CalDAV: Network protocol for comparing and synchronizing calendar data

The abbreviation CalDAV stands for Calendar Distributed Authoring and Versioning - in German, this can be roughly translated as Calendar with distributed recording and version control. It is a network protocol whose task is to manage and synchronize calendars on multiple devices via CalDAV servers. Appointments and other entries can be edited from any connected device - whether it's a smartphone, tablet PC, or computer - using various applications such as email clients. CalDAV then communicates as a network protocol over HTTP with a central CalDAV server, which globally stores the changes and distributes them to any compatible software upon request. Many Hosted Exchange offerings also include calendar management.

Function and Structure of CalDAV as a Network Protocol

To achieve optimal compatibility with different platforms such as ARM or x86 and all common consumer operating systems including Microsoft Windows, Apple OS X, Android, and Linux, the network protocol CalDAV uses the standard HTTP for data transmission, commonly used for websites. It stores all information in the universal iCalendar data format, which uniformly defines the structure and form in ASCII plaintext.

Clients update automatically by sending a request to the CalDAV server when the program starts and at regular intervals. The server then sends the current calendar data as CalDAV, making it available locally. When there are changes or new entries, the clients inform the CalDAV server, which evaluates them and centrally distributes them to the individual devices during the next update.

Possibilities and Applications of CalDAV Calendar Data

The standardized format and universal network protocol offer versatile possibilities - a factor that has significantly contributed to the widespread adoption and popularity of CalDAV. Although its primary task initially focused solely on managing calendar data, over time, additional possibilities for practical use have emerged, some of which don't even require a CalDAV server.
Typical applications include:

• Organisation of appointments and entries in a calendar
• Synchronisation of calendar data across numerous devices
• Management of access levels and rules
• Publication and booking of available and occupied time slots
• Creation and sharing of activities such as to-do lists
• Planning and organising real or virtual meetings
• Publication of schedules like speaking times, departure and arrival times
• Import of calendar data through local or published iCal files

Essentially, this is an open and multifunctional network protocol that can also be integrated into custom applications. These applications simply need to parse the data into the corresponding lines using a suitable algorithm, and then analyse them. Since the data is stored according to fixed specifications and in plain text, editing the data in local files only requires a simple text editor.

CalDAV Servers and Clients

The CalDAV Server is the central instance that receives, stores, and distributes all calendar data. As the communication is based on a universal network protocol and an open standard, its interpretation is not dependent on the operating system. Therefore, the choice of operating system for the CalDAV Server - whether Microsoft Windows, Linux, or in rare cases Apple OS X - is irrelevant. It can be set up on both external and internal hardware, with hosting on a reliable server such as a Virtual Private Server (VPS) or a Dedicated Server being highly recommended due to their fast and redundant connections. Most providers guarantee an availability of more than 99.99% throughout the year, ensuring continuous accessibility with less than 13 minutes of downtime in 365 days. This guarantees perfect accessibility and fast synchronisation between the CalDAV Server and external sources.

The CalDAV Client is a program or application that operates on a device and initiates contact with the CalDAV Server - whether to store calendar data on it or retrieve data from it. The environment in which the client operates ranges from a simple smartphone with a single or dual-core processor to a modern laptop or desktop PC.

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