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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.)

Send side T2N

Ethernet Port

Network

Ethernet Port

Receive side T2N

¬ Send request

-

®

 

 

 

2000 bytes

1472 bytes

 

 

 

° Receive request

 

 

 

 

 

 

 

 

 

 

A

 

 

¯

2000 bytes

 

 

 

 

 

B

 

A

B

 

 

528 bytes

 

 

Receive

response

 

 

 

 

Figure 6.5 Transmission Data Fragmentation in the UDP Socket Interface

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Toshiba T2N Ethernet Port Socket Interface Usage Notes, Transmission Data Fragmentation in the UDP Socket Interface