H3C Technologies H3C SR8800 - Manual (Page 31)

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Topology discovery
RPR performs automatic topology discovery to collect such information as the number of stations, ring
state, and order of the stations on the ring to build a topology database. This database does not change
after the ring topology becomes stable.
Topology database
Each RPR station maintains a topology database that describes the topology of the entire RPR ring. Based
on this database, the station creates its ringlet selection table.
A topology database contains three categories of information:
• Ringlet topology information, such as the number of stations, ring state, and available bandwidth.
• Local station topology information, such as the MAC address, protection mode, protection state,
station name, and topology checksum of the local station and the neighbor stations.
• Topology information of other stations, such as the MAC address, validity state, reachability,
protection mode, station ID, station name, and reserved bandwidth.
Topology discovery process
During the topology discovery process, RPR uses the following three types of control frames to transmit
topology data: topology protection (TP), attribute discovery (ATD), and topology checksum (TC).
• TP frames convey configuration and status information of stations. The stations on an RPR ring
broadcast TP frames to advertise their configuration and status information, and update their own
topology databases after receiving TP frames from other stations. Finally, all the stations reach an
agreement on the topology of the ring.
• ATD frames convey attributes of the local station such as the MAC address and station name. These
attributes will be included in the topology database.
• 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,
two types of interval, 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 fiber-optic or stations. The network can
then detect faults quickly and react appropriately to restore services in 50 ms.
RPR is available with two fault response methods: passthrough and protection.
Passthrough
The passthrough approach mainly applies to handle station faults. When a station detects an internal
fault, it can enter the passthrough state in which it behaves like a repeater and does not handle any