rfc3052.txt

最新的RFC

Network Working Group                                            M. Eder
Request for Comments: 3052                                         Nokia
Category: Informational                                           S. Nag
                                                            January 2001


          Service Management Architectures Issues and Review

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2001).  All Rights Reserved.

Abstract

   Many of the support functions necessary to exploit the mechanisms by
   which differing levels of service can be provided are limited in
   scope and a complete framework is non-existent.  Various efforts at
   such a framework have received a great deal of attention and
   represent a historical shift in scope for many of the organizations
   looking to address this problem.  The purpose of this document is to
   explore the problems of defining a Service management framework and
   to examine some of the issues that still need to be resolved.

1. Introduction

   Efforts to provide mechanisms to distinguish the priority given to
   one set of packets, or flows, relative to another are well underway
   and in many modern IP networks, best effort service will be just one
   of the many services being offered by the network as opposed to it
   being the only service provided.  Unfortunately, many of the support
   functions necessary to exploit the mechanisms by which network level
   service can be provided are limited in scope and a complete framework
   is non-existent.  Compounding the problem is the varied understanding
   of exactly what the scope of "service" is in an IP network.  IP, in
   contrast to connection oriented network technologies, will not be
   able to limit the definition of service management simply to end to
   end connectivity, but will combine service management with regards to
   transport with the service requirements of the actual applications
   and how they are using the network.  The phenomenal growth in data
   networks as well as the growth in application bandwidth usage has had
   the consequence that the existing methods of management are not
   sufficient to handle the growing demands of scale and complexity.



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RFC 3052            Service Management Architectures        January 2001


   The network and service management issue is going to be a major
   problem facing the networks of the future.  This realization is a
   significant motivating factor in various efforts within the IP
   community which has been traditionally reluctant to take on issues of
   this type [1].  The purpose of this document is to explore the
   problems of developing a framework for managing the network and
   services and to examine some of the issues that recent efforts have
   uncovered.

2. The Problem of Management Standards

   Network and service level issues traditionally are handled in IP
   networks by engineering the network to provide the best service
   possible for a single class of service.  Increasingly there is a
   desire that IP networks be used to carry data with specific QoS
   constraints.  IP networks will require a tremendous amount of
   management information to provision, maintain, validate, and bill for
   these new services.  The control and distribution of management
   information in complex communications networks is one of the most
   sophisticated tasks a network management framework must resolve. This
   is compounded by the likelihood that devices in IP networks will be
   varied and have differing management capabilities, ranging from
   complex computing and switching platforms to personal hand held
   devices and everything in between.  Scaling and performance
   requirements will make the task of defining a single management
   framework for these networks extremely complex.

   In the past standardization efforts have suggested a simplified model
   for management on the hypothesis that it can be extrapolated to solve
   complex systems.  This premise has often proved to be without merit
   because of the difficulty of developing such a model that meets both
   the operators heterogeneous, multi-vendor need and network equipment
   vendors specific needs.  At the center of efforts to devise a
   standard management model are attempts to develop an architecture or
   framework to control the management information. The same conflicting
   operator vs. vendor forces are present in the effort to establish a
   common framework architecture as are in the efforts to develop a
   common information model.

   Network operators requirements call for a framework that will permit
   centralized management of the network and require the minimal
   resources to operate and maintain while still providing tremendous
   flexibility in choice of equipment and creativity of defining
   services [2].  Operators may be less able to support change in their
   Operational Support Systems (OSS) then they are in the network
   infrastructure because the OSS is tightly integrated into the





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   organizations business practices.  The need for flexibility, and the
   other desires identified above, operators expect to have meet by
   having equipment vendors support open and common interfaces.

   Device manufactures have a need for management that will best
   represent the features and capabilities of the equipment they are
   developing and any management solution that hinders the ability of
   the equipment vendors to efficiently bring innovation to the market
   is contrary to their objectives.

   The common framework for solving the management needs of operators
   and equipment vendors has been based on a centralized approach with a
   the manager agent architecture.  While providing a very
   straightforward approach to the problem of information management,
   this approach, and its variations, has not proved to scale well or
   allowed the flexibility required in today's modern data networks.
   Scaling and flexibility are especially a problem where there are many
   sophisticated network devices present.  Methods of control must be
   found that work and scale at the same speeds as that of the control
   plane of the network itself if a major concern of the management
   system is with the dynamic control of traffic in a network.
   Increasingly it is a requirement that customers at the edge of the
   network be able to have access to management functionality.  A
   centralized management approach may not provide the most convenient
   architecture to allow this capability.

   Frameworks based on a decentralized approach to the management
   architecture have gained momentum in recent years, but must address
   the possibility of having redundant management information throughout
   the network.  A decentralized framework may have advantages with
   regards to scaling and speed of operation, but information and state
   management becomes complex in this approach, resulting in additional
   complication in developing such systems.

   The complexity of managing a network increases dramatically as the
   number of services and the number and complexity of devices in the
   network increases.  The success of IP networks can be partially
   traced to the successful separation of transport control mechanisms
   from the complexity of service management, including billing.  As the
   trend in IP is to allow for classes of traffic that will have both
   transport and service dependencies it has become apparent that many
   of the management problems are becoming more complex in nature and
   are starting to resemble those of the traditional telecom provisioned
   service environment.  In the telecom environment no such separation
   exists between transport control mechanisms and service.  The Telecom
   community has struggled for years to come up with a standard solution
   for the problem in national and international standardization bodies
   and achieved a debatable amount of industry acceptance.



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RFC 3052            Service Management Architectures        January 2001


   Unfortunately, the hard learned lessons of how to manage the
   interdependencies between service and transport will be of
   questionable use to the IP community because of the much more limited
   concept of service in the telecommunications environment.

   Rules based management has received much attention as a method to
   reduce much of the overhead and operator intervention that was
   necessary in traditional management systems.  The potential exists
   that a rules-based system could reduce the rate at which management
   information is increasing, but given the tremendous growth in this
   information, the problems with the control of that information will
   continue to exist.  Rules add additional issues to the complexity of
   managing a network and as such will contribute to the information
   control problem.

2.1. IP QoS Management

   Much of the current management efforts are focused on solving control
   issues for IP QoS [3].  A number of open questions exist with the IP
   QoS architecture which will make it difficult to define a management
   architecture until they are resolved.  These are well documented in
   "Next steps for the IP QoS architecture" [4], but from the management
   perspective warrant emphasizing.

   Current IP QoS architectures have not defined if the service will be
   per-application or only a transport-layer option.  This will have
   significant impact both from a control perspective and from a billing
   and service assurance one.

   The assumption is that the routing best effort path will be used for
   both best effort traffic and for traffic of a different service
   level.  In addition to those issues raised in [4], best effort path
   routing may not be able to identify the parameters necessary to
   identify routes capable of sustaining distinguished service traffic.

   In any architecture where a premium service will be offered it is a
   strong requirement that the service be measurable and sustainable.
   Provisioning that service will require a coherent view of the network
   and not just the device management view that is currently implemented
   in most networks.

2.2. Promise of rules-based Management

   Management standardization efforts in the IP community have so far
   been concerned primarily with what is commonly referred to as
   "element management" or "device management" [5].  Generally there is
   agreement as to the scope of element management.  Once outside that
   domain efforts to divide that task along clear boundaries have proved



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