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Setting TCP Performance Parameters

To customize the terminal's TCP interactions, you can change the TCP performance parameters described in this section.The default settings work properly for most installations. You should not need to adjust these parameters.

CAUTION:
Setting these parameters incorrectly might cause your terminal to stop working and lead to excess network loading.

Adjusting the TCP Send and Receive Buffers

You can adjust the buffers used by the terminal in sending and receiving TCP packets. The default of 4096 bytes works well for sending images. For text-oriented clients, 2048 bytes works better.

These parameter settings should correspond to the TCP windows advertised by the host.

The tcp-receive-buffer-size parameter specifies the maximum amount of received data that a TCP connection buffers in the terminal (Setup -> Change Setup Parameters -> TCP -> Receive Buffer Size). This corresponds to the TCP receive window advertised by the terminal to the peer (device on the other end of the connection).

Table 5-32 tcp-receive-buffer-size Parameter
Possible Values
Result
default 4096
integer Size of the receive buffer (in bytes). Range: 1024 - 65535.

The tcp-send-buffer-size parameter specifies the maximum amount of data awaiting transmission that a TCP connection buffers in the terminal (Setup -> Change Setup Parameters -> TCP -> Send Buffer Size). This corresponds to the maximum amount of the peer's TCP send window that is used by the terminal.

Table 5-33 tcp-send-buffer-size Parameter
Possible Values
Result
default 2048
integer Size of the send buffer (in bytes). Range: 1024 - 65535.

Specifying the TCP Timeout

The tcp-connect-timeout parameter specifies the amount of time that must elapse between a TCP connection attempt and a lack of response before failure is declared (Setup -> Change Setup Parameters -> TCP -> Connect Timeout).

Table 5-34 tcp-connect-timeout Parameter
Possible Values
Result
default 75
integer Elapsed time (in seconds) between TCP connection attempts before failure is declared. Range: 1 - 4294967295.

Specifying TCP Maximum Retransmissions

The tcp-max-retransmissions parameter specifies the number of retransmissions on a TCP connection before failure is declared (Setup -> Change Setup Parameters -> TCP -> Maximum Retransmissions).

Table 5-35 tcp-max-retransmissions Parameter
Possible Values
Result
default 12
integer Retransmissions on a TCP connection before failure is declared. Range: 1 - 4294967295.

Specifying the TCP Linger Time

The tcp-default-linger-time parameter specifies the default time interval during which TCP attempts reliable transmission of outstanding data on the connection's transmit queue after local software closes a connection (Setup -> Change Setup Parameters -> TCP -> Default Linger Time). This timer is optional and higher-level software can configure it for each connection.

Table 5-36 tcp-default-linger-time Parameter
Possible Values
Result
default 120
integer Time (in seconds) that TCP continues to attempt transmission after the local software closes the connection.
Range: 1 - 4294967295.

Allowing Larger Segment Sizes

When set to "false," the tcp-default-mss-for-non-local parameter allows segment sizes larger than the default to be used when communicating with non-local hosts (that is, hosts on the other side of a gateway). The default segment size is 536 bytes (Setup -> Change Setup Parameters -> TCP -> Use default maximum segment size for non-local hosts).

Table 5-37 tcp-default-mss-for-non-local Parameter
Possible Values
Result
default true
true The default segment size, 536 bytes, is used when communicating with non-local hosts.
false Segment sizes larger than the default can be used when communicating with non-local hosts.


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