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TimeHub 5500 User’s Guide
097-55501-01 Revision M – January 2009
Chapter 2 Engineering Ordering Information
NTP Server Card
The above capacity is based on the assumption that the incoming packets are
evenly distributed. If they are highly bursty and a large number of packets arrive
within a time much shorter than one second, the hardware gate keeper will let them
in if the counter has not reached 3000, but the CPU may be unable to keep up with
so many packets in a short time, and it will start to drop packets. Therefore, if the
instantaneously packet rate is high, NTP card's packet processing capacity can be
lower than the limits specified above.
Load Balancing Between Ports A and B
Load balancing only applies when the two NTP ports are not bonded. When load
balancing (traffic control for ports) is used, during each one-second interval the NTP
card will accept from port A a fixed percentage of the card processing capacity limit;
the remaining percentage will be assigned to port B.
For example, if PPAWT = 30, the system will accept up to 30% of the total packet
processing capacity from port A and 70% from port B. If all packets are
authenticated NTP packets (the long packets), the TimeHub NTP card processing
limit is 1000 packets in a one-second interval. In our example of 30% and 70% split
between port A and port B, the NTP card will accept 300 packets from port A and
700 packets from port B during a one-second interval. If the NTP traffic is 600
authenticated packets at port A and 600 authenticated packets at port B during a
one-second interval, port A will accept 300 packets and drop 300 packets, while port
B will experience no packet loss.
If PPAWT = -1, there will be no load balancing, and packets are accepted on a
first-come-first-served basis. If the traffic is still 600 long packets (authenticated
packets) at both port A and port B during a one-second interval, each port will drop
100 packets during this one-second interval.
Table 2-10. LEDs on the NTP Server Card Front Panel
Indicator
Color
Description
PWR
Green
Off = Power is not present on the card
On = The card is receiving power
FUS
Red
Off = Fuse is OK
On= Fuse is burned out
ALM
Red
Off = Card is working without alarms
On = Card is in the alarm state
FAIL
Red
Off = Card is OK
On = Card failure (component, etc.)
ST0
Green / Amber /
Red
Off = ST0 is disabled
Green = ST0 is locked
Amber = Holdover
Red = ST0 error and never locked, or ST0 error and
exceeded maximum Holdover period