CMSD

CMSD (Common Media Server Data) is the server-side companion to CMCD, standardised as CTA-5006. The CDN (or any intermediary) attaches data to its responses — host status, estimated throughput, whether the response was a cache hit, and round-trip hints — so the client and orchestrator can read what the delivery infrastructure is reporting about itself.

CMCD tells you how the viewer feels; CMSD tells you what the CDN thinks it is doing. Together they close the loop. A cache-hit signal (ec=h), for example, is a strong cost input — a hit served from edge cache costs far less than an origin pull.

m-cdn folds CMSD cache-hit ratio into the cost dimension of the score (notably for VOD, where cache efficiency dominates the bill). Broad CMSD coverage across CDNs is still maturing, so the engine treats it as a useful supplement rather than a primary signal.