Setting Description
equal to
Link address length
because
Device address
and
“Common address of ASDU“ are equal. The length must
also match the configuration throughout the network.
TX window (k)
Sliding window protocol (k) transmit window setting. This
is the maximum difference between the receive sequence
and the send state variable, that is, the maximum number
of outstanding I (information) format APDUs. The default
setting is "12". The value range is 1...20.
RX window (w)
Sliding window protocol (w) receive window setting. This
is the maximum distance to the latest acknowledged I-for-
mat APDU. The default setting is "8". The value range is
1...20. The standard recommends that this setting should
not exceed two thirds of the Tx window (k) setting.
TX timeout (t1)
Timeout for confirmation of application or test APDU mes-
sages. The default setting is 30 seconds [30000 ms]. Ad-
justable between 1 ms and 60 s.
RX timeout (t2)
Timeout for acknowledgements in case of no data mes-
sages. The default setting is 10 seconds [10000 ms]. Ad-
justable between 1 ms and 60 s. (t2) should be less than
(t1).
Test interval (t3)
Timeout for sending test APDU frames in case of long idle
state (no line activity). The default setting is 20 seconds
[20000 ms]. Adjustable between 1 ms and 60 s.
3.8.1.1 Field length setting parameters
The client’s field length configuration must match the setting of the IEC
60870-5-104 instance. Sometimes it may not be possible to configure these fields
in the client. In such a case, the IEC 60870-5-104 settings must be forced to adjust
to match the client. The default settings for COT length (1 octet) and IOA length (2
octets) are the most commonly used.
Regarding
Device address
and “Common address of ASDU”, a decision whether to
use 1 or 2 octets addressing must be taken. The default setting of
Link address
length
and
ASDU address length
, 1 octet, means that no higher addresses than 255
can be used.
IEC104 protocol has no built-in validation to check the field parameter lengths
during encoding/decoding of packets. Thus, communication engineer must verify
they are matching between client and server. Having field length parameter
mismatch between the devices can lead to unexpected behavior. If, for example,
IOA
length
is set to "1" octet, all configured data points with higher object addresses
than 255 get their higher address byte masked out. For example, IOA address 4500
(Hex 1194) occurs as 148 (Hex 94). If another data point with address 148 has been
created, these objects overlap one another.
2NGA001859 A
Vendor-specific implementation
REX615
IEC 60870-5-104 Communication Protocol Manual
27
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