Windows Server 2008: The WSD Port Monitor

 Welcome back!  If you're just returning from a weekend, hopefully you got some time to yourself to relax.  It's Day Eleven of our Windows Server 2008 Series.  Today's topic - the new WSD Port Monitor. The WSD Port Monitor is a new printer port monitor in Windows Vista and Windows Server 2008.  This port monitor […]

 Welcome back!  If you're just returning from a weekend, hopefully you got some time to yourself to relax.  It's Day Eleven of our Windows Server 2008 Series.  Today's topic - the new WSD Port Monitor.

The WSD Port Monitor is a new printer port monitor in Windows Vista and Windows Server 2008.  This port monitor supports printing to network devices that are designed to include Web Services for Devices (WSD) technology.  Web Services for Devices allows network-connected IP-based devices to advertise their functionality and offer these services to clients by using the Web Services protocol.  WSD-based devices and clients communicate over the network using a series of SOAP (Simple Object Access Protocol) messages over UDP and HTTP(S).  WSD for Devices provides a network plug-and-play experience that is similar to installing a USB device.  Web Services for Devices also defines a security profile that may be extended to provide additional protection and authentication using device-based certificates.

The WSD Port Monitor is installed by default on Windows Vista.  On Windows Server 2008, the port monitor is installed along with the Print Services server role.  Web Services for Devices is not available for Windows XP or Windows Server 2003.  These clients can print to WSD-based devices that are shared on computers running Windows Vista or Windows Server 2008.  There are four main tasks performed by the WSD Port Monitor:

  • Discover and connect to WSD-based network printers
  • Send print jobs to WSD printers
  • Monitor the status and configuration of the WSD printers and update the printer object status accordingly
  • Respond to bidirectional queries from WSD printers

These are the same functions provided by other port monitors (for example the Standard TCP/IP port monitor, tcpmon.dll).  The WSD Port Monitor is implemented in wsdmon.dll.  This DLL is loaded under the print spooler process (spoolsv.exe) and is defined as a port monitor in the following registry key: HKLM\SYSTEM\CurrentControlSet\Control\Print\Monitors\WSD Port.  For WSD-based print devices, the WSD Port Monitor is used by default.  If the print device does not support the WSD Port Monitor, then the Standard TCP/IP Port Monitor is used instead.

Now that we know what the WSD Port Monitor does, let's look at the communications mechanism used by WSD.  When a WSD-based printer is connected to a network, it sends out an unsolicited "Hello" message to advertise its presence.  Computers running Windows Vista or Windows Server 2008 listen for these advertisements and add the printer to their list of available network printer resources.  When a WSD-based device is gracefully removed from the network it sends another message (a "Bye" message) to advertise that it is no longer available.  In addition, Windows Vista and Windows Server 2008 machines can discover WSD-based printers by using a "Probe" message when searching for printers via Network Discovery or the Add Printer Wizard.  A typical WSD communication sequence is shown below[…]

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Additional Resources:

Microsoft, WS2008, Windows Server 2008, WSD, Port, Monitoring, Architecture, Printing, Knowledgebase