U
U
s
s
e
e
r
r
M
M
a
a
n
n
u
u
a
a
l
l
2.
2F SNC-P:
The principle of 2F SNC-P protection is that: “transmit data bi-directionally,
receive data bi-directionally, select one better quality signal and use the other
signal as standby”. 2F SNC-P uses one fiber to transmit service, called S fiber
(working fiber); uses another fiber for protection, called P fiber (protection fiber).
If every note of the ring works normally, the direction Tx signal and Rx signal is
the same (that is to say, if a note transmits data clockwise so does it receives
data), but the routing is not the same (e.g. if station A transmits data to station
C, the routing is A
→
B
→
C; and if station A receives data from C, the routing is
C
→
D
→
A, so the middle stations passed by are not same). See in the following
figure:
CA
AC
S
P
A
D
B
C
P
S
(a)
CA AC
CA
AC
S
P
A
D
B
C
P
S
(b)
CA AC
switch
The Tx and Rx routing is in figure (a) when it works normally: data from A to C
is transmitted both in S fiber and P fiber, S fiber will transmit the data from A to
C clockwise though middle station B, and P fiber will transmit the data from A to
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