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pSOSystem System Calls - Read

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setsockopt pNA+ <strong>System</strong> <strong>Calls</strong><br />

TCP Level Option<br />

level must be set to IPPROTO_TCP for TCP protocol level operations. The<br />

argument optname can have the following value (defined in ):<br />

TCP_KEEPALIVE_CNT Number of Keepalive strobes. Upon expiry of the Keepalive<br />

idle timer TCP will send a number of strobes<br />

separated by a fixed interval. If the other end fails to<br />

respond to the strobes (special TCP segments) then<br />

the TCP connection will be terminated. The default<br />

number of strobes in pNA+ are 8. Only valid if the<br />

SO_KEEPALIVE option is set above.<br />

TCP_KEEPALIVE_IDLE Keepalive idle time in TCP. If the connection has been<br />

idle for this time, the timer will expire causing TCP to<br />

send a special segment forcing the other end to respond.<br />

On demand-dial links for example the timer<br />

may be set long enough so as not to cause unnecessary<br />

traffic. The default in pNA+ is 120 seconds (2<br />

hrs). The timer is in seconds. Only valid if the<br />

SO_KEEPALIVE option is set above.<br />

TCP_KEEPALIVE_INTVL Keepalive strobe interval. The strobes sent out by TCP<br />

upon expiration of the Keepalive idle timer are separated<br />

by a fixed interval. The default interval between<br />

the strobes is set to 75 seconds in pNA+. The timer is<br />

in seconds. Only valid if the SO_KEEPALIVE option is<br />

set above.<br />

TCP_MSL Maximum Segment Lifetime in TCP. This controls the<br />

TIME_WAIT or 2MSL timer in TCP which is set to<br />

twice the value of the MSL. The timer is used to validate<br />

connection termination and transmits remaining<br />

data in the send queue. It is a safeguard against sequence<br />

numbers being overlapped. If set to a low<br />

value it allows the sockets to be quickly deleted. The<br />

default in pNA+ is 30 seconds. The timer is in seconds.<br />

TCP_NODELAY Disables delay acknowledgment algorithm. Data is<br />

sent immediately over the network instead of waiting<br />

for the window to be full.<br />

4-68 <strong>pSO<strong>System</strong></strong> <strong>System</strong> <strong>Calls</strong>

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