CDN Load Balancer bases its selection and switching decisions on a "global" score. In practice,
Global score = business score * QoS score
The global score is based on:
- A business score provided by the broadcaster: This business score reflects how heavily commit-based or business-based inputs should be evaluated; it can take integer values of 1 to 100.
- A Quality of Service score: At the beginning of the session, the QoS score is calculated from the metrics CDN Load Balancer gathers from across the broadcaster's user base. During the session, the QoS score is the quality perceived by the end-user device during the session: bandwidth, time to first byte, and error rate.
After the beginning of the session, quality is calculated locally. This prevents CDN Load balancer from becoming a single point of failure; during the session, CDN Load Balancer only connects to the backend to send quality statistics to be ued in initial scoring for future sessions.