There are different types of time servers. Most public time servers use the NTP protocol. But there are other time synchronization protocols available.
You set the proper protocol in the address of the time server. There are two
protocols which are supported by
NTP and SNTP. The default protocol is
NTP. If you are using NTP, you can omit the
protocol in the address as demonstrated in the previous examples.
$server = new Zend_TimeSync(array('generic' => 'ntp:\\0.pool.ntp.org',
'fallback' => 'ntp:\\1.pool.ntp.org',
'reserve' => 'ntp:\\2.pool.ntp.org'));
Zend_TimeSync can handle mixed time servers. So you are not
restricted to only one protocol; you can add any server independently from its protocol.