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1- Abstract
This paper looks at the Internet and the changing set of requirements
for the Internet that are emerging as it becomes more commercial, more
oriented towards the consumer, and used for a wider set of purposes. We
discuss a set of principles that have guided the design of the Internet,
called the end to end arguments, and we conclude that there is a risk
that the range of new requirements now emerging could have the consequence
of compromising the Internet's original design principles. Were this to
happen, the Internet might lose some of its key features, in particular
its ability to support new and unanticipated applications. We link this
possible outcome to a number of trends: the rise of new stakeholders in
the Internet, in particular Internet Service Providers; new government
interests; the changing motivations of the growing user base; and the
tension between the demand for trustworthy overall operation and the inability
to trust the behavior of individual users.
2- Introduction
The end to end arguments are a set of design principles that characterize
(among other things) how the Internet has been designed. These principles
were first articulated in the early 1980s, and they have served as an
architectural model in countless design debates for almost 20 years.
The end to end arguments concern how application requirements should be
met in a system. When a general purpose system (for example, a network
or an operating system) is built, and specific applications are then built
using this system (for example, e-mail or the World Wide Web over the
Internet), there is a question of how these specific applications and
their required supporting services should be designed. The end to end
arguments suggest that specific application-level functions usually cannot,
and preferably should not, be built into the lower levels of the system-the
core of the network. The reason why was stated as follows in the original
paper:
"The function in question can completely and correctly be implemented
only with the knowledge and help of the application standing at the endpoints
of the communications system. Therefore, providing that questioned function
as a feature of the communications systems itself is not possible."
In the original paper, the primary example of this end to end reasoning
about application functions is the assurance of accurate and reliable
transfer of information across the network. Even if any one lower level
subsystem, such as a network, tries hard to ensure reliability, data can
be lost or corrupted after it leaves that subsystem. The ultimate check
of correct execution has to be at the application level, at the endpoints
of the transfer. There are many examples of this observation in practice.
Even if parts of an application-level function can potentially be implemented
in the core of the network, the end to end arguments state that one should
resist this approach if possible. There are a number of advantages of
moving application-specific functions up out of the core of the network
and providing only general-purpose system services there.
o The complexity of the core network is reduced, which reduces costs and
facilitates future upgrades to the network.
o Generality in the network increases the chances that a new application
can be added without having to change the core of the network.
o Applications do not have to depend on the successful implementation
and operation of application-specific services in the network, which may
increase their reliability.
Of course, the end to end arguments are not offered as an absolute. There
are functions that can only be implemented in the core of the network,
and issues of efficiency and performance may motivate core-located features.
Features that enhance popular applications can be added to the core of
the network in such a way that they do not prevent other applications
from functioning. But the bias toward movement of function "up"
from the core and "out" to the edge node has served very well
as a central Internet design principle.
As a consequence of the end to end arguments, the Internet has evolved
to have certain characteristics. The functions implemented "in"
the Internet-by the routers that forward packets-have remained rather
simple and general. The bulk of the functions that implement specific
applications, such as e-mail, the World Wide Web, multi-player games,
and so on, have been implemented in software on the computers attached
to the "edge" of the Net. The edge-orientation for applications
and comparative simplicity within the Internet together have facilitated
the creation of new applications, and they are part of the context for
innovation on the Internet.
3- Moving away from end to end
For its first 20 years, much of the Internet's design has been shaped
by the end to end arguments. To a large extent, the core of the network
provides a very general data transfer service, which is used by all the
different applications running over it. The individual applications have
been designed in different ways, but mostly in ways that are sensitive
to the advantages of the end to end design approach. However, over the
last few years, a number of new requirements have emerged for the Internet
and its applications. To certain stakeholders, these various new requirements
might best be met through the addition of new mechanism in the core of
the network. This perspective has, in turn, raised concerns among those
who wish to preserve the benefits of the original Internet design.
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Source: CAnet-3-NEWS ; canarie.ca
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