Line Speed
Line speed is a commonly used term, but one that many don’t fully understand how it is arrived at and the measurement challenges some lines can present, so this page will try and explain some concepts before going into the use of the controls found on the Configure->Line Speed page of the IQrouter.
Line ‘speed’ is really a capacity metric, as the unit of measure is one of bits delivered per time-unit, not one of velocity. A 100Mbps line delivers 10 times more capacity (bits) than a 10Mbps line, it is not 10x ‘faster’. If all I need is to move is 5Mbits in a second, both lines get it done in the same time. Only when more capacity is required, will the 100Mbps deliver an advantage and be done sooner.
Measuring line speed
Measuring this capacity means we must flood the line with as much data as possible to probe for the limits of the total throughput the line can deliver. Speed tests do this by creating multiple connections to remote servers and blasting as much data as possible for 20 or 30 seconds, and then calculating the total capacity of the line during that test.
The higher the capacity of the line, the harder this is to accomplish accurately, as often, points along the way to the test servers will throttle capacity to ensure fairness to other traffic.
This also explains why so often, speed tests return such different results.
That is part of the reason an IQrouter performs tuning runs multiple times across multiple days, so it can find the high-water mark for the line’s capacity. But even so, there are times it is not able to determine the correct line capacity, either coming in too low due to path constraints (or ISP limits on traffic type / destinations) or too high due to burst over-provisioning on certain connectivity (e.g. Cable) where the ISP games the speed tests with short-term over-capacity, but then cuts back after a period.
Over-measuring is especially problematic on the upload, as managing traffic in that direction is critical to have a reasonable line speed setting that will work well at all times. So if you see too many dynamic adjustments to upload on the Status->Ping Stats upload capacity graphs, you can slightly lower the upload line speed to ensure low-latencies at all times.
Since variable capacity (wireless, Starlink, LTE/5G) technologies have changing capacities, we have a dedicated article on this subject.
Line Speed controls
To allow our users to fine-tune the metrics, the Line Speed page controls on the IQrouter are used to align the line speed setting to one that will perform better or allow access to additional capacity.
The range of the controls depends on your type of connectivity selected during the Initial Configuration, so some of these illustrations may have different bounds than shown in the page on your unit. The ranges are also scaled to the currently measured capacity.
Here are the controls:
Current Line Capacity Settings
Recommended capacity is indicated based on metrics derived by the IQrouter itself. So if you raise the upload too high, and come back to this page after a few days, the recommended capacity will show the highest capacity at which latencies were acceptable. We recommend using that value by clicking the ‘Use Recommended’ button.
Measured and Recommended Line Capacity values
If you have a 400Mbps download as confirmed by multiple independent tests, and the IQrouter only measured it as a 350Mbps line, you can push the download capacity slider to 400. But do check back after a few days to see if the recommended setting agrees.
Be very cautious when increasing the upload capacity setting, as independent speed tests often over-estimate capacity due to BufferBloat-related issues. This is especially true on DSL/VDSL, but thanks to burst over-provisioning on Cable, it happens there as well.
So, if your cable service is provisioned as 100/15, and your independent speed test shows upload is 17Mbps, it is safer to set (or leave) the upload to 15, as anything higher is likely due to burst-mode and not long-term sustainable.
Remember that setting line speed is just informing the IQrouter of the upper limit of the line capacity, and it will be used to re-calculate the traffic management settings, which will always be set lower than line capacity, meaning speed tests from individual devices will never reach the values you set here. But the sum of all traffic has access to the managed capacity.
Download capacity options
If your line happens to exhibit very low latencies on the download direction with traffic management disabled, in that case, your IQrouter will give you an additional optional mode to run the download without traffic management, allowing you access to the full download capacity.
This happens when the line has some upstream traffic shaper used to control the provisioned ‘speed’ you get to align with your subscription plan. For instance, on Fiber, the link to the home is often a gigabit, but if you are only paying for 200/200, then it is externally shaped to that capacity, and on the download, that may lead to low latencies. It also holds for some (not all) DOCSIS 3.1 Cable Internet lines.
Traffic shaping disabled on download
So if you have a gigabit DOCSIS 3.1 service, and you want unrestricted access to the total capacity, you can select to run the Download Mode as ‘Unmanaged’. The slider will disappear, and the traffic management functions for the download will be disabled. Upoad direction still has a traffic manager.
Note that running the download in unmanaged mode means no traffic prioritization nor per-device fairness. If the game console starts to download a gigabyte or two worth of a game update, then that very large surge in traffic can affect other uses. On the flip-side, the download will take less time.