Ubuntu - wireless network

The following content in /etc/network/interfaces blocked my internet connection.

auto lo
iface lo inet loopback


iface wlan0 inet dhcp
wireless-key s:
wireless-essid vvasam

auto wlan0

I deleted the following lines in the interfaces file and started wireless connection.

auto lo
iface lo inet loopback

The following are the commands for starting wireless connection

sudo ifconfig wlan0 down
sudo ifconfig wlan0 up
sudo iwconfig wlan0 essid key