When no Compression History is kept, the algorithm does not depend on a reliable link, and does not require that packets be delivered in sequence. However, per packet compression results in a lower compression ratio than it could be on a stream. When one or more compression Histories are negotiated, the packet sequence MUST be preserved within specific History Numbers. There is no sequence requirement between different History Numbers. Since this synchronization is done on a per history basis, the history number fields are required to be the same size in both directions of the link.
Any data contained in the packet is processed after the signaling bits are processed.
The transmitter MAY clear a Compression History at any time. The transmitter MUST clear a history after a receiving a Reset- Request for a given History Number. Then, packets can always be sent compressed regardless of expansion. When the expansion plus compression header exceeds the size of the peer's MRU for the link, the data MUST be sent as an uncompressed LZS-DCP packet. Packet Format A summary of the LZS-DCP packet format is shown below.