denote

I have SE w300i mob. From last few hrs I am seeing this small little squared arrow on the up-left corner. What does it denote?

what is the difference between net ID and host ID?? in a class C IP address say, 192.52.56.8 the first 3 octets denote the net ID while the last octet shows the host ID. what are the 2 used for ? again in a class B IP address say, 172.52.36.5 the first 2 octets show the net ID while the last...