Digisol DG-FS4528P, Management Manual

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37
EAPS C
OMMANDS
N
OTE
:
The information provided in this section is based on RFC 3619.
Ethernet Automatic Protection Switching
TM
(EAPS) can be used to increase
the availability and robustness of Ethernet rings. An Ethernet ring built
using EAPS can have resilience comparable to that provided by SONET
BSHR or SDH MS-SPRing configurations, at a lower cost and with fewer
constraints (for example, ring size).
Many Metropolitan Area Networks (MANs) use a ring topology. EAPS works
well in ring topologies for either MANs or LANs. MAN operators want to
minimize the recovery time in the event of a fiber cut. EAPS technology
converges in less than one second, often in less than 500 milliseconds.
Also, EAPS does not limit the number of nodes in the ring, and the
convergence time is independent of the number of nodes in the ring.
Operational Concept – An EAPS Domain exists on a single Ethernet ring.
Any VLAN that is to be protected is configured on all ports in the ring for
the given EAPS Domain. Each EAPS Domain has a single designated
“master node.” All other nodes on that ring are referred to as “transit
nodes.”
Each node has two ports connected to the ring. One port of the master
node is designated as the “primary port” to the ring, carrying control
messages and data, while the other port is designated as the “secondary
port” and runs in backup mode.
In normal operation, the master node blocks the secondary port for all
non-control Ethernet frames belonging to the given EAPS Domain, thereby
avoiding a loop in the ring. Existing Ethernet switching and learning
mechanisms operate per existing standards on this ring. This is possible
because the master node makes the ring appear as though there is no loop
from the perspective of the Ethernet standard algorithms used for
switching and learning. If the master node detects a ring fault, it unblocks
its secondary port and allows Ethernet data frames to pass through that
port. There is also a special “Control VLAN” that can always pass through
all ports in the EAPS Domain, including the secondary port of the master
node.
EAPS uses both a polling mechanism and an alert mechanism, described
below, to verify the connectivity of the ring and quickly detect any faults.
Link Down Alert – When a transit node detects a link-down on any of its
ports in the EAPS Domain, that transit node immediately sends a “link
down” control frame on the Control VLAN to the master node.