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N1 mode / S1 mode

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The terms "N1 mode" and "S1 mode" are associated with the 5G mobile network architecture and refer to specific modes of operation within the 5G system. Let's explore the technical details of each mode:

1. N1 Mode:

a. Definition:

  • N1 Mode: N1 mode refers to the Non-Standalone (NSA) mode in 5G network architecture. In the context of 5G, Non-Standalone means that the 5G radio access network (New Radio or NR) is supported by an existing 4G LTE core network (Evolved Packet Core or EPC).

b. Key Components:

  • 5G NR (New Radio): The radio access network component of 5G that introduces new frequency bands, higher data rates, and improved spectral efficiency.
  • 4G LTE EPC (Evolved Packet Core): The core network component of 4G LTE, which provides the backbone for user authentication, connectivity, and data services.

c. Operation:

  • In N1 mode, the 5G NR operates alongside the existing 4G LTE infrastructure. The 5G NR is used for data transmission, while the LTE EPC handles control signaling, user authentication, and other core network functions.

d. Use Cases:

  • N1 mode allows for the introduction of 5G capabilities, such as enhanced mobile broadband (eMBB), while leveraging the existing LTE infrastructure.
  • It is a transitional mode, enabling the gradual deployment of 5G without the need for an immediate overhaul of the entire network.

e. Advantages:

  • Faster deployment of 5G services since it relies on the existing LTE core.
  • Easier upgrade path for operators with established LTE networks.

f. Challenges:

  • Limited realization of the full potential of 5G as some advanced features may not be available in N1 mode.
  • Dependency on LTE infrastructure for certain core network functions.

2. S1 Mode:

a. Definition:

  • S1 Mode: S1 mode is associated with the Standalone (SA) mode in 5G network architecture. In the Standalone mode, both the radio access network (5G NR) and the core network (5G Core or 5GC) are entirely based on 5G specifications.

b. Key Components:

  • 5G NR (New Radio): Continues to be the radio access network, providing connectivity and data services.
  • 5G Core (5GC): The core network component designed specifically for 5G, introducing new architecture and capabilities.

c. Operation:

  • In S1 mode, the 5G NR operates independently of the LTE infrastructure. Both the radio access network and the core network are fully 5G-compliant.
  • The 5G Core supports new features and services, providing a more flexible and scalable architecture.

d. Use Cases:

  • S1 mode unlocks the full potential of 5G, enabling the deployment of advanced use cases such as ultra-reliable low latency communication (URLLC) and massive machine-type communication (mMTC).
  • It supports end-to-end 5G services without reliance on legacy LTE components.

e. Advantages:

  • Enables the deployment of advanced 5G features and use cases.
  • Provides a more flexible and scalable core network architecture.

f. Challenges:

  • Requires a comprehensive upgrade of both radio access and core network components.
  • Operators need to invest in new infrastructure to fully realize the benefits of 5G in S1 mode.

3. Transition from N1 to S1 Mode:

  • Operators often deploy networks in N1 mode initially to kickstart 5G services and gradually transition to S1 mode as they phase out the dependency on LTE infrastructure.
  • The transition involves upgrading both the radio access network and the core network to support standalone 5G operations.

4. Considerations:

  • The choice between N1 mode and S1 mode depends on operator strategies, existing network infrastructure, and the pace of 5G deployment.
  • The coexistence of N1 and S1 modes allows for a flexible and gradual migration to fully standalone 5G networks.

In summary, N1 mode represents the Non-Standalone mode, where 5G NR operates alongside the existing LTE core, facilitating a smooth transition to 5G. On the other hand, S1 mode denotes the Standalone mode, where both the radio access network and the core network are based on 5G specifications, enabling the deployment of advanced 5G services. The transition between these modes allows operators to balance the need for rapid 5G deployment with the aspiration for a fully standalone 5G network.