Switch latency reference
Cisco Nexus 3550 Latency by Mode
A Nexus 3550 has no single latency figure. Cisco publishes 3–5 ns for a 3550-F Layer 1 tap or patch path, while its FastMux, Layer 2 and Layer 3 paths do more work and have different figures. Select the model and forwarding mode that match the path you are designing.
Cisco Nexus 3550 latency comparison
| Model | Mode | Latency | What the figure describes | Source |
|---|---|---|---|---|
| Nexus 3550-F | Layer 1 tap / patch | 3–5 ns | Physical-layer path; the 3 ns figure is the minimum. | Cisco specification |
| Nexus 3550-H | Layer 1 tap / patch | 3.2 ns minimum | Dedicated datasheet figure; Cisco’s family comparison lists 5 ns. | Cisco specification |
| Nexus 3550-F | FastMux | 39–48 ns | 10GbE multiplexing with Layer 1 demultiplexing. | Cisco specification |
| Nexus 3550-F | Mux | 92–107 ns | 1/10GbE multiplexing; supports Layer 2 and VLAN demultiplexing. | Cisco specification |
| Nexus 3550-F | Layer 2 application | 95–126 ns | Switching with MAC learning; minimum depends on features and configuration. | Cisco specification |
| Nexus 3550-T | Layer 2 switching | 96 ns minimum | Layer 2 switching figure from Cisco’s model comparison. | Cisco specification |
| Nexus 3550-T | Layer 3 switching | 130 ns minimum | Layer 3 switching figure from Cisco’s model comparison. | Cisco specification |
Why the mode changes the result
A Layer 1 patch path forwards the signal without Layer 2 switching. FastMux combines traffic from multiple inputs. A Layer 2 application can learn MAC addresses and handle switching features; the 3550-T also has a Layer 3 path. These are different functions, so comparing their lowest numbers as though they measured the same work would be misleading.
Cisco notes that its 39 ns Layer 2 multiplexing minimum is unavailable at maximum fan-in or with Layer 2 features. The detailed 3550-F application datasheet publishes mode ranges; an installed configuration can differ from the stated minimum. Transceivers, cables and queuing are outside the switch figures shown here.
Using these figures in a path estimate
Choose the number for the application actually carrying traffic, then add other devices and link propagation once each. The general device latency table retains its own catalog estimates, which should not be silently substituted for a mode-specific Cisco minimum. Use the network latency calculator to build the complete path and confirm important designs with measurements.
For another FPGA-based Layer 1 platform, see the Arista 7130 and Cisco 3550 comparison.
Manufacturer sources
Cisco Nexus 3550 model comparison · Cisco 3550-F Layer 1 and multiplexer datasheet · Cisco 3550-H Layer 1 datasheet · Cisco 3550-F Layer 2 application datasheet