ProSoft Technology 5201-DFNT-104S - Manual (Page 88)

104S v2 ♦ ProLinx Gateway IEC-60870-5-104 (104S) Protocol Implementation
(Firmware v2.xx) Protocol Manual
Page 88 of 157
ProSoft Technology, Inc.
March 19, 2010
The gateway will respond to a class one data request from the controlling station
by returning the data in the event queue in the order shown in the following table.
Packet Order Content
1 M_DP_NA events 3 and 5
2 M_SP_NA events 1, 2 and 6
3 M_ST_NA event 4
Note that the events are packed into messages in order to maximize the
efficiency of the network. The following warning must be considered when
deciding to use this feature: Because events from the highest priority queues are
always reported when present before lower priority queues, events in the lower
queues may be lost due to buffer overflow.
If this feature is not utilized, each ASDU's events are stored in their own queue.
The gateway will report each queue containing events in a round-robin fashion
with all the data for each ASDU being packed. This methodology limits the
possibility of a buffer overflowing and still maximizes the use of bandwidth on the
communication channel.
3.6.6 SNTP Support
SNTP is used for time synchronization of produced and consumed commands.
When an exchange occurs the driver compares time stamps from the previous
exchange. When the new exchange time is less than the previous exchange, the
exchange is ignored. This can occur when the Ethernet packets are routed and
delayed. Time synchronization provides for data integrity. The following table lists
the parameters defined in this section:
The SNTP driver will compute a new clock value every 5 minutes using the
average value of 10 samples each collected over an approximate 6-second
period. This new value will be used to adjust the clock maintained by the SNTP
driver and used by the application. If a valid database register is specified, the
driver will place the time value into the gateway’s database. The first two
registers will contain the number of seconds and the next two registers will
contain the number of microseconds since January 1, 1970.
A list of some of the common NTP servers can be obtained at
http://www.ntp.org/, http://www.eecis.udel.edu/~mills/ntp/servers.html, along with
the appropriate IP address. Other server lists can be found on the Internet by
searching on "NTP Servers" with your browser.