ActiveSync 4.5 USB Drivers on Windows XP

This article examines how Microsoft ActiveSync 4.5 established and managed USB connections for Windows Mobile 6.5 devices on Windows XP. It details the underlying driver architecture, the role of the Remote Network Driver Interface Specification (RNDIS), fallback serial emulation mechanisms, and the networking protocols used to facilitate data synchronization between the mobile operating system and the desktop environment.

When a Windows Mobile 6.5 device was connected to a Windows XP computer via USB, ActiveSync 4.5 managed the connection primarily as a virtual network adapter rather than a traditional serial device. ActiveSync 4.5 installed a driver stack centered on the Remote Network Driver Interface Specification (RNDIS). Upon physical connection, the host operating system queried the device's USB descriptor, recognized the Microsoft-specific class or vendor ID, and loaded the host RNDIS driver (rndismp.sys) alongside the USB transport driver (usb8023.sys).

This architecture treated the USB data cable as an emulated Ethernet connection. By abstracting the physical USB bus into a standard local area network (LAN) interface, ActiveSync significantly boosted data transfer speeds compared to older serial emulation techniques. Once the RNDIS link was established, the Windows XP host and the Windows Mobile 6.5 device established a private TCP/IP network, assigning link-local IP addresses (commonly within the 169.254.2.x subnet). ActiveSync’s background processes, such as wcescomm.exe, then bound to specific network ports (primarily TCP ports 990, 999, 5678, and 5679) to manage file transfers, Outlook synchronization, and remote registry queries.

To ensure broad hardware compatibility, Windows Mobile 6.5 retained a configuration toggle labeled "Enable advanced network functionality." When this option was enabled, the device negotiated the modern RNDIS driver connection. If desktop firewalls, conflicting network policies, or legacy USB chipsets on Windows XP prevented the RNDIS adapter from communicating, users could uncheck this setting. Disabling it instructed the device to present itself via a legacy USB-to-serial profile. Windows XP would then load the Windows CE USB Serial Host driver (wceusbsh.sys), routing ActiveSync communications over an emulated virtual serial COM port at the cost of lower throughput.

Through this dual-mode driver implementation, ActiveSync 4.5 ensured that Windows Mobile 6.5 devices maintained reliable, high-speed connectivity over Windows XP's native network stack while preserving backward compatibility through serial emulation.