I've written a paper that describes and compares various proposals for providing security functions at the IP layer. These proposals include SP3 and I-NLSP swIPe the encryption and authentication options of SIPP PIPS The paper is available by anonymous ftp from software.watson.ibm.com in the file pub/tjw.reports/ipsec_review.ps. Comments to this mailing list or to me at linehan@watson.ibm.com.