What "most concurrent calls" tells you about your peak load

The most-concurrent-calls figures in the Maximum System Stats report capture the single highest number of simultaneous calls your system carried at any moment during a day — and that peak, not the daily total, is the number you use to size trunks and server capacity.

Peak versus total — why the distinction matters

A daily call total tells you throughput — how much work moved through the system. A peak Concurrent calls figure tells you density — how many calls the system had to handle at the same instant. Those are very different problems for infrastructure.

Consider two scenarios: a server that processes 3,000 short calls spread evenly over an eight-hour shift, and a server that takes the same 3,000 calls in two burst hours. The daily totals are identical. The peak simultaneous counts can differ by a factor of four. Your SIP trunk capacity, your Asterisk channel limit, and your CPU budget are all sized for the peak — not the total.

The three concurrent-calls figures and what each sizes

Maximum System Stats tracks three separate peak simultaneous call figures for each day:

• Most concurrent calls in and out — the peak combined count across all directions. This is the headline number for server and carrier trunk sizing. Your server must handle this many simultaneous active call legs at once, and your total trunk allocation must exceed it.
• Most concurrent calls inbound total — the peak simultaneous count for inbound traffic only. Use this to right-size your DID (direct inward dialing) allocations and your inbound queue Carrier trunk capacity independently of outbound.
• Most concurrent calls outbound total — the peak simultaneous count for outbound dialing. This drives how many outbound Channel slots Asterisk needs to hold open and how many simultaneous dials your campaign's dial level can sustain.

flowchart TD
  A["Peak concurrent calls combined"] --> B["Server capacity check"]
  A --> C["Total trunk allocation check"]
  D["Peak concurrent inbound"] --> E["DID trunk slots sizing"]
  D --> F["Inbound queue headroom"]
  G["Peak concurrent outbound"] --> H["Outbound dial capacity"]
  G --> I["Channel slot budget for campaigns"]
  B --> J["Resize or stay"]
  C --> J
  E --> J
  H --> J

Reading the inbound vs outbound split

The split between peak inbound and peak outbound rarely happens at the same time of day. Most call centers see outbound peaks in the morning when predictive campaigns launch and inbound peaks later in the day as callbacks and responses arrive. Watching both figures over 30 days helps you understand whether a trunk configuration change would help one direction without straining the other.

If your combined peak is well below your trunk limit but your outbound peak is consistently close to the outbound allocation, you have a configuration imbalance. Your total capacity is fine but the outbound trunk share is too narrow. These are the kinds of findings that require the split view.

Applying the peak to capacity decisions

A safe planning rule is to keep your peak at no more than 70 to 80 percent of your installed capacity. If your most-concurrent-calls combined is regularly hitting that band, it is time to expand. By the time you are hitting 90 percent or above, your Dialer pacing is already degrading under the heaviest bursts even if most hours look fine.

One detail worth tracking separately: the peak combined figure can mask a directional problem. If your combined peak is 120 simultaneous calls but your outbound peak is 115 of those, almost all of your trunk capacity is committed to outbound at the busiest moment. An unexpected inbound spike at that same moment — a callback wave, for example — would hit a wall. Watching all three peak columns together, not just the combined total, gives you that directional awareness.

Track the most-concurrent-calls figures over at least four weeks before making a resize decision. A single-day peak that is unusually high may reflect a one-off event — a large blitz campaign, a holiday callback surge — rather than the new normal. The 30-day trend tells you whether that peak is repeatable.

For the full picture of what to track and when, see our guide to monitoring VICIdial server health and capacity. To understand how real-time channel counts behave minute to minute during a shift, read VICIdial system load explained.

Need a managed VICIdial box where capacity reporting is ready from day one? Start a VICIfast trial and your server is live in under 40 seconds with Maximum System Stats already collecting.