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Dependent clients

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Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

Dependent clients

For the purposes of this documentation, the term Message Queuing server refers to a Windows Server 2003 family computer that has Message Queuing installed. The term Message Queuing client can refer to either an independent client, or a dependent client. Both of these terms are used to describe Message Queuing servers that have particular Message Queuing components installed, and such computers are referred to as having independent client functionality, or dependent client functionality.

Message Queuing servers with dependent client functionality require synchronous access to a Message Queuing server, called a supporting server, for all messaging functions. The supporting server can be any Message Queuing computer operating in domain mode with at least independent client functionality, preferably in the local site, but also in a nearby site. Note that computers configured as independent clients cannot provide Active Directory access for MSMQ 1.0 clients. These clients require Message Queuing servers running on a domain controller.

A dependent client relies on its supporting server to perform all messaging functions on its behalf, such as hosting queues, storing messages, sending messages, and receiving messages. If the supporting server goes offline, the dependent client will be unable to send and receive messages. By default, following installation, Message Queuing computers are not enabled to support dependent clients. For instructions on enabling a Message Queuing server to act as a supporting server, see Enable a supporting server. If you want to specify a Message Queuing server to act as a supporting server for a dependent client, you must also change the security configuration of the Microsoft Distributed Transaction Coordinator (DTC) on the Windows Server 2003 family computer to enable network transactions. The DTC is automatically installed on each computer during Windows Server 2003 family operating system installation for local transactions, and you need to enable network DTC. For instructions, see Enable network DTC access.

When you install a dependent client, you designate its supporting server. You can also later change the supporting server. Note that if you have the early version of a dependent client running on Windows NT 4.0 and you want to change its supporting server to a Message Queuing server running on Windows 2000 or Windows Server 2003 family, the dependent client must have Windows NT 4.0 Service Pack 4 or higher installed or else transactional messaging will not function. For instructions on changing the supporting server for a dependent client, see Change the supporting server for a dependent client.

For information on how to view the list of dependent clients currently supported by a Message Queuing server, see View the dependent client list for a server.

Dependent client considerations

Decide whether or not you want to deploy dependent clients in your organization. The advantages of using dependent clients are as follows:

  • Server disk space is used to store messages. When necessary, you upgrade only the server resources (such as memory and hard disk space) to improve Message Queuing performance, instead of upgrading all the client computers.

  • With fewer points of administration, you have fewer computers to back up and fewer journals and dead-letter queues to monitor.

  • Fewer resources are used if the dependent client is frequently offline and the server is not.

Dependent clients also have the following disadvantages:

  • Because the Message Queuing service runs on the supporting server, encrypted messages sent to or received by dependent clients travel between the dependent client and supporting server as plaintext.

  • Queue access time is slower for a dependent client than it is for an independent client. This is because queue access is through an RPC-based connection.

  • There may be performance issues if multiple dependent clients connect to their supporting server at the same time to send or receive messages.

  • Dependent client queues are located on their supporting server, and it is not obvious which queues belong to which dependent clients.

  • When dependent client software is uninstalled, the associated queues are not automatically deleted from the supporting server.

  • Because communication from a dependent client goes through the supporting server, if the communication to the supporting server is slow or expensive (such as between two sites), all dependent client communications are also slow or expensive.

  • Dependent clients cannot run under a local user account.

  • New Windows Server 2003 family Message Queuing features, such as HTTP transport, Message Queuing Triggers, and sending messages to multiple destinations, are not available to dependent clients. Thus, distribution lists, multiple-element format names, and multicast messaging are not supported for dependent clients.

  • Dependent clients cannot be installed on computers in workgroup mode or on 64-bit computers.

  • Transactional messaging is not supported for dependent clients running on Windows NT 4.0, Windows Milleninum Edition (ME), and Windows 98, Windows 95 computers that use a supporting Message Queuing server running on Windows XP Professional or Windows Server 2003 family operating systems.