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Plivo XML controls call behavior. Your answer_url returns XML instructions that Plivo executes. This page covers the essential elements for AI voice agents.

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Response

The root element for all Plivo XML. Every response must be wrapped in <Response>. 
<?xml version="1.0" encoding="UTF-8"?>
<Response>
    <!-- Elements go here -->
</Response>

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Stream

Stream real-time audio over WebSocket. See Audio Streaming XML for full details. 
<Response>
    <Stream bidirectional="true" keepCallAlive="true">
        wss://yourserver.com/websocket
    </Stream>
</Response>
AttributeDefaultDescription
bidirectionalfalseEnable two-way audio
keepCallAlivefalseWait for stream to end before continuing
audioTrackinboundinbound, outbound, or both

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Speak

Text-to-speech during calls. Useful for greetings or fallbacks. 
<Response>
    <Speak voice="WOMAN" language="en-US">
        Hello, connecting you to our AI assistant.
    </Speak>
    <Stream bidirectional="true" keepCallAlive="true">
        wss://ai.example.com/agent
    </Stream>
</Response>
AttributeDefaultDescription
voiceWOMANWOMAN or MAN
languageen-USLanguage code (e.g., en-GB, es-ES)
loop1Number of times to repeat

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Play

Play audio files (.mp3 or .wav). 
<Response>
    <Play>https://example.com/welcome.mp3</Play>
    <Stream bidirectional="true" keepCallAlive="true">
        wss://ai.example.com/agent
    </Stream>
</Response>
AttributeDefaultDescription
loop1Number of times to repeat

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Dial

Connect calls to another number, SIP endpoint, or user. 
<Response>
    <Dial callerId="+14151234567" timeout="30">
        <Number>+14157654321</Number>
    </Dial>
</Response>
AttributeDefaultDescription
callerId-Caller ID to display
timeout30Ring timeout in seconds
action-URL to call when dial completes
methodPOSTHTTP method for action URL

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Dial to SIP

<Response>
    <Dial>
        <Sip>sip:[email protected]</Sip>
    </Dial>
</Response>

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Hangup

End the call. 
<Response>
    <Speak>Thank you for calling. Goodbye.</Speak>
    <Hangup/>
</Response>
AttributeDescription
reasonOptional: rejected, busy
scheduleSeconds to wait before hanging up

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Redirect

Fetch and execute XML from a different URL. Useful for dynamic call flows. 
<Response>
    <Redirect method="POST">https://example.com/next-step</Redirect>
</Response>
AttributeDefaultDescription
methodPOSTGET or POST

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Wait

Pause execution for a specified duration. 
<Response>
    <Wait length="5"/>
    <Stream bidirectional="true" keepCallAlive="true">
        wss://ai.example.com/agent
    </Stream>
</Response>
AttributeDefaultDescription
length1Seconds to wait
silencefalseIf true, no hold music
beepfalsePlay beep after waiting

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GetDigits

Collect DTMF input from the caller. Useful for IVR before connecting to AI. 
<Response>
    <GetDigits action="https://example.com/handle-input" timeout="10" numDigits="1">
        <Speak>Press 1 for sales, 2 for support.</Speak>
    </GetDigits>
    <Speak>We didn't receive any input.</Speak>
</Response>
AttributeDefaultDescription
action-URL to send digits to
timeout5Seconds to wait for input
numDigits99Max digits to collect
finishOnKey#Key that ends input
retries1Number of retry attempts

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Record

Record call audio. Useful for compliance or training. 
<Response>
    <Speak>This call may be recorded.</Speak>
    <Record action="https://example.com/recording-done" maxLength="3600"/>
    <Stream bidirectional="true" keepCallAlive="true">
        wss://ai.example.com/agent
    </Stream>
</Response>
AttributeDefaultDescription
action-URL called when recording ends
maxLength60Max recording duration in seconds
fileFormatmp3mp3 or wav
transcriptionType-Set to auto for transcription

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Common Patterns

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AI Agent with Greeting

<Response>
    <Speak>Welcome to Acme Support. I'm connecting you with our AI assistant.</Speak>
    <Stream bidirectional="true" keepCallAlive="true" contentType="audio/x-l16;rate=16000">
        wss://ai.example.com/agent
    </Stream>
    <Speak>Thank you for calling. Goodbye.</Speak>
    <Hangup/>
</Response>

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IVR Before AI Agent

<Response>
    <GetDigits action="https://example.com/route" timeout="10" numDigits="1">
        <Speak>Press 1 for AI assistant, 2 to speak with a human.</Speak>
    </GetDigits>
    <Redirect>https://example.com/default</Redirect>
</Response>

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Transfer to Human

When your AI agent needs to transfer to a human: 
<Response>
    <Speak>Connecting you to a human agent now.</Speak>
    <Dial callerId="+14151234567" timeout="60" action="https://example.com/dial-status">
        <Number>+14157654321</Number>
    </Dial>
    <Speak>We couldn't connect you. Please try again later.</Speak>
    <Hangup/>
</Response>