SNTP/NTP Tutorial
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# Namespaces and assemblies
SNTP (Simple Network Time Protocol) described in RFC 2030
is used to synchronize computer clocks in the Internet. For list of publicly available SNTP and NTP server,
check out ntp.isc.org website.
To use the features of Rebex for .NET described here, reference
the Rebex.Net.Time.dll assembly from your project.
It contains the Ntp and other classes in Rebex.Net namespace.
In your source files, import the following namespace:
C#
using Rebex.Net;
VB.NET
Imports Rebex.Net
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# Synchronizing local time with time server
Synchronizing the local time with a time server is a single line operation. Just use the static SynchronizeSystemClock method of the Ntp class.
C#
Ntp.SynchronizeSystemClock("pool.ntp.org");
VB.NET
Ntp.SynchronizeSystemClock("pool.ntp.org")
If you need to specify some properties such as SNTP protocol version or maximum timeout,
a slightly different code is required:
C#
// initialize the Ntp object
Ntp ntp = new Ntp("pool.ntp.org");
// set timeout to 5 seconds
ntp.Timeout = 5000;
// set the desired NTP version
ntp.VersionNumber = 4;
// sync local clock
ntp.SynchronizeSystemClock();
VB.NET
' initialize the Ntp object
Dim ntp As Ntp = New Ntp("pool.ntp.org")
' set timeout to 5 seconds
ntp.Timeout = 5000
' set the desired NTP version
ntp.VersionNumber = 4
' sync local clock
ntp.SynchronizeSystemClock()
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# Determining the time difference between the local time and a time server
To obtain more info from a NTP/SNTP server, create a Ntp instance and call the GetTime method.
The returned NtpResponse contains the TimeOffset property which contains the time difference between the
local computer and a remote time server.
C#
// initialize the Ntp object
Ntp ntp = new Ntp("pool.ntp.org");
// get server time
NtpResponse response = ntp.GetTime();
// get time difference
Console.WriteLine("Time difference is {0}", response.TimeOffset);
VB.NET
' initialize the Ntp object
Dim ntp As New Ntp("pool.ntp.org")
' get server time
Dim response As NtpResponse = ntp.GetTime()
' show the time difference
Console.WriteLine("Time difference is {0}", response.TimeOffset)
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# Retrieving more SNTP/NTP server details
You might also want to know whether the time server is Stratum 1 (primary and intended for synchronization between time servers) or Stratum 2 (for general use)
or determine the supported protocol version. This and other info is available through the NtpPacket class, which is accessible as a Packet
property of the NtpResponse:
C#
// initialize the Ntp object
Ntp ntp = new Ntp("pool.ntp.org");
// since we want to know the highest version the server supports, we
// must announce the highest ourselves (otherwise the server would use
// the compatibility mode)
ntp.VersionNumber = 4;
// get info from the NTP server
NtpResponse response = ntp.GetTime();
NtpPacket packet = response.Packet;
// server stratum and NTP version
Console.WriteLine("Server has stratum {0} and runs NTP version {1}.",
packet.Stratum,
packet.VersionNumber);
// processing time
Console.WriteLine("It received our request at {0} UTC and responded to it at {1} UTC.",
packet.ReceiveTimestamp,
packet.TransmitTimestamp);
// desired time
Console.WriteLine("Local time is {0} and should be adjusted by {1}",
DateTime.Now,
response.TimeOffset.ToTimeSpan()
);
VB.NET
' initialize the Ntp object
Dim ntp As New Ntp("pool.ntp.org")
' since we want to know the highest version the server supports, we
' must announce the highest ourselves (otherwise the server would use
' the compatibility mode)
ntp.VersionNumber = 4
' get info from NTP server
Dim response As NtpResponse = ntp.GetTime()
Dim packet As NtpPacket = response.Packet
' server stratum and NTP version
Console.WriteLine("Server has stratum {0} and runs NTP version {1}.", _
packet.Stratum, packet.VersionNumber)
' processing time
Console.WriteLine("It received our request at {0} UTC and responded to it at {1} UTC.", _
packet.ReceiveTimestamp, _
packet.TransmitTimestamp)
' desired time
Console.WriteLine("Local time is {0} and should be adjusted by {1}", _
DateTime.Now, _
response.TimeOffset.ToTimeSpan())
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# Converting between NTP and .NET time formats
SNTP uses its own time format with different precision than .NET Framework. Rebex Time component encapsulates
this information in NtpTimestamp and NtpTimestampDifference value types. The
NtpTimestamp contains the time as received from a NTP server and NtpTimestampDifference contains
a difference between two timestamps.
The following table shows the most commonly-used methods and properties of the classes mentioned above.
NtpTimestamp properties and conversion methods |
|---|
| Property/Method | Description |
|---|
byte[] ToArray() | 8 bytes of raw data as received from the server. |
DateTime ToLocalTime() | The time represented as .NET's DateTime and adjusted to the local time zone. |
DateTime ToUniversalTime() | The time represented as .NET's DateTime in UTC. |
int ToUnixTime() | The number of seconds since the beginning of the Unix epoch (January 1st, 1970). |
int Microseconds | The sub-second part of the time difference, on microsecond scale. A number between 0 and 10^6-1. |
TimestampDifference properties and conversion methods |
|---|
| Property/Method | Description |
|---|
TimeSpan ToTimeSpan() | Converts the difference to .NET's TimeSpan. |
int Microseconds | The sub-second part of the time difference, on microsecond scale. A number between -10^6+1 and 10^6-1. |
double TotalSeconds | The value of this instance expressed in whole and fractional seconds. |
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# Changing the local system time
Rebex Time now includes the Rebex.SystemClock class that enables you to change
the local computer clock.
The SetClock method sets the local clock the specified time value.
C#
using Rebex;
...
// display the original local time
Console.WriteLine("Current time is {0}", DateTime.Now);
// change the current time to the end of Maya calendar
// to see what the end of mankind looks like...
SystemClock.SetClock(new DateTime(2012, 12, 21));
Console.WriteLine("Current time is {0}", DateTime.Now);
VB.NET
Imports Rebex
...
' display the original local time
Console.WriteLine("Current time is {0}", DateTime.Now)
' change the current time to the end of Maya calendar
' to see what the end of mankind looks like...
SystemClock.SetClock(New DateTime(2012, 12, 21))
Console.WriteLine("Current time is {0}", DateTime.Now)
The AdjustClock moves the local clock by the specified NtpTimestampDifference value,
for example by the TimeOffset received from an NTP server.
C#
// get the time difference
NtpTimestampDifference difference = new Ntp("pool.ntp.org").GetTime().TimeOffset;
// adjust the time by the difference
SystemClock.AdjustClock(difference);
VB.NET
' get the time difference
Dim difference As NtpTimestampDifference = New Ntp("pool.ntp.org").GetTime().TimeOffset
' adjust the time by the difference
SystemClock.AdjustClock(difference)
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