Overview
Network slicing in 5G refers to the allocation of network resources tailored to meet the specific requirements of different services. This approach allows for the creation of multiple virtual networks on a single physical infrastructure, each optimized for a particular use case such as enhanced Mobile Broadband (eMBB), Ultra Reliable Low Latency Communications (URLLC), or Massive Machine Type Communications (mMTC).
Components of Network Slicing in 5G Networks
A Network Slice includes resources from both the Core Network and Access Network, ensuring end-to-end service quality. Key elements include:
Base Station and CU-UP: - Control Plane (CP) - User Plane (UP) Separation: Supports multiple Central Units for - - User Plane (CU-UP), each potentially dedicated to different Network Slices (e.g., one for eMBB, another for URLLC). - Signaling: CU-UP communicates supported Network Slices to the Central Unit for Control Plane (CU-CP) using E1 Application Protocol (E1AP) messages like GNB-CU-UP E1 Setup Request.
Base Station and AMF: - Tracking Area Support: The Base Station provides the Access and Mobility Management Function (AMF) with supported Network Slices per Tracking Area via NGAP: NG Setup Request message. - PLMN Support: The AMF returns a list of supported Network Slices per Public Land Mobile Network (PLMN) through NGAP: NG Setup Response message. - Updates: Changes in supported Network Slices are communicated using NGAP: RAN Configuration Update and NGAP: AMF Configuration Update messages.
Core Network Functions and NRF: - Registration: Network Functions in the 5G Core Network register supported Network Slices with the Network Function Repository Function (NRF). Discovery: Other Network Functions use the NRF’s discovery service to find Network Functions supporting specific slices.
Network Slice Management
Each PDU Session belongs to only one Network Slice per PLMN, but a UE can use multiple slices by establishing multiple PDU Sessions. When roaming, a PDU Session may use different slices in the Visited and Home PLMNs.
Identification and Types of Network Slices
Network Slices are identified by Single Network Slice Selection Assistance Information (S-NSSAI), which combines:
Slice/Service Type (SST) (8 bits): Indicates expected behavior in terms of features and services. Standardized SST values include:
Slice Differentiator (SD) (24 bits, optional): Differentiates slices with the same SST, allowing operators to offer tailored services to different subscriber groups.
Network Slice Selection Assistance Information (NSSAI)
NSSAI is a set of S-NSSAI values. There are three categories of NSSAI:
Configured NSSAI: - A general set available within a specific PLMN. - Up to 16 S-NSSAI can be included. - Signaled to the UE using NAS: Registration Accept or NAS: Configuration Update Command messages.
Allowed NSSAI: - Authorized by the 5G Core Network for a specific UE. - Up to 8 S-NSSAI can be included. - Signaled to the UE and Base Station using NAS: Registration Accept and NGAP: Initial Context Setup Request messages, respectively.
Requested NSSAI: - Set of S-NSSAI the UE wishes to access, with a maximum of 8 Network Slices. - Provided to the Base Station within RRC Setup Complete message and forwarded to the AMF within NAS: Registration Request message. - The AMF uses this information to verify subscriptions and determine allowed slices.
Signaling Procedures
Key signaling procedures involving Network Slices include:
Interface and Network Function Setup: Exchange of supported Network Slices information during setup using various protocol messages.
UE Registration: Involves signaling of Requested and Allowed NSSAI.
PDU Session Establishment: UE specifies S-NSSAI for desired Network Slice within NAS: UL NAS Transport message during PDU Session request. The allocated slice is confirmed in NAS: PDU Session Establishment Accept message.
Roaming Scenarios
In a 'Home Routed' roaming scenario, the UE uses a network slice in the Visited PLMN and another in the Home PLMN, with connectivity managed between the two.
Conclusion
Network slicing in 5G networks enables tailored service delivery by creating multiple virtual networks optimized for specific use cases. This ensures efficient resource utilization and meets diverse application requirements, from high-throughput eMBB to low-latency URLLC and massive IoT connectivity through mMTC. By leveraging standardized and flexible slice configurations, 5G networks can provide enhanced user experiences and support advanced services across various industries.
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