118
Phase 2 Internal Timing
TB9400/TN9275 Installation and Operation
© Tait International Limited May 2023
6.3
Technical Description
When internal timing is selected, control channel base stations provide
timing outputs to the other channels at the site. The timing outputs are:
■
1 pulse-per-second (PPS) timing signal
: replaces the 1PPS signal
usually provided by timing units. The 1PPS timing signal requires a co-
axial cable to connect all channels at the site.
Notice
Do not connect a 1PPS signal from an external timing unit
when using internal timing. The signals will conflict, preventing suc-
cessful operation.
■
Internal timing protocol
: the Phase 2 frame structure comprising
30 ms slots, 360 ms superframes and 1440 ms ultraframes does not
divide evenly into a 1second interval. The internal timing protocol
reports the relationship between the 1 second pulse edge and the current
position in the P25 ultraframe structure. The internal timing protocol
uses IP multicast to reach all of the channels at the site. The internal
timing announcement update rate is once per second.
Configure all channels at a site the same way - using internal or external
timing (Configure > Network Interfaces > Trunking on the Web UI).
If using internal timing, give all channels the same multicast address
and port number for the internal timing protocol. Use a different multi-
cast address at each site to prevent sites from interfering with each other.
The timing protocol messages have a multicast time-to-live (TTL) value
of 1 which means that they will not pass through a network router.
Traffic channels can detect if the 1PPS and internal timing protocol inputs
are invalid or absent. In either case the result will be a Site alignment alarm
(Alarms > System > Site synchronization unaligned) and the channel will
Network Type
External
Frequency
Reference
External
Timing
Unit
Internal
Timing
Comment
Any, 700 MHz and above
Required
-
See other
table entries
Operation above 700 MHz
requires external frequency
reference
UHF, VHF, simulcast
Required
Required
Not possible Simulcast requires highly
accurate frequency and timing
across sites
UHF, VHF non-simulcast
Phase 2 capable
Not required Optional
Optional
UHF & VHF Phase 2 capable
sites require time alignment and
can use internal or external timing
UHF, VHF non-simulcast
Phase 1 only
Not required Not required Not required Phase 1 non-simulcast operation
has no special timing requirement