Unclogging Wireless Networks

July 19, 2011
Dr. Larry Roberts

Credit Suisse reported that US wireless networks are running at 80% utilization and the carriers must add capacity soon.

See: http://www.fiercewireless.com/story/credit-suisse-report-us-wireless-networks-running-80-total-capacity/2011-07-18

However, that expansion is expensive and will take more time than the demand would allow. An alternative exists that could quickly improve the situation; adding traffic management to eliminate congestion, increase the utilization and even expand the number of satisfied customers.

High Utilization and Congestion
The reason why high utilization is a problem is that with today’s queue-based rate control, congestion develops quickly as utilization goes above 60%. When congestion increases web response time above 2 seconds or their video stutters, the subscribers become unhappy. When the average utilization is 60% the peaks of the traffic exceed 100% and queuing kicks in. This quickly inflates the response time for the users. By 80% utilization, they are very unhappy. The problem however is congestion, not utilization. If the congestion were removed, utilization could go to 92% and operators would still have happy subscribers.

Congestion Threshold
The threshold for acceptable quality service where control is performed with queuing is around 60%. By applying traffic management systems to manage the traffic using Flow Rate Control (FRC) the threshold increases to about 92%, a 50% improvement in bytes delivered. The reason the threshold goes up is that FRC does not add delay or delay jitter nor does it allow TCP stalls and the resultant slow flows. This delay and rate jitter is congestion. Without the congestion, even at 92% utilization the users therefore remain happy..

Improved Web Page Response Time
Multi-packet discard causes flow stalls and added delay from queuing and must be avoided if one is to avoid the exponential degradation in response time particularly for web access where the slowest flow wins. Figure 1 shows web page response with Anagran’s Flow Rate Control (FRC) and with standard WRED Queuing.
Anagran’s Flow Rate Control avoids multi-packet drops without adding delay. As a result, a 2 second web access can be achieved with twice the number of users or, at the same number of subscribers the web access is 3.5 times as fast. Since web access is the most important factor in user satisfaction, this is of major importance.

Figure 1: Web page response time as user load increases


Conclusion
Ultimately, what customers care about is network availability and Quality of Experience (QoE) — consistent and timely web page downloads, application response time, smooth loading of their favorite streaming video. Flow Rate Control eliminates the congestive effects which arise when utilization exceeds 60% and thus users maintain acceptable QoE even when the utilization is increased to 92%.