Edge-Core ECS4110-28T, Management Manual, Page: 496 / 1514

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| Basic Administration Protocols
Ethernet Ring Protection Switching
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blocking the RPL. Each link is monitored by its two adjacent nodes using
Connectivity Fault Management (CFM) protocol messages.
Protection switching (opening the RPL to traffic) occurs when a signal
failure message generated by the Connectivity Fault Management (CFM)
protocol is declared on one of the ring links, and the detected failure has a
higher priority than any other request; or a Ring – Automatic Protection
Switching protocol request (R-APS, as defined in Y.1731) is received which
has a higher priority than any other local request.
A link/node failure is detected by the nodes adjacent to the failure. These
nodes block the failed link and report the failure to the ring using R-APS
(SF) messages. This message triggers the RPL owner to unblock the RPL,
and all nodes to flush their forwarding database. The ring is now in
protection state, but it remains connected in a logical topology.
When the failed link recovers, the traffic is kept blocked on the nodes
adjacent to the recovered link. The nodes adjacent to the recovered link
transmit R-APS (NR - no request) message indicating they have no local
request. When the RPL owner receives an R-APS (NR) message it starts the
Wait-To-Recover (WTR) timer. Once WTR timer expires, the RPL owner
blocks the RPL and transmits an R-APS (NR, RB - ring blocked) message.
Nodes receiving this message flush the forwarding database and unblock
their previously blocked ports. The ring is now returned to Idle state.
Figure 284: ERPS Ring Components
Multi-ring/Ladder Network – ERPSv2 also supports multipoint-to-multipoint
connectivity within interconnected rings, called a “multi-ring/ladder
network” topology. This arrangement consists of conjoined rings connected
by one or more interconnection points, and is based on the following
criteria:
◆
The R-APS channels are not shared across Ethernet Ring
interconnections.
◆
On each ring port, each traffic channel and each R-APS channel are
controlled (e.g., for blocking or flushing) by the Ethernet Ring
Protection Control Process (ERP Control Process) of only one ring.
◆
Each Major Ring or Sub-Ring must have its own RPL.
E ast Port
W est Port
RPL Owner
CC M essages
RPL
x
CC M essages
( I d l e State)