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To further reduce the PPP header overhead, there is an option to compress the Protocol ID field. Protocol ID values can be compressed into a single-byte form clearly distinguishable from the standard 2-byte form. In cases where the leading byte of the protocol ID is zero (network data traffic), the MSB (most significant bit) value can be omitted. Configuration of the protocol ID compression is provided on a per-port basis. Enabling compression does not guarantee that protocol ID compression is actually used; that is determined by the peer negotiation process at link establishment time. However, you can validate whether compression is used by examining the PPP negotiated parameters in PPPCON.
When address, control, and protocol ID compressions are enabled and successfully negotiated between peer data-link nodes, the result is to reduce the PPP header overhead associated with network data traffic from 9 to 5 bytes. In low-bandwidth links passing interactive traffic, this can be a savings.
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