Transmission of IPv6 over Multidrop Serial Bus/Token Passing (MS/TP) Networks

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 https://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 6 May 2027.¶

Copyright Notice

Copyright (c) 2026 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 (https://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 Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.¶

Table of Contents

1. Introduction

Multidrop Serial Bus/Token Passing (MS/TP) is a Medium Access Control (MAC) protocol for the RS-485 [TIA-485-A] physical layer and is used primarily in building automation networks. This specification defines the frame format for transmission of IPv6 [RFC8200] 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, as noted below.¶

An MS/TP device is typically based on a low-cost microcontroller with limited processing power and memory. These constraints, together with low data rates and a small MAC address space, are similar to those faced in 6LoWPAN networks. MS/TP differs significantly from 6LoWPAN in at least three respects: a) MS/TP devices are typically mains powered, b) all MS/TP devices on a segment can communicate directly so there are no hidden node or mesh routing issues, and c) the latest MS/TP specification provides support for large payloads, eliminating the need for fragmentation and reassembly below IPv6.¶

The following sections provide a brief overview of MS/TP and then describe how to form IPv6 addresses and encapsulate IPv6 packets in MS/TP frames. This specification (subsequently referred to as "6LoBAC") includes a REQUIRED header compression mechanism that is based on LOWPAN_IPHC [RFC6282] and improves MS/TP link utilization.¶

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 Code

MAC:     Medium Access Control

MSDU:    MAC Service Data Unit (MAC client data)

MTU:     Maximum Transmission Unit; the size of the largest data unit
         at the network-layer protocol that can be communicated in a
         single network transaction

UART:    Universal Asynchronous Transmitter/Receiver

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 - 1507 octets)                 .
.                                                               .
+                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                               |  Encoded CRC-32K (5 octets)   |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               +-+-+-+-+-+-+-+-+
|                                               | optional 0xFF |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  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 - 1507 octets (see Section 4 and Appendix B)
  Encoded CRC-32K       five octets (see Appendix C)
  (pad)                 (optional) at most one octet of padding: 0xFF

The Frame Type is used to distinguish between different types of MAC
frames.  The types relevant to this specification (in decimal) are:

   0  Token
   1  Poll For Manager
   2  Reply To Poll For Manager
   3  Test_Request
   4  Test_Response
      ...
  34  IPv6 over MS/TP (LoBAC) Encapsulation

2. Profile for IPv6 over MS/TP

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.¶

Nmin_COBS_length  The minimum valid Length value of any LoBAC-
                  encapsulated frame: 5

Nmax_COBS_length  The maximum valid Length value of any LoBAC-
                  encapsulated frame: 1510 (see Section 4)

Nmax_info_frames  The default maximum number of information frames
                  the node may send before it must pass the token: 1

Nmax_manager      The default highest allowable address for manager
                  nodes: 127

3. Addressing Modes

MS/TP node (MAC) addresses are one octet in length and are assigned dynamically. 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], Clause 9 specifies that addresses 0 through 127 are valid for manager nodes. The method specified in Section 6 for creating a MAC-address-derived Interface Identifier (IID) ensures that an IID of all zeros can never be generated.¶

A Destination Address of 255 (all nodes) indicates a MAC-layer broadcast. MS/TP does not support multicast; therefore, all IPv6 multicast packets MUST be broadcast at the MAC layer and filtered at the IPv6 layer. A Source Address of 255 MUST NOT be used.¶

Hosts learn IPv6 prefixes via router advertisements according to [RFC4861].¶

4. Maximum Transmission Unit (MTU)

Upon transmission, the network-layer MTU is formatted according to Section 5 and becomes the MAC service data unit (MSDU). The MSDU is then COBS encoded by MS/TP. Upon reception, the steps are reversed. [BACnet], Clause 9 supports MSDUs up to 2032 octets in length.¶

IPv6 [RFC8200] requires that every link in an internet have an MTU of 1280 octets or greater. Additionally, a node must be able to accept a fragmented packet that, after reassembly, is as large as 1500 octets. This specification defines an MTU length of at least 1280 octets and at most 1500 octets. Support for an MTU length of 1500 octets is RECOMMENDED.¶

It is possible for the LOWPAN_IPHC encoding (Section 10) to generate an MSDU longer than the MTU. With the Context Identifier Extension present and no fields elided, the 40-octet IPv6 header is encoded in 41 octets. The MSDU can therefore be at most 1501 octets for an MTU of 1500 octets. COBS adds at most one octet per 254 octets of MSDU, rounded up (see Appendix B), so the Encoded Data field is at most 1507 octets and the Length field is at most 1510 octets.¶

5. LoBAC Adaptation Layer

This section specifies an adaptation layer to support compressed IPv6 headers as specified in Section 10. IPv6 header compression MUST be implemented on all 6LoBAC nodes. Implementations MAY also support Generic Header Compression [RFC7400] for transport layer headers.¶

The LoBAC encapsulation format defined in this section describes the MSDU of an IPv6 over MS/TP frame. The LoBAC payload (i.e., an IPv6 packet) follows an encapsulation header stack. LoBAC is a subset of the LoWPAN encapsulation defined in [RFC4944], as updated by [RFC6282], so the use of "LOWPAN" in literals below is intentional. The primary difference between LoWPAN and LoBAC encapsulation is omission of the Mesh, Broadcast, Fragmentation, and LOWPAN_HC1 headers in the latter.¶

All LoBAC-encapsulated datagrams transmitted over MS/TP are prefixed by an encapsulation header stack consisting of a Dispatch value followed by zero or more header fields. The only sequence currently defined for LoBAC is the LOWPAN_IPHC header followed by payload, as shown below:¶

          +---------------+---------------+------...-----+
          | IPHC Dispatch |  IPHC Header  |    Payload   |
          +---------------+---------------+------...-----+

The Dispatch value is 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] |
+------------+-----------------------------------------------------+

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. This specification distinguishes between two types of IIDs, MAC- address-derived and semantically opaque.¶

A MAC-address-derived IID is the RECOMMENDED type for use in forming a link-local address, as it affords the most efficient header compression provided by the LOWPAN_IPHC [RFC6282] format specified in Section 10. The general procedure for creating a MAC-address-derived IID is described in Appendix A of [RFC4291], "Creating Modified EUI-64 Format Interface Identifiers", as updated by [RFC7136].¶

The Interface Identifier for link-local addresses SHOULD be formed by concatenating the node's 8-bit MS/TP MAC address to the seven octets 0x00, 0x00, 0x00, 0xFF, 0xFE, 0x00, and 0x00. For example, an MS/TP MAC address of hexadecimal value 0x4F results in the following IID:¶

|0              1|1              3|3              4|4              6|
|0              5|6              1|2              7|8              3|
+----------------+----------------+----------------+----------------+
|0000000000000000|0000000011111111|1111111000000000|0000000001001111|
+----------------+----------------+----------------+----------------+

A semantically opaque IID having 64 bits of entropy is RECOMMENDED for each globally scoped address and MAY be locally generated according to one of the methods cited in Section 12. A node that generates a 64-bit semantically opaque IID MUST register the IID with its local router(s) by sending a Neighbor Solicitation (NS) message with the Address Registration Option (ARO) and process Neighbor Advertisements (NAs) 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
+----------+-----------------------+----------------------------+
|1111111010|        (zeros)        |    Interface Identifier    |
+----------+-----------------------+----------------------------+

8. Unicast Address Mapping

The address resolution procedure for mapping IPv6 non-multicast addresses into MS/TP MAC-layer addresses follows the general description in Section 7.2 of [RFC4861], unless otherwise specified.¶

The Source/Target Link-Layer Address option has the following form when the addresses are 8-bit MS/TP MAC-layer (node) addresses.¶

 0                   1
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     Type      |    Length=1   |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     0x00      | MS/TP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                               |
+      Padding (all zeros)      +
|                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Option fields:

Type:

   1: for Source Link-Layer address.

   2: for Target Link-Layer address.

Length:  This is the length of this option (including the Type and
      Length fields) in units of 8 octets.  The value of this field
      is 1 for 8-bit MS/TP MAC addresses.

MS/TP Address:  The 8-bit address in canonical bit order [RFC2469].
      This is the unicast address the interface currently responds
      to.

9. Multicast Address Mapping

All IPv6 multicast packets MUST be sent to MS/TP Destination Address 255 (broadcast) and filtered at the IPv6 layer. When represented as a 16-bit address in a compressed header (see Section 10), it MUST be formed by padding on the left with a zero octet:¶

 0                   1
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     0x00      |     0xFF      |
+-+-+-+-+-+-+-+-+---------------+

10. Header Compression

6LoBAC REQUIRES LOWPAN_IPHC IPv6 compression, which is specified in [RFC6282] and included herein by reference. This section will simply identify substitutions that should be made when interpreting the text of [RFC6282].¶

In general, the following substitutions should be made:¶

-

Replace instances of "6LoWPAN" with "MS/TP network"¶

-

Replace instances of "IEEE 802.15.4 address" with "MS/TP address"¶

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 octet:¶

 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 router(s) directly attached to the MS/TP segment MUST disseminate the 6LoWPAN Context Option (6CO) according to Section 7.2 of [RFC6775].¶

11. IANA Considerations

This document uses values previously reserved by [RFC4944] and [RFC6282]; it does not require any IANA actions.¶

12. Security Considerations

See [RFC8065] for a general discussion of privacy threats faced by constrained nodes.¶

[RFC8065] makes a distinction between "stable" and "temporary" addresses. The former are long-lived and typically advertised by servers. The latter are typically used by clients and SHOULD be changed frequently to mitigate correlation of activities over time. Nodes that engage in both activities SHOULD support simultaneous use of multiple addresses per device.¶

Globally scoped addresses that contain MAC-address-derived IIDs may expose a network to address-scanning attacks. For this reason, it is RECOMMENDED that a 64-bit semantically opaque IID be generated for each globally scoped address in use according to, for example, [RFC3972], [RFC5535], [RFC7217], [RFC8415], or [RFC8981].¶

13. Implementation Status

[RFC Editor: please remove this section, and the reference to RFC 7942, before publication.]¶

This section records the status of known implementations of the protocol defined by this specification at the time of posting of this Internet-Draft, and is based on a proposal described in [RFC7942]. The description of implementations in this section is intended to assist the IETF in its decision processes in progressing drafts to RFCs. Please note that the listing of any individual implementation here does not imply endorsement by the IETF. Furthermore, no effort has been spent to verify the information presented here that was supplied by IETF contributors. This is not intended as, and must not be construed to be, a catalog of available implementations or their features. Readers are advised to note that other implementations may exist.¶

According to [RFC7942], "this will allow reviewers and working groups to assign due consideration to documents that have the benefit of running code, which may serve as evidence of valuable experimentation and feedback that have made the implemented protocols more mature. It is up to the individual working groups to use this information as they see fit".¶

Appendix A. Abstract MAC Interface

This Appendix is informative and not part of the standard.¶

[BACnet], Clause 9 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.¶

The semantics of the primitive are as follows:

  MA-DATA.request (
                   destination_address,
                   source_address,
                   data,
                   type
                  )

The semantics of the primitive are as follows:

  MA-DATA.indication (
                      destination_address,
                      source_address,
                      data,
                      type
                     )

Appendix B. Consistent Overhead Byte Stuffing (COBS)

This Appendix is informative and not part of the standard.¶

[BACnet], Clause 9 corrects a long-standing issue with the MS/TP specification, namely that preamble sequences were not escaped whenever they appeared in the Data or Data CRC fields. In rare 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], Clause 9 specifies the preamble octet '0x55' for removal.¶

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 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 legacy 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], Annex T.¶

<CODE BEGINS>

#include <stddef.h>
#include <stdint.h>

/*
 * Encodes 'length' octets of data located at 'from' and
 * writes one or more COBS code blocks at 'to', removing any
 * 'mask' octets that may be present 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)
{
  size_t code_index = 0;
  size_t read_index = 0;
  size_t write_index = 1;
  uint8_t code = 1;
  uint8_t data, last_code = 0;

  while (read_index < length) {
    data = from[read_index++];
    /*
     * In the case of encountering a non-zero octet in the data,
     * simply copy input to output and increment the code octet.
     */
    if (data != 0) {
      to[write_index++] = data ^ mask;
      code++;
      if (code != 255)
        continue;
    }
    /*
     * In the case of encountering a zero in the data or having
     * copied the maximum number (254) of non-zero octets, store
     * the code octet and reset the encoder state variables.
     */
    last_code = code;
    to[code_index] = code ^ mask;
    code_index = write_index++;
    code = 1;
  }
  /*
   * If the last chunk contains exactly 254 non-zero octets, then
   * this exception is handled above (and the 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;
}

/*
 * 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)
{
  size_t read_index = 0;
  size_t write_index = 0;
  uint8_t code, last_code;

  while (read_index < length) {
    code = from[read_index] ^ mask;
    last_code = code;
    /*
     * Sanity check the encoding to prevent the while() loop below
     * from overrunning the output buffer. See [Err5996].
     */
    if (code == 0 || read_index + code > length)
      return 0;

    read_index++;
    while (--code > 0)
      to[write_index++] = from[read_index++] ^ mask;
    /*
     * Restore the implicit zero at the end of each decoded block
     * except when it contains exactly 254 non-zero octets or the
     * end of data has been reached.
     */
    if ((last_code != 255) && (read_index < length))
      to[write_index++] = 0;
  }
  return write_index;
}

<CODE ENDS>

Appendix C. Encoded CRC-32K (CRC32K)

This Appendix is informative and not part of the standard.¶

Extending the payload of MS/TP to 1500 octets requires 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], Clause 9 specifies one of these, 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. After passing each octet of the [COBS] Encoded Data field 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 is shown below for illustration. Complete examples of use and test vectors are provided in [BACnet], Annex G.3.¶

<CODE BEGINS>

#include <stdint.h>

/* See ANSI/ASHRAE Standard 135-2024 [BACnet], Clause G.3.1 */
#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: 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;
      crc_value ^= CRC32K_POLY;
    } else {
      crc_value >>= 1;
    }
    data_value >>= 1;
  }
  return crc_value;
}

<CODE ENDS>

Appendix D. Example 6LoBAC Frame Decode

This Appendix is informative and not part of the standard.¶

The frame below is an ICMPv6 Echo Request forwarded by a 6LBR (MS/TP address 2) to a 6LN (MS/TP address 3). The IPv6 packet was sent from a host on the 6LBR's other interface with every field fixed, so the frame can be reproduced exactly:¶

• Source fdea:dbee:f::1, Destination aaaa::ff:fe00:3, Hop Limit 64 (63 after forwarding).¶
• ICMPv6 Echo Request, Identifier 0x6f49, Sequence 1.¶
• 767 octets of data, in which octet i has the value i modulo 256.¶

For example, with Scapy:¶

sendp(Ether(src=<host MAC>, dst=<6LBR MAC>) /
      IPv6(src='fdea:dbee:f::1', dst='aaaa::ff:fe00:3', hlim=64) /
      ICMPv6EchoRequest(id=0x6f49, seq=1,
                        data=bytes(i & 0xff for i in range(767))),
      iface=<host interface>)

The 6LBR advertises aaaa::/64 as 6LoWPAN context 0, which LOWPAN_IPHC uses to elide the destination address. Other LOWPAN_IPHC encoders may make different, equally valid compression choices for the same IPv6 packet; these result in a different MSDU and therefore a different frame. Given the MSDU shown here, any correct implementation of Appendix B and Appendix C produces exactly this frame.¶

The decode below was produced by Wireshark with context 0 configured, for example with tshark:¶

tshark -r <capture file> -V -x -o 6lowpan.context0:aaaa::/64 \
    -Y "icmpv6.echo.identifier == 0x6f49 && mstp.src == 2"

The data and the Identifier were chosen so that the frame exercises every case of the COBS encoder and decoder in Appendix B. The Encoded Data field contains zero octets, consecutive zero octets, runs of 254 non-zero octets in the middle of the data (code 0xFF, which is not followed by an implicit zero), and a final block of exactly 254 non-zero octets. The CRC-32K, c4 31 32 00 in transmission order, ends in a zero, so the Encoded CRC-32K field is two blocks (codes 4 and 1).¶

BACnet MS/TP, Src (2), Dst (3), IPv6 over MS/TP (LoBAC) Encapsulation
    Preamble 55: 0x55
    Preamble FF: 0xff
    Frame Type: IPv6 over MS/TP (LoBAC) Encapsulation (34)
    Destination Address: 3
    Source Address: 2
    Length: 801
    Header CRC: 0x4f [correct]
    [Checksum status: Good]
    Extended Data CRC: 0xc4313200 [correct]
    [Checksum status: Good]
6LoWPAN, Src: fdea:dbee:f::1, Dest: aaaa::ff:fe00:3
    IPHC Header
        011. .... = Pattern: IP header compression (0x03)
        ...1 1... .... .... = Traffic class and flow label:
                              Version, traffic class, and flow
                              label compressed (0x3)
        .... .0.. .... .... = Next header: Inline
        .... ..00 .... .... = Hop limit: Inline (0x0)
        .... .... 0... .... = Context identifier extension: False
        .... .... .0.. .... = Source address compression: Stateless
        .... .... ..00 .... = Source address mode: Inline (0x0000)
        .... .... .... 0... = Multicast address compression: False
        .... .... .... .1.. = Destination address compression:
                              Stateful
        .... .... .... ..11 = Destination address mode:
                              Compressed (0x0003)
        [Destination context: aaaa::]
    Next header: IPv6-ICMP (0x3a)
    Hop limit: 63
    Source: fdea:dbee:f::1
    [Destination: aaaa::ff:fe00:3]
Internet Protocol Version 6, Src: fdea:dbee:f::1,
                             Dst: aaaa::ff:fe00:3
    0110 .... = Version: 6
    .... 0000 0000 .... .... .... .... .... = Traffic Class: 0x00
                                              (DSCP: CS0,
                                              ECN: Not-ECT)
        .... 0000 00.. .... .... .... .... .... = Differentiated
                                                  Services Codepoint:
                                                  Default (0)
        .... .... ..00 .... .... .... .... .... = Explicit Congestion
                                                  Notification: Not
                                                  ECN-Capable
                                                  Transport (0)
    .... 0000 0000 0000 0000 0000 = Flow Label: 0x00000
    Payload Length: 775
    Next Header: IPv6-ICMP (58)
    Hop Limit: 63
    Source Address: fdea:dbee:f::1
        [Address Space: Unique Local Unicast]
        [Special-Purpose Allocation: Unique-Local]
            [Source: True]
            [Destination: True]
            [Forwardable: True]
            [Globally Reachable: False]
            [Reserved-by-Protocol: False]
    Destination Address: aaaa::ff:fe00:3
        [Address Space: Global Unicast]
Internet Control Message Protocol v6
    Type: Echo (ping) request (128)
    Code: 0
    Checksum: 0x4a1c [correct]
    [Checksum Status: Good]
    Identifier: 0x6f49
    Sequence: 1
    Data (767 bytes)
        Data [...]: 000102030405060708090a0b0c0d0e0f101112131415...
        [Length: 767]

Packet (811 bytes):
55 ff 22 03 02 03 21 4f 5c 2d 52 6f 6a a8 bf 8e   U."...!O\-Roj...
bb 57 5a 54 54 54 54 54 54 54 54 56 54 d5 50 1f   .WZTTTTTTTTVT.P.
49 3a 1c 57 54 aa 54 57 56 51 50 53 52 5d 5c 5f   I:.WT.TWVQPSR]\_
5e 59 58 5b 5a 45 44 47 46 41 40 43 42 4d 4c 4f   ^YX[ZEDGFA@CBMLO
4e 49 48 4b 4a 75 74 77 76 71 70 73 72 7d 7c 7f   NIHKJutwvqpsr}|.
7e 79 78 7b 7a 65 64 67 66 61 60 63 62 6d 6c 6f   ~yx{zedgfa`cbmlo
6e 69 68 6b 6a 15 14 17 16 11 10 13 12 1d 1c 1f   nihkj...........
1e 19 18 1b 1a 05 04 07 06 01 00 03 02 0d 0c 0f   ................
0e 09 08 0b 0a 35 34 37 36 31 30 33 32 3d 3c 3f   .....54761032=<?
3e 39 38 3b 3a 25 24 27 26 21 20 23 22 2d 2c 2f   >98;:%$'&! #"-,/
2e 29 28 2b 2a d5 d4 d7 d6 d1 d0 d3 d2 dd dc df   .)(+*...........
de d9 d8 db da c5 c4 c7 c6 c1 c0 c3 c2 cd cc cf   ................
ce c9 c8 cb ca f5 f4 f7 f6 f1 f0 f3 f2 fd fc ff   ................
fe f9 f8 fb fa e5 e4 e7 e6 e1 e0 e3 e2 ed ec ef   ................
ee e9 e8 eb ea 95 94 97 96 91 90 93 92 9d 9c 9f   ................
9e 99 98 9b 9a 85 84 87 86 81 80 83 82 8d 8c 8f   ................
8e 89 88 8b 8a b5 b4 b7 b6 b1 b0 b3 b2 bd bc bf   ................
be b9 b8 bb ba a5 a4 a7 a6 a1 a0 a3 a2 ad ac af   ................
ae a9 a8 ab 57 aa aa 54 57 56 51 50 53 52 5d 5c   ....W..TWVQPSR]\
5f 5e 59 58 5b 5a 45 44 47 46 41 40 43 42 4d 4c   _^YX[ZEDGFA@CBML
4f 4e 49 48 4b 4a 75 74 77 76 71 70 73 72 7d 7c   ONIHKJutwvqpsr}|
7f 7e 79 78 7b 7a 65 64 67 66 61 60 63 62 6d 6c   .~yx{zedgfa`cbml
6f 6e 69 68 6b 6a 15 14 17 16 11 10 13 12 1d 1c   onihkj..........
1f 1e 19 18 1b 1a 05 04 07 06 01 00 03 02 0d 0c   ................
0f 0e 09 08 0b 0a 35 34 37 36 31 30 33 32 3d 3c   ......54761032=<
3f 3e 39 38 3b 3a 25 24 27 26 21 20 23 22 2d 2c   ?>98;:%$'&! #"-,
2f 2e 29 28 2b 2a d5 d4 d7 d6 d1 d0 d3 d2 dd dc   /.)(+*..........
df de d9 d8 db da c5 c4 c7 c6 c1 c0 c3 c2 cd cc   ................
cf ce c9 c8 cb ca f5 f4 f7 f6 f1 f0 f3 f2 fd fc   ................
ff fe f9 f8 fb fa e5 e4 e7 e6 e1 e0 e3 e2 ed ec   ................
ef ee e9 e8 eb ea 95 94 97 96 91 90 93 92 9d 9c   ................
9f 9e 99 98 9b 9a 85 84 87 86 81 80 83 82 8d 8c   ................
8f 8e 89 88 8b 8a b5 b4 b7 b6 b1 b0 b3 b2 bd bc   ................
bf be b9 b8 bb ba a5 a4 a7 a6 a1 a0 a3 a2 ad ac   ................
af ae a9 a8 ab 57 aa aa 54 57 56 51 50 53 52 5d   .....W..TWVQPSR]
5c 5f 5e 59 58 5b 5a 45 44 47 46 41 40 43 42 4d   \_^YX[ZEDGFA@CBM
4c 4f 4e 49 48 4b 4a 75 74 77 76 71 70 73 72 7d   LONIHKJutwvqpsr}
7c 7f 7e 79 78 7b 7a 65 64 67 66 61 60 63 62 6d   |.~yx{zedgfa`cbm
6c 6f 6e 69 68 6b 6a 15 14 17 16 11 10 13 12 1d   lonihkj.........
1c 1f 1e 19 18 1b 1a 05 04 07 06 01 00 03 02 0d   ................
0c 0f 0e 09 08 0b 0a 35 34 37 36 31 30 33 32 3d   .......54761032=
3c 3f 3e 39 38 3b 3a 25 24 27 26 21 20 23 22 2d   <?>98;:%$'&! #"-
2c 2f 2e 29 28 2b 2a d5 d4 d7 d6 d1 d0 d3 d2 dd   ,/.)(+*.........
dc df de d9 d8 db da c5 c4 c7 c6 c1 c0 c3 c2 cd   ................
cc cf ce c9 c8 cb ca f5 f4 f7 f6 f1 f0 f3 f2 fd   ................
fc ff fe f9 f8 fb fa e5 e4 e7 e6 e1 e0 e3 e2 ed   ................
ec ef ee e9 e8 eb ea 95 94 97 96 91 90 93 92 9d   ................
9c 9f 9e 99 98 9b 9a 85 84 87 86 81 80 83 82 8d   ................
8c 8f 8e 89 88 8b 8a b5 b4 b7 b6 b1 b0 b3 b2 bd   ................
bc bf be b9 b8 bb ba a5 a4 a7 a6 a1 a0 a3 a2 ad   ................
ac af ae a9 a8 ab 51 91 64 67 54                  ......Q.dgT

Decoded Data and CRC32K (799 bytes):
78 07 3a 3f fd ea db ee 00 0f 00 00 00 00 00 00   x.:?............
00 00 00 01 80 00 4a 1c 6f 49 00 01 00 01 02 03   ......J.oI......
04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13   ................
14 15 16 17 18 19 1a 1b 1c 1d 1e 1f 20 21 22 23   ............ !"#
24 25 26 27 28 29 2a 2b 2c 2d 2e 2f 30 31 32 33   $%&'()*+,-./0123
34 35 36 37 38 39 3a 3b 3c 3d 3e 3f 40 41 42 43   456789:;<=>?@ABC
44 45 46 47 48 49 4a 4b 4c 4d 4e 4f 50 51 52 53   DEFGHIJKLMNOPQRS
54 55 56 57 58 59 5a 5b 5c 5d 5e 5f 60 61 62 63   TUVWXYZ[\]^_`abc
64 65 66 67 68 69 6a 6b 6c 6d 6e 6f 70 71 72 73   defghijklmnopqrs
74 75 76 77 78 79 7a 7b 7c 7d 7e 7f 80 81 82 83   tuvwxyz{|}~.....
84 85 86 87 88 89 8a 8b 8c 8d 8e 8f 90 91 92 93   ................
94 95 96 97 98 99 9a 9b 9c 9d 9e 9f a0 a1 a2 a3   ................
a4 a5 a6 a7 a8 a9 aa ab ac ad ae af b0 b1 b2 b3   ................
b4 b5 b6 b7 b8 b9 ba bb bc bd be bf c0 c1 c2 c3   ................
c4 c5 c6 c7 c8 c9 ca cb cc cd ce cf d0 d1 d2 d3   ................
d4 d5 d6 d7 d8 d9 da db dc dd de df e0 e1 e2 e3   ................
e4 e5 e6 e7 e8 e9 ea eb ec ed ee ef f0 f1 f2 f3   ................
f4 f5 f6 f7 f8 f9 fa fb fc fd fe ff 00 01 02 03   ................
04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13   ................
14 15 16 17 18 19 1a 1b 1c 1d 1e 1f 20 21 22 23   ............ !"#
24 25 26 27 28 29 2a 2b 2c 2d 2e 2f 30 31 32 33   $%&'()*+,-./0123
34 35 36 37 38 39 3a 3b 3c 3d 3e 3f 40 41 42 43   456789:;<=>?@ABC
44 45 46 47 48 49 4a 4b 4c 4d 4e 4f 50 51 52 53   DEFGHIJKLMNOPQRS
54 55 56 57 58 59 5a 5b 5c 5d 5e 5f 60 61 62 63   TUVWXYZ[\]^_`abc
64 65 66 67 68 69 6a 6b 6c 6d 6e 6f 70 71 72 73   defghijklmnopqrs
74 75 76 77 78 79 7a 7b 7c 7d 7e 7f 80 81 82 83   tuvwxyz{|}~.....
84 85 86 87 88 89 8a 8b 8c 8d 8e 8f 90 91 92 93   ................
94 95 96 97 98 99 9a 9b 9c 9d 9e 9f a0 a1 a2 a3   ................
a4 a5 a6 a7 a8 a9 aa ab ac ad ae af b0 b1 b2 b3   ................
b4 b5 b6 b7 b8 b9 ba bb bc bd be bf c0 c1 c2 c3   ................
c4 c5 c6 c7 c8 c9 ca cb cc cd ce cf d0 d1 d2 d3   ................
d4 d5 d6 d7 d8 d9 da db dc dd de df e0 e1 e2 e3   ................
e4 e5 e6 e7 e8 e9 ea eb ec ed ee ef f0 f1 f2 f3   ................
f4 f5 f6 f7 f8 f9 fa fb fc fd fe ff 00 01 02 03   ................
04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13   ................
14 15 16 17 18 19 1a 1b 1c 1d 1e 1f 20 21 22 23   ............ !"#
24 25 26 27 28 29 2a 2b 2c 2d 2e 2f 30 31 32 33   $%&'()*+,-./0123
34 35 36 37 38 39 3a 3b 3c 3d 3e 3f 40 41 42 43   456789:;<=>?@ABC
44 45 46 47 48 49 4a 4b 4c 4d 4e 4f 50 51 52 53   DEFGHIJKLMNOPQRS
54 55 56 57 58 59 5a 5b 5c 5d 5e 5f 60 61 62 63   TUVWXYZ[\]^_`abc
64 65 66 67 68 69 6a 6b 6c 6d 6e 6f 70 71 72 73   defghijklmnopqrs
74 75 76 77 78 79 7a 7b 7c 7d 7e 7f 80 81 82 83   tuvwxyz{|}~.....
84 85 86 87 88 89 8a 8b 8c 8d 8e 8f 90 91 92 93   ................
94 95 96 97 98 99 9a 9b 9c 9d 9e 9f a0 a1 a2 a3   ................
a4 a5 a6 a7 a8 a9 aa ab ac ad ae af b0 b1 b2 b3   ................
b4 b5 b6 b7 b8 b9 ba bb bc bd be bf c0 c1 c2 c3   ................
c4 c5 c6 c7 c8 c9 ca cb cc cd ce cf d0 d1 d2 d3   ................
d4 d5 d6 d7 d8 d9 da db dc dd de df e0 e1 e2 e3   ................
e4 e5 e6 e7 e8 e9 ea eb ec ed ee ef f0 f1 f2 f3   ................
f4 f5 f6 f7 f8 f9 fa fb fc fd fe c4 31 32 00      ............12.

Decompressed 6LoWPAN IPHC (815 bytes):
60 00 00 00 03 07 3a 3f fd ea db ee 00 0f 00 00   `.....:?........
00 00 00 00 00 00 00 01 aa aa 00 00 00 00 00 00   ................
00 00 00 ff fe 00 00 03 80 00 4a 1c 6f 49 00 01   ..........J.oI..
00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f   ................
10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f   ................
20 21 22 23 24 25 26 27 28 29 2a 2b 2c 2d 2e 2f    !"#$%&'()*+,-./
30 31 32 33 34 35 36 37 38 39 3a 3b 3c 3d 3e 3f   0123456789:;<=>?
40 41 42 43 44 45 46 47 48 49 4a 4b 4c 4d 4e 4f   @ABCDEFGHIJKLMNO
50 51 52 53 54 55 56 57 58 59 5a 5b 5c 5d 5e 5f   PQRSTUVWXYZ[\]^_
60 61 62 63 64 65 66 67 68 69 6a 6b 6c 6d 6e 6f   `abcdefghijklmno
70 71 72 73 74 75 76 77 78 79 7a 7b 7c 7d 7e 7f   pqrstuvwxyz{|}~.
80 81 82 83 84 85 86 87 88 89 8a 8b 8c 8d 8e 8f   ................
90 91 92 93 94 95 96 97 98 99 9a 9b 9c 9d 9e 9f   ................
a0 a1 a2 a3 a4 a5 a6 a7 a8 a9 aa ab ac ad ae af   ................
b0 b1 b2 b3 b4 b5 b6 b7 b8 b9 ba bb bc bd be bf   ................
c0 c1 c2 c3 c4 c5 c6 c7 c8 c9 ca cb cc cd ce cf   ................
d0 d1 d2 d3 d4 d5 d6 d7 d8 d9 da db dc dd de df   ................
e0 e1 e2 e3 e4 e5 e6 e7 e8 e9 ea eb ec ed ee ef   ................
f0 f1 f2 f3 f4 f5 f6 f7 f8 f9 fa fb fc fd fe ff   ................
00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f   ................
10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f   ................
20 21 22 23 24 25 26 27 28 29 2a 2b 2c 2d 2e 2f    !"#$%&'()*+,-./
30 31 32 33 34 35 36 37 38 39 3a 3b 3c 3d 3e 3f   0123456789:;<=>?
40 41 42 43 44 45 46 47 48 49 4a 4b 4c 4d 4e 4f   @ABCDEFGHIJKLMNO
50 51 52 53 54 55 56 57 58 59 5a 5b 5c 5d 5e 5f   PQRSTUVWXYZ[\]^_
60 61 62 63 64 65 66 67 68 69 6a 6b 6c 6d 6e 6f   `abcdefghijklmno
70 71 72 73 74 75 76 77 78 79 7a 7b 7c 7d 7e 7f   pqrstuvwxyz{|}~.
80 81 82 83 84 85 86 87 88 89 8a 8b 8c 8d 8e 8f   ................
90 91 92 93 94 95 96 97 98 99 9a 9b 9c 9d 9e 9f   ................
a0 a1 a2 a3 a4 a5 a6 a7 a8 a9 aa ab ac ad ae af   ................
b0 b1 b2 b3 b4 b5 b6 b7 b8 b9 ba bb bc bd be bf   ................
c0 c1 c2 c3 c4 c5 c6 c7 c8 c9 ca cb cc cd ce cf   ................
d0 d1 d2 d3 d4 d5 d6 d7 d8 d9 da db dc dd de df   ................
e0 e1 e2 e3 e4 e5 e6 e7 e8 e9 ea eb ec ed ee ef   ................
f0 f1 f2 f3 f4 f5 f6 f7 f8 f9 fa fb fc fd fe ff   ................
00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f   ................
10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f   ................
20 21 22 23 24 25 26 27 28 29 2a 2b 2c 2d 2e 2f    !"#$%&'()*+,-./
30 31 32 33 34 35 36 37 38 39 3a 3b 3c 3d 3e 3f   0123456789:;<=>?
40 41 42 43 44 45 46 47 48 49 4a 4b 4c 4d 4e 4f   @ABCDEFGHIJKLMNO
50 51 52 53 54 55 56 57 58 59 5a 5b 5c 5d 5e 5f   PQRSTUVWXYZ[\]^_
60 61 62 63 64 65 66 67 68 69 6a 6b 6c 6d 6e 6f   `abcdefghijklmno
70 71 72 73 74 75 76 77 78 79 7a 7b 7c 7d 7e 7f   pqrstuvwxyz{|}~.
80 81 82 83 84 85 86 87 88 89 8a 8b 8c 8d 8e 8f   ................
90 91 92 93 94 95 96 97 98 99 9a 9b 9c 9d 9e 9f   ................
a0 a1 a2 a3 a4 a5 a6 a7 a8 a9 aa ab ac ad ae af   ................
b0 b1 b2 b3 b4 b5 b6 b7 b8 b9 ba bb bc bd be bf   ................
c0 c1 c2 c3 c4 c5 c6 c7 c8 c9 ca cb cc cd ce cf   ................
d0 d1 d2 d3 d4 d5 d6 d7 d8 d9 da db dc dd de df   ................
e0 e1 e2 e3 e4 e5 e6 e7 e8 e9 ea eb ec ed ee ef   ................
f0 f1 f2 f3 f4 f5 f6 f7 f8 f9 fa fb fc fd fe      ...............

Acknowledgements

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, Carsten Bormann, and Dale Worley provided detailed reviews. Stuart Cheshire invented the very clever COBS encoding. Michael Osborne made the critical observation that encoding the data and CRC32K fields separately would allow the CRC to be calculated on the fly. Alexandru Petrescu, Brian Frank, Geoff Mulligan, and Don Sturek offered valuable comments.¶

Author's Address