The NBN connection described in part one of this series was fine for the first few days, but on 17 November I ran into a curious issue.

Aussie Broadband agreed to temporarily move me onto a 100/40 plan so I could tell you what speeds I actually experienced. Once the change had gone through, I used Speedtest to see how much difference the upgrade made. (In a comment on part one, a reader pointed out the shortcomings of using Speedtest.net, but Aussie Broadband has a private Speedtest server so I switched to that, eliminating potential issues outside the control of NBN Co and Aussie Broadband.)

You may have experienced the situation where a particular power circuit is operating at just below its maximum capacity, and when you plug in one more appliance the breaker trips. That's the best analogy I can offer for what I saw.

I had various devices connected to the Internet, and everything was working fine. The download part of the test showed higher speeds than I was getting on the 50/20 plan (more on that later), but a couple of seconds into the upload test all traffic stopped dead.

The lights on the HFC modem remained on, but all communication ceased.

Aussie Broadband's tech support agent was able to get things going, but the upload test killed it again. After various diagnostic procedures, he decided I needed a visit from an NBN Co technician.

This was no big deal, because my normal Internet use was unaffected as I had no large files to upload – I just avoided using Speedtest.

I also discovered that several Foxtel HD channels were degraded, some to the point of displaying the "no signal" error. That couldn't be a coincidence, could it?

Fortunately, the first available NBN Co appointment was on the morning of 21 November, so I didn't bother calling Foxtel at that stage.

The NBN tech arrived in the specified time window, checked signal levels at various points between the pole and the modem, and replaced the flyleads, splitter and some connectors.

That fixed the upload problem, but the speeds weren't very impressive and quite variable. In the space of about 15 minutes they ranged from 38.4 to 66.3Mbps down and 15.9 to 17.9Mpbs up.

Aussie Broadband did some internal checks on the capacity in my area at that time, and re-opened the issue with NBN Co. The first appointment available was on the morning of 23 November, i.e. two days later.

And since the Foxtel situation hadn't improved, I reported the fault and an appointment was made for the next morning (22 November), which was encouraging.

The Foxtel tech arrived — again, during the promised time window — and checked the signal levels again. The NBN frequencies were all OK, he said, but the numbers for some Foxtel channels weren't right. He knew there were similar issues in neighbouring suburbs, and said he would report my issue to the network group. So there was no improvement.

The next day, a different NBN technician knocked at my door. This must sound like a broken record, but once again his arrival was as scheduled.

He did what looked to me to be the same set of tests as his two colleagues and the Foxtel guy, but the results — or maybe his interpretation — were different. The signal was fine at the connection box on the outside wall, but substandard at the connector on the internal wall plate: only three of the four NBN upload channels were active.

So he removed the plate and found a nonstandard splitter and a kink in the cable inside the wall. Cutting off the kinked section and reconnecting the cable directly to the wall plate gave much better results. The Foxtel channels were restored to their normal quality, and the NBN connection stabilised at around 60 Mbps down and 37 Mbps up.

That left me wondering what suddenly made the cabling a problem. Did the kink in the co-ax finally degrade a few days after my NBN connection was installed? Or — as the NBN tech hinted — was it already marginal, and a change to the network in my neighbourhood pushed the situation over the edge? I'll probably never find out.

But I have to admit that what I assumed was an NBN problem (yes, I'm affected by all the bad news that circulates) was fixed by improving the wiring inside my house.

As for the Internet connection, the way I look at it, if I get within 10% of the nominal speed that's probably close enough. So the upload problem was fixed as far as I was concerned, but downloads weren't really up to scratch.

I got back to Aussie Broadband, and the tech checked the stats for my local PoI (point of interconnection), which showed the the service wasn't CVC-limited at the time I tested the speeds.

According to managing director Phillip Britt, "Aussie Broadband is constantly monitoring and upgrading our network to avoid peak hour congestion, even for customers whose lines are capable of the top speed tiers like 100/40.

"We back this with policies like not selling unlimited plans — which can lead to congestion — and stopping new connections in an area where we know there's a delay on a major bandwidth upgrade and the current customers' usage has hit 80% of available bandwidth."

In the next month or two, the company will start publishing graphs showing how much spare capacity there is at each PoI over time, helping customers and potential customers see whether it is living up to that policy.

Anyway, I'm happy that my 50/20 plan will deliver the expected speeds, and it should do what I need for the foreseeable future.

But what was limiting the download speed to around 60Mbps? That's still under investigation, and I'll report the outcome in a future instalment. (Part three has now been published.)