USB RNDIS in ActiveSync 4.0 (Windows Embedded CE 6.0)


This topic describes the implementation of the USB RNDIS specification on Windows Embedded CE-based devices. It describes different software modules implementing the solution and how ActiveSync 4.0 uses this architecture.

The RNDIS protocol provides IP connectivity over the USB serial bus. This solution hides the complexity of transferring IP packets over a physical medium and eliminates the need for the ActiveSync software to provide a separate protocol (e.g. dial up RAS server solution) to achieve this.

The Windows Embedded CE-based, ActiveSync software uses standard Winsock APIs and built in TCPIP protocol driver on the host machine to communicate with the Windows Embedded CE-based devices providing a faster data transfer rate (which is necessary for scenarios like media sync and music download).

An additional thing to consider is that the data transferred is now subjected to the same security filter as the firewall software. This is an improved security mechanism considering future devices with faster internet connectivity making it necessary to allow dual homing on the device (i.e. device is connected to the internet through Wifi or 3G radio at the same time it is connected to the host machine).

Microsoft is working with the third party security companies to ensure compatibility with ActiveSync in their future releases while still providing protection to the host machine.

This topic is intended to provide a deeper understanding of the software solution which provides network IP layer connectivity over USB serial bus to OEMs and Mobile Operator support teams.

The topic also discusses the USB driver requirements that a device manufacturer needs to implement and connection issues that may arise with other networking software installations on the host machine (a desktop machine running Windows XP or Windows 2000 platforms).

The following table shows terms related to RNDIS and describes the meaning of each term.



ActiveSync 4.0

Windows Embedded CE-based synchronization software for Windows CE 5.0 based devices.


Microsoft’s Desktop Pass Through software module providing DHCP server and proxy services for data packets between the device and the network connection the host machine is connected to.


Network Driver Interface Specification. NDIS provides a framework for network adapter driver and network protocol driver implementations and handles the binding process between them.


Remote NDIS, the topic of this documentation.


Universal Serial Bus, an external bus standard.

USB function bus driver

The lower layer driver, which directly manages the USB function controller hardware.

USB function client driver

The driver that has full control over the function controller hardware. There can only be one function client driver loaded at any given time. Examples of client drivers are RNDIS, serial and mass storage.

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