Hello, celsius, you wrote: a C> I Write the utility on VC ++, it is necessary to interrogate periodically the machine, that . A C> It is possible to write in a flow ping or at once connect with to it the PC. The C> That is better for selecting? If it is necessary to install connection the sense in preliminary ping is not present. After all if the machine on answered to do connect it is necessary. And if on did not answer, all the same it is necessary. What for then it generally did, if then all the same actions are required identical? After all the answer on does not influence possibility of establishment of connection. Well, for example, after all nobody is surprised to situations when on TCP it is possible to install connection, and on UDP - is not present. Or on the contrary. Similarly and presence of answers ICMP (through which it is made ping) does not define serviceability TCP, UDP and other (and only correlates).