RFC1134		Oldest PPP RFC
RFC1171		Older PPP RFC
RFC1331		Old PPP RFC
RFC1661		Main PPP RFC
RFC1662		HDLC-like framking

IP has a protocol number of 0021
Van Jacobson Compressed is 002d
Van Jacobson Uncompressed is 002f
IPCP has 8021

RFC791 		IP

pppd allows the option -vj to disable van jacobson compression

To run the protocol monitor, each as root do, in order

/afs/sipb/user/mkgray/bin/pppframe /dev/ttye1 /dev/ttye2
pppd -detach 10.0.0.1:18.85.5.88 /dev/ptye1 38400
pppd -detach 18.85.5.88:10.0.0.1 /dev/ptye2 38400