The contention ratio is the degree to which the sale of Internet bandwidth exceeds the bandwidth that is available and describes how an Internet service provider can oversell the backhaul capacity with minimal degradation of each customer’s Internet service. Contention ratio is a very important operational parameter when WISP's are designing and operating a network.
Pros and Cons of a High Contention Ratio
All Internet service providers oversell capacity because the probability of all customers connecting at the same time with each one using the maximum data capacity is very low. Overselling #backhaul #network capacity is beneficial for the #WISP because it will increase the profit of the wireless #Internetserviceprovider business. When many subscribers connect to the Internet at the same time the Internet data speed for each subscriber will be degraded.
Internet Service Providers have #contention #ratios for each group of #subscribers, but they don't publish the values. For example, residential customers might have a higher contention ratio than business customers who are charged more for the Internet service. A subscriber can verify that the connection speed at peak time of network use will fall below the maximum speed that the customer purchased. The fine print of the WISP’s agreement with the #subscriber will advise that the contracted data speed may vary from the maximum speed.
The WISP must evaluate the quality of service provided to customers to determine the ideal contention ratio. The WISP has to find the right balance between profitability and avoiding a noticeable deterioration of the customers Internet service, which will cause complaints. The contention ratio is a factor that affects the profit and loss statement.
Realities of Internet Use
In practice, most subscribers will be downloading much less than their maximum data speed limit because they are checking emails or interacting on social media. However if the subscriber is streaming video from a service like Netflix then it is possible to reach the maximum speed that the subscriber is permitted to download. Telephone Voice-over-IP (VoIP) services also consume considerable bandwidth, though less than video streaming. For this reason some ISP's set a different maximum download speed for video streaming and VoIP, which might be less than the permitted download speed for other applications. This procedure is called data shaping and the differential data speeds are programmed into the access control router.
“Overselling backhaul network capacity is beneficial for the WISP because it will increase the profit of the wireless Internet service provider business.”
Contention Ratio Example
The following example explains the exact meaning of contention ratio. A wireless Internet service provider tower has a backhaul of 100 Mb/s. The Internet service provider sells #rate #plans of 5 Mb/s to subscribers. This means that when 20 subscribers are connected to the network and each is using their maximum data capacity of 5 Mb/s then the backhaul circuit will be operating at the maximum data capacity of 100 Mb/s. In practice not all subscribers will be connected at the same time, and many of the connected subscribers will not be using the maximum data capacity. Data capacity use depends on the type of application being used. Email will generate a very low aggregate data rate while video streaming will generate the maximum data rate. Voice and video over IP (VoIP) applications will generate a high data rate. Knowing the data use characteristics of subscribers it is possible to oversell the backhaul capacity by a contention ratio of 5:1 or greater. With a contention ratio chosen of 5:1 then the 100 Mb/s backhaul capacity can be sold as 500 Mb/s capacity. This means that 100 data rate plans of 5 Mb/s can be sold to subscribers.
Contention Ratio Rules of Use
There are simple rules for maximizing the contention ratio in order to improve the business #profitability.
The rate plan that is sold to subscribers should be a small fraction of the backhaul capacity. For example, with a backhaul of 100 Mb/s then it is not possible to sell the service to more than one subscriber if the rate plan is 100Mb/s. The contention ratio can only be 1:1 as adding a second subscriber with the same rate plan will cause the data rate of each subscriber to fall to half when both are streaming at maximum data speeds.
“WISP’s estimate that a customer with a high network bandwidth will consume approximately 4Mb/s at peak times of use.”
However if the Internet service provider sells data rate plans of 5 Mb/s then there is a high probability that only a small proportion of the subscribers will be connected at one time, and not all connected subscribers will be using high data rates. The Internet service provider can then sell a 5 Mb/s service to many more subscribers than the theoretical 20, possibly to 100 5Mb/s subscribers with a contention ratio of 5:1. In practice the Internet service provider will offer several rate plans, from low cost low speed plans to high-speed high cost plans. The Internet service provider should try to concentrate sales to more customers at the low cost low speed end of the scale so that the contention ratio can be increased which will increase profits.
WISP’s estimate that a customer with a high network bandwidth will consume approximately 4Mb/s at peak times due to the applications that the customer uses, such as video streaming (Netflix) or VoIP (Skype). The WISP can therefore use this figure to calculate contention ratios.
Readers are invited to share this information with others. If any reader has a question regarding this information please contact us via our contact page.