Telephony

SIP Integration with NICE Engage

SIP trunking is only available on the Synthflow Enterprise Plan.

This guide covers connecting NICE Engage (on-premise / hybrid contact center) to Synthflow via SIP trunk. NICE Engage routes calls to a Synthflow AI agent through its SIP infrastructure; Synthflow handles AI conversations and transfers callers back to NICE Engage agent queues.

Prerequisites

RequirementDetail
NICE EngageActive deployment with Admin access; SIP trunking and outbound SIP routing enabled
SynthflowEnterprise Plan with a configured AI assistant (v2.0+)
Phone NumberAt least one DID provisioned in NICE Engage (E.164 format)
NetworkFirewall allows SIP (UDP/TCP 32681 or TLS 32682) and RTP media between NICE Engage SBC and Synthflow

NICE Engage Configuration

Configuration is done via the NICE Engage Administrator application and the NICE Engage SBC (Session Border Controller).

Step 1: Configure the Outbound SIP Trunk to Synthflow

  1. Open the NICE Engage Administrator application.
  2. Navigate to Configuration → Telephony → SIP Trunks.
  3. Click Add SIP Trunk and configure:
FieldValue
NameSynthflow AI
Remote SIP Proxysip.synthflow.ai
Remote Port32681 (UDP/TCP) or 32682 (TLS)
TransportUDP/TCP or TLS
Authentication TypeIP-based (whitelist Synthflow IPs) or Digest
UsernameFrom Synthflow — only required if using Digest auth
PasswordFrom Synthflow — only required if using Digest auth
Max Concurrent CallsPer your Synthflow plan / expected volume
  1. Add Synthflow’s SIP signaling IPs to the SBC access control list. Contact Synthflow support for the current IP list.
  2. Save the trunk configuration.

NICE Engage deployments typically use a Session Border Controller (SBC) for external SIP connectivity. Ensure SIP INVITE and RTP traffic is allowed through the SBC to Synthflow.

Step 2: Configure a Routing Strategy

To route inbound calls to Synthflow:

  1. In NICE Engage Administrator, go to Routing → Routing Strategies.
  2. Create a new strategy or edit an existing one for your inbound DID.
  3. Add a Transfer to SIP step:
    • SIP Destination: The DID associated with your Synthflow SIP number (E.164 format)
    • Trunk: Synthflow AI
  4. Configure timeout and fallback routing to a NICE Engage skill queue.
  5. Save and activate the strategy.

Step 3: Configure Inbound SIP Trunk (Synthflow → NICE Engage)

For Synthflow to route calls and transfers back to NICE Engage:

  1. In NICE Engage Administrator, navigate to Configuration → Telephony → SIP Access Control.
  2. Add Synthflow’s SIP signaling IP addresses to the allowed inbound list.
  3. Create an inbound SIP route mapping the Synthflow DID to the target NICE Engage skill queue.

Step 4: Enable SIP Headers for Context Passing

NICE Engage supports custom SIP X-headers for passing caller context:

  1. In the routing strategy, configure the SIP INVITE to include:
    • X-NICE-ContactId: {ContactId} (for linked reporting)
    • X-NICE-SkillName: {SkillName} (for target queue routing on transfer)
  2. On transfer back, Synthflow passes these headers to NICE Engage for proper queue routing.

Synthflow Configuration

Add the SIP Number

  1. Go to the Synthflow Phone Numbers page.
  2. Click Add Number → Custom / SIP.
  3. Enter the phone number in E.164 format (same DID configured in NICE Engage).
  4. Fill in the SIP connection details:
FieldValue
Termination URIYour NICE Engage SBC hostname or IP address
SIP UsernameYour SIP authentication username
SIP PasswordYour SIP authentication password
Outbound Proxy (if required)NICE Engage SBC proxy address (if required)

The Termination URI is your NICE Engage SBC address — this routes Synthflow outbound calls and transfers back into the NICE Engage platform.

Be precise when copying SIP credentials. Incorrect values will cause registration failure.

Attach to the Assistant

  1. Go to Assistants and create or select an assistant (v2.0+).
  2. In the assistant settings, attach the SIP number you just created.
  3. Wait 1–2 minutes for SIP registration to complete.

The SIP trunk is created at the moment of attaching the SIP number to the assistant.

Call Flow Summary

ScenarioFlow
Inbound to AICaller → PSTN → NICE Engage → Routing Strategy → SIP Transfer → Synthflow AI Agent
AI transfers to live agentSynthflow AI → SIP transfer (X-NICE-SkillName) → NICE Engage SBC → Skill Queue → Live Agent
Outbound from AISynthflow AI → SIP INVITE → NICE Engage SBC → PSTN → Callee
Outbound from NICE via AINICE Engage strategy → SIP Trunk → Synthflow AI → handles call

Verification

TestWhat to check
Inbound callCall the NICE Engage DID from an external phone. Verify the routing strategy sends the call to Synthflow AI. Check two-way audio.
Transfer to live agentTrigger escalation during a Synthflow call. Confirm the call lands in the correct NICE Engage skill queue with caller ID intact.
SIP header passthroughVerify Synthflow receives X-NICE-ContactId and relevant headers from NICE Engage.

Quick Troubleshooting

IssueFix
Registration failsCheck Termination URI is the NICE Engage SBC address. Verify credentials and firewall (UDP/TCP 32681 or TLS 32682).
Calls blocked by SBCVerify Synthflow IPs are in the NICE Engage SBC access control list.
One-way or no audioEnsure RTP ports are open through the SBC bidirectionally. Confirm G.711 codec is negotiated.
Transfer goes to wrong queueVerify X-NICE-SkillName header value matches an active NICE Engage skill name exactly.
Caller ID missingVerify From header is set to caller E.164 format. Check NICE Engage SBC caller ID passthrough settings.

Reference

  • NICE Engage Administrator Guide: nice.com/resources (search “Engage Administrator”)
  • NICE Engage SBC Configuration: Contact NICE support for SBC setup documentation
  • Synthflow SIP Overview: docs.synthflow.ai/about-sip
  • Synthflow X-EI SIP Header: docs.synthflow.ai/x-ei-sip-header