Capacity Planning 101 for WISPs

By Jim Harding

When designing or expanding your WISP network, there are several key technical considerations that are essential in providing a positive and satisfying Internet experience for your customers.

Coverage vs. Capacity

First, what’s the difference between coverage and capacity? Coverage is the geographic area your network can reach. For example, you may look at a heat map overlaying your WISP market territory and see that building one AP (access point) and one omni (antenna) on a tower should cover your whole market.

Not so fast, though – even though your coverage reaches the geographic area you need it to, you still need to consider the number of devices that need to use that network. That’s where capacity planning comes in.

Capacity is how best your network will support the needs of your customers in an area, who may be relying on their network for multiple devices for multiple users.

Here are some key questions you should answer to ensure your network can provide your customers with the capacity they need:

What speed packages will you offer?

The first step is determining what speed packages you will offer to your customers. To determine what options you can offer, you need a comprehensive understanding of the capabilities of your network and its equipment. Only plan to offer what you can truly support. Getting contracts for service that is not reliable or does not meets promised speeds can be disastrous for a business’s reputation and can also drive up help desk call volumes.

How many subscribers can one AP (access point) authenticate?

An access point is the radio that allows the customer equipment access to the internet and provides control over access to the network. Access points have a finite number of subscribers they can authenticate and can vary significantly from brand to brand. In designing your network, make sure you thoroughly research your equipment so that you can determine how many APs you need.

What is the maximum backhaul throughput?

The backhaul throughput is the amount of bandwidth that your backhaul will support. To find it, you need to know the equipment’s theoretical maximum capabilities as described in the manufacturer’s specifications, as well as the current quality of connection across that link. Whatever fiber service is contracted at the tower or whatever your microwave link provides back to the nearest fiber is the absolute upper limit on what can be supported. Loosely speaking, a 1Gb circuit with 250mbps AP’s will support 4 AP’s at that tower site at 100% utilization - no more. For example, if your microwave backhaul at that tower is only giving a 200mbps link to the nearest fiber connection, you now can only support 50mbps per AP for the same 4 AP’s.

What is the maximum AP throughput?

Your maximum AP throughput is defined by the manufacturer’s specifications as the equipment’s theoretical maximum of available bandwidth per access point. Each access point has a limit to the bandwidth it can provide. If the manufacturer says it will support 250mbps download speeds, that number is divided between the number of subscribers authenticated to that access point. For example, if you have all 250 subscribers authenticated to this hypothetical access point, they will each only get 1mbps download speeds - which brings us to the next topic.

What is your oversubscription strategy?

Oversubscription allows providers to offer more user throughput with less overall total available bandwidth. This is not to be confused with over-authenticating users to a given AP.

This topic is debated as to what the ideal number looks like - anywhere from 3:1 to 20:1 for various technologies - but the gist is this: most customers will not use 100% of their connection 100% of the time. It simply is not economically feasible to build a network to those specifications. Industry experience shows that usage percentages are MUCH lower, so we can plan accordingly. A conservative oversubscription ratio for a 5.8GHz WISP network is around 5:1, which means you can offer up to 50 customers a 25mbps package on a 250mbps AP vs only 10 customers at 1:1 on the same AP. Conversely, if your main backhaul only provides 50mbps per AP, you can now only offer 10 customers 25mbps if you maintain the same 5:1 ratio.

Here is one way AP oversubscription can be broken down:

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Different radios will have different capacity and different ratios provide different subscriber capacities, but the general concept stays the same.

In Conclusion

There are many technical considerations involved in capacity planning, but hopefully this article has outlined some of the basic principles and terms that any network professional will find helpful.

Tilson provides a deep understanding of fiber and wireless technologies and serves private enterprises, government, and utility clients around the country. For more information about how we can help with your network deployment needs, contact us for more details.

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Jim Harding

Jim Harding is the Engineering Manager with Tilson’s Network Services team, leading efforts in several regions around the country for various RF, fiber, and smart grid networking systems. He has been heavily involved with price estimating, designing, implementing, and managing team efforts for school districts, colleges, libraries, municipal and international public utilities, and ISPs at local and national levels. Prior to joining Tilson 8 years ago, Jim enjoyed a 15-year history working in technology, beginning as a Help Desk technician and developing over the years into a Windows Server Administrator and Network and RF Engineer. 

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