Will the data stream fit?

How it is calculated

The tool computes the camera data stream and compares it with the usable bandwidth of the interface, not the nominal figure on the label. For several cameras the streams are added up; for CoaXPress and Camera Link the number of lanes is considered; for frame grabbers the tool counts how many cameras fit on one board and how many boards are needed. The camera datasheet (resolution, maximum frame rate, bit depth, interface) is filled in from the catalogue by model or part number, and every field can be edited.

Formulas

• Stream of one camera: Gbit/s = width_px · height_px · fps · bits / 10⁹. Bits follow the pixel format: Mono8 and Bayer8 — 8 bits, packed 10- and 12-bit formats — 10 and 12 bits, unpacked 10- and 12-bit formats occupy 16 bits per pixel on the wire.
• System stream: the sum of all cameras sharing one link (switch, grabber port, USB controller).
• Usable interface bandwidth: GigE — 0.90 Gbit/s; 2.5GigE, 5GigE, 10GigE — 0.90 of nominal (2.25 / 4.5 / 9.0); USB3 — 3.2 Gbit/s (real-world for cameras at a nominal 5); CoaXPress — 0.8 of the lane rate (CXP-6: 5.0 per lane, CXP-12: 10.0 per lane) multiplied by the number of lanes; Camera Link base / medium / full — 2.04 / 4.08 / 5.44 Gbit/s; Fast Ethernet — 0.09 Gbit/s.
• Verdict: stream ≤ usable bandwidth — passes; above it — fails. The tool never reports “headroom” above the usable bandwidth.
• Frame grabbers: cameras per board = floor(board sustained bandwidth / camera stream), boards = ceil(cameras / cameras per board). If the board bandwidth is not in the datasheet, the board count is left to the engineer.

Worked examples

Example 1. A 5-megapixel GigE camera. 2448 × 2048 px at 24.2 fps, 8 bit: 0.971 Gbit/s. That exceeds the usable GigE bandwidth of 0.90, so this frame rate does not pass on GigE; real GigE cameras of this class deliver about 22–23 fps at 8 bit. At 12 bit unpacked the stream doubles (16 bits per pixel); packed Mono12p grows by one half. Twice the frame rate needs 2.5GigE.

Example 2. USB3. The same sensor on USB3 with 3.2 Gbit/s usable: up to 79 fps at 8 bit, up to 39 fps at unpacked 12 bit.

Example 3. CoaXPress. A 5120 × 5120 px camera at 130 fps, Mono12 packed: 40.9 Gbit/s. The CXP-12 limit on four lanes is 4 × 10.0 = 40 Gbit/s: it fails, the verdict is red, and the request records a refusal rather than “headroom”.

Example 4. Frame grabbers. Four CXP cameras at 2457.6 MB/s each. A board with 3350 MB/s sustained takes one camera — four boards are needed; a 6700 MB/s board takes two — two boards.

Example 5. Many GigE cameras. Eight cameras 2448 × 2048 at 24.2 fps, 8 bit — 7.8 Gbit/s in total. One gigabit port cannot carry that: use a switch with a 10GigE uplink, several network adapters, or a lower frame rate. A GigE adapter board is optional in this layout, and the tool says so in one sentence.

Common mistakes

• Comparing with the nominal 1 Gbit/s instead of the usable 0.9: the camera “passes” on paper and drops frames on the line.
• Treating 10- and 12-bit formats as 8-bit: the stream is underestimated by 1.5–2 times.
• Forgetting the shared link: four cameras at 0.7 Gbit/s each do not fit into one switch port.
• Not checking the CoaXPress lane count: DIN ×1 and ×4 connectors differ four-fold in bandwidth.
• Running USB3 beyond 3–5 m without an active cable or repeater.
• Skipping the PoE budget: a switch with limited power cannot feed all cameras at once.

Questions and answers

Stream rate and usable interface bandwidth