Nokia SR Platform: FP4 and FP5 Buffering
Nokia's FP (Forwarding Plane) architecture in the 7750 SR platform uses a fully buffered design — packet buffering is deeply integrated into both ingress and egress pipelines across all generations.
Both FP4 and FP5:
- Use shared packet memory pools dynamically allocated across ports, queues, and services
- Implement a pre-buffer stage that absorbs bursts before traffic classification
- Maintain QoS-aware scheduling tied to buffer state
- Support dynamic queue reallocation without changing buffer pool size
FP4 Buffering
Buffer Size and Structure
- Up to ~64 GB packet buffer per line card
- Fully shared between ingress and egress
- Buffer is not statically assigned to ports
Pre-buffer (front-end buffering)
- Multi-million packet capacity (varies by implementation)
- Used for microburst absorption, pre-classification staging, and QoS protection
Queue Model
- Default: 128k ingress + 128k egress queues
- Reallocation supported in 8k increments
Interface-Level Behavior
FP4 buffering enables:
- High fan-in aggregation (many 10G/100G feeding fewer uplinks)
- Absorption of speed mismatches and traffic bursts
- Deterministic QoS enforcement under congestion
FP4 introduced "intelligent aggregation": buffering allows oversubscription while maintaining SLA guarantees.
FP5 Buffering
Buffer Size and Pre-buffer
- 32 GB to 64 GB packet buffer per line card
- Pre-buffer capacity: ~10.8M to 21.6M packets (64-byte units)
- Example configurations: 32 GB + 10.8M packets, or 64 GB + 21.6M packets
Architectural Enhancements over FP4
Improved buffer efficiency — better utilization of shared memory, reduced head-of-line blocking, more effective burst absorption at high speeds.
Tighter pre-buffer integration — closer coupling between pre-buffer, forwarding pipeline, and QoS scheduler.
Higher scale queueing — queue reallocation increments doubled to 16k (vs 8k in FP4).
Higher throughput — FP5 approximately doubles forwarding capacity over FP4: ~3 Tbps to ~6 Tbps per NPU generation.
Interface-Level Behavior
FP5 is optimized for:
- 400G / 800G interfaces
- High-density edge and core aggregation
- Deep burst absorption at very high line rates
- More stable QoS under heavy load
FP5 does not significantly increase raw buffer size over FP4, but delivers higher effective buffer utilization, greater aggregation scale, and improved latency consistency under congestion.
FP4 vs FP5 Comparison
| Feature | FP4 | FP5 |
|---|---|---|
| Buffer size | ~64 GB/LC | 32–64 GB/LC |
| Pre-buffer | Multi-million packets | ~10.8M–21.6M packets |
| Buffer model | Fully shared | Fully shared (enhanced) |
| Queue realloc increment | 8k | 16k |
| Default queues | 128k ingress / 128k egress | 128k ingress / 128k egress |
| Pipeline integration | Pre-buffer + forwarding | Tighter integration |
| Throughput class | ~3 Tbps | ~6 Tbps |
| Target interfaces | up to 400G | 400G / 800G |
| Key strength | Deterministic buffering | Efficiency + scale |
Core Architectural Concepts
Shared Buffer Pools
Memory is dynamically allocated across ports, queues, and services. This maximizes utilization under mixed workloads — a port with no traffic does not waste buffer that a congested port could use.
Pre-buffering
The first stage of packet handling absorbs bursts before classification. This protects high-priority traffic flows from drops during transient congestion spikes, even before QoS scheduling has acted.
QoS-Coupled Buffering
Buffers are tightly linked to queue scheduling and congestion avoidance (e.g., WRED). This enables deterministic forwarding behavior: the system can make drop decisions based on queue depth with high precision.
Queue Flexibility
Queues can be reallocated between ingress and egress. This does not impact total buffer pool size — it only changes how queue resources are divided.
See Also
- Nokia 7750 SR detail page — buffer specs by FP generation
- Nokia 7730 SXR detail page — FP5 in a core/DCI platform
- Nokia Access/Aggregation platforms — merchant silicon and SAR ASIC comparison
- Back to the main buffer table
References
- Nokia SR OS QoS Guide (FP resource and queue behavior): documentation.nokia.com
- Nokia Partner Training (FP5 hardware, buffer and pre-buffer values): Scribd document 934362600
- Nokia FP4 vs FP5 architecture overview: Scribd document 931308604