Figure 9.4.2 Dual-net hot-standby mode sharing the same RCB instance
In this mode, the MMS service is provided on main MMS link, no MMS service interacts on the
standby MMS link. The definitions of two links are as follows:
Main MMS Link: Physically connected, TCP level connected, MMS report service available.
Standby MMS Link: Physically connected, TCP level connected, MMS report service not
available.
If the main net fails to operate (i.e.: “Abnormal operation status” in the above figure), the IED will
set “RptEna” to “false”. Meanwhile the client will detect the failure by heartbeat message or
“keep-alive”, it will automatically enable the RCB instance by setting “RptEna” back to “true”
through standby MMS link. By the buffer function of BRCB, the IED can provide uninterrupted
MMS service on the standby net. However, the differences of BRCB standards among different
manufacturers may cause data loss. Moreover, if duration of net switch is too long, the data loss is
positively as the capacity of BRCB’s buffer function is limited.
NOTICE!
The first mode and second mode, Net A IED host address and Net B IED host address
must be the same.
For example, if the subnet mask is “255.255.0.0”, network prefix of Net A is
“198.120.0.0”, network prefix of Net B is “198.121.0.0”, Net A IP address of the IED is
“198.120.1.2”, and then Net B IP address of the IED must be configured as
“198.121.1.2”, i.e., Net A IED host address =1x256+2=258, Net B IED host address
=1x256+2=258, Net A IED host address equals to Net B IED host address.
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