Scaling the router control plane to meet bandwidth demand

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Michael Kennedy, ACG Research

Michael Kennedy, ACG Research

As network usage moves to the cloud, personal and mobile services the quantity of network signaling-control plane-traffic is exploding. Router vendors and network architects who are already struggling to meet the bandwidth requirements of video traffic must add control plane scalability to the network design equation.

The rapid increase in network signaling traffic is driven by the move from an Internet that served fixed locations and fairly static information sources to one where users demand personalized, socially-inclusive, media-rich apps and mobile devices. Growth in fixed and mobile broadband subscribers, the number and type of network devices, and applications are all fundamental drivers of increase control plane signaling traffic. They combine to produce a multiplier effect that makes control plane traffic grow faster than data plane traffic.

According to the FCC, total U.S. broadband connections increased 10 percent over the last year. Fixed broadband connections increased 5.4 percent while mobile broadband wireless connections increased 57.5 percent. The average speed of fixed broadband connections is increasing at a 20 percent annual rate. Wireless broadband average speeds will more than double over the next couple years as mobile operators move toward 4G technology.

The CTIA reports that U.S. mobile entertainment and content services revenue increased 16 percent in the last year and that businesses will more than double annual spending on non-handsets (e.g., tablets, notebooks, e-readers) over the next five years. It also reports that 85 percent of the U.S.'s 328 million mobile devices have data capabilities. Twenty-nine percent of U.S. mobile devices are smartphones or PDAs while 5 percent are wireless enabled laptops, notebooks, tablets or wireless broadband modems. The CTIA also reports that the U.S. has more mobile Internet users than any other country and that North America is poised to lead in downloading smartphone apps by 2011, surpassing the current leader Europe and still leading Asia Pacific. These statistics show, therefore, that most mobile broadband development and therefore signaling traffic growth is yet to come.

The large number of different device types also is a fundamental driver of signaling traffic in that messages must be sent and acknowledged before data flows meeting the specific requirements of each device type can be established. More than 630 different handsets and devices are manufactured by more than 32 companies for the U.S. market and in the last year more than 120 new smart phone models were brought to the market according to the CTIA. The further development of the smart phone market is a good predictor of future growth in control plane signaling traffic. For example, Ericsson estimates that the average smart phone generates three times the signaling traffic of a mobile feature phone.

Development of mobile apps also is a driver of increased signaling traffic. The worldwide number of mobile app downloads is expected to grow annually at 46 percent and the average U.S. smartphone has 22 apps. Each app produces at least as many signaling transactions as those required to initiate and tear down a mobile voice call. Some apps are much chattier that voice. For example, while fixed broadband is always on and always in the same place mobile social networking applications, in which friends stay connected with each other for extended periods of time, inherently involve frequent back and forth messages or status updates. Instant messaging services, such as Yahoo IM and Skype, and other popular services, such as Facebook or various friend tracker applications also generate significantly more signaling traffic than mobile voice.

Fixed broadband and business services also contribute to the growth in signaling traffic. For example, broadband service providers are developing strategies that improve the quality of over the top (OTT) video delivery while at the same time earning revenue contributions from upstream content providers. This is called the two-sided business model in that the broadband service provider captures revenue from its subscribers as well as from the upstream content providers. This is accomplished through subscriber management systems (charging and policy control) that are application aware and are used to guarantee the quality of video flows for those customers who pay the upstream content provider for premium service delivery. The need to identify the service request and perform authentication, authorization, policy control and charging functions generates a substantial number of control plane signals for each OTT video request.

High-end business services, especially cloud services, also generate increased signaling traffic as charging and policy control functions are invoked to identify the subscriber, app, and location for each service request.

If we start with a typical projection of 65 percent annual growth in data plane traffic and consider all of the multiplier effects related to increasing numbers of devices, apps, subscriber management, and presence functions on the network then it is reasonable to project control plane signaling traffic growth rates in excess of 100 percent annually. This forces router vendors to rethink router designs. New designs are incorporating control plane functions into the router chassis. This simplifies communications by using the router backplane for communications among the control plane functions and the I/O cards rather than by interconnecting routers with standalone appliances and DPI processors. This provides a more scalable router control plane, improves reliability and reduces operations expenses. It also creates new points of competitive friction between appliance and router vendors.

Michael Kennedy is a regular FierceTelecom columnist and is Principal Analyst at ACG Research. He can be reached at mkennedy@acgresearch.net.