RFC 2559 - Internet X.509 PKI - LDAPv2 - The PKIX standard describes the LDAPv2-based protocol to provide access to PKI repositories for the purposes of retrieving and managing PKI information. - http://tools.ietf.org/html/rfc2559
RFC 2585 - Internet X.509 PKI - FTP and HTTP - The PKIX standard specifies the conventions for using the FTP and the HTTP to obtain certificates and certificate revocation lists (CRLs) from PKI repositories. - http://tools.ietf.org/html/rfc2585