rfc1686.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

Network Working Group                                          M. Vecchi
Request for Comments: 1686                             Time Warner Cable
Category: Informational                                      August 1994


       IPng Requirements: A Cable Television Industry Viewpoint

Status of this Memo

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

Abstract

   This document was submitted to the IETF IPng area in response to RFC
   1550.  Publication of this document does not imply acceptance by the
   IPng area of any ideas expressed within.  The statements in this
   paper are intended as input to the technical discussions within IETF,
   and do not represent any endorsement or commitment on the part of the
   cable television industry or any of its companies.  Comments should
   be submitted to the [e-mail] mailing list.

Table of Contents

   1. Executive Summary ..........................................   2
   2. Cable Television Industry Overview .........................   2
   3. Engineering Considerations .................................   5
   3.1  Scaling ..................................................   5
   3.2  Timescale ................................................   5
   3.3  Transition and deployment ................................   6
   3.4  Security .................................................   7
   3.5  Configuration, administration and operation ..............   7
   3.6  Mobile hosts .............................................   8
   3.7  Flows and resource reservation ...........................   8
   3.8  Policy based routing .....................................  10
   3.9  Topological flexibility ..................................  10
   3.10 Applicability ............................................  10
   3.11 Datagram service .........................................  11
   3.12 Accounting ...............................................  11
   3.13 Support of communication media ...........................  12
   3.14 Robustness and fault tolerance ...........................  12
   3.15 Technology pull ..........................................  12
   3.16 Action items .............................................  13
   4. Security Considerations ....................................  13
   5. Conclusions ................................................  13
   6. Author's Address ...........................................  14




Vecchi                                                          [Page 1]

RFC 1686     A Cable Television Industry Viewpoint on IPng   August 1994


1.  Executive Summary

   This paper provides comments on topics related to the IPng
   requirements and selection criteria from a cable television industry
   viewpoint. The perspective taken is to position IPng as a potential
   internetworking technology to support the global requirements of the
   future integrated broadband networks that the cable industry is
   designing and deploying. The paper includes a section describing the
   cable television industry and outlining the network architectures to
   support  the delivery of entertainment programming and interactive
   multimedia digital services, as well as telecommunication and data
   communication services.

   Cable networks touch on residences, in addition to campuses and
   business parks.  Broadband  applications will reach the average,
   computer-shy person. The applications will involve a heavy use of
   video and audio to provide communication, entertainment and
   information-access services. The deployment of these capabilities to
   the homes will represent  tens of millions of users.  Impact on the
   network and the IPng requirements that are discussed include issues
   of scalability, reliability and availability, support for real-time
   traffic,  security and privacy, and operations and network
   management, among others.

2. Cable Television Industry Overview

   Cable television networks and the Internet are discovering each
   other. It looks like a great match for a number of reasons, the
   available bandwidth being the primary driver. Nonetheless, it seems
   that the impact of the cable television industry in the deployment of
   broadband networks and services is still not fully appreciated. This
   section will provide a quick (and simplified) overview of cable
   television networks, and explain the trends that are driving future
   network architectures and services.

   Cable television networks  in the U.S. pass by approximately 90
   million homes, and have about 56 million subscribers, of a total of
   about 94 million homes (U.S. TV CENSUS figures, 9/30/93). There are
   more than 11,000 headends, and the cable TV industry has installed
   more than 1,000,000 network-miles. Installation of optical fiber
   proceeds at a brisk pace, the fiber plant in the U.S. going from
   13,000 miles in 1991 to 23,000 miles in 1992. Construction spending
   by the cable industry in 1992 was estimated to be about $2.4 billion,
   of which $1.4 billion was for rebuilds and upgrades. Cable industry
   revenue from subscriber services in 1992 was estimated to be more
   than $21 billion, corresponding to an average subscriber rate of
   about $30 per month (source:  Paul Kagan Associates, Inc.). These
   figures are based on "conventional" cable television services, and



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RFC 1686     A Cable Television Industry Viewpoint on IPng   August 1994


   are expected to grow as the cable industry moves into new interactive
   digital services and telecommunications.

   The cable industry's broadband integrated services network
   architecture is based on a hierarchical deployment of network
   elements interconnected by broadband fiber optics and coaxial cable
   links. In a very simplified manner, the following is a view of this
   architecture. Starting at the home, a coaxial cable tree-and-branch
   plant provides broadband two-way access to the network.  The local
   access coaxial cable plant is aggregated at a fiber node, which marks
   the point in the network where fiber optics becomes the broadband
   transmission medium. Current deployment is for  approximately 500
   homes passed by the coaxial cable plant for every fiber node, with
   variations (from as low as 100 to as many as 3000) that depend on the
   density of homes and the degree of penetration of broadband services.
   The multiple links from the fiber nodes reach the headend, which is
   where existing cable systems have installed equipment for
   origination, reception and distribution of television programming.
   The headends are in buildings that can accommodate weather protection
   and powering facilities, and hence represent the first natural place
   into the network where complex switching, routing and processing
   equipment can be conveniently located. Traffic from multiple headends
   can be routed over fiber optics to regional hub nodes deeper into the
   network, where capital-intensive functions can be shared in an
   efficient way.

   The cable networks are evolving quite rapidly to become effective
   two-way digital broadband networks. Cable networks will continue to
   be asymmetric,  and they will continue to deliver analog video. But
   digital capabilities are being installed very aggressively and a
   significant upstream bandwidth is rapidly being activated. The
   deployment of optical fiber deeper into the network is making the
   shared coaxial plant more effective in carrying broadband traffic in
   both directions. For instance, with fiber nodes down to where only
   about 100 to 500 homes are passed by the coaxial drops (down from
   tens of thousands of homes passed in the past), an upstream bandwidth
   of several MHz represents a considerable capacity. The recent
   announcement by Continental Cablevision and PSI to provide Internet
   access services is but one example of the many uses that these two-
   way broadband capabilities can provide.

   The cable networks are also rapidly evolving into regional networks.
   The deployment of fiber optic trunking facilities (many based on
   SONET) will provide gigabit links that interconnect regional hub
   nodes in regional networks spanning multiple cable systems. These
   gigabit networks carry digitized video programming, but will also
   carry voice (telephone) traffic, and, of course, data traffic. There
   are instances in various parts of the country where these regional



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RFC 1686     A Cable Television Industry Viewpoint on IPng   August 1994


   networks have been in successful trials. And given that compressed
   digital video is the way to deliver future video programs (including
   interactive video, video on demand, and a whole menu of other
   applications like computer supported collaborative work, multiparty
   remote games, home shopping, customized advertisement, multimedia
   information services, etc.), one can be guaranteed that gigabit
   regional networks will be put in place at an accelerated pace.

   The cable networks are evolving to provide broadband networking
   capabilities in support  of a complete suite of communication
   services. The Orlando network being built by Time Warner is an
   example of a Full Service Network(TM) that provides video, audio and
   data services to the homes. For the trial, ATM is brought to the
   homes at DS3 rates, and it is expected to go up to OC-3 rates when
   switch interfaces will be available. This trial in Orlando represents
   a peek into the way of future cable networks. The Full Service
   Network uses a "set-top" box in every home to provide the network
   interface. This "set-top" box, in addition to some specialized
   modules for video processing, is really a powerful computer in
   disguise, with a computational power comparable to high-end desktop
   workstations. The conventional analog cable video channels will be
   available, but a significant part of the network's RF bandwidth will
   be devoted to digital services. There are broadband ATM switches in
   the network (as well as 5E-type switches for telephony), and video
   servers that include all kinds of movies and information services. An
   important point to notice is that the architecture of future cable
   networks maps directly to the way networked computing has developed.
   General purpose hosts (i.e., the set-top boxes)  are interconnected
   through a broadband network to other hosts and to servers.

   The deployment of the future broadband information superhighway will
   require architectures for both the network infrastructure and the
   service support environment that truly integrate the numerous
   applications that will be offered to the users. Applications will
   cover a very wide range of scenarios.  Entertainment video delivery
   will evolve from the current core services of the cable industry to
   enhanced offerings like interactive video, near-video-on-demand and
   complete video-on-demand functions. Communication services will
   evolve from the current telephony and low-speed data to include
   interactive multimedia applications, information access services,
   distance learning, remote medical diagnostics and evaluations,
   computer supported collaborative work,  multiparty remote games,
   electronic shopping, etc. In addition to the complexity and diversity
   of the applications, the future broadband information infrastructure
   will combine a number of different networks that will have to work in
   a coherent manner. Not only will the users be connected to different
   regional networks, but the sources of information - in the many forms
   that they will take - will also belong to different enterprises and



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RFC 1686     A Cable Television Industry Viewpoint on IPng   August 1994


   may be located in remote networks. It is important to realize from
   the start that the two most important attributes of the architecture
   for the future broadband information superhighway are integration and
   interoperability. The Internet community has important  expertise and
   technology that could contribute to the definition and development of
   these future broadband networks.

3. Engineering Considerations

   The following comments represent expected requirements of future
   cable networks, based on the vision of an integrated broadband
   network that will support a complete suite of interactive video,
   voice and data services.

   3.1  Scaling

      The current common wisdom is that IPng should be able to deal with
      10 to the 12th nodes. Given that there are of the order of 10 to
      the 8th households in the US, we estimate a worldwide  number of
      households of about 100 times as many, giving a total of about 10
      to the 10th global households. This number represents about 1
      percent of the 10 to the 12th nodes, which indicates that there
      should be enough space left for business, educational, research,
      government, military and other nodes connected to the future
      Internet.

      One should be cautious, however, not to underestimate the
      possibility of multiple addresses that will be used at each node
      to specify different devices, processes, services, etc. For
      instance, it is very likely that more than one address will  be
      used at each household for different devices such as the
      entertainment system (i.e., interactive multimedia "next
      generation" television(s)), the data system (i.e., the home