A Wireless Internet Service Provider (WISP) is an Internet Service Provider (ISP) that operates using wireless networking. Technology utilized by WISPs may include commonplace WiFi wireless mesh networking; proprietary equipment designed to operate over open 900 MHz, 2.4 GHz, 4.9 GHz, 5 GHz, 24 GHz, and 60 GHz bands; or licensed frequencies in the UHF band (including the MMDS frequency band), LMDS, and other bands from 6 GHz to 80 GHz. Our Cambium Networks Access Point Comparison serves to examine some of these technologies that WISPs may use throughout their networks.
One of the leading providers of networking equipment to WISPs is Cambium Networks. In this blog post, we will conduct a comparison of Cambium Networks’ PMP series of access points. This comparison will evaluate the performance of various Cambium access points by looking at throughput, latency, and rates of oversubscription. Specifically, we will analyze Cambium Networks’ PMP 450, PMP 450i, and PMP 450m access point models. The data required for this comparison has been collected from Preseem’s customer base, spanning thousands of subscribers and access points. As a result, our numbers may differ from those found in the spec sheets of the models being compared. Therefore, the results of this comparison do not necessarily represent the full capacity of any piece of equipment being evaluated.
If you would like to learn more about the methodology behind Preseem’s data collection, check out this article.
Throughput refers to the network capacity (in bits/sec) received or sent by each active subscriber in an indicated time period. We begin our comparison of Cambium Networks’ different PMP access point models by looking at levels of throughput.
Image from Carnegie Mellon University
The following figures compare the 90th percentile of download and upload throughput achieved by subscribers during the busiest (peak) hours. Cambium claims that the throughput experienced using the PMP 450m will be higher than the PMP 450 and the PMP 450i. Our findings demonstrate as much. While the difference between Cambium’s PMP 450 and PMP 450i is small, the PMP 450m provides a significantly higher throughput.
Network latency is an expression of how much time it takes for a packet of data to get from one designated point to another.
Preseem measures latency by tracking the round trip time for individual TCP segments to obtain a detailed view of latency in a network. This approach results in thousands of latency samples per second, per subscriber. This is fundamentally different than an ICMP ping-based latency measurement because it measures true end-to-end latency including the latency in the subscriber’s home.
However, latency does not remain the same in all situations. Indeed, latency depends on distance, weather, and other factors related to landscape type.
Somewhat surprisingly, the latency difference between all three of Cambium’s PMP access point models is not significant. In fact, the difference between the PMP 450i and the PMP 450 is only 7.63 ms!
In spite of the PMP 450i’s level of latency being higher than the other two access point models, each PMP model has a low enough level of latency to ensure subscribers have a pleasant experience surfing the Internet or using VoIP services.
Comparing Overselling Using the Oversubscription Ratio
Overselling describes the sale of a service in excess of the actual supply of that service. The practice occurs as a business strategy wherein sellers anticipate that some buyers will not consume all of the resources entitled to them. Overselling is a common practice in the travel and hospitality industries, in which sellers expect that some people will cancel their reservations.
ISP networks are no different in this regard. No ISP can afford to provision enough bandwidth from the edge to the transit point in order to allow every subscriber to use their entire plan rate at the same time. Without overselling, the business model of ISPs simply cannot work. To determine the amount of a service being oversold, we calculate its oversubscription ratio.
How do you calculate an oversubscription ratio?
To calculate an oversubscription ratio, we begin with the following formula:
Now that we know the formula to calculate the oversubscription ratio of an access point, we apply it in practice using the following example: If a WISP sold twenty 10Mb/s plans on an access point that typically achieves a rate of 50Mb/s, what is its oversubscription ratio?
In this case, the oversubscription ratio is 4.
Calculating the oversubscription ratio for Cambium Networks’ PMP 450, 450m, and 450m, gives us the following results:
From the figures above, we can see that the majority of PMP 450 and PMP 450i access points are oversold by three times or less. For the PMP 450m, we can see that more than 28% of access points are oversold by 10 times! This explains why the PMP 450m can handle much more users and throughput compared to the other models of access points.
As a result of this comparison, we can see that the PMP 450 and the PMP 450i are similar. Both the PMP 450 and the PMP 450i access points have a similar oversubscription ratio, level of throughput, and latency. Moreover, this comparison has also shown that the PMP 450m model of access point provides more throughput and can handle more subscribers than both the PMP 450 and the PMP 450i.
Disclaimer: Results are based on a real-world analysis conducted by Preseem using thousands of APs and subscribers. Individual results may vary. All images belong to their respective copyright holders.
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