CalDAV - What’s behind the network protocol?

The abbreviation CalDAV stands for "Calendar Distributed Authoring and Versioning”. CalDAV is a network protocol which was first submitted to the IETF (Internet Engineering Task Force) in 2003 for review and first specified in RFC 4791 in 2007. It allows calendar data exchange via WebDAV/HTTP and thereby access to your calendar from any device and the ability to sync it from anywhere. When you add new appointments or edit existing calendar entries, the adjustments are updated automatically on all synchronized devices - whether it’s a PC, smartphone or tablet.

How does CalDAV work?

CalDAV makes it possible to manage and edit appointments, events and time blocks on all devices, regardless of the platform. The protocol manages and distributes calendar events here through the transmission protocol primarily used in the Internet HTTP. All events published by CalDAV are presented in iCalendar format whereby each standard browser can display a downloaded appointment or event in its iCalendar.

The basis for the administration and synchronization is a WebDAV environment which, thanks to CalDAV, is also extended to include an access control and iCalendar evaluation functions. Furthermore, a write lock can be set up for other users, available appointments can be forwarded and parallel changes to an entry can be merged. This way, you can not only synchronize your calendar to multiple devices, but also share it with other users. If you would also like to synchronize your contact data, there is the protocol CardDAV.

In order to be able to use CalDAV, you must implement the network protocol in your calendar applications by downloading and installing a CalDAV client. You can then use this program to create a connection to a CalDAV server which regulates the exchange of calendar data as a central instance.

What is a CalDAV client and what is a CalDAV server?

A CalDAV client is a computer program which runs on a smartphone, tablet or PC, and communicates with a central computer - referred to as a server - via the CalDAV protocol and can thereby send and receive calendar data. In addition, the terminal itself is often referred to as a client. The client software must support not only the network protocol but also your device in order to achieve this. This is why, for example, there are different clients for Windows, Android, or Apple devices.

A CalDAV server acts as the counterpart to the CalDAV client: As a contact point for all requesting clients, it forms the basis for data exchange and therefore for the entire calendar synchronization. That means you need one CalDAV server to store your data, and an appropriate client on your device that can retrieve and display the data from the server.

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The most important CalDAV servers and clients at a glance

Suitable clients for the synchronization of calendar data via CalDAV are, among others:

  • CalendarSync for Android
  • AgenDAV
  • Evolution
  • Atmail (from Version 6.0)
  • Outlook CalDAV Synchronizer (free Outlook plug-in)
  • iPhone

The iPhone is listed here as a client, as the device has a CalDAV-enabled calendar function from version 3.0 (or from version 2.1 with RemoteCalendar).

A basic version of a server is sufficient for the use of CalDAV , which many service providers offer free of charge.

  • Calendar and Contacts Server (macOS and Linux)
  • Atmail (from Version 6.0)
  • Baïkal Lightweight CalDAV+CardDAV server
  • Bedework
  • Google Calender
  • ownCloud
  • Nextcloud

How to implement CalDAV

If you would like to set up your own CalDAV server, you would need a fixed IP address. Once the server is up and running, download the CalDAV client of your choice, install it and then create an account. Connect the profile to the server by specifying the relevant data such as the previously set network address. This is followed by fine adjustments where you specify the options you want - for example, who you want to share the calendar with.

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