Specifications

Chapter 18. TCP/IP
437
18.2.2 Programming Notes for Socket API According
to UDP
The user datagram protocol (UDP) has no flow control, so send/receive data may go missing
due to poor line conditions or difference of communications capabilities between wireless and
Ethernet. To prevent data missing, be sure to incorporate some flow control process into user
programs at both the BHT and host.
Given below are message transmission examples that support retransmission controls at each
of the BHT and host.
■
BHT’s retransmission control for a transmission error
Assume that the BHT uses the protocol of receiving transmission completion message from
the host after sending a message.
If the BHT times out for waiting a transmission completion message, it will transmit the unsent
message again.
Normal end
Transmission error in a message sent from the BHT
BHT
Disconnect
Host
Data message
Transmission
completion message
BHT
Timeout for receiving
the transmission
completion message
Disconnect
Host
Data
message
Error
Transmission
completion
message
Data message
(sent again)
Transmission
completion
message