NBT SessionAlive and TCP/IP Session TerminationLast reviewed: May 15, 1997Article ID: Q115499 |
The information in this article applies to:
SUMMARYOn Windows NT build 528, if TCP/IP protocol is the transport used, then NetBIOS over TCP/IP (NBT) KeepAlive frames maintain an idle session by default. The session is terminated if the other end does not respond to these frames. This article describes NBT session termination. NOTE: This information applies only to NetBIOS over TCP/IP on Windows NT build 528. To determine which build of Windows NT you have installed:
1. In the Program Manager window, choose Run from the File menu. 2. In the Command Line field, type "winver" (without the quotation marks), and then choose the OK button. The Windows Version dialog box appears with the version number and build number of Windows NT. MORE INFORMATIONThe default value for NbtKeepAlive is 60 seconds (KEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\NBT\Parameters). This means that if there is no activity for 60 seconds, NBT generates a SessionAlive frame to probe the connection. It is the function of TCP/IP to attempt to deliver these SessionAlive frames. The number of attempts made by TCP/IP to deliver the frame is governed by "TcpMaxRetransmissionAttempts" which has a default of 7 (KEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\TCPIP\Parameters). The Retransmission (RETX) timer depends on the Smooth Round Trip Time (SRTT); it is a dynamic timer and varies between any two stations; it also cannot be set or tuned in any way. The current RETX timer (whatever it is at that moment) is used for the first RETX attempt (of the seven). The RETX timer (t) is increased for subsequent retransmissions based on the formula: t=2t. Therefore, if the initial RETX value is 1 sec, then subsequent RETX timers would expire at 2, 4, 8, 16, 32, 64, 128 intervals. In the above example, assuming there is no response, TCP/IP would report failure to the above layer after 255 seconds (1+2+4...+128, including the time until the seventh attempt expires), then the redirector would clear the session. One point to note is that NBT would submit NEW SessionAlive Frames at 60 second intervals, which TCP/IP does not attempt to retransmit. In the above example, four new SessionAlive frames may be submitted by NBT in this 255 second period. If there is a need to clear the session quicker, reducing MaxRetransmissionAttempts even by one to a value of 6 would make it dramatically quicker (two minutes less, as per the example above). Reducing NbtKeepAlive from a value of 60 seconds to a lesser value will also contribute to clearing the session quicker. The following is a network trace illustrating the above:
# DeltaT Src MAC Dst MAC Ntprotocol Description
2 0.225 MOHAK01 Mohaksta TCP ACK seq:0x20131 3 59.850 Mohaksta MOHAK01 NBT Session Keep Alive seq:0x3EE4BF 4 0.936 Mohaksta MOHAK01 NBT Session Keep Alive seq:0x3EE4BF 5 1.975 Mohaksta MOHAK01 NBT Session Keep Alive seq:0x3EE4BF 6 3.957 Mohaksta MOHAK01 NBT Session Keep Alive seq:0x3EE4BF 7 7.941 Mohaksta MOHAK01 NBT Session Keep Alive seq:0x3EE4BF 8 15.883 Mohaksta MOHAK01 NBT Session Keep Alive seq:0x3EE4BF 9 29.613 Mohaksta MOHAK01 NBT Session Keep Alive seq:0x3EE4C3 10 2.082 Mohaksta MOHAK01 NBT Session Keep Alive seq:0x3EE4BF 11 58.217 Mohaksta MOHAK01 NBT Session Keep Alive seq:0x3EE4C7 12 5.171 Mohaksta MOHAK01 NBT Session Keep Alive seq:0x3EE4BF 13 55.150 Mohaksta MOHAK01 NBT Session Keep Alive seq:0x3EE4CB 14 60.291 Mohaksta MOHAK01 NBT Session Keep Alive seq:0x3EE4CFIn the above trace, frame 2 is the last frame from MOHAK01. NBT initiates Session Alive Frames starting at #3. Frames 9,11,13,14 are "New" Session Alive Frames submitted by NBT which are not retransmitted by TCPIP.
|
Additional query words: prodnt Hang session end disconnect
© 1998 Microsoft Corporation. All rights reserved. Terms of Use. |