The Communication Service Management Function as per 3GPP (28.801, 28.805) translates the communication service-related requirements to network slice-related requirements. It also provides an interface to OSS/BSS layers.
For communication services offered to customers, the offerings can span B2C, B2B, and B2B2X. And such communication services must be supported in an optimized way by the 5G Network Slice Instance (NSI). In this way a communication service is associated with a network slice; an example of communication services using network slices. The Network Slice deployment offers communications services to UEs or Systems in B2C and B2B.
According to 3GPP, the communication service could also be the 3GPP service that makes up the NSI. An example could be customised network slices made available to customers. In this case, the native support for 5G slicing is also usable in the communication service. The amount of 5G slice management control provided to the customer is decided by the Network Slice Provider. This model describes Network Slice as a Service (NSaaS).
Relationship to Network Slice Instance
A Communication Service Instance is realized or instantiated by one or more Network Slice Instances as described by the Network Slice Information Object Class of 3GPP Spec 28.541.
The following diagram illustrates the relationship.

One Communication Service Instance (acting as Customer Facing Service = CFS) is specified by one Communication Service Profile (= CFSSpec). The CFS represents one of the service requirements of the 5G slice tenant, on the 5G slice.
Therefore the CFS is related to one Resource Facing Service (RFS), which in turn manifests the tenant’s service requirement in the Service Profile Instance. The Service Profile Spec (= RFSSpec) acts like a Service Profile Template for the Service Profile Instance.
Additional requirements on the 5G slice from the same 5G slice tenant will each require an additional CFS, instantiated from either the same, or different CFSSpec (= Communication Service Profile Template). In this way many CFSSpecs are related to one RFSSpec.
However, one CFS instance is related to one RFS instance and this CFS-RFS combination makes up the service requirement on the Network Slice Instance. As there can be many service requirements on a single Network Slice Instance (NSI), many RFSs (Service Profiles) can be related to one NSI.
The next post describe identification and management of the ids of NSIs.