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Appendix B
Ethernet Network Parameters
Note The hold time is 3 s for the UCMM service, Class 3 service, and tag data link open/close processing.
Parameter Value Description
TCP send buffer 4,096 bytes Maximum capacity of the TCP send buffer
TCP receive buffer 4,096 bytes Maximum capacity of the TCP receive buffer
UDP send buffer 9,000 bytes Maximum capacity of the UDP send buffer
UDP receive buffer 9,016 bytes Maximum capacity of the UDP receive buffer
FINS receive buffer 16,383 bytes Maximum capacity of the FINS receive buffer
RAW send buffer 2,048 bytes Maximum capacity of the RAW send buffer
RAW receive buffer 2,048 bytes Maximum capacity of the RAW receive buffer
Hold timer 75 s (See note.) The hold timer is used for active open processing of TCP sockets.
An ETIMEDOUT error will occur if connection is not completed within
75 s.
Resend timer Initial value: 250 ms
Maximum value: 64 s
The resend timer is used to monitor completion of reception of arrival
confirmations when transferring data via TCP sockets. If the timer setting
is exceeded before arrival confirmation is received, data is resent.
Resends are performed from the first timeout (1 s) through the 12th time-
out (64 s).
An ETIMEDOUT error will occur after the 12th timeout.
Continue timer Initial value: 1 s
Maximum value: 60 s
The continue timer starts if preparations have been completed to send
data but the send window is too small (either 0 or too small) to send the
data and the remote node has not requested that communications be
restarted. Confirmation of the window size is requested from the remote
node when the continue timer times out. The initial value of the timer is
5 s and confirmation processing will continue consecutively with increas-
ingly longer times until the maximum time of 60 s is reached.
2MSL timer 60 s The 2MSL timer starts at the TCP socket that first closes the socket and
will run for 60 s in the TIME_WAIT status.
IP reassemble timer 12 s A fragmented IP packet is discarded if it cannot be reassembled within
12 seconds.
ARP timer 20 min/3 min If a complete ARP table entry (with an Ethernet address) is not referred
to for 20 minutes, it is removed from the table.
An incomplete ARP table entry (no response yet returned to the ARP
request) is removed from the table after 3 minutes.
Window size
(initial value of max-
imum window size)
4,096 bytes The initial value of the maximum capacity used to control the conver-
gence of TCP sockets. Actually, the node negotiates with the remote
node and uses the smaller of the values for the two nodes. The window
size will fluctuate with the available space in the TCP reception buffers of
the remote node when processing communications.
Fragment size 1,500 bytes Data packets are fragmented into 1,500-byte IP packets. UDP data is
separated into 1,472-byte fragments before sending.
Segment size 1,024 bytes TCP data is separated into 1,024-byte units, unless the segments are dif-
ferent, in which case it will be separated into 536-byte units.
TTL (Time to Live) 30 Decremented each time an IP router is passed.
Keep-alive timer First time: 5 min
Resend: 5 s × 5 times
The keep-alive timer is used for the keep-alive function with TCP connec-
tions. It must be used with UCMM, Class 3.