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Overview Section 6-1
6-1-7 Fragmentation of Send Data
The Ethernet Unit fragments data for TCP transmission into units of 1,024
bytes and data for UDP transmission into units of 1,472 bytes. TCP requires
one reception request to receive each unit of data. UDP, however, restores the
original data before passing it to the user process, allowing all the data in a
single transmission to be received with one reception request.
Cautions when Using TCP An example of the fragmentation and transmission of data using the TCP is
shown in the following illustration.
1,2,3... 1. The sending user program sends a request to send 1,984 bytes of data.
2. The Ethernet Unit fragments the send data into Data A with 1,024 bytes
and Data B with 960 bytes.
3. Data A and Data B are sent consecutively.
4. The receiving user program sends a request to receive 1,984 bytes of data.
However, only data A is sent in the first packet, and data B is not received.
5. Another receive request to receive data must be made before the remain-
ing data, Data B, is received.
Host computer
(server)
Passive open
Ethernet Unit
(client)
Connection requested
Active open
Send data
Data send request
Data receive request
ACK (acknowledge)
Send next data
Connection established
Close Close
Send data
ACK (acknowledge)
Connection established
Data send request
Data receive request
Next data receive request
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