Network Performance Lab: Calculations and Experiments

Build this version only after you have tried the browser workbench. The extra hardware makes latency, congestion, and button-triggered tests visible on real LEDs.

/*
 * =============================================================================
 * Network Performance Measurement Simulator for ESP32
 * =============================================================================
 *
 * This comprehensive lab demonstrates key network performance concepts:
 *
 * 1. BANDWIDTH vs THROUGHPUT
 *    - Bandwidth: Maximum theoretical capacity (simulated link speed)
 *    - Throughput: Actual achieved data rate (affected by overhead, errors)
 *
 * 2. LATENCY MEASUREMENT
 *    - Base latency: Propagation delay through the network
 *    - Processing latency: Time to encode/decode data
 *    - Queuing latency: Time waiting in buffers
 *    - Total Round-Trip Time (RTT): Complete send-receive cycle
 *
 * 3. JITTER ANALYSIS
 *    - Jitter: Variation in latency between packets
 *    - Critical for real-time applications (voice, video, sensor streams)
 *    - Measured as standard deviation of latency samples
 *
 * 4. CONGESTION EFFECTS
 *    - How competing traffic affects performance
 *    - Queue buildup and increased latency
 *    - Packet loss under heavy load
 *
 * 5. GOODPUT CALCULATION
 *    - Useful application data vs total transmitted data
 *    - Impact of protocol overhead and retransmissions
 *
 * LED Indicators:
 * - Green (GPIO 4):  Simulated latency under 50ms
 * - Yellow (GPIO 5): Simulated latency from 50-200ms / transmission
 * - Red (GPIO 2):    Simulated latency over 200ms
 * - Blue (GPIO 18):  Congestion detected - queue backup or packet loss
 *
 * Button (GPIO 15): Press to run a network performance test cycle
 *
 * Author: IoT Learning Platform
 * License: Educational Use
 */

#include <Arduino.h>
#include <math.h>

// =============================================================================
// PIN DEFINITIONS
// =============================================================================

#define LED_HIGH_LATENCY   2    // Red LED - latency > 200ms
#define LED_LOW_LATENCY    4    // Green LED - latency < 50ms
#define LED_TRANSMIT       5    // Yellow LED - medium latency / transmitting
#define LED_CONGESTION     18   // Blue LED - congestion detected
#define BUTTON_PIN         15   // Push button to trigger tests

// =============================================================================
// NETWORK SIMULATION PARAMETERS
// =============================================================================

// Simulated network characteristics (adjustable)
#define SIMULATED_BANDWIDTH_KBPS    1000    // 1 Mbps theoretical bandwidth
#define BASE_LATENCY_MS             25      // Base propagation delay
#define PROCESSING_LATENCY_MS       5       // Encoding/decoding time
#define MAX_QUEUE_SIZE              10      // Packets that can be queued

// Packet parameters
#define PACKET_SIZE_BYTES           100     // Data payload size
#define HEADER_OVERHEAD_BYTES       40      // TCP/IP header overhead
#define MAX_PACKETS_PER_TEST        20      // Packets to send per test

// Congestion simulation
#define CONGESTION_THRESHOLD        0.7     // Illustrative queue onset for this toy model
#define PACKET_LOSS_PROBABILITY     0.05    // 5% base packet loss rate

// Jitter parameters
#define MAX_JITTER_MS               30      // Maximum random jitter

// =============================================================================
// DATA STRUCTURES
// =============================================================================

// Statistics for a single packet transmission
struct PacketStats {
    uint32_t sequenceNumber;
    uint32_t sendTime;
    uint32_t receiveTime;
    uint32_t latency;
    bool wasLost;
    bool wasRetransmitted;
    uint16_t payloadSize;
    uint16_t totalSize;  // payload + overhead
};

// Aggregate statistics for a test run
struct TestResults {
    // Timing metrics
    float avgLatency;
    float minLatency;
    float maxLatency;
    float jitter;           // Standard deviation of latency

    // Throughput metrics
    float theoreticalBandwidthKbps;
    float achievedThroughputKbps;
    float goodputKbps;
    float efficiency;       // delivered application bits / delivered frame bits

    // Reliability metrics
    uint32_t packetsSent;
    uint32_t packetsReceived;
    uint32_t packetsLost;
    uint32_t packetsRetransmitted;
    float packetLossRate;

    // Congestion indicators
    bool congestionDetected;
    uint32_t maxQueueDepth;
    float avgQueueDepth;
};

// Network state simulation
struct NetworkState {
    float currentUtilization;   // 0.0 to 1.0
    uint32_t queueDepth;        // Current packets in queue
    bool isCongested;
    uint32_t backgroundTraffic; // Simulated competing traffic (bytes/sec)
};

// =============================================================================
// GLOBAL VARIABLES
// =============================================================================

PacketStats packetHistory[MAX_PACKETS_PER_TEST];
TestResults currentTest;
NetworkState network;

uint32_t testNumber = 0;
bool buttonPressed = false;
bool testInProgress = false;
uint32_t lastButtonDebounce = 0;

// Latency samples for jitter calculation
float latencySamples[MAX_PACKETS_PER_TEST];
int sampleCount = 0;

// =============================================================================
// FUNCTION PROTOTYPES
// =============================================================================

void initializeHardware();
void initializeNetwork();
void updateLEDs(float latency, bool congested);
void runPerformanceTest();
float simulateLatency(bool congested);
float simulateJitter();
bool simulatePacketLoss(float congestionLevel);
float calculateThroughput(uint32_t bytesTransmitted, uint32_t durationMs);
float calculateJitter(float* samples, int count);
float calculateStandardDeviation(float* samples, int count, float mean);
void printTestHeader(int testNum);
void printPacketDetails(PacketStats* pkt);
void printTestSummary(TestResults* results);
void printBandwidthVsThroughput();
void printLatencyBreakdown();
void printJitterAnalysis();
void printCongestionAnalysis();
void printPerformanceGrade();
void demonstrateBandwidthConcept();
void demonstrateLatencyConcept();
void demonstrateJitterConcept();
void demonstrateCongestionConcept();
void runAutomatedDemo();
void blinkLED(int pin, int times, int delayMs);
void setAllLEDs(bool state);

// =============================================================================
// SETUP
// =============================================================================

void setup() {
    Serial.begin(115200);
    delay(1000);  // Allow serial to initialize

    printWelcomeBanner();
    initializeHardware();
    initializeNetwork();

    Serial.println("\n[READY] Press the button to run a network performance test");
    Serial.println("        Or wait for automatic demonstration cycles\n");
}

// =============================================================================
// MAIN LOOP
// =============================================================================

void loop() {
    // Check for button press with debouncing
    if (digitalRead(BUTTON_PIN) == HIGH && !buttonPressed) {
        if (millis() - lastButtonDebounce > 200) {  // 200ms debounce
            buttonPressed = true;
            lastButtonDebounce = millis();

            if (!testInProgress) {
                Serial.println("\n[BUTTON] Manual test triggered!\n");
                runPerformanceTest();
            }
        }
    } else if (digitalRead(BUTTON_PIN) == LOW) {
        buttonPressed = false;
    }

    // Run automated demo every 15 seconds if not testing
    static uint32_t lastAutoDemo = 0;
    if (!testInProgress && millis() - lastAutoDemo > 15000) {
        lastAutoDemo = millis();
        runAutomatedDemo();
    }

    delay(10);  // Small delay for stability
}

// =============================================================================
// INITIALIZATION FUNCTIONS
// =============================================================================

void printWelcomeBanner() {
    Serial.println("\n");
    Serial.println("+=================================================================+");
    Serial.println("|     NETWORK PERFORMANCE MEASUREMENT SIMULATOR v2.0              |");
    Serial.println("|     ESP32 IoT Learning Lab - Understanding Network Metrics      |");
    Serial.println("+=================================================================+");
    Serial.println("|  This lab teaches:                                              |");
    Serial.println("|  - Bandwidth vs Throughput - Why they're different              |");
    Serial.println("|  - Latency Measurement - RTT and its components                 |");
    Serial.println("|  - Jitter Analysis - Variation affects real-time apps           |");
    Serial.println("|  - Congestion Effects - How traffic overload degrades networks  |");
    Serial.println("|  - Goodput Calculation - Useful data vs total transmitted       |");
    Serial.println("+=================================================================+");
    Serial.println();
}

void initializeHardware() {
    Serial.println("[INIT] Configuring GPIO pins...");

    // Configure LED pins as outputs
    pinMode(LED_HIGH_LATENCY, OUTPUT);
    pinMode(LED_LOW_LATENCY, OUTPUT);
    pinMode(LED_TRANSMIT, OUTPUT);
    pinMode(LED_CONGESTION, OUTPUT);

    // Configure button pin as input
    pinMode(BUTTON_PIN, INPUT);

    // Initial LED test - all off
    setAllLEDs(false);

    // LED self-test sequence
    Serial.println("[INIT] Running LED self-test...");

    Serial.println("       Testing: Green LED (Low Latency)");
    blinkLED(LED_LOW_LATENCY, 2, 200);

    Serial.println("       Testing: Yellow LED (Transmitting)");
    blinkLED(LED_TRANSMIT, 2, 200);

    Serial.println("       Testing: Red LED (High Latency)");
    blinkLED(LED_HIGH_LATENCY, 2, 200);

    Serial.println("       Testing: Blue LED (Congestion)");
    blinkLED(LED_CONGESTION, 2, 200);

    Serial.println("[INIT] Hardware initialization complete!\n");
}

void initializeNetwork() {
    Serial.println("[INIT] Initializing simulated network...");

    network.currentUtilization = 0.1;   // Start with 10% background utilization
    network.queueDepth = 0;
    network.isCongested = false;
    network.backgroundTraffic = SIMULATED_BANDWIDTH_KBPS * 1000 / 8 / 10;  // 10% of 1,000,000 bit/s = 12,500 bytes/s

    Serial.printf("       Simulated Bandwidth: %d Kbps (%.2f Mbps)\n",
                  SIMULATED_BANDWIDTH_KBPS, SIMULATED_BANDWIDTH_KBPS / 1000.0);
    Serial.printf("       Base Latency: %d ms\n", BASE_LATENCY_MS);
    Serial.printf("       Max Queue Size: %d packets\n", MAX_QUEUE_SIZE);
    Serial.printf("       Base Packet Loss: %.1f%%\n", PACKET_LOSS_PROBABILITY * 100);
    Serial.println("[INIT] Network simulation ready!\n");
}

// =============================================================================
// MAIN TEST FUNCTION
// =============================================================================

void runPerformanceTest() {
    testInProgress = true;
    testNumber++;

    printTestHeader(testNumber);

    // Reset test results
    memset(&currentTest, 0, sizeof(TestResults));
    memset(packetHistory, 0, sizeof(packetHistory));
    sampleCount = 0;

    currentTest.theoreticalBandwidthKbps = SIMULATED_BANDWIDTH_KBPS;
    currentTest.minLatency = 999999;

    // Simulate varying network conditions for this test
    float congestionLevel = (testNumber % 4) * 0.25;  // Four illustrative load steps
    network.currentUtilization = 0.2 + congestionLevel;  // 20%, 45%, 70%, 95%
    network.queueDepth = 0;
    network.isCongested = (network.currentUtilization > CONGESTION_THRESHOLD);

    Serial.printf("\n[CONFIG] Network Conditions for Test %lu:\n", testNumber);
    Serial.printf("         Utilization Level: %.0f%%\n", network.currentUtilization * 100);
    Serial.printf("         Congestion Status: %s\n", network.isCongested ? "CONGESTED" : "Normal");
    Serial.println();

    // Update congestion LED
    digitalWrite(LED_CONGESTION, network.isCongested);

    uint32_t totalBytesTransmitted = 0;
    uint32_t totalBytesDelivered = 0;
    uint32_t totalUsefulBytes = 0;
    uint32_t simulatedDurationMs = 0;

    // Transmit packets
    Serial.println("+----------------------------------------------------------------+");
    Serial.println("|                    PACKET TRANSMISSION LOG                      |");
    Serial.println("+----------------------------------------------------------------+");

    for (int i = 0; i < MAX_PACKETS_PER_TEST; i++) {
        PacketStats* pkt = &packetHistory[i];
        pkt->sequenceNumber = i + 1;
        pkt->payloadSize = PACKET_SIZE_BYTES;
        pkt->totalSize = PACKET_SIZE_BYTES + HEADER_OVERHEAD_BYTES;

        // Indicate transmission start
        digitalWrite(LED_TRANSMIT, HIGH);

        // Record send time
        pkt->sendTime = millis();

        // Simulate network latency
        float latency = simulateLatency(network.isCongested);
        pkt->latency = (uint32_t)latency;

        // Simulate potential packet loss
        bool initialAttemptLost = simulatePacketLoss(network.currentUtilization);
        pkt->wasLost = initialAttemptLost;

        if (initialAttemptLost) {
            // One retry is attempted; it can also fail.
            pkt->wasRetransmitted = true;
            latency += simulateLatency(network.isCongested);  // Add retransmission delay
            pkt->latency = (uint32_t)latency;
            pkt->wasLost = simulatePacketLoss(network.currentUtilization);
            currentTest.packetsRetransmitted++;
        }

        // Simulate the actual delay
        delay((uint32_t)(latency / 10));  // Scaled down for demo (divide by 10)

        pkt->receiveTime = pkt->sendTime + pkt->latency;

        // Update LED based on latency
        updateLEDs(latency, network.isCongested);

        // End transmission indication
        digitalWrite(LED_TRANSMIT, LOW);

        // Update statistics
        if (!pkt->wasLost) {
            currentTest.packetsReceived++;
            totalBytesDelivered += pkt->totalSize;
            totalUsefulBytes += pkt->payloadSize;
        } else {
            currentTest.packetsLost++;
        }

        totalBytesTransmitted += pkt->totalSize * (pkt->wasRetransmitted ? 2 : 1);
        currentTest.packetsSent++;
        simulatedDurationMs += (uint32_t)latency + 50;

        // Only delivered packets contribute to observed RTT and jitter.
        if (!pkt->wasLost) {
            latencySamples[sampleCount++] = latency;
            if (latency < currentTest.minLatency) currentTest.minLatency = latency;
            if (latency > currentTest.maxLatency) currentTest.maxLatency = latency;
        }

        // Print packet details
        printPacketDetails(pkt);

        // Small delay between packets
        delay(50);
    }

    Serial.println("+----------------------------------------------------------------+");

    // Calculate final statistics
    float sumLatency = 0;
    for (int i = 0; i < sampleCount; i++) {
        sumLatency += latencySamples[i];
    }
    currentTest.avgLatency = sampleCount ? sumLatency / sampleCount : 0;
    if (!sampleCount) currentTest.minLatency = 0;

    // Calculate jitter (standard deviation of latency)
    currentTest.jitter = calculateJitter(latencySamples, sampleCount);

    // Calculate throughput and goodput
    currentTest.achievedThroughputKbps = calculateThroughput(totalBytesDelivered, simulatedDurationMs);
    currentTest.goodputKbps = calculateThroughput(totalUsefulBytes, simulatedDurationMs);
    currentTest.efficiency = totalBytesDelivered ? (float)totalUsefulBytes / totalBytesDelivered : 0;

    // Calculate packet loss rate
    currentTest.packetLossRate = (float)currentTest.packetsLost / currentTest.packetsSent;
    currentTest.congestionDetected = network.isCongested;

    // Print comprehensive summary
    Serial.printf("[MODEL] %lu attempted frame bytes (including retries); %lu delivered frame bytes over %lu simulated ms. No physical network was measured.\n",
                  totalBytesTransmitted, totalBytesDelivered, simulatedDurationMs);
    printTestSummary(&currentTest);
    printBandwidthVsThroughput();
    printLatencyBreakdown();
    printJitterAnalysis();
    printCongestionAnalysis();
    printPerformanceGrade();

    // Turn off all LEDs
    setAllLEDs(false);

    Serial.println("\n[COMPLETE] Test finished. Press button for another test or wait for auto-demo.\n");

    testInProgress = false;
}

// =============================================================================
// SIMULATION FUNCTIONS
// =============================================================================

float simulateLatency(bool congested) {
    float baseLatency = BASE_LATENCY_MS + PROCESSING_LATENCY_MS;
    float jitter = simulateJitter();
    float congestionDelay = 0;

    if (congested) {
        // Toy queue-delay curve, not a general queueing law.
        congestionDelay = pow(2, network.queueDepth) * 5;  // Doubles for each queued packet
        if (congestionDelay > 500) congestionDelay = 500;  // Cap at 500ms

        // Simulate queue buildup
        if (random(100) < 30) {  // 30% chance to increase queue
            network.queueDepth = min(network.queueDepth + 1, (uint32_t)MAX_QUEUE_SIZE);
        } else if (network.queueDepth > 0 && random(100) < 50) {
            network.queueDepth--;
        }
    }

    return max(0.0f, baseLatency + jitter + congestionDelay);
}

float simulateJitter() {
    // Three uniform draws provide an illustrative centered variation.
    float jitter = 0;
    for (int i = 0; i < 3; i++) {
        jitter += random(-MAX_JITTER_MS, MAX_JITTER_MS);
    }
    jitter /= 3;

    return jitter;
}

bool simulatePacketLoss(float congestionLevel) {
    float lossProb = PACKET_LOSS_PROBABILITY;

    // Increase loss probability during congestion
    if (congestionLevel > CONGESTION_THRESHOLD) {
        lossProb += (congestionLevel - CONGESTION_THRESHOLD) * 0.3;  // Up to +9% loss at 100%
    }

    return (random(1000) / 1000.0) < lossProb;
}

// =============================================================================
// CALCULATION FUNCTIONS
// =============================================================================

float calculateThroughput(uint32_t bytesTransmitted, uint32_t durationMs) {
    if (durationMs == 0) return 0;

    // Convert to Kbps: (bytes * 8 bits/byte) / durationMs = Kbits/s
    return (float)(bytesTransmitted * 8) / durationMs;
}

float calculateJitter(float* samples, int count) {
    if (count < 2) return 0;

    float sum = 0;
    for (int i = 0; i < count; i++) {
        sum += samples[i];
    }
    float mean = sum / count;

    return calculateStandardDeviation(samples, count, mean);
}

float calculateStandardDeviation(float* samples, int count, float mean) {
    if (count < 2) return 0;

    float sumSquaredDiff = 0;
    for (int i = 0; i < count; i++) {
        float diff = samples[i] - mean;
        sumSquaredDiff += diff * diff;
    }

    return sqrt(sumSquaredDiff / (count - 1));
}

// =============================================================================
// LED CONTROL FUNCTIONS
// =============================================================================

void updateLEDs(float latency, bool congested) {
    // Turn off all status LEDs first
    digitalWrite(LED_LOW_LATENCY, LOW);
    digitalWrite(LED_TRANSMIT, LOW);
    digitalWrite(LED_HIGH_LATENCY, LOW);

    // Set appropriate LED based on latency
    if (latency < 50) {
        digitalWrite(LED_LOW_LATENCY, HIGH);   // Green - excellent
    } else if (latency < 200) {
        digitalWrite(LED_TRANSMIT, HIGH);       // Yellow - acceptable
    } else {
        digitalWrite(LED_HIGH_LATENCY, HIGH);   // Red - poor
    }

    // Congestion LED
    digitalWrite(LED_CONGESTION, congested);
}

void blinkLED(int pin, int times, int delayMs) {
    for (int i = 0; i < times; i++) {
        digitalWrite(pin, HIGH);
        delay(delayMs);
        digitalWrite(pin, LOW);
        delay(delayMs);
    }
}

void setAllLEDs(bool state) {
    digitalWrite(LED_LOW_LATENCY, state);
    digitalWrite(LED_TRANSMIT, state);
    digitalWrite(LED_HIGH_LATENCY, state);
    digitalWrite(LED_CONGESTION, state);
}

// =============================================================================
// PRINTING FUNCTIONS
// =============================================================================

void printTestHeader(int testNum) {
    Serial.println("\n+=================================================================+");
    Serial.printf("|                    PERFORMANCE TEST #%d                          |\n", testNum);
    Serial.println("+=================================================================+");
    Serial.println("|  Simulating: Link rate, Throughput, Latency, Jitter, Goodput    |");
    Serial.println("+=================================================================+");
}

void printPacketDetails(PacketStats* pkt) {
    char status[20];
    char latencyBar[21];

    // Create visual latency bar
    int barLength = min((int)(pkt->latency / 25), 20);  // Scale to max 20 chars
    for (int i = 0; i < 20; i++) {
        latencyBar[i] = (i < barLength) ? '#' : '-';
    }
    latencyBar[20] = '\0';

    // Determine status
    if (pkt->wasLost) {
        strcpy(status, "LOST");
    } else if (pkt->wasRetransmitted) {
        strcpy(status, "RETX");
    } else if (pkt->latency < 50) {
        strcpy(status, "OK  ");
    } else if (pkt->latency < 200) {
        strcpy(status, "SLOW");
    } else {
        strcpy(status, "POOR");
    }

    Serial.printf("| PKT #%02lu | %4lu ms | [%s] | %s | %d+%d bytes |\n",
                  pkt->sequenceNumber,
                  pkt->latency,
                  latencyBar,
                  status,
                  pkt->payloadSize,
                  HEADER_OVERHEAD_BYTES);
}

void printTestSummary(TestResults* results) {
    Serial.println("\n+=================================================================+");
    Serial.println("|                       TEST RESULTS SUMMARY                       |");
    Serial.println("+=================================================================+");

    Serial.println("|                                                                 |");
    Serial.println("|  LATENCY METRICS:                                               |");
    Serial.printf("|    Average Latency:    %7.1f ms                                |\n", results->avgLatency);
    Serial.printf("|    Minimum Latency:    %7.1f ms                                |\n", results->minLatency);
    Serial.printf("|    Maximum Latency:    %7.1f ms                                |\n", results->maxLatency);
    Serial.printf("|    Jitter (StdDev):    %7.1f ms                                |\n", results->jitter);

    Serial.println("|                                                                 |");
    Serial.println("|  THROUGHPUT METRICS:                                            |");
    Serial.printf("|    Configured link rate:%7.1f Kbps                              |\n", results->theoreticalBandwidthKbps);
    Serial.printf("|    Modeled delivered rate:%7.1f Kbps                            |\n", results->achievedThroughputKbps);
    Serial.printf("|    Goodput (Useful):   %7.1f Kbps                              |\n", results->goodputKbps);
    Serial.printf("|    Payload fraction:   %7.1f%%                                 |\n", results->efficiency * 100);

    Serial.println("|                                                                 |");
    Serial.println("|  RELIABILITY METRICS:                                           |");
    Serial.printf("|    Packets Sent:       %7lu                                   |\n", results->packetsSent);
    Serial.printf("|    Packets Received:   %7lu                                   |\n", results->packetsReceived);
    Serial.printf("|    Packets Lost:       %7lu                                   |\n", results->packetsLost);
    Serial.printf("|    Retransmissions:    %7lu                                   |\n", results->packetsRetransmitted);
    Serial.printf("|    Packet Loss Rate:   %7.1f%%                                 |\n", results->packetLossRate * 100);

    Serial.println("|                                                                 |");
    Serial.println("+=================================================================+");
}

void printBandwidthVsThroughput() {
    Serial.println("\n+----------------------------------------------------------------+");
    Serial.println("|           CONCEPT: BANDWIDTH vs THROUGHPUT vs GOODPUT          |");
    Serial.println("+----------------------------------------------------------------+");
    Serial.println("|                                                                |");
    Serial.println("|  Bandwidth (Theoretical Maximum):                              |");
    Serial.printf("|  [##################################################] %4.0f Kbps |\n",
                  currentTest.theoreticalBandwidthKbps);
    Serial.println("|                                                                |");

    // Calculate bar lengths
    int throughputBar = (int)(currentTest.achievedThroughputKbps / currentTest.theoreticalBandwidthKbps * 50);
    int goodputBar = (int)(currentTest.goodputKbps / currentTest.theoreticalBandwidthKbps * 50);

    Serial.println("|  Throughput (modeled delivered rate):                          |");
    Serial.print("|  [");
    for (int i = 0; i < 50; i++) Serial.print(i < throughputBar ? "#" : "-");
    Serial.printf("] %4.0f Kbps |\n", currentTest.achievedThroughputKbps);

    Serial.println("|                                                                |");
    Serial.println("|  Goodput (Useful Application Data):                            |");
    Serial.print("|  [");
    for (int i = 0; i < 50; i++) Serial.print(i < goodputBar ? "#" : "-");
    Serial.printf("] %4.0f Kbps |\n", currentTest.goodputKbps);

    Serial.println("|                                                                |");
    Serial.println("|  WHY THE DIFFERENCE?                                           |");
    Serial.printf("|  - Protocol Overhead: %d bytes per %d-byte packet (%.0f%%)         |\n",
                  HEADER_OVERHEAD_BYTES, PACKET_SIZE_BYTES,
                  (float)HEADER_OVERHEAD_BYTES / (PACKET_SIZE_BYTES + HEADER_OVERHEAD_BYTES) * 100);
    Serial.printf("|  - Retransmissions: %lu packets resent                           |\n",
                  currentTest.packetsRetransmitted);
    Serial.printf("|  - Delivered payload fraction: %.1f%% of delivered frame bytes   |\n",
                  currentTest.efficiency * 100);
    Serial.println("|                                                                |");
    Serial.println("+----------------------------------------------------------------+");
}

void printLatencyBreakdown() {
    Serial.println("\n+----------------------------------------------------------------+");
    Serial.println("|                    LATENCY BREAKDOWN                            |");
    Serial.println("+----------------------------------------------------------------+");
    Serial.println("|                                                                |");
    Serial.println("|  Total RTT (Round-Trip Time) Components:                       |");
    Serial.println("|                                                                |");
    Serial.printf("|  +- Propagation Delay:  %3d ms (signal travel time)            |\n", BASE_LATENCY_MS);
    Serial.printf("|  +- Processing Delay:   %3d ms (encode/decode)                 |\n", PROCESSING_LATENCY_MS);
    Serial.printf("|  +- Queuing Delay:      %3.0f ms (buffer waiting)                |\n",
                  currentTest.avgLatency - BASE_LATENCY_MS - PROCESSING_LATENCY_MS - (currentTest.jitter / 2));
    Serial.printf("|  +- Jitter Variation:  +/-%3.0f ms (timing variance)             |\n", currentTest.jitter);
    Serial.println("|  ----------------------------------------------------------    |");
    Serial.printf("|  = Modeled Avg RTT:    %3.0f ms                                  |\n", currentTest.avgLatency);
    Serial.println("|                                                                |");
    Serial.println("|  LATENCY RATINGS:                                              |");
    Serial.println("|  Typical guideline: <50 ms excellent for interactive apps    |");
    Serial.println("|  Typical guideline: 50-150 ms good for most IoT apps          |");
    Serial.println("|  Typical guideline: 150-300 ms acceptable for monitoring     |");
    Serial.println("|  Typical guideline: >300 ms poor for interaction             |");
    Serial.println("|                                                                |");
    Serial.printf("|  Your Result: %.0fms = %s                                       |\n",
                  currentTest.avgLatency,
                  currentTest.avgLatency < 50 ? "EXCELLENT" :
                  currentTest.avgLatency < 150 ? "GOOD" :
                  currentTest.avgLatency < 300 ? "ACCEPTABLE" : "POOR");
    Serial.println("|                                                                |");
    Serial.println("+----------------------------------------------------------------+");
}

void printJitterAnalysis() {
    Serial.println("\n+----------------------------------------------------------------+");
    Serial.println("|                      JITTER ANALYSIS                            |");
    Serial.println("+----------------------------------------------------------------+");
    Serial.println("|                                                                |");
    Serial.println("|  What is Jitter?                                               |");
    Serial.println("|  Jitter = Variation in packet latency over time                |");
    Serial.println("|  Measured as standard deviation of latency samples             |");
    Serial.println("|                                                                |");
    Serial.println("|  Latency Distribution:                                         |");
    Serial.println("|                                                                |");

    // Create ASCII histogram of latency distribution
    int histogram[5] = {0, 0, 0, 0, 0};  // 0-50, 50-100, 100-150, 150-200, 200+
    for (int i = 0; i < sampleCount; i++) {
        int bucket = min((int)(latencySamples[i] / 50), 4);
        histogram[bucket]++;
    }

    const char* labels[] = {"  0-50ms", " 50-100ms", "100-150ms", "150-200ms", "200+ms"};
    for (int b = 0; b < 5; b++) {
        int barLen = (histogram[b] * 30) / MAX_PACKETS_PER_TEST;
        Serial.printf("|  %s: ", labels[b]);
        for (int j = 0; j < 30; j++) {
            Serial.print(j < barLen ? "#" : ".");
        }
        Serial.printf(" (%d)     |\n", histogram[b]);
    }

    Serial.println("|                                                                |");
    Serial.printf("|  Jitter (StdDev): %.1f ms                                       |\n", currentTest.jitter);
    Serial.println("|                                                                |");
    Serial.println("|  JITTER IMPACT BY APPLICATION (typical guideline):           |");
    Serial.println("|  - VoIP/Video:    <30 ms (buffer to smooth)                   |");
    Serial.println("|  - Real-time IoT: <50 ms preferred (sensor fusion)            |");
    Serial.println("|  - Monitoring:    <200 ms acceptable (dashboard display)     |");
    Serial.println("|                                                                |");
    Serial.printf("|  Modeled RTT standard deviation: %.1f ms (demo band: %s)      |\n",
                  currentTest.jitter,
                  currentTest.jitter < 30 ? "<30 ms" :
                  currentTest.jitter < 50 ? "30-49 ms" :
                  currentTest.jitter < 100 ? "50-99 ms" : ">=100 ms");
    Serial.println("|                                                                |");
    Serial.println("+----------------------------------------------------------------+");
}

void printCongestionAnalysis() {
    Serial.println("\n+----------------------------------------------------------------+");
    Serial.println("|                   CONGESTION ANALYSIS                           |");
    Serial.println("+----------------------------------------------------------------+");
    Serial.println("|                                                                |");

    if (currentTest.congestionDetected) {
        Serial.println("|  [!] CONGESTION DETECTED                                       |");
        Serial.println("|                                                                |");
        Serial.printf("|  Network Utilization: %.0f%% (threshold: %.0f%%)                  |\n",
                      network.currentUtilization * 100, CONGESTION_THRESHOLD * 100);
        Serial.println("|                                                                |");
        Serial.println("|  Congestion Effects Observed:                                  |");
        Serial.printf("|  - Increased Latency: +%.0fms above baseline                    |\n",
                      currentTest.avgLatency - BASE_LATENCY_MS - PROCESSING_LATENCY_MS);
        Serial.printf("|  - Packet Loss Rate: %.1f%%                                     |\n",
                      currentTest.packetLossRate * 100);
        Serial.printf("|  - Retransmissions Required: %lu                                |\n",
                      currentTest.packetsRetransmitted);
        Serial.println("|                                                                |");
        Serial.println("|  CONGESTION MITIGATION STRATEGIES:                             |");
        Serial.println("|  1. Traffic shaping: Rate-limit non-critical traffic           |");
        Serial.println("|  2. QoS: Prioritize critical IoT sensor data                   |");
        Serial.println("|  3. Load balancing: Distribute across multiple paths           |");
        Serial.println("|  4. Reduce payload: Compress or aggregate sensor readings      |");
    } else {
        Serial.println("|  [OK] NO CONGESTION - Network operating normally               |");
        Serial.println("|                                                                |");
        Serial.printf("|  Network Utilization: %.0f%% (below threshold: %.0f%%)            |\n",
                      network.currentUtilization * 100, CONGESTION_THRESHOLD * 100);
        Serial.println("|                                                                |");
        Serial.println("|  Network Health Indicators:                                    |");
        Serial.println("|  - Queue depth: Minimal                                        |");
        Serial.printf("|  - Packet loss: %.1f%% (within normal range)                    |\n",
                      currentTest.packetLossRate * 100);
        Serial.println("|  - Latency: Stable and predictable                             |");
    }

    Serial.println("|                                                                |");
    Serial.println("+----------------------------------------------------------------+");
}

void printPerformanceGrade() {
    Serial.println("\n+=================================================================+");
    Serial.println("|                    OVERALL PERFORMANCE GRADE                     |");
    Serial.println("+=================================================================+");

    // Calculate overall score (0-100)
    int score = 100;

    // Deduct for latency
    if (currentTest.avgLatency > 50) score -= 10;
    if (currentTest.avgLatency > 150) score -= 15;
    if (currentTest.avgLatency > 300) score -= 20;

    // Deduct for jitter
    if (currentTest.jitter > 30) score -= 10;
    if (currentTest.jitter > 50) score -= 10;
    if (currentTest.jitter > 100) score -= 15;

    // Deduct for packet loss
    score -= (int)(currentTest.packetLossRate * 100);

    // Deduct for low efficiency
    if (currentTest.efficiency < 0.7) score -= 10;
    if (currentTest.efficiency < 0.5) score -= 15;

    score = max(0, score);

    char grade;
    const char* gradeDesc;
    if (score >= 90) { grade = 'A'; gradeDesc = "Top demo band - compare with your requirements"; }
    else if (score >= 80) { grade = 'B'; gradeDesc = "Second demo band - inspect each metric"; }
    else if (score >= 70) { grade = 'C'; gradeDesc = "Middle demo band - inspect each metric"; }
    else if (score >= 60) { grade = 'D'; gradeDesc = "Low demo band - inspect each metric"; }
    else { grade = 'F'; gradeDesc = "Bottom demo band - inspect each metric"; }

    Serial.println("|                                                                 |");
    Serial.printf("|                      SCORE: %d/100                               |\n", score);
    Serial.printf("|                      GRADE: %c                                   |\n", grade);
    Serial.printf("|                                                                 |\n");
    Serial.printf("|  %s               |\n", gradeDesc);
    Serial.println("|                                                                 |");
    Serial.println("|  Toy score deducts for demo latency, jitter, loss and         |");
    Serial.println("|  payload-fraction bands. It is not a deployment pass/fail.     |");
    Serial.println("|                                                                 |");
    Serial.println("+=================================================================+");
}

// =============================================================================
// AUTOMATED DEMONSTRATION
// =============================================================================

void runAutomatedDemo() {
    static int demoStep = 0;

    switch (demoStep) {
        case 0:
            demonstrateBandwidthConcept();
            break;
        case 1:
            demonstrateLatencyConcept();
            break;
        case 2:
            demonstrateJitterConcept();
            break;
        case 3:
            demonstrateCongestionConcept();
            break;
        case 4:
            runPerformanceTest();
            break;
    }

    demoStep = (demoStep + 1) % 5;
}

void demonstrateBandwidthConcept() {
    Serial.println("\n+=================================================================+");
    Serial.println("|           MINI-LESSON: BANDWIDTH vs THROUGHPUT                  |");
    Serial.println("+=================================================================+");
    Serial.println();
    Serial.println("Think of BANDWIDTH as the SIZE of a water pipe:");
    Serial.println();
    Serial.println("  Bandwidth = Maximum theoretical capacity");
    Serial.println("  +======================================+");
    Serial.println("  |  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ->   |  1 Mbps pipe");
    Serial.println("  +======================================+");
    Serial.println();
    Serial.println("Think of THROUGHPUT as how much water ACTUALLY flows:");
    Serial.println();
    Serial.println("  +======================================+");
    Serial.println("  |  ~~~~~~~~~~~[X][X]~~~~~~~~~ ->      |  800 Kbps actual");
    Serial.println("  +======================================+");
    Serial.println("              ^   ^");
    Serial.println("          Overhead & Losses");
    Serial.println();
    Serial.println("WHY THE DIFFERENCE?");
    Serial.println("- Protocol headers consume space (TCP/IP = 40+ bytes/packet)");
    Serial.println("- Retransmissions waste capacity");
    Serial.println("- Congestion causes queuing delays");
    Serial.println("- Physical layer overhead (preambles, gaps)");
    Serial.println();

    // Visual LED demo
    digitalWrite(LED_LOW_LATENCY, HIGH);
    delay(500);
    digitalWrite(LED_TRANSMIT, HIGH);
    delay(500);
    setAllLEDs(false);
}

void demonstrateLatencyConcept() {
    Serial.println("\n+=================================================================+");
    Serial.println("|               MINI-LESSON: UNDERSTANDING LATENCY                |");
    Serial.println("+=================================================================+");
    Serial.println();
    Serial.println("LATENCY = Time for data to travel from source to destination");
    Serial.println();
    Serial.println("  [Sensor] ----------------------------------------> [Cloud]");
    Serial.println("           <--------- RTT (Round-Trip Time) ------->");
    Serial.println();
    Serial.println("Components of Latency:");
    Serial.println();
    Serial.println("  1. Propagation Delay (25ms)");
    Serial.println("     +- Speed of light through fiber/copper");
    Serial.println();
    Serial.println("  2. Processing Delay (5ms)");
    Serial.println("     +- CPU time to encode/decode packets");
    Serial.println();
    Serial.println("  3. Queuing Delay (0-500ms)");
    Serial.println("     +- Time waiting in router buffers");
    Serial.println();
    Serial.println("  4. Transmission Delay");
    Serial.println("     +- Time to push bits onto the wire");
    Serial.println();
    Serial.println("IMPORTANT: Bandwidth does NOT reduce latency!");
    Serial.println("A 10 Gbps link has the same propagation delay as 1 Mbps.");
    Serial.println();

    // Demo: Show latency progression
    Serial.println("Simulating latency levels...");

    digitalWrite(LED_LOW_LATENCY, HIGH);
    Serial.println("  [GREEN]  Demo RTT under 50ms");
    delay(1000);
    digitalWrite(LED_LOW_LATENCY, LOW);

    digitalWrite(LED_TRANSMIT, HIGH);
    Serial.println("  [YELLOW] Demo RTT from 50-200ms");
    delay(1000);
    digitalWrite(LED_TRANSMIT, LOW);

    digitalWrite(LED_HIGH_LATENCY, HIGH);
    Serial.println("  [RED]    Demo RTT over 200ms");
    delay(1000);
    digitalWrite(LED_HIGH_LATENCY, LOW);
}

void demonstrateJitterConcept() {
    Serial.println("\n+=================================================================+");
    Serial.println("|                  MINI-LESSON: WHAT IS JITTER?                   |");
    Serial.println("+=================================================================+");
    Serial.println();
    Serial.println("JITTER = Variation in latency between packets");
    Serial.println();
    Serial.println("Low Jitter (Good - Consistent timing):");
    Serial.println("  Pkt1: 50ms  .....#");
    Serial.println("  Pkt2: 52ms  .....#");
    Serial.println("  Pkt3: 48ms  .....#");
    Serial.println("  Pkt4: 51ms  .....#");
    Serial.println("  Jitter (peak-to-peak delay variation) = 52 - 48 = 4ms");
    Serial.println();
    Serial.println("High Jitter (Bad - Unpredictable timing):");
    Serial.println("  Pkt1: 50ms  .....#");
    Serial.println("  Pkt2: 120ms ............#");
    Serial.println("  Pkt3: 30ms  ...#");
    Serial.println("  Pkt4: 200ms ....................#");
    Serial.println("  Jitter (peak-to-peak delay variation) = 200 - 30 = 170ms");
    Serial.println();
    Serial.println("WHY JITTER MATTERS:");
    Serial.println("- VoIP calls: High jitter causes choppy audio");
    Serial.println("- Video streaming: Causes buffering/stutter");
    Serial.println("- Sensor fusion: Difficult to correlate readings");
    Serial.println("- Industrial control: Timing-sensitive operations fail");
    Serial.println();

    // Visual jitter demo with LEDs
    Serial.println("Demonstrating jitter with LEDs...");

    // Low jitter - consistent timing
    Serial.println("  Low jitter (consistent blinks):");
    for (int i = 0; i < 5; i++) {
        digitalWrite(LED_LOW_LATENCY, HIGH);
        delay(100);
        digitalWrite(LED_LOW_LATENCY, LOW);
        delay(100);
    }

    delay(500);

    // High jitter - inconsistent timing
    Serial.println("  High jitter (erratic blinks):");
    int jitterDelays[] = {50, 200, 30, 300, 80};
    for (int i = 0; i < 5; i++) {
        digitalWrite(LED_HIGH_LATENCY, HIGH);
        delay(jitterDelays[i]);
        digitalWrite(LED_HIGH_LATENCY, LOW);
        delay(jitterDelays[i]);
    }

    setAllLEDs(false);
}

void demonstrateCongestionConcept() {
    Serial.println("\n+=================================================================+");
    Serial.println("|                MINI-LESSON: NETWORK CONGESTION                  |");
    Serial.println("+=================================================================+");
    Serial.println();
    Serial.println("Congestion occurs when traffic exceeds network capacity");
    Serial.println();
    Serial.println("Normal Operation (30% utilization):");
    Serial.println("  ========================================");
    Serial.println("  ==> ==> ==>    ==>    ==>   ==>       ");
    Serial.println("  ========================================");
    Serial.println("  Packets flow smoothly, low latency");
    Serial.println();
    Serial.println("Congested (90% utilization):");
    Serial.println("  ========================================");
    Serial.println("  ==>==>==>==>==>==>==>==>==>==>==>==>==>");
    Serial.println("  ========================================");
    Serial.println("  ^ Packets queue up, latency increases!");
    Serial.println();
    Serial.println("CONGESTION EFFECTS:");
    Serial.println("- Latency rises sharply (non-linearly) as utilisation approaches capacity");
    Serial.println("- Packet loss increases (buffers overflow)");
    Serial.println("- Jitter becomes unpredictable");
    Serial.println("- Throughput may actually DECREASE");
    Serial.println();
    Serial.println("TCP CONGESTION COLLAPSE:");
    Serial.println("When packet loss triggers retransmissions,");
    Serial.println("which cause more congestion, which causes");
    Serial.println("more loss... throughput can drop to near zero!");
    Serial.println();

    // Visual demo - congestion building
    Serial.println("Simulating congestion buildup...");

    digitalWrite(LED_LOW_LATENCY, HIGH);
    Serial.println("  Network normal... [GREEN]");
    delay(1000);

    digitalWrite(LED_LOW_LATENCY, LOW);
    digitalWrite(LED_TRANSMIT, HIGH);
    Serial.println("  Traffic increasing... [YELLOW]");
    delay(1000);

    digitalWrite(LED_TRANSMIT, LOW);
    digitalWrite(LED_HIGH_LATENCY, HIGH);
    Serial.println("  Latency rising... [RED]");
    delay(1000);

    digitalWrite(LED_CONGESTION, HIGH);
    Serial.println("  CONGESTION DETECTED! [BLUE]");
    delay(1500);

    setAllLEDs(false);
    Serial.println("  Traffic cleared, network recovering...");
}