Packet Buffer Reference

FS N9510 / N9550 / N8610 Series (Broadcom Tomahawk 4)

FS produces four Tomahawk 4-based platforms covering high-density 400G spine and AI/ML fabric deployments. Three models use the full BCM56990 (25.6 Tbps, 64-port); one uses the half-capacity BCM56993 (12.8 Tbps, 32-port).

Models

Model ASIC Ports Capacity Buffer
N9510-64D BCM56990 (Tomahawk 4) 64x 400G QSFP-DD 25.6 Tbps 113.66 MB
N9550-64D BCM56990 (Tomahawk 4) 64x 400G QSFP-DD, 2x 10G SFP+ 25.6 Tbps 113.66 MB
N8610-64D BCM56990 (Tomahawk 4) 64x 400G QSFP-DD 25.6 Tbps 113.66 MB
N8610-32D BCM56993 (Tomahawk 4) 32x 400G QSFP-DD, 2x 10G SFP+ 12.8 Tbps 56.83 MB

The N9510-64D and N9550-64D are 1U platforms; the N8610 is a 2U platform offering different airflow and cabling configurations. All BCM56990 models carry exactly 113.66 MB of buffer — the precise on-die SRAM figure that vendors round to "~114 MB" in marketing materials.

Buffer Architecture

BCM56990 models (N9510-64D, N9550-64D, N8610-64D)

The BCM56990 carries 113.66 MB of on-chip SRAM presented as a fully shared packet buffer. Broadcom describes this as providing "up to 10x burst absorption versus alternatives." All 64 400G ports share access to the entire pool simultaneously; no bandwidth is stranded in idle pipeline slices.

The 113.66 MB figure is confirmed from the FS N9510-64D official product page and is consistent across all BCM56990-based platforms.

BCM56993 model (N8610-32D)

The BCM56993 is the half-bandwidth variant of the Tomahawk 4 family, carrying 56.83 MB of on-chip SRAM — exactly half of the BCM56990's 113.66 MB, consistent with the proportional reduction in bandwidth (12.8 Tbps vs. 25.6 Tbps). The buffer architecture is identical: fully shared, unified pool accessible to all 32 400G ports.

Key features across all models

References

See Also