Implementing Synthetic Monitoring Probes for Proactive SIP Trunk Availability Detection

What This Guide Covers

You are building an automated synthetic monitoring system that continuously tests the availability and quality of your Genesys Cloud SIP trunks (BYOC Cloud or BYOC Premise) by placing real, automated test calls through them every few minutes. When complete, your system will detect SIP trunk failures, one-way audio issues, and codec negotiation failures within 3-5 minutes of onset-before any customer or agent is impacted-and will automatically alert your Network Operations Center with actionable diagnostics.

Prerequisites, Roles & Licensing

• Genesys Cloud: BYOC Cloud or BYOC Premise with SIP trunk access.
• Permissions required:
  • Telephony > Trunk > View (to query trunk status via API)
• Infrastructure:
  • A SIP softphone or automated calling library (e.g., Python pjsua2, Asterisk with AGI scripts, or a cloud calling API like Vonage/Twilio for synthetic calls).
  • A health check receiver number: a dedicated DID that your IVR flow answers with a synthetic response.
  • CloudWatch or Prometheus for storing health check results and triggering alarms.

The Implementation Deep-Dive

1. The Three Types of SIP Trunk Failure

Synthetic monitoring must detect three distinct failure modes that standard monitoring (carrier dashboard, Genesys admin alerts) misses:

1. Complete Trunk Failure: The SIP TCP/TLS connection drops. No calls can originate or terminate. Typically caught by carrier NOC alerts in 5-15 minutes.
2. One-Way Audio (Media Failure): SIP INVITE succeeds, the call connects, but audio flows only in one direction (or not at all). The call appears “connected” in all dashboards but is completely unusable. This is the hardest failure to detect without synthetic calls.
3. Intermittent Quality Degradation: The trunk works but has elevated packet loss or jitter on 20% of calls. Random sampling won’t catch this; sustained synthetic probing does.

2. The Synthetic Call Architecture

[Scheduler: Lambda on EventBridge (every 3 min)]
          |
          v
[SIP Probe Lambda]
    |
    |-- Initiates a SIP INVITE to Test DID (+15550001234)
    |-- Plays a test tone (440 Hz for 5 seconds)
    |-- Listens for the echo response from the IVR
    |
    v
[Genesys Cloud IVR - Test Flow]
    |-- Answers the call
    |-- Plays an DTMF confirmation tone (996 Hz)
    |-- Disconnects
    |
    v
[SIP Probe Lambda captures results]
    |-- Response latency (time to answer)
    |-- Audio quality score (PESQ or basic RMS comparison)
    |-- DTMF detected (Y/N)
    |-- Publishes metrics to CloudWatch

3. The IVR Health Check Flow (Architect)

Create a dedicated, minimal Architect IVR flow for the synthetic monitoring test DID:

[Inbound Call - Test DID]
   |
   v
[Detect DNIS = +15550001234] → [Health Check Flow]
   |
   v
[Play TTS or Audio File: "Health check confirmed. Code 200."]
   |
   v
[DTMF Send: "200"] ← (Your probe detects this to confirm end-to-end audio)
   |
   v
[Disconnect]

Important: Ensure this flow is never publicly listed and the DID is not in any outbound caller ID list. It is purely for internal synthetic monitoring.

4. The Python SIP Probe (Using PJSUA2)

import pjsua2 as pj
import time
import boto3
from datetime import datetime

CW = boto3.client('cloudwatch', region_name='us-east-1')

class SipProbe:
    """Minimal SIP UA for synthetic health check calls."""
    
    def __init__(self, sip_server: str, username: str, password: str):
        self.ep = pj.Endpoint()
        self.ep.libCreate()
        
        ep_cfg = pj.EpConfig()
        ep_cfg.logConfig.level = 1
        self.ep.libInit(ep_cfg)
        
        # UDP transport
        sip_tp_cfg = pj.TransportConfig()
        sip_tp_cfg.port = 5060
        self.ep.transportCreate(pj.PJSIP_TRANSPORT_UDP, sip_tp_cfg)
        
        self.ep.libStart()
        
        # Register account
        acc_cfg = pj.AccountConfig()
        acc_cfg.idUri = f"sip:{username}@{sip_server}"
        acc_cfg.regConfig.registrarUri = f"sip:{sip_server}"
        acc_cfg.sipConfig.authCreds.append(pj.AuthCredInfo("digest", "*", username, 0, password))
        
        self.acc = pj.Account()
        self.acc.create(acc_cfg)
        
    def probe_trunk(self, test_did: str, max_wait_seconds: int = 20) -> dict:
        """Places a synthetic test call and measures key health metrics."""
        
        call_start = datetime.utcnow()
        
        call_prm = pj.CallOpParam()
        call_prm.opt.audioCount = 1
        
        call = pj.Call(self.acc)
        
        try:
            call.makeCall(f"sip:{test_did}@your-genesys-sip-endpoint.com", call_prm)
            
            # Wait for answer (or timeout)
            timeout = time.time() + max_wait_seconds
            connected = False
            dtmf_detected = False
            
            while time.time() < timeout:
                call_info = call.getInfo()
                
                if call_info.state == pj.PJSIP_INV_STATE_CONFIRMED:
                    connected = True
                    answer_latency_ms = int((datetime.utcnow() - call_start).total_seconds() * 1000)
                    
                    # Listen for DTMF "200" confirmation for 5 seconds
                    time.sleep(5)
                    # (In a real implementation, register a DTMF callback)
                    dtmf_detected = True  # Simplified
                    
                    call.hangup(pj.CallOpParam())
                    break
                
                elif call_info.state in (pj.PJSIP_INV_STATE_DISCONNECTED,):
                    break
                
                time.sleep(0.2)
            
            result = {
                "timestamp": call_start.isoformat(),
                "connected": connected,
                "dtmf_confirmed": dtmf_detected,
                "answer_latency_ms": answer_latency_ms if connected else None,
                "health": "OK" if (connected and dtmf_detected) else "DEGRADED" if connected else "DOWN"
            }
            
        except Exception as e:
            result = {
                "timestamp": call_start.isoformat(),
                "connected": False,
                "error": str(e),
                "health": "DOWN"
            }
        
        self.publish_metrics(result)
        return result
    
    def publish_metrics(self, result: dict):
        """Publishes health check results to CloudWatch."""
        metrics = [
            {"MetricName": "SipTrunkAvailability", "Value": 1 if result["health"] == "OK" else 0, "Unit": "Count"},
            {"MetricName": "SipTrunkDtmfConfirmed", "Value": 1 if result.get("dtmf_confirmed") else 0, "Unit": "Count"},
        ]
        
        if result.get("answer_latency_ms"):
            metrics.append({"MetricName": "SipTrunkAnswerLatencyMs", "Value": result["answer_latency_ms"], "Unit": "Milliseconds"})
        
        CW.put_metric_data(Namespace="GenesysSipMonitoring", MetricData=[
            {**m, "Timestamp": result["timestamp"], "Dimensions": [{"Name": "TrunkId", "Value": "primary"}]}
            for m in metrics
        ])

5. Alerting on Trunk Failure

Configure CloudWatch Alarms:

• SipTrunkAvailability < 1 for 2 consecutive data points → CRITICAL alert (PagerDuty)
• SipTrunkAnswerLatencyMs > 5000 for 3 consecutive data points → WARNING alert (Slack)
• SipTrunkDtmfConfirmed < 1 for 2 consecutive data points → CRITICAL alert (indicates one-way audio or IVR failure)

Validation, Edge Cases & Troubleshooting

Edge Case 1: Probe Calls Appearing in Contact Center Reports

The synthetic probe calls will appear in your Genesys Cloud Analytics reports as real inbound interactions, inflating your “Calls Offered” and “Avg Handle Time” metrics.
Solution: Configure a tag on the test DID’s Architect flow to set a Participant Data attribute interaction_type = "SYNTHETIC_PROBE". Add an exclusion filter to all production analytics queries and dashboards for this attribute.

Edge Case 2: Probe Rate Triggering Carrier Rate Limits

Calling your test DID every 3 minutes = 480 calls per day. Some carriers flag this as anomalous calling behavior and may throttle or block the originating number.
Solution: Use a rotating pool of 5-10 synthetic probe originating ANIs, and vary the probe interval between 2-5 minutes using jitter. Inform your carrier’s technical account manager about the monitoring pattern to whitelist the ANIs.

Edge Case 3: False Positives During Planned Maintenance

If Genesys Cloud or your SBC is under planned maintenance, the synthetic probe will fire alerts even though the outage was expected.
Solution: Implement a maintenance mode flag in SSM Parameter Store or DynamoDB. Your probe Lambda checks the flag before placing a call and suppresses CloudWatch metric publication (and thus alarms) during the maintenance window.

Official References

• Genesys Cloud BYOC Cloud Trunk Configuration
• AWS CloudWatch Alarms
• PJSUA2 Python Library Documentation