R3303-HP HSR6800 Routers High Availability Configuration Guide

• TC frames convey topology checksum information. They are sent between adjacent stations to check

whether the topology databases on them are synchronized, identifying stability of the RPR ring

topology.

All these control frames are sent at regular intervals, which are user configurable. For TP and TC frames,

fast sending interval and slow sending interval are used.

• When a station on the ring starts initializing or detects a topology change, it sends TP frames to

propagate topology information throughout the network. When doing that, it sends the first nine TP

frames at fast intervals and subsequent TP frames at slow intervals.

• After the RPR ring topology converges, the station starts to send TC frames. When doing that, it

sends first five TC frames at fast intervals and then subsequent TC frames at slow intervals.

• Only one type of interval is available for sending ATD frames, regardless of topology change.

Fault response methods

RPR delivers strong self-recovery capability. Its protection mechanism provides event detection, quick

self-recovery, and fast service recovery when faults occur to the optical fiber or stations. The network can

then detect faults quickly and react appropriately to restore services in 50 ms.

RPR supports the protection fault response method.

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.