Terminology in IPv6 over Timeslotted Channel Hopping
Author(s): Maria Palattella, Qin Wang, Pascal Thubert, Thomas Watteyne
6TSCH proposes an architecture for an IPv6 multilink subnet that is composed of a high speed powered backbone and a number of IEEE802.15.4e TSCH wireless networks attached and synchronized by backbone routers. This document extends existing terminology documents...
6TSCH MR. Palattella, Ed. Internet-Draft SnT/Univ. of Luxembourg Intended status: Informational P. Thubert Expires: January 16, 2014 cisco T. Watteyne Linear Technology / Dust Networks Q. Wang Univ. of Sci. and Tech. Beijing July 15, 2013 Terminology in IPv6 over Timeslotted Channel Hopping draft-palattella-6tsch-terminology-01 Abstract 6TSCH proposes an architecture for an IPv6 multilink subnet that is composed of a high speed powered backbone and a number of IEEE802.15.4e TSCH wireless networks attached and synchronized by backbone routers. This document extends existing terminology documents available for Low-power and Lossy Networks to provide additional terminology elements. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC 2119]. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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." This Internet-Draft will expire on January 16, 2014. Palattella, et al. Expires January 16, 2014 [Page 1] Internet-Draft 6tsch-terminology July 2013 Copyright Notice Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 4. Security Considerations . . . . . . . . . . . . . . . . . . . 8 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 6.1. Normative References . . . . . . . . . . . . . . . . . . 8 6.2. Informative References . . . . . . . . . . . . . . . . . 8 6.3. External Informative References . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 1. Introduction A new breed of Time Sensitive Networks is being developed to enable traffic that is highly sensitive to jitter and quite sensitive to latency. Such traffic is not limited to voice and video, but also includes command and control operations such as in industrial automation or in-vehicle sensors and actuators. At IEEE802.1, the "Audio/Video Task Group", was renamed TSN for Time Sensitive Networking. The IEEE802.15.4 Medium Access Control (MAC) has evolved with IEEE802.15.4e which provides in particular the Time Slotted Channel Hopping (TSCH) mode for industrial-type applications. Both provide deterministic capabilities to the point that a packet that pertains to a certain flow crosses the network from node to node following a very precise schedule, like a train leaves intermediate stations at precise times along its path. This document provides additional terminology elements to cover terms that are new to the context of TSCH wireless networks and other deterministic networks. Palattella, et al. Expires January 16, 2014 [Page 2] Internet-Draft 6tsch-terminology July 2013 2. Terminology The draft extends [I-D.ietf-roll-terminology] which is included here by reference. The draft does not reuse terms from IEEE802.15.4e such as "path" or "link" which bear a meaning that is quite different from classical IETF parlance. This document adds the following terms: 6TSCH: IPv6 over Time Slotted Channel Hopping (pronounced "sixtus"). It defines a set of IETF sublayers and protocols (in particular, for setting up a schedule with a centralized or distributed approach, managing the resource allocation), as well as the architecture to bind them together, for use in IPv6 TSCH based networks. 6F: IPv6 Forwarding. One of the three forwarding model supported by 6TSCH. Packets are routed at layer 3, where QoS and RED operations are expected to prioritize flows with differentiated services. 6top: 6top is the adaptation layer between TSCH and upper layers like 6LoWPAN and RPL. It is defined in [I-D.draft-wang-6tsch-6top]. 6top Data Convey Model: Model describing how the 6top adaptation layer feeds the data flow coming from upper layers into TSCH. It is composed by an I-MUX module, a MUX module, a set of priority queues, and a PDU (Payload Data Unit). ASN: Absolute Slot Number, the timeslot counter, incremented by one at each timeslot. It is wide enough to not roll over in practice. See [I-D.watteyne-6tsch-tsch-lln-context]. Blacklist: Set of frequencies which should not be used for communication. BBR: Backbone Router. In the 6TSCH architecture, it is an LBR and also a NEAR. It performs ND proxy operations between registered devices and classical ND devices that are located over the backbone. Bundle: A group of equivalent scheduled cells, i.e. cells identified by different [slotOffset, channelOffset], which are scheduled for a same purpose, with the same Palattella, et al. Expires January 16, 2014 [Page 3] Internet-Draft 6tsch-terminology July 2013 neighbor, with the same flags, and the same slotframe. The size of the bundle refers to the number of cells it contains. Given the length of the slotframe, the size of the bundle translates directly into bandwidth, either logical, or physical. Cell: A single element in the TSCH sloframe, identified by a slotOffset value, a channelOffset value, a slotframe_ID and Hopping_Sequence_ID. A cell can be scheduled or unscheduled. During an unscheduled cell, the node does not communicate. When a cell is scheduled, it is assigned a MAC-layer slotframe identifier, a neighbor MAC address (which can be the broadcast address), and one or more of the following flags: TX, RX, shared, timeskeeping, hard. A broadcast cell is an alias for "a scheduled cell with neighbor address the broadcast address". ChannelOffset: Identifies a row in the TSCH slotframe. The number of available channelOffsets is equal to the number of available frequencies. The channelOffset translates into a frequency when the communication takes place, resulting in channel hopping, as detailed in [I-D.watteyne-6tsch-tsch-lln-context]. Dedicated Cell: A cell that is reserved for a given node to transmit to a specific neighbor. Distributed cell reservation: A reservation of a cell done by one or more in-network entities (typically a connection endpoint). Distributed track reservation: A reservation of a track done by one or more in-network entities (typically a connection endpoint). EB: Enhanced Beacon frame used by an advertising node to announce the presence of the network. It contains information about the timeslot length, the current ASN value, the slotframes and timeslots the beaconing mote is listening on, and a 1-byte join priority (i.e., number of hops separating the node sending the EB, and the PAN coordinator). Palattella, et al. Expires January 16, 2014 [Page 4] Internet-Draft 6tsch-terminology July 2013 FF: 6LoWPAN Fragment Forwarding. It is one of the three forwarding model supported by 6TSCH. The 6LoWPAN Fragment is used as a label for switching at the 6LoWPAN sublayer, as defined in [I-D.thubert-roll-forwarding-frags]. GMPLS: Generalized Multi-Protocol Label Switching, a 2.5 layer service that is used to forward packets based on the concept of generalized labels. Hard Cell: A scheduled cell that is locked, i.e., it cannot be moved by 6top in the schedule. See [I-D.draft-wang-6tsch-6top]. Hopping Sequence: Sequence of frequencies, identified by a Hopping_Sequence_ID, used for channel hopping, when translating the channel offset value into a frequency (i.e., PHY channel). See [I-D.watteyne-6tsch-tsch-lln-context]. IE: Information Elements, a list of Type-Length-Value containers placed at the end of the MAC header, used to pass data between layers or devices. A small number of types are defined by TSCH, but a range of types is available for extensions, and thus, is exploitable by 6TSCH. See [I-D.watteyne-6tsch-tsch-lln-context]. I-MUX module: Inverse-Multiplexer, a classifier that receives 6LoWPAN frames and places them into priority queues. KMP: Key Managment Protocol. LBR: LLN Border Router. It is an LLN device, usually powered, that acts as a Border Router to the outside within the 6TSCH architecture. Link: A communication facility or medium over which nodes can communicate at the link layer, i.e., the layer immediately below IP. Thus, the IETF parlance for the term "Link" is adopted, as opposed to the incompatible IEEE802.15.4e terminology. In the context of the 6TSCH architecture, which applies to Low Power Lossy Networks (LLNs), an IPv6 subnet is usually not congruent to a single link and techniques such as IPv6 Neighbor Discovery Proxying and Routing Over LLNs are required to achieve reachability within the multilink subnet. A link is distinct from a track. In fact, link local addresses are not expected to be used over a track for end to end Palattella, et al. Expires January 16, 2014 [Page 5] Internet-Draft 6tsch-terminology July 2013 communication. Finally, from the Layer 3 perspective (where the inner complexities of TSCH operations are hidden to enable classical IP routing and Forwarding), a single radio interface may be seen as a number of Links with different capabilities for unicast or multicast services. Logical Cell: A cell that corresponds to granted bandwidth but is only lazily associated to a physical cell, based on usage. MAC: Medium Access Control. MUX module: Multiplexer, the entity that dequeues frames from priority queues and associates them to a cell for transmission. NEAR: Energy Aware Default Router, as defined in [I-D.chakrabarti-nordmark-6man-efficient-nd]. PANA: Protocol for carrying Authentication for Network Access, as defined in [RFC5191] . It is the protocol used in the 6TSCH architecture for handling authentication during the join process. PCE: Path Computation Element, the entity in the network which is responsible for building and maintaining the TSCH schedule, when centralized scheduling is used. PCE cell reservation: The reservation of a cell done by the PCE. PCE track reservation: The reservation of a track done by the PCE. QoS: Quality of Service. SA: Security Association. Shared Cell: A cell that is used by more than one transmitter nodes at the same time and on the same channelOffset. Only cells with TX flag can be marked as "shared". A backoff algorithm is used to resolve contention. SlotOffset: Identifies a column in the TSCH schedule, i.e., the number of timeslots since the beginning of the current iteration of the slotframe. Slotframe: A MAC-level abstraction that is internal to the node and contains a series of timeslots of equal length and Palattella, et al. Expires January 16, 2014 [Page 6] Internet-Draft 6tsch-terminology July 2013 priority. It is characterized by a slotframe_ID, and a slotframe_size. Multiple slotframes can coexist in a node's schedule, i.e., a node can have multiple activities scheduled in different slotframes, based on the priority of its packets/traffic flows. The timeslots in the Slotframe are indexed by the SlotOffset; the first timeslot is at SlotOffset 0. Soft Cell: A scheduled cell that is not locked, i.e., it may be moved in the schedule within a same slotframe by 6top, as described in [I-D.draft-wang-6tsch-6top]. TF: Track Forwarding. It is the simplest and fastest forwarding model supported by 6TSCH. It is a G-MPLS-like forwarding model. The input cell characterises the flow and indicates the output cell. Timeslot: A basic communication unit in TSCH which allows a transmitter node to send a frame to a receiver neighbor, and that receiver neighbor to optionally send back an acknowledgment. The length of the timeslot determines the maximum size of the frame that can be exchanged. Time Source Neighbor: A neighbor a node uses as its time reference, and to which it needs to keep its clock synchronized. A node can have one or more time source neighbors. Track: A determined sequence of cells along a multi-hop path. It is typically the result of a reservation. The node that initializes the process for establishing a track is the owner of the track. The latter assigns a unique identifier to the track, called TrackID. TrackID: Unique identifier of a track, assigned by the owner of the track. TSCH: Time Slotted Channel Hopping, a medium access mode of the [IEEE802154e] standard which uses time synchronization to achieve ultra low-power operation and channel hopping to enable high reliability. Palattella, et al. Expires January 16, 2014 [Page 7] Internet-Draft 6tsch-terminology July 2013 TSCH Schedule: A matrix of cells, each cell indexed by a slotOffset and a channelOffset. The slotframe size (the "width" of the matrix) is the number of timeslots it contains. The number of channelOffset values (the "height" of the matrix) is equal to the number of available frequencies. The TSCH schedule contains all the scheduled cells from all slotframes and is sufficient to qualify the communication in the TSCH network. 3. IANA Considerations This specification does not require IANA action. 4. Security Considerations This specification is not found to introduce new security threat. 5. Acknowledgements Thanks to the IoT6 European Project (STREP) of the 7th Framework Program (Grant 288445). 6. References 6.1. Normative References [RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC5191] Forsberg, D., Ohba, Y., Patil, B., Tschofenig, H., and A. Yegin, "Protocol for Carrying Authentication for Network Access (PANA)", RFC5191, May 2008. 6.2. Informative References [I-D.chakrabarti-nordmark-6man-efficient-nd] Chakrabarti, S., Nordmark, E., and M. Wasserman, "Efficiency aware IPv6 Neighbor Discovery Optimizations", draft-chakrabarti-nordmark-6man-efficient-nd-01 (work in progress), November 2012. [I-D.draft-wang-6tsch-6top] Wang, Q., Ed., Vilajosana, X., and T. Watteyne, "6TSCH Operation Sublayer (6top). draft-wang-6tsch-6top-00 (work in progress) ", July 2013. [I-D.ietf-roll-terminology] Palattella, et al. Expires January 16, 2014 [Page 8] Internet-Draft 6tsch-terminology July 2013 Vasseur, J., "Terminology in Low power And Lossy Networks", draft-ietf-roll-terminology-12 (work in progress), March 2013. [I-D.ohba-6tsch-security] Chasko, S., Das, S., Lopez, R., Ohba, Y., Thubert, P., and A. Yegin, "Security Framework and Key Management Protocol Requirements for 6TSCH", draft-ohba-6tsch-security-01 (work in progress), July 2013. [I-D.thubert-6tsch-architecture] Thubert, P., Assimiti, R., and T. Watteyne, "An Architecture for IPv6 over Time Slotted Channel Hopping", draft-thubert-6tsch-architecture-01 (work in progress), April 2013. [I-D.thubert-roll-forwarding-frags] Thubert, P. and J. Hui, "LLN Fragment Forwarding and Recovery", draft-thubert-roll-forwarding-frags-01 (work in progress), February 2013. [I-D.vilajosana-6tsch-basic] Vilajosana, X. and K. Pister, "Minimal 6TSCH Configuration", draft-vilajosana-6tsch-basic-01 (work in progress), July 2013. [I-D.watteyne-6tsch-tsch-lln-context] Watteyne, T., Palattella, M., and L. Grieco, "Using IEEE802.15.4e TSCH in an LLN context: Overview, Problem Statement and Goals", draft-watteyne-6tsch-tsch-lln- context-02 (work in progress), May 2013. 6.3. External Informative References [IEEE802154e] IEEE standard for Information Technology, "IEEE std. 802.15.4e, Part. 15.4: Low-Rate Wireless Personal Area Networks (LR-WPANs) Amendament 1: MAC sublayer", April 2012. Authors' Addresses Palattella, et al. Expires January 16, 2014 [Page 9] Internet-Draft 6tsch-terminology July 2013 Maria Rita Palattella (editor) University of Luxembourg Interdisciplinary Centre for Security, Reliability and Trust 4, rue Alphonse Weicker Luxembourg L-2721 LUXEMBOURG Phone: (+352) 46 66 44 5841 Email: firstname.lastname@example.org Pascal Thubert Cisco Systems, Inc Village d'Entreprises Green Side 400, Avenue de Roumanille Batiment T3 Biot - Sophia Antipolis 06410 FRANCE Phone: +33 497 23 26 34 Email: email@example.com Thomas Watteyne Linear Technology / Dust Networks 30695 Huntwood Avenue Hayward, CA 94544 USA Phone: +1 (510) 400-2978 Email: firstname.lastname@example.org Qin Wang Univ. of Sci. and Tech. Beijing 30 Xueyuan Road Beijing, Hebei 100083 China Phone: +86 (10) 6233 4781 Email: email@example.com Palattella, et al. Expires January 16, 2014 [Page 10]