28-03-2012, 12:41 PM
Dense wavelength division multiplexing (Download Full Seminar Report)
dwdm-prerequisite[1].pdf (Size: 785.07 KB / Downloads: 338)
Purpose
This tutorial provides prerequisite information about dense wavelength division
multiplexing (DWDM) systems. Since DWDM systems are derived from wavelength
division multiplexing (WDM) systems, and recently the introduction of coarse
wavelength division multiplexing (CWDM) systems each of these similar technologies
will be discussed and inter related to DWDM. This material is applicable to all DWDM
courses offered by Fujitsu Network Communications, Inc. (FNC). A list of acronyms
used in this tutorial is in Table 2, and Table 3 provides DWDM terminology.
Why DWDM?
Dense wavelength division multiplexing permits rapid network deployment and
significant network cost reduction. Use of DWDM allows deployment of less fiber and
hardware with more bandwidth being available relative to standard SONET networks.
Discrete Transport Channels vs DWDM Transport
Traditional SONET, TCP/IP, ATM, and voice over Internet Protocol (VoIP)1 are
transmitted over discrete channels, each requiring a fiber pair between the end points.
Figure 1 shows nine channels, each at 10 Gb/s, using nine discrete fiber pairs. This
traditional SONET method requires 3 regenerators to condition the signals across each
fiber path between each of the nine nodes, a total of 27 regenerators.
Service Provider Advantages
The service provider uses an existing installed fiber plant more effectively by
incorporating DWDM systems. Comparing Figure 1 to Figure 2, the service provider
recovers eight fiber pairs to expand its network for its investment in two 9-channel
(wavelength) DWDM terminals and three in-line amplifiers (ILAs), as described below.
Multiplexing reduces the cost per bit sent and received over the network. In Figure 1,
the distances require three regenerator sites for traditional SONET traffic. In Figure 2,
these 27 regenerators are removed and replaced by three ILAs. The cost of an ILA is
typically 50 percent of the cost of a SONET regenerator and the single ILA carries all
nine wavelengths.
Types of Multiplexing
Multiplexing is sending multiple signals or streams of information through a circuit at
the same time in the form of a single, complex signal and then recovering the separate
signals at the receiving end. Basic types of multiplexing include frequency division
(FDM), time division (TDM), and wavelength division (WDM), with TDM and WDM
being widely utilized by telephone and data service providers over optical circuits.
Time Division Multiplexing
Time-division multiplexing (TDM), as represented in Figure 3, is a method of combining
multiple independent data streams into a single data stream by merging the signals
according to a defined sequence. Each independent data stream is reassembled at the
receiving end based on the sequence and timing.
Fiber Attenuation
All transmission fiber suffers from the losses brought about by attenuation, as shown in
Figure 40. The characteristics of the common fibers have the following in common:
• The 1550-nm window has the lowest attenuation.
• The large spike is due to absorption by water molecules. This has been
greatly reduced on today’s fibers, allowing almost optimum minimum
attenuation.
Attenuation of Optical Signal
Amplification is needed in an optical network because photons leak out or are
absorbed by the fiber.
Fiber nonlinearities limit the allowable launch power into a fiber. These include a
variety of effects, such as self-phase modulation (SPM), cross-phase modulation
(XPM), stimulated Raman scattering (SRS), stimulated Brillouin scattering (SBS), and
four-wave mixing (FWM).
Light is limited to power increments of photons, so there is a lower limit to the amount
of power/number of photons a receiver needs to correctly detect 1s and 0s.
Signal Amplification
An optical power budget is maintained throughout the network. Distributed
amplification overcomes the power limits of transmission over fiber
• Amplifiers add noise to the desired signal as well as amplification.
• The number of amplifications that are possible before a signal must be
terminated is limited by the effects of noise.
• Some amplifier cross-talk and intersymbol interference1 restricts the
transmission distance.
Chromatic Dispersion Tolerance
• Standard SMF fiber has an average of 17 ps/nm/km of dispersion
• A 10-Gb/s receiver can tolerate about 800 ps/nm of dispersion
• A 500-km system generates 17 ps/nm/km x 500 km = 8500 ps/nm of
dispersion
dwdm-prerequisite[1].pdf (Size: 785.07 KB / Downloads: 338)
Purpose
This tutorial provides prerequisite information about dense wavelength division
multiplexing (DWDM) systems. Since DWDM systems are derived from wavelength
division multiplexing (WDM) systems, and recently the introduction of coarse
wavelength division multiplexing (CWDM) systems each of these similar technologies
will be discussed and inter related to DWDM. This material is applicable to all DWDM
courses offered by Fujitsu Network Communications, Inc. (FNC). A list of acronyms
used in this tutorial is in Table 2, and Table 3 provides DWDM terminology.
Why DWDM?
Dense wavelength division multiplexing permits rapid network deployment and
significant network cost reduction. Use of DWDM allows deployment of less fiber and
hardware with more bandwidth being available relative to standard SONET networks.
Discrete Transport Channels vs DWDM Transport
Traditional SONET, TCP/IP, ATM, and voice over Internet Protocol (VoIP)1 are
transmitted over discrete channels, each requiring a fiber pair between the end points.
Figure 1 shows nine channels, each at 10 Gb/s, using nine discrete fiber pairs. This
traditional SONET method requires 3 regenerators to condition the signals across each
fiber path between each of the nine nodes, a total of 27 regenerators.
Service Provider Advantages
The service provider uses an existing installed fiber plant more effectively by
incorporating DWDM systems. Comparing Figure 1 to Figure 2, the service provider
recovers eight fiber pairs to expand its network for its investment in two 9-channel
(wavelength) DWDM terminals and three in-line amplifiers (ILAs), as described below.
Multiplexing reduces the cost per bit sent and received over the network. In Figure 1,
the distances require three regenerator sites for traditional SONET traffic. In Figure 2,
these 27 regenerators are removed and replaced by three ILAs. The cost of an ILA is
typically 50 percent of the cost of a SONET regenerator and the single ILA carries all
nine wavelengths.
Types of Multiplexing
Multiplexing is sending multiple signals or streams of information through a circuit at
the same time in the form of a single, complex signal and then recovering the separate
signals at the receiving end. Basic types of multiplexing include frequency division
(FDM), time division (TDM), and wavelength division (WDM), with TDM and WDM
being widely utilized by telephone and data service providers over optical circuits.
Time Division Multiplexing
Time-division multiplexing (TDM), as represented in Figure 3, is a method of combining
multiple independent data streams into a single data stream by merging the signals
according to a defined sequence. Each independent data stream is reassembled at the
receiving end based on the sequence and timing.
Fiber Attenuation
All transmission fiber suffers from the losses brought about by attenuation, as shown in
Figure 40. The characteristics of the common fibers have the following in common:
• The 1550-nm window has the lowest attenuation.
• The large spike is due to absorption by water molecules. This has been
greatly reduced on today’s fibers, allowing almost optimum minimum
attenuation.
Attenuation of Optical Signal
Amplification is needed in an optical network because photons leak out or are
absorbed by the fiber.
Fiber nonlinearities limit the allowable launch power into a fiber. These include a
variety of effects, such as self-phase modulation (SPM), cross-phase modulation
(XPM), stimulated Raman scattering (SRS), stimulated Brillouin scattering (SBS), and
four-wave mixing (FWM).
Light is limited to power increments of photons, so there is a lower limit to the amount
of power/number of photons a receiver needs to correctly detect 1s and 0s.
Signal Amplification
An optical power budget is maintained throughout the network. Distributed
amplification overcomes the power limits of transmission over fiber
• Amplifiers add noise to the desired signal as well as amplification.
• The number of amplifications that are possible before a signal must be
terminated is limited by the effects of noise.
• Some amplifier cross-talk and intersymbol interference1 restricts the
transmission distance.
Chromatic Dispersion Tolerance
• Standard SMF fiber has an average of 17 ps/nm/km of dispersion
• A 10-Gb/s receiver can tolerate about 800 ps/nm of dispersion
• A 500-km system generates 17 ps/nm/km x 500 km = 8500 ps/nm of
dispersion