Interoperability with IBM Host Systems

Windows 2000 Professional includes a protected-mode, 32-bit, Data Link Control (DLC) protocol driver. You can use the DLC protocol to connect directly to an IBM host. However, you need third-party host emulation software to do so; DLC functions at the data-link layer of the Open Systems Interconnection (OSI) model. Because DLC functions at the data-link layer, it does not depend on other LAN protocols (for example, TCP/IP) for host connectivity; it is possible to have only the DLC protocol installed and bound to your network adapter.

To install the DLC Protocol

1. Open Network and Dial-Up Connections in Control Panel.

2. Right-click the local area connection for which you want to install the DLC protocol, and then click Properties .

3. On the General tab, click Install .

4. In the Select Network Component Type dialog box, click Protocol , and then click Add .

5. In the Select Network Protocol dialog box, click DLC Protocol , and then click OK .

In most cases, it is not necessary to change the default values for the DLC protocol. Generally, the only reason to change any of these parameters is if you are told to do so by the customer support department of the company from which you have obtained your third-party host emulation software. If you do have to change the default values, you might be able to change some of them by using the third-party host emulation software, for example by specifying a service access point (SAP). There are also some parameters that you can modify in the registry of Windows 2000 Professional, as Table 26.4 illustrates.

Caution

Do not use a registry editor to edit the registry directly unless you have no alternative. The registry editors bypass the standard safeguards provided by administrative tools. These safeguards prevent you from entering conflicting settings or settings that are likely to degrade performance or damage your system. Editing the registry directly can have serious, unexpected consequences that can prevent the system from starting and require that you reinstall Windows 2000. To configure or customize Windows 2000, use the programs in Microsoft Management Console (MMC) or Control Panel whenever possible.

To change any of these DLC parameters, go to the following path in a registry editor:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\DLC\Parameters

Table 26.4 DLC Registry Parameters

DLC Parameter	Description	Default	Range
Swap	When DLC is bound to an Ethernet or token-ring driver, set this parameter to 1 (enable) to turn on address bit-swapping.	1	0-1(Boolean)
T1TickOne	Sets the retransmission-timer short tick value. This timer determines the delay (in units of 40 milliseconds) before retransmitting a link-level frame when no acknowledgment is received.	5	1-255
T1TickTwo	Sets the retransmission-timer long tick value. This timer determines the delay (in units of 40 milliseconds) before retransmitting a link-level frame when no acknowledgment is received.	25	1-255
T2TickOne	Sets the delayed-acknowledgment timer short tick value. This timer determines the delay (in units of 40 milliseconds) before acknowledging a received frame when the receive window has not been reached.	1	1-255
T2TickTwo	Sets the delayed-acknowledgment timer long tick value. This timer determines the delay (in units of 40 milliseconds) before acknowledging a received frame when the receive window has not been reached.	10	1-255
TiTickOne	Sets the inactivity-timer short tick value (in units of 40 milliseconds). This timer determines how often DLC checks an inactive link to see whether it is still operational.	25	1-255
TiTickTwo	Sets the inactivity-timer long tick value (in units of 40 milliseconds). This timer determines how often DLC checks an inactive link to see whether it is still operational.	125	1-255
UseDixOverEthernet	This parameter is used when transmitting DLC packets over an Ethernet network. When this parameter is set to 1, the DLC packets are transmitted using Ethernet DIX (Ethernet II) frames. For all other types of Ethernet frame, this parameter should be left at the default value of 0.	0	0-1(Boolean)