ECS4100 Series Web Management Guide-R07

Table Of Contents
Chapter 13
| Basic Administration Protocols
Ethernet Ring Protection Switching
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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 304: 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.
Figure 305 on page 471 (Normal Condition) depicts an example of a multi-ring/
ladder network. If the network is in normal operating condition, the RPL owner
node of each ring blocks the transmission and reception of traffic over the RPL for
that ring. This figure presents the configuration when no failure exists on any ring
link.
In the figure for the Normal Condition there are two interconnected rings. Ring
ERP1 is composed of ring nodes A, B, C and D and the ring links between these
nodes. Ring ERP2 is composed of ring nodes C, D, E and F and the ring links C-to-F,
F-to-E, E-to-D. The ring link between D and C is used for traffic on rings ERP1 and
ERP2. On their own ERP2 ring links do not form a closed loop. A closed loop may be
East Port
West Port
RPL Owner
CC Messages
RPL
x
CC Messages
(Idle State)