Standard PBX
Diagram & Operation
In a typical office environment, the PBX system connects multiple incoming phone lines to multiple telephone extensions. Basic PBX switches do little more than cross-connect these lines. As system price rises, functions are added. Some added features can be provided through software and/or firmware upgrades inside the basic hardware. For other features add-on modules are required.
Usually, the PBX device is a piece of hardware that hangs on a wall or mounts in a rack. Some type of patch panel is included that allows connection to internal and external telephone wires. Sometimes, PBX functionality is provided through software. In this type of system, a personal computer controls system operation and adapter cards and add-on modules provide connectivity.
Operation is fairly straightforward. Callers that want to reach someone in the company place their calls from any type of telephone. The call is routed through the Public Switched Telephone Network (PSTN) to company-specific lines leased on a monthly basis from a telephone company. The PBX system answers the call with a recorded greeting, plays a menu of connection options to the caller, and then routes the call to the appropriate employee extension or to a holding queue (ACD queue or hunt group) for a department, such as sales or support. In installations where the company wants calls answered by a person instead of a machine, the calls are first routed to an operator or receptionist who then forwards the call to the proper extension or department.
Calls transferred to an extension will ring at a particular phone, usually a desk phone somewhere in the office. If the extension owner picks up the phone the call is connected. If not, the call is usually transferred to voice mail.
When callers know what department they want but don't have the name or extension number for a particular individual, they usually have the option to be sent to a holding queue to wait for the next available agent (employee) to take the call. Many low-end systems do not offer any type of holding queue, and callers must know who they want to speak with before they call. Other low-end systems send callers to a "hunt group" - a list of phone numbers to try and find someone available. Hunt groups usually have the drawback that every extension number must be tried, in the same order each time, in an attempt to find an employee that can take the call. In such cases, the first extension on the hunt list usually gets swamped with calls while other extensions are used only when there is a heavy load. Another disadvantage of hunt groups is the time it takes to try each extension to find one that isn't busy and has someone ready to pick up the phone.
Higher-end PBX systems employ a variety of techniques to assure that calls to a holding queue are answered more efficiently. The most prevalent approach is through the use of Automatic Call Distribution (ACD) queues. A system with ACD queuing keeps track of which employees are already taking calls and how long it has been since each person finished prior calls. Incoming calls are put into the queue waiting for the next available employee and then routed automatically to the employee that has been off the phone the longest. ACD queuing evenly distributes calls to employees while insuring a minimum wait time for each caller on hold. The ACD queue feature can add considerably to the cost of the PBX system but is often a major factor in customer/caller satisfaction. Serious businesses usually need the advantages of true ACD queuing.