DLC Driver Parameters in the Registry

Unlike other Windows NT protocol drivers, DLC does not bind to a MAC driver until an adapter open command is issued. When an adapter is opened for the first time, the DLC protocol driver writes some default values into the Registry for that adapter. These values control the various timers that DLC uses, whether DIX frames should be used over an Ethernet link, and whether bits in a destination address should be swapped (used when going over a bridge that swaps destination addresses).

The timer entries in the Registry are supplied because program-supplied timer values might not be sufficient. There are three timers used by DLC link communication:

• T1 is the response timer.
• T2 is the acknowledgment delay timer.
• Ti is the inactivity timer.

Each timer is split into two groups—TxTickOne and TxTickTwo, where x is 1, 2, or i.

Typically, these timer values are set when a program opens an adapter and/or creates a Service Access Point (SAP).

The Registry contains entries used to modify timer values. Registry entries for DLC are found in the following location:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\DLC\Parameters   \<Adapter Name>

When you edit a timer entry value, the change takes effect the next time the adapter is opened (for example, by rerunning the application). For more information, including the ranges and default values for the timers, see "DLC System Driver Entries" in Chapter 14, "Registry Value Entries."