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Feature Article
March 2003

go directly to How To Manage An IP Centrex Service (sidebar)

Making The Case For IP Centrex


There is no question that businesses of all sizes are migrating to IP-based telephone systems. The battle lines being drawn are over how business communications services will be managed and delivered to these new systems -- via IP PBXs or network-hosted IP Centrex? After a decade of losing significant market share to PBXs and other CPE, IP Centrex is poised to make a serious challenge, for a number of business and technical reasons:

� Enterprises demanding immediate cost reduction -- business are looking to lower the cost of voice and data communications while still accommodating the distribution of their workforce through the implementation of teleworking policies. Enterprises would like to have four-digit dialing and other flexible call routing options to lower voice costs between locations, universal VPN access to proprietary applications, and a simpler way to do moves, adds, and changes.

� Businesses emphasizing disaster recovery -- ongoing concerns about the safety and integrity of communications networks have pushed disaster recovery to the top of every business� communications wish list. Enterprises will look to service providers to offer them solutions that can ensure the integrity of their applications and communications.

� Enterprises converging voice and data for efficiency -- in a growing number of businesses, combining the attributes of both voice and data services into new converged services, such as find me/follow me and integration with e-mail and calendar applications, is essential to increase productivity and efficiency.

� Service providers implementing sensible packet networks -- service providers are deploying IP- and service-based networks to complement and enhance their existing infrastructure. With the wholesale replacement of circuit switches a distant inevitability, service providers are now looking to IP-based platforms to offer converged services alongside and through circuit switches.

� Service providers focusing squarely on enterprise customers -- for practically all service providers, competition for business customers remains fierce and the need for differentiating on the basis of new features and services paramount. With ILECs, IXCs, CLECs, and now cable MSOs vying for enterprise dollars, service providers must offer the most adaptive and wide-ranging services to consistently match the unique business needs of each customer, in order to succeed.

But beyond these particular developments, the success of IP Centrex as a service offering depends upon the service provider�s ability to not only sell the service to new enterprises, but also to carefully migrate existing Centrex customers with traditional CPE. Whether service providers can build a bridge to IP Centrex services for those customers with traditional PBXs, POTS phones, and analog IADs, will help to ensure IP Centrex�s success as a service offering with a future.

In order to accomplish this, service providers have to begin thinking about their networks as being more than just physical onramps for customers. Every part of their network, from access to core, must contain the ability to offer and customize features and services. That is the only way service providers will have the flexibility to deliver complex, network-hosted voice and data features to every single enterprise customer in every location. And as more businesses and teleworkers disperse into suburban industrial parks and neighborhoods, network-wide intelligence, particularly throughout access and edge networks, serves to reduce the costs of feature creation and provisioning.

Service providers are recognizing the need to deploy equipment that allows them to combine the physical access, switching, and service creation and control closer to enterprise customers. In addition, it is essential that service providers support both new and traditional CPE and traffic types, so they may offer converged voice and data services to both IP- and traditional, TDM-based CPE. Service providers must be cognizant of the fact that every enterprise�s timeline for the addition of new CPE is different, and that the goal is the availability of the service, regardless of the CPE.

The support for a range of CPE also puts an end to one of the chief complaints against network-hosted IP Centrex: unlike IP PBXs, you can�t migrate gradually, on a department by department basis, because of the coordination necessary between the service and CPE. With service providers pushing network intelligence closer to their customers through network elements that consolidate service creation and management and physical access, the per-line CPE migration that so many enterprises require can occur without difficulty.

Another longstanding benefit of Centrex has been the consistent delivery of new features and services on a network-wide basis. Enterprises never had to worry about upgrading their PBX and then managing multiple versions of software should there be any difficulties. IP Centrex through intelligent access network elements only enhances this benefit by managing software upgrades and implementing them on a per-CPE basis. Because network intelligence resides much closer to the customer than before, individual enterprises can choose how they would like network-wide software upgrades implemented throughout their communications network. This feature is essential for the effective management of converged voice and data features.

With the addition of network elements that push service creation and control closer to subscribers, service providers offering IP Centrex can deliver it not only to enterprises, but also to small- and home-office customers. With DSL, many of these customers have been forgoing second lines for Internet connectivity and fax machines, negatively affecting service providers� revenues. In response, many carriers are now pursuing a strategy of offering derived lines over which they are offering much more cost-effective second line services. Primarily being marketed as teen lines, these derived voice lines can just as easily be dedicated to providing IP Centrex services for home offices, offering a full range of Centrex features without necessitating the need for the user to purchase an IP PBX.

For some time, the enhanced functionality of IP PBXs, when compared to traditional service provider Centrex offerings, made the choice for enterprises very simple. The range of calling features and the ease with which they could be customized clearly outweighed the overall reliability and disaster recovery benefits offered through Centrex.

But now that businesses view data as an equally essential method of communications and see their workplaces becoming virtual entities, stretched across multiple locations, managing multiple PBXs amidst constrained budgets seems less desirable than ever before.

By implementing IP Centrex using network elements that push subscriber access, intelligence, and management as close to the enterprise as possible, service providers can regain many of the coveted business customers they have lost over the years. By melding the traditional benefits of Centrex, including scalability, reliability, and disaster recovery, with the multilocation and Web-enabled change capabilities of IP Centrex, service providers have a differentiated and proven service to secure enterprise customers.

William Flanagan is vice president, product management at sentitO Networks. sentitO Networks is a leading provider of convergence solutions delivering access, switching and service creation to global communications service providers. For more information, please visit the company�s Web site at www.sentito.com.

[ Return To The March 2003 Table Of Contents ]

How To Manage An IP Centrex Service


IP Centrex offers many benefits to subscribers and service providers alike. Among the many benefits to subscribers is the sheer operational simplicity of an �outsourced� managed service. Provider�s benefits include having a very competitive offering to new enterprise IP-PBXs that they can migrate their current traditional Centrex users to. To realize these benefits, however, the service must be �end to end� manageable and, as IP telephony is the central feature of the service, capable of measuring voice quality and determining the major contributors to call quality degradation.

However, IP Centrex providers face a significant dilemma when aspiring to �end to end� management as voids exist in its �end to end� visibility because the entire transport infrastructure is not owned and operated by the service provider. At the same time, IP Centrex subscribers would be loath to learn that their service is only partly managed.

IP Centrex is an enterprise phone system where the call control and service logic functions (such as providing dial tone when the caller goes �off hook�) are provided by a service provider and located on the service provider�s premises. Enterprise users then make use of SIP, H.323, or MGCP-based IP phones to make calls and use typical �internal� supplementary services such as �call hold� as if they had their own PBX.

But voice traffic travels over the customer�s LAN as well as the service provider�s IP network and is hence susceptible to problems that occur on both. Problems that occur on the customer�s LAN are normally �outside the control and view� of the service provider as most often the customer�s LAN will be shielded from the outside world (including the service provider) by a firewall. The dilemma, then, is how can the service provider get visibility into the customer�s LAN to provide the �end to end� quality and management that the service subscriber demands?

Telchemy, AT&T, and others are driving a solution, called XRTCP, in the IETF�s AVT working group. XRTCP is designed to extend the current data set supported by RTCP sender and receiver reports to include metrics that directly indicate the call quality experienced by each user on the customer�s LAN as well as important transport performance statistics used for troubleshooting. RTCP is the control protocol used in conjunction with RTP (RFC 1889) to transport voice over IP networks and which makes use of the holes already created in the firewall to transport the RTP-based voice traffic. These metrics, incorporated in the �VoIP Metrics Report Block� envisioned in draft-ietf-avt-rtcp-report-extns-01.txt, include per call quality ratings expressed as an R factor and MOS for both listener and conversational quality, the jitter buffer discard rate, burst density and duration, and jitter buffer operational settings.

XRTCP-aware voice quality agents that can make such measurements (and insert them into the appropriate XRTCP report blocks) can be installed into the IP Phones used by the enterprise customer as well as the packet collection and parsing devices deployed in the service provider�s network. In this way, the service provider can gain immediate visibility of the per call quality experienced by the enterprise users along with the major contributing degradation factors in real time and provide an �end to end� managed IP Centrex service to the customer�s satisfaction.

Bob Massad is vice president, marketing at Telchemy. Telchemy solutions provide real-time monitoring and QoS control for every call made in a VoIP network. Telchemy is challenging the traditional network oriented view of QoS by developing sophisticated models that focus on end-user-perception and experience. For more information visit the company online at www.telchemy.com.

[ Return To The March 2003 Table Of Contents ]

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