72
6 F 3 B 0 3 6 2
6.2 Ethernet Port Socket Interface Usage Notes
This section presents points that require attention when using the socket interface on the Ethernet
Port for data transmission.

1. Data handling and data segmentation in UDP socket interface transmission and reception

a. In UDP socket interface transmission, data sent in a single transmission is handled by the
receiving Ethernet Port as a single data unit, and that data is transmitted to the T2N in a batch
operation by a receive request.
b. The size of data units that can be handled by the Ethernet Port socket interface in a single
operation is limited to a maximum of 2000 bytes. If the sending port sends a data unit larger
than 2000 bytes, the Ethernet Port UDP socket interface will not be able to receive that data.
Users should determine the maximum size of the data units to be sent or received at the
system design stage.
c. Transmitted data that exceeds 1472 bytes is divided (fragmented) into units of 1472 bytes.
This is the limit of the length of packets (data units flowing on the network) transmitted over
the network (10BASE-T). (See figure 6.8.)
For example, when transmitting a 2000 byte data set, which is the largest data size that can be
handled by the Ethernet Port, the phenomenon shown in figure 6.5 can occur.
(1) The sending T2N user program requests a transmission of 2000 bytes.
(2) The transmitted data is divided into two fragments, A (with 1472 bytes) and B (with 528
bytes) by the send side Ethernet Port.
(3) A and B are put onto the network in order.
(4) The receive side Ethernet Port connects the received data A and B, recovering the
original data.
(5) The data is accepted by a receive request from the receive side T2N for 2000 bytes of
data and the data is stored in the specified register. (See section 6.4 (3).)
d. In the UDP socket interface, after the transmitted data is reassembled to the original data it is
passed to the user program and stored in the specified register.
(The fragments A and B are reassembled to the original data by UDP/IP processing.)
Figure 6.5 Transmission Data Fragmentation in the UDP Socket Interface
- ®
¯
°Receive request
2000 bytes
¬Send request
2000 bytes
Receive side T2N
528 bytes
1472 bytes
Send side T2N Ethernet PortNetwork
Receive response
Ethernet Port
BA
B
A