USB redirection (Universal Serial Bus redirection) is a technology that allows an end user to plug an external device into a USB port on their endpoint and access the device from within a remote desktop or application. The redirection process involves forwarding the USB device's functionality from a local device to a virtual desktop over the network. USB redirection works on both wide area networks (WANs) and local area networks (LANs), but it is often easier over a LAN because LANs usually provide a stronger network connection than WANs.
Organizations supporting USB redirection on virtual desktops must use servers that are compatible with the remote display protocol in its VDI software. For example, VMware USB redirection for Horizon View desktops does not support Windows Server 2003 or 2008. Redirection capabilities also depend on the version of VDI software a company uses. For example, Citrix added support for USB devices that use a stylus in XenDesktop and XenApp 7.6 Service Pack 3. Additionally, VMware's Horizon View did not support USB redirection prior to version 5.2.
Administrators can choose which USB devices they allow users to redirect. Common USB devices that are candidates for redirection include flash and other storage drives, smart card devices, printers, and audio, video and image devices. Some devices -- such as scanners and sometimes audio or video devices -- require a lot of bandwidth and can increase latency. Some USB redirection tools block certain device types all together. Other USB devices, such as mice and keyboards, are integrated into the VDI software already.
Citrix supports USB redirection through its HDX remote display technologies, and similarly Microsoft uses its RemoteFX technologies. VMware uses Teradici's PC-over-IP protocol and Microsoft Remote Desktop Protocol for USB redirection.