Detecting Fax Tones in NICE CXone Voice API with Java

What You Will Build

• A Java service that submits fax detection payloads to a live CXone call session, validates tone thresholds against engine constraints, and triggers automatic T.38 mode switching upon verified fax identification.
• The implementation uses the NICE CXone Voice API POST /api/v1/voice/calls/{callId}/actions/detect endpoint and the official CXone Java SDK.
• The tutorial covers Java 17 with Spring Boot 3.x for callback handling, Jackson for payload serialization, and SLF4J for audit logging.

Prerequisites

• CXone OAuth client credentials with the voice:call:control scope
• CXone Java SDK v5.0+ (com.nice.ccx:cxone-java-sdk)
• Java 17 runtime with Maven or Gradle
• Spring Boot 3.2+ for callback endpoint exposure
• Dependencies: jackson-databind, slf4j-api, spring-boot-starter-web
• A deployed CXone environment with Voice API access enabled

Authentication Setup

The CXone platform uses OAuth 2.0 client credentials flow. You must cache the access token and refresh it before expiration to prevent 401 errors during detection windows.

import com.nice.ccx.cxone.core.auth.CxoneAuth;
import com.nice.ccx.cxone.core.auth.OAuth2ClientCredentialsGrant;
import com.nice.ccx.cxone.core.client.CxoneClient;
import com.nice.ccx.cxone.core.http.RestClient;

import java.time.Instant;
import java.util.concurrent.ConcurrentHashMap;

public class CxoneAuthManager {
    private static final String OAUTH_TOKEN_URL = "https://api.mynicecx.com/oauth/token";
    private final String clientId;
    private final String clientSecret;
    private final String region;
    private volatile String cachedToken;
    private volatile Instant tokenExpiry;

    public CxoneAuthManager(String clientId, String clientSecret, String region) {
        this.clientId = clientId;
        this.clientSecret = clientSecret;
        this.region = region;
    }

    public synchronized String getAccessToken() throws Exception {
        if (cachedToken != null && Instant.now().isBefore(tokenExpiry.minusSeconds(30))) {
            return cachedToken;
        }
        return refreshToken();
    }

    private String refreshToken() throws Exception {
        // CXone SDK handles the actual token exchange via RestClient
        var grant = new OAuth2ClientCredentialsGrant(clientId, clientSecret);
        var auth = new CxoneAuth(OAUTH_TOKEN_URL, grant);
        var tokenResponse = auth.getAccessToken();
        cachedToken = tokenResponse.getAccessToken();
        tokenExpiry = Instant.now().plusSeconds(tokenResponse.getExpiresIn());
        return cachedToken;
    }

    public CxoneClient buildClient() throws Exception {
        return new CxoneClient(region, new RestClient.Builder()
                .setBaseUri("https://api." + region + ".mynicecx.com")
                .setTokenSupplier(this::getAccessToken)
                .build());
    }
}

OAuth scope required: voice:call:control

Implementation

Step 1: Construct Detect Payload with Call Session References and Threshold Matrices

The Voice API detection engine requires explicit timeout limits and type directives. Fax detection relies on CNG (Calling Tone) and V.21 answer sequence recognition. You must define a maximum detection window to prevent the telephony engine from holding the media path indefinitely.

import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;

import java.util.Map;

public class FaxDetectPayload {
    private final String type;
    private final int timeout;
    private final Map<String, Object> options;
    private final String callbackUrl;

    public FaxDetectPayload(String callbackUrl, int maxDetectionWindowMs) {
        this.type = "fax";
        this.timeout = Math.min(maxDetectionWindowMs, 60000); // Engine hard limit: 60s
        this.callbackUrl = callbackUrl;
        this.options = Map.of(
            "cngThreshold", 0.75,        // CNG tone confidence threshold
            "v21SequenceRequired", true, // Enforce V.21 handshake detection
            "snrMinimum", 20,            // Signal-to-noise ratio floor in dB
            "frequencyRange", Map.of("low", 300, "high", 2400) // V.21 spectrum bounds
        );
    }

    public String toJson() throws Exception {
        var mapper = new ObjectMapper().enable(SerializationFeature.INDENT_OUTPUT);
        return mapper.writeValueAsString(this);
    }
}

Expected payload structure aligns with CXone telephony engine constraints. The timeout parameter caps the detection window. The options object passes threshold matrices directly to the media processor.

Step 2: Submit Detection Request with Validation and Retry Logic

The SDK method postCallsIdActionsDetect sends the payload to the active call session. You must handle 429 rate limits with exponential backoff and validate the request schema before transmission.

import com.nice.ccx.cxone.voice.api.VoiceApi;
import com.nice.ccx.cxone.voice.model.PostCallsIdActionsDetectRequest;
import com.nice.ccx.cxone.core.exception.ApiException;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.time.Duration;
import java.util.concurrent.TimeUnit;

public class FaxDetectorService {
    private static final Logger log = LoggerFactory.getLogger(FaxDetectorService.class);
    private final VoiceApi voiceApi;
    private final String callbackBaseUrl;

    public FaxDetectorService(VoiceApi voiceApi, String callbackBaseUrl) {
        this.voiceApi = voiceApi;
        this.callbackBaseUrl = callbackBaseUrl;
    }

    public void initiateFaxDetection(String callId, int detectionWindowMs) throws Exception {
        var payload = new FaxDetectPayload(callbackBaseUrl + "/fax/callback", detectionWindowMs);
        var requestBody = payload.toJson();

        // Schema validation against engine constraints
        if (detectionWindowMs > 60000) {
            throw new IllegalArgumentException("Detection window exceeds maximum 60000ms limit");
        }

        var startTime = System.nanoTime();
        var request = new PostCallsIdActionsDetectRequest(callId, requestBody);

        try {
            // SDK call: POST /api/v1/voice/calls/{callId}/actions/detect
            var response = voiceApi.postCallsIdActionsDetect(request);
            
            if (response.getStatusCode() == 200 || response.getStatusCode() == 202) {
                var latencyMs = Duration.ofNanos(System.nanoTime() - startTime).toMillis();
                log.info("Fax detection initiated for call {} | Latency: {}ms", callId, latencyMs);
                return;
            }
            throw new ApiException(response.getStatusCode(), "Detection submission failed", response.getResponseBody());
        } catch (ApiException e) {
            handleApiError(e, callId);
        }
    }

    private void handleApiError(ApiException e, String callId) throws Exception {
        if (e.getCode() == 429) {
            var retryAfter = parseRetryAfter(e.getResponseHeaders());
            log.warn("Rate limited on detection for call {}. Retrying after {}s", callId, retryAfter);
            TimeUnit.SECONDS.sleep(retryAfter);
            throw e; // Caller decides if retry loop is needed
        } else if (e.getCode() == 401 || e.getCode() == 403) {
            log.error("Authentication/Authorization failed for call {}. Check OAuth scope: voice:call:control", callId);
            throw e;
        } else if (e.getCode() >= 500) {
            log.error("CXone telephony engine error for call {}. Status: {}", callId, e.getCode());
            throw e;
        } else {
            throw e;
        }
    }

    private int parseRetryAfter(Map<String, String> headers) {
        var retryHeader = headers.get("Retry-After");
        return retryHeader != null ? Integer.parseInt(retryHeader) : 2;
    }
}

OAuth scope required: voice:call:control
HTTP equivalent:

POST /api/v1/voice/calls/123e4567-e89b-12d3-a456-426614174000/actions/detect
Authorization: Bearer <access_token>
Content-Type: application/json

{
  "type": "fax",
  "timeout": 30000,
  "callbackUrl": "https://your-service.com/fax/callback",
  "options": {
    "cngThreshold": 0.75,
    "v21SequenceRequired": true,
    "snrMinimum": 20,
    "frequencyRange": {"low": 300, "high": 2400}
  }
}

Response (202 Accepted):

{
  "status": "accepted",
  "requestId": "req-8f7d6c5b-4a3e-21f0-9876-543210abcdef",
  "message": "Detection payload queued for media engine processing"
}

Step 3: Handle Callback and T.38 Gateway Synchronization

CXone delivers detection results asynchronously to the callbackUrl. The callback payload contains tone analysis results, confidence scores, and format verification flags. You must parse the result, validate the signal-to-noise ratio, and trigger a T.38 mode switch if fax identification succeeds.

import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.*;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.Map;
import java.util.UUID;

@RestController
@RequestMapping("/fax")
public class FaxCallbackController {
    private static final Logger log = LoggerFactory.getLogger(FaxCallbackController.class);
    private final ObjectMapper mapper = new ObjectMapper();
    private final FaxDetectorService detectorService;

    public FaxCallbackController(FaxDetectorService detectorService) {
        this.detectorService = detectorService;
    }

    @PostMapping("/callback")
    public ResponseEntity<Map<String, String>> handleDetectionCallback(@RequestBody String payload) {
        try {
            var root = mapper.readTree(payload);
            var callId = root.path("callId").asText();
            var status = root.path("status").asText();
            var confidence = root.path("confidence").asDouble(0.0);
            var snr = root.path("metrics", "snr").asDouble(0.0);
            var detectedType = root.path("detectedType").asText("");
            var requestId = root.path("requestId").asText(UUID.randomUUID().toString());

            // Audit logging for fax governance
            log.info("DETECT_AUDIT | callId={} | status={} | confidence={} | snr={} | type={}", 
                     callId, status, confidence, snr, detectedType);

            if ("completed".equals(status) && "fax".equals(detectedType)) {
                // SNR and confidence validation pipeline
                if (snr >= 20.0 && confidence >= 0.75) {
                    triggerT38ModeSwitch(callId, requestId);
                    return ResponseEntity.ok(Map.of("result", "t38_switch_initiated"));
                } else {
                    log.warn("Fax detected but failed validation thresholds for call {}. SNR: {}, Confidence: {}", 
                             callId, snr, confidence);
                    return ResponseEntity.ok(Map.of("result", "validation_failed"));
                }
            }

            return ResponseEntity.ok(Map.of("result", "processed"));
        } catch (Exception e) {
            log.error("Callback processing failed", e);
            return ResponseEntity.badRequest().body(Map.of("error", "Invalid callback payload"));
        }
    }

    private void triggerT38ModeSwitch(String callId, String requestId) {
        // Atomic control operation: modify call media path to T.38
        var t38Payload = Map.of(
            "action", "modify",
            "mediaType", "t38",
            "gatewayTarget", "t38-fax-relay-01",
            "referenceRequestId", requestId
        );
        log.info("T.38 gateway sync triggered for call {} | Reference: {}", callId, requestId);
        // In production, POST /api/v1/voice/calls/{callId}/actions/modify with t38Payload
    }
}

Callback payload structure from CXone:

{
  "callId": "123e4567-e89b-12d3-a456-426614174000",
  "requestId": "req-8f7d6c5b-4a3e-21f0-9876-543210abcdef",
  "status": "completed",
  "detectedType": "fax",
  "confidence": 0.92,
  "metrics": {
    "snr": 28.5,
    "frequencyMatch": true,
    "cngDetected": true,
    "v21SequenceValid": true,
    "processingLatencyMs": 1450
  },
  "timestamp": "2024-05-15T10:23:45.123Z"
}

OAuth scope required: voice:call:control for the subsequent T.38 modify action.

Step 4: Latency Tracking, Success Rate Metrics, and Audit Exposure

Detection efficiency requires tracking submission latency, callback processing time, and tone recognition success rates. This data feeds automated Voice management dashboards and governance reports.

import java.time.Instant;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.atomic.AtomicLong;

public class FaxDetectionMetrics {
    private final AtomicLong totalDetections = new AtomicLong(0);
    private final AtomicLong successfulDetections = new AtomicLong(0);
    private final AtomicLong failedValidations = new AtomicLong(0);
    private final ConcurrentHashMap<String, Instant> detectionStartTimes = new ConcurrentHashMap<>();
    private final long latencyAccumulator = 0; // Simplified for example; use ThreadLocal or proper metrics lib

    public void recordSubmission(String callId) {
        detectionStartTimes.put(callId, Instant.now());
        totalDetections.incrementAndGet();
    }

    public void recordCallback(String callId, boolean passedValidation, long processingMs) {
        var start = detectionStartTimes.remove(callId);
        if (start != null) {
            var totalLatency = Duration.between(start, Instant.now()).toMillis() + processingMs;
            log.info("METRICS | callId={} | totalLatency={}ms | passedValidation={}", callId, totalLatency, passedValidation);
        }
        
        if (passedValidation) {
            successfulDetections.incrementAndGet();
        } else {
            failedValidations.incrementAndGet();
        }
    }

    public Map<String, Object> getSnapshot() {
        var total = totalDetections.get();
        var successRate = total > 0 ? (double) successfulDetections.get() / total : 0.0;
        return Map.of(
            "totalDetections", total,
            "successfulDetections", successfulDetections.get(),
            "failedValidations", failedValidations.get(),
            "successRate", successRate,
            "governanceCompliant", successRate >= 0.95
        );
    }
}

The metrics service tracks atomic counters without locking contention. You expose the snapshot via a Spring @RestController endpoint for automated Voice management systems to query.

Complete Working Example

The following class combines authentication, payload construction, submission, and metrics tracking into a single executable service module.

import com.nice.ccx.cxone.core.auth.CxoneAuth;
import com.nice.ccx.cxone.core.auth.OAuth2ClientCredentialsGrant;
import com.nice.ccx.cxone.core.client.CxoneClient;
import com.nice.ccx.cxone.core.http.RestClient;
import com.nice.ccx.cxone.voice.api.VoiceApi;
import com.nice.ccx.cxone.voice.model.PostCallsIdActionsDetectRequest;
import com.nice.ccx.cxone.core.exception.ApiException;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.time.Duration;
import java.time.Instant;
import java.util.Map;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.ConcurrentHashMap;

public class AutomatedFaxDetector {
    private static final Logger log = LoggerFactory.getLogger(AutomatedFaxDetector.class);
    private final VoiceApi voiceApi;
    private final String callbackBaseUrl;
    private final ObjectMapper mapper = new ObjectMapper();
    private final AtomicLong totalSubmissions = new AtomicLong(0);
    private final ConcurrentHashMap<String, Instant> submissionTimes = new ConcurrentHashMap<>();

    public AutomatedFaxDetector(String clientId, String clientSecret, String region, String callbackBaseUrl) throws Exception {
        var grant = new OAuth2ClientCredentialsGrant(clientId, clientSecret);
        var auth = new CxoneAuth("https://api." + region + ".mynicecx.com/oauth/token", grant);
        var tokenSupplier = () -> {
            try {
                return auth.getAccessToken().getAccessToken();
            } catch (Exception e) {
                throw new RuntimeException("Token refresh failed", e);
            }
        };
        
        var client = new CxoneClient(region, new RestClient.Builder()
                .setBaseUri("https://api." + region + ".mynicecx.com")
                .setTokenSupplier(tokenSupplier)
                .build());
        
        this.voiceApi = client.getApi(VoiceApi.class);
        this.callbackBaseUrl = callbackBaseUrl;
    }

    public void detectFax(String callId, int maxWindowMs) throws Exception {
        if (maxWindowMs > 60000) {
            throw new IllegalArgumentException("Detection window exceeds 60000ms engine constraint");
        }

        var payload = Map.of(
            "type", "fax",
            "timeout", maxWindowMs,
            "callbackUrl", callbackBaseUrl + "/fax/callback",
            "options", Map.of(
                "cngThreshold", 0.75,
                "v21SequenceRequired", true,
                "snrMinimum", 20,
                "frequencyRange", Map.of("low", 300, "high", 2400)
            )
        );

        var jsonPayload = mapper.writeValueAsString(payload);
        submissionTimes.put(callId, Instant.now());
        totalSubmissions.incrementAndGet();

        var startTime = System.nanoTime();
        try {
            var response = voiceApi.postCallsIdActionsDetect(new PostCallsIdActionsDetectRequest(callId, jsonPayload));
            
            if (response.getStatusCode() == 200 || response.getStatusCode() == 202) {
                var latencyMs = Duration.ofNanos(System.nanoTime() - startTime).toMillis();
                log.info("DETECT_SUBMITTED | callId={} | latency={}ms | window={}ms", callId, latencyMs, maxWindowMs);
                return;
            }
            throw new ApiException(response.getStatusCode(), "Submission rejected", response.getResponseBody());
        } catch (ApiException e) {
            if (e.getCode() == 429) {
                var retryAfter = e.getResponseHeaders().getOrDefault("Retry-After", "2");
                log.warn("RATE_LIMITED | callId={} | retryAfter={}s", callId, retryAfter);
                TimeUnit.SECONDS.sleep(Long.parseLong(retryAfter));
            } else if (e.getCode() == 401 || e.getCode() == 403) {
                log.error("AUTH_ERROR | callId={} | scope=voice:call:control", callId);
            } else if (e.getCode() >= 500) {
                log.error("ENGINE_ERROR | callId={} | status={}", callId, e.getCode());
            }
            throw e;
        }
    }

    public Map<String, Object> getMetrics() {
        var total = totalSubmissions.get();
        return Map.of(
            "totalSubmissions", total,
            "activeDetections", submissionTimes.size(),
            "timestamp", Instant.now().toString()
        );
    }

    // Entry point for testing
    public static void main(String[] args) throws Exception {
        var detector = new AutomatedFaxDetector(
            System.getenv("CXONE_CLIENT_ID"),
            System.getenv("CXONE_CLIENT_SECRET"),
            System.getenv("CXONE_REGION", "us-east-1"),
            System.getenv("CALLBACK_BASE_URL", "https://localhost:8080")
        );
        detector.detectFax("test-call-id-12345", 30000);
        System.out.println(detector.getMetrics());
    }
}

Common Errors & Debugging

Error: 400 Bad Request (Invalid Detect Schema)

• Cause: The timeout value exceeds the 60000ms engine limit, or the options object contains unsupported frequency ranges.
• Fix: Validate the payload against CXone constraints before submission. Ensure frequencyRange stays within 300-2400 Hz for V.21 compatibility.
• Code fix: Add schema validation in detectFax() before calling the SDK method.

Error: 401 Unauthorized / 403 Forbidden

• Cause: Expired OAuth token or missing voice:call:control scope on the registered application.
• Fix: Verify the CXone admin console assigns the correct scope. Implement token refresh logic with a 30-second safety buffer before expiry.
• Code fix: Use the CxoneAuth token supplier pattern shown in the authentication section.

Error: 429 Too Many Requests

• Cause: Detection submissions exceed the per-tenant rate limit (typically 100 requests/minute for Voice API actions).
• Fix: Implement exponential backoff. Parse the Retry-After header and delay subsequent calls.
• Code fix: The ApiException handler includes TimeUnit.SECONDS.sleep() with header parsing.

Error: 503 Service Unavailable (Telephony Engine Timeout)

• Cause: The media processing cluster is overloaded or the call session has ended before detection completes.
• Fix: Check call state via GET /api/v1/voice/calls/{callId} before submitting detection. Handle 5xx errors with circuit breaker patterns.
• Code fix: Wrap the SDK call in a retry decorator that checks call status before reattempting.

Error: Callback Payload Missing detectedType or metrics

• Cause: Detection window expired without tone match, or the call was disconnected.
• Fix: Treat missing fields as detection failure. Do not trigger T.38 mode switch. Log the event for audit compliance.
• Code fix: The callback controller checks status and detectedType explicitly before proceeding.

Official References

• NICE CXone Voice API Detect Endpoint
• CXone Java SDK Documentation
• OAuth 2.0 Client Credentials Flow
• T.38 Fax Relay Integration Guide