Calls
Call queues and ACD explained: how calls reach the right agent
19 Oct 2026 · 8 min read
The short answer
A call queue holds callers in order until an agent is free. Automatic call distribution (ACD) is the rule that picks which agent rings: the one idle longest, the next in turn, everyone at once, or a fixed order. Set the ring order, a wait limit and a missed-call plan on day one.
A call queue is a waiting line for callers. Automatic call distribution, or ACD, is the rule that decides which free agent gets the next caller. Together they replace a ringing phone on one desk with a shared line that a whole team answers fairly.
What is a call queue?
A call queue is a group of agents who share incoming calls for one purpose, such as sales or support. When every agent is busy, new callers wait in line instead of hearing a busy tone. When an agent frees up, the system connects the caller who has waited longest.
Most teams have one queue per type of work. A clinic might have bookings and results. A shop might have orders and returns. Callers reach the right queue through a phone menu, which is covered in what is IVR.
What is automatic call distribution (ACD)?
ACD is the logic that answers the question “which agent rings for this call?”. It looks at which agents are available and applies the rule you chose. Twilio’s glossary notes that IVR menus work together with ACD and skill-based routing to send callers to suitable agents.
The rule matters because it shapes both the customer’s wait and the agents’ day. A rule that always rings the same person burns that person out. A rule that rings everyone at once makes a noisy floor.
What are the call routing methods?
Zoom’s explainer on call queuing names the standard set: simultaneous, sequential, rotating (round robin), longest idle and skills-based. Here is how they compare, with the SautiDesk equivalent where one exists.
| Method | How it works | Good for | SautiDesk ring order |
|---|---|---|---|
| Longest idle | The call goes to the agent who has been free longest | Spreading work evenly when calls vary in length | Longest idle |
| Round robin | Calls rotate through agents one after another | Giving everyone the same number of calls | Take turns |
| Simultaneous | All free agents ring at once, first to answer takes it | Small teams where speed matters most | Ring everyone |
| Sequential | Agents ring in a fixed order, moving on if no answer | A main person with a backup | Same order every time |
| Skills-based | The call goes to an agent with the right expertise | Mixed teams, languages or products | Use a separate queue for each skill |
SautiDesk also has a fifth ring order, fairest by talk time, which rings whoever has talked least over the last eight hours. It suits teams where a few long calls would otherwise leave one person with all the hard ones.
Which routing method should you choose?
Start with longest idle for a team of three or more. It needs no tuning and keeps the load level. Use ring everyone for a team of two or three where nobody should wait. Use a fixed order only when one person is clearly the first choice and another is a true backup.
Skills-based routing without a skills engine
SautiDesk does not match calls to individual skill tags. It gets the same result with queues: one queue for Swahili support, one for billing, one for sales. Each key on the phone menu sends the caller to the matching queue, and you add the agents who belong there.
How should you treat callers who are on hold?
Tell callers what is happening. Zoom’s guide advises hold music or branded audio and announcing a caller’s position and expected wait, and notes that callers who know where they stand tend to be more patient than those who hear silence. Keep any recorded message short and update it so it never goes stale.
- Say something within the first few seconds. Silence leaves callers guessing whether the call connected.
- Do not repeat the menu. They have already chosen.
- Avoid promises you cannot keep. “Your call will be answered in two minutes” is a promise. “We will be with you shortly” is not.
- Offer a way out. Tell callers they can message you on WhatsApp instead.
What is overflow, and when does a call spill over?
Overflow is what happens when a call has waited too long or the queue is too full. Zoom’s guide suggests a maximum wait time and then sending the caller to voicemail, a callback option or another team. The point is that no caller waits with no end in sight.
In SautiDesk, the safety net is the ticket. If a caller hangs up while waiting, or nobody answers, the missed call still opens a ticket with an owner, with the caller’s number on it. Your team then rings back. Treat the daily missed-call list as part of the queue, not a separate chore.
What is a callback and how does it differ from voicemail?
A callback means the business rings the customer instead of the customer waiting on hold. Zoom describes a version where the caller keeps their place in line and the team rings back when someone is free. Voicemail leaves the task with the customer to explain again. A ticket with a number on it leaves the task with you.
Whichever you use, set a rule for how fast a call back happens. The missed calls routine gives a timing rule and a script.
What should you configure on day one?
Set six things on day one: the queue name, the ring order, who is in it, what callers hear, what happens when nobody answers, and who checks the missed-call list. Everything else can wait for the first week of real calls.
- Name each queue after the job. “Sales” and “Support” beat “Queue 1”.
- Choose the ring order. Longest idle unless you have a reason not to.
- Add the agents. Only people who will actually answer. Agents on a break are not rung, so ask people to set their status when they step away.
- Write the greeting and keys. Cover every queue, and pick the queue for callers who press nothing.
- Agree the missed-call rule. Who owns the list each morning and how soon a call back happens.
- Test it. Call from two outside phones at once and check both ring.
How many queues do you need?
Start with the fewest that match how work is really split. SautiDesk Basic includes 1 queue, which suits a single team answering one line. SautiDesk Pro has as many queues as you need, plus the live floor view and reports that show how each queue performs. If you have two or more distinct teams, choose Pro.
To estimate how many agents a queue needs at your call volume, read Erlang explained. To price a team, use the pricing calculator.
Worked example: a 4-person support line
A repair shop in Nairobi has four people on its support line and about 60 calls a day. The owner sets longest idle so the call goes to whoever has been free longest. Mid-morning, all four are on calls and two more callers arrive. They wait in order. When one agent finishes first, the longest-waiting caller rings that agent. If one caller hangs up after 40 seconds, a ticket with their number is waiting for the morning list.
With ring everyone, all free agents ring at once. That can get calls answered a little faster, but every free phone rings for every call, and the quickest agent ends up with the most calls. Longest idle spreads the load.