Edge-Core ECS4110-28T Management Manual page 497

| Basic Administration Protocols
C 14
HAPTER
Ethernet Ring Protection Switching
Figure 285 on page 498 (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 formed by the ring links of
ERP2 and the ring link between the interconnection nodes that is controlled
by ERP1. ERP2 is a sub-ring. Ring node A is the RPL owner node for ERP1,
and ring node E is the RPL owner node for ERP2. These ring nodes (A and
E) are responsible for blocking the traffic channel on the RPL for ERP1 and
ERP2 respectively. There is no restriction on which ring link on an ring may
be set as the RPL. For example the RPL of ERP1 could be set as the link
between ring node C and D.
Ring nodes C and D, that are common to both ERP1 and ERP2, are called
interconnection nodes. The ring link between the interconnection nodes are
controlled and protected by the ring it belongs to. In the example for the
Normal Condition, the ring link between ring nodes C and D is part of ERP1,
and, as such, are controlled and protected by ERP1. Ethernet characteristic
information traffic corresponding to the traffic channel may be transferred
over a common Ethernet connection for ERP1 and ERP2 through the
interconnection nodes C and D. Interconnection nodes C and D have
separate ERP Control Processes for each Ethernet Ring.
Figure 285 on page 498 (Signal Fail Condition) illustrates a situation where
protection switching has occurred due to an SF condition on the ring link
between interconnection nodes C and D. The failure of this ring link
triggers protection only on the ring to which it belongs, in this case ERP1.
The traffic and R-APS channels are blocked bi-directionally on the ports
where the failure is detected and bi-directionally unblocked at the RPL
connection point on ERP1. The traffic channels remain bi-directionally
blocked at the RPL connection point on ERP2. This prevents the formation
of a loop.
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