org.mjsip.rtp

Class NtpTimeStamp

java.lang.Object

org.mjsip.rtp.NtpTimeStamp

All Implemented Interfaces:

java.lang.Comparable

public class NtpTimeStamp
extends java.lang.Object
implements java.lang.Comparable

Wallclock time (absolute date and time) represented using the timestamp format of the Network Time Protocol (NTP).
It is the absolute time in seconds relative to 0h UTC on January 1, 1900. The full resolution NTP timestamp is a 64-bit unsigned fixed-point number with the integer part in the first 32 bits and the fractional part in the last 32 bits. In some fields where a more compact representation is appropriate, only the middle 32 bits are used; that is, the low 16 bits of the integer part and the high 16 bits of the fractional part. The high 16 bits of the integer part must be determined independently.

Since only 32 bits are used for the integer part, February 7, 2036, at 6h:28m:15s is the last absolute time returned by the method getTime(), while at 6h:28m:16s it wraps and go back to January 1, 1900.
In order to have a longer absolute period, the time returned by method getTime() is within the interval from January 20, 1968, at 4h:14m:8s GMT, until February 26, 2014, at 9h:42m:23s GMT.

However, for RTP purposes, only differences between pairs of NTP timestamps are used. So long as the pairs of timestamps can be assumed to be within 68 years of each other, using modular arithmetic for subtractions and comparisons makes the wraparound irrelevant.

The Network Time Protocol and the timestamp format are defined in RFC 1305 (Network Time Protocol (Version 3) Specification, Implementation and Analysis), and RFC 2030 (Simple Network Time Protocol (SNTP) Version 4 for IPv4, IPv6 and OSI).

Field Summary

Fields

Modifier and Type	Field and Description
static long	NTP_TIME_0 NTP time 0 (Jan 1, 1900), in Java time format (that is from January 1, 1970)

Constructor Summary

Constructors

Constructor and Description
NtpTimeStamp(long time) Creates a new NtpTimeStamp.
NtpTimeStamp(long seconds, long fraction) Creates a new NtpTimeStamp.

Method Summary

Modifier and Type	Method and Description
int	compareTo(java.lang.Object obj) From interface Comparable.
boolean	equals(java.lang.Object obj) Whether it is equal to the specified object.
long	getNtpFraction() Gets the fractional part of NTP seconds.
long	getNtpSeconds() Gets the integer part of NTP seconds.
long	getNtpTime() Gets the NTP timestamp time (in NTP format).
long	getTime() Gets the timestamp time (in Java format, thati is from Java epoch time January 1, 1970).
java.lang.String	toString() Gets a string representation of this object.

Methods inherited from class java.lang.Object

clone, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

NTP_TIME_0

public static final long NTP_TIME_0

NTP time 0 (Jan 1, 1900), in Java time format (that is from January 1, 1970)

See Also:

Constant Field Values

Constructor Detail

NtpTimeStamp

public NtpTimeStamp(long seconds,
                    long fraction)

Creates a new NtpTimeStamp.

Parameters:

seconds - the integer part of NTP seconds (in NTP format, that is from January 1, 1900)

fraction - the fractional part of NTP seconds (in NTP format, that is from January 1, 1900)

NtpTimeStamp

public NtpTimeStamp(long time)

Creates a new NtpTimeStamp.

Parameters:

time - the timestamp time value (in Java format, that is from Java epoch time January 1, 1970)

Method Detail

getNtpTime

public long getNtpTime()

Gets the NTP timestamp time (in NTP format).

Returns:

the NTP timestamp time value (in NTP format).

getNtpSeconds

public long getNtpSeconds()

Gets the integer part of NTP seconds.

Returns:

the seconds of this NTP timestamp.

getNtpFraction

public long getNtpFraction()

Gets the fractional part of NTP seconds.

Returns:

the fractional seconds of this NTP timestamp.

getTime

public long getTime()

Gets the timestamp time (in Java format, thati is from Java epoch time January 1, 1970). It returns the correct time only until February 26, 2014, at 9h:42m:23s GMT; after this date the time wraps and goes back to January 20, 1968, at 4h:14m:8s GMT.

Returns:

the timestamp time value (in Java format, thati is from Java epoch time January 1, 1970)

compareTo

public int compareTo(java.lang.Object obj)
              throws java.lang.ClassCastException

From interface Comparable. Compares this object with the specified object for order.

Specified by:

compareTo in interface java.lang.Comparable

Parameters:

obj - the Object to be compared

Returns:

a negative integer, zero, or a positive integer as this object is less than, equal to, or greater than the specified object

Throws:

java.lang.ClassCastException

equals

public boolean equals(java.lang.Object obj)

Whether it is equal to the specified object.

Overrides:

equals in class java.lang.Object

Parameters:

obj - the Object to be compared

Returns:

true it is equal to the specified object

toString

public java.lang.String toString()

Gets a string representation of this object.

Overrides:

toString in class java.lang.Object