\n \n

\n\n\n\n\n",[133],"4820f447-5950-42db-92c2-0aa4f976aff0","index.html","006a8192-84a5-11f1-9543-1607ee4eb77e",["D",1784670391353],5,"\n\n\n\n\nVapi Platform Knowledge Base\n\n\n\n

\n \n

\n\n

\n \n

\n\n\n\n\n\n",[139],"84d23682-4313-4237-948e-82b7e5dbec0a","flow-outbound.html","747ecd56-854d-11f1-a638-1607ee4eb77e",["D",1784670313854],"\n\n\n\n\nPOST /call — Outbound Call E2E Flow\n\n\n\n\n\nCALLS · FLOWCHART\n

POST /call — Outbound Call E2E Flow

Full lifecycle of an outbound phone call: HTTP entry → initialization → transport routing (two paths) → carrier dial → callWorker pipeline → call end. Latency-bearing steps are flagged.

\n\n\n

01HTTP Entryapps/api

\n call.controller.ts:91 — CallController.create()\n

\n • Auth + CASL scope check (ACTION_AUTH.CREATE, SUBJECT_AUTH.CALL)\n • If dto.type === 'outboundPhoneCall' → fires async Dodgeball fraud tracking event\n • If dto.transport.provider === 'websocket' → diverges to callService.websocketCallCreate()\n • Otherwise → callService.createPhoneCall()\n

↓

\n call.service.ts:201 — createPhoneCall()\n

\n • dto.customers (batch) → callBatch() → different path (fan-out)\n • dto.schedulePlan → callSchedule() (writes scheduled row, no immediate dial)\n • Otherwise → callOutbound() ← the normal path\n

\n\n

callOutbound()↓

\n\n\n

02Call InitializationphoneCallFunctions.ts:276

\n 1\n

Pre-load org + feature flags db read

callOrgGet() / featureFlagGet(). Validates billing (concurrency limits, subscription). Returns 400 here if over limit — no DB write yet.

\n 2\n

Resolve assistant version db read

assistantVersionForCallDispatch(). Handles assistantId, inline assistant, squadId/squad, workflowId/workflow, or pinned assistantVersionId. Error → 400 before any call row is written.

\n 3\n

Write call row to DB db write

callInitialize(). Inserts call with status: 'queued'. From this point a call record exists.

\n 4\n

Fetch resources multiple db reads

callResourcesGet(): full assistant (tools, credentials), phone number, customer record, all credentials. Missing → callEndOnError() + error.

\n 5\n

Guard checks each failure marks call ended

\n • Free Vapi number → international → call.start.error-vapi-number-international\n • Dodgeball fraud check (ENABLE_OUTBOUND_CALL_FRAUD_CHECK + Vapi number)\n • Daily outbound limit (resets if outboundCallsCounterNextResetAt passed)\n

\n\n

↓

\n\n\n

03Transport Routingtwo paths

Branch

ENABLE_OUTBOUND_CALL_QUEUING feature flag?

Path A · Queuing ON

\n pendingOutboundCallEnqueue() pushes the call into a Redis/Valkey pending queue. API returns immediately with the queued call. A separate callScheduler worker dequeues and calls callOutboundTransportAndQueue() when capacity is available.

Backpressure valve — prevents thundering-herd on carrier APIs.\n

Path B · Direct (flag off)

\n callOutboundTransportAndQueue() is called inline from the API request, adding its latency directly to the HTTP response. Also taken when phoneCallProviderBypassEnabled.

This is why POST /call sometimes takes >5s — the carrier API is hit synchronously.\n

\n\n

both converge on callOutboundTransportAndQueue()↓

\n\n\n

04Transport + QueuephoneCallFunctions.ts:132

\n callTransportGet() — carrier dial latency 1–5s+\n

Contacts Twilio / Telnyx / Vonage to actually dial the phone — creates the PSTN leg. TwiML/SIP URI streams audio back to Vapi's WebSocket server. Primary latency source on Path B.
• Error → callTransportErrorHandle() + Kafka callOutboundInitiatedEventEmit(status: 'failure')

↓

\n liveCallRequired()\n

Constructs the LiveCall object, stamping all resolved resources (org, assistant, phone number, customer, credentials, feature flags) onto the call.

↓

\n callStoreAndQueue()\n

Updates the call row (transport info, phone provider ID, increments concurrency counter) and enqueues a BullMQ job to the CALL queue for the callWorker.

↓

\n Kafka + API response\n

• Kafka callOutboundInitiatedEventEmit(status: 'success')• API returns the call object (status: queued) — the call.status === 'queued' webhook fires here.

\n\n

BullMQ CALL queue↓

\n\n\n

05callWorker — Live Pipelineapps/callWorker

\n streamBundleConstruct.ts → streamBundleConnectPipes.ts\n

BullMQ picks up the job and creates the LiveCallPipeline. The stream pipeline is constructed, then wired:

Carrier WebSocket audio in ↓

VadStreamvoice activity detection

DenoiserStreamoptional

BackgroundSpeechFilteroptional

CombinedAudioBufferrecording mix

SttStreamDeepgram / AssemblyAI / …

ConversationBuffermessage history

EndpointingBufferend-of-turn detection

LlmStreamOpenAI / Anthropic / …

TtsStreamElevenLabs / Cartesia / …

SampleRateConverter

TurnTakingBuffer

VolumeControlBufferbot speaking state, audio mixing

TransportStream→ carrier WebSocket audio out

↓

\n callStart()\n

All streams start corked (buffering). callStart() uncorks them, fires the assistant-request → assistant-response webhook sequence (server-URL-based configs), then fires status-update: in-progress.

\n\n

on end condition: silence / maxDuration / endCall / hangup↓

\n\n\n

06Call Endmanager.end()

manager.end()

Waits ~2.5s for final STT transcripts to drain.

Cost collection (bottom-up)

STT (per min per channel), LLM (per token), TTS (per character). BYOK credentials (org provides key) → marked user-fault, not billed to subscription.

streamBundleArtifacts()

Uploads recording WAV + transcript JSON to S3.

callComplete()

Writes final DB state: endedAt, endedReason, costs, artifact URLs, analysis (structuredData + successEvaluation + summary from the analysis plan).

end-of-call-report webhook

Delivered to your server URL.

\n\n\n

Key latency sources on POST /call

\n \n \n \n \n \n \n \n \n \n \n

Source	When it hits
callOrgGet + featureFlagGet	always DB reads
assistantVersionForCallDispatch	always DB read
callInitialize	always DB write
callResourcesGet	always multiple DB reads (assistant + phone number + credentials)
Dodgeball fraud check	conditional Vapi numbers only, flag-gated
callTransportGet (carrier API)	path B only biggest variable, 1–5s+ (queuing flag off)

\n If queuing (ENABLE_OUTBOUND_CALL_QUEUING) is on for your org, the carrier dial is deferred and the API returns fast. On the standard path it's all synchronous — which explains the >5s responses seen in the earlier investigation.\n

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POST /call — Outbound Call E2E Flow

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