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+.. This work is licensed under a Creative Commons Attribution 4.0 International License.
+.. http://creativecommons.org/licenses/by/4.0
+.. (c) Georg Kunz
+
+
+Shared Service Functions
+------------------------
+
+Description
+^^^^^^^^^^^
+
+This use case aims at binding multiple networks or network services to a single
+vNIC (port) of a given VM. There are several specific application scenarios for
+this use case:
+
+* Shared Service Functions: A service function connects to multiple (tenant)
+  networks by means of a single vNIC.
+
+  Typically, a vNIC is bound to a single (tenant) network. Hence, in order to
+  directly connect a service function to multiple (tenant) networks at the same
+  time, multiple vNICs are needed - each vNIC binding the service function to a
+  separate network. For service functions requiring connectivity to a large
+  number of networks, this approach does not scale as the number of vNICs per VM
+  is limited and additional vNICs occupy additional resources on the hypervisor.
+
+  A more scalable approach is to bind multiple networks to a single vNIC
+  and let the service function, which is now shared among multiple networks,
+  handle the separation of traffic itself.
+
+
+* Multiple network services: A service function connects to multiple different
+  network types such as a L2 network, a L3(-VPN) network, a SFC domain or
+  services such as DHCP, IPv6 NDP, firewall/security, etc.
+
+
+In order to achieve a flexible binding of multiple services to vNICs, a logical
+separation between a vNIC (instance port) - that is, the entity that is used by
+the compute service as hand-off point between the network and the VM - and a
+service interface - that is, the interface a service binds to - is needed.
+
+Furthermore, binding network services to service interfaces instead of to the
+vNIC directly enables a more dynamic management of the network connectivity of
+network functions as there is no need to add or remove vNICs.
+
+
+Requirements
+^^^^^^^^^^^^
+
+Northbound API
+""""""""""""""
+
+The API has to cover the following functionality:
+
+* management of instance ports
+
+* management of service ports
+
+* binding of services to service ports
+
+
+Data models
+"""""""""""
+
+TBD
+
+
+Orchestration
+"""""""""""""
+
+None.
+
+
+Dependencies on other resources
+"""""""""""""""""""""""""""""""
+
+The compute service needs to be enabled to consume instance ports instead of
+classic Neutron ports.
+
+
+Implementation Proposal
+^^^^^^^^^^^^^^^^^^^^^^^
+
+TBD