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pSOSystem System Calls - Read

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pNA+ <strong>System</strong> <strong>Calls</strong> getsockopt<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:<br />

TCP_KEEPALIVE_<br />

CNT<br />

TCP_KEEPALIVE_<br />

IDLE<br />

TCP_KEEPALIVE_<br />

INTVL<br />

Number of Keepalive strobes. Upon expiration of the Keepalive<br />

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

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

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

will be terminated. The default number of strobes in pNA+ is<br />

set to 8. Only valid if the SO_KEEPALIVE option is set above.<br />

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

this time, the timer will expire causing TCP to send a special<br />

segment forcing the other end to respond. On demand-dial<br />

links for example the timer may be set long enough so as not<br />

to cause unnecessary traffic. The default in pNA+ is 120<br />

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

SO_KEEPALIVE option is set above.<br />

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

expiration of the Keepalive idle timer are separated by a fixed<br />

time interval. The default interval between the strobes is set<br />

to 75 seconds in pNA+. The time interval is in seconds. Only<br />

valid if the SO_KEEPALIVE option is 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 twice the<br />

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

termination and transmits remaining data in the send<br />

queue. It is a safeguard against sequence numbers being<br />

overlapped. If set to a low value it allows the sockets to be<br />

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

timer is in seconds.<br />

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

over the network instead of waiting for the window<br />

to be full.<br />

<strong>pSO<strong>System</strong></strong> <strong>System</strong> <strong>Calls</strong> 4-19<br />

4

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