Preseem Auto AP Capacity Management enables operators to maintain a high quality of experience (QoE) when an Access Point is overloaded.
When network elements like Access Points reach their capacity, the subscriber quality of experience (QoE) degrades significantly. This occurs because these devices implement buffering with simple FIFO queues which increase latency and eventually loss when the outgoing link reaches capacity. Preseem's shaping uses modern active queue management (AQM) techniques that do not have this behavior and deliver a great subscriber experience even when the link is busy. Preseem's traffic management can be deployed on one or both of the subscriber plan and the Access Point levels.
On the subscriber level, we refer to this as QoE-optimized plan enforcement. This feature ensures that a subscriber hitting the limit of their plan continues to get a good experience. Concretely, this solves problems like games or VoIP calls not working when other members of the household watch streaming video or do a big download.
A subscriber hitting the limit of their plan is the most common bottleneck in the network. Another common location is at the Access Point itself. Preseem's Access Point shaping enables the operator to set a bandwidth limit for the Access Point as a whole and (within that) apply intelligent AQM algorithms and share the traffic between subscribers. The rate to shape to can be configured directly in Preseem when viewing an individual Access Point.
Auto AP Capacity Management strives to automatically balance throughput and latency as a significant improvement over manual shaping. As this might not meet specific business goals on every AP, you can control how shaping is applied and enable or disable Auto or manual shaping for individual APs at will.
When an Access Point is not under load, enabling a shaper will not dramatically affect QoE. However, even a nearly idle AP will receive some benefit, as traffic downstream from the Internet can have microbursts that exceed the link rate of the AP. Shaping those microbursts helps.
At the other end of the range, when an Access Point has < 25% airtime free, we find dramatic improvements in the 95th percentile — in the range of 20 to 40 ms of lowered latency — when shaping is properly calculated and applied at the Access Point level.
Auto AP Capacity Management
Daily, automatic rates are calculated for all supported models. If Auto is enabled on a supported AP, the calculated rates are applied to the enabled shaper. Metric charts in the Performance tab show over time when shapers are used (Tx and Rx direction) and the shaped rates.
For a single AP, checking or unchecking the 'Auto AP Shaping Enabled' box under Access Point -> Config is sufficient to enable or disable full Auto.
If a model is not yet supported, Auto cannot be enabled, but Manual can still be used.
To enable auto shapers as new APs come online or new models become supported, toggle Auto Shapers For New APs, available in the hamburger menu at Network -> Access Points -> Shapers, to "On". This sets a company-wide default:
To make a global change to all currently supported APs, use 'Enable All Auto Shapers' or 'Disable All Auto Shapers'.
To view all shapers, use the Shapers list at Network -> Access Points -> Shapers which contains shaper condition, rates, and any errors or other informational alerts.
There are several classes of errors possible on a given shaper:
- This model is currently unsupported for auto-shaping but may be manually shaped.
- Tx/Rx Low
- This AP exhibits unusually poor RF link rates, under 2 bits per herz in efficiency. (Some very old equipment may exhibit this under normal conditions.) It is challenging to produce good QoE results by limiting APs at the lower end of the efficiency scale, so while we can calculate auto AP rates, we apply them less aggressively. We recommend improving the link rates on clients connected to these APs for the best business value. Plus BV and RF scores can help with this process.
- Low Samples
- This AP was not pollable and online at the current channel width for at least 80% of the previous day; the most recent shaper updates skipped this AP. This error will clear (and rates will be updated) when the channel width is stable, and enough data is collected.
- Flex Framing
- Auto AP shapers might not match business intent, as this AP is in flexible framing mode. Applying shapers to a flexible framing AP essentially turns it into virtual fixed framing but without the benefit of synchronizing clocks with other APs. While Preseem's algorithm is adaptive to user demand, it might not fully express your business intent, and you may prefer other rates (or no shaping).
- What are the prerequisites for using shaping?
- Access Point shaping requires Preseem 1.6 or greater (preferably the newest release) configured with the TwoLevelMQ policy. This has been the default for new installs for some time. Preseem support can verify that your node is ready for Access Point shaping if you have any concerns.
- What are the requirements for Auto?
- An AP model must be supported for shaping, and the AP must not be in an Error state in the AP list — common errors might be a lack of SNMP or HTTPS credentials. In general, 80% of daily records at a given channel width must be present for Auto rates to calculate.
- What should I do when I change RF channel width, and shaping is on?
- You have two choices. You can set manual rates that match the bandwidth of the new channel width (or enter 0 or blank to turn shaping effectively off) or leave the existing rates as they are. If Auto is on, the newly calculated rates will take effect on the second day. (A full day's worth of samples is required to calculate new rates.)
Manual AP Shaping
When first enabling Access Point shaping, Preseem recommends one of two approaches:
- If the Access Point is congested, set the rates to 10% below the observed peak rates. This should bring the capacity below the pain threshold measured by latency and other metrics such as TCP retransmissions. If no improvement is observed, further reduce the limits by another 10%.
- If the Access Point is not currently congested, the Access Point comparisons (as displayed by the orange line on the charts) provide the best starting point. The Access Point comparisons are built from data collected from hundreds of customers and tens of thousands of Access Points and give a very robust indication of what the Access Point should be capable of in the real world (vs. marketing numbers). For more real-world Access Point performance information, see our Fixed Wireless Report.