Network Domains
Every telco service traverses one or more network domains on its journey from customer to content. Understanding these domains is essential for knowing where BSS/OSS orchestration reaches into the network, and which systems own each layer.
Click a domain box for details. Toggle extended view to see example technologies.
Customer
End-user devices and customer-premises equipment. Everything on the customer side of the UNI (User Network Interface). The operator typically supplies and manages CPE (ONT, router, STB) but does not own the customer's devices.
Technologies
- CPE / ONT
- Home router / Wi-Fi
- Mobile handset
- STB / Smart TV
- IoT devices
4G EPC vs 5G Core — What Changed
The mobile core architecture changed fundamentally between 4G and 5G. This matters for BSS/OSS because it changes how SOM provisions subscribers, how ROM activates network functions, and what APIs are available.
| Aspect | 4G EPC | 5G 5GC |
|---|---|---|
| Architecture | Monolithic network elements (MME, SGW, PGW) — tightly coupled | Service-based architecture (SBA) — microservices communicating via HTTP/2 |
| Control / User Plane | Coupled — SGW/PGW handle both signalling and data forwarding | Fully separated (CUPS) — SMF controls, UPF forwards. UPF can be deployed at the edge independently |
| Subscriber DB | HSS (Home Subscriber Server) — single monolithic database | UDM (Unified Data Management) + UDR (data repository) — separated compute from storage |
| Policy | PCRF — Diameter Gx/Rx interfaces | PCF — HTTP/2 SBI (Npcf). Supports network slicing policies per slice |
| Mobility | MME handles all mobility, authentication, and bearer management | AMF (mobility/auth) + SMF (session) — split responsibilities. AUSF handles authentication separately |
| Network Slicing | Not supported — single shared network for all subscribers | Native — dedicated virtual networks per slice with isolated resources, QoS, and charging |
| SOM/ROM Interface | Proprietary vendor APIs or Diameter adapters. Each NE has its own activation interface | RESTful SBI APIs (HTTP/2). NRF provides service discovery — SOM can discover available NFs dynamically |
| Scaling | Scale the whole node — vertical scaling, capacity planning per element | Each function scales independently — horizontal scaling, Kubernetes-native auto-scaling |
| Deployment | VNFs on OpenStack (Gen 1 NFVI) or dedicated hardware | CNFs on Kubernetes (Gen 2 NFVI) — cloud-native, CI/CD compatible |
Why this matters for BSS/OSS: In 4G, SOM provisions each subscriber by calling proprietary vendor APIs or Diameter adapters on the HSS, PCRF, and OCS — each with its own interface. In 5G, SOM can use standardised HTTP/2 REST APIs via the SBI, and NRF provides dynamic service discovery so SOM doesn't need to hardcode NF endpoints. Network slicing adds a new dimension: SOM must now provision per-slice resources, policies, and charging — a CFS may decompose into slice-specific RFS items that didn't exist in 4G.
IMS — Voice in the Core Network
The IP Multimedia Subsystem (IMS) is the operator's voice and rich communication platform. It sits inside the core network alongside the packet core, providing three primary capabilities: voice (VoLTE, VoNR, VoWiFi, SIP trunking), Rich Communication Services (RCS — messaging, video, presence), and supplementary services (conferencing, call forwarding, voicemail). IMS was not replaced in 5G — 3GPP kept it as the voice platform, connected via the UPF instead of the PGW.
Why this matters for BSS/OSS: SOM does not orchestrate inside the IMS at runtime — the IMS handles SIP session signalling autonomously. What SOM provisions is the subscriber profile (HSS/UDM record, SIP credentials, number assignment) and, for B2B SIP trunking, the SBC configuration (trunk capacity, codec policy, routing rules). The IMS internal signalling chain (P-CSCF → S-CSCF → I-CSCF) is self-orchestrating and does not require per-order configuration from BSS/OSS.
ETSI MANO: VNFs and CNFs running in the Mobile Core and Service Platforms domains are lifecycle-managed by the ETSI MANO framework — NFVO (orchestrates VNF/CNF deployment), VNFM (manages individual NF instances), and VIM (manages the underlying compute/storage/network infrastructure). MANO sits in the management plane, not the data plane — it does not carry traffic, but it controls which network functions exist, where they run, and how they scale. In 5G cloud-native deployments, NFVO increasingly delegates to Kubernetes for CNF lifecycle, but the orchestration responsibility remains.
Which Examples Touch Which Domains
| Worked Example | Access | Aggreg. | IP Core | Mobile | Svc Plat. |
|---|---|---|---|---|---|
| Enterprise VPN (L3VPN) | · | ● | ● | · | · |
| Enterprise SD-WAN | · | ● | ● | · | ● |
| SIP Trunk / Hosted Voice | · | · | ● | · | ● |
| IoT / M2M Connectivity | ● | · | · | ● | · |
| Satellite (Maritime LEO) | ● | · | ● | · | ● |
| Mobile SIM Activation | ● | · | · | ● | · |
| Broadband Internet (FTTH) | ● | ● | ● | · | · |
| IPTV / Triple-Play | ● | ● | ● | · | ● |
| VOD / Streaming | · | · | · | · | ● |
| 5G Network Slice (B2B) | ● | · | · | ● | · |