Rally Vertical Pairing theory of operation

Updated: July 29, 2013

This topic discusses the Windows Rally Vertical Pairing theory of operation.

This information applies for the following operating systems:

  • Windows Server 2008 R2
  • Windows 7

In this section


Rally Vertical Pairing device implementation overview

This topic provides an overview of how to implement Rally Vertical Pairing devices.

WCN-NET protocol

The Windows Rally suite of protocols includes the Microsoft implementation of WPS, which is known as Windows Connect Now-NET (WCN-NET). This protocol is used to set up Wi-Fi networks and to add wireless devices to Wi-Fi networks.

Rally Vertical Pairing PnP-X support

All Rally devices must support PnP-X. In Windows, PnP-X provides the mechanism to discover the presence of a paired Rally device.

Rally Vertical Pairing device drivers

After Windows has configured a Rally device's Wi-Fi settings and has paired with the device, Windows detects that the device is online and starts the Plug and Play process. This process installs and loads the appropriate device drivers for the device. Plug and Play determines which device driver is the most appropriate driver for the device by examining drivers that are included with Windows, drivers that were previously installed on the system, and drivers on Windows Update. A Rally device that uses drivers that are included with Windows or drivers that are available on Windows Update does not require the user to install software from a CD-ROM or software that was manually downloaded from the device manufacturer's web site.

Rally Vertical Pairing devices and printers presence

Windows automatically detects the presence of PnP-X devices, including devices that use Rally Vertical Pairing, and displays them in Devices and Printers. Windows uses each device’s PnP-X metadata to correctly categorize and display the device. If a device manufacturer defines a metadata package for a device and submits the metadata package to Microsoft, Windows automatically downloads it from WMIS when Devices and Printers detects the presence of the device. Windows displays any photorealistic icons for the device and any rich metadata in Devices and Printers.


Consider a device that implements a DPWS print service (WS-Print). When a user first tries to connect to the print service on the device, Windows discovers that the device’s internal topology specifies that the device's print service depends on a Wi-Fi radio. Windows determines that it must first configure the device's Wi-Fi settings before it can communicate with the DPWS print service. Therefore, Windows performs the task of Wi-Fi provisioning and then pairs with the device.

It is important for wireless devices to communicate the internal device topology to Windows. This is the fundamental technology behind Rally Vertical Pairing. It enables Windows to discover and pre-pair with the high-level service before the device comes online. This is considered an out-of-band pairing. By pre-pairing with the high-level service, Windows can install the device as soon as it discovers the device, which occurs as soon as the device comes online.

Pre-pairing with high-level services is not necessary for wired devices because Windows discovers the high-level services only after the lower level dependencies, such as the wired Ethernet radio, have already been configured. A wired device must first configure its network interface and connect to the wired network by using its low-level dependency (the network radio) before Windows can discover the high-level services.

Windows 7 uses Rally Vertical Pairing when it connects to an unconfigured Wi-Fi device. The device uses the Wi-Fi alliance Wi-Fi Protected Setup (WPS) protocol to communicate the device’s topology to Windows by using a WPS vendor extension. The vendor extension identifies the protocols and unique identifiers that the device uses in its higher level services. The device sends the vendor extension with all WPS M1 messages so that the information about the device's topology is communicated during WPS discovery.

Windows uses this information to perform PnP-X out-of-band pairing while it configures the device's Wi-Fi settings during the WPS exchange. This pre-pairs the device with Windows before the device is actually available on the network.

After the device connects to the network and announces itself, PnP-X detects the device and starts the standard PnP process to install and load the appropriate device drivers for the device.

Related topics

Using Windows Rally Vertical Pairing to automatically install Wi Fi devices



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