Is web calendar publishing (.ical or ics) pushed by publisher or pulled by subscriber?

Question

In my custom php web application I want to publish an ical calendar using calendar events I'm selecting from my own database. After I create the ical file and create a link to it, and then the (iphone subscriber for example) sets up their subscription information to pull it, how do changes get sync'ed back to the subscriber after the initial pull? Is the subscriber software regularly polling for changes? Or do I have to push the changes somehow?

I've looked around for this information but there is not a concise answer.

Answer 1

An iCalendar feed is pulled by the client. There's no standard for how often or when it does this, it depends on your client when it decides to refresh.

• Microsoft Outlook respects the X-PUBLISHED-TTL field.
• Google Calendar refreshes every up to 8 hours.
• Apple's iCal has a Refresh option in the menu.
• Mozilla Thunderbird's Lightning add-on has a configurable refresh option.