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-rw-r--r--docs/requirements/use_cases/shared-service-functions.rst48
1 files changed, 42 insertions, 6 deletions
diff --git a/docs/requirements/use_cases/shared-service-functions.rst b/docs/requirements/use_cases/shared-service-functions.rst
index 12b2f5c..3d370c0 100644
--- a/docs/requirements/use_cases/shared-service-functions.rst
+++ b/docs/requirements/use_cases/shared-service-functions.rst
@@ -6,21 +6,56 @@
Shared Service Functions
------------------------
-
Description
^^^^^^^^^^^
-TBD
+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
""""""""""""""
-TBD
+The API has to cover the following functionality:
+
+* management of instance ports
+
+* management of service ports
+
+* binding of services to service ports
Data models
@@ -32,13 +67,14 @@ TBD
Orchestration
"""""""""""""
-TBD
+None.
Dependencies on other resources
"""""""""""""""""""""""""""""""
-TBD
+The compute service needs to be enabled to consume instance ports instead of
+classic Neutron ports.
Implementation Proposal