RFC1686

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 [email protected] mailing list.

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.

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

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

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

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.

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
  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

  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

  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

  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

  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

  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
  to specific users and achieve some degree of customer lock-in. The
  information providers will be able to optimize the placement and
  distribution of their servers, based on either point-to-point
  streams or on multicasting to selected subgroups. The ability of
  IPng to dynamically specify the network routing would be an
  attractive feature that will facilitate the flexible offering of
  network services.

3.9 Topological flexibility

  It is hard to predict what the topology of the future Internet
  will be. The current model developed in response to a specific set
  of technological drivers, as well as an open administrative
  process reflecting the non-commercial nature of the sector. The
  future Internet will continue to integrate multiple administrative
  domains that will be deployed by a variety of network operators.
  It is likely that there will be more "gateway" nodes (at the
  headends or even at the fiber nodes, for instance) as local and
  regional broadband networks will provide connectivity for their
  users to the global Internet.

3.10 Applicability

  The future broadband networks that will be deployed, by both the
  cable industry and other companies, will integrate a diversity of
  applications. The strategies of the cable industry are to reach
  the homes, as well as schools, business, government and other
  campuses. The applications will focus on entertainment, remote
  education, telecommuting, medical, community services, news
  delivery and the whole spectrum of future information networking
  services. The traffic carried by the broadband networks will be
  dominated by real-time video and audio streams, even though there

  will also be an important component of traffic associated with
  non-time-critical services such messaging, file transfers, remote
  computing, etc. The value of IPng will be measured as a general
  internetworking technology for all these classes of applications.
  The future market for IPng could be much wider and larger than the
  current market for IP, provided that the capabilities to support
  these diverse interactive multimedia applications are available.

  It is difficult to predict how pervasive the use of IPng and its
  related technologies might be in future broadband networks. There
  will be extensive deployment of distributed computing
  capabilities, both for the user applications and for the network
  management and operation support systems that will be required.
  This is the area where IPng could find a firm stronghold,
  especially as it can leverage on the extensive IP technology
  available. The extension of IPng to support video and audio real-
  time applications, with the required performance, quality and cost
  to be competitive, remains a question to be answered.

3.11 Datagram service

  The "best-effort", hop-by-hop paradigm of the existing IP service
  will have to be reexamined if IPng is to provide capabilities for
  resource reservation or flows. The datagram paradigm could still
  be the basic service provided by IPng for many applications, but
  careful thought should be given to the need to support real-time
  traffic with (soft and/or hard) quality of service requirements.

3.12 Accounting

  The ability to do accounting should be an important consideration
  in the selection of IPng. The future broadband networks will be
  commercially motivated, and measurement of resource usage by the
  various users will be required. The actual billing may or may not
  be based on session-by-session usage, and accounting will have
  many other useful purposes besides billing. The efficient
  operation of networks depends on maintaining availability and
  performance goals, including both on-line actions and long term
  planning and design. Accounting information will be important on
  both scores. On the other hand, the choice of providing accounting
  capabilities at the IPng level should be examined with a general
  criterion to introduce as little overhead as possible. Since
  fields for "to", "from" and time stamp will be available for any
  IPng choice, careful examination of what other parameters in IPng
  could be useful to both accounting and other network functions so
  as to keep IPng as lean as possible.

3.13 Support of communication media

  The generality of IP should be carried over to IPng. It would not
  be an advantage to design a general internetworking technology
  that cannot be supported over as wide a class of communications
  media as possible. It is reasonable to expect that IPng will start
  with support over a few select transport technologies, and rely on
  the backwards compatibility with IP to work through a transition
  period. Ultimately, however, one would expect IPng to be carried
  over any available communications medium.

3.14 Robustness and fault tolerance

  Service availability, end-to-end and at expected performance
  levels, is the true measure of robustness and fault-tolerance. In
  this sense, IPng is but one piece of a complex puzzle. There are,
  however, some vulnerability aspects of IPng that could decrease
  robustness. One general class of bugs will be associated with the
  change itself, regardless of any possible enhancement in
  capabilities. The design, implementation and testing process will
  have to be managed very carefully. Networks and distributed
  systems are tricky. There are plenty of horror stories from the
  Internet community itself to make us cautious, not to mention the
  brief but dramatic outages over the last couple of years
  associated with relatively small software bugs in the control
  networks (i.e., CCS/SS7 signaling) of the telephone industry, both
  local and long distance.

  A second general class of bugs will be associated with the
  implementation of new capabilities. IPng will likely support a
  whole set of new functions, such as larger (multiple?) address
  space(s), source routing and flows, just to mention a few.
  Providing these new capabilities will require in most cases
  designing new distributed algorithms and testing implementation
  parameters very carefully. In addition, the future Internet will
  be even larger, have more diverse applications and have higher
  bandwidth. These are all factors that could have a multiplying
  effect on bugs that in the current network might be easily
  contained. The designers and implementers of IPng should be
  careful. It will be very important to provide the best possible
  transition process from IP to IPng. The need to maintain
  robustness and fault-tolerance is paramount.

3.15 Technology pull

  The strongest "technology pull" factors that will influence the
  Internet are the same that are dictating the accelerated pace of
  the cable, telephone and computer networking world. The following

  is a partial list: higher network bandwidth, more powerful CPUs,
  larger and faster (static and dynamic) memory, improved signal
  processing and compression methods, advanced distributed computing
  technologies, open and extensible network operating systems, large
  distributed database management and directory systems, high
  performance and high capacity real-time servers, friendly
  graphical user interfaces, efficient application development
  environments. These technology developments, coupled with the
  current aggressive business strategies in our industry and
  favorable public policies, are powerful forces that will clearly
  have an impact on the evolution and acceptance of IPng. The
  current deployment strategies of the cable industry and their
  partners do not rely on the existence of commercial IPng
  capabilities, but the availability of new effective networking
  technology could become a unifying force to facilitate the
  interworking of networks and services.

3.16 Action items

  We have no suggestions at this time for changes to the
  directorate, working groups or others to support the concerns or
  gather more information needed for a decision. We remain available
  to provide input to the IPng process.

Security Considerations

No comments on general security issues are provided, beyond the considerations presented in the previous subsection 3.4 on network security.

Conclusions

The potential for IPng to provide a universal internetworking solution is a very attractive possibility, but there are many hurdles to be overcome. The general acceptance of IPng to support future broadband services will depend on more than the IPng itself. There is need for IPng to be backed by the whole suite of Internet technology that will support the future networks and applications. These technologies must include the adequate support for commercial operation of a global Internet that will be built, financed and administered by many different private and public organizations.

The Internet community has taken pride in following a nimble and efficient path in the development and deployment of network technology. And the Internet has been very successful up to now. The challenge is to show that the Internet model can be a preferred technical solution for the future. Broadband networks and services will become widely available in a relatively short future, and this

puts the Internet community in a fast track race. The current process to define IPng can be seen as a test of the ability of the Internet to evolve from its initial development - very successful but also protected and limited in scope - to a general technology for the support of a commercially viable broadband marketplace. If the Internet model is to become the preferred general solution for broadband networking, the current IPng process seems to be a critical starting point.

Author's Address

Mario P. Vecchi Time Warner Cable, 160 Inverness Drive West Englewood, CO 80112

Phone: (303) 799-5540 Fax: (303) 799-5651 EMail: [email protected]