8-2
Section
Communications Cycle Time
119
Communications conditions are as follows:
Type:
Optical Ring
Transmission medium:
H-PCF cable
Transmission distance:
8 km
Baud rate:
2 Mbps (fixed)
Network parameters:
Defaults
Max node address:
62
Polled nodes per comm cycle: 4
Event-frames per comm cycle: 35
Network configuration:
8 nodes
Nodes that send messages:
2 nodes
Bytes in all messages sent:
2,012
2 bytes
In this example, B to F in the equation have the following values.
B:
4
C:
8
D:
2
E:
4,024
F:
7
8
The communications cycle time for Token Ring Mode is thus as follows:
1,740
×
4 + 450
×
8 + 1,100
×
2 + 4
×
4,024 + 2
7
8 + 3,000 = 31,968 (
µ
s)
≅
32 (ms)
The communications cycle time for Token Bus Mode is thus as follows:
1,300
×
4 + 110
×
8 + 320
×
2 + 4
×
4,024 + 2
7
8 + 1,800 = 24,728 (
µ
s)
≅
25 (ms)
8-2-3 Maximum Delay for Line Disconnections in Token Ring Mode
Although the duplicated transmission lines used in Token Ring Mode for Optical
Ring Networks will ensure that communications continue even if the transmis-
sion line is broken in one location, the communications cycle time will be af-
fected.
The data that is received first from the SL1 or SL2 reception interfaces is actually
used, but the data that would normally be received first may be lost. The differ-
ence in time to receive the same data on SL1 and SL2 is thus the delay that can
occur for line disconnections.
This delay results as the token is passed between nodes. The delay for the entire
network will thus be the total of all the delays between each node pair, and the
total delay time will increase the communications cycle time.
With a Controller Link Network, the token is moved for the following.
•
Normal token passing
•
Token passing for new node checks by the polling node (depends on the num-
ber of polled nodes set in the network parameters)
•
Token passing for responses to messages.
Although the actually delay time will depend on the location of the line discon-
nection point, differences in the time required to receive the token can be re-
duced by setting node addresses in order on the network.
Calculation Example for
Optical Ring Networks
with H-PCF Cable
