INFO: Comparing SNA client TCP/IP named pipes vs sockets (128985)

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Named Pipes over TCP/IP

When communicating over named pipes, the SNA Server client opens a named pipe resource (\\server\PIPE\...) which is created by the SNA Server. A named pipe is an interprocess communication facility supported by the client redirector (that is, Windows for Workgroups protected mode redirector) and the Windows NT Server. The SNA Server client and server send messages to each other over this named pipe.

As with shared file and printer connections, named pipe session traffic flows over a NetBIOS session between the client redirector and the Windows NT server using the "Server Message Block" (SMB) protocol. The following illustrates the message flow:

  SNA Client         <- Named Pipe ->           SNA Server

  Redirector   <- SMB over NetBIOS session ->   NT Server

  TCP/IP          <- TCP/IP connection ->       TCP/IP

  Network card <---------------------------->   Network card
				

A typical message packet would include the following information:

   [ IP | TCP [ NetBios [ SMB ( SNA application data ) ] ] ]
				

Disadvantages of Using Named Pipes

The client redirector and Windows NT server process all messages passed between the SNA Server client and the server. All named pipe messages are formatted within "SMB" requests by the client redirector and NT server which flow over a NetBios session.

Each NetBios session requires "keep-alive" messages to flow between the client redirector and Windows NT server. These NetBIOS level acknowledgments lead to network overhead, and the possibility of NetBIOS-level timeout conditions when traveling across a routed IP network.

A NetBIOS session over TCP/IP requires NetBIOS-to-IP address name resolution, requiring a client LMHOSTS file entry for each server, or a WINS server to provide this name resolution. DNS servers don't provide this name resolution.

Since each SNA Server client has one outstanding read request pending on the sponsor connection, and one read pending on the SNA application session, Windows NT server resources are required to handle these pending I/O requests even when the SNA client session is idle.

Advantages of Using Named Pipes

Windows NT user validation is performed by the client redirector and the Windows NT server (as part of the SMB protocol). This allows the user's initial network login to be used.

TCP/IP Sockets

When communicating over TCP/IP sockets, the SNA Server client opens a TCP/IP socket number created by the SNA Server. A socket is a session- oriented interprocess communication facility supported directly over the TCP/IP transport. The following illustrates the message flow:

  SNA Client         <- TCP/IP socket ->         SNA Server

  TCP/IP           <- TCP/IP connection ->       TCP/IP

  Network card  <---------------------------->   Network card
				

A typical message packet includes the following information:

   [ IP | TCP ( SNA application data ) ]
				

Advantages of Using TCP/IP Sockets

The SNA Server client and server communicate directly over the Windows sockets interface, bypassing NetBIOS, the SMB protocol, and overhead introduced using the named pipes interface.

TCP/IP name-to-IP address resolution is provided by the client HOSTS file, DNS server, or WINS server

TCP/IP session keep-alive timeout processing is handled directly by the SNA Server client and server. The SNA Server WatchDogTimeOut setting controls the timeout value, as described in the SNA Server 2.1 readme file (the default is 60 seconds).

The SNA Server Win 3.x client uses a larger buffer size to exchange data with the server than does the SNA client named pipe interface. Also, data transfer is performed using byte stream protocol which makes better use of network resources (named pipes uses message mode protocol).

Disadvantages of Using TCP/IP Sockets

User authentication is handled by the SNA Server client and server. This requires the user to "login" to the Windows NT network when the SNA client software is loaded. This client login can be automated to some degree, as described on page 208 of the SNA Server 2.1 Reference Guide. In SNA Server 2.11, more enhancements have been made in this area. For additional information, see the following article in the Microsoft Knowledge Base: NOTE: Windows 95 and Windows NT support secure programmatic methods to impersonate the currently logged on user. Therefore, there is no need to automate the client logon request when using the SNA Server Windows 95 or Windows NT client software.