IP over DWDM
Author: Melissa Gan Hwee Bee (1-29) EE01457
Dense Wavelength Division Multiplexing (DWDM): Process of multiplexing signal of different wavelength onto a
single fiber. It creates many virtual fibers each capable of carrying a different signal. DWDM system can be viewed
as a parallel set of optical channels, each using a slightly different light wavelength, but all sharing a single
transmission medium. This increases the capacity of existing networks without the need for expensive re-cabling
and can tremendously reduce the cost of network upgrades.
IP over DWDM is the concept of sending data packets over an optical layer using DWDM for its capacity and other
operations. In the modern day world, the optical layer has been supplemented with more functionality, which were
once in the higher layers. This creates a vision of an all-optical network where all management is carried out in the
photonic layer. The optical network is proposed to provide end-to-end services completely in the optical domain,
without having to convert the signal to the electrical domain during transit.
The advantages of IP over DWDM
Multistage Protocol
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Eliminates the multi-stack protocol, which presents more problems, such as:
 Function overlapping: So many layers are doing the same thing. In case of routing for example: DWDM,
SONET and ATM and IP all do the routing.
 Excessive overhead data bits, which reduces the capacity of the system to deliver actual information and
increases latency
Increases bandwidth and transmission speed
Facilitates faster restoration, provisioning & path determination
Absence of vendor specific component makes the system service transparent and improves interoperability
DWDM system
DWDM allows multiple wavelength channels to be simultaneously transmitted on a fiber. Currently available
commercial systems can support up to 100 channels, and future systems may support up to 1000 channels. The
primary advantage of DWDM is that existing fiber networks may be scaled to support even more bandwidth by
simply replacing the end electrical components. This high-speed high-volume transmission using DWDM is made
possible by the use of optical amplifiers, wavelength converters, wavelength add/drop multiplexers, optical cross
connect switches and other such components described below.
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Optical amplifier: used to amplify a weak, distorted signal with the aim of generating a good signal. It operates
in the optical domain, without converting the signal into electrical pulses. Erbium Doped Fiber Amplifier
(EDFA) is a common amplifier found in most networks.
Wavelength converter: convert the input wavelength into possibly different output wavelength within the
operational bandwidth of the DWDM system.
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Optical add/drop multiplexer: serves as the entry/exit point for different wavelengths in the DWDM network.
The practical utilization of the fiber is achieved by being able to selectively remove or reinsert individual
wavelengths without having to regenerate all the DWDM channels in the fiber.
Optical cross-connect switch: provides switching functionality between N input ports and N output ports with
each port handling a bundle of multiplexed single-wavelength signals. It also performs important network
management functions like signal monitoring, provisioning and restoration at the network layer itself.
Optical gateway: performs the function of provisioning and grooming of the data passing in and out of the
optical layer
IP/DWDM Architecture
The closed architecture was designed to serve the
SONET systems better. It increases the capacity in
the SONET system, by utilizing the necessary
components and the technology of DWDM in the
standard SONET terminal.
IP/DWDM systems adopted the alternative approach,
which yields a whole new transport layer, called the
Open architecture. It is open in the sense that it is not
tied with SONET or other TDM systems.
IP over DWDM issues
 Service transparency: a feature where in the network transporting the signal does not need any extra
information about it. This is required in order to treat all types of client in a unified manner.
 Interoperability: standards to be developed to facilitate multi-vendor internetworking
 Technology comparison:
Multiprotocol Lambda Switching (MPLS)
 a switching protocol that uses a set of labels for forwarding the packet
 implement routing protocols, enforce QoS & perform protection
 many limitations: does not support TDM and implementation of the Lambda switching, currently, is vendor
specific, thereby hindering interoperability between the systems.
The future of IP over DWDM
Probably the next big technical hurdle in IP over DWDM systems would be the development of key components
like add/drop multiplexers that can handle more than hundreds of wavelengths as IP routers are now able to achieve
very high speeds and hundreds of wavelengths over a single fiber may be requires to use such routers effectively in
terabit systems. Set in to increase the bandwidth and to reduce the latency, IP over DWDM seems to have much
potential as the architecture of the future. DWDM is the first step on the road to full optical networking and the
realization of the optical layer.