ECS4110-52T_Management Guide

C HAPTER 14 | Basic Administration Protocols
Ethernet Ring Protection Switching
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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.
Figure 287: Sub-ring with Virtual Channel
■
Sub-ring without R-APS Virtual Channel – Under certain
circumstances it may not be desirable to use a virtual channel to
interconnect the sub-ring over an arbitrary Ethernet network. In
this situation, the R-APS messages are terminated on the
interconnection points. Since the sub-ring does not provide an R-
APS channel nor R-APS virtual channel beyond the interconnection
points, R-APS channel blocking is not employed on the normal ring
links to avoid channel segmentation. As a result, a failure at any
ring link in the sub-ring will cause the R-APS channel of the sub-ring
to be segmented, thus preventing R-APS message exchange
between some of the sub-ring’s ring nodes.
No R-APS messages are inserted or extracted by other rings or sub-
rings at the interconnection nodes where a sub-ring is attached.
Hence there is no need for either additional bandwidth or for
different VIDs/Ring IDs for the ring interconnection. Furthermore,
protection switching time for a sub-ring is independent from the
configuration or topology of the interconnected rings. In addition,
this option always ensures that an interconnected network forms a
tree topology regardless of its interconnection configuration. This
means that it is not necessary to take precautions against forming a
loop which is potentially composed of a whole interconnected
network.
Sub-ring
with Virtual
Channel
Virtual
Channel
RPL Port
Interconnection Node
Ring Node
Major Ring