CDN back-to-origin traffic refers to the data that is pulled from the original server (origin server) to the CDN edge servers when the requested content is not available on the edge servers. This typically happens when the content is updated, or the cache has expired. For example, if a user requests a video that hasn't been watched recently and thus isn't cached on the nearest CDN edge server, the CDN will fetch this video from the origin server, which counts as back-to-origin traffic.
On the other hand, CDN traffic generally refers to all data transmitted between the CDN edge servers and the end users. This includes both cached content delivery (where content is served directly from the edge servers without needing to go back to the origin) and back-to-origin traffic. Using the previous example, once the video is fetched from the origin server and cached on the edge server, subsequent requests for that video will be served directly from the edge server, which counts as CDN traffic but not back-to-origin traffic.
In cloud services, platforms like Tencent Cloud offer comprehensive CDN services that efficiently manage both types of traffic to ensure fast and reliable content delivery. Their services include features to optimize back-to-origin traffic by using smart caching strategies and efficient routing to reduce latency and improve performance.