Chapter 20
| ERPS Commands
– 540 –
may be affected if R-APS messages traverse a long distance over an R-APS
virtual channel.
Figure 4: 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.
Figure 5: Sub-ring without Virtual Channel
Example
Console(config-erps)#raps-without-vc
Console(config-erps)#
Sub-ring
with Virtual
Channel
Virtual
Channel
RPL Port
Interconnection Node
Ring Node
Major Ring
Sub-ring
with Virtual
Channel
RPL Port
Interconnection Node
Ring Node
Major Ring
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