Acceptance Testing
Understanding Acceptance Testing (FAT & SAT)
If AT&T buys a massive, $50 Million 5G Core Network upgrade from Nokia, they do not just send a check and hope it works. The contract legally mandates a brutal, two-phase gauntlet known as Acceptance Testing to mathematically prove the hardware is flawless.
Phase 1: Factory Acceptance Testing (FAT)
Before Nokia is legally allowed to put the massive servers on a truck, the FAT must occur.
- AT&T engineers fly directly to the Nokia factory in Finland.
- The equipment is fully assembled on the factory floor in a perfectly clean, climate-controlled environment.
- The engineers run thousands of automated test scripts, blasting the hardware with simulated data to prove it hits every single specification in the contract (e.g., "It must successfully process 1 million simultaneous phone calls without the CPU exceeding 70%.").
- If the hardware fails even one parameter, it cannot leave the building.
Phase 2: Site Acceptance Testing (SAT)
A machine that works flawlessly in a pristine factory will often instantly crash when placed in the real world. This requires the SAT.
- The hardware is bolted into a dusty, hot data center in Texas, and wired directly into the live, chaotic fiber-optic network.
- The engineers run the exact same tests. However, now the hardware must survive real-world power spikes, real-world dirty fiber-optic cables, and real-world massive heat loads.
- If the hardware survives the SAT, the AT&T executive officially signs the final Acceptance Document. The exact second the ink dries, the multi-million dollar check is released to Nokia, and the hardware officially belongs to AT&T.
Key Equations
Coverage = (parameters tested)/(total parameters)×100%
Yield:
Y = (pass count)/(total tested)×100%
Cpk (process capability):
Cpk = min((USL−μ),(μ−LSL))/(3σ)
Cpk ≥ 1.33: capable process
Cpk ≥ 1.67: excellent process
Comparison
| Level | Coverage | Time | Cost | Application |
|---|---|---|---|---|
| Incoming (IQC) | Spot check | Minutes | Low | Verify supplier |
| In-process (IPQC) | Key params | Hours | Medium | WIP monitoring |
| Final (OQC) | Full spec | Hours–days | High | Ship decision |
| Qualification | Extended | Weeks | Very high | New product |
| Reliability | Life test | Months | Highest | Certification |
Frequently Asked Questions
What happens if the SAT fails but the FAT passed?
This is a massive contractual nightmare. Because the equipment proved it was flawless in the factory (FAT), the manufacturer will blame the carrier, claiming the data center is too hot or the carrier's fiber optic cables are dirty. The carrier will blame the manufacturer, claiming the hardware is too fragile. This often triggers a massive 'Root Cause Analysis' investigation to legally determine who has to pay to fix the broken system.
What is a 'Punch List'?
During the SAT, the engineers will find minor bugs (like a spelling error in the software interface, or a yellow warning light blinking incorrectly). These minor bugs are not critical enough to fail the entire multi-million dollar test. They are added to the 'Punch List.' The executive signs the Acceptance Document (releasing 90% of the money), and the manufacturer is legally given 30 days to fix the minor Punch List items before they receive the final 10% of the cash.
Is User Acceptance Testing (UAT) the same thing?
No. FAT and SAT are deep, technical hardware validations performed by advanced RF and network engineers. UAT is the final phase of software development where normal, non-technical humans (the actual end-users) click the buttons to ensure the software makes logical sense and is easy to use before it is released to the public.