IEC 62439-5:2010
(Main)Industrial communication networks - High availability automation networks - Part 5: Beacon Redundancy Protocol (BRP)
Industrial communication networks - High availability automation networks - Part 5: Beacon Redundancy Protocol (BRP)
IEC 62439-5:2010 is applicable to high-availability automation networks based on the ISO/IEC 8802-3 (IEEE 802.3) (Ethernet) technology. This part of the IEC 62439 series specifies a redundancy protocol that is based on the duplication of the network, the redundancy protocol being executed within the end nodes, as opposed to a redundancy protocol built in the switches. Fast error detection is provided by two beacon nodes, the switchover decision is taken in every node individually. The cross-network connection capability enables single attached end nodes to be connected on either of the two networks. This standard cancels and replaces IEC 62439 published in 2008. This first edition constitutes a technical revision. It includes the following significant technical changes:
- adding a calculation method for RSTP (rapid spanning tree protocol, IEEE 802.1Q),
- adding two new redundancy protocols: HSR (High-availability Seamless Redundancy) and DRP (Distributed Redundancy Protocol),
- moving former Clauses 1 to 4 (introduction, definitions, general aspects) and the Annexes (taxonomy, availability calculation) to IEC 62439-1, which serves now as a base for the other documents,
- moving Clause 5 (MRP) to IEC 62439-2 with minor editorial changes,
- moving Clause 6 (PRP) was to IEC 62439-3 with minor editorial changes,
- moving Clause 7 (CRP) was to IEC 62439-4 with minor editorial changes, and
- moving Clause 8 (BRP) was to IEC 62439-5 with minor editorial changes,
- adding a method to calculate the maximum recovery time of RSTP in a restricted configuration (ring) to IEC 62439-1 as Clause 8, adding specifications of the HSR (High-availability Seamless Redundancy) protocol, which shares the principles of PRP to IEC 62439-3 as Clause 5, and
-introducing the DRP protocol as IEC 62439-6.
This bilingual version (2012-04) corresponds to the English version, published in 2010-02.
This publication is to be read in conjunction with IEC 62439-1:2010.
Réseaux industriels de communication - Réseaux d'automatisme à haute disponibilité - Partie 5: Protocole de redondance à balise (BRP)
La CEI 62439-5:2010 concerne les réseaux d'automatisme à haute disponibilité reposant sur la technologie (Ethernet) de l'ISO/CEI 8802-3 (IEEE 802.3). La présente partie de la série CEI 62439 porte sur un protocole de redondance reposant sur la duplication du réseau, ce protocole étant exécuté dans les noeuds d'extrémité, par opposition à un protocole de redondance intégré aux commutateurs. La détection rapide des erreurs est assurée par deux noeuds balise, la décision de basculement étant prise dans chaque noeud individuellement. La capacité de connexion inter-réseau permet à des noeuds d'extrémité à une seule association d'être connectés sur l'un ou l'autre des deux réseaux. La présente norme annule et remplace la CEI 62439 publiée en 2008. Cette première édition constitue une révision technique. Cette édition inclut les modifications techniques majeures suivantes:
- ajout d'une méthode de calcul pour le protocole RSTP (Rapid Spanning Tree Protocol, IEEE 802.1Q),
- ajout de deux nouveaux protocoles de redondance: HSR (redondance transparente de haute disponibilité) et DRP (protocole de redondance distribuée),
- déplacement des Articles 1 à 4 (Introduction, Définitions, Aspects généraux) et des Annexes (Taxinomie, Calcul de disponibilité) dans la CEI 62439-1, qui servent à présent de base aux autres documents,
- déplacement de l'Article 5 (MRP, Media Redundancy Protocol) dans la CEI 62439-2 avec peu de modifications éditoriales,
- déplacement de l'Article 6 (PRP, Protocole de Redondance Parallèle) dans la CEI 62439-3 avec peu de modifications éditoriales,
- déplacement de l'Article 7 (CRP, Protocole de Redondance Transréseau) dans la CEI 62439-4 avec peu de modifications éditoriales, et
- déplacement de l'Article 8 (BRP, Protocole de Redondance à Balise) dans la CEI 62439-5 avec peu de modifications éditoriales,
- ajout d'une méthode de calcul du temps de reprise maximal du protocole RSTP dans une configuration restreinte (anneau) dans la CEI 62439-1 (Article 8),
- ajout de spécifications du protocole HSR, qui partage les principes du protocole PRP dans la CEI 62439-3 (Article 5), et
- introduction du protocole DRP (CEI 62439-6).
La présente version bilingue (2012-04) correspond à la version anglaise monolingue publiée en 2010-02.
Cette publication doit être lue conjointement avec la CEI 62439-1:2010.
General Information
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Standards Content (Sample)
IEC 62439-5 ®
Edition 1.0 2010-02
INTERNATIONAL
STANDARD
colour
inside
Industrial communication networks – High availability automation networks –
Part 5: Beacon Redundancy Protocol (BRP)
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IEC 62439-5 ®
Edition 1.0 2010-02
INTERNATIONAL
STANDARD
colour
inside
Industrial communication networks – High availability automation networks –
Part 5: Beacon Redundancy Protocol (BRP)
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
X
ICS 25.040, 35.040 ISBN 978-2-88910-708-7
– 2 – 62439-5 © IEC:2010(E)
CONTENTS
FOREWORD.4
INTRODUCTION.6
1 Scope.7
2 Normative references .7
3 Terms, definitions, abbreviations, acronyms, and conventions.7
3.1 Terms and definitions .7
3.2 Abbreviations and acronyms.8
3.3 Conventions .8
4 BRP overview.8
5 BRP principle of operation.8
5.1 General .8
5.2 Network topology.8
5.3 Network components .10
5.4 Rapid reconfiguration of network traffic .11
6 BRP stack and fault detection features .11
7 BRP protocol specification.13
7.1 MAC addresses .13
7.2 EtherType .13
7.3 Fault detection mechanisms .13
7.4 End node state diagram .13
7.5 Beacon end node state diagram .21
8 BRP message structure .27
8.1 General .27
8.2 ISO/IEC 8802-3 (IEEE 802.3) tagged frame header.28
8.3 Beacon message.28
8.4 Learning_Update message .28
8.5 Failure_Notify message.29
8.6 Path_Check_Request message .29
8.7 Path_Check_Response message .29
9 BRP fault recovery time.29
10 BRP service definition .30
10.1 Supported services.30
10.2 Common service parameters .31
10.3 Set_Node_Parameters service .31
10.4 Get_Node_Parameters service.33
10.5 Add_Node_Receive_Parameters service .35
10.6 Remove_Node_Receive_Parameters service .37
10.7 Get_Node_Status service.38
11 BRP Management Information Base (MIB).39
Bibliography.41
Figure 1 – BRP star network example .9
Figure 2 – BRP linear network example .9
Figure 3 – BRP ring network example .10
Figure 4 – BRP stack architecture.11
62439-5 © IEC:2010(E) – 3 –
Figure 5 – BRP state diagram of end node.14
Figure 6 – BRP state diagram for beacon end node .21
Table 1 – BRP end node flags .16
Table 2 – BRP end node state transition table .17
Table 3 – BRP beacon end node flags .23
Table 4 – BRP beacon end node state transition table .24
Table 5 – BRP common header with ISO/IEC 8802-3 (IEEE 802.3) tagged frame format.28
Table 6 – BRP beacon message format .28
Table 7 – BRP Learning_Update message format .28
Table 8 – BRP Failure_Notify message format .29
Table 9 – BRP Path_Check_Request message format .29
Table 10 – BRP Path_Check_Response message format .29
Table 11 – BRP Set_Node_Parameters service parameters.32
Table 12 – BRP Get_Node_Parameters service parameters .34
Table 13 – BRP Add_Node_Receive_Parameters service parameters .36
Table 14 – BRP Remove_Node_Receive_Parameters service parameters.37
Table 15 – BRP Get_Node_Status service parameters .38
– 4 – 62439-5 © IEC:2010(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
INDUSTRIAL COMMUNICATION NETWORKS –
HIGH AVAILABILITY AUTOMATION NETWORKS –
Part 5: Beacon Redundancy Protocol (BRP)
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
International Standard IEC 62439-5 has been prepared by subcommittee 65C: Industrial
Networks, of IEC technical committee 65: Industrial-process measurement, control and
automation.
This standard cancels and replaces IEC 62439 published in 2008. This first edition constitutes
a technical revision.
This edition includes the following significant technical changes with respect to IEC 62439
(2008):
– adding a calculation method for RSTP (rapid spanning tree protocol, IEEE 802.1Q),
– adding two new redundancy protocols: HSR (High-availability Seamless Redundancy)
and DRP (Distributed Redundancy Protocol),
– moving former Clauses 1 to 4 (introduction, definitions, general aspects) and the
Annexes (taxonomy, availability calculation) to IEC 62439-1, which serves now as a
base for the other documents,
– moving Clause 5 (MRP) to IEC 62439-2 with minor editorial changes,
62439-5 © IEC:2010(E) – 5 –
– moving Clause 6 (PRP) was to IEC 62439-3 with minor editorial changes,
– moving Clause 7 (CRP) was to IEC 62439-4 with minor editorial changes, and
– moving Clause 8 (BRP) was to IEC 62439-5 with minor editorial changes,
– adding a method to calculate the maximum recovery time of RSTP in a restricted
configuration (ring) to IEC 62439-1 as Clause 8,
– adding specifications of the HSR (High-availability Seamless Redundancy) protocol,
which shares the principles of PRP to IEC 62439-3 as Clause 5, and
– introducing the DRP protocol as IEC 62439-6.
The text of this standard is based on the following documents:
FDIS Report on voting
65C/583/FDIS 65C/589/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This International Standard is to be read in conjunction with IEC 62439-1:2010, Industrial
communication networks – High availability automation networks – Part 1: General concepts
and calculation methods.
A list of the IEC 62439 series can be found, under the general title Industrial communication
networks – High availability automation networks, on the IEC website.
This publication has been drafted in accordance with ISO/IEC Directives, Part 2.
The committee has decided that the contents of this amendment and the base publication will
remain unchanged until the stability date indicated on the IEC web site under
"http://webstore.iec.ch" in the data related to the specific publication. At this date, the
publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this standard may be issued at a later date.
IMPORTANT – The “colour inside” logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct understanding
of its contents. Users should therefore print this publication using a colour printer.
– 6 – 62439-5 © IEC:2010(E)
INTRODUCTION
The IEC 62439 series specifies relevant principles for high availability networks that meet the
requirements for industrial automation networks.
In the fault-free state of the network, the protocols of the IEC 62439 series provide
ISO/IEC 8802-3 (IEEE 802.3) compatible, reliable data communication, and preserve
determinism of real-time data communication. In cases of fault, removal, and insertion of a
component, they provide deterministic recovery times.
These protocols retain fully the typical Ethernet communication capabilities as used in the
office world, so that the software involved remains applicable.
The market is in need of several network solutions, each with different performance
characteristics and functional capabilities, matching diverse application requirements. These
solutions support different redundancy topologies and mechanisms which are introduced in
IEC 62439-1 and specified in the other Parts of the IEC 62439 series. IEC 62439-1 also
distinguishes between the different solutions, giving guidance to the user.
The IEC 62439 series follows the general structure and terms of IEC 61158 series.
The International Electrotechnical Commission (IEC) draws attention to the fact that it is
claimed that compliance with this document may involve the use of a patent concerning fault-
tolerant Ethernet provided through the use of special interfaces providing duplicate ports that
may be alternatively enabled with the same network address. Switching between the ports
corrects for single faults in a two-way redundant system. This is given in Clauses 5 and 6.
IEC takes no position concerning the evidence, validity and scope of this patent right.
The holder of this patent right has assured the IEC that he/she is willing to negotiate licences
either free of charge or under reasonable and non-discriminatory terms and conditions with
applicants throughout the world. In this respect, the statement of the holder of this patent
right is registered with IEC. Information may be obtained from:
Rockwell Automation Technologies
1 Allen-Bradley Drive
Mayfield Heights
Ohio
USA
Attention is drawn to the possibility that some of the elements of this document may be the
subject of patent rights other than those identified above. IEC shall not be held responsible for
identifying any or all such patent rights.
ISO (www.iso.org/patents) and IEC (http://www.iec.ch/tctools/patent_decl.htm) maintain on-
line data bases of patents relevant to their standards. Users are encouraged to consult the
data bases for the most up to date information concerning patents.
62439-5 © IEC:2010(E) – 7 –
INDUSTRIAL COMMUNICATION NETWORKS –
HIGH AVAILABILITY AUTOMATION NETWORKS –
Part 5: Beacon Redundancy Protocol (BRP)
1 Scope
The IEC 62439 series is applicable to high-availability automation networks based on the
ISO/IEC 8802-3 (IEEE 802.3) (Ethernet) technology.
This part of the IEC 62439 series specifies a redundancy protocol that is based on the
duplication of the network, the redundancy protocol being executed within the end nodes, as
opposed to a redundancy protocol built in the switches. Fast error detection is provided by
two beacon nodes, the switchover decision is taken in every node individually. The cross-
network connection capability enables single attached end nodes to be connected on either of
the two networks.
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 60050-191, International Electrotechnical Vocabulary – Chapter 191: Dependability and
quality of service
IEC 62439-1:2010, Industrial communication networks – High availability automation networks
– Part 1: General concepts and calculation methods
ISO/IEC/TR 8802-1, Information technology – Telecommunications and information exchange
between systems – Local and metropolitan area networks – Specific requirements – Part 1:
Overview of Local Area Network Standards (IEEE 802.1)
ISO/IEC 8802-3:2000, Information technology – Telecommunications and information
exchange between systems – Local and metropolitan area networks – Specific requirements –
Part 3: Carrier sense multiple access with collision detection (CSMA/CD) access method and
physical layer specifications
IEEE 802.1D, IEEE standard for local Local and metropolitan area networks Media Access
Control (MAC) Bridges
IEEE 802.1Q, IEEE standards for local and metropolitan area network. Virtual bridged local
area networks
3 Terms, definitions, abbreviations, acronyms, and conventions
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60050-191, as well
as in IEC 62439-1, apply.
– 8 – 62439-5 © IEC:2010(E)
3.2 Abbreviations and acronyms
For the purposes of this document, the abbreviations and acronyms given in IEC 62439-1,
apply, in addition to the following:
BRP Beacon Redundancy Protocol
DANB Double attached node implementing BRP
3.3 Conventions
This part of the IEC 62439 series follows the conventions defined in IEC 62439-1.
4 BRP overview
This clause specifies a protocol for an Ethernet network tolerant to all single point failures.
This protocol is called Beacon Redundancy Protocol or BRP. A network based on the BRP is
called a BRP network. The BRP network is based on switched ISO/IEC 8802-3 (IEEE 802.3)
(Ethernet) and ISO/IEC/TR 8802-1 (IEEE 802.1) technologies and redundant infrastructure. In
this network, the decision to switch between infrastructures is made individually in each end
node.
5 BRP principle of operation
5.1 General
Subclauses 5. 2 t o 5.4 are an explanation of overall actions performed by the BRP state
machine. If a difference in the interpretation occurs between these subclauses and the state
machines in 7, then the state machines take precedence.
5.2 Network topology
The BRP network topology can be described as two interconnected top switches, each
heading an underlying topology of star, line, or ring. Beacon end nodes shall be connected to
the top switches. Examples of star, linear and ring BRP networks are shown in Figure 1,
Figure 2 and Figure 3 respectively.
62439-5 © IEC:2010(E) – 9 –
aggregated links
switch
switch
network network
infrastructure A infrastructure B
beacon interswitch
switch beacon
switch
node lport
node
edge
ports
interswitch
end end
link end
interswitch
node node
node enendd
link
nonodede
switch
switch switch switch
edge
ports
leaf
end
link
node
leaf
link
leaf
link
end enenenddd enendd end end enendd end
node nononodedede nonodede node node nnodeode node
IEC 385/10
Figure 1 – BRP star network example
interswitch link interswitch link
switch switch
interswitch interswitch
port port
beacon
beacon
node
node
leaf link leaf link
end
node
end
end
node node
edge
edge
ports
ports
end end
end end
node node
node node
end end end
end
node node node
node
IEC 386/10
Figure 2 – BRP linear network example
switch switch
switch
switch switch
switch
– 10 – 62439-5 © IEC:2010(E)
interswitch link interswitch link
switch switch
interswitch interswitch
port port
beacon
beacon
node
node
leaf link leaf link
end
node
end
end
node
node
edge edge
ports ports
end end
end end
node node node node
end end end
end
node node node
node
IEC 387/10
Figure 3 – BRP ring network example
5.3 Network components
The BRP network is built from layer 2 switches compliant with IEEE 802.1D and
ISO/IEC 8802-3 (IEEE 802.3). No support of the BRP protocol in switches is required.
Figure 1 shows an example of a BRP star network in the 2-way redundancy mode. It uses two
sets of network infrastructure A and B (shown in two different colours). The number of levels
of switches and number of switches on each level are dependent only on application
requirements. Even with three levels of hierarchy it is possible to construct very large
networks. For example, a BRP star network built from switches with eight regular ports and
one uplink port can contain 500 nodes maximum. Two switches at the top level shall be
connected to each other with one or more links providing sufficient bandwidth. With link
aggregation capability, traffic is shared among bundle of links and failure of one link does not
bring the network down. With such an arrangement infrastructures A and B form a single
network.
Two types of end nodes can be connected to the BRP network: doubly attached and singly
attached. A doubly attached end node can function as a BRP end node or a BRP beacon end
node. A BRP beacon end node is a special case of a doubly attached end node that is
connected directly to the top switches. Though doubly attached BRP end nodes have two
network ports they use only one MAC address.
At any given point in time a BRP end node actively communicates through only one of its
ports, while blocking all transmit and receive traffic on its other port, with the exception of
received beacon messages and Failure_Notify messages. Fault tolerance is achieved in a
switch switch
switch
switch
switch switch
62439-5 © IEC:2010(E) – 11 –
distributed fashion by BRP end nodes switching between their ports from inactive to active
mode and vice versa.
As shown in Figure 1, Figure 2 and Figure 3, two beacon end nodes shall be connected to top
level switches. Beacon end nodes multi/broadcast a short beacon message on the network
periodically. Similarly to BRP end nodes, beacon end node at any given point in time actively
communicates through only one of its ports, while blocking all traffic on its other port, with the
exception of received Failure_Notify messages. Fault tolerance is achieved by beacon end
nodes switching between their ports from inactive to active mode and vice versa.
Singly attached end nodes may also be connected to BRP network but they do not support the
BRP protocol. A singly attached node can communicate with doubly attached nodes as well as
other singly attached nodes on the network.
Since switches are IEEE 802.1D compliant, they support the RSTP protocol. This eliminates
loop formation in BRP ring networks like in the one shown in Figure 3.
5.4 Rapid reconfiguration of network traffic
For fast reconfiguration, multicast control features in the switches shall be disabled. The
multicast traffic is therefore treated as the broadcast traffic.
Unicast packets are affected by switches learning and filtering features. After end node port
reconfiguration, switches have invalid knowledge. A switch implementing learning shall update
its database when a packet with a learned MAC address in the source field is received on a
different port from the learned port stored in the database.
When a BRP end node switches to the inactive port, its first action is to send a short multicast
message, called Learning_Update message, through its newly enabled port. As this message
propagates through the network, switches update their MAC address database resulting in
rapid reconfiguration of the unicast traffic. This message is of no interest to other end nodes
in the network and is dropped by them.
6 BRP stack and fault detection features
Figure 4 shows the BRP stack architecture. It is applicable to both BRP and beacon end
nodes.
upper layer protocols
UDP
TCP
non-TCP/IP
stack
IP
LRE
Management link redundancy entity
(Service)
IEEE 802.3 MAC IEEE 802.3 MAC
IEEE 802.3 PHY IEEE 802.3 PHY
Port A Port B
IEC 388/10
Figure 4 – BRP stack architecture
– 12 – 62439-5 © IEC:2010(E)
The BRP stack contains two identical ISO/IEC 8802-3 (IEEE 802.3) ports, identified here as
ports A and B, connected to the network. These ports interface with the MAC sub-layer
compliant with ISO/IEC 8802-3 (IEEE 802.3). Though there are two physical ports, a BRP end
node uses only a single MAC address.
The link redundancy entity continuously monitors the status of leaf links between both ports
and corresponding ports on the switches. When a failure of the leaf link between the end node
active port and the corresponding port on the switch is detected, the link redundancy entity
shall reconfigure end node ports, provided the inactive port was not in the fault mode as well.
After reconfiguration, all traffic flows through the newly activated port. Some messages may
be lost during the failure detection and reconfiguration process, and their recovery is
supported by upper layer protocols which also deal with messages lost due to other network
errors.
The link redundancy entity also monitors arrival of beacon messages on both ports. When a
beacon message fails to arrive at the active port for a configured timeout period, the port is
declared to be in the fault mode, and the link redundancy entity shall reconfigure end node
ports, provided the other port was not in the fault mode as well. After reconfiguration all traffic
starts flowing through newly activated port. Failure of beacon messages to arrive at inactive
ports shall also be detected.
If one of the top switches fails, then all BRP nodes connected directly to it, or to network
infrastructure below it, switch to the other network infrastructure. If, for example, the top
switch of the LAN A fails, then all BRP nodes connected to LAN A switch over to LAN B.
If the fault occurred on a beacon end node, the network continues to operate without any
problems, since the other beacon end node is active. The rate of beacon message arrival
decreases from approximately two messages per beacon timer interval to one.
It is possible for transmit path failures to occur in the opposite direction to the flow of beacon
messages. If such a fault manifests itself in the physical layer, it is detected by end nodes or
switches adjacent to the faulty link. This results in a BRP end node reconfiguring its ports
immediately or results in traffic being blocked on the affected link. The latter event leads to
loss of beacon messages at the downstream end nodes, so they reconfigure themselves at
expiry of the beacon timeout.
In a case when such failures are not detectable in the physical layer, the following mechanism
is employed by the BRP link redundancy entity to detect them. The fault detection method for
identifying all transmission failures shall be implemented using lists of communication nodes
including a receive timeout value for each transmitting end node of interest to the node. This
list may be communicated to the link redundancy entity manually or dynamically configured
utilizing LRE management entity.
When a frame from a transmitting end node of interest fails to arrive before expiry of the
associated Node_Receive timer, the receiving end node shall send a Failure_Notify message
to the transmitting end node and send a Path_Check_Request message to beacon end nodes.
Upon reception of a Failure_Notify message, the transmitting end node shall attempt to verify
the transmit path by sending the Path_Check_Request message to beacon end nodes. When
beacon end nodes receive these messages, they shall respond with Path_Check_Response
messages. When Path_Check_Request fails to elicit response, an end node shall place its
active port in faulted state and activate its inactive port, provided it is not in fault mode as well.
BRP beacon end nodes also behave in a similar way. When a frame from a transmitting end
node of interest fails to arrive before expiry of the associated Node_Receive timer, the
receiving beacon end node shall send a Failure_Notify message to the transmitting end node
and send a Path_Check_Request message to a designated set of end nodes. When beacon
end nodes receive Failure_Notify messages themselves, they shall verify their transmit path
by sending a Path_Check_Request message to a designated set of end nodes. Upon
receiving Path_Check_Request message, the designated end nodes shall respond with
62439-5 © IEC:2010(E) – 13 –
Path_Check_Response message. When Path_Check_Request fails to elicit response, a
beacon end node shall place its active port in faulted state and activate its inactive port,
provided it is not in fault mode as well.
When the faulted port is restored, it shall stay idle until a switchover is initiated or the
currently active port fails. When both ports are operational, the BRP end node shall
periodically switch its message activity from one port to the other. This switchover is
controlled by the Active_Port_Swap timer.
The LRE management entity is used to select an end node type (normal or beacon), configure
protocol parameters (for example, beacon timer) and obtain the end node port status (active,
failed, idle).
All detected failures shall be reported to the LRE management entity to trigger further
diagnosis and repair. Fault diagnostics services shall be provided by LRE management entity
or other accessible entities in the network.
7 BRP protocol specification
7.1 MAC addresses
BRP protocol shall use multicast address 01-15-4E-00-02-01. Both ports of a BRP node shall
have the same MAC address for active communication.
7.2 EtherType
The BRP protocol shall use assigned EtherType 0x80E1.
7.3 Fault detection mechanisms
The following fault detection mechanisms are used:
• Link fault detection
This mechanism covers physical layer failures in transmit and receive directions on a link
directly connected to the end node.
• Receive path fault detection
This is accomplished utilizing the beacon message transmission mechanism.
• Transmit path fault detection
This is accomplished utilizing Failure_Notify, Path_Check_Request, and
Path_Check_Response messages. The periodic switchover between active and inactive
ports ensures coverage of all transmit paths in the network.
7.4 End node state diagram
Figure 5.
The BRP end node state diagram is shown in
– 14 – 62439-5 © IEC:2010(E)
power on
INITIALIZATION
initialization completed
port A failed port B failed
IDLE
port B is
port A is
operational
operational
at least one
both ports
port is operational
failed
PORT_A_ACTIVE PORT_B_ACTIVE
FAULT
beacon
beacon
Active port swap timer expired
IEC 389/10
Figure 5 – BRP state diagram of end node
The BRP end node protocol state machine shall perform in accordance with the state
transition table presented in Table 2.
When the node is powered up and passed the initialization process (the
Initialization_Completed flag is set), it resets the protocol state machine and transitions to the
IDLE state.
Since Port_A_Failed and Port_B_Failed flags were initially set, the node immediately
transitions from the IDLE to the FAULT state.
If link A is active and a beacon message is received on this link, then the node transitions
from the FAULT state back to the IDLE. A Learning_Update message is generated on this port
and the node transitions from the IDLE to the PORT_A_ACTIVE state.
The node tests port B simultaneously with port A using the procedure described above. If both
ports are operational, either one can be selected as the default.
Periodic reception of beacon messages (Beacon_A_Received is set) keeps the node in the
PORT_A_ACTIVE state and trigger reset of the No_Beacon_A timer.
If, when in the PORT_A_ACTIVE state, link A becomes inactive (Link_A_Active is reset) or no
beacon messages were received for a given time period (No_Beacon_A timer expired and
Beacon_A_Received is reset), the node sets the Port_A_Failed flag and transitions to the
IDLE state where it attempts to switch to port B.
Operation of port B is identical to operation of port A.
62439-5 © IEC:2010(E) – 15 –
If a Node_Receive timer expires, the receiving node sends a Failure_Notify message to the
associated transmitting end node and sends Path_Check_Request message on its active port
to beacon end nodes. When the transmitting end node receives the Failure_Notify message, it
attempts to verify transmission path on its active port by sending a Path_Check_Request
message on this port to beacon end nodes. When beacon nodes receive these messages,
they issue Path_Check_Response messages addressed to the requesting node.
When Path_Check_Request fails to elicit response (Path_A_Check/Path_B_Check timer
expired), the node sets the Path_A_Failed/Path_B_Failed flag and Port_A_Failed/
Port_B_Failed flag, and transitions to the IDLE state where it attempts to switch to port B/A.
If both ports failed, then the node transitions from the IDLE to the FAULT state and stays
there until one of the ports becomes operational. In FAULT state, a node continuously
monitors link status (Link_A_Active/Link_B_Active flags) and beacon arrival status
(Beacon_A_Received/Beacon_B_Received flags). If Path_A_Failed and/or Path_B_Failed
flags were set, the node also sends Path_Check_Request and monitors arrival of
Path_Check_Response message for corresponding ports. When one of the ports becomes
operational (Port_A_Failed/Port_B_Failed is reset), the node transitions back to the IDLE
state and then to PORT_A_ACTIVE/PORT_B_ACTIVE as appropriate.
When a node receives a Path_Check_Request message in PORT_A_ACTIVE or
PORT_B_ACTIVE states, it responds with the Path_Check_Response message and stays in
current state.
When in PORT_A_ACTIVE/PORT_B_ACTIVE state and the Active_Port_Swap timer expires,
the node transitions to PORT_B_ACTIVE/PORT_A_ACTIVE state provided
PORT_B_FAILED/PORT_A_FAILED is not set.
The No_Beacon timer period is a configuration parameter selected for a specific system. The
mandatory default value of the beacon period is 450 µs, resulting in the default value of the
No_Beacon period of 950 µs. The timeout period is chosen in such a way that at least two
beacon messages from each beacon end node have to be lost before fault is declared on a
port.
A BRP compliant end node shall be able to receive beacon messages over both of its ports
sent from both beacon end nodes at the mandatory default value of the beacon period.
The Path_A_Check and Path_B_Check timer periods are configuration parameters selected
for a specific system. The mandatory default value is 2 ms.
The Active_Port_Swap timer period is a configuration parameter selected for a specific
system. The mandatory default value is 1 h.
Table 1 specifies the flags used in the BRP end node state machine.
– 16 – 62439-5 © IEC:2010(E)
Table 1 – BRP end node flags
Name Description Data Type
Initialization_Completed Used to indicate initialization completed successfully BOOL
Link_A_Active Used to indicate physical layer link status of port A BOOL
Beacon_A_Received Used to indicate beacon message was received on port A BOOL
Path_A_Failed Used to indicate if Path_Check_Response message was BOOL
received for Path_Check_Request message on port A
Link_B_Active Used to indicate physical layer link status of port B BOOL
Beacon_B_Received Used to indicate beacon message was received on port B BOOL
Path_B_Failed Used to indicate if Path_Check_Response message was BOOL
received for Path_Check_Request message on port B
Path_A_Request Used to indicate if Path_Check_Request message was BOOL
sent on port A
Path_B_Request Used to indicate if Path_Check_Request message was BOOL
sent on port B
Port_A_Failed Used to indicate if port A has failed BOOL
Port_B_Failed Used to indicate if port B has failed BOOL
NOTE In this table, BOOL means Boolean.
Table 2 specifies the BRP end node state transition table.
62439-5 © IEC:2010(E) – 17 –
Table 2 – BRP end node state transition table
State Current state Event Next state
number /Condition
=>Action
1 INITIALIZATION Initialization is completed IDLE
=>
Set Initialization_Completed
Reset Link_A_Active
Reset Beacon_A_Received
Stop No_Beacon_A timer
Reset Path_A_Failed
Stop Path_A_Check timer, reset Path_A_Request
Reset Link_B_Active
Reset Beacon_B_Received
Stop No_Beacon_B timer
Reset Path_B_Failed
Stop Path_B_Check timer
Reset Path_B_Request
Set Port_A_Failed
Set Port_B_Failed
Stop Node_Receive timers
Stop Active_Port_Swap timer
2 IDLE, FAULT, Port A link pass status STAY IN CURRENT
PORT_A_ACTIVE, STATE
=>
PORT_B_ACTIVE
Set Link_A_Active
3 IDLE, FAULT, Port A link fail status STAY IN CURRENT
PORT_A_ACTIVE, STATE
=>
PORT_B_ACTIVE
Reset Link_A_Active
4 IDLE, FAULT, Port B link pass status STAY IN CURRENT
PORT_A_ACTIVE, STATE
=>
PORT_B_ACTIVE
Set Link_B_Active
5 IDLE, FAULT, Port B link fail status STAY IN CURRENT
PORT_A_ACTIVE, STATE
=>
PORT_B_ACTIVE
Reset Link_B_Active
6 IDLE, FAULT, Beacon message received on port A STAY IN CURRENT
PORT_A_ACTIVE, STATE
=>
PORT_B_ACTIVE
Set Beacon_A_Received
Start No_Beacon_A timer
7 IDLE, FAULT, No_Beacon_A timer expired STAY IN CURRENT
PORT_A_ACTIVE, STATE
=>
PORT_B_ACTIVE
Reset Beacon_A_Received
8 Beacon message received on port B
IDLE, FAULT, STAY IN CURRENT
PORT_A_ACTIVE, STATE
=>
PORT_B_ACTIVE
Set Beacon_B_Received
Start No_Beacon_B timer
9 IDLE, FAULT, No_Beacon_B timer expired STAY IN CURRENT
PORT_A_ACTIVE, STATE
=>
– 18 – 62439-5 © IEC:2010(E)
State Current state Event Next state
number /Condition
=>Action
PORT_B_ACTIVE
Reset Beacon_B_Received
10 PORT_A_ACTIVE Failure_Notify message is received PORT_A_ACTIVE
=>
Send Path_Check_Request message on Port A
Set Path_A_Request
Start Path_A_Check timer
11 PORT_B_ACTIVE Failure_Notify message is received PORT_B_ACTIVE
=>
Send Path_Check_Request message on port B
Set Path_B_Request
Start Path_B_Check timer
12 PORT_A_ACTIVE, Path_A_Check timer expired STAY IN CURRENT
FAULT STATE
=>
Set Path_A_Failed
Reset Path_A_Request
13 PORT_B_ACTIVE, Path_B_Check timer expired STAY IN CURRENT
FAULT STATE
=>
Set Path_B_Failed
Reset Path_A_Request
14 PORT_A_ACTIVE, Path_Check_Response message is received on port A STAY IN CURRENT
FAULT STATE
=>
Stop Path_A_Check timer
Reset Path_A_Failed
Reset Path_A_Request
15 PORT_B_ACTIVE, Path_Check_Response message is received on port B STAY IN CURRENT
FAULT STATE
=>
Stop Path_B_Check timer
Reset Path_B_Failed
Reset Path_B_Request
16 Link_A_Active is set
IDLE, FAULT, STAY IN CURRENT
PORT_A_ACTIVE, AND STATE
PORT_B_ACTIVE Beacon_A_Received is set
AND
Path_A_Failed is reset
=>
Reset Port_A_Failed
17 IDLE, FAULT, Link_A_Active is reset STAY IN CURRENT
PORT_A_ACTIVE, OR STATE
Beacon_A_Received is reset
PORT_B_ACTIVE
OR
Path_A_Failed is set
=>
Set Port_A_Failed
18 IDLE Port_A_Failed is reset PORT_A_ACTIVE
=>
Send Learning_Update message on port A
Start Node_Receive timers
62439-5 © IEC:2010(E) – 19 –
State Current state Event Next state
number /Condition
=>Action
Start Active_Port_Swap timer
19 PORT_A_ACTIVE Port_A_Failed is set IDLE
=>
Stop Path_A_Check timer
Reset Path_A_Request
Stop Node_Receive timers
Stop Active_Port_Swap timer
20 IDLE, FAULT, Link_B_Active is set STAY IN CURRENT
PORT_A_ACTIVE, AND STATE
PORT_B_ACTIVE Beacon_B_Received is set
AND
Path_B_Failed is reset
=>
Reset Port_B_Failed
21 IDLE, FAULT, Link_B_Active is reset STAY IN CURRENT
PORT_A_ACTIVE, OR STATE
PORT_B_ACTIVE Beacon_B_Received is reset
OR
Path_B_Failed is set
=>
Set Port_B_Failed
22 IDLE Port_B_Failed is reset PORT_B_ACTIVE
=>
Send Learning_Update message on port B
Start Node_Receive timers
Start Active_Port_Swap timer
23 PORT_B_ACTIVE Port_B_Failed is set IDLE
=>
Stop Path_B_Check timer
Reset Path_B_Request
Stop Node_Receive time
...
IEC 62439-5 ®
Edition 1.0 2010-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Industrial communication networks – High availability automation networks –
Part 5: Beacon Redundancy Protocol (BRP)
Réseaux industriels de communication – Réseaux d’automatisme à haute
disponibilité –
Partie 5: Protocole de redondance à balise (BRP)
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IEC 62439-5 ®
Edition 1.0 2010-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Industrial communication networks – High availability automation networks –
Part 5: Beacon Redundancy Protocol (BRP)
Réseaux industriels de communication – Réseaux d’automatisme à haute
disponibilité –
Partie 5: Protocole de redondance à balise (BRP)
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
X
CODE PRIX
ICS 25.040; 35.040 ISBN 978-2-8322-0060-5
– 2 – 62439-5 IEC:2010
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms, definitions, abbreviations, acronyms, and conventions . 7
3.1 Terms and definitions . 7
3.2 Abbreviations and acronyms . 8
3.3 Conventions . 8
4 BRP overview . 8
5 BRP principle of operation . 8
5.1 General . 8
5.2 Network topology. 8
5.3 Network components . 10
5.4 Rapid reconfiguration of network traffic . 11
6 BRP stack and fault detection features . 11
7 BRP protocol specification . 13
7.1 MAC addresses . 13
7.2 EtherType . 13
7.3 Fault detection mechanisms . 13
7.4 End node state diagram . 13
7.5 Beacon end node state diagram . 21
8 BRP message structure . 27
8.1 General . 27
8.2 ISO/IEC 8802-3 (IEEE 802.3) tagged frame header . 28
8.3 Beacon message . 28
8.4 Learning_Update message . 28
8.5 Failure_Notify message . 29
8.6 Path_Check_Request message . 29
8.7 Path_Check_Response message . 29
9 BRP fault recovery time . 29
10 BRP service definition . 30
10.1 Supported services . 30
10.2 Common service parameters . 30
10.3 Set_Node_Parameters service . 31
10.4 Get_Node_Parameters service . 33
10.5 Add_Node_Receive_Parameters service . 35
10.6 Remove_Node_Receive_Parameters service . 37
10.7 Get_Node_Status service . 38
11 BRP Management Information Base (MIB) . 39
Bibliography . 41
Figure 1 – BRP star network example . 9
Figure 2 – BRP linear network example . 9
Figure 3 – BRP ring network example . 10
62439-5 IEC:2010 – 3 –
Figure 4 – BRP stack architecture . 11
Figure 5 – BRP state diagram of end node . 14
Figure 6 – BRP state diagram for beacon end node . 21
Table 1 – BRP end node flags . 16
Table 2 – BRP end node state transition table . 17
Table 3 – BRP beacon end node flags . 23
Table 4 – BRP beacon end node state transition table . 24
Table 5 – BRP common header with ISO/IEC 8802-3 (IEEE 802.3) tagged frame format. 28
Table 6 – BRP beacon message format . 28
Table 7 – BRP Learning_Update message format . 28
Table 8 – BRP Failure_Notify message format . 29
Table 9 – BRP Path_Check_Request message format . 29
Table 10 – BRP Path_Check_Response message format . 29
Table 11 – BRP Set_Node_Parameters service parameters . 32
Table 12 – BRP Get_Node_Parameters service parameters . 34
Table 13 – BRP Add_Node_Receive_Parameters service parameters . 36
Table 14 – BRP Remove_Node_Receive_Parameters service parameters . 37
Table 15 – BRP Get_Node_Status service parameters . 38
– 4 – 62439-5 IEC:2010
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
INDUSTRIAL COMMUNICATION NETWORKS –
HIGH AVAILABILITY AUTOMATION NETWORKS –
Part 5: Beacon Redundancy Protocol (BRP)
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
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2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
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3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
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5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
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6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
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Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
International Standard IEC 62439-5 has been prepared by subcommittee 65C: Industrial
Networks, of IEC technical committee 65: Industrial-process measurement, control and
automation.
This standard cancels and replaces IEC 62439 published in 2008. This first edition constitutes
a technical revision.
This edition includes the following significant technical changes with respect to IEC 62439
(2008):
– adding a calculation method for RSTP (rapid spanning tree protocol, IEEE 802.1Q),
– adding two new redundancy protocols: HSR (High-availability Seamless Redundancy)
and DRP (Distributed Redundancy Protocol),
– moving former Clauses 1 to 4 (introduction, definitions, general aspects) and the
Annexes (taxonomy, availability calculation) to IEC 62439-1, which serves now as a
base for the other documents,
– moving Clause 5 (MRP) to IEC 62439-2 with minor editorial changes,
62439-5 IEC:2010 – 5 –
– moving Clause 6 (PRP) was to IEC 62439-3 with minor editorial changes,
– moving Clause 7 (CRP) was to IEC 62439-4 with minor editorial changes, and
– moving Clause 8 (BRP) was to IEC 62439-5 with minor editorial changes,
– adding a method to calculate the maximum recovery time of RSTP in a restricted
configuration (ring) to IEC 62439-1 as Clause 8,
– adding specifications of the HSR (High-availability Seamless Redundancy) protocol,
which shares the principles of PRP to IEC 62439-3 as Clause 5, and
– introducing the DRP protocol as IEC 62439-6.
This bilingual version (2012-04) corresponds to the English version, published in 2010-02.
The text of this standard is based on the following documents:
FDIS Report on voting
65C/583/FDIS 65C/589/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
The French version of this standard has not been voted upon.
This International Standard is to be read in conjunction with IEC 62439-1:2010, Industrial
communication networks – High availability automation networks – Part 1: General concepts
and calculation methods.
A list of the IEC 62439 series can be found, under the general title Industrial communication
networks – High availability automation networks, on the IEC website.
This publication has been drafted in accordance with ISO/IEC Directives, Part 2.
The committee has decided that the contents of this amendment and the base publication will
remain unchanged until the stability date indicated on the IEC web site under
"http://webstore.iec.ch" in the data related to the specific publication. At this date, the
publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The “colour inside” logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct understanding
of its contents. Users should therefore print this publication using a colour printer.
– 6 – 62439-5 IEC:2010
INTRODUCTION
The IEC 62439 series specifies relevant principles for high availability networks that meet the
requirements for industrial automation networks.
In the fault-free state of the network, the protocols of the IEC 62439 series provide
ISO/IEC 8802-3 (IEEE 802.3) compatible, reliable data communication, and preserve
determinism of real-time data communication. In cases of fault, removal, and insertion of a
component, they provide deterministic recovery times.
These protocols retain fully the typical Ethernet communication capabilities as used in the
office world, so that the software involved remains applicable.
The market is in need of several network solutions, each with different performance
characteristics and functional capabilities, matching diverse application requirements. These
solutions support different redundancy topologies and mechanisms which are introduced in
IEC 62439-1 and specified in the other Parts of the IEC 62439 series. IEC 62439-1 also
distinguishes between the different solutions, giving guidance to the user.
The IEC 62439 series follows the general structure and terms of IEC 61158 series.
The International Electrotechnical Commission (IEC) draws attention to the fact that it is
claimed that compliance with this document may involve the use of a patent concerning fault-
tolerant Ethernet provided through the use of special interfaces providing duplicate ports that
may be alternatively enabled with the same network address. Switching between the ports
corrects for single faults in a two-way redundant system. This is given in Clauses 5 and 6.
IEC takes no position concerning the evidence, validity and scope of this patent right.
The holder of this patent right has assured the IEC that he/she is willing to negotiate licences
either free of charge or under reasonable and non-discriminatory terms and conditions with
applicants throughout the world. In this respect, the statement of the holder of this patent right
is registered with IEC. Information may be obtained from:
Rockwell Automation Technologies
1 Allen-Bradley Drive
Mayfield Heights
Ohio
USA
Attention is drawn to the possibility that some of the elements of this document may be the
subject of patent rights other than those identified above. IEC shall not be held responsible for
identifying any or all such patent rights.
ISO (www.iso.org/patents) and IEC (http://www.iec.ch/tctools/patent_decl.htm) maintain on-
line data bases of patents relevant to their standards. Users are encouraged to consult the
data bases for the most up to date information concerning patents.
62439-5 IEC:2010 – 7 –
INDUSTRIAL COMMUNICATION NETWORKS –
HIGH AVAILABILITY AUTOMATION NETWORKS –
Part 5: Beacon Redundancy Protocol (BRP)
1 Scope
The IEC 62439 series is applicable to high-availability automation networks based on the
ISO/IEC 8802-3 (IEEE 802.3) (Ethernet) technology.
This part of the IEC 62439 series specifies a redundancy protocol that is based on the
duplication of the network, the redundancy protocol being executed within the end nodes, as
opposed to a redundancy protocol built in the switches. Fast error detection is provided by
two beacon nodes, the switchover decision is taken in every node individually. The cross-
network connection capability enables single attached end nodes to be connected on either of
the two networks.
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 60050-191, International Electrotechnical Vocabulary – Chapter 191: Dependability and
quality of service
IEC 62439-1:2010, Industrial communication networks – High availability automation networks
– Part 1: General concepts and calculation methods
ISO/IEC/TR 8802-1, Information technology – Telecommunications and information exchange
between systems – Local and metropolitan area networks – Specific requirements – Part 1:
Overview of Local Area Network Standards (IEEE 802.1)
ISO/IEC 8802-3:2000, Information technology – Telecommunications and information
exchange between systems – Local and metropolitan area networks – Specific requirements –
Part 3: Carrier sense multiple access with collision detection (CSMA/CD) access method and
physical layer specifications
IEEE 802.1D, IEEE standards for local and metropolitan area networks: Media Access Control
(MAC) Bridges
IEEE 802.1Q, IEEE standards for local and metropolitan area networks: Virtual bridged local
area networks
3 Terms, definitions, abbreviations, acronyms, and conventions
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60050-191, as well
as in IEC 62439-1, apply.
– 8 – 62439-5 IEC:2010
3.2 Abbreviations and acronyms
For the purposes of this document, the abbreviations and acronyms given in IEC 62439-1,
apply, in addition to the following:
BRP Beacon Redundancy Protocol
DANB double attached node implementing BRP
3.3 Conventions
This part of the IEC 62439 series follows the conventions defined in IEC 62439-1.
4 BRP overview
This clause specifies a protocol for an Ethernet network tolerant to all single point failures.
This protocol is called Beacon Redundancy Protocol or BRP. A network based on the BRP is
called a BRP network. The BRP network is based on switched ISO/IEC 8802-3 (IEEE 802.3)
(Ethernet) and ISO/IEC/TR 8802-1 (IEEE 802.1) technologies and redundant infrastructure. In
this network, the decision to switch between infrastructures is made individually in each end
node.
5 BRP principle of operation
5.1 General
Subclauses 5.2 to 5.4 are an explanation of overall actions performed by the BRP state
machine. If a difference in the interpretation occurs between these subclauses and the state
machines in Clause 7, then the state machines take precedence.
5.2 Network topology
The BRP network topology can be described as two interconnected top switches, each
heading an underlying topology of star, line, or ring. Beacon end nodes shall be connected to
the top switches. Examples of star, linear and ring BRP networks are shown in Figure 1,
Figure 2 and Figure 3 respectively.
62439-5 IEC:2010 – 9 –
aggregated links
switch
switch
network network
infrastructure A infrastructure B
beacon interswitch
switch beacon
switch
lport
node node
edge
ports
interswitch
end end
end
link interswitch
node node
node endend
link
nodenode
switch
switch switch switch
edge
ports
leaf
end
link node
leaf
link
leaf
link
end endendend endend end end endend end
node nodenodenode nodenode node node nodenode node
IEC 385/10
Figure 1 – BRP star network example
interswitch link interswitch link
switch
switch
interswitch interswitch
port port
beacon
beacon
node
node
leaf link leaf link
end
node
end end
node node
edge
edge
ports
ports
end end
end end
node node node node
end end end
end
node node node node
IEC 386/10
Figure 2 – BRP linear network example
switch switch
switch
switch switch
switch
– 10 – 62439-5 IEC:2010
interswitch link interswitch link
switch switch
interswitch interswitch
port port
beacon
beacon
node
node
leaf link leaf link
end
node
end
end
node
node
edge edge
ports ports
end end
end end
node node
node node
end end end
end
node node node
node
IEC 387/10
Figure 3 – BRP ring network example
5.3 Network components
The BRP network is built from layer 2 switches compliant with IEEE 802.1D and
ISO/IEC 8802-3 (IEEE 802.3). No support of the BRP protocol in switches is required.
Figure 1 shows an example of a BRP star network in the 2-way redundancy mode. It uses two
sets of network infrastructure A and B (shown in two different colours). The number of levels
of switches and number of switches on each level are dependent only on application
requirements. Even with three levels of hierarchy it is possible to construct very large
networks. For example, a BRP star network built from switches with eight regular ports and
one uplink port can contain 500 nodes maximum. Two switches at the top level shall be
connected to each other with one or more links providing sufficient bandwidth. With link
aggregation capability, traffic is shared among bundle of links and failure of one link does not
bring the network down. With such an arrangement infrastructures A and B form a single
network.
Two types of end nodes can be connected to the BRP network: doubly attached and singly
attached. A doubly attached end node can function as a BRP end node or a BRP beacon end
node. A BRP beacon end node is a special case of a doubly attached end node that is
connected directly to the top switches. Though doubly attached BRP end nodes have two
network ports they use only one MAC address.
At any given point in time a BRP end node actively communicates through only one of its
ports, while blocking all transmit and receive traffic on its other port, with the exception of
received beacon messages and Failure_Notify messages. Fault tolerance is achieved in a
switch switch
switch
switch
switch switch
62439-5 IEC:2010 – 11 –
distributed fashion by BRP end nodes switching between their ports from inactive to active
mode and vice versa.
As shown in Figure 1, Figure 2 and Figure 3, two beacon end nodes shall be connected to top
level switches. Beacon end nodes multi/broadcast a short beacon message on the network
periodically. Similarly to BRP end nodes, beacon end node at any given point in time actively
communicates through only one of its ports, while blocking all traffic on its other port, with the
exception of received Failure_Notify messages. Fault tolerance is achieved by beacon end
nodes switching between their ports from inactive to active mode and vice versa.
Singly attached end nodes may also be connected to BRP network but they do not support the
BRP protocol. A singly attached node can communicate with doubly attached nodes as well as
other singly attached nodes on the network.
Since switches are IEEE 802.1D compliant, they support the RSTP protocol. This eliminates
loop formation in BRP ring networks like in the one shown in Figure 3.
5.4 Rapid reconfiguration of network traffic
For fast reconfiguration, multicast control features in the switches shall be disabled. The
multicast traffic is therefore treated as the broadcast traffic.
Unicast packets are affected by switches learning and filtering features. After end node port
reconfiguration, switches have invalid knowledge. A switch implementing learning shall update
its database when a packet with a learned MAC address in the source field is received on a
different port from the learned port stored in the database.
When a BRP end node switches to the inactive port, its first action is to send a short multicast
message, called Learning_Update message, through its newly enabled port. As this message
propagates through the network, switches update their MAC address database resulting in
rapid reconfiguration of the unicast traffic. This message is of no interest to other end nodes
in the network and is dropped by them.
6 BRP stack and fault detection features
Figure 4 shows the BRP stack architecture. It is applicable to both BRP and beacon end
nodes.
upper layer protocols
UDP
TCP
non-TCP/IP
stack
IP
LRE
Management link redundancy entity
(Service)
IEEE 802.3 MAC IEEE 802.3 MAC
IEEE 802.3 PHY IEEE 802.3 PHY
Port A Port B
IEC 388/10
Figure 4 – BRP stack architecture
– 12 – 62439-5 IEC:2010
The BRP stack contains two identical ISO/IEC 8802-3 (IEEE 802.3) ports, identified here as
ports A and B, connected to the network. These ports interface with the MAC sub-layer
compliant with ISO/IEC 8802-3 (IEEE 802.3). Though there are two physical ports, a BRP end
node uses only a single MAC address.
The link redundancy entity continuously monitors the status of leaf links between both ports
and corresponding ports on the switches. When a failure of the leaf link between the end node
active port and the corresponding port on the switch is detected, the link redundancy entity
shall reconfigure end node ports, provided the inactive port was not in the fault mode as well.
After reconfiguration, all traffic flows through the newly activated port. Some messages may
be lost during the failure detection and reconfiguration process, and their recovery is
supported by upper layer protocols which also deal with messages lost due to other network
errors.
The link redundancy entity also monitors arrival of beacon messages on both ports. When a
beacon message fails to arrive at the active port for a configured timeout period, the port is
declared to be in the fault mode, and the link redundancy entity shall reconfigure end node
ports, provided the other port was not in the fault mode as well. After reconfiguration all traffic
starts flowing through newly activated port. Failure of beacon messages to arrive at inactive
ports shall also be detected.
If one of the top switches fails, then all BRP nodes connected directly to it, or to network
infrastructure below it, switch to the other network infrastructure. If, for example, the top
switch of the LAN A fails, then all BRP nodes connected to LAN A switch over to LAN B.
If the fault occurred on a beacon end node, the network continues to operate without any
problems, since the other beacon end node is active. The rate of beacon message arrival
decreases from approximately two messages per beacon timer interval to one.
It is possible for transmit path failures to occur in the opposite direction to the flow of beacon
messages. If such a fault manifests itself in the physical layer, it is detected by end nodes or
switches adjacent to the faulty link. This results in a BRP end node reconfiguring its ports
immediately or results in traffic being blocked on the affected link. The latter event leads to
loss of beacon messages at the downstream end nodes, so they reconfigure themselves at
expiry of the beacon timeout.
In a case when such failures are not detectable in the physical layer, the following mechanism
is employed by the BRP link redundancy entity to detect them. The fault detection method for
identifying all transmission failures shall be implemented using lists of communication nodes
including a receive timeout value for each transmitting end node of interest to the node. This
list may be communicated to the link redundancy entity manually or dynamically configured
utilizing LRE management entity.
When a frame from a transmitting end node of interest fails to arrive before expiry of the
associated Node_Receive timer, the receiving end node shall send a Failure_Notify message
to the transmitting end node and send a Path_Check_Request message to beacon end nodes.
Upon reception of a Failure_Notify message, the transmitting end node shall attempt to verify
the transmit path by sending the Path_Check_Request message to beacon end nodes. When
beacon end nodes receive these messages, they shall respond with Path_Check_Response
messages. When Path_Check_Request fails to elicit response, an end node shall place its
active port in faulted state and activate its inactive port, provided it is not in fault mode as well.
BRP beacon end nodes also behave in a similar way. When a frame from a transmitting end
node of interest fails to arrive before expiry of the associated Node_Receive timer, the
receiving beacon end node shall send a Failure_Notify message to the transmitting end node
and send a Path_Check_Request message to a designated set of end nodes. When beacon
end nodes receive Failure_Notify messages themselves, they shall verify their transmit path
by sending a Path_Check_Request message to a designated set of end nodes. Upon
receiving Path_Check_Request message, the designated end nodes shall respond with
62439-5 IEC:2010 – 13 –
Path_Check_Response message. When Path_Check_Request fails to elicit response, a
beacon end node shall place its active port in faulted state and activate its inactive port,
provided it is not in fault mode as well.
When the faulted port is restored, it shall stay idle until a switchover is initiated or the
currently active port fails. When both ports are operational, the BRP end node shall
periodically switch its message activity from one port to the other. This switchover is
controlled by the Active_Port_Swap timer.
The LRE management entity is used to select an end node type (normal or beacon), configure
protocol parameters (for example, beacon timer) and obtain the end node port status (active,
failed, idle).
All detected failures shall be reported to the LRE management entity to trigger further
diagnosis and repair. Fault diagnostics services shall be provided by LRE management entity
or other accessible entities in the network.
7 BRP protocol specification
7.1 MAC addresses
BRP protocol shall use multicast address 01-15-4E-00-02-01. Both ports of a BRP node shall
have the same MAC address for active communication.
7.2 EtherType
The BRP protocol shall use assigned EtherType 0x80E1.
7.3 Fault detection mechanisms
The following fault detection mechanisms are used:
• Link fault detection
This mechanism covers physical layer failures in transmit and receive directions on a link
directly connected to the end node.
• Receive path fault detection
This is accomplished utilizing the beacon message transmission mechanism.
• Transmit path fault detection
This is accomplished utilizing Failure_Notify, Path_Check_Request, and
Path_Check_Response messages. The periodic switchover between active and inactive
ports ensures coverage of all transmit paths in the network.
7.4 End node state diagram
The BRP end node state diagram is shown in Figure 5.
– 14 – 62439-5 IEC:2010
power on
INITIALIZATION
initialization completed
port A failed port B failed
IDLE
port B is
port A is
operational
operational
at least one
both ports
port is operational
failed
PORT_A_ACTIVE PORT_B_ACTIVE
FAULT
beacon
beacon
Active port swap timer expired
IEC 389/10
Figure 5 – BRP state diagram of end node
The BRP end node protocol state machine shall perform in accordance with the state
transition table presented in Table 2.
When the node is powered up and passed the initialization process (the
Initialization_Completed flag is set), it resets the protocol state machine and transitions to the
IDLE state.
Since Port_A_Failed and Port_B_Failed flags were initially set, the node immediately
transitions from the IDLE to the FAULT state.
If link A is active and a beacon message is received on this link, then the node transitions
from the FAULT state back to the IDLE. A Learning_Update message is generated on this port
and the node transitions from the IDLE to the PORT_A_ACTIVE state.
The node tests port B simultaneously with port A using the procedure described above. If both
ports are operational, either one can be selected as the default.
Periodic reception of beacon messages (Beacon_A_Received is set) keeps the node in the
PORT_A_ACTIVE state and trigger reset of the No_Beacon_A timer.
If, when in the PORT_A_ACTIVE state, link A becomes inactive (Link_A_Active is reset) or no
beacon messages were received for a given time period (No_Beacon_A timer expired and
Beacon_A_Received is reset), the node sets the Port_A_Failed flag and transitions to the
IDLE state where it attempts to switch to port B.
Operation of port B is identical to operation of port A.
62439-5 IEC:2010 – 15 –
If a Node_Receive timer expires, the receiving node sends a Failure_Notify message to the
associated transmitting end node and sends Path_Check_Request message on its active port
to beacon end nodes. When the transmitting end node receives the Failure_Notify message, it
attempts to verify transmission path on its active port by sending a Path_Check_Request
message on this port to beacon end nodes. When beacon nodes receive these messages,
they issue Path_Check_Response messages addressed to the requesting node.
When Path_Check_Request fails to elicit response (Path_A_Check/Path_B_Check timer
expired), the node sets the Path_A_Failed/Path_B_Failed flag and Port_A_Failed/
Port_B_Failed flag, and transitions to the IDLE state where it attempts to switch to port B/A.
If both ports failed, then the node transitions from the IDLE to the FAULT state and stays
there until one of the ports becomes operational. In FAULT state, a node continuously
monitors link status (Link_A_Active/Link_B_Active flags) and beacon arrival status
(Beacon_A_Received/Beacon_B_Received flags). If Path_A_Failed and/or Path_B_Failed
flags were set, the node also sends Path_Check_Request and monitors arrival of
Path_Check_Response message for corresponding ports. When one of the ports becomes
operational (Port_A_Failed/Port_B_Failed is reset), the node transitions back to the IDLE
state and then to PORT_A_ACTIVE/PORT_B_ACTIVE as appropriate.
When a node receives a Path_Check_Request message in PORT_A_ACTIVE or
PORT_B_ACTIVE states, it responds with the Path_Check_Response message and stays in
current state.
When in PORT_A_ACTIVE/PORT_B_ACTIVE state and the Active_Port_Swap timer expires,
the node transitions to PORT_B_ACTIVE/PORT_A_ACTIVE state provided
PORT_B_FAILED/PORT_A_FAILED is not set.
The No_Beacon timer period is a configuration parameter selected for a specific system. The
mandatory default value of the beacon period is 450 µs, resulting in the default value of the
No_Beacon period of 950 µs. The timeout period is chosen in such a way that at least two
beacon messages from each beacon end node have to be lost before fault is declared on a
port.
A BRP compliant end node shall be able to receive beacon messages over both of its ports
sent from both beacon end nodes at the mandatory default value of the beacon period.
The Path_A_Check and Path_B_Check timer periods are configuration parameters selected
for a specific system. The mandatory default value is 2 ms.
The Active_Port_Swap timer period is a configuration parameter selected for a specific
system. The mandatory default value is 1 h.
Table 1 specifies the flags used in the BRP end node state machine.
– 16 – 62439-5 IEC:2010
Table 1 – BRP end node flags
Name Description Data Type
Initialization_Completed Used to indicate initialization completed successfully BOOL
Link_A_Active Used to indicate physical layer link status of port A BOOL
Beacon_A_Received Used to indicate beacon message was received on port A BOOL
Path_A_Failed Used to indicate if Path_Check_Response message was BOOL
received for Path_Check_Request message on port A
Link_B_Active Used to indicate physical layer link status of port B BOOL
Beacon_B_Received Used to indicate beacon message was received on port B BOOL
Path_B_Failed Used to indicate if Path_Check_Response message was BOOL
received for Path_Check_Request message on port B
Path_A_Request Used to indicate if Path_Check_Request message was BOOL
sent on port A
Path_B_Request Used to indicate if Path_Check_Request message was BOOL
sent on port B
Port_A_Failed Used to indicate if port A has failed BOOL
Port_B_Failed Used to indicate if port B has failed BOOL
NOTE In this table, BOOL means Boolean.
Table 2 specifies the BRP end node state transition table.
62439-5 IEC:2010 – 17 –
Table 2 – BRP end node state transition table
State Current state Event Next state
number /Condition
=>Action
1 Initialization is completed
INITIALIZATION IDLE
=>
Set Initialization_Completed
Reset Link_A_Active
Reset Beacon_A_Received
Stop No_Beacon_A timer
Reset Path_A_Failed
Stop Path_A_Check timer, reset Path_A_Request
Reset Link_B_Active
Reset Beacon_B_Received
Stop No_Beacon_B timer
Reset Path_B_Failed
Stop Path_B_Check timer
Reset Path_B_Request
Set Port_A_Failed
Set Port_B_Failed
Stop Node_Receive timers
Stop Active_Port_Swap timer
2 IDLE, FAULT, Port A link pass status STAY IN CURRENT
PORT_A_ACTIVE, STATE
=>
PORT_B_ACTIVE
Set Link_A_Active
3 IDLE, FAULT, Port A link fail status STAY IN CURRENT
PORT_A_ACTIVE, STATE
=>
PORT_B_ACTIVE
Reset Link_A_Active
4 IDLE, FAULT, Port B link pass status STAY IN CURRENT
PORT_A_ACTIVE, STATE
=>
PORT_B_ACTIVE
Set Link_B_Active
5 IDLE, FAULT, Port B link fail status STAY IN CURRENT
PORT_A_ACTIVE, STATE
=>
PORT_B_ACTIVE
Reset Link_B_Active
6 IDLE, FAULT, Beacon message received on port A STAY IN CURRENT
PORT_A_ACTIV
...
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