ActiveSync Desktop Pass-through (DTPT) for Portable Navigation Devices
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10/16/2008
Applies to Windows Embedded NavReady
ActiveSync Desktop Pass-through (DTPT) is a technology that enables a Windows Embedded NavReady powered device to transparently access external networks, such as the Internet, through the desktop computer to which it is connected. In Windows Embedded NavReady, DTPT can be used to connect to a desktop computer and download information such as search results or navigation maps.
Note
There is full connectivity between the desktop and the device. However, there is limited connectivity between the desktop running ActiveSync and the external host. Only outgoing TCP/IPv4 packets are routed through the DTPT Server to the external host.
DTPT Overview
ActiveSync Desktop Pass-through (DTPT) consists of the following components:
- DTPT Client
The DTPT Client service runs on the Windows Embedded CE powered device. This component is responsible for addressing and forwarding connection requests and name service-provider requests to the desktop.
- DTPT Server
The DTPT Server service runs on the desktop to which the Windows Embedded CE powered device is connected and is integrated with ActiveSync. This component is used by the device as a proxy server to connect to external networks to which the desktop is connected. It also processes NSP requests sent by the DTPT Client.
DTPT Addressing
After the device connects to the desktop, the DTPT Client and the DTPT Server try to discover one another.
The DTPT Client performs addressing by detecting the presence of a DTPT-compatible network interface. After an appropriate interface is detected, the DTPT Client assigns an IPv4 address for the device from the Auto IP range of addresses and then sends the address to the desktop by using the DHCP protocol.
Note
If an application that is running on the device tries to change the IP address of the device, the DTPT functionality might fail.
After the addressing is performed, a connection is established and the DTPT Server listens on a predetermined port for messages sent by the DTPT Client. Based on the type of message that is received, the DTPT Server functions as a proxy server or a name service provider.
DTPT as a Proxy Server
The purpose of DTPT is to enable a Windows Embedded NavReady powered device to connect to and communicate with remote hosts on the network to which the desktop is connected. The DTPT Server functions as a proxy forwarding data between the device and the remote host. The DTPT Client intercepts the proxy calls and sends requests to the desktop for processing.
DTPT as a Name Service Provider
DTPT also supports name service-provider service. When a Winsock application that is running on the device makes a request for name resolution, the DTPT Client intercepts the call and forwards it to the DTPT Server for processing. The DTPT Server receives the NSP message and retrieves the requested service information and returns it to the DTPT Client.
DTPT Security
DTPT has potential security risks typically associated with networking because it supports the transfer of non-encrypted data over a network.
Best Practices
Disable bridging on the desktop running the DTPT Server
We recommend that you do not enable bridging on the desktop running the DTPT Server as this might expose the attached Windows Embedded NavReady powered device to security concerns from other networks to which the desktop is connected.
DTPT Limitations
The following list shows the limitations for ActiveSync Desktop Pass-through (DTPT).
DTPT functions over a point-to-point connection. Do not bridge the Windows Embedded CE adapter connection; use it together with Internet Connection Sharing, or manually configure the connection.
At a given time, only one Windows Embedded NavReady powered device can use DTPT.
Only outgoing TCP/IPv4 packets are routed through the DTPT Server to the external host. However, you can transfer non-TCP and non-IPv4 packets to and from the host without using the DTPT technology.
Applications that are running on the client are not able to change the address of the Windows Embedded NavReady powered device, which is assigned by the DTPT Server.
The connected Windows Embedded NavReady powered device cannot have more than 1000 concurrent requests to the desktop.
Nonsecure DTPT connections are not supported. DTPT was designed to work as an encrypted channel.
Note
Nonsecure DTPT connections are DTPT connections provisioned using the CM_NetEntries Configuration Service Provider with the Secure parameter set to 0. For more information, see Configuration Service Providers for Connection Manager.
See Also
Concepts
Connection Manager OS Design Development for Portable Navigation Devices
How to Make a Data Connection by Using Connection Manager