USB Redirection

With USB Redirection, the signotec signature pad is passed through into the remote session as a complete USB device. On the server the pad appears as if it were connected locally; the USB data stream is transported through the remote protocol. Citrix refers to this function as Generic USB Redirection, Microsoft RDP uses the term USB device redirection (historically also RemoteFX USB Redirection).

This variant does not require any signotec-specific components and is therefore attractive in environments where no driver distribution is possible. However, based on the experience of signotec and many customers, it is the weakest of the options documented here — especially with Microsoft RDP. If any of the other connection methods is applicable, it should be preferred. A side-by-side comparison of the options is available at Options at a glance.

How it works

The USB stack of the client does not pass the pad to the local operating system but to the Citrix or RDP client. The latter tunnels the USB communication through the remote protocol. On the server, the pad is detected by the USB stack there and made available to an application. From the server application's perspective, the pad behaves identically to a locally connected device.

Because the raw USB frames are transported over the network, the variant is sensitive to latency, bandwidth, and session interruptions. On a session reconnect, the USB device is re-enumerated, which depending on the application can lead to a brief disconnection from the pad.

Prerequisites

• signotec signature pad in the USB variant (article number ending in U100)

• PC or thin client with Citrix Workspace App or Microsoft Remote Desktop Client

• USB redirection enabled in the remote protocol (Citrix policy or RDP Group Policy)

• Administrative privileges for configuring the policies

For FT100 devices, USB Redirection is not the intended path. The integrated FTDI chip is designed for the pad to be addressed via a COM port; the appropriate connection mechanisms are therefore the Virtual Serial Connection or the Citrix Virtual Channel.

Citrix configuration

The Citrix default rules do not automatically allow input devices (class HID) in many configurations. For signotec signature pads, an explicit Allow rule is therefore usually required. The rules follow the scheme Allow: or Deny: followed by any combination of tags (VID, PID, REL, Class, SubClass, Prot). Details on the full syntax are available in the Citrix documentation.

Variant 1 — Allow all signotec pads

For most environments it is sufficient to allow all devices from the manufacturer signotec. The Vendor ID (VID) of signotec is 2133:

Allow: VID=2133 # signotec Unterschriftenpads

Variant 2 — Allow only specific models

If redirection is to be restricted to individual pad models, the Product ID (PID) of the respective model is specified in addition to the VID. The Product IDs of the current signotec pads:

Example for a targeted allow rule for signotec Sigma and signotec Delta:

Allow: VID=2133 PID=0001 # signotec Sigma
Allow: VID=2133 PID=0015 # signotec Delta

If additional pad models are used, add a separate rule for each model.

Additionally, the Client USB device redirection — Auto connect policy (German: Automatische Verbindung der USB-Geräte) can be enabled so that the pad is connected automatically when the session starts.

RDP configuration

USB redirection over RDP is still referred to in the Microsoft tools by its historical name RemoteFX USB Device Redirection — even after Microsoft discontinued RemoteFX vGPU in 2020. USB redirection itself remains part of RDP.

It is enabled via Group Policy on the client:

Computer Configuration → Administrative Templates → Windows Components → Remote Desktop Services → Remote Desktop Connection Client → RemoteFX USB Device Redirection

Here the Allow RDP redirection of other supported RemoteFX USB devices from this computer policy is to be set to Enabled. In the options of the policy you can choose whether redirection is available to administrators and/or users.

After the policy has been enabled and the client restarted, the pad is available for selection in the Remote Desktop Client under Local Resources → Local devices and resources → More. Selecting the checkbox forwards the device into the session.

Verification

After USB redirection has been enabled, the pad appears in the Device Manager of the remote session — for the U100 variant as a USB input device, for the FT100 variant as a USB-to-serial converter with an assigned COM port. A signotec-compatible application in the session (e.g. signoSign/2 or a line-of-business application using the signoPAD-API) must then be able to address the pad.

In case of problems, check in the following order: detection of the pad on the client (Device Manager), USB redirection enabled in the remote protocol, correct VID/PID in the Citrix rule or selection of the device in the Remote Desktop Client, detection of the pad in the server session.

If a session reconnect results in a disconnection from the pad, this is not a configuration error but a known behavior of USB redirection: the device is re-enumerated on reconnect. The application must then re-establish the connection to the pad.