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Retell AI

Import a Vonyx number into Retell AI over SIP trunking for outbound and inbound agent calls.

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Import your Vonyx number into Retell with Retell's custom telephony (elastic SIP trunking). Retell dials out through your Vonyx trunk, and Vonyx forwards inbound calls to Retell's SIP server.

Before you start

  • A Vonyx SIP trunk with a number attached
  • The trunk's username and password, from the Vonyx console
  • A Retell account, an API key and an agent (note its agent ID)

Retell requires numbers in E.164 format, so in Retell write your Vonyx number and the numbers you call as +91XXXXXXXXXX.

Outbound calls

Import your Vonyx number

In Retell, open Phone Numbers, click + and choose Connect to your number via SIP trunking. Fill in:

FieldValue
Phone number+91XXXXXXXXXX (your Vonyx number)
Termination URI43.204.9.41:5060
Outbound TransportTCP (UDP also works; Vonyx doesn't support TLS)
SIP Trunk User Nameyour_trunk_username
SIP Trunk Passwordyour_trunk_password

Click Save.

Bind an outbound agent

In Retell, open the number and set Outbound Agent. If you used the API call above, outbound_agents already did this.

Place a call

create-call.sh
curl -X POST https://api.retellai.com/v2/create-phone-call \
  -H "Authorization: Bearer $RETELL_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "from_number": "+91XXXXXXXXXX",
    "to_number": "+91XXXXXXXXXX"
  }'

from_number is your imported Vonyx number, and it is also the caller ID, which must be one of your Vonyx numbers. To use a different agent for one call, add override_agent_id.

Inbound calls

Bind an inbound agent

In Retell, open the number and set Inbound Agent (or set inbound_agents on import). Retell won't take inbound calls on a number with no inbound agent. To choose the agent per call, set an inbound_webhook_url on the number instead.

Point Vonyx at Retell

In the Vonyx console, open the trunk, turn on Inbound calls and set the inbound address to:

sip.retellai.com

Retell has one SIP server for every account. Vonyx forwards calls to it over UDP.

Test inbound before going live

Vonyx forwards the called number as 91XXXXXXXXXX, without +, while Retell stores your number as +91XXXXXXXXXX. Call your number once after setup to confirm Retell matches it to your agent.

Test the connection

  1. In Retell, open the number's … menu, choose Edit Phone Number Settings and click Test SIP Connection. Retell sends a SIP OPTIONS request to the termination URI. A 2xx means Retell reached Vonyx. It doesn't check routing or audio.
  2. Place an outbound call with create-phone-call to your own phone.
  3. Call your Vonyx number from another phone. The inbound agent answers.

Limitations

  • DTMF and call transfer are not available on Vonyx yet, so Retell's transfer and DTMF features won't work on these calls.
  • New accounts make 1 call at a time (raise limits). Keep Retell's concurrency and CPS settings at or below your Vonyx limits.
  • No TLS or SRTP: use TCP or UDP in Retell.
  • Audio is PCMU or PCMA. Retell's G.722 (HD) isn't available on Vonyx.

Troubleshooting

ProblemFix
Test SIP Connection returns 401 or 407Re-enter the Vonyx trunk username and password.
Test SIP Connection gets no responseCheck that the termination URI is 43.204.9.41:5060 and the transport is TCP or UDP, not TLS.
Outbound call is rejectedMake sure from_number is a Vonyx number attached to the trunk and both numbers are +91XXXXXXXXXX.
Inbound calls don't reach the agentCheck that Inbound calls is on, the inbound address is sip.retellai.com, and the number has an inbound agent in Retell.
Call connects with no audioMedia flows directly between Vonyx (RTP on UDP 10000–20000) and Retell (RTP on UDP 10000–65535). If anything between them filters traffic, allow Retell's ranges: 18.98.16.120/30 (signaling), 3.42.144.0/23 and 153.57.128.0/18 (all regions), and 143.223.88.0/21 and 161.115.160.0/19 (some US traffic). Then contact Vonyx support.

More fixes: SIP troubleshooting.

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