RFC 1975 (rfc1975) - Page 2 of 6
PPP Magnalink Variable Resource Compression
Alternative Format: Original Text Document
RFC 1975 PPP Magnalink Variable Resource Compression August 1996
MVRCA Packets
Before any MVRCA packets may be communicated, PPP must reach the
Network-Layer Protocol phase[1], and the Compression Control Protocol
must reach the Opened state.
The text of a Packet to be compressed begins with PPP Protocol
number. The Packet header including the PPP Protocol number may have
already been compressed when Protocol-Field-Compression has been
negotiated.
Reliability and Sequencing
MVRCA packets may be sent across an unreliable link or may use a
reliable link as described in "PPP Reliable Transmission"[3] if the
reliable link has been negotiated. If frames are delivered out of
order or a frame is dropped, the decompressor will detect this and
requests a resynchronization using the Reset-Req and Reset-Ack types
of the CCP[2], with the compressor for the affected context.
Data Expansion
Although the compression algorithm may occasionally expand a data
packet, there is no expansion in MVRCA since any expanded data is
instead sent uncompressed. Dictionary synchronization is maintained
across uncompressed packets.
Encapsulation
The encapsulation consists of the PPP Protocol Identifier, a bit to
indicate if the data is compressed, the Context Identifier(CID), a
proprietary flag bit (E), a Packet Integrity Byte(PIB), and the
Compressed data.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PPP Protocol Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|C|E| CID | PIB | C compressed flag
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1 data is compressed
| Compressed data ... 0 data is not compressed
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Schremp, Black & Weiss Informational