Westermo ODW-632 - Manual (Page 13)

13 6650-2253
System delay in an optical network
Data exchange between a serial master and slave via ODW-632 fibre optic link, will be
delayed due to the length of the optical fibre and the signal processing within the ODW-
632. The signal processing delay is dependent on the data rate, and the fibre delay is
dependent on the total length of the optical fibre.
There is no limitation of the total length of optical fibre for Multi-drop applications. In
Redundant ring applications the data transfer time in a ring is limited to 10 milliseconds.
This means the total length of the optical fibre ring is about 2 000 km, excluding the
1 microsecond delay at each optical repeater unit.
The additional time resulting from the optical fibre and ODW-632 is the Overall system
delay. The Redundant ring and Multidrop application Overall system delays differ, see
below.
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)
… Redundant ring, one data exchange.
• The data exchange between master and slave via ODW-632 fibre optic link will run one direc-
tion through all units of the ring. The system delay is calculated by summing the following:
1. Fibre: The total optical fibre ring length delay.
2. Optical repeaters: The optical repeater delay x Number of optical repeaters (excluding the
ODW-632 units connected to a master and addressed slave).
3. Converter electrical to fibre: Signal processing delay x 2
(ODW-632 units connected to serial master and addressed slave).
4. Converter fibre to electrical: Signal processing delay x 2 (ODW-632 units connected
to a master and addressed slave).
Multi drop, one data exchange.
• The data exchange between a master and slave via ODW-632 fibre optic link will run from
the ODW-632 units connected to a master to the slave and the same way back to the master.
The system delay is calculated by summing the following:
1. Fibre: The optical fibre length a master to addressed slave delay x 2.
2. Optical repeaters: The optical repeater delay * Number of optical repeaters
(excluding the ODW-632 units connected to a master and addressed slave) x 2.
3. Converter electrical to fibre: Signal processing delay x 2
(ODW-632 units connected to a master and addressed slave).
4. Converter fibre to electrical: Signal processing delay x 2
(ODW-632 units connected to a master and addressed slave).