Services
7210 SAS-X, R6 OS Services Guide Page 43
topology. When there is any one link failure or any one node failure in the ring, G.8032 protocols
are capable of restoring traffic between all remaining nodes in these data instances.
There is no limit on the number of control channels on a port but,the current implementation on
7210-X allows a maximum of four control channels per port that use hardware CCM. This is
based on the assumption that multiple ring instances are used for load balancing during fail over,
and four ring instances per port are sufficient for that purpose.
Note: This is not a hardware limitation. Each ring control instance can be tied to any number of
data services.
Ethernet R-APS can be configured on any port configured for access mode using dot1q, q-in-q
encapsulation enabling support for Ethernet R-APS protected services on the service edge towards
the customer site, or within the Ethernet backbone. ELINE and ELAN services can be afforded
Ethernet R-APS protection and, although the Ethernet Ring providing the protection uses a ring
for protection the services are configured independent of the Ring properties. The intention of this
is to cause minimum disruption to the service during Ethernet R-APS failure detection and
recovery.
In the 7210 SAS implementation, the Ethernet Ring is built from a VPLS service on each node
with VPLS SAPs that provides Ring path with SAPs. As a result, most of the VPLS SAP features
are available on Ethernet rings if desired. This results in a fairly feature rich ring service.
The control tag defined under each eth-ring is used for encapsulating and forwarding the CCMs
and the G.8032 messages used for the protection function. If a failure of a link or node affects an
active Ethernet ring segment, the services will fail to receive the CC messages exchanged on that
segment or will receive a fault indication from the Link Layer OAM module.
For fault detection using CCMs three CC messages plus a configurable hold-off timer must be
missed for a fault to be declared on the associated path. The latter mechanism is required to
accommodate the existence of additional, 50 ms resiliency mechanism in the optical layer. After it
receives the fault indication, the protection module will declare the associated ring link down and
the G.8032 state machine will send the appropriate messages to open the RPL and flush the
learned addresses.
Flushing is triggered by the G.8032 state machine and the 7210 SAS implementation allows
flooding of traffic during the flushing interval to expedite traffic recovery.
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