Web Management Guide-R05

Chapter 13 | Basic Administration Protocols
Ethernet Ring Protection Switching
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The ring node identifier is used to identify a node in R-APS messages for both
automatic and manual switching recovery operations.
For example, a node that has one ring port in SF condition and detects that the
condition has been cleared, will continuously transmit R-APS (NR) messages
with its own Node ID as priority information over both ring ports, informing its
neighbors that no request is present at this node. When another recovered
node holding the link blocked receives this message, it compares the Node ID
information with its own. If the received R-APS (NR) message has a higher
priority, this unblocks its ring ports. Otherwise, the block remains unchanged.
The node identifier may also be used for debugging, such as to distinguish
messages when a node is connected to more than one ring.
◆ R-APS with VC – Configures an R-APS virtual channel to connect two
interconnection points on a sub-ring, allowing ERPS protocol traffic to be
tunneled across an arbitrary Ethernet network. (Default: Enabled)
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A sub-ring may be attached to a primary ring with or without a virtual
channel. A virtual channel is used to connect two interconnection points
on the sub-ring, tunneling R-APS control messages across an arbitrary
Ethernet network topology. If a virtual channel is not used to cross the
intermediate Ethernet network, data in the traffic channel will still flow
across the network, but the all R-APS messages will be terminated at the
interconnection points.
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Sub-ring with R-APS Virtual Channel – When using a virtual channel to
tunnel R-APS messages between interconnection points on a sub-ring, the
R-APS virtual channel may or may not follow the same path as the traffic
channel over the network. R-APS messages that are forwarded over the
sub-ring’s virtual channel are broadcast or multicast over the
interconnected network. For this reason the broadcast/multicast domain of
the virtual channel should be limited to the necessary links and nodes. For
example, the virtual channel could span only the interconnecting rings or
sub-rings that are necessary for forwarding R-APS messages of this sub-
ring. Care must also be taken to ensure that the local RAPS messages of the
sub-ring being transported over the virtual channel into the
interconnected network can be uniquely distinguished from those of other
interconnected ring R-APS messages. This can be achieved by, for example,
by using separate VIDs for the virtual channels of different sub-rings.
Note that the R-APS virtual channel requires a certain amount of
bandwidth to forward R-APS messages on the interconnected Ethernet
network where a sub-ring is attached. Also note that the protection
switching time of the sub-ring may be affected if R-APS messages traverse a
long distance over an R-APS virtual channel.