Requirements translator
Turn what the application and the vehicle need into what the wireless design must deliver. Every number comes from a published formula or a sourced requirement, with the source beside it.
Wireless design spec from the OT Wireless requirements translator
https://otwireless.com/requirements-translator/?a=cip-safety-input%3Arpi%3D10%2Ctm%3D2%2Cndm%3D200
1. What rides the link
Add everything the vehicle or machine needs over this wireless link. The tightest timeout sets the budget for all of it.
2. The path, the vehicle, and the place
3. Your wireless spec
| Application | CIP Safety input connection: Input RPI 10 ms, Timeout multiplier 2, Network delay multiplier 200 % |
|---|---|
| Wired path and endpoints | 0 ms |
| Measured worst-case roam | Not entered |
| Vehicle | Not listed |
| Environment | Any |
| Vehicle speed | Not entered |
In plain words
The tightest timeout on this link is the CIP Safety input connection: 40 ms (RPI x (timeout multiplier + network delay multiplier)).
With no allowance entered for the wired path and the endpoints, the whole 40 ms is the wireless budget. Part of it is always spent before the radio is involved, so measure that and enter it.
Measure the worst-case roam on the real vehicle and client, with your security settings, and enter it. Published typical figures are not a substitute for your own.
| Wireless outage budget (budget) | 40 ms | Budget |
|---|---|---|
| PSK four-way handshake (no fast roaming) | 55 ms to 520 ms | Overruns |
| 802.11r fast BSS transition | 15 ms to 90 ms | May overrun |
| Vendor fast-roam and make-before-break schemes (vendor claim) | 63 ms to 150 ms | Overruns |
Not drawn, because no source publishes a comparable measured range: Full 802.1X reauthentication, PMK caching and opportunistic key caching, Wi-Fi 7 multi-link operation, 802.11bn seamless mobility domain. Measure these on your own vehicles.
Design rules for this link
- Design and test for the worst gap, not the average one: a timeout fires on a single gap. Why (https://otwireless.com/guides/the-timing-budget/)
- Keep control traffic off DFS channels. A radar detection forces the access point off the channel, and every client on that radio drops. Why (https://otwireless.com/causes/dfs-radar-events/)
- Enable fast roaming on both sides. If the client and the network disagree on 802.11r, roams fall back to slow ones or fail. Why (https://otwireless.com/causes/fast-roam-mismatch/)
- Keep bulk transfers off the radio that carries control traffic. Prioritization improves the odds; it does not reserve the channel. Why (https://otwireless.com/guides/airtime-is-finite/)
- Safety runs over this link. The safety layer in the endpoints decides the stop; the network has to stay inside the timeout, and the timing is the machine builder’s to set. Why (https://otwireless.com/guides/safety-over-wireless/)
Sources (10)
- Rockwell Automation, Connection Reaction Time Limit https://www.rockwellautomation.com/en-ca/docs/technical/logix5000/_online/1756-rm015/logix-sis-safety-reference-manual-ditamap/reaction-times/connection-reaction-time-limit.html
- Aalborg University (pre-print of European Wireless 2021, VDE) https://vbn.aau.dk/ws/files/414266206/EW_accepted.pdf
- VŠB Technical University of Ostrava (DSpace) http://hdl.handle.net/10084/160276
- vendor documentation https://www.cisco.com/c/dam/en/us/td/docs/voice_ip_comm/cuipph/8821/english/Deployment/8821_wlandg.pdf
- Buletin Poltanesa 26(1), Politeknik Pertanian Negeri Samarinda https://doi.org/10.51967/tanesa.v26i1.3086
- Microsoft Learn https://learn.microsoft.com/en-us/windows-hardware/drivers/network/fast-roaming-with-802-11k--802-11v--and-802-11r
- Apple (Apple Platform Deployment) https://support.apple.com/guide/deployment/wi-fi-roaming-support-dep98f116c0f/web
- vendor documentation https://www.cisco.com/c/en/us/products/collateral/wireless/ultra-reliable-wireless-backhaul/reliable-wireless-automation-so.html
- Rockwell Automation https://literature.rockwellautomation.com/idc/groups/literature/documents/td/enet-td006_-en-p.pdf
- vendor documentation https://www.moxa.com/en/products/industrial-network-infrastructure/wireless-ap-bridge-client/wlan-ap-bridge-client/awk-3131a-series
The translator runs in your browser and keeps its inputs in the link. It is a planning aid: it shows what the sources say and what your own measurements mean against them. It does not certify a design.