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Communications Service

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The Communications Service support with the Real-time Communications (RTC) client API enables you to build applications that perform text messaging using Voice over IP (VoIP), IP telephony bridging from an IP device to a PSTN phone through a Gateway, presence information accessing of your contacts to see if they are on line, and control of your own presence information so it can be accessed or blocked by other clients on the network. Microsoft® Windows® CE provides Communications Service application programming interfaces (APIs) built on the Session Initiation Protocol (SIP), an IETF standard (RFC 2543). The SIP allows a device to call, or receive calls from, any SIP client. A SIP client can be a Windows CE device, a Windows XP machine, or a third-party SIP user agent. The Windows Messenger application supports the Communications Service as a backend.

The RTC client APIs supports the following:

  • Setting up VoIP connections between Windows CE devices, Windows XP systems, third-party SIP user agents, or Public Switched Telephone Network (PSTN) phones.
  • Initiating text-messaging sessions, which can occur simultaneously with voice connections.
  • Receiving presence information to see if your contacts are online, changing your own presence state and send notifications, and monitoring who is watching your online presence.

Windows CE .NET 4.2 and later supports RTC Client API version 1.2. The following list shows the new functionalities for RTC 1.2:

  • Multiparty instant messaging and content branching. RTC version 1.0 supported only single PC-PC conversations. In RTC 1.2, multiple clients can converse in the same session.
  • SIP profile searching. To provide a more convenient facility for search and retrieval of user profiles stored on the RTC server, RTC 1.2 supports both a dedicated set of interfaces and an event. The interfaces are IRTCUserSearch, IRTCUserSearchQuery, IRTCUserSearchResult, IRTCUserSearchResultsEvent. The event is RTC_USERSEARCH.
  • Profile and contact roaming. Contact lists can be enabled to travel with a profile as it moves between locations.
  • Support for customizable and extensible presence properties.
  • Group management for buddies. Buddy-groups allow the client to associate buddies logically and display this organization in an application user interface.
  • Support for access control list (ACL) based contact access. This allows for tighter integration in the Windows security model.

Windows CE .NET 4.2 and later also includes VoIP Application Interface Layer (VAIL) that enables OEMs to quickly build IP telephony solutions. The following list shows the tasks that the interface layer automates:

  • Provisioning the IP phone.
  • Registering the phone with a SIP server.
  • Logging calls.

In addition, an IP Telephony User Interface (TUI) sample application that uses the VoIP Application Interface Layer is included. The sample is located in the %_WINCEROOT%\Public\Directx\Oak\Voip\Voipui.

The following table shows the scenarios that are supported by the Communications Service.

Scenario Requirements
Windows CE-SIP client Requires a Windows CE device and a SIP client. These devices must be logged on to the network. Direct voice connections can occur as peer-to-peer or through a SIP server.
Windows CE-phone Requires a Windows CE device, a gateway, and a PSTN phone.
Phone-phone Requires a Windows CE device, a gateway, and two or more PSTN phones.

See Also

Communications Service Security | RTC Client Reference | VoIP Application Interface Layer Architecture

 Last updated on Saturday, April 10, 2004

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