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When using the Hewlett-Packard Network Printer Interface to support network-attached printers, the HPREDIR software communicates with the printer over an 802.2 DLC class II session using the LAN Manager COMTOKR device driver and ACSLAN.DLL interface. This article describes the various DLC timers, default settings, and suggested values in order to make the printer connection more reliable. HP network printer versions A.00.02 and A.00.03 are discussed below.
The DLC class II protocol uses three timers:
T1 - Response timerThe timer values are specified in timer ticks. Each timer requires a short timer tick (tick_one) and long timer tick (tick_two). The length of these ticks are specified in the PROTOCOL.INI file (see below) in 40 millisecond increments.
T2 - Acknowledgment timer
Ti - Inactivity timer
The actual length of each timer (T1, T2, Ti) is selected with parameters provided when the DLC_OPEN_SAP, DLC_OPEN_STATION, or DLC_MODIFY command is 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 (tick_one) is used. The timer value will be 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 (tick_two) is used. In this case the timer value will be equal to the selected number minus 5 multiplied by the long timer tick value.
timer value = selected number * short tick value * 40ms
The response timer (T1) is used to detect a failure to receive an acknowledgment or a response from the remote link station.
timer value = (selected number - 5) * long tick value * 40ms
The link station starts T1 when it transmits either an I- or S-frame (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 the 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. The suggested default value for T1 is 1 second.
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 suggested default value for T2 is 100 milliseconds.
The inactivity timer 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. The suggested value for Ti is 30 seconds.
RecommendationsGiven this, here are the values used by HPREDIR (versions A.00.02 and A.00.03):
Note the following settings for the COMTOKR driver in PROTOCOL.INI. However, because HPREDIR explicitly sets the maxretrycnt to 0A (10), COMTOKR's dlcretries entry is ignored.
A.00.02 A.00.03 ------- ------- DLC_OPEN_SAP timer_t1 05 (same) timer_t2 02 . timer_ti 03 . maxout 04 . maxin 04 . maxincr 01 . maxretrycnt 1E . sap_value C4 . options_priority 04 . sap_station_count 06 07 DLC_OPEN_STATION timer_t1 01 05 timer_t2 01 02 timer_ti 01 03 maxout 04 (same) maxin 04 . maxoutincr 01 . maxretrycnt 0A . rsap_value B4 . max_i_field 0104 . accesspriority 00 .
These default settings yield the following timeout periods and recommendations:
Min Max Default --- --- ------- t1_tick_one 1 255 5 t2_tick_one 1 255 1 ti_tick_one 1 255 25 dlcretries 1 65000 30
Article ID: 94084 - Last Review: October 14, 2013 - Revision: 3.0
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