1.3.4 Data Compression

RDP uses a bulk compressor to compress virtual channel data and some data in PDUs sent from server to client. Capability advertising for various versions of the bulk compressor occurs in the Client Info PDU (the Secure Settings Exchange phase of the connection sequence, as specified in section 1.3.1.1).

One version of the bulk compressor (the RDP 4.0 bulk compressor) is based on the Microsoft Point-To-Point Compression (MPPC) Protocol, as described in [RFC2118], and uses an 8 kilobyte history buffer. A more advanced version of the compressor (the RDP 5.0 bulk compressor) is derived from the RDP 4.0 bulk compressor, but uses a 64 kilobyte history buffer and modified Huffman-style encoding rules.

Besides employing bulk compression for generic data, RDP also uses variations of run length encoding (RLE) rules to implement compression of bitmap data sent from server to client. All clients have to be capable of decompressing compressed bitmap data; this capability is not negotiable.

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