Network & Telecom

CSMF

Q: How does the CSMF differ from the NSMF and NSSMF?

The three functions form a top-down hierarchy defined in 3GPP TS 28.530. The CSMF is customer-facing: it accepts a communication service order (for example, an enterprise eMBB service with a 1 Gbps downlink and 10 ms latency target) and translates it into network slice requirements expressed as a Service Profile. The NSMF (Network Slice Management Function) receives those requirements, decomposes the end-to-end slice into per-domain Slice Profiles, and manages the Network Slice Instance lifecycle. The NSSMF (Network Slice Subnet Management Function) operates one technology domain such as RAN, transport, or core, mapping its Slice Profile to concrete resource configurations. In short, the CSMF speaks the language of services and SLAs, the NSMF speaks the language of end-to-end slices, and the NSSMF speaks the language of domain resources.

Q: What inputs and outputs does the CSMF handle?

The CSMF takes business-level inputs: the communication service order, the service-level agreement with KPIs such as guaranteed throughput, end-to-end latency, availability, and coverage area, plus commercial constraints. Its primary output to the NSMF is a Service Profile, the standardized container of slice requirements including SST and SD values that identify the slice type (eMBB SST=1, URLLC SST=2, mMTC SST=3), area of service, density, and performance targets. The CSMF also reports service status and KPI fulfillment back to the customer or business support system, closing the loop between the order and the running slice.

Q: Does the CSMF live in the OSS or the BSS?

The CSMF straddles the boundary. It exposes a northbound interface toward the Business Support System (BSS) and customer portals, where orders, catalogs, and SLAs originate, and a southbound interface toward the Operations Support System (OSS) and the NSMF, where slices are realized. In TM Forum ODA terms the CSMF aligns with service order management and service catalog functions. Vendors implement it as a microservice in a service orchestrator that consumes TMF641 service-ordering APIs on the north side and drives slice-management APIs on the south side. Because it carries no slice resources of its own, the CSMF is a control and translation function rather than a data-plane element.

/see-ess-em-eff/ · Communication Service Management Function

The customer-facing top layer of the 3GPP network slice management hierarchy defined in TS 28.530. The CSMF accepts a communication service order along with its service-level agreement, translates the business requirements into a Service Profile, and hands that profile down to the NSMF for end-to-end slice realization. It carries no transport or radio resources of its own; it is a control and translation function that bridges the business support system to the orchestration that drives network slicing. By cleanly separating the service order from the slice that fulfills it, the CSMF lets an operator expose eMBB, URLLC, and mMTC offerings as catalog products while the underlying slice templates evolve independently.

Category: Network & Telecom

Standard: 3GPP TS 28.530

Hands off to: NSMF

Where the CSMF Sits in the Slice Management Stack

When 3GPP defined management for end-to-end network slicing, it split the problem into three nested management functions so that business intent and technical realization stay loosely coupled. The CSMF is the entry point. A customer, an enterprise account team, or a business support system submits a communication service request, typically over a TM Forum TMF641 service-ordering API, describing what the service must do rather than how a slice should be built. The CSMF interprets that request, validates it against the service catalog, and produces a Service Profile, the standardized requirement bundle that the Network Slice Management Function consumes.

The Service Profile is where business language becomes slice language. It carries the Slice/Service Type (SST) and an optional Slice Differentiator (SD) that together form the S-NSSAI identifying the slice, plus quantitative targets: guaranteed and maximum downlink and uplink throughput, end-to-end latency budget, availability class, coverage area, and connection density. The CSMF does not decide which RAN cells, transport links, or core network functions satisfy those numbers; that decomposition belongs to the NSMF and, one layer further down, to each per-domain NSSMF. This separation is what lets an operator change radio vendors or re-home a slice across data centers without touching the customer-facing order.

For a millimeter-wave deployment, the CSMF is where a fixed-wireless-access or private-5G customer's coverage and capacity promises are captured before any front-haul, antenna, or converter hardware is engaged. The KPIs the CSMF records, such as a 2 ms air-interface latency target or a 1 Gbps cell-edge throughput, ultimately constrain the physical-layer link budget that RF hardware must close, which is why service management and RF system design meet at this interface.

The CSMF / NSMF / NSSMF Hand-off

Each layer narrows scope. The CSMF owns one or more communication services; the NSMF owns the end-to-end Network Slice Instance and its lifecycle (allocation, modification, supervision, termination); the NSSMF owns a single technology domain such as RAN, transport, or core and produces the concrete configuration applied to network functions. Status and KPI telemetry flow back up the same chain so the CSMF can report SLA fulfillment to the customer.

Service Profile to Slice Profile Mapping

Slice identity (sent in the Service Profile):
S-NSSAI = SST (8 bits) + SD (24 bits, optional)
SST = 1 (eMBB) · SST = 2 (URLLC) · SST = 3 (mMTC)

Admission constraint for N slices sharing a node:
R_guaranteed = ∑_i=1..N (GBR_i × A_i) ≤ C_node

End-to-end latency budget decomposed per domain:
L_e2e = L_RAN + L_transport + L_core ≤ L_SLA

Where GBR_i = guaranteed bit rate of slice i, A_i = activity factor (0–1), R_guaranteed = aggregate guaranteed throughput the node must reserve, C_node = the node's available capacity, L_SLA = latency promised in the CSMF service order, and each L term is allocated by the NSMF to its corresponding NSSMF domain.

Slice Management Function Comparison

Function	Layer	Manages	Key input	Key output	Interface peers
CSMF	Service	Communication service	Service order + SLA	Service Profile	BSS / customer ↔ NSMF
NSMF	End-to-end slice	Network Slice Instance	Service Profile	Slice Profile(s)	CSMF ↔ NSSMF
NSSMF	Domain subnet	Slice subnet (RAN/TN/CN)	Slice Profile	Resource config	NSMF ↔ domain EMS/NFVO
NFVO	Resource	VNF / CNF lifecycle	Resource config	Instantiated functions	NSSMF ↔ VIM

Common Questions

Frequently Asked Questions

How does the CSMF differ from the NSMF and NSSMF?

The three form a top-down hierarchy in 3GPP TS 28.530. The CSMF is customer-facing: it accepts a communication service order (say, enterprise eMBB at 1 Gbps downlink, 10 ms latency) and emits a Service Profile of slice requirements. The NSMF decomposes that into per-domain Slice Profiles and manages the end-to-end Network Slice Instance lifecycle. The NSSMF handles one domain (RAN, transport, or core), mapping its Slice Profile to concrete resource configuration. The CSMF speaks services and SLAs, the NSMF speaks end-to-end slices, the NSSMF speaks domain resources.

What inputs and outputs does the CSMF handle?

Inputs are business-level: the service order plus an SLA with KPIs such as guaranteed throughput, end-to-end latency, availability, and coverage. Its main output to the NSMF is the Service Profile, carrying SST and SD values that identify the slice (eMBB SST=1, URLLC SST=2, mMTC SST=3), area of service, density, and performance targets. The CSMF also reports KPI fulfillment back to the customer or BSS, closing the loop between the order and the running slice.

Does the CSMF live in the OSS or the BSS?

It straddles the boundary. The CSMF exposes a northbound interface toward the BSS and customer portals (orders, catalogs, SLAs) and a southbound interface toward the OSS and the NSMF (slice realization). In TM Forum ODA it aligns with service order management and consumes TMF641 ordering APIs on the north side while driving slice-management APIs on the south side. Carrying no slice resources of its own, the CSMF is a control and translation function, not a data-plane element.

Related Terms

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