Network Working Group M. Jansky Internet-Draft T. Pohjolainen Expires: April 4, 2006 Nokia October 2005 NTP Timestamp Extension for ALC draft-jansky-alc-timestamp-extension-00.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working 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 inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on April 4, 2006. Copyright Notice Copyright (C) The Internet Society (2005). Abstract This document defines a variable length ALC PI specific LCT Header Extension, NTP Timestamp Header (EXT_NTP). This extension can be used within an ALC session for multiple purposes, for example, to signal the last moment of time there was a change in the session. Jansky & Pohjolainen Expires April 4, 2006 [Page 1] Internet-Draft NTP Timestamp Extension for ALC October 2005 Table of Contents 1. Requirements notation . . . . . . . . . . . . . . . . . . . . . 3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. NTP Timestamp Header . . . . . . . . . . . . . . . . . . . . . 3 4. Security Considerations . . . . . . . . . . . . . . . . . . . . 4 5. Normative references . . . . . . . . . . . . . . . . . . . . . 4 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6 Intellectual Property and Copyright Statements . . . . . . . . . . 7 Jansky & Pohjolainen Expires April 4, 2006 [Page 2] Internet-Draft NTP Timestamp Extension for ALC October 2005 1. Requirements notation The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [1]. 2. Introduction This document defines a variable length ALC PI specific LCT Header Extension, NTP Timestamp Header (EXT_NTP) [2]. This extension can be used within an ALC session for multiple purposes. The semantics of the EXT_NTP can be declared within the Header Extension itself (through the "Use" field). Although the specification of EXT_NTP does not limit the use of the timestamp information any particular use, this specification defines one use - the signaling of the last moment of time there was a change in the session. The purpose of that use of the EXT_NTP extension is to allow the sender of the ALC session to signal changes in the session for the receivers of the session. This is particularly useful in the cases where the receivers of the ALC session sporadically enter and leave the session. In such cases the receiver may receive the session for a period of time, stop reception for another period of time and continue reception again. Examples of such cases are relatively long ALC sessions that deliver a number of Transport Objects so that the number of Transport Objects dynamically changes, or, cases where the receiver has temporary connection to the transmission medium. 3. NTP Timestamp Header NTP Timestamp Header (EXT_NTP) is a variable length, ALC PI specific LCT Header Extension [2]. The Header Extension Type (HET) for the extension is 65. Its format is defined as follows: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | HET = 65 | HEL = 2 | Use | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | NTP Timestamp | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Header Extension Type (HET), 8 bits: Jansky & Pohjolainen Expires April 4, 2006 [Page 3] Internet-Draft NTP Timestamp Extension for ALC October 2005 Value of this field MUST be set to 65. Header Extension Length (HEL), 8 bits: The length of the whole Header Extension field, expressed in multiples of 32-bit words. For EXT_NTP, this field MUST be set to 2. Use, 8 bits: This field expresses the exact semantics how the sender of the ALC session intens the receiver to interpret the use of the timestamp. This specification defines the semantics for the case when "Use" equals "0". Other values for this field are possible but not in scope of this specification. Reserved, 8 bits: This field is reserved for future use and SHOULD be set to 0. NTP Timestamp, 32 bits: The value of this field is to be interpreted as the seconds-part (32 most significant bits) of NTP timestamp [3]. When the field When use equals "0", this timestamp signals the NTP time the ALC session was last changed. That is, it expresses the last moment of time a Transport Object was added to the session for delivery. The EXT_NTP MAY be carried in any ALC packet delivered within the ALC session. This specification does not define further guidelines on how frequently or when to use the EXT_NTP as these choices are depenent on the usage scenario of the extension. 4. Security Considerations As the NTP Timestamp Header is to be used with ALC packets within ALC sessions, the security considerations of ALC apply. Beyond that, there are no further security considerations related to this header extension. 5. Normative references [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, BCP 14, March 1997. [2] Luby, M., Gemmell, J., Vicisano, L., Rizzo, L., Handley, M., and J. Crowcroft, "Layered Coding Transport (LCT) Building Block", RFC 3451, December 2002. Jansky & Pohjolainen Expires April 4, 2006 [Page 4] Internet-Draft NTP Timestamp Extension for ALC October 2005 [3] Mills, D., "Network Time Protocol (Version 3), Specification, Implementation and Analysis", RFC 1305, March 1992. Jansky & Pohjolainen Expires April 4, 2006 [Page 5] Internet-Draft NTP Timestamp Extension for ALC October 2005 Authors' Addresses Martin Jansky Nokia Itamerenkatu 11-13 Helsinki FIN-00180 Finland Email: martin.jansky@nokia.com Topi Pohjolainen Nokia Itamerenkatu 11-13 Helsinki FIN-00180 Finland Email: topi.pohjolainen@nokia.com Jansky & Pohjolainen Expires April 4, 2006 [Page 6] Internet-Draft NTP Timestamp Extension for ALC October 2005 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. 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