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FAQ-What Are the Meanings of the OLT Recovery Time and ONU Switching Time

Publication Date:  2012-07-25 Views:  47 Downloads:  0
Issue Description
Q:
In the GPON and EPON accesses, the OLT recovery time and ONU switching time are specified in protocols. What are their meanings? 
 
Alarm Information
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Handling Process
A:
1. OLT recovery time refers to the time required for obtaining the clock information from the upstream burst data that is received by the OLT from the ONU.
2. ONU switching time refers to the duration from the time when the optical transceiver is started to the time when the expected optical power is reached plus the duration from the time when the expected power is reached to the time when the optical transceiver is closed, when the ONU sends upstream burst data to the OLT in the TDMA mode.
3. In the GPON, the OLT recovery time is 60.8 ns and the ONU switching time is 12.8 ns.
4. In the EPON, the OLT recovery time is 400 ns and the ONU switching time is 512 ns. 
 
Root Cause
The OLT recovery time and ONU switching time in the GPON and EPON are specified in the ITU-T984 and IEEE802.3ah protocols respectively. They are one of the performance indexes of the optical transceiver. 
Suggestions
The OLT recovery time and ONU switching time are one of the important indexes of the optical transceiver in the GPON and EPON. If the time is very long, performances, such as the DBA efficiency are affected. If the time is very short, requirements on the optical transceiver are high and thus the device cost is affected. 

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