Add new use case of multiple back-ends, which is separate from L3VPN

Change-Id: Ife3a9c29057f6055f1db07168d06c46910d759d6
Signed-off-by: Bin Hu <bh526r@att.com>

2 files changed, 38 insertions, 0 deletions

diff --git a/docs/requirements/use_cases.rst b/docs/requirements/use_cases.rst
index 0248b13..a8356ea 100644
--- a/docs/requirements/use_cases.rst
+++ b/docs/requirements/use_cases.rst
@@ -7,6 +7,7 @@ Use cases
 The following sections address networking use cases that have been identified to be relevant in the scope of NFV and NetReady.
 
 .. toctree::
+    use_cases/multiple_backends.rst
     use_cases/l3vpn.rst
     use_cases/service-binding-pattern.rst
     use_cases/programmable_provisioning.rst
diff --git a/docs/requirements/use_cases/multiple_backends.rst b/docs/requirements/use_cases/multiple_backends.rst
new file mode 100644
index 0000000..0d4ab13
--- /dev/null
+++ b/docs/requirements/use_cases/multiple_backends.rst
@@ -0,0 +1,37 @@
+.. This work is licensed under a Creative Commons Attribution 4.0 International License.
+.. http://creativecommons.org/licenses/by/4.0
+.. (c) Bin Hu
+
+Network Function Virtualization (NFV) brings the need of supporting multiple networking
+back-ends in virtualized infrastructure environment.
+
+First of all, a Service Providers' virtualized network infrastructure will consist of
+multiple SDN Controllers from different vendors for obvious business reason.
+Those SDN Controllers may be managed within one cloud or multiple clouds.
+Jointly, those VIMs (e.g. OpenStack instances) and SDN Controllers need to work
+together in an interoperable framework to create NFV services in the Service
+Providers' virtualized network infrastructure. It is needed that one VIM (e.g. OpenStack
+instance) shall be able to support multiple SDN Controllers at back-end.
+
+Secondly, a Service Providers' virtualized network infrastructure will serve multiple,
+heterogeneous administrative domains, such as mobility domain, access networks,
+edge domain, core networks, WAN, enterprise domain, etc. The architecture of
+virtualized network infrastructure needs different types of SDN Controllers that are
+specialized and targeted for specific features and requirements of those different domains.
+The architectural design may also include global and local SDN Controllers. And multiple
+local SDN Controllers may be managed by one VIM (e.g. OpenStack instance).
+
+Furthermore, even within one administrative domain, NFV services could also be quite diversified.
+Specialized NFV service needs specialized and dedicated SDN Controller too. Thus a Service
+Provider needs to use multiple APIs and back-ends simultaneously in order to provide
+users with diversified services at the same time. At the same time, for a particular NFV service,
+the new networking APIs need to be agnostic of the back-ends.
+
+Therefore, it is expected that in NFV networking service domain:
+
+* One OpenStack instance shall support multiple APIs and SDN Controllers simultaneously
+
+* Interoperability is needed among multi-vendor SDN Controllers at back-end
+
+* New NFV Networking APIs  shall be agnostic of back-ends
+