IP-Centrex or IP-PBX

IP-Centrex

IP-PBX

Service Availability

IP-Centrex service availability is limited in North America. In some locations, IP-Centrex is not available at all. The ILECs (Incumbent Local Exchange Carriers) have, to date, been reluctant to deploy IP-Centrex services within their own territories. That will change over time, but today competition in IP-Centrex services is limited.

Small vs. Large Business

IP-Centrex services are best suited for small to medium organizations (10 to 200) users. IP-Centrex can offer a rich set of features and functionality that small organizations cannot typically afford to build on their own. In addition, many small companies lack the staff and expertise to implement IP Telephony on their own.

IP-PBX solutions are available for the smallest to largest organizations.

Capital vs. Operational Expenditures

IP-Centrex will require less initial capital expenditures and may offer more predictable operational spending. However, typically the two most costly factors in an IP Telephony solution are network upgrades and telephones. These two elements may necessitate a significant initial capital investment. A service provider may be willing to bundle these costs into the monthly fee. Operations of the internal infrastructure may also result in increased operational expenses above the recurring cost of the service.

An IP-PBX is subject to the same potential costly network upgrade costs as IP-Centrex. These, and all other solution costs, will require a greater initial investment than IP-Centrex.

Operational costs should be lower than IP-Centrex but these may be more difficult to predict and control.

Customization

In general, service providers build their solutions so that they can be reliably replicated, delivered and managed across their customer base. This is important since customization for thousands of customers could result in an operation that would be impractical to manage and operate. Your organization will likely be limited to a specific set of features and products that are predefined in the IP-Centrex service. This may result in less flexibility and ability to adapt to new business requirements. I am not aware of an IP-Centrex solution that offers an API to individual end-customers.

IP-PBX solutions will offer more customization options. In addition, an IP-PBX solution may have APIs that allow the integration with external business processes and applications.

Company Staff, Expertise and History

Organizations that are currently Centrex customers may not have the experience required to install and operate an IP-PBX solution. However, it is important to note, that unless you also outsource the network infrastructure, your company will still be required to manage and operate the infrastructure required to deliver the IP-Centrex service within your organization.

Designing, installing and operating an IP-PBX solution requires skills not typically found in either Telecom or IT. An IP-PBX solution will necessitate associated training and may require the use of external expertise during the design, implementation and early stages of operations.

E911

Enhanced 911 capabilities vary among service providers. Most will be able to deal effectively with locations that are directly connected to the IP-Centrex service. However, if your organization has other locations where IP-Centrex is being delivered across your network from a central service-provider connection point, the IP-Centrex solution may not be able to identify the location of the 911 caller.

Enterprise-class IP-PBX solutions from the major vendors can be engineered to provide reliable E911 services to users located within a predefined geographic network boundary.

Integrated Applications

Integrated applications such as Call Centres, Instant Messaging, Presence and Meet-Me Conferencing may not be available from an IP-Centrex based solution. Additional monthly or usage charges may apply if these types of services are available.

Integrated applications are available with IP-PBX solutions. They may be included in the core software or they may require a one-time purchase and follow up maintenance charges.

Admission Control

Unless the IP-Centrex solution supports RSVP (I’m not aware of any that do so) it will likely be unaware of bandwidth utilization conditions inside your network and will therefore be incapable of rejecting a call attempt, even if insufficient network resources are available to support the call.

Some IP-PBX vendor solutions incorporate devices distributed at key locations within your network or support RSVP to allow the system to determine if sufficient network resources exist to allow a call and ensure voice quality.

Disaster Recovery & Survivability

With a typical IP-Centrex solution, if part or all of your organization’s network was non-functional, incoming calls could still be handled by the IP-Centrex system, in a couple of different ways:

1. When the system detects that the destination (IP Telephone) is not available, the system could direct the call to the service’s hosted voicemail system.
2. The system could redirect calls to devices or locations that are still available. For example, calls could be redirected to an employee’s home phone, cell phone or an alternative functional location.

The circuit connection(s) from your organization’s data network to the service provider can potentially be a single point of failure. The survivability aspects already discussed, and the addition of redundant circuits and components, can mitigate the risk.

Some IP-PBX solutions can compensate (at least partially) for data network circuit failures with some form of local (on-site) backup systems. At a minimum, these backup systems will allow extension-to-extension calling and will allow outgoing calls, including 911 calls.

Distributed call control and PSTN connectivity or additional data network redundancy can mitigate the risk.

Primary call control system failure would result in the inability to process incoming calls unless some form of alternate call routing had been previously arranged with the telephone company. It would also be necessary for the associated supporting systems and processes to have been in place prior to the failure event.