SIP-2
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USER GUIDE - Rev. 3 (January 2018)
APCI:
In the IEC 60870-5-104 standard the use of the APCI protocol to transport information
packets at application level (ASDU) over standard transport layers is detailed. The
APCI protocol acts as a client of the TCP transport layer. The standard also indicates
the parameters that the user has available to establish its behaviour, apart from
establish procedures to be followed by the APCI protocol.
This submenu allows the user to configure all the parameters detailed by the
IEC 60870-5-104 standard, except for the
t0
parameter that does not apply to the
telecontrol remotes but applies to the control center.
The parameters, their meaning and range of possible values are described below.
•
Parameter t1.
The
t1
parameter sets the maximum waiting time for receiving
confirmation of a message at APCI level. When the established time is elapsed, the
connection will be finished. The possible values are from 1 to 255 seconds with a
resolution of 1 second.
•
Parameter t2.
The
t2
parameter sets the maximum time that an APCI entity can
wait from receiving an APCI message and sending the confirmation message,
either through an information message on the contrary direction or by a control
message for this purpose.
The standard establishes that it is imperative that the value of the parameter
t2
be
lower than the parameter
t1
. The possible values and resolution are identical to
those of
t1
parameter.
•
Parameter t3.
The
t3
parameter sets the period of inactivity on an established
APCI connection, which involves the transmission of TEST messages to ensure the
persistence of the connection. The possible values and resolution are identical to
those of
t1
and
t2
parameters.
•
Parameter k.
The
k
parameter sets the maximum number of pending confirmation
messages that can manage the APCI entity for each established connection. It
admits a range from 1 to 32767.
•
Parameter w.
The
w
parameter
sets the maximum number of messages received
by an APCI entity that involves the corresponding confirmation message
transmission, either through a user message on the contrary direction or, in the
absence of traffic in transmission, by a control message. It admits a range equal to
that of
k
parameter.
The standard recommends that the value of
w
be less or equal to two thirds of the
value of
k
, in order to avoid a blocking situation in the absence of traffic in one of
the two ways. The system indicates the user this situation when configuring data
but does not require compliance with the recommendation.
