Monitoring Dedicated Switch Selection: How to Calculate Backplane Bandwidth, Packet Forwarding Rate, and Number of Ports

Release time：2026-09-05 00:00 Views：69 author：Xinlaida Security Technology Department source：technical knowledge
Starting from the actual code stream of the camera, calculate how much bandwidth and packet forwarding capacity the access layer and aggregation layer switches need to avoid "port enough but not enough forwarding".

Calculate the total front-end bandwidth first

Do not estimate by port rate, but by actual bitstream.Taking 4 megapixel H.265 as an example, the main bitstream is about 4 Mbps, and the sub-bitstream is about 0.5 Mbps.A 24-port switch with 24 cameras:

  • Main stream: 24 × 4 = 96 Mbps (upstream to NVR)
  • Sub-stream: 24 × 0.5 = 12 Mbps (for preview)
  • The total is about 108 Mbps, and 30% of the margin is also reserved. It is recommended to select the model at 150 Mbps.

Two easily overlooked metrics

< table border = "1" cellpadding = "8" cellspacing = "0" style = "border-collapse: collapse; width: 100%" > MetricsMeaningCommon pits Backplane bandwidthSwitch internal bus total throughputIt is marked with the theoretical value of "non-blocking", and it is necessary to confirm whether it is true Packet Forwarding RateNumber of packets that can be forwarded per secondVideo is a dense flow of small packets, a metric that is more likely to be a bottleneck than bandwidth CacheBurstTraffic buffering capabilityMultiple simultaneous bursts will drop packets when the cache is insufficient

Differences between the Access Layer and the Aggregation Layer

The access layer focuses on the number of ports, PoE power supply power, and overall PoE budget. It should be noted that "nominal 24-port PoE" does not mean that 24-ports can be fully powered, and the power budget of the whole machine is often only half of the full power of the port.

The convergence layer focuses on uplink bandwidth and packet forwarding rates.The main bitstream of all access layers should be converged here, if the convergenceThere is only 1 gigabit port upstream of the switch, but when the actual traffic is close to gigabit, there will be periodic stuttering.

Helpful tips

  • When the number of cameras exceeds 40, it is recommended to go up the aggregation layer and do link aggregation, not all plugged into one access switch.
  • Prefer a managed switch that supports VLAN isolation from ports for fast positioning during broadcast storms.
  • The PoE switch should have a 20% power margin, and the low-temperature starting current will be greater in winter.

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