Networking
SCADA Polling Bandwidth
Bandwidth a polling scheme consumes across a set of remote sites, and whether the communication path can carry it.
Calculated reference results
- Required bandwidth
- 3.20kbps
- Link utilization
- 16.7%
- Fits the link
- Yes
- Sites this link supports
- 120
- Data per day
- 34.6 MB
- Data per month
- 1.04 GB
- Per site, per month
- 25.9 MB
Against a 19.2 kbps link with 50% usable
At this interval and payload size
Relevant on a metered cellular plan, per site if each has its own SIM.
The arithmetic
- Bytes per second = 40 sites x 300 bytes / 30.0 s = 400.0 B/s
- Bits per second = 400.0 x 8 = 3,200 bps = 3.20 kbps
- Usable capacity = 19.2 kbps x 50% = 9.60 kbps
What this does not account for
- Designing to the full link speed does not work. Protocol overhead, retries, and contention mean a path is effectively full well below its nominal rate.
- Report by exception, where a site transmits only when a value changes beyond a threshold, uses a fraction of this bandwidth. It is why DNP3 suits distributed utilities better than continuous polling.
- Alarm and event bursts during an upset are far above the steady-state figure, and that is exactly when the path matters most.
- On cellular, the monthly figure drives cost. Keepalives, VPN overhead, and retries all add to it and are easy to overlook.
How this is calculated
Polling bandwidth is the number of sites multiplied by the bytes exchanged per poll, divided by the poll interval, converted to bits per second. On a constrained path such as licensed radio or a metered cellular plan, this figure decides whether the poll rate is achievable, and it is why report by exception suits distributed utilities better than continuous polling.
Formulas
kbps = (sites x bytes per poll / interval) x 8 / 1000
Assumptions and limitations built into this calculator
- Uniform polling of every site at the same interval.
- Payload size includes protocol overhead, which you supply.
- Does not model retries, contention, or burst traffic.
Frequently asked questions
- How fast should I poll a lift station?
- Fast enough that an operator can act on a change, slow enough that the path stays healthy. Every fifteen to sixty seconds for analog values, with immediate reporting of alarms and state changes, is typical on licensed radio.
Direct contact
Have a controls question?
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