Applying Network Policy Control to Asymmetric Traffic: Considerations and Solutions
An Industry Whitepaper
Traffic asymmetry is widespread and pervasive throughout networks, and broadly speaking takes two forms: Flow Asymmetry, occurring when a flow’s packets traverse different links; and IP Asymmetry, occurring where multiple flows from the same IP address traverse different links.
Routing asymmetry increases network efficiency and redundancy, but also complicates some other matters.
In the context of network policy control, routing asymmetry causes serious challenges that must be overcome so that CSPs can implement critical use cases such as accurate charging, policy-based measurements, and congestion management.
To be a viable policy control platform, a system deployed in the network’s data path must be able to operate in the presence of all types of asymmetry, for all types of traffic. If these conditions aren’t met, then the CSP will not be able to make full, consistent use of policy control.
There are a handful of approaches to overcoming asymmetry, but only three actually preserve complete functionality: deploying only where traffic is guaranteed to be symmetric, intersecting all possible paths with one (large) platform, and clustering to preserve processor core affinity.
Of these three approaches, only clustering offers a combination of versatility, efficiency, and an attractive redundancy model.