Schweitzer Engineering Laboratories SEL-751 - Table 7.5 Settings Associated with SNTP

7.15
Date Code 20170927 Instruction Manual SEL-751 Relay
Communications
Communications Protocols
Configuring SNTP Client in the Relay
To enable SNTP in the relay, make Port 1 setting ESNTP = UNICAST,
MANYCAST, or BROADCAST. Table 7.5 shows each setting associated with
SNTP.
SNTP Operation Modes
The following sections explain the setting associated with each SNTP
operation mode (UNICAST, MANYCAST, and BROADCAST).
ESNTP = UNICAST. In UNICAST mode of operation, the SNTP client in
the relay requests time updates from the primary (IP address setting
SNTPPSIP) or backup (IP address setting SNTPBSIP) NTP server at a rate
defined by setting SNTPRATE. If the NTP server does not respond with the
period defined by setting SNTPTO, then the relay tries the other SNTP server.
When the relay successfully synchronizes to the primary NTP time server,
Relay Word bit TSNTPP asserts. When the relay successfully synchronizes to
the backup NTP time server, Relay Word bit TSNTPB asserts.
ESNTP = MANYCAST. In the MANYCAST mode of operation, the relay
initially sends an NTP request to the broadcast address contained in setting
SNTPPSIP. The relay continues to broadcast requests at a rate defined by
setting SNTPRATE. When a server replies, the relay considers that server to
be the primary NTP server, and switches to UNICAST mode, asserts Relay
Word bit TSNTPP, and thereafter requests updates from the primary server. If
the NTP server stops responding for time SNTPTO, the relay deasserts
TSNTPP and begins to broadcast requests again until the original or another
server responds.
ESNTP = BROADCAST. If setting SNTPPSIP = 0.0.0.0 while setting
ESNTP = BROADCAST, the relay listens for and synchronizes to any
broadcasting NTP server. If setting SNTPPSIP is set to a specific IP address
while setting ESNTP = BROADCAST, then the relay listens for and
synchronizes to only NTP server broadcasts from that address. When
synchronized, the relay asserts Relay Word bit TSNTPP. Relay Word bit
TNSTPP deasserts if the relay does not receive a valid broadcast within five
seconds after the period defined by setting SNTPRATE.
Table 7.5 Settings Associated With SNTP
Setting Range Description
ESNTP UNICAST,
MANYCAST,
BROADCAST
Selects the mode of operation of SNTP. See descrip-
tions in SNTP Operation Modes on page 7.15.
SNTPPSIP Valid IP Address Selects primary NTP server when
ENSTP = UNICAST, or broadcast address when
ESNTP = MANYCAST or BROADCAST.
SNTPPSIB Valid IP Address Selects backup NTP server when ESNTP = UNICAST.
SNTPPORT 1–65534 Ethernet port used by SNTP. Leave at default value
unless otherwise necessary.
SNTPRATE 15–3600 s Determines the rate at which the relay asks for updated
time from the NTP server when ESNTP = UNICAST
or MANYCAST. Determines the time the relay waits
for an NTP broadcast when ENSTP = BROADCAST.
SNTPTO 5–20 s Determines the time the relay waits for the NTP master
to respond when ENSTP = UNICAST or MANY-
CAST.