Two WDM technologies for EPON data transmission
Time: 2014-09-30 Published by: Fiberall China
EPON use WDM technology to realize bidirectional (Bi-Di) transmission via single fiber.
In order to separate uplink and downlink signals for different users, adopt two different WDM technologies as below:
(1)Use broadcast for upstream:
Assign a unique LLID after the OUN is registered;
Add a LLID before each Ethernet frame, replace the last two bytes of the Ethernet preamble (without changing the original frame structure);
The ONU only receive frame which is compatible with its own LLID or broadcast frames.
(2)Use TDM for downstream:
Principle: the system can not work normally when only one ONU send uplink signal;
Different ONU assign different time slices and take turns to transmit upstream; time slice of each ONU upstream can be dynamic, time slice size and number present as bandwidth size macroscopically.
Since the data rate is very high, so subtle delay which is aroused by different ONU distance has to be considered when upstream is sending and distance measurement is necessary.