Service Entities
Page 48 7210 SAS M Services Guide
to one instance the rest of the services that need to be interconnected to those services must be on
the same instance. In other words each data instance is a separate data VLAN on the same physical
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.
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.
The Figure 8 below illustrates a resilient Ring Service. In the ring example, a PBB ring (solid line)
using VID 500 carries 2 service VLANs on I-SID 1000 and 1001 for Service VIDs (Dot1q 100 and
QinQ 400.1 respectively). The RPL for the PBB ring is between A and B where B is the RPL
owner. Also, illustrated in the figure below is a QinQ service on the (dotted line) ring that uses
Dot1q VID 600 for the ring to connect service VLAN 100.50. The two rings have RPLs on
different nodes which allow a form of load balancing. The example serves to illustrate that service
encapsulations and ring encapsulation can be mixed in various combinations. Also, note that
neither of the rings is a closed loop. A ring can restore connectivity when any one node or link
fails to all remaining nodes within the 50ms transfer time (signaling time after detection).
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