In an application level multicast (ALM), multiple flows of data packets containing shared material are destined for different devices. A packet compression device is used to compress the data packets to reduce traffic load. This compression device includes a cache for recording the payloads of selected data packets which currently are not of record in the cache. If it is determined that the cache has therein a record of an identical version of the payload of a data packet, the compression device releases a compressed version of the data packet which includes a representation of the payload in lieu of the actual payload.