NetBIOS is an acronym for Network Basic Input/Output System. The NetBIOS API allows applications on separate computers to communicate over a local area network. It provides services related to the session layer of the OSI model.
The default NetBIOS name for the Modtronix SBC65EC Web Server is "MXBOARD". This name can be used in stead of the board's IP address in many programs. For example, to access the web based interface of the board, type "http://mxboard" in the address field of a web browser. The following description of NetBIOS was taken from Wikipedia, the free encyclopedia. The Modtronix SBC65EC Web Server only implements a small part of the protocol!
NetBIOS provides three distinct services:
- Name service for name registration and resolution
- Session service for connection-oriented communication
- Datagram distribution service for connectionless communication
Note: SMB, an upper layer, is a service that runs on top of the Session Service and the Datagram service, and is not to be confused as a necessary and integral part of NetBIOS itself. It can now run atop TCP with a small adaptation layer that adds a packet length to each SMB message; this is necessary because TCP only provides a byte-stream service with no notion of packet boundaries.
In order to start Sessions or distribute Datagrams, an application must register its NetBIOS name using the Name service. NetBIOS names are 16 bytes in length and vary based on the particular implementation. Frequently, the 16th byte is used to designate a "type" similar to the use of ports in TCP/IP. In NBT, the name service operates on UDP port 137 (TCP port 137 can also be used, but it is rarely if ever used).
The name service primitives offered by NetBIOS are:
- Add Name - registers a NetBIOS name
- Add Group Name - registers a NetBIOS "group" name
- Delete Name - un-registers a NetBIOS name or group name
- Find Name - looks up a NetBIOS name on the network
Session mode lets two computers establish a connection for a "conversation," allows larger messages to be handled, and provides error detection and recovery. In NBT, the session service runs on TCP port 139.
The session service primitives offered by NetBIOS are:
- Call - opens a session to a remote NetBIOS name
- Listen - listen for attempts to open a session to a NetBIOS name
- Hang Up - close a session
- Send - sends a packet to the computer on the other end of a session
- Send No Ack - like Send, but doesn't require an acknowledgment
- Receive - wait for a packet to arrive from a Send on the other end of a session
In the original protocol used to implement NetBIOS services on PC-Network, to establish a session, the computer establishing the session sends an Open request which is responded to by an Open acknowledgment. The computer that started the session will then send a Session Request packet which will prompt either a Session Accept or Session Reject packet. Data is transmitted during an established session by data packets which are responded to with either acknowledgment packets (ACK) or negative acknowledgment packets (NACK). Since NetBIOS is handling the error recovery, NACK packets will prompt retransmission of the data packet. Sessions are closed by the non-initiating computer by sending a close request. The computer that started the session will reply with a close response which prompts the final session closed packet.
Datagram mode is "connectionless". Since each message is sent independently, they must be smaller; the application becomes responsible for error detection and recovery. In NBT, the datagram service runs on UDP port 138.
The datagram service primitives offered by NetBIOS are:
- Send Datagram - send a datagram to a remote NetBIOS name
- Send Broadcast Datagram - send a datagram to all NetBIOS names on the network
- Receive Datagram - wait for a packet to arrive from a Send Datagram operation
- Receive Broadcast Datagram - wait for a packet to arrive from a Send Broadcast Datagram operation
For details on configuring this module, see
Configuration section of
nbns.h file.
