol
implementations. An ALG may be either a component of a session controller or
a stand-alone system. Deployed at the carrierï¿½s network, an ALG provides the
best available solution to the connectivity problem. It receives
vendor-specific messages sent by the IP PBX and translates them into a
generally comprehensible form that will be easily recognized and processed
by any standard gateway. In other words, the ALG acts as an efficient
interface between a customer IP PBX and carrierï¿½s equipment, creating a
reliable enterprise communications system.
VoIP Reality Check: Is There A Solution?
The ideal solution to the carrier-enterprise interoperability problem has
not evolved yet. Protocols are not standing still, and existing H.323
capabilities will eventually be extended to tie together IP PBX and
softswitch technologies. VoIP vendors are already making their contribution
to the creation of this new industry standard by offering interop
applications like ALG that translate diverse protocol implementations into a
generally comprehensible format. In a longer-term prospect, vendors of
carrier-class and IP PBX solutions should join their efforts to achieve the
true interoperability of their equipment. Meanwhile, connectivity assurance
remains a challenge that can be best addressed by service providers. It is
the one critical step carriers need to take to ensure that enterprises have
all the tools necessary for efficient management of business communications.
Konstantin Nikashov is vice president of business development at MERA
Networks, a leading supplier of VoIP technologies delivering the
functionality and features needed for successful operation of service
providers. MERA solutions offer a powerful combination of security,
scalability, and affordable price, bringing added value and
revenue-generating opportunities to carriers globally. For more information,
visit the company online at
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