Tanda waktu paket

Pengantar

Banyak kartu antarmuka jaringan (NIC, atau adaptor jaringan) dapat menghasilkan tanda waktu di perangkat keras mereka setiap kali paket diterima atau dikirimkan. Tanda waktu dihasilkan menggunakan jam perangkat keras NIC sendiri. Fitur ini digunakan khususnya oleh Precision Time Protocol (PTP), yang merupakan protokol sinkronisasi waktu. PTP menyediakan untuk menggunakan tanda waktu perangkat keras tersebut dalam protokol itu sendiri.

Tanda waktu dapat, misalnya, digunakan untuk menghitung waktu yang dihabiskan oleh paket dalam tumpukan jaringan komputer sebelum dikirim ke atau diterima dari kawat. Perhitungan tersebut kemudian dapat digunakan oleh PTP untuk meningkatkan akurasi sinkronisasi waktu. Dukungan tanda waktu paket adaptor jaringan diarahkan terkadang khusus untuk protokol PTP. Dalam kasus lain, dukungan yang lebih umum disediakan.

API tanda waktu memberi Windows kemampuan untuk mendukung kemampuan stempel waktu perangkat keras adaptor jaringan untuk protokol PTP versi 2. Secara keseluruhan, fitur ini termasuk menyediakan kemampuan untuk driver adaptor jaringan untuk mendukung tanda waktu, dan untuk aplikasi mode pengguna untuk menggunakan tanda waktu yang terkait dengan paket melalui Windows Sockets (lihat Tanda waktu Winsock). Selain itu, kemampuan untuk menghasilkan tanda waktu perangkat lunak juga tersedia, yang memungkinkan driver jaringan untuk menghasilkan tanda waktu dalam perangkat lunak. Tanda waktu perangkat lunak tersebut dihasilkan oleh driver NIC menggunakan mode kernel yang setara dengan QueryPerformanceCounter (QPC). Namun, mengaktifkan tanda waktu perangkat keras dan perangkat lunak bersama-sama tidak didukung.

Secara khusus, API tanda waktu paket Internet Protocol Helper (IP Helper) yang dijelaskan dalam topik ini menyediakan kemampuan bagi aplikasi mode pengguna untuk menentukan kemampuan tanda waktu adaptor jaringan, dan untuk mengkueri tanda waktu dari adaptor jaringan dalam bentuk tanda waktu silang (dijelaskan di bawah).

Mendukung Protokol Waktu Presisi versi 2

Seperti disebutkan, tujuan utama dukungan tanda waktu di Windows adalah untuk mendukung protokol Protokol Waktu Presisi versi 2 (PTPv2). Dalam PTPv2, tidak semua pesan memerlukan tanda waktu. Secara khusus, pesan peristiwa PTP memang menggunakan tanda waktu. Saat ini, dukungan dilingkupkan ke PTPv2 melalui User Datagram Protocol (UDP). PTP melalui ethernet mentah tidak didukung.

Tanda waktu didukung untuk PTPv2 yang beroperasi dalam mode 2 langkah . 2 langkah mengacu pada mode di mana tanda waktu aktual dalam paket PTP tidak dihasilkan dengan cepat di perangkat keras, tetapi sebaliknya diambil dari perangkat keras dan disampaikan sebagai pesan terpisah (misalnya, menggunakan pesan tindak lanjut).

Singkatnya, Anda dapat menggunakan API tanda waktu paket Internet Protocol Helper (IP Helper), bersama dengan dukungan tanda waktu Winsock, dalam aplikasi PTPv2 untuk meningkatkan akurasi sinkronisasi waktunya.

Mengambil kemampuan penandaan waktu adaptor jaringan

Aplikasi seperti layanan sinkronisasi waktu PTP perlu menentukan kemampuan tanda waktu adaptor jaringan. Dengan menggunakan kemampuan yang diambil, aplikasi kemudian dapat memutuskan apakah aplikasi ingin menggunakan tanda waktu atau tidak.

Bahkan jika adaptor jaringan mendukung tanda waktu, diperlukan untuk menjaga kemampuan dimatikan secara default. Adaptor mengaktifkan tanda waktu saat diinstruksikan untuk melakukannya. Windows menyediakan API untuk aplikasi guna mengambil kemampuan perangkat keras, serta kemampuan mana yang diaktifkan.

Untuk mengambil kemampuan tanda waktu adaptor jaringan yang didukung, Anda memanggil fungsi GetInterfaceSupportedTimestampCapabilities , menyediakan pengidentifikasi unik lokal (LUID) adaptor jaringan, dan sebagai gantinya mengambil kemampuan tanda waktu yang didukung dalam bentuk objek INTERFACE_TIMESTAMP_CAPABILITIES .

Kode yang dikembalikan dari GetInterfaceSupportedTimestampCapabilities menunjukkan apakah panggilan berhasil atau tidak, dan apakah nilai INTERFACE_TIMESTAMP_CAPABILITIES yang diisi diambil atau tidak.

Untuk mengambil kemampuan tanda waktu adaptor jaringan yang saat ini diaktifkan, Anda memanggil fungsi GetInterfaceActiveTimestampCapabilities , menyediakan pengidentifikasi unik lokal (LUID) adaptor jaringan, dan sebagai gantinya mengambil kemampuan tanda waktu yang diaktifkan dalam bentuk objek INTERFACE_TIMESTAMP_CAPABILITIES .

Sekali lagi, kode yang dikembalikan dari GetInterfaceActiveTimestampCapabilities menunjukkan keberhasilan atau kegagalan, dan apakah nilai INTERFACE_TIMESTAMP_CAPABILITIES yang valid diambil atau tidak.

Adaptor jaringan dapat mendukung berbagai kemampuan tanda waktu. Misalnya, beberapa adaptor dapat memberi tanda waktu setiap paket selama pengiriman dan penerimaan, sementara yang lain hanya mendukung paket PTPv2. Struktur INTERFACE_TIMESTAMP_CAPABILITIES menjelaskan kemampuan persis yang didukung adaptor jaringan.

Mengambil tanda waktu silang dari adaptor jaringan

Saat menggunakan tanda waktu perangkat keras, aplikasi PTP perlu membangun hubungan (misalnya, dengan menggunakan teknik matematika yang sesuai) antara jam perangkat keras adaptor jaringan dan jam sistem. Ini diperlukan agar nilai yang mewakili waktu dalam satu unit jam dapat dikonversi menjadi unit jam lain. Tanda waktu silang disediakan untuk tujuan ini, dan aplikasi Anda dapat mengambil sampel tanda waktu silang secara berkala untuk membangun hubungan tersebut.

Untuk melakukannya, panggil fungsi CaptureInterfaceHardwareCrossTimestamp , menyediakan pengidentifikasi unik lokal (LUID) adaptor jaringan, dan sebagai gantinya mengambil tanda waktu dari adaptor jaringan dalam bentuk objek INTERFACE_HARDWARE_CROSSTIMESTAMP .

Pemberitahuan perubahan kapabilitas tanda waktu

Untuk diberi tahu jika kemampuan tanda waktu untuk adaptor jaringan berubah, panggil fungsi RegisterInterfaceTimestampConfigChange , menyediakan pointer ke fungsi panggilan balik yang telah Anda terapkan, bersama dengan konteks yang dialokasikan pemanggil opsional.

RegisterInterfaceTimestampConfigChange mengembalikan handel yang kemudian dapat Anda teruskan ke UnregisterInterfaceTimestampConfigChange untuk membatalkan pendaftaran fungsi panggilan balik Anda.

Contoh kode 1—mengambil kemampuan tanda waktu dan tanda waktu silang

// main.cpp in a Console App project.

#include <stdio.h>
#include <winsock2.h>
#include <iphlpapi.h>
#pragma comment(lib, "Iphlpapi")

BOOL
IsPTPv2HardwareTimestampingSupportedForIPv4(PINTERFACE_TIMESTAMP_CAPABILITIES timestampCapabilities)
{
    // Supported if both receive and transmit side support is present
    if (((timestampCapabilities->HardwareCapabilities.PtpV2OverUdpIPv4EventMessageReceive) ||
         (timestampCapabilities->HardwareCapabilities.PtpV2OverUdpIPv4AllMessageReceive) ||
         (timestampCapabilities->HardwareCapabilities.AllReceive))
         &&
        ((timestampCapabilities->HardwareCapabilities.PtpV2OverUdpIPv4EventMessageTransmit) ||
         (timestampCapabilities->HardwareCapabilities.PtpV2OverUdpIPv4AllMessageTransmit) ||
         (timestampCapabilities->HardwareCapabilities.TaggedTransmit) ||
         (timestampCapabilities->HardwareCapabilities.AllTransmit)))
    {
        return TRUE;
    }

    return FALSE;
}

BOOL
IsPTPv2HardwareTimestampingSupportedForIPv6(PINTERFACE_TIMESTAMP_CAPABILITIES timestampCapabilities)
{
    // Supported if both receive and transmit side support is present
    if (((timestampCapabilities->HardwareCapabilities.PtpV2OverUdpIPv6EventMessageReceive) ||
         (timestampCapabilities->HardwareCapabilities.PtpV2OverUdpIPv6AllMessageReceive) ||
         (timestampCapabilities->HardwareCapabilities.AllReceive))
         &&
        ((timestampCapabilities->HardwareCapabilities.PtpV2OverUdpIPv6EventMessageTransmit) ||
         (timestampCapabilities->HardwareCapabilities.PtpV2OverUdpIPv6AllMessageTransmit) ||
         (timestampCapabilities->HardwareCapabilities.TaggedTransmit) ||
         (timestampCapabilities->HardwareCapabilities.AllTransmit)))
    {
        return TRUE;
    }

    return FALSE;
}

enum SupportedTimestampType
{
    TimestampTypeNone = 0,
    TimestampTypeSoftware = 1,
    TimestampTypeHardware = 2
};

// This function checks and returns the supported timestamp capabilities for an interface for
// a PTPv2 application
SupportedTimestampType
CheckActiveTimestampCapabilitiesForPtpv2(NET_LUID interfaceLuid)
{
    DWORD result = NO_ERROR;
    INTERFACE_TIMESTAMP_CAPABILITIES timestampCapabilities;
    SupportedTimestampType supportedType = TimestampTypeNone;

    result = GetInterfaceActiveTimestampCapabilities(
                 &interfaceLuid,
                 &timestampCapabilities);
    if (result != NO_ERROR)
    {
        printf("Error retrieving hardware timestamp capabilities: %d\n", result);
        goto Exit;
    }

    if (IsPTPv2HardwareTimestampingSupportedForIPv4(&timestampCapabilities) &&
        IsPTPv2HardwareTimestampingSupportedForIPv6(&timestampCapabilities))
    {
        supportedType = TimestampTypeHardware;
        goto Exit;
    }
    else
    {
        if ((timestampCapabilities.SoftwareCapabilities.AllReceive) &&
            ((timestampCapabilities.SoftwareCapabilities.AllTransmit) ||
             (timestampCapabilities.SoftwareCapabilities.TaggedTransmit)))
        {
            supportedType = TimestampTypeSoftware;
        }
    }

Exit:
    return supportedType;
}

// Helper function which does the correlation between hardware and system clock
// using mathematical techniques
void ComputeCorrelationOfHardwareAndSystemTimestamps(INTERFACE_HARDWARE_CROSSTIMESTAMP *crossTimestamp);

// An application would call this function periodically to gather a set 
// of matching timestamps for use in converting hardware timestamps to
// system timestamps
DWORD
RetrieveAndProcessCrossTimestamp(NET_LUID interfaceLuid)
{
    DWORD result = NO_ERROR;
    INTERFACE_HARDWARE_CROSSTIMESTAMP crossTimestamp;

    result = CaptureInterfaceHardwareCrossTimestamp(
                 &interfaceLuid,
                 &crossTimestamp);
    if (result != NO_ERROR)
    {
        printf("Error retrieving cross timestamp for the interface: %d\n", result);
        goto Exit;
    }

    // Process crossTimestamp further to create a relation between the hardware clock
    // of the NIC and the QPC values using appropriate mathematical techniques
    ComputeCorrelationOfHardwareAndSystemTimestamps(&crossTimestamp);

Exit:
    return result;
}

int main()
{
}

Contoh kode 2—mendaftar untuk pemberitahuan perubahan kemampuan tanda waktu

Contoh ini menunjukkan bagaimana aplikasi Anda dapat menggunakan tanda waktu secara end to end.

// main.cpp in a Console App project.

#include <stdlib.h>
#include <stdio.h>
#include <winsock2.h>
#include <mswsock.h>
#include <iphlpapi.h>
#include <mstcpip.h>
#pragma comment(lib, "Ws2_32")
#pragma comment(lib, "Iphlpapi")

// Globals and function declarations used by the application.
// The sample functions and skeletons demonstrate:
// - Checking timestamp configuration for an interface to determine if timestamping can be used
// - If timestamping is enabled, starts tracking changes in timestamp configuration
// - Performing correlation between hardware and system timestamps using cross timestamps
//   on a separate thread depending on the timestamp type configured
// - Receiving a packet and computing the latency between when the timestamp
//   was generated on packet reception, and when the packet was received by
//   the application through the socket
// The sample tries to demonstrate how an application could use timestamps. It is not thread safe 
// and does not do exhaustive error checking.
// Lot of the functions are provided as skeletons, or only declared and invoked
// but are not defined. It is up to
// the application to implement these suitably.

// An application could use the functions below by e.g.
// - Call InitializeTimestampingForInterface for the interface it wants to track for timestamping capability.
// - Call EstimateReceiveLatency to estimate the receive latency of a packet depending on the timestamp 
//   type configured for the interface.

enum SupportedTimestampType
{
    TimestampTypeNone = 0,
    TimestampTypeSoftware = 1,
    TimestampTypeHardware = 2
};

// interfaceBeingTracked is the interface the PTPv2 application
// intends to use for timestamping purpose.
wchar_t* interfaceBeingTracked;

// The active timestamping type determined for
// interfaceBeingTracked.
SupportedTimestampType timestampTypeEnabledForInterface;

HANDLE correlationThread;
HANDLE threadStopEvent;
HIFTIMESTAMPCHANGE TimestampChangeNotificationHandle = NULL;

// Function from sample above to check if an interface supports timestamping for PTPv2.
SupportedTimestampType CheckActiveTimestampCapabilitiesForPtpv2(NET_LUID interfaceLuid);

// Function from sample above to retrieve cross timestamps and process them further.
DWORD RetrieveAndProcessCrossTimestamp(NET_LUID interfaceLuid);

// Helper function which registers for timestamp configuration changes.
DWORD RegisterTimestampChangeNotifications();

// Callback function which is invoked when timestamp configuration changes
// for some network interface.
INTERFACE_TIMESTAMP_CONFIG_CHANGE_CALLBACK TimestampConfigChangeCallback;

// Function which does the correlation between hardware and system clock
// using mathematical techniques. It is periodically invoked and provided
// a sample of cross timestamp to compute a correlation.
void ComputeCorrelationOfHardwareAndSystemTimestamps(INTERFACE_HARDWARE_CROSSTIMESTAMP *crossTimestamp);

// Helper function which converts a hardware timestamp from the NIC clock
// to system timestamp (QPC) values. It is assumed that this works together
// with the ComputeCorrelationOfHardwareAndSystemTimestamps function
// to derive the correlation.
ULONG64 ConvertHardwareTimestampToQpc(ULONG64 HardwareTimestamp);

// Start function of thread which periodically samples
// cross timestamps to correlate hardware and software timestamps.
DWORD WINAPI CorrelateHardwareAndSystemTimestamps(LPVOID);

// Helper function which starts a new thread at CorrelateHardwareAndSystemTimestamps.
DWORD StartCorrelatingHardwareAndSytemTimestamps();

// Helper function which restarts correlation when some change is detected.
DWORD RestartCorrelatingHardwareAndSystemTimestamps();

// Stops the correlation thread.
DWORD StopCorrelatingHardwareAndSystemTimestamps();

DWORD
FindInterfaceFromFriendlyName(wchar_t* friendlyName, NET_LUID* interfaceLuid)
{
    DWORD result = 0;
    ULONG flags = 0;
    ULONG outBufLen = 0;
    PIP_ADAPTER_ADDRESSES pAddresses = NULL;
    PIP_ADAPTER_ADDRESSES currentAddresses = NULL;

    result = GetAdaptersAddresses(0,
        flags,
        NULL,
        pAddresses,
        &outBufLen);
    if (result == ERROR_BUFFER_OVERFLOW)
    {
        pAddresses = (PIP_ADAPTER_ADDRESSES)malloc(outBufLen);

        result = GetAdaptersAddresses(0,
            flags,
            NULL,
            pAddresses,
            &outBufLen);
        if (result != NO_ERROR)
        {
            goto Done;
        }
    }
    else if (result != NO_ERROR)
    {
        goto Done;
    }

    currentAddresses = pAddresses;
    while (currentAddresses != NULL)
    {
        if (wcscmp(friendlyName, currentAddresses->FriendlyName) == 0)
        {
            result = ConvertInterfaceIndexToLuid(currentAddresses->IfIndex, interfaceLuid);
            goto Done;
        }

        currentAddresses = currentAddresses->Next;
    }

    result = ERROR_NOT_FOUND;

Done:

    if (pAddresses != NULL)
    {
        free(pAddresses);
    }

    return result;
}

// This function checks if an interface is suitable for
// timestamping for PTPv2. If so, it registers for timestamp
// configuration changes and initializes some globals.
// If hardware  timestamping is enabled it also starts
// correlation thread.
DWORD
InitializeTimestampingForInterface(wchar_t* friendlyName)
{
    DWORD error;
    SupportedTimestampType supportedType = TimestampTypeNone;

    NET_LUID interfaceLuid;

    error = FindInterfaceFromFriendlyName(friendlyName, &interfaceLuid);
    if (error != 0)
    {
        return error;
    }

    supportedType = CheckActiveTimestampCapabilitiesForPtpv2(interfaceLuid);

    if (supportedType != TimestampTypeNone)
    {
        error = RegisterTimestampChangeNotifications();
        if (error != NO_ERROR)
        {
            return error;
        }

        if (supportedType == TimestampTypeHardware)
        {
            threadStopEvent = CreateEvent(
                NULL,
                FALSE,
                FALSE,
                NULL
            );
            if (threadStopEvent == NULL)
            {
                return GetLastError();
            }            

            error = StartCorrelatingHardwareAndSytemTimestamps();
            if (error != 0)
            {
                return error;
            }
        }

        interfaceBeingTracked = friendlyName;
        timestampTypeEnabledForInterface = supportedType;

        return error;
    }

    return ERROR_NOT_SUPPORTED;
}

DWORD
RegisterTimestampChangeNotifications()
{
    DWORD retcode = NO_ERROR;

    // Register with NULL context
    retcode = RegisterInterfaceTimestampConfigChange(TimestampConfigChangeCallback, NULL, &TimestampChangeNotificationHandle);
    if (retcode != NO_ERROR)
    {
        printf("Error when calling RegisterIfTimestampConfigChange %d\n", retcode);
    }

    return retcode;
}

// The callback invoked when change in some interface’s timestamping configuration
// happens. The callback takes appropriate action based on the new capability of the
// interface. The callback assumes that there is only 1 NIC. If multiple NICs are being
// tracked for timestamping then the application would need to check all of them.
VOID
WINAPI
TimestampConfigChangeCallback(
    _In_ PVOID /*CallerContext*/
    )
{
    SupportedTimestampType supportedType;

    NET_LUID interfaceLuid;
    DWORD error;

    error = FindInterfaceFromFriendlyName(interfaceBeingTracked, &interfaceLuid);
    if (error != NO_ERROR)
    {
        if (timestampTypeEnabledForInterface == TimestampTypeHardware)
        {
            StopCorrelatingHardwareAndSystemTimestamps();
            timestampTypeEnabledForInterface = TimestampTypeNone;
        }
        return;
    }

    supportedType = CheckActiveTimestampCapabilitiesForPtpv2(interfaceLuid);

    if ((supportedType == TimestampTypeHardware) &&
        (timestampTypeEnabledForInterface == TimestampTypeHardware))
    {
        // NIC could have been restarted, restart the correlation between hardware and 
        // system timestamps.
        RestartCorrelatingHardwareAndSystemTimestamps();
    }
    else if (supportedType == TimestampTypeHardware)
    {
        // Start thread correlating hardware and software timestamps
        StartCorrelatingHardwareAndSytemTimestamps();
    }
    else if (supportedType != TimestampTypeHardware)
    {
        // Hardware timestamps are not enabled, stop correlation
        StopCorrelatingHardwareAndSystemTimestamps();
    }

    timestampTypeEnabledForInterface = supportedType;
}

DWORD 
StartCorrelatingHardwareAndSytemTimestamps()
{
    // Create a new thread which starts at CorrelateHardwareAndSoftwareTimestamps
    correlationThread = CreateThread(
        NULL,
        0,
        CorrelateHardwareAndSystemTimestamps,
        NULL,
        0,
        NULL); 

    if (correlationThread == NULL)
    {
        return GetLastError();
    }
}

// Thread which periodically invokes functions to 
// sample cross timestamps and use them to compute
// correlation between hardware and system timestamps.
DWORD WINAPI
CorrelateHardwareAndSystemTimestamps(LPVOID /*lpParameter*/)
{
    DWORD error;
    NET_LUID interfaceLuid;
    DWORD result;

    result = FindInterfaceFromFriendlyName(interfaceBeingTracked, &interfaceLuid);
    if (result != 0)
    {
        return result;
    }

    while (TRUE)
    {
        error = RetrieveAndProcessCrossTimestamp(interfaceLuid);

        // Sleep and repeat till the thread gets a signal to stop
        result = WaitForSingleObject(threadStopEvent, 5000);
        if (result != WAIT_TIMEOUT)
        {
            if (result == WAIT_OBJECT_0)
            {
                return 0;
            }
            else if (result == WAIT_FAILED)            
            {
                return GetLastError();
            }

            return result;
        }
    }
}

DWORD
StopCorrelatingHardwareAndSystemTimestamps()
{
    SetEvent(threadStopEvent);
    return 0;
}

// Function which receives a packet and estimates the latency between the 
// point at which receive timestamp (of appropriate type) was generated
// and when the packet was received in the app through the socket.
// The sample assumes that there is only 1 NIC in the system. This is the NIC which is tracked through
// interfaceBeingTracked for correlation purpose, and through which packets are being
// received by the socket.
// The recvmsg parameter is of type LPFN_WSARECVMSG and an application can
// retrieve it by issuing WSAIoctl
// with SIO_GET_EXTENSION_FUNCTION_POINTER control
// and WSAID_WSARECVMSG. Please refer to msdn.
void EstimateReceiveLatency(SOCKET sock, LPFN_WSARECVMSG recvmsg)
{
    DWORD numBytes;
    INT error;
    CHAR data[512];
    CHAR control[WSA_CMSG_SPACE(sizeof(UINT64))] = { 0 };
    WSABUF dataBuf;
    WSABUF controlBuf;
    WSAMSG wsaMsg;
    UINT64 socketTimestamp = 0;
    ULONG64 appLevelTimestamp;
    ULONG64 packetReceivedTimestamp;

    dataBuf.buf = data;
    dataBuf.len = sizeof(data);
    controlBuf.buf = control;
    controlBuf.len = sizeof(control);
    wsaMsg.name = NULL;
    wsaMsg.namelen = 0;
    wsaMsg.lpBuffers = &dataBuf;
    wsaMsg.dwBufferCount = 1;
    wsaMsg.Control = controlBuf;
    wsaMsg.dwFlags = 0;

    // Configure rx timestamp reception.
    TIMESTAMPING_CONFIG config = { 0 };
    config.Flags |= TIMESTAMPING_FLAG_RX;
    error =
        WSAIoctl(
            sock,
            SIO_TIMESTAMPING,
            &config,
            sizeof(config),
            NULL,
            0,
            &numBytes,
            NULL,
            NULL);
    if (error == SOCKET_ERROR)
    {
        printf("WSAIoctl failed %d\n", WSAGetLastError());
        return;
    }

    error =
        recvmsg(
            sock,
            &wsaMsg,
            &numBytes,
            NULL,
            NULL);
    if (error == SOCKET_ERROR)
    {
        printf("recvmsg failed %d\n", WSAGetLastError());
        return;
    }

    if (timestampTypeEnabledForInterface != TimestampTypeNone)
    {
        // Capture system timestamp (QPC) upon message reception.
        LARGE_INTEGER t1;
        QueryPerformanceCounter(&t1);
        appLevelTimestamp = t1.QuadPart;

        printf("received packet\n");

        // Look for socket rx timestamp returned via control message.
        BOOLEAN retrievedTimestamp = FALSE;
        PCMSGHDR cmsg = WSA_CMSG_FIRSTHDR(&wsaMsg);
        while (cmsg != NULL)
        {
            if (cmsg->cmsg_level == SOL_SOCKET && cmsg->cmsg_type == SO_TIMESTAMP)
            {
                socketTimestamp = *(PUINT64)WSA_CMSG_DATA(cmsg);
                retrievedTimestamp = TRUE;
                break;
            }
            cmsg = WSA_CMSG_NXTHDR(&wsaMsg, cmsg);
        }

        if (retrievedTimestamp)
        {
            // Compute socket receive path latency.
            LARGE_INTEGER clockFrequency;
            ULONG64 elapsedMicroseconds;

            if (timestampTypeEnabledForInterface == TimestampTypeHardware)
            {
                packetReceivedTimestamp = ConvertHardwareTimestampToQpc(socketTimestamp);
            }
            else
            {
                packetReceivedTimestamp = socketTimestamp;
            }
        
            QueryPerformanceFrequency(&clockFrequency);

            // Compute socket receive path latency.
            elapsedMicroseconds = appLevelTimestamp - packetReceivedTimestamp;
            elapsedMicroseconds *= 1000000;
            elapsedMicroseconds /= clockFrequency.QuadPart;
            printf("RX latency estimation: %lld microseconds\n",
                 elapsedMicroseconds);
        }
        else
        {
            printf("failed to retrieve RX timestamp\n");
        }
    }
}

int main()
{
}