Westermo ODW-631 - Manual (Page 13)

13 6650-2243
System delay in an optical network
Serial data transferred from one ODW-631 via an optical network to a second one, will
be delayed due to the length of optical fibre and the signal processing within the units.
The signal processing delay is dependent on the data rate and conversions, and the fibre
delay is dependent on the total length of the optical fibre.
Item Functions Delay
1 Fibre:
Optical fibre length delay (typical) 5 ms/km
2 Converter electrical to fibre:
Signal processing 0.6 ms (synchronous mode)
1 t
Bit
+ 0.6 ms
(asynchronous mode)
3 Converter fibre to electrical:
Signal processing 0.6 ms
Note t
bit
= 1 / Baud rate (Baud rate in bit/s)
The system delay when transferring data from the serial input at one ODW-631 to the
serial output of other one is calculated by adding the following:
1. Fibre: The optical fibre length delay.
2. Converter electrical to fibre: Signal processing delay.
3. Converter fibre to electrical: Signal processing delay.
Example 1: Synchronous data data transfer from one ODW-631 to a second
converter with a total fibre length of 25 km. Data rate of 9 600 bit/s.
1. Fibre: The total optical fibre length delay 25 * 5 ms = 125 ms.
2. Converter electrical to fibre: Signal processing delay 1 t
bit
+ 0.6 ms = 105 ms + 1.0 ms
= 106 ms.
3. Converter fibre to electrical: Signal processing delay = 0.6 ms.
4. The system delay is calculated by adding the delays in items 1 to 3 above = 232 ms
Example 2: Synchronous data transfer from one ODW-631 to a second converter
with a total fibre length of 25 km. Data rate of 9 600 bit/s.
5. Fibre: The total optical fibre length delay 25 * 5 ms = 125 ms.
6. Converter electrical to fibre: Signal processing delay = 0.6 ms.
7. Converter fibre to electrical: Signal processing delay = 0.6 ms.
8. The system delay is calculated by adding the delays in item 1 to 3 above = 126 ms