H3C Technologies H3C S7500E Series Switches - Manual (Page 44)

3-2
ONU. By configuring a maximum RTT at the OLT side, you can set the coverage range of the EPON
system. An ONU whose RTT is greater than the RTT configured on the OLT cannot be registered.
Setting a short RTT prevents ONUs too far away from the OLT from being registered with the EPON
system (a far-away ONU suffers high optical power attenuation). Setting a long RTT can expand the
coverage range of the EPON system, allowing as many ONUs as possible to be registered
successfully.
The process of RTT measurement is as follows:
1) The OLT sends an ONU a discovery GATE message containing the OLT local time T
0
, namely,
the time stamp in the discovery GATE message is T
0.
2) Upon receiving the discovery GATE message, the ONU modifies its local time to be the time
stamp T
0
in the message and sends a REGISTER_REQ message to the OLT at T
1
after a delay
(the time stamp of the REGISTER_REQ message is T
1
).
3) The OLT receives the REGISTER_REQ message at T
2
.
4) The OLT calculates the ONU RTT by using the formula: RTT=(T
2
-T
0
)-(T
1
-T
0
)=T
2
-T
1
.
5) If the OLT becomes idle at T
3
and remains idle for a period of ∆T, the timeslot assigned to the
ONU is { T3-RTT, ∆T }. That is, the ONU will start sending data at T3-RTT and send data for a
period of ∆T.
Follow these steps to configure EPON system parameters:
To do… Use the command… Remarks
Enter system view system-view —
Enter OLT port view interface olt interface-number —
Configure the Maximum ONU-OLT
RTT
max-rtt value
Optional
13524 TQ by default
Exit to system view quit —
Enter FTTH view ftth —
Configure OUI and extended OAM
version number list
epon-parameter ouilist { oui
oui-value oam-version
version-value } &<1-9> slot
slot-number
Required
By default, the OUI and extended
OAM version number must be
configured as 111111 and 1
respectively.
Configure the key update time and
encryption reply timeout time of
the encryption
encryption timer { update
update-time | no-reply-timeout
timeout }* slot slot-number
Optional
By default, the key update time is
10 seconds and the encryption
reply timeout time is 3000
milliseconds.