Internet DRAFT - draft-vecchi-tvcable-viewpt
draft-vecchi-tvcable-viewpt
Internet Draft Mario P. Vecchi
Time Warner Cable
28 Feb 1994
Expire: Sept 94
IPng Requirements: a cable television industry viewpoint
<draft-vecchi-ipng-tvcable-viewpt-00.txt>
Status of this Memo
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. Comments should
be submitted to the big-internet@munnari.oz.au mailing list.
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Abstract
This memo is a response to RFC 1550, IP: Next Generation (IPng) White Paper
Solicitation. 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.
Table of Contents
1 Executive Summary 1
2 Cable Television Industry Overview 2
3 Engineering Considerations 4
3.1 Scaling - 4
3.2 Timescale - 4
3.3 Transition and deployment - 5
3.4 Security - 5
3.5 Configuration, administration and operation - 5
3.6 Mobile hosts - 6
3.7 Flows and resource reservation - 6
3.8 Policy based routing - 7
3.9 Topological flexibility - 7
3.10 Applicability - 8
3.11 Datagram service - 8
3.12 Accounting - 8
3.13 Support of communication media - 8
3.14 Robustness and fault tolerance - 9
3.15 Technology pull - 9
3.16 Action items - 9
4 Security Considerations 10
5 Conclusions 10
6 Author's Address 10
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
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.
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 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.
4 Security Considerations
No comments on general security issues are provided, beyond the considerations
presented in the previous subsection 3.4 on network security.
5 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.
6 Author's Address
Mario P. Vecchi
Time Warner Cable,
160 Inverness Drive West
Englewood, CO 80112
Phone: (303)799-5540
Fax: (303)799-5651
E-mail: mpvecchi@twcable.com
From mpvecchi@twcable.com Mon Mar 21 16:33:29 1994
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From: "Mario P. Vecchi" <mpvecchi@twcable.com>
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Status: R
Scott,
here is the version with the prepend.
Regards,
Mario
********** ********** ********** ********** ********** **********
IPng Requirements: a cable television industry
viewpoint
Mario P.
Vecchi
Time Warner
Cable
28 Feb 1994
Status of this Memo
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. Comments
should
be submitted to the big-internet@munnari.oz.au mailing list.
Distribution of this memo is unlimited.
This document is an Internet Draft. Internet Drafts are working
documents of the Internet Engineering Task Force (IETF), its
Areas,
and its Working Groups. Note that other groups may also
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Table of Contents
1 Executive Summary 2
2 Cable Television Industry Overview 2
3 Engineering Considerations 4
3.1 Scaling - 4
3.2 Timescale - 5
3.3 Transition and deployment - 5
3.4 Security - 6
3.5 Configuration, administration and operation - 6
3.6 Mobile hosts - 7
3.7 Flows and resource reservation - 7
3.8 Policy based routing - 8
3.9 Topological flexibility - 8
3.10 Applicability - 8
3.11 Datagram service - 9
3.12 Accounting - 9
3.13 Support of communication media - 9
3.14 Robustness and fault tolerance - 10
3.15 Technology pull - 10
3.16 Action items - 10
4 Security Considerations 10
5 Conclusions 11
6 AuthorUs Address 11
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 RconventionalS 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.
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 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 usersU 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 RgatewayS 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 Rbest-effortS, 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 RtoS, RfromS
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 Rtechnology pullS 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.
4 Security Considerations
No comments on general security issues are provided, beyond the
considerations presented in the previous subsection 3.4 on network
security.
5 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.
6 AuthorUs Address
Mario P. Vecchi
Time Warner Cable,
160 Inverness Drive West
Englewood, CO 80112
Phone: (303)799-5540
Fax: (303)799-5651
E-mail: mpvecchi@twcable.com
