Inter-domain Management: Specification Translation - Summary of Similarities and Differences

Inter-domain Management: Specification Translation

Inter-domain Management: Specification Translation
Copyright © 1997 The Open Group

Summary of Similarities and Differences

This chapter gives a summary and analysis of the similarities and differences between the OSI, OMG and Internet Management Models.

Summary

Interoperability and Portability

OSI Mgmt: CMIP allows different implementations to interoperate through specification of communications interface. However application portability is not provided.
OMG: Application portability is provided by specification of programmatic interface. CORBA 2.0 provides a common protocol for different implementations to interoperate.
Internet Mgmt: SNMP allows different implementations to interoperate through specification of communications interface. However application portability is not provided.

Re-usable Components

OSI Mgmt: Library/catalogue of management information.
OMG: Type library (interface repository).
Internet Mgmt: MIBs containing object type definitions.

Encapsulation

OSI Mgmt: Supported.
OMG: Supported.
Internet Mgmt: Not supported.

Object Operations

OSI Mgmt: Supported.
OMG: Supported. No built-in create service provided.
Internet Mgmt: Not supported.

Behaviour

OSI Mgmt: Supported.
OMG: Supported.
Iternet Mgmt: Supported.

Attributes and Attribute Operations

OSI Mgmt: Supported. Specific exceptions can be specified.
OMG: Supported. Specific exceptions cannot be specified.
Internet Mgmt: Supported.

Taxonomy

OSI Mgmt: Managed object class type-hierarchy/graph supported by multiple inheritance. Attributes, actions, and notifications may be repeated in derived classes, with additional properties.
OMG: Interface Type hierarchy/graph supported by multiple inheritance. Attributes and operations cannot be repeated in a derived interface specification.
Internet Mgmt: No inheritance supported.

Direct Selection

OSI Mgmt: By global or local distinguished name.
OMG: By object reference. The form of object references is ORB-specific.
Internet Mgmt: By object name (OID + index).

Intended Use

OSI Mgmt: Distributed network management.
OMG: Object-oriented software development.
Internet Mgmt: Management of inter-networked devices.

Interface Type

OSI Mgmt: Communications.
OMG: Programmatic.
Internet Mgmt: Communications.

Interface Concurrency

OSI Mgmt: Support required for confirmed events and operations/notifications on the same association.
OMG: Not required, but concurrency is implicit in the model, especially where deferred synchronous calls are made (as in the DII).
Internet Mgmt: Not precluded.

Protocol Model

OSI Mgmt: Remote operations (invoke, returnResult, returnError, and reject messages).
OMG: Procedure call. CORBA2 defines protocol(s) for interoperability.
Internet Mgmt: Message passing, requests have agent responses, traps are sent by agent and are unconfirmed.

Multiple Replies

OSI Mgmt: Supported explicitly by CMIP.
OMG: Although not specified explicitly in CORBA, multiple replies can be achieved by passing a reference on the call and implementing a call-back style of programming, by defining pairs or sets of definitions going in both directions. The service may invoke many calls on the reference to pass results and the return on the original request.
Internet Mgmt: Not supported (although the SNMPv2 get-bulk operator provides a self-repeating request which provokes several responses).

Object Events

OSI Mgmt: Supported by CMIP. Notifications are specified as part of managed object definition.
OMG: There is now a standard models of events - the OMG Event Service. Notifications are not specified as part of the sender's interface definition. The event receiver registers the event receipt interface. Typed events are specified as part of a receiver's interface definition. Fine filtering of events is not supported.
Internet Mgmt: Provides limited event support in the form of Traps and Inform-Requests. The philosophy is typically characterised as trap-directed polling.

Late Binding

OSI Mgmt

Some degree of optionality is handled in GDMO via conditional binding of a package to a managed object instance of a class defined with conditional packages.

OMG

In OMG, the implementation of a particular object instance is determined when the instance is created, by the implementation repository. It is even possible to change implementations, although the semantics are currently unclear. Attribute and parameter values may be defined with discriminated choice types including a NULL alternative.

IDL has no direct equivalent of managed object class. However, simply supporting an interface does not actually require an implementation of all operations. An object is perfectly at liberty to implement a function simply by raising an exception. Clearly this is not covered in the specification part.

Internet Mgmt

Not formally supported, except through compliance specifications.

Associated Selection

OSI Mgmt: Supported through scoping and filtering on the managed object instance tree.
OMG: Permitted. Trader services will enable this in the future.
Internet Mgmt: Very limited support.

Associated Selection Scope

OSI Mgmt: Sub-trees of the tree of managed object instances.
OMG: Eventually will have an arbitrary scope when using a Trader for two phase selection.
Internet Mgmt: Agent's entire MIB registration tree, or a subset (MIB View) of that tree.

Specification

OSI Mgmt: Piecemeal, in that Attributes, Notifications, Actions, and Parameters are defined first, then combined into packages, which are then combined into managed object class definitions.
OMG: Object specification in OMG is at the granularity of interfaces. Via inheritance, an object may support many interfaces, so it is not really monolithic. Operations and attributes specified separately could be achieved by putting these individual declarations in their own interface and combining them as required.
Internet Mgmt: Largely monolithic. There is little specification re-useuse except as provided by SNMPv2 (Textual Conventions and Table Augmentation).

Specification Tools

OSI Mgmt: GDMO.
OMG: IDL.
Internet Mgmt: ASN.1 macros.

Specification Formality

OSI Mgmt: Syntax.
OMG: Syntax.
Internet Mgmt: Syntax.

Analysis of Similarities and Differences

Up to and including Direct Selection , there is an encouraging degree of agreement between the fundamental aspects of the OSI and OMG models. The basic notions of objects, object taxonomy, attributes, operations, state, behaviour, and encapsulation are virtually identical. This is important in realising our goal of using object-oriented software development systems to implement OSI-conformant network-management products. The closer the two models are, the less incidental code has to be written to fit the specification (that is, OSI management) model to the implementation (that is, OMG) model. This will not only result in less code, but will also improve accuracy and robustness of implementation.

The OSI and OMG models differ:

in four major aspects:
- support for events
- support for multiple replies
- support for attribute groups
- late binding.
in a number of incidental aspects, such as specification techniques and associative references
in two complementary aspects:
- interface type
- intended use.

Therefore, the OSI management and OMG models only fundamentally differ in late binding (possibly) and multiple replies. The latter is implementable and is a common style for event driven systems, for example, X-windows (DII even enables callback style of programming). The possibility of interworking is strengthened by existence of OMG Object Services.

The following chapter outlines the approach to reconciling the differences between these object models.

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