GigE camera network planning: switch ports and bandwidth

You are putting two or three GigE Vision cameras on one PC, and the option sheets are no help: "Gigabit Ethernet ready, quantity 2" tells you nothing about the host. The engineering answer is short. One gigabit link carries about 100 MB/s after overhead, one busy camera consumes all of it, so the plan is one host port per busy camera, camera traffic on its own network, and a switch only for slow cameras. This guide gives you the data-rate formula, the port rules, a worked example with the arithmetic shown, and the checks to run before ordering network cards.

What one gigabit link really carries

Gigabit Ethernet moves 1,000 Mbit/s, which is 125 MB/s on paper. Interpacket gaps, headers and host overhead take roughly a fifth of that, so the planning number is 100 MB/s per link. That figure matches standard camera-bus selection practice and is the number to use for bandwidth planning for machine vision cameras: a camera producing more than 100 MB/s on average cannot be fixed with settings, only with a faster link or fewer bytes per frame.

Sharing a link costs more than the obvious division. When two cameras send through one port, their packets interleave and each frame takes longer to transfer than it would alone; the stretch is worst exactly when both cameras expose together. That packet delay under load is why a shared gigabit uplink gets an 80 MB/s budget rather than 100, and why GigE Vision frame arrival jitter shows up first on shared links.

The port rules that settle the question

Four rules cover nearly every cell:

1. Compute each camera's average data rate with the formula below.
2. Any camera above 60 MB/s gets a dedicated gigabit port.
3. Cameras may share a switch uplink only while their combined rate stays under 80 MB/s.
4. Camera traffic lives on its own network; the plant LAN keeps the business traffic.

Typical rates for mono 8-bit cameras:

Read the table as decisions. A 5 MP camera at 20 fps fills one port exactly. A 12 MP or 20 MP camera at 10 fps already exceeds gigabit, so it runs at a lower frame rate, crops at the sensor, or moves to 10GigE. Cabling follows the same budget — the GigE Vision camera selection walkthrough covers the camera-side half of that choice.

Worked example: one PC, a 12 MP camera and two 5 MP cameras

Inputs:

• Camera in place: the LS-CMR-0053, a 12 MP GigE camera that runs at 9 fps.
• Two new cameras: 5 MP mono, 2448 × 2048 pixels, 15 fps each, one frame per part.
• Host: a PC whose single onboard port already carries the plant network.

Arithmetic:

• 12 MP mono frame: 4000 × 3000 × 1 byte = 12,000,000 bytes = 12 MB. At 9 fps: 12 × 9 = 108 MB/s.
• Each 5 MP mono frame: 2448 × 2048 × 1 = 5,007,104 bytes ≈ 5 MB. At 15 fps: 5 × 15 = 75 MB/s.
• Combined demand: 108 + 75 + 75 = 258 MB/s.

Decisions:

• Shared gigabit uplink: 258 MB/s against an 80 MB/s budget — rejected by better than a factor of three. No switch fixes this.
• Dedicated ports: 108 MB/s sits under the 125 MB/s line rate, so the 12 MP camera keeps a port to itself with jumbo frames enabled; if late frames still appear, 8 fps brings it to 96 MB/s. Each 5 MP camera at 75 MB/s fits its own port with margin.
• Hardware: one four-port gigabit card — three ports used, one spare. A fourth camera of the same type still fits; past four cameras, move the uplink to 10GigE.

Host ports: which cards to buy

An option line that sells "Gigabit Ethernet ready" ports by quantity buys ports inside the controller, not in the PC. Ordering two puts two ports on the controller chassis; your PC still has only what you fit in it. The onboard port belongs to the plant network, so the cameras need their own PCIe cards — one port per busy camera plus a spare, in as few cards as you have slots.

For three or four cameras, the default is a multi-port card:

The MV-GE1104 is a 4-port GigE frame grabber: four cameras, four full links, one slot.

For cameras that take power over Ethernet, a PoE card; for a 10-gigabit uplink, a 10GbE card:

The MV-GE2002P is a dual-port PoE NIC: each port carries a camera's data and its power on one cable. The LS-FGB-0004 is a PCIe x4, 4-port PoE Gigabit Ethernet card. The MV-GT2104 is a quad-port copper 10GbE NIC for switch uplinks, and the MV-GT1102P is a dual 10GigE frame grabber when two uplinks are enough. All of these sit in the frame grabbers category alongside the 10GigE and Camera Link options.

Plan the cable at the same time as the card: shielded Cat5e or better, locking connectors, high-flex only where the cable moves. The LS-CBL-0199 is a 3 m high-flex GigE camera cable with screw locks for drag-chain duty; the LS-CBL-0117 is a 15 m RJ45 camera data cable with a locking stud for static runs. Browse camera cables by type and length, and give each camera a fixed address before it reaches the cell — assigning cameras to ports reliably saves a day of commissioning. On the robot side, the same one-port-per-camera logic applies when connecting a GigE camera to a robot controller.

When a switch is the right answer

A switch belongs in three situations: many slow cameras whose rates sum under 80 MB/s; a camera and a controller sharing one cable run to the host; or cameras mounted far from the PC, where a switch shortens each copper segment to 100 m or less.

The switch must be managed: jumbo frames end to end, and IGMP snooping so camera streams do not flood every port. Keep the whole camera network on its own card or VLAN — vision cell network isolation is the pattern that stops plant broadcast traffic from eating your frame time. For the hardware itself, DIN-rail industrial Ethernet switches for camera networks covers port counts, mounting and cabinet power for exactly this use.

When the camera count outgrows gigabit, keep the switch and uplink it at 10G. A 10-gigabit link carries about 1,000 MB/s in practice, ten times a gigabit port, into the quad-port 10GbE card above. That single change turns "one port per camera" into "one uplink per cell" without touching the cameras.

Checks before you order

These extend the checks in multi camera system design for reliable image capture to the network layer:

1. Port count: cameras plus one spare, on the cards your slots allow.
2. Rate budget: run the formula per camera; every camera above 60 MB/s gets its own port, shared uplinks stay under 80 MB/s total.
3. PoE budget: add the camera draws and compare with the card's per-port and total supply.
4. Cables: shielded Cat5e or better, locking connectors, high-flex where the camera moves, each copper segment under 100 m.
5. Jumbo frames: enabled on camera, card and switch together, or not at all.
6. Isolation: camera VLAN or dedicated card, with one controlled route to the plant LAN.

When the usual answer is wrong

• Triggered snapshots invert the port rule. A 5 MP camera taking one frame every 500 ms produces 10 MB/s; six of them share one gigabit uplink with room to spare, so buy one card and a switch instead of six ports.
• One camera, one host: the PC's onboard port carries a single camera under 90 MB/s well enough — move it to a card the day a second camera arrives, not before.
• Short runs: USB3 cameras at 3 m or less remove the switch and port-counting question entirely; the camera finder lists both interfaces side by side.
• Growth: four gigabit cards in four slots lose to one 10GbE card and a switch. Past about six cameras, buy the topology, not the cards.

Run the formula on your own cameras first, then size the hardware in the frame grabbers category or start the system configurator at the network step. For cells with more than eight cameras or a mix of GigE and 10GigE, send the camera list through the contact page and we will lay out the ports with you.