Centrex

For companies that do not want to invest in their own communications infrastructure and get bogged down with management complexities, Centrex can provide a viable alternative to obtaining telephone services and advanced calling features. This service is intended as an alternative to buying a PBX—in fact, Centrex can be considered a remote PBX. Not only does Centrex free up a company’s scarce capital for other purchases, it puts responsibility for maintenance and management on the telephone company. Today’s Centrex services boast 100 percent feature parity with the most advanced digital PBXs currently available—including support for wireless communications and LANs.

The switches that implement Centrex services use computer-controlled time-division switching and have distributed architectures consisting of a host module and multiple microprocessor-controlled switching modules. These switches can directly interface with T-carrier systems to provide 24 digitized voice channels over twisted-pair wire at 1.544 Mbps. These capabilities enable Centrex offerings to include interfaces to the Digital Access and Cross-Connect System (DACS), thereby providing gateways to a variety of services over the public telephone network.

Centrex services offer a wealth of call processing and management features. Many Centrex offices routinely offer automatic route selection, local area networking, facilities management and control, message center services, and voice mail capabilities. In addition to basic rate Integrated Services Digital Network (ISDN), Centrex exchanges are in the process of being upgraded to provide primary rate ISDN service.

Centrex offers a variety of options to help communications managers monitor usage and control costs. Among these cost-management features is Station Message Detail Recording to Premises (SMDR-P), which transmits call records directly to the customer premises from the central office. SMDR-P arrangements provide virtually immediate access to call record data.

Centrex also provides on-line management features. With an on-premises terminal and an interactive software program, users can control the numbers, features, services, and billing codes assigned to each line within their systems. Not only can users review the status of their current Centrex configurations; they can also plan ahead to meet future communications demands by determining what changes need to be made and controlling the date of implementation. All such changes are input to a central management system on the carrier’s network; individual Centrex exchanges poll the system daily for any customer changes and automatically update the telephone company’s internal records.

Wireless communications is supported by some Centrex systems. The service enables employees in a building to send and receive telephone calls on low-power wireless telephones while moving around their offices. The system is based on a network of small, low-power transmission cells distributed strategically around the building and linked to a local exchange carrier by a central controller. This controller coordinates the handoff of calls from one cell to the next as the user moves about the workplace.

Despite the many advantages of subscribing to Centrex services, it does have its share of liabilities. In addition to being dependent on the local phone company for service and support, the contracts usually run from 5 to 10 years—the longer the commitment, the better the pricing. However, this can lock you, as a network manager, out of any new technologies that may come along and prevent your company from taking advantage of efficiencies and economies they may offer.

Types of Centrex CPE

Centrex Phones

Centrex phones let you hold, transfer and forward calls by simply pressing a button. Many have message waiting lights that flash for stutter dial tone (CO voicemail) and offer other “smart” features.

Call Accounting

Centrex-compatible call accounting packages bring Message Detail Records straight from the CO to your desktop. You can use this info for charts, graphs and reports. These packages monitor the CO directly via a CO-supplied SMDI (Station Message Detail Interface). Alternatively, there are site-monitoring boxes that live in your office, monitor your trunks and deliver SMDR records via a serial interface, just like you get from a conventional phone system.

Voicemail

Central Office voicemail is fine for small businesses, but is not flexible enough for larger firms requiring auto attendant functionality, dial-by-name and other applications. Fortunately, most general-purpose voicemail systems can be used with Centrex so you have lots of choices.

ACDs

Centrex-compatible ACDs let you queue calls, manage agents and generate realtime reports-all from CO trunks.

Paging Systems

Centrex-compatible voice paging systems give you all the features of classic, switch-based paging equipment.

Attendant Consoles

Centrex answering consoles can take many shapes; multi-button phone, conventional-appearing attendant console, or PC-based system.

Set Handlers

These systems convert analog or digital Centrex service to proprietary digital formats and distribute the service to full-featured digital station-sets. They employ CO features to handle transfer, forward and other functions, while giving you much of the appearance and functionality of an onsite digital switch.

Administration Systems

Centrex administration systems let you reconfigure your Centrex service. Platform-based consoles let you turn enhanced CO services (such as CO voicemail) on and off; activate or deactivate lines; add or reassign trunks and rearrange long-distance dialing patterns to route calls over the least expensive carriers.

Multiple Site Centrex

Almost all of the above categories of CPE come in both single- and multi-site versions. If your company has multiple locations, you should get the appropriate CPE. 

Centrex Buying Tips

Decide how you want to set up your phones. Do you want to run the system like a PBX (where calls come in at a central number and are transferred to extensions by a human or mechanical attendant) or make extensive use of Centrex’ DID (Direct Inward Dial) capabilities to give everybody a number? If you go with a PBX-type setup and use a receptionist, you’ll probably need an attendant console.

If you go with a departmentalized setup (clustered workgroups like sales, accounting, administration, etc.) a KSU-less Centrex-compatible phone system can give you a non-squared configuration. This provides private lines on multi-line phones, common lines and intercom groups on a department basis.

Look for Centrex CPE (Customer Premisess Equipment) that gives you some control over Centrex features. Some of today’s CPE lets you control music-on-hold selections, call accounting, overhead paging systems, and station displays.

Smaller sites (roughly five to 75 stations) can usually get package deals on Centrex services from RBOCs (Regional Bell Operating Companies). Ask about these deals, that include services like conferencing, transfer, call forward and more, if you’re considering Centrex for a relatively small number of stations.

Look for Centrex CPE (particularly attendant positions and desk phones) that also supports digital lines, like ISDN. You will have a wider range of applications to choose from.

Many RBOCs are offering ISDN as an enhancement for Centrex. Use digital ISDN lines for fast, high-bandwidth intensive applications (data and videoconferencing) and the analog Centrex lines for traditional call processing, voicemail, etc.

Other recent Centrex enhancements include wireless capabilities, automatic call distribution, voicemail, fax services, call accounting and PC-based call routing systems.

When your switch is inside the CO (as it is with Centrex), it’s harder to provide yourself with modern phone system adjuncts like unified messaging, operator consoles, call accounting and other facilities.

This is where Centrex CPE steps in. There is plenty of Centrex CPE available, and the products are starting to support advanced applications and equipment.

Basic Centrex Features

Call Transfer transfers calls to another line either inside or outside your Centrex system.

Direct Inward and Outward Dialing allows you to control whether incoming or outgoing calls are routed directly to an employee’s desk or to an attendant.

Hunting automatically sends an incoming call from a busy line to the next designated line.

Line Restriction limits phone access on selected lines, so that only authorized numbers or regions can be called.

Station Line Identification provides a record of calls made by each extension.

Station-to-Station Dialing allows station users to intercom between stations by using abbreviated dialing, usually four digits.

Three-Way Calling allows you to add a third person to a regular two-way call.

Optional Centrex Features(Available at an additional cost per line)

Call Forwarding-Busy Line automatically routes calls to another extension or to your voice mail if your line is busy.

Call Forwarding-Don’t Answer automatically reroutes calls to another phone if you haven’t responded within a preset number of rings.

Call Forwarding-Variable sends your calls immediately to another number and is set by the user by entering a three digit code and the destination number.

Call Hold puts a call on hold and returns dial tone.

Call Park lets you hold a call on one Centrex line and pick up a call on another.

Call Pickup lets you use your extension to answer any ringing phone in your designated group.

Call Return lets you return your last incoming call with a code or a single button.

Call Screen allows up to 10 predetermined numbers to be routed directly to a prerecorded announcement.

Call Waiting-Incoming signals you with a tone when another call is coming through on your line.

Caller ID displays the caller’s phone number (on compatible equipment).

Directed Call Pickup use your extension to answer a specific ringing phone in your designated group.

Direct Inward Dial to Direct Outward Dial Transfer allows you to transfer an incoming direct-dialed call to a location, either within, or outside the Centrex system. The caller doesn’t have to hang up and dial the new number.

Distinctive Ringing lets you know if a call is originating inside your office. A single ring means an inside call, a double ring means the call came from outside.

Executive Busy Override permits an interruption on a station that has a call in progress. Parties engaged in conversation hear a warning tone before new caller joins the conversation.

Flexible Route Selection automatically routes calls over designated carriers. You can cut costs if your business does a high volume of statewide or nationwide calling by using your preselected carrier.

Meet Me Conference allows you to meet with a maximum of either 6 or 30 people on a conference call.

Message Waiting Indicator alerts you with a stutter dial tone when someone has left a message for you in your voicemail box.

Music On Hold provides music or an announcement to callers on hold.

Paging provides access to customer-owned paging systems.

Priority Ringing special ringing indicates when any of up to ten numbers you select are calling. If you also subscribe to Call Waiting, a unique call waiting tone alerts you that the caller is one you’ve selected on your Priority Ringing list.

Remote Access to Call Forwarding allows you to control remotely the destination of your forwarded calls.

With Repeat Dialing you can program your phone to keep dialing when your call can’t go through. A special ring lets you know when the line is free.

Sectional Billing permits you to group individual Centrex lines by department, agency or work group.

Select Call Acceptance only callers whose numbers are on your selected list will be allowed to complete the call. Automatically accepts calls from up to 31 telephone numbers you choose.

Select Call Forwarding forwards calls from up to ten numbers you select to any number you designate. Important calls can reach you directly, rather than forwarding to voice mail. Calls not on your special list can be forwarded to yet another number by using Call Forwarding/Variable, Call Forwarding/Busy Line, or Call Forwarding/Don’t Answer.

Speed Calling (also called abbreviated dialing) lets you press fewer digits to make a call.