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Được đăng lên bởi Nguyen Thanh Sinh
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CHAPTER 13

Architectural Models

This chapter describes the architectural models that can be applied to GMPLS networks. These architectures are not only
useful for driving the ways in which networking equipment is deployed, but they are equally important in determining how
the protocols themselves are constructed, and the responsibilities of the various protocol components.
Several distinct protocol models have been advanced and the choice between them is far from simple. To some extent,
the architectures reflect the backgrounds of their proponents: GMPLS sits uncomfortably between the world of the Internet
Protocol and the sphere of influence of more traditional telecommunications companies. As a result, some of the architectures
are heavily influenced by the Internet, while others have their roots in SONET/SDH, ATM, and even the telephone system
(POTS).
The supporters of the different architectures tend to be polarized and fairly dogmatic. Even though there are many
similarities between the models, the proponents will often fail to recognize the overlaps and focus on what is different,
making bold and forceful statements about the inadequacy of the other approaches. This chapter does not attempt to anoint
any architecture as the best, nor does it even try to draw direct comparisons. Instead, each architecture is presented in its own
right, and the reader is left to make up her own mind.
Also introduced in this chapter is the end-to-end principle that underlies the IETF’s Internet architecture and then describes
three different GMPLS architectural models. The peer and overlay models are simple views of the network and are natural
derivatives of the end-to-end architectural model: They can be combined into the third model, the hybrid model, which has the
combined flexibility of the two approaches. The architectural model specified by the International Telecommunication Union
(ITU) for the Automatically Switched Optical Network (ASON) presents a different paradigm based on significant experience
deploying and managing transport networks; it is presented at the end of the chapter and is followed by a discussion of the
various ways
to realize the architecture and the attempts to bridge the gap between the two architectures.

13.1

The Internet's End-to-End Model

The architectural principles of the Internet are described in RFC 1958, but, as that document points out, the Internet
is continuously growing and evolving so that principles that seemed safe and ob...
C H A P T E R 1 3
Architectural Models
This chapter describes the architectural models that can be applied to GMPLS networks. These architectures are not only
useful for driving the ways in which networking equipment is deployed, but they are equally important in determining how
the protocols themselves are constructed, and the responsibilities of the various protocol components.
Several distinct protocol models have been advanced and the choice between them is far from simple. To some extent,
the architectures reflect the backgrounds of their proponents: GMPLS sits uncomfortably between the world of the Internet
Protocol and the sphere of influence of more traditional telecommunications companies. As a result, some of the architectures
are heavily influenced by the Internet, while others have their roots in SONET/SDH, ATM, and even the telephone system
(POTS).
The supporters of the different architectures tend to be polarized and fairly dogmatic. Even though there are many
similarities between the models, the proponents will often fail to recognize the overlaps and focus on what is different,
making bold and forceful statements about the inadequacy of the other approaches. This chapter does not attempt to anoint
any architecture as the best, nor does it even try to draw direct comparisons. Instead, each architecture is presented in its own
right, and the reader is left to make up her own mind.
Also introduced in this chapter is the end-to-end principle that underlies the IETF’s Internet architecture and then describes
three different GMPLS architectural models. The peer and overlay models are simple views of the network and are natural
derivatives of the end-to-end architectural model: They can be combined into the third model, the hybrid model, which has the
combined flexibility of the two approaches. The architectural model specified by the International Telecommunication Union
(ITU) for the Automatically Switched Optical Network (ASON) presents a different paradigm based on significant experience
deploying and managing transport networks; it is presented at the end of the chapter and is followed by a discussion of the
various ways
to realize the architecture and the attempts to bridge the gap between the two architectures.
13.1 The Internet's End-to-End Model
The architectural principles of the Internet are described in RFC 1958, but, as that document points out, the Internet
is continuously growing and evolving so that principles that seemed safe and obvious ten years ago are now no
longer quite as straightforward. As new technologies and ideas are developed, it is possible to conceive of new
architectural frameworks within which the Internet can continue to expand. Still, it is important to note that the
Internet cannot be dismantled and rebuilt into a new network — it is a live network that must continue to operate in
the face of innovation, and so new architectural paradigms must be integrated into the existing concepts in order to
ensure a gentle migration.
The basic premise underlying the Internet’s architecture is the delivery of end- to-end connectivity for the
transport of data using intelligence that, as much as possible, is placed at the edges of the network. That is, an
application wishing to supply a service across the Internet looks into the network to make an intelligent decision
about how to achieve the service, and then makes specific directed requests to facilitate the service. The end-to-end
principle means that information is only made available within the network on a‘need-to-know’ basis; the core of
the network should be spared knowledge about the services that it is carrying, thus making the Internet massively
more scalable. It also allows transit nodes to implement only basic protocols associated with data delivery, and
avoid awareness of application protocols required to realize specific services. This makes the core nodes simpler to
implement and, more important, means that new services and applications can be delivered over the Internet without
the need to upgrade the core network.
A secondary determination is to make the Internet as independent as possible of the underlying physical
technology; that is, it must be possible to construct the Internet from a wide variety of devices and connections that
support a huge range of data speeds and very different switching granularities. The protocol layering architecture
that is often described goes a long way to resolve this, and one of the key purposes of IP itself is to build up all data
link layers to a common level of service for use by transport and application technologies.
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