public function createSubnet($vpcId, $cidrBlock, $availabilityZone = null)
{
$result = null;
$options = array('VpcId' => (string) $vpcId, 'CidrBlock' => (string) $cidrBlock);
if ($availabilityZone !== null) {
$options['AvailabilityZone'] = (string) $availabilityZone;
}
$response = $this->client->call(ucfirst(__FUNCTION__), $options);
if ($response->getError() === false) {
$sxml = simplexml_load_string($response->getRawContent());
$result = $this->_loadSubnetData($sxml->subnet);
}
return $result;
}