Appendix H. Using AIXLink/X.25 over the IBM 2-Port Multiprotocol Adapter

This chapter describes the use of the AIXLink/X.25 product over the IBM 2-Port Multiprotocol adapter.

Overview

The AIXLink/X.25 product supports the use of the IBM 2-Port Multiprotocol dpmp adapter for X.25 communications. In this configuration, minor differences from previous releases of the AIXLink/X.25 product are necessary. However, it is important to note that these differences are primarily internal to the product and do not change the product's capabilities or usage.

The dpmp adapter is different from the adapters historically used by the AIXLink product, most notably because it has no internal CPU with its own resident operating system (microcode). The dpmp adapter is called a "shallow" adapter, whereas other adapters supported by the AIXLink product are called "deep", since they have the capability to change their operation by loading and running a different microcode.

Also, the dpmp adapter driver has its own interface, different from the interface to the existing AIXLink/X.25 twd driver. The twd driver uses a STREAMS interface, and the dpmp driver (called hdlc) presents a CDLI (non-STREAMS) interface.

The net effect of these differences is the following:

1. AIXLink/X.25 ports are configured over instances of either the twd driver or the hdlc driver, depending on which adapter type is available for use in the system.
2. The Frame layer of the X.25 product runs in the AIX kernel when a port is configured over the hdlc driver. Standard AIX kernel trace utilities provide diagnostics.
3. Applications which use the AIXLink DLPI interface to ports that are configured over the hdlc driver no longer require the twd driver as an intermediary. These user streams are linked directly to the frame layer running in the kernel.
4. The AIXLink/X.25 'sx25debug' utility, which interfaces with microcode running on a deep adapter, cannot be used on ports which are configured over the hdlc driver. The AIX kernel trace is used for diagnosing frame layer problems in this case.
5. hdlc driver utilities are available for diagnosing problems below the Frame layer for AIXLink ports on dpmp adapters.

Note: Item 3 above requires existing applications which use the AIXLink DLPI interface to "open" the DLPI devices differently. Note that this change is required only if the application needs to utilize AIXLink ports configured over dpmp adapters.

The AIXLink/X.25 sample programs included with the product show how to perform the new "open". The updated "open" method allows DLPI applications to communicate with all adapter types supported by the AIXLink/X.25 product.

Configuration Object Model

The relationships between objects of the AIXLink/X.25 product is different for ports using the dpmp driver.

As the figure below shows, the overall structure is similar, but different drivers and adapters are used.

The physical linking of STREAMS devices is also different for the AIXLink/X.25 ports using the dpmp driver.

The figure below illustrates these differences.

Note: The "glue" layer shown in the figure above presents the physical layer interface to the frame layer. It's purpose is to translate the CDLI interface presented by the hdlc driver into a STREAMS interface that the Frame layer requires.

The X.25 applications attached above the Stream head are shielded from these internal differences.