Guaranteed Bit Rate (GBR) Slice

The defining feature of a GBR slice is a hard-coded minimum bit rate that is permanently reserved, regardless of overall network load. Unlike non-GBR slices that rely on statistical multiplexing, this slice type pre-allocates Physical Resource Blocks (PRBs) to satisfy the Guaranteed Flow Bit Rate (GFBR). This ensures that a remote-controlled robotic arm always has the exact uplink capacity required for real-time telemetry, even during peak hours in a congested cell.

GBR slices enforce a deterministic latency profile defined by the Packet Delay Budget (PDB). This parameter specifies an upper bound for the time a packet can spend traversing the 5G system between the User Equipment (UE) and the N6 interface. For industrial automation, this is often configured to sub-5ms values, requiring slice-aware scheduling at the MAC layer to prioritize GBR traffic over non-GBR flows, preventing jitter that would destabilize a motion control loop.

To protect existing sessions, a GBR slice implements strict admission control. When a new Protocol Data Unit (PDU) session requests resources, the Slice Admission Control function calculates if the remaining unreserved PRBs can satisfy the new request's GFBR without violating the guarantees of active sessions. If resources are insufficient, the request is rejected immediately, preserving the deterministic quality of service for all admitted users. This prevents the tragedy of the commons seen in non-GBR slices.

While a floor is guaranteed, a ceiling is also enforced via the Maximum Flow Bit Rate (MFBR). This parameter caps the throughput a session can achieve, preventing a single UE from monopolizing excess resources. This is critical for slice isolation—it ensures that a misbehaving application on one GBR slice cannot burst into the capacity reserved for another tenant's critical slice. Traffic exceeding the MFBR is shaped or policed at the User Plane Function (UPF).

GBR slices present a fundamental challenge for energy-saving features like Cell DTX or Sleep Mode Coordination. Because resources are permanently reserved, the base station cannot easily deactivate carriers or mute resource blocks during low activity without risking a violation of the GFBR. Advanced energy-aware schedulers must therefore use predictive analytics from the NWDAF to identify genuine idle periods within the GBR allocation before triggering low-power states, balancing the SLA against the Slice Carbon Footprint.

Within a GBR slice, the actual guarantee is enforced at the QoS Flow level, not the PDU session level. A single PDU session can host multiple QoS Flows, each with its own GFBR and MFBR. The Service Data Adaptation Protocol (SDAP) layer maps these flows to Data Radio Bearers (DRBs). This granularity allows a single industrial sensor to simultaneously transmit a GBR flow for safety-critical shutdown signals and a separate non-GBR flow for firmware telemetry, all within the same slice instance.

A radio resource management technique where the MAC-layer scheduler prioritizes and allocates physical resource blocks to users based on the specific latency, throughput, and reliability requirements of their assigned network slice. For a GBR Slice, the scheduler must strictly enforce resource reservations to meet the fixed bandwidth commitment, often using reservation-based scheduling algorithms that pre-allocate time-frequency resources before serving non-GBR traffic.

A formal contract between a slice tenant and a network operator that defines the quantifiable performance metrics a network slice instance must deliver. For a GBR Slice, the SLA explicitly specifies:

• Guaranteed Flow Bit Rate (GFBR) — the bit rate the network commits to maintain
• Maximum Flow Bit Rate (MFBR) — the upper limit for the flow
• Packet Delay Budget (PDB) — the maximum latency tolerated Violations of these parameters typically trigger financial penalties.

A mechanism that accepts or rejects a request to establish a new PDU session within a network slice based on resource availability and slice policies. For a GBR Slice, the admission control function must verify that sufficient dedicated resources exist to satisfy the requested GFBR without degrading existing GBR sessions. If resources are insufficient, the request is rejected to preserve the deterministic guarantees of active flows.

A 5G network slice type engineered for extremely low latency (<1ms) and high reliability (99.999%). While distinct from a standard GBR Slice, URLLC slices represent the extreme end of deterministic performance. A GBR slice may be configured with URLLC-like parameters for industrial automation use cases, combining fixed bandwidth commitments with stringent latency bounds for applications like closed-loop control and remote surgery.

The ability of a network slice to dynamically scale its allocated virtualized resources up or down in response to real-time workload fluctuations. For a GBR Slice, elasticity is constrained by the fixed bandwidth commitment — resources cannot scale below the GFBR floor. However, the slice can elastically expand up to the MFBR ceiling during traffic bursts, provided the underlying physical infrastructure has available capacity.

The capability to contain faults, performance degradation, and security attacks within a single network slice instance. For a GBR Slice, strict isolation is critical — a traffic surge or denial-of-service attack on a neighboring non-GBR slice must not steal the dedicated resources reserved for the GBR flow. This is enforced through resource partitioning at the RAN, transport, and core network levels.