The method to reduce the bandwidth necessary for the renewal of subscription message is achieved using group messages in which each member of the group is associated with a bit of a bitmap. In order to have the maximum members in a group, the size dedicated for the bitmap is determined first by calculating the size remaining after putting the command and other necessary data into the message, and using an iterative process to determine whether the bitmap, once compressed, will fit this remaining size. The iterative process adds a new member into the group, thus increasing the bitmap size, then compresses the resulting bitmap and checks if the compressed bitmap will fit into the remaining size.