Evaluating IP Centrex

The Attractions of IP-Centrex
As IP-Centrex proliferates, the benefits inherent to the technology should translate into functional and service-level gains for customer organizations. Network convergence, packet-switching, and the removal of various physical restrictions are among the prime elements that should promote IP-Centrex to the forefront of outsourced telephony services. We can summarize these benefits as follows.

Capital Costs
The most immediate and obvious benefit of Centrex services is the elimination of most capital expenditure. We should note, however, that in the case of IP-Centrex, the LAN infrastructure within an organization must be brought up to specification in order to support the technology of IP telephony.

Convergence
Data and voice requirements are now combined into a single infrastructure. Network convergence provides the benefits of reduced management overhead and the leveraging of existing IT skill sets that lead to reduced operational costs and improved service levels.

Multiple Locations and Mobility
IP-Centrex provides a simpler and more effective means to create a seamless telephony environment when considering multiple geographic locations. An organization can have a number of offices, along with individual remote users, that can all be part of a single unified environment at lower expected costs than with legacy Centrex.

Computer-Telephony Integration
CTI is significantly enhanced and simplified by the use of IP-Centrex. Access to network-based applications via a phone (such as Web browsing or basic task- or lookup-oriented software applications) can now be accomplished with much less integration time and effort, through the use of simplified software interfaces.

Unified Messaging
UM is significantly less difficult and expensive to implement with Centrex than with other technologies. With network-based softswitches and IP-Centrex servers, voice mail information can be integrated with e-mail and fax to form a unified messaging environment, usually provided as the single "inbox" for an individual user.

Simplification of MACs
As IP telephony removes the barriers imposed by hardwired phones, the complexity, time, and cost of moves, adds, and changes are significantly reduced. IP phones can be easily relocated within a facility by attaching them to any appropriate connection on the internal Ethernet LAN. In most cases, a MAC can be accomplished by the user unplugging the set, moving to a new location, and plugging the set back into an operational network jack (such as in the case of moving an individual's office location).

Local Access Cabling
Legacy Centrex generally requires a separate pair of copper wires from the CO to support each phone. This cable plant requirement sometimes resulted in delays with implementation (adding more copper cabling) and put limits on the wired building capacity. Since IP-Centrex utilizes a broadband extension to a site, the cabling requirement from the CO is significantly reduced, as only two fiber-optic cable strands or a limited number of pairs of copper cable are required to provide broadband connectivity. With the elimination of copper cabling requirements from each phone to the CO, the potential issues of electrical interference or damaging currents and voltages induced on such cable are also eliminated.

Inside Wiring
In most cases, legacy Centrex telephone sets within a building must connect directly back to the CO with copper cabling . As a result, multipair copper riser cable is required to interconnect the telco cabling at the point of entry into the building with each wiring distribution closet. Such cabling is also a requirement with traditional digital PBX installations, in addition to individual drop-cabling to each telephone set. In Centrex nomenclature, this cabling is often called "inside wiring." Since IP telephony requires no main distribution frame (MDF) or secondary distribution frame (SDF) termination points, a significant reduction in copper cabling can be realized, negating the requirement for multipair riser cabling within a building and dedicated drop-cabling per telephone set.

Provider Infrastructure
Added to these benefits, the IP-Centrex service provider also gains from the significant reduction in physical space, management complexity, and support requirements at the CO (or provider location). IP-Centrex and packet-switching systems have a higher packing density on the equipment racks, while at the same time being smaller, lower-powered, and requiring less environmental support than the traditional CO-based circuit-switching equipment.

Provider WAN
IP-Centrex has the opportunity to deliver seamless services to an organization that is geographically dispersed. In a customer-owned solution, voice traffic may have traveled over an internal network (TDM or VoIP) to interconnect remote sites for toll bypass and networked voice requirements. Voice traffic in an IP-Centrex environment has the option of flowing over the carrier's data infrastructure, relieving the customer of implementing and managing QoS factors on their internal WAN, while avoiding the burden of additional traffic on the corporate network.