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CFS, RFS & Resource Explained

The Three-Layer Service Model

Below the product layer, the catalog defines three progressively more technical layers: Customer-Facing Service (CFS), Resource-Facing Service (RFS), and Resource. This decomposition is the core of how commercial products translate into network reality. It is the most important modeling concept in OSS architecture.

Each layer serves a different audience and answers a different question. Understanding which layer you are talking about eliminates most of the confusion in BSS/OSS conversations.

CFS to RFS to Resource decomposition -- how a customer-facing service breaks down into network components

Figure 2.2 — CFS → RFS → Resource decomposition model

Customer-Facing Service (CFS)

A CFS represents a service as experienced by the customer. It is the highest-level service abstraction — the bridge between the commercial product and technical delivery. A CFS describes WHAT the customer gets, not HOW it is delivered. Examples: "Internet Access", "Voice Line", "IPTV Service", "Managed WiFi".

CFS is the translation layer between product and technology. When a Product Specification links to a CFS, it says: "to deliver this product, you need this service." The CFS is technology-neutral — it describes the service outcome, not the implementation.

CFS Characteristics

Attribute	Description	Example
Service Type	What kind of service this is	Internet Access, Voice, IPTV
Customer-Visible Parameters	Attributes the customer cares about	Download speed, number of channels, call minutes
SLA Parameters	Service level commitments	Availability: 99.9%, Max latency: 20ms
State	Lifecycle state of the service	Designed, Active, Suspended, Terminated

Resource-Facing Service (RFS)

An RFS represents a technical service component that is needed to deliver a CFS. It describes HOW a customer-facing service is implemented using specific technology. An RFS maps directly to resource configurations. Examples: "GPON Bearer Service", "SIP Trunk", "VLAN Assignment", "QoS Profile".

RFS is where technology choices become visible. A CFS "Internet Access" might decompose into different RFS combinations depending on the access technology: GPON, DOCSIS, Fixed Wireless, or DSL. This is where the service model becomes technology-specific.

CFS to RFS Decomposition Example

CFS: Internet Access (200Mbps) decomposes differently based on technology: (a) GPON: RFS:GPON-Bearer + RFS:VLAN-Service + RFS:IP-Profile + RFS:QoS-Profile. (b) DOCSIS: RFS:DOCSIS-Bearer + RFS:Cable-Modem-Config + RFS:IP-Profile + RFS:QoS-Profile. (c) Fixed Wireless: RFS:5G-FWA-Bearer + RFS:Radio-Profile + RFS:IP-Profile + RFS:QoS-Profile. The CFS remains the same — only the RFS decomposition changes per technology.

Resource

A Resource represents a physical or logical entity on the network that can be allocated, configured, and managed. Resources are the building blocks that RFS specifications consume. Examples: Physical — OLT port, ONT device, cable modem, antenna. Logical — VLAN ID, IP address, DHCP scope, routing table entry.

Resources are the concrete reality of the network. They are the actual things being configured. Each RFS maps to one or more resources. Resource management includes allocation (find a free one), configuration (set it up), and lifecycle management (monitor and eventually release).

Physical vs Logical Resources

Type	Examples	Management Concern
Physical Resource	OLT, ONT, Router, Switch, Antenna, Cable	Inventory tracking, capacity planning, field operations
Logical Resource	VLAN, IP Address, Port, QoS Policy, Routing Entry	Allocation, configuration, namespace management
Compound Resource	Network Slice, Virtual Network Function (VNF)	Orchestration, scaling, performance monitoring

The Full Decomposition Chain

Product → CFS → RFS → Resource

Product Specification

BSS — Product Catalog

Defines the product structure and links to required CFS types. Example: "Fixed Broadband" spec requires CFS:Internet-Access.

CFS (Customer-Facing Service)

OSS — Service Catalog

Describes the service outcome. Technology-neutral. Example: CFS:Internet-Access with speed=200Mbps.

RFS (Resource-Facing Service)

OSS — Service Catalog

Describes the technology-specific implementation. Example: RFS:GPON-Bearer, RFS:VLAN-Service, RFS:IP-Profile.

Resource

OSS — Resource Catalog/Inventory

The actual network elements to allocate and configure. Example: OLT Port 3 on OLT-EAST-07, VLAN 1042, IP 10.42.1.0/24.

Why Three Layers?

Think of ordering a meal at a restaurant. The product is "Steak Dinner" on the menu. The CFS is the experience: "a cooked steak with sides." The RFS is the kitchen's recipe: specific cuts, cooking method, plating. The resources are the actual ingredients: the steak, the potatoes, the pan, the oven.

Three layers provide separation of concerns:

CFS isolates the product from technology choices — you can change the network without changing what the customer sees
RFS allows technology-specific logic without polluting the customer experience layer
Resources can be managed independently — capacity planning, allocation, and lifecycle
Each layer can evolve at its own pace with clear interfaces between them

In TM Forum SID, the Service domain is separate from the Resource domain. TMF633 (Service Catalog Management) manages CFS and RFS specifications. TMF634 (Resource Catalog Management) manages Resource specifications. TMF638 (Service Inventory) tracks instantiated CFS/RFS. TMF639 (Resource Inventory) tracks instantiated resources.

The decomposition rules in the service catalog define how CFS maps to RFS, and how RFS maps to Resources. These rules are what Service Order Management (SOM) uses to orchestrate fulfilment. The rules can include conditional logic: "if access technology = GPON, use these RFS; if DOCSIS, use those."

Key Takeaways

CFS = what the customer experiences (technology-neutral service outcome)
RFS = how it is implemented (technology-specific service component)
Resource = what is physically/logically allocated on the network
One CFS can decompose into different RFS combinations based on technology
The three-layer model enables independent evolution of commercial, service, and resource domains
TMF633 manages CFS/RFS specifications; TMF634 manages Resource specifications