Abstract: The method relates to a method for header compression between a compressor and a decompressor. The method includes providing a set of configuration parameters to be negotiated between the compressor and the decompressor, wherein the set includes a specific parameter whose value indicates whether reordering and/or packet loss is tolerated between the compressor and the decompressor. The method further includes indicating in a full header whether subsequent compressed headers will contain small packet sequence numbers (pkt_nr). These small packet sequence numbers (pkt_nr) are used in order to detect a reordering of packets and/or packet loss between the compressor and the decompressor.