1. Field
The following description relates to time synchronization technology, and more particularly, to a parallel processing-based time synchronization apparatus, which provides more precise and reliable time synchronization between a master device and a slave device based on parallel processing.
2. Description of the Related Art
In general, to establish time synchronization between at least two devices located in a packet switching network, a protocol specific for time synchronization is required. A device which provides a reference time for the time synchronization is set as a master, and a device which is to be time synchronized to the master device is set as a slave, and then a message containing time information of each device is exchanged between the master and the slave to realize the time synchronization therebetween.
Packet switching networks which deploy low cost Ethernet technologies are gradually replacing circuit switching networks, and the need for high precision time synchronization protocol is increasing for a real time streaming service. To this end, the Institute of Electrical and Electronics Engineers (IEEE) has developed and standardized the precision time protocol (PTP) which is a synchronization protocol with high precision.
FIG. 1 illustrates a diagram of a procedure of establishing time synchronization between a master device and a slave device according to the PTP. The PTP is a synchronization protocol that synchronizes a slave device to a master device by allowing the slave and master devices to exchange synchronization messages, each of which is formed of synchronization packets and delay packets and contains Time of Day (ToD) which is time information, at intervals of a predetermined period TP when clocks of the devices to be synchronized have a master-slave relationship.
According to the synchronization protocol, the slave device computes differences (hereinafter, referred to as “time offset”) between its time information and time information of the master device at intervals of a synchronization message exchange period of the synchronization protocol by use of Equations 1 and 2 below, and filters the computed value using a filter to obtain a filtered time offset value. The slave device uses the filtered time offset value to adjust time information and frequency information driven by a local clock, thereby establishing time synchronization with the master device.Propagation delay Dly=[(TM4−TM1)−(TS3−TS2)]/2  (1)Time offset Offs=TS2−TM1−Dly  (2)
Here, Offs represents a time offset value between a master device and a slave device, and Dly represents a propagation delay value between the master device and the slave device. Furthermore, TM1/represents time information about when a synchronization packet departs from the master device, TM4 represents time information about when a delay packet arrives at the master device, TS2 represents time information about when the synchronization packet arrives at the slave device, and TS3 represents time information about when the delay packet departs from the slave device.
The precision of the time synchronization indicates the degree of accuracy in time synchronization between a master device and a slave device through computation of a time offset value and delay time. Factors that improve the precision of the time synchronization include a synchronization message exchange period, a filter design, and a time stamping method.
For example, to achieve high precision time synchronization, the synchronization message exchange period may be shortened, a low-pass filter may be designed to have a narrow bandwidth or time stamping procedures for identifying starting or arrival time of synchronization messages may be implemented in a hardware fashion so that precision of a time stamp value can be increased.
In general, a series of procedures for time synchronization using synchronization protocol are implemented by software, except for a time stamp procedure. However, when it is required to accelerate the synchronization message exchange period for higher precision time synchronization, or when the load of general packets to be processed by software is increased, it is difficult to update a filter output computed by software to the slave device at each synchronization message exchange period, and if delays occur periodically, the updating of time information is accordingly delayed. Thus it becomes very difficult for reliable time synchronization to be achieved.
Moreover, when the entire time information value of the slave device is simultaneously changed in order to update a time offset value computed at each synchronization message exchange period to the slave device, phase changes abruptly occur according to the change of the time information, and as a result a problem occurs which leads to the phase noise of a reference clock generated based on the slave device increasing.
That is, when time synchronization is performed in a software manner, a processing speed is decreased due to overload of the operation processing or short synchronization message exchange period, and hence time synchronization performance deterioration and failure in synchronization may occur. On the other hand, when the time synchronization is performed in a hardware manner in order to expedite the processing speed, the design of such hardware and implementation thereof may be complicated. Thus, a need for a technology providing a more precise and reliable time synchronization between a slave device and a master device is increasing.