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SMB Connection Limitations

8/22/2007

Microsoft Corporation.

November 2006.

Learn about the Server Message Block (SMB) protocol and the connection limits imposed by Windows® XP Embedded licensing guidelines.

Microsoft SMB protocol in Windows XP Embedded is an implementation of the SMB Protocol, a file sharing protocol that employs a client-server method of communication.

SMB works at the application layer of the OSI reference model and depends on Transmission Control Protocol (TCP) and Internet Protocol (IP), at the transport and internet layers, respectively. Although no licensing restrictions apply to the number of simultaneous TCP/IP connections, Windows® XP Embedded licensing guidelines restrict the number of concurrent SMB connections.

The Microsoft implementation uses the set of message packets that are specified for Common Internet File System (CIFS) protocol, which is a "dialect" of the SMB Protocol. Microsoft SMB clients use CIFS to request file and print services from network servers.

While it is typically used to share files over a network, Microsoft SMB Protocol offers capabilities including:

  • Locating other Microsoft SMB Protocol servers on a network
  • Network printing
  • Authentication of access to files, directories, and shares
  • Locking files and records
  • Change notifications for files and directories
  • Negotiating protocol dialects
  • Handling extended file attributes
  • Unicode support
  • Opportunistic locks

Although Microsoft SMB Protocol does not require a separate transport protocol, it is frequently implemented with NetBIOS—a session-level interface—over TCP/IP; on Windows-based systems, this implementation is known as NetBT.

NetBT is typically used to provide backward compatibility; however, a NetBIOS network often uses a broadcast-based method of name resolution, which has disadvantages including:

  • No interoperability over routers in a routed network
  • Broadcast traffic requires significant network bandwidth
  • Normal network operations require the consumption of resources on every network node in the broadcast area

NetBIOS-based networks are effective in a small local area network (LAN) environment; however, they are not workable for large LAN or wide area network (WAN) environments, or in environments where routers are used.

To enable NetBT functionality, add the NetBIOS over TCP/IP component to your run-time image configuration. This component provides the TCP/IP NetBIOS Helper service, which runs within the context of SvcHost.exe, in the ImhSvc.dll file. The NetBIOS component is also included as a dependency in the TCP/IP Networking component.

The File Sharing component provides file and print services through the SMB protocol. The File Sharing component is included in the TCP/IP Networking with File Sharing and Client for MS Networks component, which bundles the components that are required to provide basic TCP/IP services. For more information about these components, see the Component Help documentation that is included with Windows XP Embedded.

Windows XP Embedded licensing guidelines permit no more than 10 simultaneous connections over Microsoft SMB Protocol to a Windows XP Embedded system.

This white paper briefly examines the SMB file sharing protocol. It discusses the licensing-imposed limitation of 10 concurrent SMB connections.

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