Automatic call distributor

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The automatic call distributor (ACD) is usually a telephone switch (circuit switch) with the ability to use information about the call to route it to a specific agent. Actually, modern ACDs can also manage information associated with the call as well as perform the routing function. The ACD is the heart of the call center. The technology has evolved to support both inbound and outbound calls, route calls to agents and also route the data traffic associated with each call. These devices also support extensive data collection on numbers of calls, call holding times, number of calls in queue, longest time in queue, customer abandonment rate, agent occupancy and other measures necessary to effectively manage the call center.

Routing of calls can be based on a variety of factors. One obvious criterion is where is there an available agent. However, beyond that, routing can account for agent occupancy by routing a call to the agent who has been idle the longest time or occupied the least amount of time over some period. Routing can be based on knowing what number the customer dialed using the dialed number identification service (DNIS) that carriers offer. This allows, for example, a single call center to accept calls destined for more than one company or type of service, by assigning different telephone numbers to each and configuring the ACD to route the calls accordingly. Other factors that can influence routing are the customer's calling number. This allows calls to be routed based on the customer’s geographic location. It also allows decisions to be made based on geography. For example, calls from an area code in Puerto Rico could be routed to Spanish-speaking agents. Calls can also be routed differently based upon time of day or day of the week. In the case where multiple call centers are in use, this permits calls to be routed to different call centers depending on day or time. For example, calls could be routed to an East Coast call center in the morning hours and a West Coast call center in the afternoon and evening hours allowing more hours of call coverage without having to schedule agents beyond a normal 8AM to 5PM workday. Finally, announcements can be used to elicit information from the customer via the telephone dialing pad. That information can then be used to route the call.

Agents behind the ACD are arranged into groups or “splits” based on a variety of factors. Obvious breakdowns are one group to handle sales calls, another to handle customer service, another for technical support. Beyond that, particular agent skills can be used to establish groups. For example, agents who speak a particular language can be in one group. The routing can even be sophisticated enough to account for the fact that more calls can be routed to an experienced agent than to an agent in training.

Note that while ACDs route phone calls they can also route information related to the call. For example, a server may be connected to the ACD and interrogated with calling line identification (CLID) to access a customer database record, which can then be forwarded with the phone call to an agent position.

ACD Types

We noted that ACD are usually, but not always, telephone switches. Vendors of large telephone switches such as Lucent and Nortel have long been offering ACD functions as an option in their large CO switches. Call centers implemented using a CO-based ACD can avoid the capital expense of having a switch on their premises.

Likewise, PBX vendors (Avaya, Nortel, etc.) also offer ACD functions in the PBX switch. This permits the corporation to exercise a greater degree of control over switch configuration and operation, but requires the obvious expenditure of capital money.

For very small call centers, key systems may suffice for a limited number of agents. While this limits the expense involved, key systems also suffer from limited capability.

With the transition to computer controlled telephone switches, it should be no surprise that ACDs can be built using computers that are not circuit switches at all. These server or PC-based ACDs can be connected to ISDN lines and used to route calls and related data to agent positions.

Central Office-Based ACD

Central office-based ACD is a Centrex feature that supports many of the same services provided by premises-based PBX and stand-alone ACD equipment. Generally, the station sets for the ACD splits are proprietary, offering some set of features, such as CLID display, which are not found on standard analog sets.

The advantage of CO-based ACD is that there is no (or very little) capital cost associated with the system. The user need only purchase the premises sets; the capital cost of the switch and the ACD functionality are embedded in the monthly fee.

ISDN, coupled with CO-based ACD, provides the opportunity to set up call centers on a telecommuting basis. Agents working from their homes have access to the voice calls and to data provided from the home office facility based on the CLID. To callers, the telecommuting agents are indistinguishable from agents located at the call center facility itself. Their performance can be monitored by management reports that are part of the CO ACD product offering.

The ISDN D-channel can also be used in a single line configuration between a CO and an ACD. Signaling is exchanged between the CO and ACD over a single D-channel in a Basic Rate Interface (BRI), reducing the number of trunks required.

Note that the availability of an out-of-band signaling path allows the creation of ACD structures on a geographical framework much larger than that spanned by a single central office. With the ability to redirect calls using Signaling System 7 (SS7) packets, it is possible to involve a number of CO in such a system. This allows a user to use a local access and transport area (LATA) Centrex system to provide a totally decentralized call center.

CO-based ACD is not a panacea, however. One still needs some form of uninterruptable power supply to power the proprietary digital sets in general use. Furthermore, the cost of centrex lines to the CO can become prohibitive in large call center operations when compared with the large pricing advantages that can be obtained using T-1 oriented trunking to a premises-based PBX.

ACD Functions

ACDs are often extremely flexible devices, providing a very broad set of call center support features. On the facing visual we have listed characteristics that are generally found in ACD systems; different systems will provide different feature sets.

Routing will generally be to the first idle agent if all agents are busy when the call arrives, and to the most idle agent when more than one agent is available (the definition of “most idle agent” varies from ACD to ACD). The most sophisticated systems literally keep track of “air time” for each agent, and assign calls to the agent who has spent the least time on the phone. Alternatively, most idle agent could also mean the agent who has been idle for the longest period, not necessarily the agent who has handled the least amount of traffic over the entire work day. This approach to identifying the most idle agent does tend to provide a reasonably close approximation to global as well as short-term load balancing, and is very easy to implement.

Agents are organized into splits, with each split having its associated lines, stations, recordings, and queues. It is typical to separate calls by split on the basis of the DNIS. One 800 number is published per split, and a hunt group extension number is associated with the DNIS. This can easily be done if the ACD function is integrated with the PBX; otherwise, the PBX forwards the DNIS provided by the network to the ACD. The number of splits can be quite large, and it is not atypical to support a division of the workforce into several hundred splits.

The total number of agents supported by an ACD can be quite large. Although ACDs are justifiable with only tens of agents, systems are available that can support thousands of agents organized into hundreds of splits.

Calls for which no agent is available are placed in a queue, with a maximum queue length programmable by the user. If the maximum queue length is reached, calls can be redirected to a separate path or given a busy signal, as determined by the user. The so-called call coverage path to which calls are redirected might even, for example, give an announcement requesting that the caller try at another time, and then simply hang up.

Priorities can be assigned within a queue. For example, one could establish a priority system to allow customers who have dialed an emergency number to be handled ahead of other users.

When a queue for a specific split exceeds some trigger point, two different types of overflow are possible. First, intraflow allows the call to be answered by someone in a different split, but at the same switch. In contrast, interflow allows new calls to be sent to a different split, on a different switch. Interflow is most easily accomplished when the PBX and ACD are integrated, although it can be done with a separate ACD as well. One simply invokes a call forwarding procedure when the queue overflows.

All ACDs provide substantial management support capability. Status of queues, agent productivity, etc., are all provided to the call center management. The ability to track performance in real time allows managers to intervene (e.g., by calling in additional agents, or allowing longer queues) during times of unusual traffic, long agent hold times, and so on.