H3C Technologies H3C SR8800 - Manual (Page 32)

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services on the ring. Frames arriving at this station are forwarded directly as if it was transparent, and the
station is invisible on the ring. Station B shown in Figure 6 is an example.
Figure 6 Passthrough approach
Protection
If a station is unable to forward traffic as the result of power failure or fiber cut for example, it should enter
protection mode. RPR provides the following protection modes:
• Wrapping—After a span or station fails, protected traffic is directed at the point of failure to the
opposing ringlet. The two ringlets (Ringlet 0 and Ringlet 1) then form a closed single ring around the
point of the failure. The wrapping mode minimizes the data frame loss, because the wrapping
mode allows quick switchover, However, this mode wastes bandwidth.
• Steering—The two stations at the two sides of a point of failure update their topology databases,
and then send TP frames at fast intervals to the other stations on the ring. After a new topology
database is stabilized, the source station directs protected frames to the ringlet that retains
connectivity to their destinations. The steering mode can avoid the bandwidth waste. However, it
can cause frame loss and service interruption because it requires topology reconvergence.