Methods, apparatuses, and systems for improving utilization of a communications system (e.g., a satellite communications system) are provided, using techniques referred to herein as “deltacasting.” Embodiments operate in a client-server context, in which the server-side of the communication link intercepts requests and responses using a client-server optimizer (e.g., a transparent proxy or in-line optimizer between a client web browser and an Internet content provider). The optimizer uses techniques, such as dictionary coding techniques, to create fingerprints of content traversing the links of the communications system. These fingerprints are used to identify and exploit multicasting and/or other opportunities for increased utilization of the communications links.