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S2989G-24TX Operation Manual

Chapter 7 Reliability Configuration

7-35

RPL, and restore the forwarding status of the fault link. At this time, the forwarding path

of the data packet is same as the last once when it is normal. Another one is Non-

revertive switch. After the ring link restored to be normal, the link will keep the block

status. The data packet will continue to be forwarded with the current path.

The environments of the two methods are different. When the block RPL can make

the data flow transmission path be the best, use the Revertive switch; when the path

costs are similar, there is no difference no matter which path will be blocked, for

preventing the secondary interruption of data flow, use the Non-revertive switch.

1. Revertive switch

The following is the single-ring and single link fault.

Figure 7-16 Revertive switch fault restoration of single link

The steps:

a) The fault still existed, the node which has detected the fault will send the R-APS

(SF) packets with the fault message periodically;

b) Fault restoration on the link;

c) The nodes of C and D detects the fault restoration, they will start the guard timer

and send the fault restoration packets of R-APS (NR) on the ports of the ring

network at the same time;

d) When the RPL owner node detected R-APS (NR) packets, it will start the WTR

timer and clear the local node fault message at the same time;

e) After the nodes C and D are time out, they receives the R-APS (NR) packets

from the peer. The node D thinks the priority of node C is higher, so it will stop

sending the R-APS (NR) packets with the local message and relieve the block of

the port;

f) When the WTR timer of RPL owner node G is time out, it will block the port

connected to RPL and send the R-APS (NR, RB) packets through the ring