Network Working Group W. Simpson Internet Draft DayDreamer expires in six months July 1997 PPP LCP CallBack draft-ietf-pppext-callback-ds-01.txt Status of this Memo Distribution of this memo is unlimited. This document is an Internet-Draft. Internet Drafts are working doc- uments of the Internet Engineering Task Force (IETF), its Areas, and its Working Groups. Note that other groups may also distribute work- ing documents as Internet Drafts. Internet Drafts are draft documents valid for a maximum of six months, and may be updated, replaced, or obsoleted by other documents at any time. It is not appropriate to use Internet Drafts as refer- ence material, or to cite them other than as a ``working draft'' or ``work in progress.'' To learn the current status of any Internet-Draft, please check the ``1id-abstracts.txt'' listing contained in the internet-drafts Shadow Directories on: ftp.is.co.za (Africa) nic.nordu.net (Europe) ds.internic.net (US East Coast) ftp.isi.edu (US West Coast) munnari.oz.au (Pacific Rim) Abstract The Point-to-Point Protocol (PPP) [1] provides a standard method for transporting multi-protocol datagrams over point-to-point links. PPP defines an extensible Link Control Protocol (LCP) for establishing, configuring, and testing the data-link connection. This document defines the CallBack option. Simpson expires in six months [Page i] DRAFT PPP CallBack July 1997 1. Introduction CallBack is a facility that permits a call originating party (caller) to request that the call terminating party (callee) originate a sub- sequent call in the reverse direction. This might be used for many diverse purposes, such as savings on toll charges. Unlike most PPP operations, CallBack is not a strictly peer-to-peer service. The semantics of CallBack differ depending on which peers are the caller and callee. The successful operation of CallBack requires a significant amount of administrative configuration. Such configuration might include per- mission to use the CallBack facility, locations and time of day for which the CallBack is allowed, and time delays prior to and following disconnection. - The callee might disconnect quickly, and return the call as soon as possible. - CallBack might be used to re-establish service at later time, when sufficient additional traffic arrives at the callee to warrant another connection. - When the user is roaming, CallBack might be used to register a variable contact location. Such policy considerations are beyond the scope of this specifica- tion. 2. Additional LCP Configuration Options The Configuration Option format and basic options are already defined for LCP [1]. Up-to-date values of the LCP Option Type field are specified in the most recent "Assigned Numbers" [2]. This document concerns the fol- lowing values: 13 CallBack Simpson expires in six months [Page 1] DRAFT PPP CallBack July 1997 2.1. CallBack Description This Configuration Option provides a method for an implementation to request a dial-up peer to call back. By default, no call back occurs. Nota Bene: Like all such PPP options, this indicates that the installation has the capability to be called back. If the option is rejected, link operation continues normally [1 page 39]. Moreover, acknowlegement of the option does not require that the peer take any additional action [ibid]. A peer that Configure-Acks this option SHOULD Configure-Request the Authentication-Protocol option. The user information learned during authentication can be used to determine the user location, or limit a user to certain locations, or merely to determine whom to bill for the service. When CallBack is successfully negotiated, and the Authentication phase is complete, the peer will eventually enter the Link Termi- nation phase. At the conclusion of the Link Termination phase, the peer will disconnect the link. Then, after a suitable interval of time, the peer will re- establish the link. When mutual authentication is desired, the implementation SHOULD Configure-Request the Authentication- Protocol option as it answers the call. Implementation Notes: The delay times between calls are characteristics of the call- ing environment, and MUST be configured on a per user and loca- tion basis. Since the information is redundant, the implementation is not required to Configure-Request the CallBack option as it answers the call. However, inclusion MUST NOT affect the operation of the protocol. A summary of the CallBack Option format is shown below. The fields are transmitted from left to right. Simpson expires in six months [Page 2] DRAFT PPP CallBack July 1997 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Operation | Message ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 13 Length >= 3 Operation The Operation field is one octet and indicates the contents of the Message field. Up-to-date values of the CallBack Operation field are specified in the most recent "Assigned Numbers" [2]. This document defines the following values: 0 Identification from the Authentication phase will be used for a database lookup to determine the callback parame- ters. The Message field is not present. This method is required to be supported in all conformant implementations. 1 Dialing string, the format and contents of which assumes configuration knowledge of the specific device that is making the callback. A North American example might be: 10222,,,(800)555-1212. This method is commonly supported, but suffers from fre- quent configuration error. 2 Location identifier, which may or may not be human read- able, used together with Authentication phase information for a database lookup to determine the callback parame- ters. 3 E.164 number. The implementation converts this to an appropriate signalling sequence. Simpson expires in six months [Page 3] DRAFT PPP CallBack July 1997 4 X.500 distinguished name, used together with Authentica- tion phase information for a database lookup to determine the callback parameters. 5 E.165 number. The implementation converts this to an appropriate signalling sequence. Message The Message field is zero or more octets, and its general contents are determined by the Operation field. The actual format of the information is site or application specific, and a robust imple- mentation SHOULD support the field as undistinguished octets. The size is determined from the Length field. It is intended that only an authorized user will have correct site specific information to make use of the CallBack. The codifica- tion of the range of allowed usage of this field is beyond the scope of this specification. Security Considerations Unauthenticated and unrestricted use of CallBack could lead to a sig- nificant denial of service, or excessive service charges. Authenti- cation is required to be supported. In addition, it is recommended that an implementation be capable of logging usage. Acknowledgements Special thanks to Ascend Communications for providing computing resources and network access support for writing this specification. Simpson expires in six months [Page 4] DRAFT PPP CallBack July 1997 References [1] Simpson, W., Editor, "The Point-to-Point Protocol (PPP)", STD-51, RFC-1661, December 1993. [2] Reynolds, J.K., Postel, J.B., "Assigned Numbers", RFC-1700, July 1992. [3] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, Harvard University, March 1997. Contacts Comments about this document should be discussed on the ietf-ppp@merit.edu mailing list. This document is a submission to the Point-to-Point Protocol Working Group of the Internet Engineering Task Force (IETF). The working group can be contacted via the current chair: Karl Fox Ascend Communications 3518 Riverside Drive Suite 101 Columbus, Ohio 43221 karl@MorningStar.com karl@Ascend.com Questions about this document can also be directed to: William Allen Simpson DayDreamer Computer Systems Consulting Services 1384 Fontaine Madison Heights, Michigan 48071 wsimpson@UMich.edu wsimpson@GreenDragon.com (preferred) bsimpson@MorningStar.com Simpson expires in six months [Page 5]