Description
The Shared Network Area Code (SNAC) is a critical identifier within the UMTS architecture, specifically defined in the Radio Access Network Application Part (RANAP) protocol as per 3GPP TS 25.413. It operates within the context of a shared network, a scenario where multiple Public Land Mobile Network (PLMN) operators utilize a common radio access network (RAN) infrastructure, such as Node Bs and Radio Network Controllers (RNCs), but maintain independent core network (CN) elements like Mobile Switching Centers (MSCs) and Serving GPRS Support Nodes (SGSNs). The SNAC's primary function is to provide unambiguous identification of a specific shared network area, which is a geographical region served by the shared RAN.
From an architectural perspective, the SNAC is used by the RNC to route signaling and user data to the correct core network operator's node. When a User Equipment (UE) initiates a connection in a shared network area, the RNC receives the UE's International Mobile Subscriber Identity (IMSI) or Temporary Mobile Subscriber Identity (TMSI). The RNC uses configuration mapping, often based on the Mobile Network Code (MNC) part of the IMSI or other routing information, to determine the appropriate core network operator. The SNAC is then included in relevant RANAP messages, such as the Initial UE Message or the Relocation Required message, to inform the core network about the specific shared area from which the connection originates. This allows the core network node to apply correct subscriber policies, charging rules, and mobility management procedures specific to that shared area.
The protocol handling involves the SNAC being a parameter within RANAP information elements. It ensures that during procedures like handover, paging, or location updating, the network can correctly associate the UE's activity with the right operator's domain within the shared infrastructure. Without the SNAC, ambiguity could arise, leading to routing errors, failed handovers, or incorrect service provisioning. Therefore, the SNAC is a foundational element for the practical implementation of 3GPP-specified network sharing models, such as Multi-Operator Core Network (MOCN) and Gateway Core Network (GWCN), enabling technical and commercial collaboration between operators.
Purpose & Motivation
SNAC was created to address the technical challenges of infrastructure sharing between mobile network operators. Prior to its specification, each operator typically deployed its own exclusive RAN and CN. As spectrum and site acquisition became more expensive and regulatory pressures for coverage increased, operators sought ways to reduce capital and operational expenditures through sharing. The initial approaches lacked a standardized method for the RAN to distinctly identify and route traffic to multiple core networks over the same physical infrastructure.
The introduction of SNAC in Release 5 provided this standardized identifier. It solved the problem of unambiguous area identification within a shared RAN, which is essential for core network selection, lawful interception, charging, and mobility management. For example, during a handover from a non-shared area to a shared area, the target RNC needs to signal to the correct core network operator which specific shared area is involved. SNAC provides this critical piece of information, ensuring seamless service continuity and proper administrative segregation between sharing partners. Its creation was motivated by the industry's move towards network sharing as a strategic tool for rapid deployment, especially for 3G/UMTS networks, and for providing coverage in rural or challenging areas where individual network deployment was not economically viable.
Key Features
- Uniquely identifies a shared network area within a PLMN
- Enables correct routing of signaling and user data to the appropriate core network operator in a shared RAN scenario
- Parameter within the RANAP (Radio Access Network Application Part) protocol
- Essential for mobility procedures like handover and relocation in shared networks
- Supports network sharing architectures like MOCN (Multi-Operator Core Network)
- Facilitates separate operation and maintenance for each operator in the shared area
Evolution Across Releases
Introduced as a new parameter in the RANAP protocol (TS 25.413) to support the initial standardization of network sharing features. It provided the basic mechanism for a Radio Network Controller (RNC) to identify and signal the specific shared network area to the Core Network, enabling foundational shared network operations.
Defining Specifications
| Specification | Title |
|---|---|
| TS 25.413 | 3GPP TS 25.413 |