VoIP Call-Center

We always identify a call centre as a specialized place where many calls are generated or received. They generally handle customer service, support, telemarketing, telemarketing, telesales and collections functions. Employees working in call centres are referred to as “agents” or “customer service representatives”. Call centres can be as small as five agents or massive and highly optimized with hundreds or thousands of agents.

Call centres use specialized technologies to maximize productivity. Telephony switching systems, or telephone plants as we call them in Colombia, are configured and used to queue and route incoming calls to agents based on a wide variety of criteria. Outbound calls are often generated by an automated system called “Predictive Dialer – go to HexaDialer” that monitors agent status and places calls on their behalf. Other common call centre tools include desktop integration (often referred to as “pop-up display” – go to HexaHUD -), Interactive Voice Response (IVR – see Enterprise VoIP -) applications, call recording solutions, productivity monitoring utilities, workforce planning systems, and various methods of historical and near real-time reporting – go to HexaReports.

Photo by Petr Macháček on Unsplash

Call queuing

A simple ACD system consists of a call source (a group of lines, trunks or virtual trunks), a FIFO (first-in, first-out) queue and a group of agents that are selected using a “ring all” strategy. In this case, when a call comes in, the system rings the phones of all agents who are not already on a call. The first agent to answer the call is connected to the caller. A more complex (and probably more helpful) configuration would have the ring offered to the agent who had been in the idle state for the longest time. This “most idle” strategy is often used when all agents are considered equally qualified to handle a task. Other standard techniques include random rotation, linear search, last recent calls, last calls, and random. In some cases, the ACD may weigh its selection based on the caller’s need (usually gathered through an IVR application) and a list of skills associated with each agent. This is generally referred to as “skills-based routing”.
Automatic Call Distributor (ACD)
An ACD is a specialized telephone system that routes (distributes) incoming calls to teams of agents assigned to various call queues. The queues are simply an ordered list of calls to be routed to agents. The ACD oversees the process of placing incoming calls into the appropriate queue, assigning priority to those calls based on several factors (the order of their arrival, the importance of the caller, the urgency of the caller’s situation) and ultimately routes those calls to an available agent. The algorithm by which calls are dispatched is called queuing strategy.

Call experience

While waiting in the queue, callers typically hear a combination of marketing messages, queue status messages, and music. Marketing messages are audio recordings that are periodically piped into the queue. Status messages provide the caller with specific information about their status: the number of people waiting for them in the queue, the estimated waiting time, and sometimes alternatives to waiting in the queue. Some more advanced call queuing systems support virtual queues. A virtual queuing system allows callers to provide a callback number and then disconnect. Their position in the queue is retained, and when an agent becomes available, the system places an outbound call to the caller.


Asterisk is a powerful tool for building VoIP systems and solutions, especially for call centres. With support for call queuing, IVR, outbound dialling, recording, live monitoring and reporting, Asterisk includes