This clock type can function as grandmaster or slave in the PTP domain.
#NETWORK TIMING SOLUTIONS SOFTWARE#
For devices where there is a delay between the software sending a packet and it leaving a port, the extra delay time is sent in a follow-up packet.
#NETWORK TIMING SOLUTIONS MAC#
To prevent uncertain delays within a switch from causing inaccuracies in the time synchronization, the timestamps are added to packets between the MAC and PHY layer, exactly when a packet enters or leaves a port. Network switches and other devices that include IEEE 1588v2 support have the ability at the hardware level to timestamp packets as they ingress and egress network ports. If a grandmaster clock is no longer available on the network, the Best Master Clock algorithm defines which is the new grandmaster clock and adjusts other clocks accordingly. By accurately measuring the network delays between the grandmaster and slave clocks, precise offsets are determined to keep the slave clocks in synchronization with the grandmaster. The grandmaster clock sends “sync” packets with embedded timestamps to “slave” clocks across the network. PTP uses what is called the Best Master Clock algorithm to determine the most accurate clock in a network, and then synchronizes all other clocks to the “grandmaster” clock. The current PTP protocol provides fault-tolerant synchronization among clocks embedded in devices across a network. The PTP synchronization described in this Technology Brief refers to the IEEE 1588v2 protocol. In 2008, the PTP protocol was revised to be even more accurate, often referred to as IEEE 1588v2 or PTPv2, providing a potential accuracy down to the nanosecond level. Although NTP is capable of millisecond accuracy, this was not accurate enough for some applications and in 2002 a more accurate network synchronization standard was released, called IEEE 1588 or the Precision Time Protocol (PTP). The following table lists some of the more common timing signals and standards that are in use, as well as current network time protocols.įor many years, the Network Time Protocol (NTP) has been the standard method for time synchronization across networks and is still widely used today. Time of day codes, frequency and phase signals in various formats can be found integrated into all kinds of equipment.
The need for time synchronization in radio broadcasts, telecommunications, and test and measurement applications has a long history. To maintain accurate time between network devices requires continuous synchronization from a reference time source that has a more accurate, reliable clock. This reality is due to slight physical differences between crystal oscillators and temperature variations that affect the exact output frequency and therefore the clock time. However, when precise time synchronization is required, it is found that even identical devices still lose synchronization over time. When synchronized time between devices is important, clocks can therefore track the time with good accuracy. Accurate time synchronization in any application therefore involves the distribution of the time of day, frequency, and phase between devices.Īll network devices contain components that count time, typically based on crystal oscillators that output an electrical signal with a precise frequency. Phase synchronization is when two separate repeating events happen at the same point in time. Frequency is the measure of a repeating event within a period of time, normally stated in Hertz or the number of events in a second. Time is measured by clocks, which can simply be defined as a device with a stable source frequency and a counter.
Time of day, frequency, and phase are all-important elements in synchronizing time.