Configuring SIP INVITE Header Manipulation for ANI Override in CXone Trunk Routing Policies

How-To-Articles
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Configuring SIP INVITE Header Manipulation for ANI Override in CXone Trunk Routing Policies

What This Guide Covers

This guide details the exact configuration of SIP INVITE header transformations within NICE CXone trunk routing policies to override Automatic Number Identification (ANI) values before PSTN egress or internal ACD distribution. The end result is a production-grade routing policy that reliably substitutes ANI headers, enforces E.164 normalization, maintains STIR/SHAKEN cryptographic integrity, and prevents carrier rejection or internal routing failures.

Prerequisites, Roles & Licensing

  • Licensing Tier: CXone Professional or Enterprise. Advanced routing transformations and STIR/SHAKEN attestation management are gated behind these tiers. CXone Standard lacks the transformation engine required for header manipulation.
  • Role Permissions:
    • routingPolicy:edit (Routing > Policy > Edit)
    • telephony:trunk:edit (Telephony > Trunk > Edit)
    • studio:edit (Studio > Flow > Edit) if Studio nodes are used for fallback logic
    • telephony:sipHeader:view for diagnostic trace access
  • OAuth Scopes: routing:edit, telephony:edit, studio:edit, telephony:trace:read
  • External Dependencies:
    • Provisioned SIP trunk with outbound routing enabled
    • STIR/SHAKEN signing certificate or carrier attestation agreement
    • E.164 normalization rules configured in Telephony > Number Formatting
    • CRM or middleware endpoint capable of receiving the overridden ANI value (if routing downstream)

The Implementation Deep-Dive

1. Define the Routing Policy Transformation Logic

CXone evaluates routing policies sequentially before passing the call to Studio or the PSTN gateway. Header manipulation must occur at the policy layer to ensure the SIP INVITE carries the correct ANI before any downstream carrier validation or internal ACD routing occurs. The transformation engine intercepts the INVITE, applies the override, and reconstructs the SIP message before egress.

Use the CXone Routing Policy API to inject header transformations. The transformation array accepts header type operations with explicit operation and value fields.

API Endpoint: PUT /api/v2/routing/policies/{routingPolicyId}

JSON Payload:

{
  "name": "ANI Override - Enterprise Outbound Trunk",
  "description": "Overrides P-Asserted-Identity and From headers for compliant ANI substitution",
  "enabled": true,
  "type": "outbound",
  "priority": 1,
  "conditions": [
    {
      "attribute": "trunkId",
      "operator": "equals",
      "value": "trk_8f3a9c2e-4b11-4d0a-9e7f-22c8d1b5a001"
    }
  ],
  "transformations": [
    {
      "type": "header",
      "headerName": "P-Asserted-Identity",
      "operation": "set",
      "value": "+15551234567"
    },
    {
      "type": "header",
      "headerName": "From",
      "operation": "set",
      "value": "<sip:+15551234567@pstn.nice-incontact.com>;tag=cxone_ani_override"
    },
    {
      "type": "header",
      "headerName": "Request-URI",
      "operation": "preserve",
      "value": null
    }
  ],
  "actions": [
    {
      "type": "route",
      "destination": "trunk_8f3a9c2e-4b11-4d0a-9e7f-22c8d1b5a001"
    }
  ]
}

The Trap: Modifying the From header without synchronously updating P-Asserted-Identity breaks SIP identity verification chains. Carriers that enforce strict RFC 3325 compliance will reject the INVITE with a 403 Forbidden or 603 Decline because the asserted identity no longer matches the cryptographic signature or the originating carrier credentials. Additionally, setting Request-URI to a static value breaks CXone’s internal call control, which relies on the original Request-URI for callback routing and ACD queue assignment.

Architectural Reasoning: CXone’s routing engine processes transformations before the SIP stack serializes the INVITE. By applying the override at the policy layer, you avoid Studio execution latency and prevent header conflicts that occur when Studio nodes attempt to modify headers that have already been normalized by the telephony gateway. The preserve operation on Request-URI ensures CXone retains the original destination for billing and routing analytics while allowing the identity headers to reflect the override. This separation of identity and destination is mandatory for compliant PSTN handoff.

2. Configure SIP Header Normalization and E.164 Enforcement

Carriers reject non-E.164 formatted ANI values without exception. CXone normalizes inbound and outbound numbers by default, but an override bypasses the normalization pipeline unless explicitly validated. The transformation engine does not automatically strip formatting characters, add country codes, or validate length. You must enforce E.164 compliance before the override takes effect.

Implement a validation rule within the routing policy conditions or use a Studio pre-rout node to sanitize the value. For pure policy-level enforcement, inject a conditional check that verifies the value matches the ^\+[1-9]\d{9,14}$ regex pattern before applying the transformation.

API Endpoint: PUT /api/v2/routing/policies/{routingPolicyId} (conditional enhancement)

JSON Payload (Condition Block):

{
  "conditions": [
    {
      "attribute": "trunkId",
      "operator": "equals",
      "value": "trk_8f3a9c2e-4b11-4d0a-9e7f-22c8d1b5a001"
    },
    {
      "attribute": "overrideAni",
      "operator": "matchesRegex",
      "value": "^\\+[1-9]\\d{9,14}$"
    }
  ]
}

The Trap: Injecting formatted numbers with parentheses, dashes, or leading zeros into the override value. The PSTN gateway will either strip the formatting unpredictably or reject the call entirely. More critically, CXone’s internal ACD routing uses the normalized ANI for skills-based routing, WFM forecasting, and callback logic. A malformed ANI breaks queue assignment, causing calls to fall through to the overflow queue or drop entirely.

Architectural Reasoning: E.164 normalization is not optional for PSTN interconnect. The ITU-T E.164 standard dictates that subscriber numbers must not exceed 15 digits and must begin with a country code. CXone’s telephony stack expects this format for routing table lookups and STIR/SHAKEN signing. By enforcing the regex condition at the policy level, you prevent malformed values from reaching the SIP stack. This approach also ensures that downstream systems (CRM, WFM, Speech Analytics) receive a consistent identifier for record linkage. The conditional check acts as a circuit breaker, failing fast before header manipulation occurs.

3. Integrate STIR/SHAKEN Attestation Headers

The FCC mandates STIR/SHAKEN attestation for voice calls in the United States. When you override ANI, you must also update the attestation headers to reflect the new identity. CXone signs the INVITE using a private key tied to the registered ANI. Changing the ANI without updating the attestation causes a signature mismatch, resulting in an A (Attestation) or B (Bypass) attestation level, which carriers may flag as spam or reject.

Inject the Identity and X-GoIP-Attestation headers alongside the ANI override. The Identity header contains the cryptographic signature, while X-GoIP-Attestation indicates the attestation level (A, B, or C).

JSON Payload (Transformation Extension):

{
  "transformations": [
    {
      "type": "header",
      "headerName": "P-Asserted-Identity",
      "operation": "set",
      "value": "+15551234567"
    },
    {
      "type": "header",
      "headerName": "From",
      "operation": "set",
      "value": "<sip:+15551234567@pstn.nice-incontact.com>;tag=cxone_ani_override"
    },
    {
      "type": "header",
      "headerName": "Identity",
      "operation": "set",
      "value": "info=\"stir-shaken-v1\";alg=\"rsa-sha256\";u=\"https://attestation.nice-incontact.com/verify\";sig=\"base64encodedsignatureplaceholder\";req=\"A\""
    },
    {
      "type": "header",
      "headerName": "X-GoIP-Attestation",
      "operation": "set",
      "value": "A"
    }
  ]
}

The Trap: Hardcoding a static signature or attestation level without verifying the signing certificate covers the new ANI. Carriers validate the signature against the registered P-Asserted-Identity. A mismatch triggers a downgrade to B or C attestation, which many downstream carriers treat as unverified. This directly impacts call delivery rates and triggers spam labeling on consumer devices.

Architectural Reasoning: STIR/SHAKEN relies on cryptographic binding between the originating identity and the signature. CXone’s attestation service generates the signature at the time of INVITE construction. When you override the ANI, the platform must re-sign the message with the new identity. If your use case requires dynamic ANI substitution (CRM-driven), you must integrate with CXone’s Attestation API to request a fresh signature for the substituted number. Static overrides require pre-provisioned certificates that cover the substituted range. The req="A" parameter signals full attestation, but only applies if the certificate authority recognizes the new ANI. Failing to align the signature with the override breaks the trust chain and violates FCC 47 CFR 64.2501 requirements.

4. Deploy and Bind to Trunk Routing Policy

The routing policy must be attached to the correct trunk configuration and assigned a priority that prevents policy conflicts. CXone evaluates policies in ascending priority order. Lower numbers execute first. If multiple policies match the same trunk and call attributes, the first match wins, and subsequent policies are skipped.

Use the CXone Telephony API to bind the routing policy to the trunk and verify the policy order.

API Endpoint: PUT /api/v2/telephony/trunks/{trunkId}

JSON Payload (Trunk Binding):

{
  "name": "Enterprise Outbound SIP Trunk",
  "type": "sip",
  "enabled": true,
  "outboundRouting": {
    "policyId": "pol_9d2e7a1f-3c44-4b8a-8e6f-11d7c0a9b002",
    "policyOrder": [
      {
        "policyId": "pol_9d2e7a1f-3c44-4b8a-8e6f-11d7c0a9b002",
        "priority": 1
      }
    ]
  },
  "sipSettings": {
    "headerManipulationEnabled": true,
    "normalizeAni": true
  }
}

The Trap: Assigning a lower priority number to a legacy policy that lacks header transformations. The legacy policy matches first, bypasses the ANI override, and sends the original ANI to the carrier. This creates intermittent failures that are difficult to trace because the override policy exists but never executes. Additionally, enabling headerManipulationEnabled without binding the policy to the trunk results in silent drops, as CXone will not apply transformations to unbound policies.

Architectural Reasoning: CXone’s routing engine uses a first-match-wins evaluation model. Policy ordering determines execution sequence. By explicitly defining policyOrder and assigning priority 1 to the ANI override policy, you guarantee it executes before fallback or legacy routing rules. The headerManipulationEnabled flag on the trunk configuration activates the transformation pipeline. Without this flag, CXone ignores all transformations arrays and passes the INVITE unmodified. This design prevents accidental header corruption but requires explicit enablement. Binding the policy to the trunk ensures the transformation engine intercepts the call at the correct hop in the routing chain.

Validation, Edge Cases & Troubleshooting

Edge Case 1: Carrier Rejection on 603 Decline Due to Header Mismatch

  • The failure condition: Outbound calls fail immediately with a 603 Decline response. The SIP trace shows the carrier rejecting the INVITE.
  • The root cause: The P-Asserted-Identity header does not match the Identity signature, or the From header URI domain does not align with the registered carrier credentials. CXone’s attestation service may have signed the original ANI instead of the overridden value.
  • The solution: Verify the attestation certificate covers the substituted ANI range. Use the CXone Attestation API to request a fresh signature for the override value. Ensure the From header URI matches the PSTN gateway domain registered with the carrier. Re-sign the INVITE by toggling the policy enabled state to force a cache refresh. Validate the SIP trace using GET /api/v2/telephony/trace/{callId} to confirm header alignment.

Edge Case 2: Internal ACD Routing Failure After ANI Override

  • The failure condition: Calls reach the contact center but route to the overflow queue instead of the intended skills-based queue. WFM and Speech Analytics show missing ANI data.
  • The root cause: The override replaced the X-CXone-ANI or X-CXone-Original-ANI headers, which CXone uses for internal routing and analytics. The platform relies on these custom headers for queue assignment and record linkage.
  • The solution: Add preservation rules for internal tracking headers in the transformation array. Include X-CXone-Original-ANI with an operation: "preserve" to maintain analytics continuity. Update the Studio routing logic to reference X-CXone-ANI instead of P-Asserted-Identity for queue assignment. Verify the ACD routing profile uses the correct header attribute for skills matching.

Edge Case 3: STIR/SHAKEN Attestation Downgrade to Partial (B)

  • The failure condition: Calls deliver successfully, but consumer devices display “Potential Spam” or “Unknown Caller”. The SIP trace shows X-GoIP-Attestation: B.
  • The root cause: The substituted ANI lacks a registered attestation certificate, or the certificate authority does not recognize the number as owned by your organization. The platform downgrades to B attestation to prevent call blocking.
  • The solution: Register the substituted ANI range with your certificate authority and update the CXone attestation profile. Use the POST /api/v2/telephony/attestation/certificates endpoint to upload the new certificate. Configure the routing policy to validate attestation eligibility before applying the override. If full attestation is unavailable, document the B attestation level with downstream carriers to prevent filtering.

Official References