ASR and ACD Explained for Call Center Traffic
Every carrier conversation eventually lands on two acronyms: ASR and ACD. They show up in route reports, in support tickets and in that slightly tense call where someone asks why "the trunk feels off today." If you run a call center or a BPO, these two numbers are the closest thing you have to a vital-signs monitor for your voice traffic.
The good news: neither one is complicated. The catch: both are easy to misread. This guide covers what ASR and ACD mean, how they're calculated, what pushes them up or down, and how to read them together without jumping to the wrong conclusion.
What Is ASR?
ASR stands for Answer Seizure Ratio. It's the share of call attempts that actually get answered.
A "seizure" is simply a call attempt that grabs a channel on the trunk. An "answer" is a call that the far end picks up, meaning the network signals that the call connected (in SIP terms, a 200 OK to your INVITE).
The ASR Formula
ASR = (answered calls ÷ total call attempts) × 100
Illustrative example: if your dialer sends 1,000 attempts in an hour and 420 of them are answered, your ASR for that hour is 42 percent. Those numbers are made up for the math, not a benchmark.
What Counts as "Answered"?
This is where ASR gets slippery. An answer is a network event, not a human event. A voicemail greeting, an IVR or an answering machine all "answer" the call. A busy signal, a ring-no-answer or a rejected call does not. So ASR tells you how often the network connected you to something, not how often a person said hello. Your dialer's own dispositions (human, machine, no answer) give you the human side.
Also note that carriers and dialers can count attempts slightly differently, for example whether a call you cancelled after two rings counts. When you compare reports, compare like with like.
What Is ACD?
ACD stands for Average Call Duration. It's how long answered calls last, on average.
The ACD Formula
ACD = total billed (connected) minutes ÷ answered calls
Illustrative example: 420 answered calls that add up to 1,260 connected minutes give you an ACD of 3.0 minutes. Again, those are example numbers only.
Only answered calls count. Unanswered attempts have no duration, so they never pull ACD down directly. (Heads-up: in call center software, "ACD" can also mean Automatic Call Distributor, the system that routes inbound calls to agents. Same letters, different job. In carrier and route talk, it means Average Call Duration.)
Why Do ASR and ACD Matter to a Call Center?
Because they're the quickest way to tell whether a problem lives in your routes, your lists or your campaign.
- Route quality. A healthy route connects calls that should connect and keeps them up. A struggling route shows up as falling ASR, shrinking ACD, or both.
- Agent productivity. Low ASR means agents wait longer between conversations. Very short ACD can mean calls are dropping before anyone gets a sentence out.
- Early warning. A sudden change in either number, compared with your own normal, is often the first sign something changed: a route, a caller ID reputation issue, a firewall rule or a bad list.
ASR and ACD don't replace your dialer's contact rate, conversion rate or agent metrics. They sit underneath them, describing the plumbing.
What Moves ASR Up or Down?
Plenty of things, and not all of them are the carrier's fault.
Things on the Network Side
- Route quality. Tier-1 routes with clean signaling connect calls more consistently than long chains of hops.
- Capacity and errors. If calls are hitting channel limits or getting SIP errors (think 403, 486, 503), attempts fail before anyone can answer. Your dialer and carrier logs will show the codes.
- Caller ID trust. If called parties see your number flagged, fewer people pick up. STIR/SHAKEN helps authenticate that you're allowed to use your caller ID; it doesn't control how carriers or apps label calls. More on that in our post on STIR/SHAKEN and spam labels.
Things on Your Side
- List quality. Disconnected, wrong or stale numbers can't be answered. Scrub and refresh your data.
- Time of day. Calling when people are at work, asleep or commuting changes who picks up, and calling hours are also a compliance matter.
- Dial pacing. An over-aggressive dial ratio can create abandoned calls and frustrated people, which can make answer rates worse over time.
- Caller ID choice. Use numbers you're authorized to use, registered and consistent with your brand. Registering your outbound numbers (see our Free Caller Registry guide) and using properly provisioned US DIDs are the honest levers here.
What Moves ACD Up or Down?
ACD is mostly about what happens after the answer.
- Answering machines and voicemail. If your dialer hangs up quickly on machines, those short calls drag ACD down. That's normal for many outbound campaigns.
- Call drops and audio problems. One-way audio, choppy calls and early disconnects create lots of very short calls. These often point to NAT, firewall, codec or timer settings, and sometimes to the route.
- Campaign type. A quick survey, an appointment confirmation and a complex sales call will naturally have very different ACDs. Compare a campaign with itself, not with a different kind of campaign.
- Agent handling. Scripts, training and how fast agents reach the point all show up here.
How Do You Read ASR and ACD Together?
One number alone can fool you. Read them as a pair, and always against your own baseline for the same campaign, time window and list.
| What you see | What it often suggests | First thing to check |
|---|---|---|
| ASR down, ACD steady | Fewer calls connect, but connected calls behave normally | List quality, caller ID labeling, SIP error codes |
| ASR steady, ACD down | Calls connect, then end fast | Drops, one-way audio, machine detection settings |
| Both down at once | Something broader changed | Recent route, network or config changes |
| ASR up, ACD sharply down | Possible false answers or very short connects | Call recordings and SIP traces on a sample of calls |
That last row deserves a note: a route that "answers" calls that never really connected can make ASR look great while ACD collapses. That's why you never judge a route on ASR alone.
What's a "Good" ASR or ACD?
Honest answer: it depends. Your industry, your lists, your calling hours, your campaign type and whether you dial mobile or landline numbers all shift the numbers. Any single industry-wide "good ASR" you see quoted is a rough rule of thumb at best.
A more useful approach:
- Set your own baseline. Track ASR and ACD per campaign and per route for a few normal weeks.
- Watch for changes, not absolutes. A sudden drop against your baseline matters more than how you compare with someone else's call center.
- Segment before you panic. Split by route, by caller ID, by area code and by hour. A problem that only affects one slice is easier to find.
- Bring data to your carrier. Sample call IDs, timestamps, numbers dialed and SIP response codes turn "calls feel bad" into a fixable ticket.
How to Track ASR and ACD in Vicidial or GoAutoDial
You don't need fancy tooling. Vicidial-based dialers keep call logs with statuses and lengths, so you can work out both numbers from your own data: count attempts, count answered calls, add up talk time. Many teams build a simple daily report or spreadsheet per campaign and per carrier.
If you're still wiring up your trunk, start with our guides to Vicidial SIP trunk setup and GoAutoDial SIP trunk setup. A clean carrier entry, correct codecs and sane timers remove a lot of "mystery" short calls before they ever show up in your ACD.
A Quick Compliance Note
Better metrics never justify cutting corners. For outbound calling in the US, follow the TCPA and the National Do Not Call Registry rules, keep your internal do-not-call list current, respect calling-hour limits, and get the consent the law requires before you call or text, especially for autodialed or prerecorded calls to mobile numbers. State rules can be stricter. This isn't legal advice, so check with counsel for your specific campaigns.
Where Connectivity King Fits
Connectivity King runs carrier-grade SIP trunking for call centers on Tier-1 routes, with 99.99% uptime, US local and toll-free DIDs, and a support team that will dig into your ASR and ACD questions with you, Monday to Friday, 9am ET to 9pm PT. Prefer not to run the dialer yourself? A hosted Vicidial dialer comes with VoIP and DIDs connected.
ASR and ACD FAQ
What does ASR mean in VoIP?
ASR means Answer Seizure Ratio: the share of call attempts that get answered. Divide answered calls by total attempts and multiply by 100.
What does ACD mean in VoIP?
In carrier and route reports, ACD means Average Call Duration: total connected minutes divided by the number of answered calls. In call center software, ACD can also mean Automatic Call Distributor.
Does a voicemail count as an answered call for ASR?
Yes. ASR counts network answers, so voicemail, IVRs and answering machines count as answered. Use your dialer's dispositions to see how many answers were real people.
Why is my ACD so short?
Common causes are quick hang-ups on answering machines, dropped calls, one-way audio or a campaign that's simply short by design. Listen to a sample of short calls and check SIP traces before blaming the route.
What is a good ASR for a call center?
There's no single number. It varies with lists, calling hours, campaign type and number types. Set a baseline for each campaign and route, then watch for changes against it.
Does STIR/SHAKEN improve ASR?
STIR/SHAKEN helps authenticate that you're allowed to use your caller ID. It doesn't control spam labels, so it isn't a direct ASR fix. Clean lists, registered numbers, consent and sensible pacing matter too.
Ready for Routes Worth Measuring?
Want routes that look good on your ASR and ACD reports? Tell us about your traffic and campaigns, and we'll put together a quote, usually the same day. Request a quote.
