rfc1686.txt

RFC 的详细文档！

      personal computer(s)), and other new terminal devices that will
      emerge in the future (such as networked games, PDAs, etc.).
      Finally, the administration of the address space is of importance.
      If there are large blocks of assigned but unused addresses, the
      total number of available addresses will be effectively reduced
      from the 10 to the 12th nodes that have been originally
      considered.

   3.2  Timescale

      The cable industry is already making significant investments in
      plant upgrades, and the current estimates for the commercial
      deployment indicate that by the year 1998 tens of millions of
      homes will be served by interactive and integrated cable networks
      and services. This implies that during 1994 various trials will be



Vecchi                                                          [Page 5]

RFC 1686     A Cable Television Industry Viewpoint on IPng   August 1994


      conducted and evaluated, and the choices of technologies and
      products will be well under way by the year 1995. That is to say,
      critical investment and technological decisions by many of the
      cable operators, and their partners, will be made over the next 12
      to 24 months.

      These time estimates are tentative, of course, and subject to
      variations depending on economic, technical and public policy
      factors. Nonetheless, the definition of the IPng capabilities and
      the availability of implementations should not be delayed beyond
      the next year, in order to meet the period during which many of
      the early technological choices for the future deployment of cable
      networks and services will be made. The full  development and
      deployment of IPng will be, of course, a long period that will be
      projected beyond the next year. Availability of early
      implementations will allow experimentation in trials to validate
      IPng choices and to provide early buy-in from the developers of
      networking products that will support the planned roll out.

      It is my opinion that the effective support for high quality video
      and audio streams is one of the critical capabilities that should
      be demonstrated by IPng in order to capture the attention of
      network operators and information providers of interactive
      broadband services (e.g., cable television industry and partners).
      The currently accepted view is that IP is a great  networking
      environment for the control side of an interactive broadband
      system. It is a challenge for IPng to demonstrate that it can be
      effective in transporting the broadband video and audio data
      streams, in addition to providing the networking support for the
      distributed control system.

   3.3  Transition and deployment

      The transition from the current version to IPng has to consider
      two aspects: support for existing applications and availability of
      new capabilities. The delivery of digital video and audio programs
      requires the capability to do broadcasting and selective
      multicasting efficiently. The interactive applications that the
      future cable networks will provide will be based on multimedia
      information streams that will have real-time constraints. That is
      to say, both the end-to-end delays and the jitter associated with
      the delivery across the network have to be bound. In addition, the
      commercial nature of these large private investments will require
      enhanced network capabilities for routing choices, resource
      allocation, quality of service controls, security, privacy, etc.
      Network management will be an increasingly important issue in the
      future. The extent to which the current IP fails to provide the
      needed capabilities will provide additional incentive for the



Vecchi                                                          [Page 6]

RFC 1686     A Cable Television Industry Viewpoint on IPng   August 1994


      transition to occur, since there will be no choice but to use IPng
      in future applications.

      It is very important, however, to maintain backwards compatibility
      with the current IP. There is the obvious argument that the
      installed technological base developed around IP cannot be
      neglected under any reasonable evolution scenario. But in
      addition, one has to keep in mind that a global Internet will be
      composed of many interconnected heterogeneous networks, and that
      not all subnetworks, or user communities, will provide the full
      suite of interactive multimedia services. Interworking between
      IPng and IP will have to continue for a very long time in the
      future.

   3.4  Security

      The security needed in future networks falls into two general
      categories: protection of the users and protection of the network
      resources. The users of the future global Internet will include
      many communities that will likely expect a higher level of
      security than is currently available. These users include
      business, government, research, military, as well as private
      subscribers. The protection of the users' privacy is likely to
      become a hot issue as new commercial services are rolled out. The
      possibility of illicitly monitoring traffic patterns by looking at
      the headers in IPng packets, for instance, could be disturbing to
      most users that subscribe to new information and entertainment
      services.

      The network operators and the information providers will also
      expect effective protection of their resources. One would expect
      that most of the security will be dealt at higher levels than
      IPng, but some issues might have to be considered in defining IPng
      as well. One issue relates, again, to the possibility of illicitly
      monitoring addresses and traffic patterns by looking at the IPng
      packet headers. Another issue of importance will be the capability
      of effective network management under the presence of benign or
      malicious bugs, especially if both source routing and resource
      reservation functionality is made available.

   3.5  Configuration, administration and operation

      The operations of these future integrated broadband networks will
      indeed become more difficult, and not only because the networks
      themselves will be larger and more complex, but also because of
      the number and diversity of applications running on or through the
      networks. It is expected that most of the issues that need to be
      addressed for effective operations support systems will belong to



Vecchi                                                          [Page 7]

RFC 1686     A Cable Television Industry Viewpoint on IPng   August 1994


      higher layers than IPng, but some aspects should be considered
      when defining IPng.

      The area where IPng would have most impact would be in the
      interrelated issues of resource reservation, source routing and
      quality of service control. There will be tension to maintain high
      quality of service and low network resource usage simultaneously,
      especially if the users can specify preferred routes through the
      network. Useful capabilities at the IPng level would enable the
      network operator, or the user, to effectively monitor and direct
      traffic in order to meet quality and cost parameters. Similarly,
      it will be important to dynamically reconfigure the connectivity
      among end points or the location of specific processes (e.g., to
      support mobile computing terminals), and the design of IPng should
      either support, or at least not get in the way of, this
      capability. Under normal conditions, one would expect that
      resources for the new routing will be established before the old
      route is released in order to minimize service interruption. In
      cases where reconfiguration is in response to abnormal (i.e.,
      failure) conditions, then one would expect longer interruptions in
      the service, or even loss of service.

      The need to support heterogeneous multiple administrative domains
      will also have important implications on the available addressing
      schemes that IPng should support. It will be both a technical and
      a business issue to have effective means to address nodes,
      processes and users, as well as choosing schemes based on fair and
      open processes for allocation and administration of the address
      space.

   3.6  Mobile hosts

      The proliferation of personal and mobile communication services is
      a well established trend by now. Similarly, mobile computing
      devices are being introduced to the market at an accelerated pace.
      It would not be wise to disregard the issue of host mobility when
      evaluating proposals for IPng.  Mobility will have impact on
      network addressing and routing, adaptive resource reservation,
      security and privacy, among other issues.

   3.7  Flows and resource reservation

      The largest fraction of the future broadband traffic will be due
      to real-time voice and video streams. It will be necessary to
      provide performance bounds for bandwidth, jitter, latency and loss
      parameters, as well as synchronization between media streams
      related by an application in a given session. In addition, there
      will be alternative network providers that will compete for the



Vecchi                                                          [Page 8]

RFC 1686     A Cable Television Industry Viewpoint on IPng   August 1994


      users and that will provide connectivity to a given choice of many
      available service providers. There is no question that IPng, if it
      aims to be a general protocol useful for interactive multimedia
      applications, will need to support some form of resource
      reservation or flows.

      Two aspects are worth mentioning. First, the quality of service
      parameters are not known ahead of time, and hence the network will
      have to include flexible capabilities for defining these
      parameters. For instance, MPEG-II packetized video might have to
      be described differently than G.721 PCM packetized voice, although
      both data streams represent real-time traffic channels. In some
      cases, it might be appropriate to provide soft guarantees in the
      quality parameters, whereas in other cases hard guarantees might
      be required. The tradeoff between cost and quality could be an
      important capability of future IPng-based networks, but much work
      needs to be advanced on this.

      A second important issue related to resource reservations is the
      need to deal with broken or lost end-to-end state information. In
      traditional circuit-switched networks, a considerable effort is
      expended by the intelligence of the switching system to detect and
      recover resources that have been lost due to misallocation. Future
      IPng networks will provide resource reservation capabilities by
      distributing the state information of a given session in several
      nodes of the network. A significant effort will be needed to find
      effective methods to maintain consistency and recover from errors
      in such a distributed environment. For example, keep-alive
      messages to each node where a queuing policy change has been made
      to establish the flow could be a strategy to make sure that
      network resources do not remain stuck in some corrupted session
      state. One should be careful, however, to assume that complex
      distributed algorithms can be made robust by using time-outs. This
      is a problem that might require innovation beyond the reuse of
      existing solutions.

      It should be noted that some aspects of the requirements for
      recoverability are less stringent in this networking environment
      than in traditional distributed data processing systems. In most
      cases it is not needed (or even desirable) to recover the exact
      session state after failures, but only to guarantee that the
      system returns to some safe state. The goal would be to guarantee
      that no network resource is reserved that has not been correctly
      assigned to a valid session. The more stringent requirement of
      returning to old session state is not meaningful since the value
      of a session disappears, in most cases, as time progresses. One
      should keep in mind, however, that administrative and management
      state, such as usage measurement, is subject to the same



Vecchi                                                          [Page 9]

RFC 1686     A Cable Television Industry Viewpoint on IPng   August 1994


      conventional requirements of recoverability that database systems
      currently offer.

   3.8  Policy based routing

      In future broadband networks, there will be multiple network
      operators and information providers competing for customers and
      network traffic.  An important capability of IPng will be to
      specify, at the source, the specific network for the traffic to
      follow. The users will be able to select specific networks that
      provide performance, feature or cost advantages. From the user's
      perspective, source routing is a feature that would enable a wider
      selection of network access options, enhancing their ability to
      obtain features, performance or cost advantages. From the network
      operator and service provider perspective, source routing would
      enable the offering of targeted bundled services that will cater