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Web-caching performance is hard to increase further due to the growing number of non-cachable dynamic Web-documents. Delta-encoding is a promising technique that exploits temporal correlation among different snapshots of a dynamic document, and renders dynamic traffic cachable. However, it has not yet been deployed due to the significant scalability concerns related to the storage requirements for base-files on the server-side. We introduce class-based delta-encoding, a scalable scheme to perform delta-encoding on dynamic Web-traffic. The idea is to group documents into classes, and store one document per class on the server-side. Thus, the proposed scheme exploits both temporal correlation in a dynamically evolving document, and spatial correlation among different documents. Finally, we present an architecture to deploy the scheme, that is transparent to clients, proxy-caches, and Web-servers. Experimental results report that class-based delta-encoding combined with compression reduces the bandwidth consumption by a factor of 30, and the latency perceived by most users by a factor of 10 on average, without suffering from enormous storage requirements on the server-side.