Editing NetBIOS Frames (section)

===Session service===
Session mode lets two computers establish a connection for a "conversation," allows larger messages to be handled, and provides error detection and recovery.

Sessions are established by exchanging packets. The computer establishing the session sends a "Name Query" request, specifying that a session should be initialized. The computer with which the session is to be established will respond with a "Name Recognized" response indicating either that no session can be established (either because that computer is not listening for sessions being established to that name or because no resources are available to establish a session to that name) or that a session can be established (in which case the response will include a local session number to be used in subsequent packets). The computer that is starting the session will then send a "Session Initialize" request which will prompt a "Session Confirm" response.

Data is transmitted during an established session by data packets. IEEE 802.2 handles flow control and retransmission of data packets. Because NetBIOS/NetBEUI allows packets to be sent that are larger than the largest packet that could be transmitted on a particular [[MAC layer]], a NetBIOS/NetBEUI packet might have to be transmitted as a sequence of "Data First Middle" packets and a "Data Only Last" packet; packets that do not need to be segmented in that fashion will be sent as a single "Data Only Last" packet. An acknowledgment will be sent for all "Data Only Last" packets that are successfully received; this will also acknowledge all preceding "Data First Middle" packets.

Sessions are closed by sending a "Session End" request.