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US carriers judge outbound traffic on behavior. Campaigns with too many abandoned or very short calls get flagged as “Spam Likely,” lose answer rates, and incur Plivo surcharges. Staying deliverable takes two things, both covered here:
  • Quality: Keep your traffic within Plivo’s quality thresholds.
  • Pacing: Stay within your allocated CPS (calls per second). On the SIP trunking path, calls above your limit are rejected rather than queued, so pace your dialer accordingly.
This guide applies to US destinations only. Expectations, limits, and carrier behavior differ in other countries.

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Why call behavior matters

US carriers continuously analyze call traffic for patterns associated with unwanted calling. Two signals matter most for outbound voice agent campaigns:
  • Answer rate: the share of your call attempts that recipients pick up
  • Call duration: how long answered calls last
Campaigns with low answer rates and a high share of very short calls look like untargeted cold calling to carriers and analytics providers. The consequences compound: your numbers get flagged as “Spam Likely” on recipients’ devices, answer rates drop further, and your traffic may be subject to surcharges or account review. Calling only recipients who expect your calls, with proper consent where required, is the single most effective way to keep these metrics healthy.

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Call quality thresholds

Plivo enforces monthly thresholds on two categories of outbound calls: Calls above these thresholds incur per-call surcharges. See Abandoned and short-duration call thresholds for current surcharge rates. These thresholds apply to both SIP trunking and audio streaming traffic, and exclude calls to India. Rates moderately above the thresholds indicate low-intent traffic: for example, stale contact lists or overly aggressive campaign pacing. Substantially higher abandonment rates are a strong signal of untargeted cold calling and can trigger an account review.

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Keep your metrics healthy

Voice agent campaigns commonly trip these thresholds through automation choices that are easy to fix:
  • Call opted-in, expecting recipients. Purchased or scraped lists produce low answer rates by definition.
  • Pace campaigns within your CPS limit. Configure your platform’s batch or campaign dialer conservatively; launching more call attempts than recipients can answer creates abandoned calls.
  • Do not hang up on every voicemail. An agent that detects an answering machine and immediately disconnects generates short-duration calls at scale. Leave a brief message or schedule a retry instead. On audio streaming and Voice API calls, use machine detection; on SIP trunking, use your orchestration platform’s voicemail detection.
  • Make the opening line count. Recipients who hang up within the first few seconds create short-duration calls. Have your agent identify itself and the reason for the call immediately.
  • Establish your caller identity. Use a Plivo number you own as caller ID for full STIR/SHAKEN attestation, and register your business name with Caller Reputation so recipients see who is calling.
  • Spread retries out. Redialing the same number many times in a short window increases abandonment and spam complaints. Keep contact lists current and remove numbers that repeatedly go unanswered.

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How CPS allocation works

CPS (calls per second) controls how fast you can initiate new outbound calls through your outbound SIP trunk. All accounts start with a default of 2 CPS. See Account Limits for how CPS relates to concurrent calls.
SIP trunking rejects call attempts above your CPS limit; it does not queue them.
  • Calls that exceed your rate fail with hangup code 5180 (cps_limit_reached).
  • Configure your orchestration platform’s campaign or batch dialer to pace outbound calls within your allocated CPS.

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Estimating your CPS needs

Most voice agent deployments need far less CPS than expected, because CPS governs how quickly new calls are placed, not how many calls can run at the same time: To size your requirement, divide your peak concurrent calls by your average call duration in seconds. For example, a fleet of agents holding 100 simultaneous conversations that average three minutes needs less than 1 CPS.

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Requesting a higher CPS limit

Every account starts at 2 CPS, which comfortably supports most use cases. If you need more, ask Buddy, Plivo’s in-console chat agent, in the Plivo console to move to an Enterprise plan, and our team will follow up to tailor an allocation to your volume.