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High-availability Seamless Redundancy

January 01, 1970

Not to be confused with Hot Standby Router Protocol.

High-availability Seamless Redundancy (HSR) is a network protocol for Ethernet that provides seamless failover against failure of any single network component. PRP and HSR are independent of the application-protocol and can be used by most Industrial Ethernet protocols in the IEC 61784 suite. HSR does not cover the failure of end nodes, but redundant nodes can be connected via HSR.

HSR nodes have two ports and act as a bridge, which allows arranging them into a ring or meshed structure without dedicated switches. This is in contrast to the companion standard Parallel Redundancy Protocol (PRP),[1] with which HSR shares the operating principle. PRP and HSR are standardized by the IEC 62439-3:2016.[2]

PRP and HSR are suited for applications that request high availability and short switchover time.[3] For such applications, the recovery time of commonly used protocols such as the Rapid Spanning Tree Protocol (RSTP) is too long. It has been adopted for electrical substation automation in the framework of IEC 61850.[4] It is used in synchronized drives (e.g. in printing machines) and high power inverters.[5]

The cost of HSR is that nodes require hardware support (FPGA or ASIC) to forward or discard frames within microseconds. This cost is compensated because no Ethernet switches are required. Hardware support is anyhow needed when the node supports clock synchronization or security.

Topology edit

  •  
    HSR network operation (multicast)
  •  
    HSR frame format (with tag)
  •  
    HSR nodes (DANH) interaction

An HSR network node (DANH) has at least two Ethernet ports, each attached to a neighbour HSR node, so that always two paths exist between two nodes. Therefore, as long as one path is operational, the destination application always receives one frame. HSR nodes check the redundancy continuously to detect lurking failures.

HSR is typically used in a ring topology or in another mesh topology.

Nodes with single attachment (such as a printer) are attached through a RedBox (Redundancy Box).

Redundant connections to other networks are possible, especially to a Parallel Redundancy Protocol (PRP) network.

Since HSR and PRP use the same duplicate identification mechanism, PRP and HSR networks can be connected without single point of failure and the same nodes can be built to be used in both PRP and HSR networks.

Operation edit

Every HSR node is a switching node, i.e. it can forward a frame received on one port to at least one other port in cut-through mode.

A source node sends the same frame over all ports to the neighbour nodes.

A destination node should receive, in the fault-free state, two identical frames within a certain time skew, forward the first frame to the application and discard the second frame when (and if) it comes.

A node forwards a frame unless it detects a frame that it sent itself or that it already sent. To reduce unicast traffic, a node does not forward a frame for which it is the sole destination (Mode U). This does not apply when traffic supervision is needed.

To reduce traffic, a node may refrain from sending a frame that it already received from the opposite direction on the same port (Mode X),[6] but this does not apply to all frames.

Also, several algorithms that relies on network node location learning can serve in the HSR traffic reduction, such as the Port Locking and Enhanced Port Locking, (PL) and (EPL) respectively, which work on closing the ports that leads to a non existed node,[7]

Especially, Precision Time Protocol frames (multicast) are no duplicates of each other since they are modified by each node to correct the time. Such frames can only be retired by the node that originally inserted them, or by another node that already sent them. Also, this mode cannot be used when deterministic operation is required.

A special treatment is given to link-specific frames such as LLDP or Pdelay_Req / Pdelay_Resp Precision Time Protocol frames, for which the HSR tag is ignored, but must be present.

Frame format edit

To simplify the detection of duplicates, the frames are identified by their source address and a sequence number that is incremented for each frame sent according to the HSR protocol. The sequence number, the frame size and the path identifier are appended in a 6-octet HSR tag (header).

NOTE: all legacy devices should accept Ethernet frames up to 1528 octets, this is below the theoretical limit of 1535 octets.

Performance edit

In an HSR ring, only about half of the network bandwidth is available to applications for multicast traffic (compared to RSTP). This is because all frames are sent twice over the same network, even when there is no failure. However, since also the network infrastructure is also doubled in closed ring topologies the nominal network bandwidth is available. E.g. in a 100 Mbit/s Ethernet ring 100 Mbit/s are available (but not 200 Mbit/s).

Implementation edit

Since the forwarding delay of every node in an HSR ring adds to the total network latency, frames are forwarded within microseconds.
In practice, hardware support (FPGA) [8] is required to bring down the per-hop latency to a reasonable value (some 5μs at 100 Mbit/s), using cut-through switching.
To this purpose, each frame has an HSR tag that allows recognition of whether the frame should be forwarded or not, to avoid store-and-forward. This means that corrupted frames will not be removed from the ring until they reach a node that already sent them.

Clock synchronization edit

IEC 62439-3 Annex C specifies a Precision Time Protocol Industry Profile (PIP L2P2P), that allows a clock synchronization down to an accuracy of 1 μs in a ring of 16 HSR nodes. This PTP protocol also allows operating the HSR ring deterministically for a dedicated class of traffic, for instance Sampled Values in IEC 61850. It has been adopted by IEEE as IEC/IEEE 61850-9-3, .[9]

See also edit

References edit

  1. ^ IEC 62439-3 Clause 4
  2. ^ International Electrotechnical Commission IEC 62439-3:2016 Industrial communication networks - High availability automation networks - Part 3: Parallel Redundancy Protocol (PRP) and High-availability Seamless Redundancy (HSR)
  3. ^ Kirrmann, Hubert; Dzung, Dacfey.Selecting a Standard Redundancy Method for Highly Available Industrial Networks, 2006 IEEE International Workshop on Factory Communication Systems, June 27, 2006 Page(s):386 – 390
  4. ^ Kirrmann, Hubert Seamless redundancy - bumpless Ethernet redundancy for substations with IEC 61850 ABB review special report, 2013
  5. ^ Pustylnik, Michael; Zafirovic-Vukotic, Mira; Moore, Roger Performance Of The Rapid Spanning Tree Protocol In Ring Network Topology, RUGGEDCOM
  6. ^ Allawi, Saad; Rhee Jong Myung Improvement of high-availability seamless redundancy (HSR) traffic performance for smart grid communications, Journal of Communications and Networks ( Volume: 14, Issue: 6, Dec. 2012 )
  7. ^ Altaha, Ibraheem; Rhee Jong Myung [1], Journal of Communications and Networks ( Volume: E98, No.:9 Sept. 2015 )
  8. ^ SoCe HSR-PRP Switch IP Core
  9. ^ Kirrmann, H.; Dickerson W. IEC IEEE Precision Time Protocol 2017-02-05 at the Wayback Machine, Pacworld, September 2016

Historical Note edit

Originally, the protocol was named HASAR for the initial of the five companies working for electrical utilities that created it (Hirschmann, ABB, Siemens, Alstom and RuggedCom). Marketing renamed it HSR, for "High-availability Seamless Ring", but HSR is not limited to a simple ring topology.

Further reading edit

  • Heine, Holger; Kleineberg, Oliver; "The High-Availability Seamless redundancy protocol (HSR): Robust fault tolerant networking and loop prevention through duplicate discard", WFCS 2012, Lemgo, Germany
  • Heine, Holger; Bindrich, Diana; "Designing reliable high-performance IEC61850 substation communication networks based on PRP and HSR topologies" In Electricity Distribution (CIRED 2013), 22nd International Conference and Exhibition, Stockholm, Sweden
  • Hoga, Clemens "Network Solutions and their Usability in Substation Applications" in PacWorld, 2010 September
  • Ilie, Diana; Honegger, Claudio; Kirrmann, Hubert; Sotiropoulos, Ioannis "Performance of a full-hardware PTP implementation for an IEC 62439-3 redundant IEC 61850 substation automation network", ISPCS 2012

External links edit

  • IEC 62439-3
  • Tutorial on HSR
  • Tutorial on Parallel Redundancy Protocol (PRP)
  • Tutorial on the fault-tolerant precision time protocol profiles in IEC 62439-3
  • IEC 62439-3 Tissues (Technical issues) database for IEC 62439-3 / IEC/IEEE 61850-9-3
  • ZHAW High-availability Seamless Redundancy Protocol
  • MOXA, Solutions for PRP/HSR Substations
  • HIRSCHMANN HSR High Availability Seamless Redundancy
  • Flexibilis High-availability Seamless Redundancy (HSR)
  • Siemens Redundant networks for industry
  • RuggedCom Migration Paths for IEC 61850 Substation Communication Networks Towards Superb Redundancy Based on Hybrid PRP and HSR Topologies
  • netModule PRP und HSR Protokolle für Redundantes Industrielles Ethernet

January 01, 1970
high, availability, seamless, redundancy, confused, with, standby, router, protocol, network, protocol, ethernet, that, provides, seamless, failover, against, failure, single, network, component, independent, application, protocol, used, most, industrial, ethe. Not to be confused with Hot Standby Router Protocol High availability Seamless Redundancy HSR is a network protocol for Ethernet that provides seamless failover against failure of any single network component PRP and HSR are independent of the application protocol and can be used by most Industrial Ethernet protocols in the IEC 61784 suite HSR does not cover the failure of end nodes but redundant nodes can be connected via HSR HSR nodes have two ports and act as a bridge which allows arranging them into a ring or meshed structure without dedicated switches This is in contrast to the companion standard Parallel Redundancy Protocol PRP 1 with which HSR shares the operating principle PRP and HSR are standardized by the IEC 62439 3 2016 2 PRP and HSR are suited for applications that request high availability and short switchover time 3 For such applications the recovery time of commonly used protocols such as the Rapid Spanning Tree Protocol RSTP is too long It has been adopted for electrical substation automation in the framework of IEC 61850 4 It is used in synchronized drives e g in printing machines and high power inverters 5 The cost of HSR is that nodes require hardware support FPGA or ASIC to forward or discard frames within microseconds This cost is compensated because no Ethernet switches are required Hardware support is anyhow needed when the node supports clock synchronization or security Contents 1 Topology 2 Operation 3 Frame format 4 Performance 5 Implementation 6 Clock synchronization 7 See also 8 References 9 Historical Note 10 Further reading 11 External linksTopology edit nbsp HSR network operation multicast nbsp HSR frame format with tag nbsp HSR nodes DANH interaction An HSR network node DANH has at least two Ethernet ports each attached to a neighbour HSR node so that always two paths exist between two nodes Therefore as long as one path is operational the destination application always receives one frame HSR nodes check the redundancy continuously to detect lurking failures HSR is typically used in a ring topology or in another mesh topology Nodes with single attachment such as a printer are attached through a RedBox Redundancy Box Redundant connections to other networks are possible especially to a Parallel Redundancy Protocol PRP network Since HSR and PRP use the same duplicate identification mechanism PRP and HSR networks can be connected without single point of failure and the same nodes can be built to be used in both PRP and HSR networks Operation editEvery HSR node is a switching node i e it can forward a frame received on one port to at least one other port in cut through mode A source node sends the same frame over all ports to the neighbour nodes A destination node should receive in the fault free state two identical frames within a certain time skew forward the first frame to the application and discard the second frame when and if it comes A node forwards a frame unless it detects a frame that it sent itself or that it already sent To reduce unicast traffic a node does not forward a frame for which it is the sole destination Mode U This does not apply when traffic supervision is needed To reduce traffic a node may refrain from sending a frame that it already received from the opposite direction on the same port Mode X 6 but this does not apply to all frames Also several algorithms that relies on network node location learning can serve in the HSR traffic reduction such as the Port Locking and Enhanced Port Locking PL and EPL respectively which work on closing the ports that leads to a non existed node 7 Especially Precision Time Protocol frames multicast are no duplicates of each other since they are modified by each node to correct the time Such frames can only be retired by the node that originally inserted them or by another node that already sent them Also this mode cannot be used when deterministic operation is required A special treatment is given to link specific frames such as LLDP or Pdelay Req Pdelay Resp Precision Time Protocol frames for which the HSR tag is ignored but must be present Frame format editTo simplify the detection of duplicates the frames are identified by their source address and a sequence number that is incremented for each frame sent according to the HSR protocol The sequence number the frame size and the path identifier are appended in a 6 octet HSR tag header NOTE all legacy devices should accept Ethernet frames up to 1528 octets this is below the theoretical limit of 1535 octets Performance editIn an HSR ring only about half of the network bandwidth is available to applications for multicast traffic compared to RSTP This is because all frames are sent twice over the same network even when there is no failure However since also the network infrastructure is also doubled in closed ring topologies the nominal network bandwidth is available E g in a 100 Mbit s Ethernet ring 100 Mbit s are available but not 200 Mbit s Implementation editSince the forwarding delay of every node in an HSR ring adds to the total network latency frames are forwarded within microseconds In practice hardware support FPGA 8 is required to bring down the per hop latency to a reasonable value some 5ms at 100 Mbit s using cut through switching To this purpose each frame has an HSR tag that allows recognition of whether the frame should be forwarded or not to avoid store and forward This means that corrupted frames will not be removed from the ring until they reach a node that already sent them Clock synchronization editIEC 62439 3 Annex C specifies a Precision Time Protocol Industry Profile PIP L2P2P that allows a clock synchronization down to an accuracy of 1 ms in a ring of 16 HSR nodes This PTP protocol also allows operating the HSR ring deterministically for a dedicated class of traffic for instance Sampled Values in IEC 61850 It has been adopted by IEEE as IEC IEEE 61850 9 3 9 See also editRedundancy engineering Resilient Packet Ring Spanning Tree Protocol Token RingReferences edit IEC 62439 3 Clause 4 International Electrotechnical Commission IEC 62439 3 2016 Industrial communication networks High availability automation networks Part 3 Parallel Redundancy Protocol PRP and High availability Seamless Redundancy HSR Kirrmann Hubert Dzung Dacfey Selecting a Standard Redundancy Method for Highly Available Industrial Networks 2006 IEEE International Workshop on Factory Communication Systems June 27 2006 Page s 386 390 Kirrmann Hubert Seamless redundancy bumpless Ethernet redundancy for substations with IEC 61850 ABB review special report 2013 Pustylnik Michael Zafirovic Vukotic Mira Moore Roger Performance Of The Rapid Spanning Tree Protocol In Ring Network Topology RUGGEDCOM Allawi Saad Rhee Jong Myung Improvement of high availability seamless redundancy HSR traffic performance for smart grid communications Journal of Communications and Networks Volume 14 Issue 6 Dec 2012 Altaha Ibraheem Rhee Jong Myung 1 Journal of Communications and Networks Volume E98 No 9 Sept 2015 SoCe HSR PRP Switch IP Core Kirrmann H Dickerson W IEC IEEE Precision Time Protocol Archived 2017 02 05 at the Wayback Machine Pacworld September 2016Historical Note editOriginally the protocol was named HASAR for the initial of the five companies working for electrical utilities that created it Hirschmann ABB Siemens Alstom and RuggedCom Marketing renamed it HSR for High availability Seamless Ring but HSR is not limited to a simple ring topology Further reading editHeine Holger Kleineberg Oliver The High Availability Seamless redundancy protocol HSR Robust fault tolerant networking and loop prevention through duplicate discard WFCS 2012 Lemgo Germany Heine Holger Bindrich Diana Designing reliable high performance IEC61850 substation communication networks based on PRP and HSR topologies In Electricity Distribution CIRED 2013 22nd International Conference and Exhibition Stockholm Sweden Hoga Clemens Network Solutions and their Usability in Substation Applications in PacWorld 2010 September Ilie Diana Honegger Claudio Kirrmann Hubert Sotiropoulos Ioannis Performance of a full hardware PTP implementation for an IEC 62439 3 redundant IEC 61850 substation automation network ISPCS 2012External links editIEC 62439 3 Tutorial on HSR Tutorial on Parallel Redundancy Protocol PRP Tutorial on the fault tolerant precision time protocol profiles in IEC 62439 3 IEC 62439 3 Tissues Technical issues database for IEC 62439 3 IEC IEEE 61850 9 3 ZHAW High availability Seamless Redundancy Protocol MOXA Solutions for PRP HSR Substations HIRSCHMANN HSR High Availability Seamless Redundancy Flexibilis High availability Seamless Redundancy HSR Siemens Redundant networks for industry RuggedCom Migration Paths for IEC 61850 Substation Communication Networks Towards Superb Redundancy Based on Hybrid PRP and HSR Topologies netModule PRP und HSR Protokolle fur Redundantes Industrielles Ethernet Retrieved from https en wikipedia org w index php title High availability Seamless Redundancy amp oldid 1220808241, wikipedia, wiki, book, books, library,

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