Minimizing network delay or latency is a critical factor in delivering mobile broadband services; businesses and users expect network response will be close to instantaneous. Excess latency can have a profound effect on user experience—from excess delay during a simple phone conversation, reducing throughput at edge of cell coverage areas by reducing effectiveness of RAN optimization techniques, to slow- loading webpages and delays with streaming video. Response delays negatively impact revenue. In financial institutions, low latency networks have become a competitive advantage where even a few extra microseconds, can enable trades to execute ahead of the competition.
The direct correlation between delay and revenue in the web browsing experience is well documented. Amazon famously claimed that every 100 millisecond reduction in delay led to a one percent increase in sales. Google also stated that for every half second delay, it saw a 20 percent reduction in traffic.
For LTE network operators, control of latency is growing in importance as both an operational and business issue. Low latency is not only critical to maintaining the quality user experience (and therefore, the operator competitive advantage) of growing social, M2M, and real-time services, but latency reduction is fundamental to meeting the capacity expectations of LTE-A, where latency budgets will be cut in half and X2 will need to perform at microsecond speed.
Total network latency is the sum of delay from all the network components, including air interface, the processing, switching, and queuing of all network elements (core and RAN) along the path, and the propagation delay in the links. With ever tightening latency expectations, the relative contribution of any individual network element, such as a security gateway, must be minimized. For example, when latency budgets were targeting 150ms, a network node providing packet processing at 250μs was only adding 0.17% to the budget. However, in LTE-A, with latency targets slashed to 10ms, that same network node will consume almost 15x more of the budget. More important, when placed on the S1 with a target of only 1ms, 250 μs is 25% of the entire S1 latency allocation, and endangers meeting the microsecond latency needed at the X2. Clearly, operators need to apply stringent latency requirements for all network nodes, when designing LTE and LTE-A networks.