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Overview Section 6-1
data request is set smaller than the actual length of the data, all received data
exceeding the set data length will be discarded.
6-1-8 Maximum Transmission Delays
The transmission delays for socket service is calculated as the sum of the
communications processing times for both nodes.
Transmission delay = Remote node send processing time + Local node re-
ceive processing time + Local node send processing time + Remote node
receive processing time
Calculate the maximum Ethernet Unit transmission delays for sending and
receiving using the following formulas. These times are the same for both
UDP and TCP.
Note The delay times calculated here ignore delays that can occur on the Ethernet
network. Actual delays can be much longer depending on actual conditions on
the network.
Delay Time for Socket Service using Socket Service Request Switches =
Send processing time = receive processing time = PC cycle time x 5 + A x 2 +
B (ms)
Delay Time for Socket Service using CMND(490)= Send processing time =
receive processing time = PC cycle time x 14 + A (ms)
A is the lowest multiple of the PC cycle time that is greater than or equal to 20
ms.
B is the lowest multiple of the PC cycle time that is greater than or equal to 20
ms + 0.01 x number of send/receive bytes.
Note 1. The formulas above calculate guideline figures for the transfer delays when
the Ethernet Unit uses a single socket only. The user program execution
time is not included in these calculations.
2. The communications time for the remote node varies according to the
equipment used. If the remote node is not an Ethernet Unit, refer to the
documentation for the actual equipment to calculate the communications
time.
3. The delay times may exceed the calculated values due to the operating en-
vironment. Factors affecting the delay times are the network load ratio
(amount of network traffic), the window size of each node, the load on the
Ethernet Unit (including operating multiple socket services, FTP server,
etc.), and the system configuration.
4. The values for A and B given above are guideline values for when the pe-
ripheral service time in the PC Setup in the CPU Unit is set to the default
value of 4%. If the peripheral service time setting is increased, the values
of A and B will decrease.
Example
The following table shows calculation of the approximate maximum transfer
delay for sending 512 bytes of data between two PCs using CMND(490) for a
TCP socket.
Local PC cycle time: 5 ms
Remote PC cycle time: 10 ms
Item Formula
Local receive processing time 5 x 5 + 20 x 2 + 30 = 95 ms
Local send processing time 5 x 5 + 20 x 2 + 30 = 95 ms