--- 1/draft-ietf-6lo-6lobac-00.txt 2015-03-09 17:14:45.027222343 -0700 +++ 2/draft-ietf-6lo-6lobac-01.txt 2015-03-09 17:14:45.071223427 -0700 @@ -1,23 +1,23 @@ 6Lo Working Group K. Lynn, Ed. -Internet-Draft Consultant +Internet-Draft Verizon Intended status: Standards Track J. Martocci -Expires: January 5, 2015 Johnson Controls +Expires: September 10, 2015 Johnson Controls C. Neilson Delta Controls S. Donaldson Honeywell - July 4, 2014 + March 9, 2015 Transmission of IPv6 over MS/TP Networks - draft-ietf-6lo-6lobac-00 + draft-ietf-6lo-6lobac-01 Abstract Master-Slave/Token-Passing (MS/TP) is a contention-free access method for the RS-485 physical layer, which is used extensively in building automation networks. This specification defines the frame format for transmission of IPv6 packets and the method of forming link-local and statelessly autoconfigured IPv6 addresses on MS/TP networks. Status of This Memo @@ -28,44 +28,44 @@ 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 5, 2015. + This Internet-Draft will expire on September 10, 2015. Copyright Notice - Copyright (c) 2014 IETF Trust and the persons identified as the + Copyright (c) 2015 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. MS/TP Mode for IPv6 . . . . . . . . . . . . . . . . . . . . . 6 + 2. MS/TP Mode for IPv6 . . . . . . . . . . . . . . . . . . . . . 5 3. Addressing Modes . . . . . . . . . . . . . . . . . . . . . . 6 4. Maximum Transmission Unit (MTU) . . . . . . . . . . . . . . . 6 - 5. LoBAC Adaptation Layer . . . . . . . . . . . . . . . . . . . 7 + 5. LoBAC Adaptation Layer . . . . . . . . . . . . . . . . . . . 6 6. Stateless Address Autoconfiguration . . . . . . . . . . . . . 9 7. IPv6 Link Local Address . . . . . . . . . . . . . . . . . . . 10 8. Unicast Address Mapping . . . . . . . . . . . . . . . . . . . 10 9. Multicast Address Mapping . . . . . . . . . . . . . . . . . . 11 10. Header Compression . . . . . . . . . . . . . . . . . . . . . 11 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 12. Security Considerations . . . . . . . . . . . . . . . . . . . 12 13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 Appendix A. Abstract MAC Interface . . . . . . . . . . . . . . . 14 @@ -85,21 +85,21 @@ networks. An MS/TP device is typically based on a low-cost microcontroller with limited processing power and memory. Together with low data rates and a small address space, these constraints are similar to those faced in 6LoWPAN networks and suggest some elements of that solution might be leveraged. MS/TP differs significantly from 6LoWPAN in at least three respects: a) MS/TP devices typically have a continuous source of power, b) all MS/TP devices on a segment can communicate directly so there are no hidden node or mesh routing issues, and c) - recent changes to MS/TP will support payloads of up to 1501 octets, + recent changes to MS/TP provide support for large payloads, eliminating the need for link-layer fragmentation and reassembly. The following sections provide a brief overview of MS/TP, then describe how to form IPv6 addresses and encapsulate IPv6 packets in MS/TP frames. This document also specifies a header compression mechanism, based on [RFC6282], that is RECOMMENDED in order to make IPv6 practical on low speed MS/TP networks. 1.1. Requirements Language @@ -112,24 +112,24 @@ ASHRAE: American Society of Heating, Refrigerating, and Air- Conditioning Engineers (http://www.ashrae.org) BACnet: An ISO/ANSI/ASHRAE Standard Data Communication Protocol for Building Automation and Control Networks CRC: Cyclic Redundancy Check MAC: Medium Access Control - MTU: Maximum Transmission Unit - MSDU: MAC Service Data Unit (MAC client data) + MTU: Maximum Transmission Unit + UART: Universal Asynchronous Transmitter/Receiver 1.3. MS/TP Overview This section provides a brief overview of MS/TP, which is specified in ANSI/ASHRAE 135-2012 (BACnet) Clause 9 [Clause9] and included herein by reference. BACnet [Clause9] also covers physical layer deployment options. MS/TP is designed to enable multidrop networks over shielded twisted @@ -153,21 +153,21 @@ MS/TP COBS-encoded* frames have the following format: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x55 | 0xFF | Frame Type* | DA | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SA | Length (MS octet first) | Header CRC | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . . - . Encoded Data* (2 - 1512 octets) . + . Encoded Data* (2 - 1507 octets) . . . + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | Encoded CRC-32K* (5 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+ | | optional 0xFF | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: MS/TP COBS-Encoded Frame Format *Note: BACnet Addendum 135-2012an [Addendum_an] defines a range of @@ -185,55 +185,54 @@ Frame Type one octet Destination Address one octet address Source Address one octet address Length two octets, most significant octet first Header CRC one octet Encoded Data 2 - 1512 octets (see Appendix B) Encoded CRC-32K five octets (see Appendix C) (pad) (optional) at most one octet of trailer: 0xFF The Frame Type is used to distinguish between different types of MAC - frames. The types relevent to this specification (in decimal) are: + frames. The types relevant to this specification (in decimal) are: 0 Token 1 Poll For Master 2 Reply To Poll For Master ... 34 IPv6 over MS/TP (LoBAC) Encapsulation - ASHRAE reserves undefined MS/TP Frame Type values 8 through 31 and 34 - through 127, inclusive. Frame Types 32 through 127 designate COBS- - encoded frames and MUST convey Encoded Data and Encoded CRC-32K - fields. All master nodes MUST understand Token, Poll For Master, and - Reply to Poll For Master control frames. See Section 2 for - additional details. + Frame Types 8 through 127 are reserved for assignment by ASHRAE. + Frame Types 32 through 127 designate COBS-encoded frames and MUST + convey Encoded Data and Encoded CRC-32K fields. All master nodes + MUST understand Token, Poll For Master, and Reply to Poll For Master + control frames. See Section 2 for additional details. The Destination and Source Addresses are each one octet in length. See Section 3 for additional details. For COBS-encoded frames, the Length field specifies the combined length of the [COBS] Encoded Data and Encoded CRC-32K fields in octets, minus two. (This adjustment is required for backward compatibility with legacy MS/TP devices.) See Section 4 and Appendices for additional details. The Header CRC field covers the Frame Type, Destination Address, Source Address, and Length fields. The Header CRC generation and check procedures are specified in BACnet [Clause9]. 1.4. Goals and Non-goals The primary goal of this specification is to enable IPv6 directly on wired end devices in building automation and control networks by leveraging existing standards to the greatest extent possible. A secondary goal is to co-exist with legacy MS/TP implementations. - Only the minimal changes necessary to support IPv6 over MS/TP are + Only the minimum changes necessary to support IPv6 over MS/TP are specified in BACnet [Addendum_an] (see Note in Section 1.3). Non-goals include making changes to the MS/TP frame header format, control frames, Master Node state machine, or addressing modes. Also, while the techniques described here may be applicable to other data links, no attempt is made to define a general design pattern. 2. MS/TP Mode for IPv6 ASHRAE must assign a new MS/TP Frame Type to indicate IPv6 over MS/TP @@ -264,27 +263,27 @@ (all nodes). A Source Address of 255 MUST NOT be used. MS/TP does not support multicast, therefore all IPv6 multicast packets MUST be sent as link-level broadcasts and filtered at the IPv6 layer. This specification assumes that a unique IPv6 subnet prefix is assigned to each MS/TP segment. Hosts learn IPv6 prefixes via router advertisements according to [RFC4861]. 4. Maximum Transmission Unit (MTU) - BACnet [Addendum_an] supports MPDUs up to 2032 octets in length. - This specification defines an MPDU length of at least 1281 octets and + BACnet [Addendum_an] supports MSDUs up to 2032 octets in length. + This specification defines an MSDU length of at least 1281 octets and at most 1501 octets. This is sufficient to convey the minimum MTU required by IPv6 [RFC2460] without the need for link-layer fragmentation and reassembly. - However, the relatively low data rates of MS/TP still make a + The relatively low data rates of MS/TP, however, still make a compelling case for header compression. An adaptation layer to indicate compressed or uncompressed IPv6 headers is specified in Section 5 and the compression scheme is specified in Section 10. 5. LoBAC Adaptation Layer The encapsulation formats defined in this section (subsequently referred to as the "LoBAC" encapsulation) comprise the MSDU (payload) of an MS/TP frame. The LoBAC payload (i.e., an IPv6 packet) follows an encapsulation header stack. LoBAC is a subset of the LoWPAN @@ -366,21 +365,21 @@ Figure 3: Dispatch Value Bit Patterns NALP: Specifies that the following bits are not a part of the LoBAC encapsulation, and any LoBAC node that encounters a Dispatch value of 00xxxxxx shall discard the packet. Non-LoBAC protocols that wish to coexist with LoBAC nodes should include an octet matching this pattern immediately following the MS/TP header. ESC: Specifies that the following header is a single 8-bit field for the Dispatch value. It allows support for Dispatch values larger - than 127 (see [RFC6282] section 5). + than 127 (see Section 5 of [RFC6282]). IPv6: Specifies that the following header is an uncompressed IPv6 header [RFC2460]. LOWPAN_IPHC: A value of 011xxxxx specifies a LOWPAN_IPHC compression header (see Section 10.) Reserved: A LoBAC node that encounters a Dispatch value in the range 01000010 through 01011111 or 1xxxxxxx SHALL discard the packet. @@ -406,20 +405,27 @@ |0 1|1 3|3 4|4 6| |0 5|6 1|2 7|8 3| +----------------+----------------+----------------+----------------+ |0000000000000000|0000000011111111|1111111000000000|0000000001001111| +----------------+----------------+----------------+----------------+ This is the RECOMMENDED method of forming an IID, as it supports the most efficient header compression provided by the LOWPAN_IPHC [RFC6282] scheme specified in Section 10. + Optionally, an opaque 64-bit IID (for non-link-local addresses) MAY + be formed by the technique discussed in [I-D.ietf-6man-default-iids] + or alternate method. A node that generates a non-link-local address + IID MUST register it with its local router(s) by sending a Neighbor + Solicitation (NS) message with the Address Registration Option (ARO) + and process Neighbor Advertisements (NA) according to [RFC6775]. + An IPv6 address prefix used for stateless autoconfiguration [RFC4862] of an MS/TP interface MUST have a length of 64 bits. 7. IPv6 Link Local Address The IPv6 link-local address [RFC4291] for an MS/TP interface is formed by appending the Interface Identifier, as defined above, to the prefix FE80::/64. 10 bits 54 bits 64 bits @@ -435,23 +441,23 @@ The Source/Target Link-layer Address option has the following form when the addresses are 8-bit MS/TP link-layer (node) addresses. 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length=1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | - +- Padding (all zeros) -+ + + Padding (all zeros) + | | - +- +-+-+-+-+-+-+-+-+ + + +-+-+-+-+-+-+-+-+ | | MS/TP Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Option fields: Type: 1: for Source Link-layer address. 2: for Target Link-layer address. @@ -520,25 +526,26 @@ We are grateful to the authors of [RFC4944] and members of the IETF 6LoWPAN working group; this document borrows liberally from their work. 14. References 14.1. Normative References [Addendum_an] - ASHRAE, "Proposed Addendum an to ANSI/ASHRAE Standard - 135-2012, BACnet - A Data Communication Protocol for - Building Automation and Control Networks (Second Public - Review)", March 2014, . + ASHRAE, "ANSI/ASHRAE Addenda an, at, au, av, aw, ax, and + az to ANSI/ASHRAE Standard 135-2012, BACnet - A Data + Communication Protocol for Building Automation and Control + Networks", July 2014, + . [Clause9] American Society of Heating, Refrigerating, and Air- Conditioning Engineers, "BACnet - A Data Communication Protocol for Building Automation and Control Networks", ANSI/ASHRAE 135-2012 (Clause 9), March 2013. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 @@ -581,20 +588,26 @@ Applications", IEEE/IFIP International Conference on Dependable Systems and Networks (DSN 2002) , June 2002, . [EUI-64] IEEE, "Guidelines for 64-bit Global Identifier (EUI-64) Registration Authority", March 1997, . + [I-D.ietf-6man-default-iids] + Gont, F., Cooper, A., Thaler, D., and W. Will, + "Recommendation on Stable IPv6 Interface Identifiers", + draft-ietf-6man-default-iids-02 (work in progress), + January 2015. + [IEEE.802.3] "Information technology - Telecommunications and information exchange between systems - Local and metropolitan area networks - Specific requirements - Part 3: Carrier Sense Multiple Access with Collision Detection (CMSA/CD) Access Method and Physical Layer Specifications", IEEE Std 802.3-2008, December 2008, . [RFC2469] Narten, T. and C. Burton, "A Caution On The Canonical @@ -631,21 +644,21 @@ MA-DATA.request ( destination_address, source_address, data, priority, type ) The 'destination_address' parameter may specify either an individual or a broadcast MAC entity address. It must contain sufficient - information to create the Destination Address field (see Section 10) + information to create the Destination Address field (see Section 1.3) that is prepended to the frame by the local MAC sublayer entity. The 'source_address' parameter, if present, must specify an individual MAC address. If the source_address parameter is omitted, the local MAC sublayer entity will insert a value associated with that entity. The 'data' parameter specifies the MAC service data unit (MSDU) to be transferred by the MAC sublayer entity. There is sufficient information associated with the MSDU for the MAC sublayer entity to determine the length of the data unit. @@ -704,21 +717,21 @@ The 'priority' parameter specifies the priority desired for the data unit transfer. The priority parameter is ignored by MS/TP. The 'type' parameter is the value of the MS/TP Frame Type field of the incoming frame. A.2.3. When Generated The MA_DATA.indication is passed from the MAC sublayer entity to the - MAC client entity or entites to indicate the arrival of a frame to + MAC client entity or entities to indicate the arrival of a frame to the local MAC sublayer entity that is destined for the MAC client. Such frames are reported only if they are validly formed, received without error, and their destination address designates the local MAC entity. Frames destined for the MAC Control sublayer are not passed to the MAC client. A.2.4. Effect on Receipt The effect of receipt of this primitive by the MAC client is unspecified. @@ -737,25 +750,25 @@ COBS is a run-length encoding method that nominally removes '0x00' octets from its input. Any selected octet value may be removed by XOR'ing that value with each octet of the COBS output. BACnet [Addendum_an] specifies the preamble octet '0x55' for removal. The minimum overhead of COBS is one ectet per encoded field. The worst-case overhead is bounded to one octet in 254, or less than 0.5%, as described in [COBS]. - Frame encoding proceeds logically in two passes. The Extended Data + Frame encoding proceeds logically in two passes. The Encoded Data field is prepared by passing the MSDU through the COBS encoder and XOR'ing the preamble octet '0x055' with each octet of the output. - The Extended Data CRC field is then prepared by calculating a CRC-32K - over the Extended Data field and formatting it for transmission as + The Encoded CRC-32K field is then prepared by calculating a CRC-32K + over the Encoded Data field and formatting it for transmission as described in Appendix C. The combined length of these fields, minus two octets for compatibility with existing MS/TP devices, is placed in the MS/TP header Length field before transmission. Example COBS encoder and decoder functions are shown below for illustration. Complete examples of use and test vectors are provided in BACnet [Addendum_an]. #include #include @@ -813,21 +825,20 @@ write_index--; else to[code_index] = code ^ mask; return write_index; } #include #include #define CRC32K_INITIAL_VALUE (0xFFFFFFFF) - #define CRC32K_RESIDUE (0x0843323B) #define MSTP_PREAMBLE_X55 (0x55) /* * Decodes 'length' octets of data located at 'from' and * writes the original client data at 'to', restoring any * 'mask' octets that may present in the encoded data. * Returns the length of the encoded data or zero if error. */ size_t cobs_decode (uint8_t *to, const uint8_t *from, size_t length, @@ -866,25 +877,25 @@ This Appendix is informative and not part of the standard. Extending the payload of MS/TP to 1501 octets required upgrading the Data CRC from 16 bits to 32 bits. P.Koopman has authored several papers on evaluating CRC polynomials for network applications. In [CRC32K], he surveyed the entire 32-bit polynomial space and noted some that exceed the [IEEE.802.3] polynomial in performance. BACnet [Addendum_an] specifies the CRC-32K (Koopman) polynomial. The specified use of the calc_crc32K() function is as follows. - Before a frame is transmitted, 'crc_value' is initialized to all ones - before the function is called. After passing all octets of the - [COBS] Encoded Data through the function, the ones complement of the - resulting 'crc_value' is arranged in LSB-first order and is itself - [COBS] encoded. + Before a frame is transmitted, 'crc_value' is initialized to all + ones. After passing each octet of the [COBS] Encoded Data through + the function, the ones complement of the resulting 'crc_value' is + arranged in LSB-first order and is itself [COBS] encoded. The length + of the resulting Encoded CRC-32K field is always five octets. Upon reception of a frame, 'crc_value' is initialized to all ones. The octets of the Encoded Data field are accumulated by the calc_crc32K() function before decoding. The Encoded CRC-32K field is then decoded and the resulting four octets are accumulated by the calc_crc32K() function. If the result is the expected residue value 'CRC32K_RESIDUE', then the frame was received correctly. An example CRC-32K function in shown below for illustration. Complete examples of use and test vectors are provided in BACnet @@ -902,44 +913,43 @@ /* * Accumulate 'data_value' into the CRC in 'crc_value'. * Return updated CRC. * * Note: crcValue must be set to CRC32K_INITIAL_VALUE * before initial call. */ uint32_t calc_crc32K (uint8_t data_value, uint32_t crc_value) { - uint8_t data, b; - uint32_t crc; - - data = data_value; - crc = crc_value; + int b; - for (b = 0; b < 8; b++) { - if ((data & 1) ^ (crc & 1)) { - crc >>= 1; - crc ^= CRC32K_POLY; + for (b = 0; b < sizeof(uint8_t); b++) { + if ((data_value & 1) ^ (crc_value & 1)) { + crc_value >>= 1; + crc_value ^= CRC32K_POLY; } else { - crc >>= 1; + crc_value >>= 1; } - data >>= 1; + data_value >>= 1; } - return crc; + return crc_value; } Authors' Addresses Kerry Lynn (editor) - Consultant + Verizon + 50 Sylvan Rd + Waltham , MA 02451 + USA - Phone: +1 978 460 4253 + Phone: +1 781 296 9722 Email: kerlyn@ieee.org Jerry Martocci Johnson Controls, Inc. 507 E. Michigan St Milwaukee , WI 53202 USA Phone: +1 414 524 4010 Email: jerald.p.martocci@jci.com