Endpoints, Netlibs, IPC and stuff…

Its been a while since my last post. No special reason, just a combination of lot of work and I didn’t feel I had something pressing to say…

This topic is basically on how the client app communicates with SQL Server. Not the API level (like ADO or ODBC), or the packet level (TDS), but in between. Basicaly we’re talking IPC, Inter Process Communication – in a SQL Server context:

Here’s how I understand it (I probably gonna get some points wrong and you are all welcome to correct me):

There are network protocols, such as:

  • TCP/IP (has routing functionality of course)
  • NetBEUI (very limited, if any, routing functionality)
  • IPX (the original protocol for Novell networks)
  • SNA (mainly used in IBM mainframe and such environments)

A network protocol is of little use if we can’t send data back and fort between application over that network protocol. So, there are APIs to facilitate IPC:

  • NETBIOS (originally developed for NetBEUI, but is also supported over IP (requires WINS or LMHOST for name resolution))
  • Sockets (not available for NetBEUI AFAIK, only TCP/IP)
  • Named Pipes (built on top of NETBIOS)
  • RPC (implemented and available over both NetBEUI and IP)
  • SPX (as I understand it, the API over IPX)
  • APPC (program-to-program protocol over SNA)

When MS released “their” SQL Server, they needed a way for the client app to communicate to the server. They decided to go for Named Pipes and developed what we call “netlib”. I.e., the MS deveopers used the Named Pipes API (which is similar to reading and writing to a file from the programmers perspective) when developing the Named Pipes netlib.

Over time, new netlibs were developed, where in SQL Server 2000, this culminated in below list:

  • Shared Memory (only for local connections, obviously) 
  • Named Pipes
  • Sockets
  • RPC
  • VIA
  • SPX

There was never a netlib deveoped directly on top of NETBIOS, but indirectly through Named Pipes. Named Pipes uses NETBIOS, which available over IP, and hence is routable. In 2005, the list has shrunk to:

  • Shared Memory 
  • Named Pipes
  • Sockets
  • VIA

And I have a feeling that in the end Named Pipes will go away. I don’t have any experience with VIA, but I believe that it is closer to the metal than Sockets so it might stick around for dedicated AppServer-to-SqlServer networks.

So, what does above have to do with Endpoints? Well, MS are categorizing netlibs as endpoint nowadays. This makes sense since the netlibs are a “way in” to SQL Server, as are HTTP, Service Broker and Database Mirroring endpoints.

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