CalConnect: 7 Things You Should Know About PUSH

  1. What is it?

    Push notifications allow servers to notify clients of changes to the stored data in a timely manner – possibly as soon as the changes occur – rather than waiting for the client to ask the server about any changes (polling). See

  2. What scenarios and/or problems does it address, or what new advantage(s) does it confer?

    To keep client and server data synchronized, CalDAV and CardDAV clients need to refresh their state from the server. One option is for clients to "poll" servers at regular intervals to determine if any changes have been made.

    Users want to be notified of changes as soon as they occur (in particular for changes to events that may be happening in the next few hours), so it is tempting to use a short polling interval to achieve that. However, polling may cause higher network bandwidth, higher CPU consumption (and thus more power drain) on both the client and the server, particularly during periods of time when the data on the server is not changing very much (e.g., outside of "work" hours, a business calendar may not change very often).

    Also, with polling a synchronization will not happen right after a change on the server, so the client database may be out of synchronization for longer periods. A better approach is for the server to send a (push) notification to the client. This is more efficient as it avoids unnecessary network activity on the part of the client when the data on the server changes infrequently. Plus this gives users a more "real time" experience, since the server can signal the client very soon after a change occurs. It also provides more control on the server in situations where it may need to control the frequency of client updates based on available network bandwidth and server load.

  3. How does it work?

    Existing solutions to this problem typically involve the client sending some sort of "subscription" request to the server, to identify itself as wanting to receive push notifications from the server. The information the client sends will indicate how it wants the server to contact it when a push notification needs to be sent (which may be an entirely different protocol than the one used to actually access the data). The server will store the client subscription and use the information to send push notifications as needed. Clients may be allowed to subscribe to specific types of changes on the server (e.g., a client might want to know about changes only on one specific calendar, rather than all possible calendars). Current implementations of this are vendor specific.

  4. Who's doing it?

    Push notifications are of particular importance to mobile devices, and other types of devices constrained by power limitations (battery charge time). Many of the leading vendors of mobile devices have implemented some form of push notification for calendar and contacts data. These are often in the form of a generic push protocol that is not specific to any type of data or protocol (e.g., it can be used for email, instant messaging, etc as well as calendar and contacts data). Push has also been extended to desktop devices to provide the same level of improved user performance on those platforms. Typically, these implementations of push notifications are vendor specific, so devices from one vendor are only able to receive push notifications from that vendor's data service.

  5. Why is it significant?

    Mobile devices have become a major part of many people's lives, providing a convenient way to manage their personal and business data "on the go". In particular, calendar and contact data is a key component of this, and users expect to be kept informed of changes as soon as they happen, as they could impact their current activities. Thus the immediacy of push notifications both on mobile devices and desktop systems have come to be expected by users, and thus push notifications have become a key requirement for vendors to support. Push also provides a significant benefit in being able to keep multiple devices simultaneously up to date.

  6. What needs to be done, and what is CalConnect doing?

    A generic framework for push notifications within CalDAV and CardDAV needs to be defined to address the problems outlined in this document. CalConnect has established the PUSH technical committee to develop a common set of properties that servers advertise to clients that describe the various push mechanisms supported by the server in a standard way. Clients can then use that information to determine which push mechanism is appropriate for them to use based on their current environment. The technical committee will also define one standard push protocol which servers will be encouraged to support, though proprietary push protocols will also be supported in the framework. The technical committee will also produce an implementation guide describing how servers and clients can efficiently implement push and poll-based strategies based on overall load and other factors, such as importance of the change.

  7. What are the implications for calendaring and scheduling?

    Improving push support in calendaring and scheduling products will lead to an improved user experience. Some key benefits include keeping users up to date with invitation status changes - particularly important when status may change right before a meeting. Push can also be used to implement an efficient method for simultaneously dismissing alarms across multiple devices. This will encourage more direct use of calendaring and scheduling tools over other "out-of-band" methods for scheduling meetings (such as email, instant message, sms, telephone etc), because of the added reliability and promptness of updates. It also opens up the possibility for 3rd party products or automated systems to make better use of calendaring data for the same reasons.

Need more information?
Calendaring and Scheduling Glossary of Terms

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