User Manual

SGD-SB2025NT-TUM, Part 2
Jan 12 Page 69 SOLAR (SYNC) TIMING
The data flow in a Solar network may be divided into four discrete parts:
• Central NI to TM.
• TM to Station NI.
• Station NI to TM.
• TM to Central NI.
‘Sync Timing’ which is part of the TM Engineering as shown in Figures 50 and 51 and described
briefly in Section 5.3.1 – Sync Timing , has been arranged to reflect this separation of data flow.
One page is concerned with the data flow between Central NI and TM and the other page with the
data flow between TM and Station NI. Each one of these pages is then divided into two further
parts by considering the “GO” traffic and “RTN” traffic separately.
Individual Sync Timing values need to be entered for each direction of traffic flow for the entire
Solar network. Even though significant time differences should not be observed between the two
directions, this facility does cater for unusual network situations, e.g. asymmetric network speeds.
It is the alignment of the audio signal timing to a common and consistent overall figure at every NI
that ensures true signal phase coherence; this value is the Total Output Time or ‘TOT’. Part of the
‘TOT’ is allocated to be the TM input buffer time, ‘GO TM Buffer’ and ‘RTN TM Buffer’, the
remainder becomes the NI input buffer time, which has no specific name. Therefore, it can be
seen that the ‘GO TM Buffer’ and ‘RTN TM Buffer’ cannot be greater than their respective ‘TOT’
times and that increasing a TM input buffer size is likely to mean that the ‘TOT’ for that direction
will need to be increased accordingly.
7.2.3 Solar Buffer Size
The input buffers on Solar are capable of holding 50 packets, which means that the maximum
delay that Solar can accommodate is 1 second. As this amount of delay on a PMR system would
be totally unacceptable, this is limited in the software to 500 ms even though this figure should far
exceed the packet delays experienced in practice.
7.3 P ARAMETER C HECKING T OOL
As an aid to setting the timing values, checking their validity and to assist with timing optimisation,
a checking tool using Excel™ is available from the Team Simoco web site. This is designed to
replicate the TM ‘Sync Timing’ page and requires entry of the four main timing values, which must
be entered first, and the PAT reports for every NI. As the spreadsheet makes extensive use of
macros, these must be enabled for the tool to function.
Using this tool, it is possible to see the effect of a progressive increase in network delay (every NI
is deemed to be affected in the same way), which helps to give an indication of whether the timing
values in use have a reasonable margin or are close to the limit.
7.4 L OSS OF 1PPS T IMING
Whilst the TM expects to be connected to a timing signal (1PPS), operation can continue if the
timing signal is lost. Whilst 1PPS timing is present, the TM builds and maintains a table of the PAT
values from every NI. If 1PPS is subsequently lost, the TM will adjust its own clock timing based
upon the average PAT value from the first NI in the table that has a valid 1PPS signal, usually
Central NI #1. If Central NI #1 is also suffering from loss of 1PPS (it may be co-sited with the TM
and share the same 1PPS signal) or simply doesn’t exist, the TM will look to take timing from the
next NI in the table and so on down the table until an NI with a valid timing signal is found.
This method of timing will not give the degree of accuracy that a 1PPS signal produces. However,
it is more than sufficient to ensure that the packets arrive at all the NIs at a time that still allows full