Telstra 250M Plan Testing in the Tens of Mbps: the Router Had Switched to Its Backup SIM (Burwood)

Student · BurwoodTelstra 250MOpticomm auto IPTesting in the tens of MbpsBackup SIM activeBack to ~250M

A student in Burwood was on a Telstra 250Mbps plan over an Opticomm connection, but speed tests on Telstra’s own test site kept coming back in the tens of Mbps. Telstra and Opticomm had each sent someone out — no result. On-site, the answer was hiding in the router’s admin page: the Telstra router’s backup SIM feature was on and its signal light was lit. At some point the router had failed over to the mobile network and never switched back, so every speed test was measuring the backup link, not the 250M fixed line.

Speed tests · on the backup SIM vs back on the fixed line

Backup SIM

tens of Mbps

Fixed line

~250 Mbps

~250Mbps — full plan speed again, wired and on WiFi, several runs in a row.

Why so slow? The router was quietly on its backup SIM

Fixed line vs backup SIM · what the tests were really measuring

	Fixed line (Opticomm)	Backup SIM (mobile)
Tested this visit	~250 Mbps	tens of Mbps
Its job	Everyday connection on the 250M plan	Emergency fallback if the line drops
How to spot it	Open the router admin page and check the mobile/SIM status, and look at the router itself — a lit mobile-signal indicator means you are not on the fixed line.

Telstra’s router has a mobile backup: if the fixed line has trouble, it fails over to a built-in SIM so you are not completely offline. That safety net became the trap here — the router had switched over at some point and stayed there. Everything technically “worked”, just at backup speeds, which is exactly why two technician visits focused on the line itself found nothing wrong: the line was fine.

How we confirmed it on-site

Opened the router admin page first

Backup SIM on · signal light lit

Swapped in our own test router

Speedtest reached ~250 Mbps, several runs

Wired laptop in + Mac on WiFi

Both reached ~250 Mbps

Real-world test: gaming and downloads

LoL lag-free · downloads at tens of MB/s

One variable at a time:

The admin page told the story before any cable was touched — the backup SIM was carrying the traffic.
A known-good router we brought along took the line to ~250 Mbps on Speedtest, ruling out a line fault and pointing back at the original router’s state.
Wired and WiFi tests both landed around 250 Mbps — consistent with the plan, from more than one device.
The complaint was “laggy games, downloads at a crawl”, so we tested exactly that: a round of League of Legends with no lag spikes, and file downloads running at tens of MB per second.

Different test sites, different numbers

One wrinkle from this visit: the student mainly used Telstra’s official speed-test page, we used Speedtest — and on the day the two tools gave noticeably different numbers. When judging whether a plan delivers:

Test wired first, so WiFi is not part of the question.
Try more than one test tool before drawing conclusions.
Sanity-check with real use — large downloads and game latency tell you what the numbers mean in practice.

Result

Root cause: the Telstra router had failed over to its backup SIM, so every test was measuring the mobile fallback — not the 250M Opticomm line, which was healthy all along. Back on the fixed line, wired and WiFi tests reached ~250 Mbps, downloads ran at tens of MB/s and an on-the-spot LoL session had no lag.

Telstra guide NBN slow speed troubleshooting How much speed for gaming Opticomm active but no internet (case)TP-Link routers

Telstra 250M Plan Testing in the Tens of Mbps: the Router Had Switched to Its Backup SIM (Burwood)

Why so slow? The router was quietly on its backup SIM

How we confirmed it on-site

Different test sites, different numbers

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