KB: Graphics update freezes on a Windows Server 2012-based RD Session Host server that is under a heavy load

A new KB hotfix was released today (KB 2797502) regarding graphics update for all the connected RDP clients freezes for at least 100 milliseconds when a client connects that runs Windows 7 Service Pack 1 (SP1) with RDP 8.0 installed.

“…Consider the following scenario:

• You have a Remote Desktop Session Host (RD Session Host) server that is running Windows Server 2012.
• The RD Session Host server has more than 50 Remote Desktop Services (RDS) clients connected, and that causes the RD Session Host server to be under a heavy load. 
• The RD Session Host server receives a Remote Desktop Protocol (RDP) session from a Windows 7 Service Pack 1 (SP1)-based RDS client that has RDP 8.0 installed. 
  Note For more information about how to install and enable RDP 8.0 on a computer that is running Windows 7 SP1, click the following article number to view the article in the Microsoft Knowledge Base:

  2592687

  (http://support.microsoft.com/kb/2592687/ )

  Description of the Remote Desktop Protocol 8.0 update for Windows 7 SP1 and Windows Server 2008 R2 SP1

In this scenario, the graphics update for all the connected clients freezes for at least 100 milliseconds. Additionally, this issue recurs when the RD Session Host server receives new RDP sessions from any other clients…”

“…This issue occurs because a User Datagram Protocol (UDP) connection object is not created immediately after an Acknowledgement (ACK) packet is received. This behavior provides an opportunity for all the other connections that have a pending date to be sent. Additionally, when multiple connections are established at the same time, if the higher layers of some connections are not ready, a 100-millisecond delay occurs to let the higher layer be registered by using the RDP-UDP layer..”

Source and download: http://support.microsoft.com/kb/2797502/en-us?sd=rss&spid=16526

RD Gateway in Windows Server 8 supports UDP

Remote Desktop Services in Windows Server 8 (Beta) supports the UDP protocol. The UDP transport protocol provides a better experience for users that connect to a RDS session on a server running Windows Server 8. TCP as well as UDP protocols can now be used for the RDP session.

The Remote Desktop Gateway (RD Gateway) in Windows Server 8 extends this UDP functionality by supporting it in the gateway. If the client or endpoint does not support UDP, RD Gateway will automaticially switch back and thus the selection process of the best possible transport protocol is completely transparent to the end-user as long as the it has been enabled in the RD Gateway and the client and RDP endpoint support a UDP connection. The client has to be equipped with Remote Desktop Client 8 to support UDP.

To configure the RD Gateway to use UDP when possible, open the RD Gateway manager and then select the "Transport Settings" tab. Here you have the option to enable UDP support. Of course, the UDP settings can also be configured using GPO's. E.g. there is a setting "Turn off UDP On Client" to configure it on the the client and setting "Connections - Turn Off UDP On Server" to force it to turn of on the RDSH server.