Web Management Guide-R04

Table Of Contents
Chapter 13
| Basic Administration Protocols
Ethernet Ring Protection Switching
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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 323: 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