Mobile Ad hoc Networking (MANET) T. Clausen Internet-Draft LIX, Ecole Polytechnique, France Expires: August 12, 2007 C. Dearlove BAE Systems Advanced Technology Centre February 8, 2007 Representing multi-value time in MANETs draft-clausen-manet-timetlv-00 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 August 12, 2007. Copyright Notice Copyright (C) The IETF Trust (2007). Clausen & Dearlove Expires August 12, 2007 [Page 1] Internet-Draft Time TLV February 2007 Abstract This document describes a general and flexible TLV (type-length-value structure) for representing time using the generalized MANET packet/ message format. It defines two message TLVs for representing validity and interval times for MANET routing protocols. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Applicability Statement . . . . . . . . . . . . . . . . . . . 5 4. Protocol Overview and Functioning . . . . . . . . . . . . . . 6 5. Representing Time . . . . . . . . . . . . . . . . . . . . . . 7 6. General Time TLV Structure . . . . . . . . . . . . . . . . . . 8 7. Message TLVs . . . . . . . . . . . . . . . . . . . . . . . . . 10 7.1. VALIDITY_TIME TLV . . . . . . . . . . . . . . . . . . . . 10 7.2. INTERVAL_TIME TLV . . . . . . . . . . . . . . . . . . . . 10 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 9. Security Considerations . . . . . . . . . . . . . . . . . . . 12 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13 10.1. Normative References . . . . . . . . . . . . . . . . . . . 13 10.2. Informative References . . . . . . . . . . . . . . . . . . 13 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 14 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15 Intellectual Property and Copyright Statements . . . . . . . . . . 16 Clausen & Dearlove Expires August 12, 2007 [Page 2] Internet-Draft Time TLV February 2007 1. Introduction The generalized packet/message format [1] specifies a signaling format which MANET routing protocols can employ for exchanging protocol information. This format presents the ability to express and associate attributes to packets, messages or addresses, by way of a general TLV (type-length-value) mechanism. This document specifies a general Time TLV structure, which can be used by any MANET routing protocol that needs to express either single time values or a set of time values with each value associated with a range of distances. This allows a receiving node to determine a single time value if either it knows its distance from the originator node, which [1] may provide, or the Time TLV specifies a single time value. This document also specifies two message TLV types, which use the TLV structure proposed. These TLV types are INTERVAL_TIME and VALIDITY_TIME, specifying respectively the maximum time before another message of the same type as this message from the same originator should be received, and the duration for which the information in this message is valid after receipt. Note that, if both are present, then the latter will usually be greater than the former in order to allow for possible message loss. Clausen & Dearlove Expires August 12, 2007 [Page 3] Internet-Draft Time TLV February 2007 2. Terminology The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC2119 [2]. Additionally, this document uses terminology from [1], and introduces the following terminology: Distance - the number of hops from the message originator to the message recipient, as may be indicated using the field in the full message header defined in [1], after being incremented on reception. Time Value - a time, measured in seconds. Time Code - an 8 bit field, representing a time value. Clausen & Dearlove Expires August 12, 2007 [Page 4] Internet-Draft Time TLV February 2007 3. Applicability Statement The TLV described in this document is applicable whenever a single time value, or a time value that varies with distance from the originator of a message, is required in a protocol using the generalized MANET packet/message format [1]. Examples of time values that may be included in a protocol message are: o The maximum time interval until the next message of the same type is to be generated by the message's originator node. o The validity time of the information with which the time value is associated. Either of these may vary with the distance between the originating and receiving nodes if messages of the same type are sent with different hop limits as defined in [1]. Note that if using [1], then distance information is available as the hop count field in a full message header (after being incremented). Parts of this document have been generalized from material in the proactive MANET routing protocol OLSR (The Optimized Link State Routing Protocol) [3]. Clausen & Dearlove Expires August 12, 2007 [Page 5] Internet-Draft Time TLV February 2007 4. Protocol Overview and Functioning This document does not specify a protocol nor does it mandate specific node or protocol behavior. Rather, it outlines mechanisms for encoding time values using the TLV mechanism of [1]. Protocols using the mechanisms and TLVs specified in this document must ensure that they do so in a coherent way. Clausen & Dearlove Expires August 12, 2007 [Page 6] Internet-Draft Time TLV February 2007 5. Representing Time This document specifies a TLV structure in which time values are each represented in an 8 bit time code, one or more of which may be used in a TLV's value field. Of these 8 bits, the least significant four bits represent the mantissa (a), and the most significant four bits represent the exponent (b), so that: o time value = (1 + a/16) * 2^b * C o time code = 16 * b + a All nodes in the network MUST use the same value of C, which will be specified in seconds, hence so will be all time values. Note that ascending values of the time code represent ascending time values, time values may thus be compared by comparison of time codes. An algorithm for computing the time code representing the smallest representable time value not less than the time value t is: 1. find the largest integer b such that t/C >= 2^b; 2. set a = 16 * (t / (C * 2^b) - 1), rounded up to the nearest integer; 3. if a == 16 then set b = b + 1 and set a = 0; 4. if a and b are in the range 0 and 15 then the required time value can be represented by the time code 16 * b + a, otherwise it can not. The minimum time value that can be represented in this manner is C. The maximum time value that can be represented in this manner is 63488 * C. Clausen & Dearlove Expires August 12, 2007 [Page 7] Internet-Draft Time TLV February 2007 6. General Time TLV Structure A Time TLV may be a packet, message or address block TLV. If it is a packet or message TLV then it must be a single value TLV as defined in [1]; if it is an address block TLV then it may be single value or multivalue TLV. The specific Time TLVs specified in this document, in Section 7 are message, and hence single value, TLVs. Note that even a single value Time TLV may contain a multiple octet field. The purpose of a single value Time TLV is to allow a single time value to be determined by a node receiving an entity containing the Time TLV, based on its distance from the entity's originator. The Time TLV may contain information that allows that time value to be a function of distance, and thus different receiving nodes may determine different time values. If a receiving node will not be able to determine its distance from the originating node, then the form of this Time TLV with a single time code in a field (or single value subfield) SHOULD be used. The field of a single value Time TLV is specified, using the regular expression syntax of [1], by: = {