--- 1/draft-ietf-6lo-6lobac-04.txt 2016-06-16 07:16:02.337936990 -0700 +++ 2/draft-ietf-6lo-6lobac-05.txt 2016-06-16 07:16:02.385938208 -0700 @@ -1,23 +1,23 @@ 6Lo Working Group K. Lynn, Ed. Internet-Draft Verizon Labs Intended status: Standards Track J. Martocci -Expires: August 25, 2016 Johnson Controls +Expires: December 18, 2016 Johnson Controls C. Neilson Delta Controls S. Donaldson Honeywell - February 22, 2016 + June 16, 2016 Transmission of IPv6 over MS/TP Networks - draft-ietf-6lo-6lobac-04 + draft-ietf-6lo-6lobac-05 Abstract Master-Slave/Token-Passing (MS/TP) is a medium access control 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 @@ -28,21 +28,21 @@ 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 August 25, 2016. + This Internet-Draft will expire on December 18, 2016. Copyright Notice Copyright (c) 2016 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 @@ -63,44 +63,44 @@ 7. IPv6 Link Local Address . . . . . . . . . . . . . . . . . . . 8 8. Unicast Address Mapping . . . . . . . . . . . . . . . . . . . 9 9. Multicast Address Mapping . . . . . . . . . . . . . . . . . . 9 10. Header Compression . . . . . . . . . . . . . . . . . . . . . 10 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 12. Security Considerations . . . . . . . . . . . . . . . . . . . 10 13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 11 Appendix A. Abstract MAC Interface . . . . . . . . . . . . . . . 13 Appendix B. Consistent Overhead Byte Stuffing [COBS] . . . . . . 16 - Appendix C. Encoded CRC-32K [CRC32K] . . . . . . . . . . . . . . 20 - Appendix D. Example 6LoBAC Packet Decode . . . . . . . . . . . . 22 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27 + Appendix C. Encoded CRC-32K [CRC32K] . . . . . . . . . . . . . . 19 + Appendix D. Example 6LoBAC Packet Decode . . . . . . . . . . . . 21 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 26 1. Introduction Master-Slave/Token-Passing (MS/TP) is a medium access control (MAC) protocol for the RS-485 [TIA-485-A] physical layer, which is used extensively in building automation networks. This specification defines the frame format for transmission of IPv6 [RFC2460] packets and the method of forming link-local and statelessly autoconfigured IPv6 addresses on MS/TP networks. The general approach is to adapt elements of the 6LoWPAN specifications [RFC4944], [RFC6282], and [RFC6775] to constrained wired 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 MAC 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 provide support for large payloads, + recent changes to MS/TP provide support for larger payloads, eliminating the need for fragmentation and reassembly below IPv6. 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 REQUIRED in order to reduce latency and make IPv6 practical on MS/TP networks. 1.1. Requirements Language @@ -128,65 +128,65 @@ 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 pair wiring. It can support network segments up to 1000 meters in - length at a data rate of 115,200 baud, or segments up to 1200 meters - in length at lower baud rates. An MS/TP link requires only a UART, - an RS-485 [TIA-485-A] transceiver with a driver that can be disabled, + length at a data rate of 115,200 bit/s, or segments up to 1200 meters + in length at lower bit rates. An MS/TP link requires only a UART, an + RS-485 [TIA-485-A] transceiver with a driver that can be disabled, and a 5ms resolution timer. These features make MS/TP a cost- effective field bus for the most numerous and least expensive devices in a building automation network. The differential signaling used by [TIA-485-A] requires a contention- free MAC. MS/TP uses a token to control access to a multidrop bus. A master node may initiate the transmission of a data frame when it holds the token. After sending at most a configured maximum number of data frames, a master node passes the token to the next master - node (as determined by MAC address). Slave nodes do not support the - frame format required to convey IPv6 over MS/TP and therefore SHALL - NOT be considered part of this specification. + node (as determined by MAC address). If present on the link, legacy + MS/TP implementations (including all slave nodes) ignore the frame + format defined in this specification. - MS/TP COBS-encoded* frames have the following format: + BACnet Addendum 135-2012an [Addendum_an] defines a range of Frame + Type values to designate frames that contain larger data and data CRC + fields, encoded using Consistent Overhead Byte Stuffing [COBS] (see + Appendix B). The purpose of COBS encoding is to eliminate preamble + sequences from the Encoded Data and Encoded CRC-32K fields. The + maximum length of an MSDU as defined by this specification is 1500 + octets (before encoding). The Encoded Data is covered by a 32-bit + CRC [CRC32K] (see Appendix C). The CRC-32K is then COBS encoded. + + 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 | + | 0x55 | 0xFF | Frame Type | DA | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SA | Length (MS octet first) | Header CRC | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . . - . Encoded Data* (2 - 1506 octets) . + . Encoded Data (2 - 1506 octets) . . . + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ - | | Encoded CRC-32K* (5 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 - Frame Type values to designate frames that contain data and data CRC - fields encoded using Consistent Overhead Byte Stuffing [COBS] (see - Appendix B). The purpose of COBS encoding is to eliminate preamble - sequences from the Encoded Data and Encoded CRC-32K fields. The - maximum length of an MSDU as defined by this specification is 1500 - octets (before encoding). The Encoded Data is covered by a 32-bit - CRC [CRC32K] (see Appendix C), which is itself then COBS encoded. - MS/TP COBS-encoded frame fields have the following descriptions: Preamble two octet preamble: 0x55, 0xFF 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 - 1506 octets (see Appendix B) Encoded CRC-32K five octets (see Appendix C) @@ -203,80 +203,78 @@ Frame Types 8 - 31 and 35 - 127 are reserved for assignment by ASHRAE. Frame Types 32 - 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. + For COBS-encoded frames, the Length field indicates the size of the + [COBS] Encoded Data field in octets, plus three. (This adjustment is + required in order for legacy MS/TP devices to ignore COBS-encoded + frames.) 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 Constraints 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 minimum changes necessary to support IPv6 over MS/TP were - specified in BACnet [Addendum_an] (see Note in Section 1.3). + specified in BACnet [Addendum_an] (see Section 1.3). In order to co-exist with legacy devices, no changes are permitted to the MS/TP addressing modes, frame header format, control frames, or Master Node state machine as specified in BACnet [Clause9]. 2. MS/TP Mode for IPv6 ASHRAE has assigned an MS/TP Frame Type value of 34 to indicate IPv6 over MS/TP (LoBAC) Encapsulation. This falls within the range of values that designate COBS-encoded data frames. All MS/TP master nodes (including those that support IPv6) must - understand Token, Poll For Master, and Reply to Poll For Master - control frames and support the Master Node state machine as specified - in BACnet [Clause9]. MS/TP master nodes that support IPv6 must also - support the Receive Frame state machine as specified in [Clause9] and + implement the Master Node state machine specified in BACnet [Clause9] + and handle Token, Poll For Master, and Reply to Poll For Master + control frames. MS/TP master nodes that support IPv6 must also + implement the Receive Frame state machine specified in [Clause9] as extended by BACnet [Addendum_an]. All MS/TP nodes that support IPv6 MUST support a data rate of 115,200 - baud and MAY optionally support lower data rates as defined in BACnet - [Clause9]. + bit/s and MAY optionally support lower data rates as defined in + BACnet [Clause9]. 3. Addressing Modes MS/TP node (MAC) addresses are one octet in length. The method of assigning MAC addresses is outside the scope of this specification. However, each MS/TP node on the link MUST have a unique address in order to ensure correct MAC operation. BACnet [Clause9] specifies that addresses 0 through 127 are valid for master nodes. The method specified in Section 6 for creating a MAC- layer-derived Interface Identifier (IID) ensures that an IID of all zeros can never result. A Destination Address of 255 (all nodes) indicates a MAC-layer broadcast. MS/TP does not support multicast, therefore all IPv6 multicast packets SHOULD be broadcast at the MAC layer and filtered at the IPv6 layer. A Source Address of 255 MUST NOT be used. - This specification assumes that at most one unique local and/or - global IPv6 prefix is assigned to each MS/TP segment. Hosts learn - IPv6 prefixes via router advertisements according to [RFC4861]. + Hosts learn IPv6 prefixes via router advertisements according to + [RFC4861]. 4. Maximum Transmission Unit (MTU) BACnet [Addendum_an] supports MSDUs up to 2032 octets in length. This specification defines an MSDU length of at least 1280 octets and at most 1500 octets (before encoding). This is sufficient to convey the minimum MTU required by IPv6 [RFC2460] without the need for link- layer fragmentation and reassembly. Support for an MSDU length of 1500 octets is RECOMMENDED. @@ -315,22 +313,22 @@ The Dispatch value may be treated as an unstructured namespace. Only a single pattern is used to represent current LoBAC functionality. Pattern Header Type +------------+-----------------------------------------------------+ | 01 1xxxxx | LOWPAN_IPHC - LOWPAN_IPHC compressed IPv6 [RFC6282] | +------------+-----------------------------------------------------+ Figure 3: LoBAC Dispatch Value Bit Pattern - Other IANA-assigned 6LoWPAN Dispatch values do not apply to this - specification. + Other IANA-assigned 6LoWPAN Dispatch values do not apply to 6LoBAC + unless otherwise specified. 6. Stateless Address Autoconfiguration This section defines how to obtain an IPv6 Interface Identifier. The general procedure for creating a MAC-address-derived IID is described in [RFC4291] Appendix A, "Creating Modified EUI-64 Format Interface Identifiers", as updated by [RFC7136]. The IID SHOULD NOT embed an [EUI-64] or any other globally unique hardware identifier assigned to a device (see Section 12). @@ -343,22 +341,22 @@ |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 for use in link- local addresses, as it affords the most efficient header compression provided by the LOWPAN_IPHC [RFC6282] format specified in Section 10. - A 64-bit privacy IID is RECOMMENDED for routable addresses and SHOULD - be locally generated according to one of the methods cited in + A 64-bit privacy IID is RECOMMENDED for each forwardable address and + SHOULD be locally generated according to one of the methods cited in Section 12. A node that generates a 64-bit privacy 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 @@ -436,53 +434,53 @@ When a 16-bit address is called for (i.e., an IEEE 802.15.4 "short address") it MUST be formed by padding the MS/TP address to the left with a zero: 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x00 | MS/TP address | +-+-+-+-+-+-+-+-+---------------+ - If LOWPAN_IPHC compression [RFC6282] is used with context, the border + If LOWPAN_IPHC compression [RFC6282] is used with context, the router(s) directly attached to the MS/TP segment MUST disseminate the 6LoWPAN Context Option (6CO) according to [RFC6775], Section 7.2. 11. IANA Considerations This document uses values previously reserved by [RFC4944] and [RFC6282] and makes no further requests of IANA. Note to RFC Editor: this section may be removed upon publication. 12. Security Considerations - Routable addresses that contain IIDs generated using MS/TP node + Forwardable addresses that contain IIDs generated using MS/TP node addresses may expose a network to address scanning attacks. For this reason, it is RECOMMENDED that a different (but stable) IID be - generated for each routable address in use according to, for example, - [RFC3315], [RFC3972], [RFC4941], [RFC5535], or [RFC7217]. + generated for each forwardable address in use according to, for + example, [RFC3315], [RFC3972], [RFC4941], [RFC5535], or [RFC7217]. - MS/TP networks are by definition wired and not susceptible to to - casual eavesdropping. By the same token, MS/TP nodes are stationary - and correlation of activities or location tracking of individuals is + MS/TP networks are by definition wired and not susceptible to casual + eavesdropping. By the same token, MS/TP nodes are stationary and + correlation of activities or location tracking of individuals is unlikely. 13. Acknowledgments We are grateful to the authors of [RFC4944] and members of the IETF 6LoWPAN working group; this document borrows liberally from their work. Ralph Droms and Brian Haberman provided indispensable guidance and support from the outset. Peter van der Stok, James Woodyatt, and Carsten Bormann provided detailed reviews. Stuart Cheshire invented the very clever COBS encoding. Michael Osborne made the critical - observation that seperately encoding the data and CRC32K fields would + observation that separately encoding the data and CRC32K fields would allow the CRC to be calculated on-the-fly. Alexandru Petrescu, Brian Frank, Geoff Mulligan, and Don Sturek offered valuable comments. 14. References 14.1. Normative References [Addendum_an] ASHRAE, "ANSI/ASHRAE Addenda an, at, au, av, aw, ax, and az to ANSI/ASHRAE Standard 135-2012, BACnet - A Data @@ -603,61 +601,57 @@ [TIA-485-A] Telecommunications Industry Association, "TIA-485-A, Electrical Characteristics of Generators and Receivers for Use in Balanced Digital Multipoint Systems (ANSI/TIA/EIA- 485-A-98) (R2003)", March 2003. Appendix A. Abstract MAC Interface This Appendix is informative and not part of the standard. - BACnet [Clause9] defines support for MAC-layer clients through its + BACnet [Clause9] provides support for MAC-layer clients through its SendFrame and ReceivedDataNoReply procedures. However, it does not define a network-protocol independent abstract interface for the MAC. This is provided below as an aid to implementation. A.1. MA-DATA.request A.1.1. Function This primitive defines the transfer of data from a MAC client entity to a single peer entity or multiple peer entities in the case of a broadcast address. A.1.2. Semantics of the Service Primitive The semantics of the primitive are as follows: 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 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. - The 'priority' parameter specifies the priority desired for the data - unit transfer. The priority parameter is ignored by MS/TP. - The 'type' parameter specifies the value of the MS/TP Frame Type field that is prepended to the frame by the local MAC sublayer entity. A.1.3. When Generated This primitive is generated by the MAC client entity whenever data shall be transferred to a peer entity or entities. This can be in response to a request from higher protocol layers or from data generated internally to the MAC client, such as a Token frame. @@ -679,38 +673,34 @@ broadcast address. A.2.2. Semantics of the Service Primitive The semantics of the primitive are as follows: MA-DATA.indication ( destination_address, source_address, data, - priority, type ) The 'destination_address' parameter may be either an individual or a broadcast address as specified by the Destination Address field of the incoming frame. The 'source_address' parameter is an individual address as specified by the Source Address field of the incoming frame. The 'data' parameter specifies the MAC service data unit (MSDU) as received by the local MAC entity. There is sufficient information associated with the MSDU for the MAC sublayer client to determine the length of the data unit. - 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 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 @@ -732,43 +722,40 @@ cases, this resulted in dropped frames due to loss of frame synchronization. The solution is to encode the Data and 32-bit Data CRC fields before transmission using Consistent Overhead Byte Stuffing [COBS] and decode these fields upon reception. 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 in long fields is bounded to one octet in 254, or - less than 0.4%, as described in [COBS]. + The minimum overhead of COBS is one octet per encoded field. The + worst-case overhead in long fields is bounded to one octet per 254, + or less than 0.4%, as described in [COBS]. 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 '0x55' with each octet of the output. 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 - #define CRC32K_INITIAL_VALUE (0xFFFFFFFF) - #define MSTP_PREAMBLE_X55 (0x55) - /* * Encodes 'length' octets of data located at 'from' and * writes one or more COBS code blocks at 'to', removing any * 'mask' octets that may present be in the encoded data. * Returns the length of the encoded data. */ size_t cobs_encode (uint8_t *to, const uint8_t *from, size_t length, uint8_t mask) @@ -807,27 +793,26 @@ * this exception is handled above (and returned length must be * adjusted). Otherwise, encode the last chunk normally, as if * a "phantom zero" is appended to the data. */ if ((last_code == 255) && (code == 1)) write_index--; else to[code_index] = code ^ mask; return write_index; + } + #include #include - #define CRC32K_INITIAL_VALUE (0xFFFFFFFF) - #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, uint8_t mask) { @@ -894,21 +879,21 @@ #define CRC32K_INITIAL_VALUE (0xFFFFFFFF) #define CRC32K_RESIDUE (0x0843323B) /* CRC-32K polynomial, 1 + x**1 + ... + x**30 (+ x**32) */ #define CRC32K_POLY (0xEB31D82E) /* * Accumulate 'data_value' into the CRC in 'crc_value'. * Return updated CRC. * - * Note: crcValue must be set to CRC32K_INITIAL_VALUE + * Note: crc_value must be set to CRC32K_INITIAL_VALUE * before initial call. */ uint32_t calc_crc32K (uint8_t data_value, uint32_t crc_value) { int b; for (b = 0; b < 8; b++) { if ((data_value & 1) ^ (crc_value & 1)) { crc_value >>= 1; @@ -918,54 +903,28 @@ } data_value >>= 1; } return crc_value; } Appendix D. Example 6LoBAC Packet Decode This Appendix is informative and not part of the standard. - No. Time Source Destination - 5161 8.816048 aaaa::1 aaaa::ff:fe00:1 - Protocol Length Info - ICMPv6 547 Echo (ping) request id=0x2ee5, seq=2, - hop limit=63 (reply in 5165) - - Frame 5161: 547 bytes on wire (4376 bits), 547 bytes captured - (4376 bits) on interface 0 - Interface id: 0 (/tmp/pipe) - Encapsulation type: BACnet MS/TP (63) - Arrival Time: Sep 3, 2015 19:46:44.377881000 EDT - [Time shift for this packet: 0.000000000 seconds] - Epoch Time: 1441324004.377881000 seconds - [Time delta from previous captured frame: 0.050715000 seconds] - [Time delta from previous displayed frame: 0.050715000 seconds] - [Time since reference or first frame: 8.816048000 seconds] - Frame Number: 5161 - Frame Length: 547 bytes (4376 bits) - Capture Length: 547 bytes (4376 bits) - [Frame is marked: False] - [Frame is ignored: False] - [Protocols in frame: mstp:6lowpan:ipv6:ipv6.nxt:icmpv6:data] - [Coloring Rule Name: ICMP] - [Coloring Rule String: icmp || icmpv6] BACnet MS/TP, Src (2), Dst (1), IPv6 Encapsulation Preamble 55: 0x55 Preamble FF: 0xff Frame Type: IPv6 Encapsulation (34) Destination Address: 1 Source Address: 2 Length: 537 Header CRC: 0x1c [correct] - [Good: True] - [Bad: False] Extended Data CRC: 0x9e7259e2 [correct] 6LoWPAN IPHC Header 011. .... = Pattern: IP header compression (0x03) ...1 1... .... .... = Traffic class and flow label: Version, traffic class, and flow label compressed (0x0003) .... .0.. .... .... = Next header: Inline .... ..00 .... .... = Hop limit: Inline (0x0000) .... .... 1... .... = Context identifier extension: True