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Introduction
The emergence of optical transport systems has dramatically increased the raw
capacity of optical networks and has enabled new sophisticated applications. For
example, network-based storage, bandwidth leasing, data mirroring, add/drop multiplexing
[ADM], dense wavelength division multiplexing [DWDM], optical cross-connect [OXC],
photonic cross-connect [PXC], and multiservice switching platforms are some of
the devices that may make up an optical network and are expected to be the main
carriers for the growth in data traffic.
Multiple Types of Switching
and Forwarding Hierarchies
Generalized MPLS (GMPLS) differs from
traditional MPLS in that it supports multiple types of switching, i.e. the addition
of support for TDM, lambda, and fiber (port) switching. The support for the additional
types of switching has driven GMPLS to extend certain base functions of traditional
MPLS and, in some cases, to add functionality. These changes and additions impact
basic LSP properties, how labels are requested and communicated, the unidirectional
nature of LSPs, how errors are propagated, and information provided for synchronizing
the ingress and egress LSRs.
1. Packet Switch Capable (PSC) interfaces:
Interfaces that recognize packet boundaries and can forward data based on the
content of the packet header. Examples include interfaces on routers that forward
data based on the content of the IP header and interfaces on routers that forward
data based on the content of the MPLS "shim" header. 2
. Time-Division Multiplex Capable (TDM) interfaces:
Interfaces that forward
data based on the data's time slot in a repeating cycle. An example of such an
interface is that of a SDH/SONET Cross-Connect (XC), Terminal Multiplexer (TM),
or Add-Drop Multiplexer (ADM). 3 . Lambda
Switch Capable (LSC) interfaces:
Interfaces that forward data based on
the wavelength on which the data is received. An example of such an interface
is that of a Photonic Cross-Connect (PXC) or Optical Cross-Connect (OXC) that
can operate at the level of an individual wavelength. Additional examples include
PXC interfaces that can operate at the level of a group of wavelengths, i.e. a
waveband. 4. Fiber-Switch Capable (FSC)
interfaces:
Interfaces that forward data based on a position of the data
in the real world physical spaces. An example of such an interface is that of
a PXC or OXC that can operate at the level of a single or multiple fibers. The
diversity and complexity in managing these devices have been the main driving
factors in the evolution and enhancement of the MPLS suite of protocols to provide
control for not only packet-based domains, but also time, wavelength, and space
domains. GMPLS further extends the suite of IP-based protocols that manage and
control the establishment and release of label switched paths (LSP) that traverse
any combination of packet, TDM, and optical networks. GMPLS adopts all technology
in MPLS.
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