The information in this article applies to:
SUMMARY
By default, the SNA Server Admin program sets the t1, t2 and ti timers on
all 802.2 connections to a value of "Default". This article describes the
actual timer values used by SNA Server when this default setting is
configured, as well the various DLC timers and default settings.
MORE INFORMATIONDLC Timer ParametersThe following information describes various DLC timer parameters and how DLC timer values are calculated.The DLC class II protocol uses three timers:
The timer values are specified in timer ticks. Each timer requires a short
timer tick (xxTickOne, where xx is t1, t2, or ti) and long timer tick
(xxTickTwo, where xx is t1, t2 or ti). The length of these timer ticks are
specified within the Windows NT DLC Transport driver (in the registry) in
40 millisecond increments.
The actual length of each timer (t1, t2, ti) is selected with parameters provided by the DLC application (SNA Server in this case) when the DLC_OPEN_SAP, DLC_OPEN_STATION, or DLC_MODIFY commands are issued. In these commands, the timer value is selected with a number between 1 and 10. If the number is between 1 and 5, the short timer tick (xxTickOne) is used. The timer value is equal to the selected number multiplied by the short timer tick value:
If the selected number is between 6 and 10, the long timer tick (xxTickTwo)
is used. In this case the timer value is equal to the selected number minus
5 multiplied by the long timer tick value.
The response timer (t1) is used to detect a failure to receive an
acknowledgment or a response from the remote link station.
The link station starts t1 when it transmits either an Information (I-frame) or Supervisory (S-frame, such as a RR/RNR/REJ) with the poll bit set. The t1 will be reset when the station receives a response frame with the final bit set. If t1 expires, the link station sends an S-frame with the poll bit set in order to query the status of the remote link station. The link station then restarts t1. If there is no recovery after the specified number of retries, the link station assumes that the link is inoperative and disconnects the link. The duration of t1 must take into account any delays introduced by the source routing bridges or routers separating SNA Server and the remote system. In some networks the T1 value will be increased to allow for propogation delay. DLC extends the T1 value using an algorithm based on the average poll response time of the connection:
The poll response time is the time it takes for the remote end to respond
to a frame sent with a Poll bit.
The link station uses the acknowledgment timer (t2) to delay the sending of an acknowledgment for a received I-frame. The t2 timer is started when a link station receives an I-frame. The t2 timer is reset when a link station sends an acknowledgment in an I-frame or in an S-frame. If the t2 expires, the link station must send an acknowledgment as soon as possible. The value of t2 must be less than the value of t1 of the remote station. This ensures that the remote link station will receive the acknowledgment before its response timer expires. The inactivity timer (ti) is used to detect an inoperative condition in the remote link station or in the transmission medium. If a station does not receive any S- or I-frames before its ti expires, it must query the status of the remote link station with an S-frame with the poll bit set. If it does not get a response after specified number of retries, it disconnects the link. SNA Server and 802.2 Connection TimersWhen an SNA Server 802.2 connection is activated, SNA Server sends a TEST frame to the remote network address configured for the connection.On Token Ring, the local ring is tried first. If there is no response to the TEST frame, SNA Server resends the TEST frame with the "all routes broadcast" setting enabled which is then forwarded by source routing bridges. If there is source routing data present in the TEST frame response from the remote system, then long tick timers are used on the connection. Otherwise, short tick timers are used. On Ethernet, since there is no source routing data, the short tick timers are always used. Here are the short tick and long tick timers used by SNA Server:
These multiplier values are used in conjunction with Windows NT Data Link
Control transport settings to calculate the actual timer value used on the
connection. The Windows NT DLC transport is configured with the following
default timer values:
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correct them. Microsoft cannot guarantee that any problems resulting
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These default settings yield the following timeout periods: If SNA Server is connecting to the remote system over Ethernet or Token Ring where no source routing bridges are involved, then short tick timers are used, giving the following default timer settings:
If SNA Server is connecting to the remote system over Token Ring across
source routing bridges, then long tick timers are used, giving the
following default timer settings:
The SNA Server ti, t2 and ti timers can be manually set for each
connection. The maximum value of each timer is 10, which yields the
following timeout periods:
To increase these timers further, the DLC transport timer settings must be
increased within the registry. However, caution should be taken before
changing these settings.
Additional query words: prodsna
Keywords : kbnetwork kbusage nthowto ntprotocol ntconfig snadlc sna211 sna3 sna4 sna2 sna21 |
Last Reviewed: September 17, 1999 © 2000 Microsoft Corporation. All rights reserved. Terms of Use. |