Analysis of GPON and EPON Time Synchronization Technology (Part 3)

- Aug 16, 2019-

EPON/10G EPON Time Synchronization Standard

The time synchronization mechanism of EPON/10G EPON is shown in Figure 2.

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EPON/10G EPON Time Synchronization Mechanism www.elecfans.com

Figure 2 EPON/10G EPON time synchronization mechanism

The specific steps of the method shown in Figure 2 are as follows:

(1) OLT first synchronizes with the completion time of the superior equipment.

(2) OLT calculates ToDx, I when the local time of ONUi is X.

(3) OLT informs ONUi of ToDx when localTime is X through OSSP message.

(4) When ONUi receives the OSSP message, it compensates ToDx and I to get the time real_ToDx, I when the exact local time is X.

(5) When the local time count reaches X, ONUi sets the local time to real_ToDx, I is the completion of time synchronization.

The error of this scheme is mainly introduced by three parts: different up/down wavelength, Serdes, ranging. Similar to GPON.

Because the upstream/downstream wavelength of EPON is the same as the upstream/downstream wavelength of GPON, the error of the upstream/downstream wavelength of EPON is the same.

The error introduced by the Serdes part is the same, except that the EPON rate is low, and the error introduced is (+12.8ns).

In the ranging part, the guard Threshold OLT threshold of EPON is 12 TIme Quantas, each time Quanta is 16 ns, converted to 192ns, and the maximum error introduced in one-way delay is 96 ns (but the worst case is a small probability event, which usually does not occur). This error cannot be compensated without changing the existing EPON standard. Payment.

In summary, for the errors introduced by different upstream and downstream wavelengths, it is about 17 ns at the limit of 20 km, which can be compensated by simple calculation; for the errors introduced by the series-to-parallel conversion of Serdes, the error can also be compensated by using 16 bit wide Serdes, but the implementation is more complicated and not pushed. Recommended; for the error introduced in ranging, it is 96 ns, which can not be compensated without changing the existing standard; therefore, the theoretical accuracy can reach 96 ns when all compensation is realized; without any compensation, the accuracy is within 130ns; and the error analysis of 10G EPON is similar.

The scheme was discussed at the IEEE 802.1AS meeting in January 2009, and was approved by the majority of participants. It is considered that the scheme is simple to implement by using the results of EPON/10G EPON ranging and the synchronization mechanism of EPON/10G EPON itself. At present, 802.1AS standard is basically finalized, and the scheme has been covered by the formal content of standard text.


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