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Feature Article
May 2004

Harmonizing Carrier-Grade And Customer-Premises Equipment


Today, as the enterprise IP telephony market gains momentum, migration to IP telephony is no longer a question of �if� but rather a question of �when� 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. Today�s 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 or businesses.

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 doesn�t leave the office network. But as soon as you want to talk to someone located outside, interoperability of the IP PBX with your service provider�s 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 you�ve 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 carrier�s gateway in order to make the transfer happen. And there�s the rub! The carrier�s 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 customer�s 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 � perhaps more importantly � 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 carrier�s 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 softswitch systems.

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 carrier�s 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 carrier�s 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 www.meranetworks.com.

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