1    Overview of DIGITAL UNIX ATM Architecture

Asynchronous Transfer Mode (ATM) networks promise to become the dominant network interconnect because they provide the following capabilities:

• Speeds from 25 M/bps to up to 622 M/bps or greater through cell-switching.

• Multiple qualities of service.

• Connection-oriented interconnection with resource reservation for individual connections. These connections might be for conversations between two applications or for a connection over which many conversations between many applications and protocols are multiplexed.

Presently, interest in implementing ATM networks, particularly in the local area, comes from applications that need the high speed and the low latency (switched, full duplex network infrastructure) that ATM networks provide.

Caution

Because of changes in the DIGITAL UNIX kernel, ATM code compiled under previous versions of the operating system must be recompiled. In addition, because of changes to the ATM interfaces, you should verify and change, if necessary, the correct number and type of arguments in ATM function calls before recompiling.

1.1    ATM Subsystem

The DIGITAL UNIX ATM subsystem is a separately configurable kernel subsystem with the following characteristics:

• Provides a set of ATM-related services to kernel and user applications. These applications, in turn, must provide their own interface to ATM.

• Provides a well-defined set of interfaces for using these services. Chapter 3 through Chapter 10 describe the interfaces and services.

• Is optimized for ATM functions; does not provide support for a specific set of user protocols.

• Is flexible and easy to expand and adapt to changing requirements.

• Provides an open interface for ATM hardware designers and for software developers to interface new or existing protocols to ATM.

The DIGITAL UNIX ATM subsystem consists of the following parts:

• Connection Management Module (CMM)

  This module handles all communications between the various elements of the ATM subsystem as well as managing all virtual circuits (VCs) and communications with protocol stacks that use ATM.

• One or more ATM hardware adapter device drivers

  These device drivers handle the hardware-specific details for controlling specific adapters.

• One or more signaling protocol modules

  These modules implement specific protocols for communicating connection management information between the end system and the switch. In this implementation, UNI 3.0/3.1 is the default signaling protocol module that the DIGITAL UNIX ATM subsystem uses.

Figure 1-1 illustrates the ATM subsystem.

Figure 1-1:  DIGITAL UNIX ATM Subsystem

The DIGITAL UNIX ATM subsystem supports any number of ATM device drivers and signaling protocol modules as long as the actions of these modules do not interfere with each other. ATM modules should communicate only with the CMM as the CMM coordinates all communications between ATM modules. ATM modules should never bypass the CMM and communicate with each other directly.

The three elements of the ATM subsystem provide only raw ATM services. They do not implement any specific protocol for carrying data over the ATM network. That is, the ATM subsystem is entirely protocol independent. If a specific protocol wants to use the ATM network to transport data, the protocol must provide an interface into the ATM subsystem.

The programs that provide the interface between the ATM subsystem and specific protocols are called convergence modules. These modules, using the ATM subsystem interface Kernel Programming Interface (KPI), control the creation and use of ATM virtual circuits (VCs) in a manner appropriate for the protocol. Since different protocols have different requirements, the ATM subsystem leaves the adaptation of the protocol to use ATM entirely up to the protocol implementor. The ATM subsystem does not provide any protocol-specific services.

1.1.1    Connection Management Module

The CMM is the central module in the DIGITAL UNIX ATM subsystem and has the following duties:

• Manages all activities of the ATM subsystem, including subsystem configuration. All data to and from the ATM networks must pass through the CMM to get properly routed to the correct destination.

• Handles all circuit connection requests from protocol modules (convergence modules) and manages all VCs from the time they are created until they are torn down.

• Provides interface points for other elements of the ATM subsystem, as well as the interfaces for accessing the ATM subsystem from kernel protocol stacks. These interfaces permit the modular addition of drivers, signaling modules, management modules, and protocol stack interfaces without having to make changes to the CMM.

• Provides the only interface into the ATM subsystem from the DIGITAL UNIX kernel. ATM modules are accessed only through the CMM.

1.1.2    CMM Interfaces

The CMM provides the following interfaces:

• ATM device driver interface

  ATM adapter device drivers use this interface to access the ATM subsystem. See Chapter 4 for more information.

• Signaling module interface

  Modules that implement ATM signaling protocols use this interface. This interface allows multiple signaling modules to provide services to protocol stacks on a per-VC basis, as long the signaling modules do not conflict on the ATM network. See Chapter 5 for more information.

• Convergence module interface

  Kernel protocol stacks use this external interface to the ATM subsystem to gain access to the ATM subsystem services. See Chapter 6 for more information.

These interfaces are registration-type interfaces. Each makes calls to the CMM to inform the CMM of its presence. The CMM places no limit on the number of each type of module that may register, the total number being limited only by system resources.

1.2    ATM Subsystem Configuration

Before you communicate on the ATM network, you must install the DIGITAL DGLTA ATM adapter and configure the ATM software. See the installation and service documentation shipped with the adapter for information on installing the ATM adapter and Chapter 2 for information on configuring the ATM software.