Requesting the time from a time server is simple. First, you provide the time server from which you want to request the time.

So what is happening in the background of Zend_TimeSync? First the syntax of the time server is checked. In our example, '0.pool.ntp.org' is checked and recognised as a possible address for a time server. Then when calling getDate() the actual set time server is requested and it will return its own time. Zend_TimeSync then calculates the difference to the actual time of the server running the script and returns a Zend_Date object with the correct time.

For details about Zend_Date and its methods see the Zend_Date documentation.

Not all time servers are always available to return their time. Servers may be unavailable during maintenance, for example. When the time cannot be requested from the time server, you will get an exception.

Zend_TimeSync is a simple solution that can handle multiple time servers and supports an automatic fallback mechanism. There are two supported ways; you can either specify an array of time servers when creating the instance, or you can add additional time servers to the instance using the addServer() method.

There is no limit to the number of time servers you can add. When a time server can not be reached, Zend_TimeSync will fallback and try to connect to the next time server.

When you supply more than one time server- which is considered a best practice for Zend_TimeSync- you should name each server. You can name your servers with array keys, with the second parameter at instantiation, or with the second parameter when adding another time server.

Naming the time servers allows you to request a specific time server as we will see later in this chapter.

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 Zend_TimeSync: 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.

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.

As with every protocol within the world wide web, the NTP and SNTP protocols use standard ports. NTP uses port 123 and SNTP uses port 37.

But sometimes the port that the protocols use differs from the standard one. You can define the port which has to be used for each server within the address. Just add the number of the port after the address. If no port is defined, then Zend_TimeSync will use the standard port.

There is only one option within Zend_TimeSync which will be used internally: timeout. You can set any self-defined option you are in need of and request it, however.

The option timeout defines the number of seconds after which a connection is detected as broken when there was no response. The default value is 1, which means that Zend_TimeSync will fallback to the next time server if the requested time server does not respond in one second.

With the setOptions() method, you can set any option. This function accepts an array where the key is the option to set and the value is the value of that option. Any previously set option will be overwritten by the new value. If you want to know which options are set, use the getOptions() method. It accepts either a key which returns the given option if specified, or, if no key is set, it will return all set options.

As you can see, the options for Zend_TimeSync are static. Each instance of Zend_TimeSync will use the same options.

Zend_TimeSync's default behavior for requesting a time is to request it from the first given server. But sometimes it is useful to set a different time server from which to request the time. This can be done with the setServer() method. To define the used time server set the alias as a parameter within the method. To get the actual used time server call the getServer() method. It accepts an alias as a parameter which defines the time server to be returned. If no parameter is given, the current time server will be returned.

Time servers not only offer the time itself, but also additional information. You can get this information with the getInfo() method.

The returned information differs with the protocol used and can also differ with the server used.

Exceptions are collected for all time servers and returned as an array. So you can iterate through all thrown exceptions as shown in the following example: