SWIS allows the client to tailor the protection method to the service preferences:
services that require minimum packet loss can be wrapped while services that require
minimum delay can be steered.
Figure 12.11 Wrap protection
S1 S2 S3 S4 S5 S6
S1 S2 S3 S4 S5 S6
No edge in ring
Ring failure between
S3 and S4
Resilient Packet Ring (RPR) 343
Protection Hierarchy
The MAC supports the protection hierarchy listed in Table 12.2. The protection conditions
and the resulting topologies are described in Figure 12.12.
As described in Figure 12.12, only FS and SF conditions can coexist and severe the
ring in more than one span. Tie condition of non fatal span failures (e.g., SD, MS) is
ignored and no protection operation is performed.
The topology and protection (TP) frames are used to detect that the ringlet0 transmit
signal of one station as been wrongly connected to the ringlet1 receive of its neighboring,
and vice versa. This defect is known as a miscabling defect. A station declares a
miscabling defect if the TP frame from its neighbor indicates that it has been transmitted
in a ringlet different from the one it was received.
As already mentioned in the fairness clause, the fairness frames are transmitted
regularly at short intervals.
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