Liaison statement
Control plane resilience

Submission date 2005-11-25
From ITU-T SG 15 (Greg Jones)
Response contact,
Technical contact,
Purpose For information
Attachments Control plane resilience
ITU-T Rec. G.8080/Y.1304 (2001) Amendment 2 (02/05)
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> :!Amd2