Microsoft KB Archive/102942

= Key Differences Between NetBEUI and NBF =

Article ID: 102942

Article Last Modified on 10/31/2006

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APPLIES TO


 * Microsoft Windows NT Advanced Server 3.1
 * Microsoft Windows NT Workstation 3.1
 * Microsoft Windows NT Advanced Server 3.1
 * Microsoft Windows NT Server 4.0 Standard Edition
 * Microsoft Windows NT Workstation 4.0 Developer Edition

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This article was previously published under Q102942



The NBF (NetBIOS Frame) protocol is no different from the NetBEUI protocol. To someone monitoring a network line, there is no difference in network packets; and, this holds true for any combination of Windows NT and non-Windows NT computers. The differences lie in the Windows NT implementation of the NetBIOS protocol.

Use of TDI
NBF uses the upper edge of the TDI interface. NetBEUI uses the upper edge of the NetBIOS interface.

With OS/2 and Windows for Workgroups, the server and redirector (and any other transport clients) submit network control blocks (NCBs) to NetBEUI. NCBs submitted by a NetBIOS application are also passed directly to NetBEUI. The format of all of these NCBs is the same, as defined by the IBM specification.

With Windows NT, the server and redirector submit TDI requests to NetBEUI. The set of TDI calls implement the same general semantics as the NetBIOS NCBs, but are optimized for a 32-bit kernel interface. An NCB passed in by a NetBIOS application is passed to the NetBIOS driver (NETBIOS.SYS), which examines the NCB and then submits the corresponding TDI call or calls to NetBEUI.

TDI is also used by all other transports, such as the streams environment or native TDI transports such as AppleTalk. There is no user mode TDI interface currently; applications should use NetBIOS or Windows Sockets.

Use of NDIS 3.0
NBF uses the lower edge of the NDIS 3.0 interface. NDIS 3.0 is functionally similar to NDIS 2.0 but has some improvements that benefit transports. The interface is a fully 32-bit asynchronous interface.

Removal of NetBIOS Session Number Limits
One of the benefits of TDI is that it does not use a one byte session number to identify a session, but rather a 32-bit handle. Therefore, a single TDI client may establish a virtually infinite number of sessions over a given TDI provider. For example, the server has been run over NBF with more than 1000 clients connected simultaneously on a single network adapter.

NBF is still constrained by the fact that the on-the-wire protocol used by NetBEUI and NBF also uses a one byte session number. For any connection between two adapters, there will be a local session number (assigned by this machine) and a remote session number (assigned by the other machine).

With NetBEUI the local session numbers were assigned globally, limiting NetBEUI to a total of 254 sessions (the session numbers and 255 cannot be used). NBF gets around this by assigning its local session numbers on a per-remote-adapter basis. That is, it may use local session number 1 when talking to adapter A and also have a session locally numbered 1 when talking to adapter B. The two remote computers will not get confused because adapter A does not see frames destined for B, and vice versa. However, if NBF establishes another session to A at the same time, it must use a session number other than 1 to keep things in order.

NBF can only do this when it is able to determine beforehand which adapter the connection is going to be made to. There are three cases that need to be considered:


 * A client connecting to NBF. When a client connects to a computer running NBF, NBF can inspect the incoming frame to determine the remote adapter's address and assign a session number for that adapter.
 * NBF connecting to a remote client with a unique NetBIOS name. When NBF is connecting to a remote client, it first sends a FIND.NAME frame. If the remote client responds, indicating the name is a unique name, NBF can look at the remote adapter address in the response and assign a session number for that adapter because it knows only that remote owns this name.
 * NVB connecting to a remote client with a group NetBIOS name. If the FIND.NAME response indicates that the connection is being made to a group name, NBF has no way of knowing which adapter belonging to the group will respond when it tries to connect, so it has to assign a session number on a global basis, just as NetBEUI did for all connections.

So, NBF has no limit on sessions, unless it is establishing connections to group names in which case the old NetBEUI limit still applies. To be accurate, if you have n group name connections, then you can have 254-n connections to any given remote client. If n is 0, then you can have a full 254 connections to a remote. If n is 253, you can still have 1 connection to each remote, but if n is 254, then no connections can be made until one of the existing ones is disconnected.

T1 Tuning
NBF tunes its T1 parameter dynamically on a per-link basis, based on link conditions and throughput. The T1 parameter specified in the Registry is used as a starting point, so if it is known that NBF is going to be talking over a slow link, this can be increased. If this is not done, however, NBF will detect the slow link quickly and adapt to it.

T2 and Ti are not adapted dynamically.

No ASyncBEUI Needed for RAS
There is no separate ASyncBEUI product for RAS. NBF handles communications over the RAS link as well as over the LAN. In general NBF's auto-tuning makes specific RAS parameters unnecessary. The exception is the WanNameQueryRetries parameter which corresponds to NameQueryRetries but is used for connections going over the RAS line.

Memory Usage Tuning
NBF automatically allocates memory when it needs to satisfy the requests made by its clients. Therefore, NBF does not need to be configured with the number of sessions, packets, buffers, etc. to allocate. However, there are hidden Registry parameters in NBF that can be used to control these if desired. (Query in the Microsoft Knowledge Base for more information using the following key words: NBF and REGISTRY.) This also means that NBF uses memory only when needed. On an inactive machine it will consume very little memory.

No Session Alives
NBF does not use NetBIOS session alive frames to determine if the remote client is up. Instead, it sends LLC poll frames which serve the same purpose. This may confuse people who are sniffing the network and are used to seeing session alive frames from NetBEUI. NBF will respond correctly to session alive frames, so this should cause no interoperability problems with other implementations of NetBEUI.

Additional query words: wfw wfwg prodnt

Keywords: kbnetwork KB102942

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