Switch
A B D
1 2 3
Switch
C
1 2 3
Switch
E
1 2 3
Hx5x IED C264 IED Hx5x
Primary Fibre
S
econdary Fibre
Tx (Ep)Rx (Ep)
Rx (Rs)Tx (Es)
V01013
Figure 63: Redundant Ethernet ring architecture with IED, bay computer and Ethernet switches
Switch
A B D
1 2 3
Switch
C
1 2 3
Switch
E
1 2 3
Hx5x IED C264 IED Hx5x
Primary Fibre
T
x (Ep)Rx (Ep)
Rx (Rs)Tx (Es)
Secondary Fibre
V01014
Figure 64: Redundant Ethernet ring architecture with IED, bay computer and Ethernet switches after
failure
4.4 DUAL-HOMING PROTOCOL (DHP)
Unlike RSTP, the Alstom Grid DHP solution responds to the constraints of critical time applications such as
the GOOSE messaging of IEC 61850.
DHP is applied to double-star network topologies. If the optical fibre connection between two devices is
broken, the network continues to operate correctly.
The Dual Homing Manager (DHM) handles topologies where a device is connected to two independent
networks, one being the "main" path, the other being the "backup" path. Both are active at the same time.
In sending mode, packets from the device are sent by the DHM to the two networks. In receive mode, the
duplicate discard principle is used. This means that when both links are up, the MiCOM Alstom H16x switch
receives the same Ethernet frame twice. The DHM transmits the first frame received to upper layers for
processing, and the second frame is discarded. If one link is down, the frame is sent through the link,
received by the device, and passed to upper layers for processing.
Alstom Grid’s DHM fulfils automation requirements by delivering a very fast recovery time for the entire
network (less than 1 ms).
To increase reliability some specific mechanisms are used:
● Each frame carries a sequence number which is incremented and inserted into both frames.
● Specific frames are used to synchronize the discard mechanism.
MiCOM P747 Chapter 8 - Redundant Ethernet
P747-TM-EN-1 249
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