< draft-ietf-6lo-6lobac-01.txt   draft-ietf-6lo-6lobac-02.txt >
6Lo Working Group K. Lynn, Ed. 6Lo Working Group K. Lynn, Ed.
Internet-Draft Verizon Internet-Draft Verizon Labs
Intended status: Standards Track J. Martocci Intended status: Standards Track J. Martocci
Expires: September 10, 2015 Johnson Controls Expires: January 7, 2016 Johnson Controls
C. Neilson C. Neilson
Delta Controls Delta Controls
S. Donaldson S. Donaldson
Honeywell Honeywell
March 9, 2015 July 6, 2015
Transmission of IPv6 over MS/TP Networks Transmission of IPv6 over MS/TP Networks
draft-ietf-6lo-6lobac-01 draft-ietf-6lo-6lobac-02
Abstract Abstract
Master-Slave/Token-Passing (MS/TP) is a contention-free access method Master-Slave/Token-Passing (MS/TP) is a medium access control method
for the RS-485 physical layer, which is used extensively in building for the RS-485 physical layer, which is used extensively in building
automation networks. This specification defines the frame format for automation networks. This specification defines the frame format for
transmission of IPv6 packets and the method of forming link-local and transmission of IPv6 packets and the method of forming link-local and
statelessly autoconfigured IPv6 addresses on MS/TP networks. statelessly autoconfigured IPv6 addresses on MS/TP networks.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
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Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 10, 2015. This Internet-Draft will expire on January 7, 2016.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
skipping to change at page 2, line 17 skipping to change at page 2, line 17
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. MS/TP Mode for IPv6 . . . . . . . . . . . . . . . . . . . . . 5 2. MS/TP Mode for IPv6 . . . . . . . . . . . . . . . . . . . . . 5
3. Addressing Modes . . . . . . . . . . . . . . . . . . . . . . 6 3. Addressing Modes . . . . . . . . . . . . . . . . . . . . . . 6
4. Maximum Transmission Unit (MTU) . . . . . . . . . . . . . . . 6 4. Maximum Transmission Unit (MTU) . . . . . . . . . . . . . . . 6
5. LoBAC Adaptation Layer . . . . . . . . . . . . . . . . . . . 6 5. LoBAC Adaptation Layer . . . . . . . . . . . . . . . . . . . 6
6. Stateless Address Autoconfiguration . . . . . . . . . . . . . 9 6. Stateless Address Autoconfiguration . . . . . . . . . . . . . 7
7. IPv6 Link Local Address . . . . . . . . . . . . . . . . . . . 10 7. IPv6 Link Local Address . . . . . . . . . . . . . . . . . . . 8
8. Unicast Address Mapping . . . . . . . . . . . . . . . . . . . 10 8. Unicast Address Mapping . . . . . . . . . . . . . . . . . . . 8
9. Multicast Address Mapping . . . . . . . . . . . . . . . . . . 11 9. Multicast Address Mapping . . . . . . . . . . . . . . . . . . 9
10. Header Compression . . . . . . . . . . . . . . . . . . . . . 11 10. Header Compression . . . . . . . . . . . . . . . . . . . . . 9
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
12. Security Considerations . . . . . . . . . . . . . . . . . . . 12 12. Security Considerations . . . . . . . . . . . . . . . . . . . 10
13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12 13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
Appendix A. Abstract MAC Interface . . . . . . . . . . . . . . . 14 Appendix A. Abstract MAC Interface . . . . . . . . . . . . . . . 13
Appendix B. Consistent Overhead Byte Stuffing [COBS] . . . . . . 16 Appendix B. Consistent Overhead Byte Stuffing [COBS] . . . . . . 15
Appendix C. Encoded CRC-32K [CRC32K] . . . . . . . . . . . . . . 20 Appendix C. Encoded CRC-32K [CRC32K] . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21
1. Introduction 1. Introduction
Master-Slave/Token-Passing (MS/TP) is a contention-free access method Master-Slave/Token-Passing (MS/TP) is a medium access control (MAC)
for the RS-485 [TIA-485-A] physical layer, which is used extensively protocol for the RS-485 [TIA-485-A] physical layer, which is used
in building automation networks. This specification defines the extensively in building automation networks. This specification
frame format for transmission of IPv6 [RFC2460] packets and the defines the frame format for transmission of IPv6 [RFC2460] packets
method of forming link-local and statelessly autoconfigured IPv6 and the method of forming link-local and statelessly autoconfigured
addresses on MS/TP networks. The general approach is to adapt IPv6 addresses on MS/TP networks. The general approach is to adapt
elements of the 6LoWPAN [RFC4944] specification to constrained wired elements of the 6LoWPAN specifications [RFC4944], [RFC6282], and
networks. [RFC6775] to constrained wired networks.
An MS/TP device is typically based on a low-cost microcontroller with An MS/TP device is typically based on a low-cost microcontroller with
limited processing power and memory. Together with low data rates limited processing power and memory. Together with low data rates
and a small address space, these constraints are similar to those and a small MAC address space, these constraints are similar to those
faced in 6LoWPAN networks and suggest some elements of that solution faced in 6LoWPAN networks and suggest some elements of that solution
might be leveraged. MS/TP differs significantly from 6LoWPAN in at might be leveraged. MS/TP differs significantly from 6LoWPAN in at
least three respects: a) MS/TP devices typically have a continuous least three respects: a) MS/TP devices typically have a continuous
source of power, b) all MS/TP devices on a segment can communicate 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) 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 large payloads,
eliminating the need for link-layer fragmentation and reassembly. eliminating the need for fragmentation and reassembly below IPv6.
The following sections provide a brief overview of MS/TP, then The following sections provide a brief overview of MS/TP, then
describe how to form IPv6 addresses and encapsulate IPv6 packets in describe how to form IPv6 addresses and encapsulate IPv6 packets in
MS/TP frames. This document also specifies a header compression MS/TP frames. This document also specifies a header compression
mechanism, based on [RFC6282], that is RECOMMENDED in order to make mechanism, based on [RFC6282], that is REQUIRED in order to reduce
IPv6 practical on low speed MS/TP networks. latency and make IPv6 practical on MS/TP networks.
1.1. Requirements Language 1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
1.2. Abbreviations Used 1.2. Abbreviations Used
ASHRAE: American Society of Heating, Refrigerating, and Air- ASHRAE: American Society of Heating, Refrigerating, and Air-
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resolution timer. These features make MS/TP a cost-effective field resolution timer. These features make MS/TP a cost-effective field
bus for the most numerous and least expensive devices in a building bus for the most numerous and least expensive devices in a building
automation network. automation network.
The differential signaling used by [TIA-485-A] requires a contention- 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. 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 A master node may initiate the transmission of a data frame when it
holds the token. After sending at most a configured maximum number holds the token. After sending at most a configured maximum number
of data frames, a master node passes the token to the next master of data frames, a master node passes the token to the next master
node (as determined by node address). Slave nodes transmit only when node (as determined by MAC address). Slave nodes do not support the
polled and SHALL NOT be considered part of this specification. frame format required to convey IPv6 over MS/TP and therefore SHALL
NOT be considered part of this specification.
MS/TP COBS-encoded* frames have the following format: MS/TP COBS-encoded* frames have the following format:
0 1 2 3 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 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 | | SA | Length (MS octet first) | Header CRC |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. . . .
. Encoded Data* (2 - 1507 octets) . . Encoded Data* (2 - 1506 octets) .
. . . .
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Encoded CRC-32K* (5 octets) | | | Encoded CRC-32K* (5 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
| | optional 0xFF | | | optional 0xFF |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: MS/TP COBS-Encoded Frame Format Figure 1: MS/TP COBS-Encoded Frame Format
*Note: BACnet Addendum 135-2012an [Addendum_an] defines a range of *NOTE: BACnet Addendum 135-2012an [Addendum_an] defines a range of
Frame Type values to designate frames that contain data and data CRC Frame Type values to designate frames that contain data and data CRC
fields encoded using Consistent Overhead Byte Stuffing [COBS] (see fields encoded using Consistent Overhead Byte Stuffing [COBS] (see
Appendix B). The purpose of COBS encoding is to eliminate preamble Appendix B). The purpose of COBS encoding is to eliminate preamble
sequences from the Encoded Data and Encoded CRC-32K fields. The sequences from the Encoded Data and Encoded CRC-32K fields. The
maximum length of an MSDU as defined by this specification is 1501 maximum length of an MSDU as defined by this specification is 1500
octets (before encoding). The Encoded Data is covered by a 32-bit octets (before encoding). The Encoded Data is covered by a 32-bit
CRC [CRC32K] (see Appendix C), which is then itself COBS encoded. CRC [CRC32K] (see Appendix C), which is itself then COBS encoded.
MS/TP COBS-encoded frame fields have the following descriptions: MS/TP COBS-encoded frame fields have the following descriptions:
Preamble two octet preamble: 0x55, 0xFF Preamble two octet preamble: 0x55, 0xFF
Frame Type one octet Frame Type one octet
Destination Address one octet address Destination Address one octet address
Source Address one octet address Source Address one octet address
Length two octets, most significant octet first Length two octets, most significant octet first
Header CRC one octet Header CRC one octet
Encoded Data 2 - 1512 octets (see Appendix B) Encoded Data 2 - 1506 octets (see Appendix B)
Encoded CRC-32K five octets (see Appendix C) Encoded CRC-32K five octets (see Appendix C)
(pad) (optional) at most one octet of trailer: 0xFF (pad) (optional) at most one octet of trailer: 0xFF
The Frame Type is used to distinguish between different types of MAC The Frame Type is used to distinguish between different types of MAC
frames. The types relevant to this specification (in decimal) are: frames. The types relevant to this specification (in decimal) are:
0 Token 0 Token
1 Poll For Master 1 Poll For Master
2 Reply To Poll For Master 2 Reply To Poll For Master
... ...
34 IPv6 over MS/TP (LoBAC) Encapsulation 34 IPv6 over MS/TP (LoBAC) Encapsulation
Frame Types 8 through 127 are reserved for assignment by ASHRAE. Frame Types 8 - 31 and 35 - 127 are reserved for assignment by
Frame Types 32 through 127 designate COBS-encoded frames and MUST ASHRAE. Frame Types 32 - 127 designate COBS-encoded frames and MUST
convey Encoded Data and Encoded CRC-32K fields. All master nodes convey Encoded Data and Encoded CRC-32K fields. All master nodes
MUST understand Token, Poll For Master, and Reply to Poll For Master MUST understand Token, Poll For Master, and Reply to Poll For Master
control frames. See Section 2 for additional details. control frames. See Section 2 for additional details.
The Destination and Source Addresses are each one octet in length. The Destination and Source Addresses are each one octet in length.
See Section 3 for additional details. See Section 3 for additional details.
For COBS-encoded frames, the Length field specifies the combined For COBS-encoded frames, the Length field specifies the combined
length of the [COBS] Encoded Data and Encoded CRC-32K fields in length of the [COBS] Encoded Data and Encoded CRC-32K fields in
octets, minus two. (This adjustment is required for backward octets, minus two. (This adjustment is required for backward
compatibility with legacy MS/TP devices.) See Section 4 and compatibility with legacy MS/TP devices.) See Section 4 and
Appendices for additional details. Appendices for additional details.
The Header CRC field covers the Frame Type, Destination Address, The Header CRC field covers the Frame Type, Destination Address,
Source Address, and Length fields. The Header CRC generation and Source Address, and Length fields. The Header CRC generation and
check procedures are specified in BACnet [Clause9]. check procedures are specified in BACnet [Clause9].
1.4. Goals and Non-goals 1.4. Goals and Constraints
The primary goal of this specification is to enable IPv6 directly on The primary goal of this specification is to enable IPv6 directly on
wired end devices in building automation and control networks by wired end devices in building automation and control networks by
leveraging existing standards to the greatest extent possible. A leveraging existing standards to the greatest extent possible. A
secondary goal is to co-exist with legacy MS/TP implementations. secondary goal is to co-exist with legacy MS/TP implementations.
Only the minimum changes necessary to support IPv6 over MS/TP are 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 Note in Section 1.3).
Non-goals include making changes to the MS/TP frame header format, In order to co-exist with legacy devices, no changes are permitted to
control frames, Master Node state machine, or addressing modes. the MS/TP addressing modes, frame header format, control frames, or
Also, while the techniques described here may be applicable to other Master Node state machine as specified in BACnet [Clause9].
data links, no attempt is made to define a general design pattern.
2. MS/TP Mode for IPv6 2. MS/TP Mode for IPv6
ASHRAE must assign a new MS/TP Frame Type to indicate IPv6 over MS/TP ASHRAE has assigned an MS/TP Frame Type value of 34 to indicate IPv6
Encapsulation from the range reserved for designating COBS-encoded over MS/TP (LoBAC) Encapsulation. This falls within the range of
frames. The Frame Type requested for IPv6 over MS/TP Encapsulation values that designate COBS-encoded data frames.
is 34 (0x22).
All MS/TP master nodes (including those that support IPv6) must All MS/TP master nodes (including those that support IPv6) must
understand Token, Poll For Master, and Reply to Poll For Master understand Token, Poll For Master, and Reply to Poll For Master
control frames and support the Master Node state machine as specified control frames and support the Master Node state machine as specified
in BACnet [Clause9]. MS/TP master nodes that support IPv6 must also in BACnet [Clause9]. MS/TP master nodes that support IPv6 must also
support the Receive Frame state machine as specified in [Clause9] and support the Receive Frame state machine as specified in [Clause9] and
extended by BACnet [Addendum_an]. extended by BACnet [Addendum_an].
3. Addressing Modes 3. Addressing Modes
MS/TP link-layer (node) addresses are one octet in length. The MS/TP node (MAC) addresses are one octet in length. The method of
method of assigning a node address is outside the scope of this assigning MAC addresses is outside the scope of this specification.
document. However, each MS/TP node on the link MUST have a unique However, each MS/TP node on the link MUST have a unique address in
address or a mis-configuration condition exists. order to ensure correct MAC operation.
BACnet [Clause9] specifies that addresses 0 through 127 are valid for BACnet [Clause9] specifies that addresses 0 through 127 are valid for
master nodes. The method specified in Section 6 for creating the master nodes. The method specified in Section 6 for creating a MAC-
Interface Identifier (IID) ensures that an IID of all zeros can never layer-derived Interface Identifier (IID) ensures that an IID of all
result. zeros can never result.
A Destination Address of 255 (0xFF) denotes a link-level broadcast A Destination Address of 255 (all nodes) indicates a MAC-layer
(all nodes). A Source Address of 255 MUST NOT be used. MS/TP does broadcast. MS/TP does not support multicast, therefore all IPv6
not support multicast, therefore all IPv6 multicast packets MUST be multicast packets SHOULD be broadcast at the MAC layer and filtered
sent as link-level broadcasts and filtered at the IPv6 layer. at the IPv6 layer. A Source Address of 255 MUST NOT be used.
This specification assumes that a unique IPv6 subnet prefix is This specification assumes that at most one unique local and/or
assigned to each MS/TP segment. Hosts learn IPv6 prefixes via router global IPv6 prefix is assigned to each MS/TP segment. Hosts learn
advertisements according to [RFC4861]. IPv6 prefixes via router advertisements according to [RFC4861].
4. Maximum Transmission Unit (MTU) 4. Maximum Transmission Unit (MTU)
BACnet [Addendum_an] supports MSDUs up to 2032 octets in length. BACnet [Addendum_an] supports MSDUs up to 2032 octets in length.
This specification defines an MSDU length of at least 1281 octets and This specification defines an MSDU length of at least 1280 octets and
at most 1501 octets. This is sufficient to convey the minimum MTU at most 1500 octets (before encoding). This is sufficient to convey
required by IPv6 [RFC2460] without the need for link-layer the minimum MTU required by IPv6 [RFC2460] without the need for link-
fragmentation and reassembly. layer fragmentation and reassembly.
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 5. LoBAC Adaptation Layer
The encapsulation formats defined in this section (subsequently The relatively low data rates of MS/TP indicate header compression as
referred to as the "LoBAC" encapsulation) comprise the MSDU (payload) a means to reduce latency. This section specifies an adaptation
of an MS/TP frame. The LoBAC payload (i.e., an IPv6 packet) follows layer to support compressed IPv6 headers and the compression format
an encapsulation header stack. LoBAC is a subset of the LoWPAN is specified in Section 10.
encapsulation defined in [RFC4944], therefore the use of "LOWPAN" in
literals below is intentional. The primary differences between LoBAC
and LoWPAN are: a) omission of the Fragmentation, Mesh, and Broadcast
headers, and b) use of LOWPAN_IPHC [RFC6282] in place of LOWPAN_HC1
header compression (which is deprecated by [RFC6282]).
All LoBAC encapsulated datagrams transmitted over MS/TP are prefixed
by an encapsulation header stack. Each header in the stack consists
of a header type followed by zero or more header fields. Whereas in
an IPv6 header the stack would contain, in the following order,
addressing, hop-by-hop options, routing, fragmentation, destination
options, and finally payload [RFC2460]; in a LoBAC encapsulation the
analogous sequence is (optional) header compression and payload. The
header stacks that are valid in a LoBAC network are shown below.
A LoBAC encapsulated IPv6 datagram:
+---------------+-------------+---------+
| IPv6 Dispatch | IPv6 Header | Payload |
+---------------+-------------+---------+
A LoBAC encapsulated LOWPAN_IPHC compressed IPv6 datagram:
+---------------+-------------+---------+
| IPHC Dispatch | IPHC Header | Payload |
+---------------+-------------+---------+
All protocol datagrams (i.e., IPv6 or compressed IPv6 headers) SHALL
be preceded by one of the valid LoBAC encapsulation headers. This
permits uniform software treatment of datagrams without regard to
their mode of transmission.
The definition of LoBAC headers consists of the dispatch value, the
definition of the header fields that follow, and their ordering
constraints relative to all other headers. Although the header stack
structure provides a mechanism to address future demands on the LoBAC
(LoWPAN) adaptation layer, it is not intended to provided general
purpose extensibility. This format document specifies a small set of
header types using the header stack for clarity, compactness, and
orthogonality.
5.1. Dispatch Value and Header
The LoBAC Dispatch value begins with a "0" bit followed by a "1" bit. Implementations MAY also support Generic Header Compression (GHC)
The Dispatch value and header are shown here: [RFC7400] for transport layer headers. A node implementing [RFC7400]
MUST probe its peers for GHC support before applying GHC.
0 1 2 3 The encapsulation format defined in this section (subsequently
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 referred to as the "LoBAC" encapsulation) comprises the MSDU of an
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ IPv6 over MS/TP frame. The LoBAC payload (i.e., an IPv6 packet)
|0|1| Dispatch | Type-specific header follows an encapsulation header stack. LoBAC is a subset of the
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ LoWPAN encapsulation defined in [RFC4944] and extended by [RFC6282],
therefore the use of "LOWPAN" in literals below is intentional. The
primary difference between LoWPAN and LoBAC is omission of the Mesh,
Broadcast, Fragmentation, and LOWPAN_HC1 headers.
Dispatch 6-bit selector. Identifies the type of header All LoBAC encapsulated datagrams transmitted over MS/TP are prefixed
immediately following the Dispatch value. 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:
Type-specific header A header determined by the Dispatch value. +---------------+---------------+------...-----+
| IPHC Dispatch | IPHC Header | Payload |
+---------------+---------------+------...-----+
Figure 2: Dispatch Value and Header Figure 2: A LoBAC Encapsulated LOWPAN_IPHC Compressed IPv6 Datagram
The Dispatch value may be treated as an unstructured namespace. Only The Dispatch value may be treated as an unstructured namespace. Only
a few symbols are required to represent current LoBAC functionality. a single pattern is used to represent current LoBAC functionality.
Although some additional savings could be achieved by encoding
additional functionality into the dispatch value, these measures
would tend to constrain the ability to address future alternatives.
Pattern Header Type
+------------+-----------------------------------------------------+
| 00 xxxxxx | NALP - Not a LoWPAN (LoBAC) frame |
| 01 000000 | ESC - Additional Dispatch octet follows |
| 01 000001 | IPv6 - Uncompressed IPv6 Addresses |
| ... | reserved - Defined or reserved by [RFC4944] |
| 01 1xxxxx | LOWPAN_IPHC - LOWPAN_IPHC compressed IPv6 [RFC6282] |
| 1x xxxxxx | reserved - Defined or reserved by [RFC4944] |
+------------+-----------------------------------------------------+
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 Section 5 of [RFC6282]).
IPv6: Specifies that the following header is an uncompressed IPv6 Pattern Header Type
header [RFC2460]. +------------+-----------------------------------------------------+
| 01 1xxxxx | LOWPAN_IPHC - LOWPAN_IPHC compressed IPv6 [RFC6282] |
+------------+-----------------------------------------------------+
LOWPAN_IPHC: A value of 011xxxxx specifies a LOWPAN_IPHC compression Figure 3: LoBAC Dispatch Value Bit Pattern
header (see Section 10.)
Reserved: A LoBAC node that encounters a Dispatch value in the range Other IANA-assigned 6LoWPAN Dispatch values do not apply to this
01000010 through 01011111 or 1xxxxxxx SHALL discard the packet. specification.
6. Stateless Address Autoconfiguration 6. Stateless Address Autoconfiguration
This section defines how to obtain an IPv6 Interface Identifier. The This section defines how to obtain an IPv6 Interface Identifier. The
general procedure is described in Appendix A of [RFC4291], "Creating general procedure for creating a MAC-address-derived IID is described
Modified EUI-64 Format Interface Identifiers", as updated by in [RFC4291] Appendix A, "Creating Modified EUI-64 Format Interface
[RFC7136]. Identifiers", as updated by [RFC7136].
The Interface Identifier MAY be based on an [EUI-64] identifier The IID SHOULD NOT embed an [EUI-64] or any other globally unique
assigned to the device but this is not typical for MS/TP. In this hardware identifier assigned to a device (see Section 12).
case, the EUI-64 to IID transformation defined in the IPv6 addressing
architecture [RFC4291] MUST be used. This will result in a globally
unique Interface Identifier.
If the device does not have an EUI-64, then the Interface Identifier The Interface Identifier for link-local addresses SHOULD be formed by
SHOULD be formed by concatenating its 8-bit MS/TP node address to the concatenating its 8-bit MS/TP MAC address to the seven octets 0x00,
seven octets 0x00, 0x00, 0x00, 0xFF, 0xFE, 0x00, 0x00. For example, 0x00, 0x00, 0xFF, 0xFE, 0x00, 0x00. For example, an MS/TP MAC
an MS/TP node address of hexadecimal value 0x4F results in the address of hexadecimal value 0x4F results in the following IID:
following Interface Identifier:
|0 1|1 3|3 4|4 6| |0 1|1 3|3 4|4 6|
|0 5|6 1|2 7|8 3| |0 5|6 1|2 7|8 3|
+----------------+----------------+----------------+----------------+ +----------------+----------------+----------------+----------------+
|0000000000000000|0000000011111111|1111111000000000|0000000001001111| |0000000000000000|0000000011111111|1111111000000000|0000000001001111|
+----------------+----------------+----------------+----------------+ +----------------+----------------+----------------+----------------+
This is the RECOMMENDED method of forming an IID, as it supports the This is the RECOMMENDED method of forming an IID for use in link-
most efficient header compression provided by the LOWPAN_IPHC local addresses, as it affords the most efficient header compression
[RFC6282] scheme specified in Section 10. provided by the LOWPAN_IPHC [RFC6282] format specified in Section 10.
Optionally, an opaque 64-bit IID (for non-link-local addresses) MAY A 64-bit privacy IID is RECOMMENDED for routable addresses and SHOULD
be formed by the technique discussed in [I-D.ietf-6man-default-iids] be locally generated according to [I-D.ietf-6man-default-iids]. A
or alternate method. A node that generates a non-link-local address node that generates a 64-bit privacy IID MUST register it with its
IID MUST register it with its local router(s) by sending a Neighbor local router(s) by sending a Neighbor Solicitation (NS) message with
Solicitation (NS) message with the Address Registration Option (ARO) the Address Registration Option (ARO) and process Neighbor
and process Neighbor Advertisements (NA) according to [RFC6775]. Advertisements (NA) according to [RFC6775].
An IPv6 address prefix used for stateless autoconfiguration [RFC4862] An IPv6 address prefix used for stateless autoconfiguration [RFC4862]
of an MS/TP interface MUST have a length of 64 bits. of an MS/TP interface MUST have a length of 64 bits.
7. IPv6 Link Local Address 7. IPv6 Link Local Address
The IPv6 link-local address [RFC4291] for an MS/TP interface is The IPv6 link-local address [RFC4291] for an MS/TP interface is
formed by appending the Interface Identifier, as defined above, to formed by appending the Interface Identifier, as defined above, to
the prefix FE80::/64. the prefix FE80::/64.
10 bits 54 bits 64 bits 10 bits 54 bits 64 bits
+----------+-----------------------+----------------------------+ +----------+-----------------------+----------------------------+
|1111111010| (zeros) | Interface Identifier | |1111111010| (zeros) | Interface Identifier |
+----------+-----------------------+----------------------------+ +----------+-----------------------+----------------------------+
8. Unicast Address Mapping 8. Unicast Address Mapping
The address resolution procedure for mapping IPv6 non-multicast The address resolution procedure for mapping IPv6 non-multicast
addresses into MS/TP link-layer addresses follows the general addresses into MS/TP MAC-layer addresses follows the general
description in Section 7.2 of [RFC4861], unless otherwise specified. description in Section 7.2 of [RFC4861], unless otherwise specified.
The Source/Target Link-layer Address option has the following form The Source/Target Link-layer Address option has the following form
when the addresses are 8-bit MS/TP link-layer (node) addresses. when the addresses are 8-bit MS/TP MAC-layer (node) addresses.
0 1 0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length=1 | | Type | Length=1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+ Padding (all zeros) + + Padding (all zeros) +
| | | |
+ +-+-+-+-+-+-+-+-+ + +-+-+-+-+-+-+-+-+
skipping to change at page 10, line 47 skipping to change at page 9, line 27
Option fields: Option fields:
Type: Type:
1: for Source Link-layer address. 1: for Source Link-layer address.
2: for Target Link-layer address. 2: for Target Link-layer address.
Length: This is the length of this option (including the type and 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 length fields) in units of 8 octets. The value of this field is 1
for 8-bit MS/TP node addresses. for 8-bit MS/TP MAC addresses.
MS/TP Address: The 8-bit address in canonical bit order [RFC2469]. MS/TP Address: The 8-bit address in canonical bit order [RFC2469].
This is the unicast address the interface currently responds to. This is the unicast address the interface currently responds to.
9. Multicast Address Mapping 9. Multicast Address Mapping
All IPv6 multicast packets MUST be sent to MS/TP Destination Address All IPv6 multicast packets SHOULD be sent to MS/TP Destination
255 (broadcast) and filtered at the IPv6 layer. When represented as Address 255 (broadcast) and filtered at the IPv6 layer. When
a 16-bit address in a compressed header (see Section 10), it MUST be represented as a 16-bit address in a compressed header (see
formed by padding on the left with a zero: Section 10), it MUST be formed by padding on the left with a zero:
0 1 0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x00 | 0xFF | | 0x00 | 0xFF |
+-+-+-+-+-+-+-+-+---------------+ +-+-+-+-+-+-+-+-+---------------+
10. Header Compression 10. Header Compression
LoBAC uses LOWPAN_IPHC IPv6 compression, which is specified in LoBAC uses LOWPAN_IPHC IPv6 compression, which is specified in
skipping to change at page 11, line 43 skipping to change at page 10, line 21
with a zero: with a zero:
0 1 0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x00 | MS/TP address | | 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 border
router(s) directly attached to the MS/TP segment MUST disseminate the router(s) directly attached to the MS/TP segment MUST disseminate the
6LoWPAN Context Option (6CO) as specified in [RFC6775]. 6LoWPAN Context Option (6CO) according to [RFC6775], Section 7.2.
11. IANA Considerations 11. IANA Considerations
This document uses values previously reserved by [RFC4944] and This document uses values previously reserved by [RFC4944] and
[RFC6282] and makes no further requests of IANA. [RFC6282] and makes no further requests of IANA.
Note to RFC Editor: this section may be removed upon publication. Note to RFC Editor: this section may be removed upon publication.
12. Security Considerations 12. Security Considerations
The method of deriving Interface Identifiers from MAC addresses is The security and privacy implications of embedding a link-layer
intended to preserve global uniqueness when possible. However, there address in an IPv6 IID are discussed in
is no protection from duplication through accident or forgery. [I-D.ietf-6man-ipv6-address-generation-privacy]. The issue most
relevant to MS/TP networks is address scanning. This is mainly an
issue for routable addresses and probably only for those hosted on
the global Internet. This specification RECOMMENDS mitigating this
threat according to [I-D.ietf-6man-default-iids].
13. Acknowledgments 13. Acknowledgments
We are grateful to the authors of [RFC4944] and members of the IETF We are grateful to the authors of [RFC4944] and members of the IETF
6LoWPAN working group; this document borrows liberally from their 6LoWPAN working group; this document borrows liberally from their
work. work.
14. References 14. References
14.1. Normative References 14.1. Normative References
[Addendum_an] [Addendum_an]
ASHRAE, "ANSI/ASHRAE Addenda an, at, au, av, aw, ax, and ASHRAE, "ANSI/ASHRAE Addenda an, at, au, av, aw, ax, and
az to ANSI/ASHRAE Standard 135-2012, BACnet - A Data az to ANSI/ASHRAE Standard 135-2012, BACnet - A Data
Communication Protocol for Building Automation and Control Communication Protocol for Building Automation and Control
Networks", July 2014, Networks", July 2014,
<https://www.ashrae.org/File%20Library/docLib/ <https://www.ashrae.org/File%20Library/docLib/StdsAddenda/
StdsAddenda/135_2012_an_at_au_av_aw_ax_az_Final.pdf>. 07-31-2014_135_2012_an_at_au_av_aw_ax_az_Final.pdf>.
[Clause9] American Society of Heating, Refrigerating, and Air- [Clause9] American Society of Heating, Refrigerating, and Air-
Conditioning Engineers, "BACnet - A Data Communication Conditioning Engineers, "BACnet - A Data Communication
Protocol for Building Automation and Control Networks", Protocol for Building Automation and Control Networks",
ANSI/ASHRAE 135-2012 (Clause 9), March 2013. ANSI/ASHRAE 135-2012 (Clause 9), March 2013.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
skipping to change at page 13, line 17 skipping to change at page 11, line 50
September 2011. September 2011.
[RFC6775] Shelby, Z., Chakrabarti, S., Nordmark, E., and C. Bormann, [RFC6775] Shelby, Z., Chakrabarti, S., Nordmark, E., and C. Bormann,
"Neighbor Discovery Optimization for IPv6 over Low-Power "Neighbor Discovery Optimization for IPv6 over Low-Power
Wireless Personal Area Networks (6LoWPANs)", RFC 6775, Wireless Personal Area Networks (6LoWPANs)", RFC 6775,
November 2012. November 2012.
[RFC7136] Carpenter, B. and S. Jiang, "Significance of IPv6 [RFC7136] Carpenter, B. and S. Jiang, "Significance of IPv6
Interface Identifiers", RFC 7136, February 2014. Interface Identifiers", RFC 7136, February 2014.
[RFC7400] Bormann, C., "6LoWPAN-GHC: Generic Header Compression for
IPv6 over Low-Power Wireless Personal Area Networks
(6LoWPANs)", RFC 7400, November 2014.
14.2. Informative References 14.2. Informative References
[COBS] Cheshire, S. and M. Baker, "Consistent Overhead Byte [COBS] Cheshire, S. and M. Baker, "Consistent Overhead Byte
Stuffing", IEEE/ACM TRANSACTIONS ON NETWORKING, VOL.7, Stuffing", IEEE/ACM TRANSACTIONS ON NETWORKING, VOL.7,
NO.2 , April 1999, NO.2 , April 1999,
<http://www.stuartcheshire.org/papers/COBSforToN.pdf>. <http://www.stuartcheshire.org/papers/COBSforToN.pdf>.
[CRC32K] Koopman, P., "32-Bit Cyclic Redundancy Codes for Internet [CRC32K] Koopman, P., "32-Bit Cyclic Redundancy Codes for Internet
Applications", IEEE/IFIP International Conference on Applications", IEEE/IFIP International Conference on
Dependable Systems and Networks (DSN 2002) , June 2002, Dependable Systems and Networks (DSN 2002) , June 2002,
<http://www.ece.cmu.edu/~koopman/networks/dsn02/ <http://www.ece.cmu.edu/~koopman/networks/dsn02/
dsn02_koopman.pdf>. dsn02_koopman.pdf>.
[EUI-64] IEEE, "Guidelines for 64-bit Global Identifier (EUI-64) [EUI-64] IEEE, "Guidelines for 64-bit Global Identifier (EUI-64)
Registration Authority", March 1997, Registration Authority", March 1997,
<http://standards.ieee.org/regauth/oui/tutorials/ <http://standards.ieee.org/regauth/oui/tutorials/
EUI64.html>. EUI64.html>.
[I-D.ietf-6man-default-iids] [I-D.ietf-6man-default-iids]
Gont, F., Cooper, A., Thaler, D., and W. Will, Gont, F., Cooper, A., Thaler, D., and S. LIU,
"Recommendation on Stable IPv6 Interface Identifiers", "Recommendation on Stable IPv6 Interface Identifiers",
draft-ietf-6man-default-iids-02 (work in progress), draft-ietf-6man-default-iids-04 (work in progress), June
January 2015. 2015.
[I-D.ietf-6man-ipv6-address-generation-privacy]
Cooper, A., Gont, F., and D. Thaler, "Privacy
Considerations for IPv6 Address Generation Mechanisms",
draft-ietf-6man-ipv6-address-generation-privacy-07 (work
in progress), June 2015.
[IEEE.802.3] [IEEE.802.3]
"Information technology - Telecommunications and "Information technology - Telecommunications and
information exchange between systems - Local and information exchange between systems - Local and
metropolitan area networks - Specific requirements - Part metropolitan area networks - Specific requirements - Part
3: Carrier Sense Multiple Access with Collision Detection 3: Carrier Sense Multiple Access with Collision Detection
(CMSA/CD) Access Method and Physical Layer (CMSA/CD) Access Method and Physical Layer
Specifications", IEEE Std 802.3-2008, December 2008, Specifications", IEEE Std 802.3-2012, December 2012,
<http://standards.ieee.org/getieee802/802.3.html>. <http://standards.ieee.org/getieee802/802.3.html>.
[RFC2469] Narten, T. and C. Burton, "A Caution On The Canonical [RFC2469] Narten, T. and C. Burton, "A Caution On The Canonical
Ordering Of Link-Layer Addresses", RFC 2469, December Ordering Of Link-Layer Addresses", RFC 2469, December
1998. 1998.
[TIA-485-A] [TIA-485-A]
Telecommunications Industry Association, "TIA-485-A, Telecommunications Industry Association, "TIA-485-A,
Electrical Characteristics of Generators and Receivers for Electrical Characteristics of Generators and Receivers for
Use in Balanced Digital Multipoint Systems (ANSI/TIA/EIA- Use in Balanced Digital Multipoint Systems (ANSI/TIA/EIA-
485-A-98) (R2003)", March 2003. 485-A-98) (R2003)", March 2003.
Appendix A. Abstract MAC Interface Appendix A. Abstract MAC Interface
This Appendix is informative and not part of the standard. This Appendix is informative and not part of the standard.
BACnet [Clause9] defines support for MAC-layer clients through its BACnet [Clause9] defines support for MAC-layer clients through its
SendFrame and ReceivedDataNoReply procedures. However, it does not SendFrame and ReceivedDataNoReply procedures. However, it does not
define a protocol independent abstract interface for the data link. define a network-protocol independent abstract interface for the MAC.
This is provided below as an aid to implementation. This is provided below as an aid to implementation.
A.1. MA-DATA.request A.1. MA-DATA.request
A.1.1. Function A.1.1. Function
This primitive defines the transfer of data from a MAC client entity 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 to a single peer entity or multiple peer entities in the case of a
broadcast address. broadcast address.
skipping to change at page 16, line 49 skipping to change at page 15, line 41
synchronization. The solution is to encode the Data and 32-bit Data synchronization. The solution is to encode the Data and 32-bit Data
CRC fields before transmission using Consistent Overhead Byte CRC fields before transmission using Consistent Overhead Byte
Stuffing [COBS] and decode these fields upon reception. Stuffing [COBS] and decode these fields upon reception.
COBS is a run-length encoding method that nominally removes '0x00' COBS is a run-length encoding method that nominally removes '0x00'
octets from its input. Any selected octet value may be removed by octets from its input. Any selected octet value may be removed by
XOR'ing that value with each octet of the COBS output. BACnet XOR'ing that value with each octet of the COBS output. BACnet
[Addendum_an] specifies the preamble octet '0x55' for removal. [Addendum_an] specifies the preamble octet '0x55' for removal.
The minimum overhead of COBS is one ectet per encoded field. The 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 worst-case overhead in long fields is bounded to one octet in 254, or
0.5%, as described in [COBS]. less than 0.4%, as described in [COBS].
Frame encoding proceeds logically in two passes. The Encoded Data Frame encoding proceeds logically in two passes. The Encoded Data
field is prepared by passing the MSDU through the COBS encoder and field is prepared by passing the MSDU through the COBS encoder and
XOR'ing the preamble octet '0x055' with each octet of the output. XOR'ing the preamble octet '0x55' with each octet of the output. The
The Encoded CRC-32K field is then prepared by calculating a CRC-32K Encoded CRC-32K field is then prepared by calculating a CRC-32K over
over the Encoded Data field and formatting it for transmission as the Encoded Data field and formatting it for transmission as
described in Appendix C. The combined length of these fields, minus described in Appendix C. The combined length of these fields, minus
two octets for compatibility with existing MS/TP devices, is placed two octets for compatibility with existing MS/TP devices, is placed
in the MS/TP header Length field before transmission. in the MS/TP header Length field before transmission.
Example COBS encoder and decoder functions are shown below for Example COBS encoder and decoder functions are shown below for
illustration. Complete examples of use and test vectors are provided illustration. Complete examples of use and test vectors are provided
in BACnet [Addendum_an]. in BACnet [Addendum_an].
#include <stddef.h> #include <stddef.h>
#include <stdint.h> #include <stdint.h>
skipping to change at page 20, line 9 skipping to change at page 19, line 9
if ((last_code != 255) && (read_index < length)) if ((last_code != 255) && (read_index < length))
to[write_index++] = 0; to[write_index++] = 0;
} }
return write_index; return write_index;
} }
Appendix C. Encoded CRC-32K [CRC32K] Appendix C. Encoded CRC-32K [CRC32K]
This Appendix is informative and not part of the standard. This Appendix is informative and not part of the standard.
Extending the payload of MS/TP to 1501 octets required upgrading the Extending the payload of MS/TP to 1500 octets required upgrading the
Data CRC from 16 bits to 32 bits. P.Koopman has authored several Data CRC from 16 bits to 32 bits. P.Koopman has authored several
papers on evaluating CRC polynomials for network applications. In papers on evaluating CRC polynomials for network applications. In
[CRC32K], he surveyed the entire 32-bit polynomial space and noted [CRC32K], he surveyed the entire 32-bit polynomial space and noted
some that exceed the [IEEE.802.3] polynomial in performance. BACnet some that exceed the [IEEE.802.3] polynomial in performance. BACnet
[Addendum_an] specifies the CRC-32K (Koopman) polynomial. [Addendum_an] specifies the CRC-32K (Koopman) polynomial.
The specified use of the calc_crc32K() function is as follows. The specified use of the calc_crc32K() function is as follows.
Before a frame is transmitted, 'crc_value' is initialized to all Before a frame is transmitted, 'crc_value' is initialized to all
ones. After passing each octet of the [COBS] Encoded Data through ones. After passing each octet of the [COBS] Encoded Data through
the function, the ones complement of the resulting 'crc_value' is the function, the ones complement of the resulting 'crc_value' is
skipping to change at page 21, line 26 skipping to change at page 20, line 26
* Return updated CRC. * Return updated CRC.
* *
* Note: crcValue must be set to CRC32K_INITIAL_VALUE * Note: crcValue must be set to CRC32K_INITIAL_VALUE
* before initial call. * before initial call.
*/ */
uint32_t uint32_t
calc_crc32K (uint8_t data_value, uint32_t crc_value) calc_crc32K (uint8_t data_value, uint32_t crc_value)
{ {
int b; int b;
for (b = 0; b < sizeof(uint8_t); b++) { for (b = 0; b < 8; b++) {
if ((data_value & 1) ^ (crc_value & 1)) { if ((data_value & 1) ^ (crc_value & 1)) {
crc_value >>= 1; crc_value >>= 1;
crc_value ^= CRC32K_POLY; crc_value ^= CRC32K_POLY;
} else { } else {
crc_value >>= 1; crc_value >>= 1;
} }
data_value >>= 1; data_value >>= 1;
} }
return crc_value; return crc_value;
} }
Authors' Addresses Authors' Addresses
Kerry Lynn (editor) Kerry Lynn (editor)
Verizon Verizon Labs
50 Sylvan Rd 50 Sylvan Rd
Waltham , MA 02451 Waltham , MA 02451
USA USA
Phone: +1 781 296 9722 Phone: +1 781 296 9722
Email: kerlyn@ieee.org Email: kerlyn@ieee.org
Jerry Martocci Jerry Martocci
Johnson Controls, Inc. Johnson Controls, Inc.
507 E. Michigan St 507 E. Michigan St
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