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Dan Rayburn provides a very thorough overview of transparent caching and its role in the CDN market. Definitely worth a read if you are interested in learning about a different flavor of content delivery and caching.
Don’t have time to read the entire overview? This passage does a great job of drawing a distinction between traditional content caching through a CDN like Akamai compared to transparent caching:
Most traditional content caching sits outside the network in a peering location, data center, or collocation space. It is usually managed by someone other than the network operator. The network operator has little or no control over cache servers, and as a result has little visibility into the actual productivity of those servers or what is being delivered from them.
In contrast, because transparent caching works across a much broader set of over the top content and traffic. it is embedded inside the carriers network and provides the operator control over what to cache, when to cache, and how fast to accelerate the delivery.