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Overview

To simulate inbound calls, add your agent’s phone number or SIP address in an evaluation template. Requirements: Add your agent’s phone number or SIP address in a Coval Template.

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How It Works

When you launch an evaluation with an inbound voice agent:
  1. Coval’s simulated user calls your agent’s phone number
  2. The conversation follows the test set scenarios you’ve defined
  3. The simulated user behaves according to the persona you’ve configured
  4. Metrics are automatically evaluated after the call completes

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Identifying Simulation Calls

Coval includes a custom SIP header in the outgoing call: 
X-Coval-Simulation-Id: <simulation-id>
This header lets you correlate incoming calls with their corresponding simulation runs in Coval.
This header is carried inside the SIP signaling layer. Whether your agent can read it depends on how the call is routed — see below.

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When the Header Is Available

SIP trunking — If your agent receives calls via a SIP trunk (e.g., Twilio SIP Trunking, Telnyx SIP Trunking, or your own SBC), the custom header is preserved end-to-end and your telephony provider will surface it in the inbound call event. Regular phone numbers (PSTN) — If your agent receives calls on a standard phone number, the call routes through the public telephone network. PSTN carriers strip non-standard SIP headers, so X-Coval-Simulation-Id will not be available to your application. You can still identify simulation calls by the calling phone number or by matching timestamps in the Coval dashboard.

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Retrieving the Header (SIP Trunking)

How you access custom SIP headers depends on your telephony provider. Twilio Twilio exposes custom SIP headers as parameters prefixed with SipHeader_ on incoming call webhooks. The simulation ID will be available as SipHeader_X-Coval-Simulation-Id in the request parameters sent to your webhook. See Twilio’s SIP documentation for more details. Telnyx Telnyx includes custom SIP headers in the sip_headers array on the call.initiated webhook event. Look for the header with the name X-Coval-Simulation-Id in that array. See Telnyx’s SIP documentation for more details.

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Firewall & IP Allowlist

When Coval places a simulation call to your agent, the call arrives from specific IP addresses. If your telephony infrastructure has firewall rules, access control lists (ACLs), or security groups that restrict which IPs can send SIP traffic, you must allowlist the IPs below — otherwise simulation calls will be silently dropped before they reach your agent.
This only applies if you receive calls on your own SIP infrastructure (SBC, IP-PBX, or SIP trunk endpoint) and restrict inbound traffic by IP address. If your agent receives calls on a regular phone number through a cloud provider like Twilio or Telnyx, calls arrive through your provider’s normal flow and no allowlisting is needed.
Two types of traffic need to be allowed:

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Signaling IPs (SIP)

SIP signaling is how calls are initiated (the SIP INVITE that starts the call, plus responses). Allow these IPs on ports UDP/TCP 5060 and TLS 5061.
RegionPrimarySecondary
US192.76.120.1064.16.250.10
Europe185.246.41.140185.246.41.141
Australia103.115.244.145103.115.244.146
Canada192.76.120.3164.16.250.13
Asia (Beta)103.115.244.158103.115.244.159

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Media IP Subnets (RTP)

RTP carries the actual audio once the call is connected. Allow these subnets on UDP ports 16384–32768. 
36.255.198.128/25
50.114.136.128/25
50.114.144.0/21
64.16.226.0/24
64.16.227.0/24
64.16.228.0/24
64.16.229.0/24
64.16.230.0/24
64.16.248.0/24
64.16.249.0/24
103.115.244.128/25
185.246.41.128/25
If simulation calls are failing with no audio or immediate hangups, a missing IP allowlist entry is a common cause. Verify that both the signaling IPs and media subnets are allowed in your firewall.

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Setup Steps

  1. Navigate to your Template configuration
  2. Add your agent’s phone number or SIP address in the agent connection settings
  3. Configure your test sets with scenarios you want to test
  4. Select the personas for your simulated callers
  5. Choose the metrics you want to evaluate
  6. Launch your evaluation

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Best Practices

  • Use realistic phone numbers that your agent can receive calls on
  • Test with different personas to cover various customer types
  • Include both happy path and edge case scenarios in your test sets
  • Monitor latency and interruption metrics for voice quality