Liaison statement
Control plane resilience

At the recent Q12/15 and Q14/15 Rapporteur meeting, it was reported that CCAMP
is discussing the issue of control plane resilience.  This topic has been
considered in the development of ASON Recommendations in SG15 and we would like
to draw to your attention some of this work that may be helpful to CCAMP.
G.8080 Section 12 discusses resilience by describing principles to follow, and
Appendix II describes resilience in terms of pair-wise relationships between
planes/components.  Resilience refers to the ability of the control plane to
continue operating under failure conditions.  These may occur as a result of
disruption of communication between control plane components (e.g., SCN
failure) or failure of control plane components themselves. When communication
between the control plane and transport (bearer) plane becomes available, four
principles apply (from G.8080): 1.      The control plane relies on the
transport plane for information about transport plane resources. 2.     
Consistency between the control plane view and the corresponding transport
network element is established first (vertical consistency). 3.      Once local
consistency is established, horizontal consistency is attempted.  Here, control
plane components synchronize with their adjacent components.  This is used to
re-establish a consistent view of routing, call, and connection state. 4.     
Existing connections in the transport plane are not altered if the control
plane fails and/or recovers.  Control plane components are therefore dependent
on transport state (existing cross connections). Note that the transport plane
in G.8080 refers to G.805 layer networks, which includes connection-oriented
packet layers such as ATM.

Attachment: <ITU-T G.8080 Amendment 2> :
http://www.itu.int/rec/recommendation.asp?type=items&lang=e&parent=T-REC-G.8080-200502-I!Amd2