robust header compression offers a way to compress packet header information for more efficient transmission of data . the compression is achieved through various confidence modes set up by the transmitter and the receiver . the initialization and refresh state is the first state of the compressor . this provides a complete , uncompressed context of the data that is being transmitted . in typically operation , the rohc compressor will periodically transmit ir packets providing context information allowing the rohc decompressor to decompress one or more packets following the ir packet . however , under certain conditions such as decompressor start - up , it is possible for the decompressor to miss an ir packet . exemplary methods and apparatus are described in which a decompressor uses a later - received ir packet to decompress earlier packets for which the decompressor had not received context information .