Case Studies案例研究 / Latest Case最新案例 Telstra 250M Plan Testing in the Tens of Mbps: the Router Had Switched to Its Backup SIM (Burwood)
Telstra 250兆套餐测速只有几十兆：路由器悄悄切到了备用SIM卡网络（Burwood）
Student · Burwood学生 · BurwoodTelstra 250MTelstra 250兆Opticomm auto IPOpticomm 自动IPTesting in the tens of Mbps测速只有几十兆Backup SIM active备用SIM卡在联网Back to ~250M回到~250兆
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.
一位住在 Burwood 的同学，用的是 Telstra 250兆套餐、Opticomm 自动IP联网，但用 Telstra 官方测速网站测出来一直只有几十兆。Telstra 和 Opticomm 都派人上门看过，问题依旧。我们上门后，答案就藏在路由器后台：这台 Telstra 路由器的备用 SIM 卡联网功能处于开启状态、移动信号灯亮着——不知从什么时候起，它切到了移动网络兜底，再也没切回来，于是每次测速测的其实是备用链路，而不是那条 250 兆的固网。
Speed tests · on the backup SIM vs back on the fixed line测速 · 备用SIM联网时 vs 回到固网后
~250Mbps — full plan speed again, wired and on WiFi, several runs in a row.兆——回到套餐满速，有线和WiFi、连测几次都到位。
Why so slow? The router was quietly on its backup SIM
为什么这么慢？路由器在悄悄用备用SIM卡上网
Fixed line vs backup SIM · what the tests were really measuring固网 vs 备用SIM · 测速测的到底是谁
| Fixed line (Opticomm)固网 (Opticomm) | Backup SIM (mobile)备用SIM (移动网络) |
|---|
| Tested this visit本次实测 | ~250 Mbps | tens of Mbps几十兆 |
| Its job它的角色 | Everyday connection on the 250M plan日常主用的250兆宽带 | Emergency fallback if the line drops断网时的应急兜底 |
| How to spot it怎么发现 | 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.打开路由器后台看移动网络/SIM 状态，再看路由器机身——移动信号灯亮着，就说明你走的不是固网。 |
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.
Telstra 路由器有移动网络兜底功能：固网出问题时，会自动切到内置 SIM 卡，让你不至于完全断网。这张安全网在这里反而成了坑——路由器在某个时点切了过去，就一直停在那儿。一切"看起来都能用"，只是速度是兜底级别的。这也正好解释了为什么两拨上门的技术人员都没查出问题：因为线路本身真的没问题。
How we confirmed it on-site
现场怎么一步步确认
How we confirmed it on-site现场怎么一步步确认
1
Opened the router admin page first先看路由器后台
Backup SIM on · signal light lit备用SIM开启 · 信号灯亮着
2
Swapped in our own test router换上自带路由器排除硬件问题
Speedtest reached ~250 Mbps, several runsSpeedtest 多次测到 ~250兆
3
Wired laptop in + Mac on WiFi网线直连电脑 + Mac 连WiFi测
Both reached ~250 Mbps两种方式都到 ~250兆
4
Real-world test: gaming and downloads实际使用测试：游戏 + 下载
LoL lag-free · downloads at tens of MB/sLoL 无延迟 · 下载几十MB每秒
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.
每次只改一个变量：
- 还没碰网线，后台已经说明了问题——流量走的是备用 SIM。
- 换上我们自带、确定没问题的路由器，Speedtest 多次测到 ~250 兆，排除线路故障，问题指回原路由器的状态。
- 有线直连和 WiFi 都在 250 兆左右——不止一台设备、结果和套餐一致。
- 原始反馈是"游戏延迟高、下载只有几兆甚至几KB"，那就照着测：现场打 LoL 无延迟，下载文件每秒几十 MB。
Different test sites, different numbers
不同测速网站，数字可能不一样
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.
这次上门的一个小插曲：该同学主要用 Telstra 官方测速页，我们用 Speedtest——当天两个工具给出的数字差异不小。判断套餐到底达不达标时：
- 先用有线测，把 WiFi 这个变量排除掉。
- 多换一两个测速工具再下结论。
- 用实际使用来交叉验证——大文件下载速度和游戏延迟，最能说明数字在现实里意味着什么。
Result最终结果
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.
根因：Telstra 路由器切到了备用 SIM 卡联网，每次测速测的都是移动兜底网络——那条 250 兆的 Opticomm 固网从头到尾都是好的。回到固网后，有线和 WiFi 都测到 ~250 兆，下载每秒几十 MB，现场打 LoL 也没有延迟。