Cambium Networks Access Point Comparison

Cambium Networks Access Point Comparison blog by Preseem

by | April 15, 2020 | Networking

Cambium Networks Access Point Comparison

Cambium Networks is one of the leading providers of networking equipment to Internet Service Providers (ISPs). In this blog post, we’ll conduct a comparison of Cambium’s PMP series of access points (APs). This comparison will evaluate the performance of various Cambium APs by looking at throughput, latency, and rates of oversubscription. Specifically, we’ll analyze Cambium’s PMP 450, PMP 450i, and PMP 450m AP models.

The data required for this comparison has been collected from Preseem’s customer base, spanning thousands of subscribers and APs. 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.

Comparing Throughput

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’s different PMP access point models by looking at levels of throughput.

Image showing a car trip from San Francisco to Pittsburgh as a metaphor for latency vs. 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 says that the throughput experienced using the PMP 450m will be higher than the PMP 450 and the PMP 450i. Our findings corroborate that. While the difference between Cambium’s PMP 450 and PMP 450i is small, the PMP 450m provides significantly higher throughput.

Graph showing upload rates of Cambium AP models
Graph showing download rates of Cambium AP models

Comparing Latency

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 (RTT) for individual TCP segments to obtain a detailed view of latency in a network. This approach results in thousands of latency samples per subscriber per second. 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. In fact, latency also depends on distance, weather, and other factors related to landscape type.

Somewhat surprisingly, the latency difference between all three of Cambium’s PMP models is not significant. In fact, the difference between the PMP 450i and the PMP 450 is only 7.63 ms.

Graph showing latency of Cambium AP models

Despite the PMP 450i’s level of latency being higher than the other two APs, each PMP model has a low enough level of latency to ensure subscribers have a good quality of experience using the internet.

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 when 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.

ISPs 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 can’t 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:

Formula for access point oversubscription ratio

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?

Calculation of AP oversubscription ratio for specific access point

In this case, the oversubscription ratio is 4. Calculating the oversubscription ratio for Cambium’s PMP 450, 450m, and 450m APs gives us the following results:

Graph showing latency on oversold PMP 450 APs
Graph showing latency on oversold PMP 450i APs
Graph showing latency on oversold PMP 450m APs

From the figures above, we can see that the majority of PMP 450 and PMP 450i APs are oversold by three times or less. For the PMP 450m, we can see that more than 28% of them are oversold by 10 times! This explains why the PMP 450m can handle more users and throughput compared to the other models.

As a result of this comparison, we can see that the PMP 450 and the PMP 450i are similar. Both APs have a similar oversubscription ratio, level of throughput, and latency. Our comparison has also shown that the PMP 450m model 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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