DWDM Fundamentals

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DWDM

Transcript of DWDM Fundamentals

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How long in the Telecommunications Industry?
India
International
Expectations
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Student Guide
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Learning Objectives -
On successful completion of this course the participants would be able to:
Describe the key elements of Transport in a Ring topology
Identify the limitations of PDH transmission
Define the concept of Virtual Containers
Describe the process of mapping PDH payload into SDH frame
Describe the SDH multiplexing hierarchy
Identify the Lower and Higher order Path Overheads
Define the Regenerator section & Multiplexer section overheads
Identify the Protection mechanisms
Describe the Synchronisation process
Describe the concept of Dense Wave Division Multiplexing
Identify the critical elements of DWDM
Describe the functioning of Optical ADM and Amplifiers
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The only dumb question is one that is not asked!
Raise your hand!
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Why Communicate
Communication is the means to convey one’s needs, feelings, urgency, etc. or to provide information to someone specific, to a group or to everyone in general.
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Participants to give one example for each need and rate the importance of Communication on a 1 to 5 scale
For each Need what kind of reliability is required from the system
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What are the limits of Systems available today?
Is Video conferencing an important means of communication?
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What has changed over the last 5000 years?
What is a Message and What is a Connection?
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Generally all Telecommunication system can be modeled with a few basic blocks:
Access a means to connect to users, convert their talk into electronic signals and vice versa.
Switch a means to connect A to B while there are a thousands other connections between C to Z possible
Transport a means to carry traffic & signals between several switches & also between switch & access equipment.
Services that’s what customers need; dial-tone, std, callerID, voice nail, sms, wake-up call, call debar, …..
Operation Support that’s what network operators need to operate their networks efficiently and effectively.
Each of these has it’s importance and value for the customer. The Access equipment would mean how easily and reliably the customer gets a connection. Switch would mean how many subscribers can be connected. Transport would mean what bandwidth he gets (how fast does he download, say). Services like Caller ID or SMS are as obvious as dial tone and STD these days, customer expects more of it. And finally OSS decides how efficiently you run the network, repair faults, raise correct bills, etc.
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Optical through OFC
Optical through free air
Guided and Un-guided Media
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Simple and easy to use, least in cost
Bandwidth-distance limitation, Attenuation, Interference, …
Simple & easy to use, least in cost
Power Output & Sensitivity is a function of various factors
Guided Media: Electrical
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Very high Bandwidth, very low Attenuation, No Interference, …
Connecting is a high skill job
Maintenance problems
Costly, difficult to maintain, hazardous
Power Output & Sensitivity has a wide range
Guided Media: Optical
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Maintenance problems
Tran receivers: complicated mW/ RF driver/ receivers
Costly, difficult to maintain, hazardous
Power Output & Sensitivity have to be fine tuned
Guided Media: mW and RF
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Air (media) & Frequency band (for separation)
Air is free (till now!) but Frequency bands are licensed (mostly)
Mostly Line-of-sight communication, but for low frequencies
Limited Bandwidth, Attenuation depend on several factors, …
Tran receivers: complicated mW/ RF driver/ receivers
Costly, difficult to maintain, hazardous
Power Output & Sensitivity have to be fine tuned
Location and geography are factors
Maintenance problems
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Journey through the “Optical Tunnel”
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Transmission through a OFC is like light ball traveling down a tunnel. It reflects several time time on the “wall” before reaching the end of the tunnel.
Advantages of OFC over other media like Cu wire are:
Very low attenuation
OFC are far thinner in diameter.
Disadvantages are
OFC is fragile.
OFC are difficult to join.
OFC has it’s own set of losses – dispersion, absorption, etc.
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*
Acceptance angle 1 is the maximum angle of incidence onto a fiber such that the refracted wave inside the fiber doesn’t cross the Critical angle (of TIR).
1 = sin-1[( n12 - n22)]
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Multiple wave-fronts enter and propagate through the core
Different wave-fronts would take different time period to travel through the entire distance of the core.
This is because different wave-fronts are traversing different distances.
Net effect is that a sharp square pulse gets distorted and spread out
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There are two general categories of optical fiber in use today, multimode fiber and single-mode fiber. Multimode, the first type of fiber to be commercialized, has a larger core than single-mode fiber. It gets its name from the fact that numerous modes, or light rays, can be carried simultaneously through the waveguide. Slide shows an example of light transmitted in the first type of multimode fiber, called step-index. Step-index refers to the fact that there is a uniform index of refraction throughout the core; thus there is a step in the refractive index where the core and cladding interface. Notice that the two modes must travel different distances to arrive at their destinations. This disparity between the times that the light rays arrive is called modal dispersion. This phenomenon results in poor signal quality at the receiving end and ultimately limits the transmission distance. This is why multimode fiber is not used in wide-area applications.
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To compensate for the dispersion drawback of step-index multimode fiber, graded-index fiber was invented. Graded-index refers to the fact that the refractive index of the core is graded—it gradually decreases from the center of the core outward. The higher refraction at the center of the core slows the speed of some light rays, allowing all the rays to reach their destination at about the same time and reducing modal dispersion.
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A single pulse would have several wavelengths
Each wavelength would travel at different speed
Thereby causing Chromatic dispersion
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A. Rayleigh Scattering
Rayleigh scattering is caused by small variations in the density of glass as it cools.
These variations are smaller than the wavelengths used and therefore act as scattering objects.
Scattering affects short wavelengths more than long wavelengths and limits the use of wavelengths below 800 nm.
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Attenuation in Optical Fiber
B. Stimulated Raman Scattering
Stimulated Raman scattering (SRS)is an effect which transfers power from a signal at a shorter wavelength to a signal at a longer wavelength.
The process is caused by the interaction of signal light waves with vibrating molecules (optical phonons) within the silica fiber. Light is then scattered in all directions. This effect has its maximum for a wavelength difference between the two signals of about 100 nm (13.2 THz).
l
l
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Stimulated Brillouin scattering (SBS)is a backscattering process causing loss of power.
With high power, the signal lightwaves induce periodic changes in the refractive index of the fiber.
This can be described as a virtual grating traveling away from the signal as an acoustic wave.
The signal itself is then scattered, but mostly reflected off this induced grating.
This effect occurs when only a few channels are transmitted.
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D. Absorption
Caused by the intrinsic properties of the material itself, the impurities in the glass, and any atomic defects in the glass.
These impurities absorb the optical energy, causing the light to become dimmer.
Intrinsic absorption is an issue at longer wavelengths and increases dramatically above 1700 nm.
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Fiber Optic Windows
Scattering and Absorption causes optical fiber to be suitable for transmission at specific frequencies only.
These frequency bands are called Bands or Windows.
Four Windows are identified in the IR range
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What’s Power in dbm terms
It’s simple to relate to attenuation if Power is also expressed in terms of db.
So if mW is the reference: Power in dbm = 10log10(P/mW)
Where mW is the reference: Power in dbm = 10log10(P/mW)
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For the above please calculate the following:
Attenuation in dB =
Attenuation per km =
Pout in dBm =
Pout in dBm = 2 mW (i.e 3 dBm) – 9.03 dB = -6.97 dBm
Please check your calculations as per the results shown by the instructor.
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As discussed earlier, and shown in Figure 2-1, there are four windows within the infrared spectrum that have been exploited for fiber transmission. The first window, near 850 nm, was used almost exclusivelyfor short-range, multimode applications. Non-dispersion-shifted fibers, commonly called standard single-mode (SM) fibers, were designed for use in the second window, near 1310 nm. To optimize the fiber’s performance in this window, the fiber was designed so that chromatic dispersion would be close to zero near the 1310-nm wavelength.
As optical fiber use became more common and the needs for greater bandwidth and distance increased, a third window, near 1550 nm, was exploited for single-mode transmission. The third window, or C band, offered two advantages: it had much lower attenuation, and its operating frequency was the same as that of the new erbium-doped fiber amplifiers (EDFAs). However, its dispersion characteristics were severely limiting. This was overcome to a certain extent by using narrower linewidth and higher power lasers. But because the third window had lower attenuation than the 1310-nm window, manufacturers came up with the dispersion-shifted fiber design, which moved the zero-dispersion point to the 1550-nm region.
Although this solution now meant that the lowest optical attenuation and the zero-dispersion points coincided in the 1550-nm window, it turned out that there are destructive nonlinearities in optical fiber near the zero-dispersion point for which there is no effective compensation. Because of this limitation, these fibers are not suitable for DWDM applications.
The third type, non-zero dispersion-shifted fiber, is designed specifically to meet the needs of DWDM applications. The aim of this design is to make the dispersion low in the 1550-nm region, but not zero. This strategy effectively introduces a controlled amount of dispersion, which counters nonlinear effects such as four-wave mixing (see the “Other Nonlinear Effects” section on page 2-11) that can hinder the performance of DWDM systems.
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Optical Fiber Standards
Designs of single-mode fiber have evolved over several decades. The three principle types and their ITU-T specifications are:
• Non-dispersion-shifted fiber (NDSF), G.652
• Dispersion-shifted fiber (DSF), G.653
Minimum dispersion at 1550 nm
Non-linear amplification for various wavelengths
• Non-zero dispersion-shifted fiber (NZ-DSF), G.655
Optimum dispersion at 1550 nm
Linear amplification for various wavelengths
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As optical fiber use became more common and the needs for greater bandwidth and distance increased, a third window, near 1550 nm, was exploited for single-mode transmission. The third window, or C band, offered two advantages: it had much lower attenuation, and its operating frequency was the same as that of the new erbium-doped fiber amplifiers (EDFAs). However, its dispersion characteristics were severely limiting. This was overcome to a certain extent by using narrower linewidth and higher power lasers. But because the third window had lower attenuation than the 1310-nm window, manufacturers came up with the dispersion-shifted fiber design, which moved the zero-dispersion point to the 1550-nm region.
Although this solution now meant that the lowest optical attenuation and the zero-dispersion points coincided in the 1550-nm window, it turned out that there are destructive nonlinearities in optical fiber near the zero-dispersion point for which there is no effective compensation. Because of this limitation, these fibers are not suitable for DWDM applications.
The third type, non-zero dispersion-shifted fiber, is designed specifically to meet the needs of DWDM applications. The aim of this design is to make the dispersion low in the 1550-nm region, but not zero. This strategy effectively introduces a controlled amount of dispersion, which counters nonlinear effects such as four-wave mixing (see the “Other Nonlinear Effects” section on page 2-11) that can hinder the performance of DWDM systems.
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during cabling causes light to couple out of the fiber.
Macro bending
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Exercise 2: Star vs Ring Topology
Let’s consider a location with 16 Access nodes, equidistant from a Switch located at the center.
What would be the total distance of media in Star Topology:
What would be the total media distance in Ring Topology with two rings as shown:
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Exercise 2: Star vs Ring Topology contd.
In a similar location let’s consider 8 Access nodes with a Switch located at the center. Now:
What would be the total distance of media in Star Topology:
What would be the total media distance in Ring Topology with two rings as shown:
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Star vs Ring Topology
Total media distance is not necessary more/ less for Star/ Ring topology.
It should be examined on a case to case basis.
In Star transmission remains point to point between each node.
In Ring a Add-drop function/ technique is needed at each node.
In Star link failure is isolated, in ring it needs to be overcome by protection technique.
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Although a major advantage, the Ring topology doesn’t necessarily reduce the amount of media used in the network. In this example the length of media used in the Star topology is 16r (r= radius of the circle, where the Access nodes are located, the Switch is located at the centre). The length of the two Rings (not necessarily the only solution, you can think of using just one ring as well) work out to 2*( 2r+ pr) ~10r. That is certainly less than 16r used in the Star topology. But if the number of nodes were say 6 or 8 (anything less than 10) the media required in Star would have reduced to 6r or 8r, less than the Ring topology.
The planners still prefer to go for the Ring, keep the future needs in mind.
The second advantage is offcourse the availability of protection, if a section fails the ring still work.
But the ring topology brings in it’s complexity. The transmission is no more point-to-point as in star. Information from the Switch to a Node x, has to travel to many other nodes before reaching it’s destination. It also means each such set of info actually moves on the ring with several other sets of info. How these information are picked up, added to the collection and than segregated and delivered at the right node is the technology what we will study in this course.
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In a Ring each node is called a Add-Drop Multiplexer (ADM). An ADM have grossly three parts:
Tributory Interfaces with the non-ring nodes to bring in Traffic
Payload Manager Manages multiplexing & de-multiplexing activities.
Aggregate Interfaces with the OFC Ring
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Network scenario of near future!
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There is also rapidly increasing demand on access networks, which function primarily to connect end users over low-speed connections, such as dial-up lines, DSL, cable, and wireless, to a local POP. These connections are typically aggregated and carried over a SONET ring, which at some point attaches to a local POP that serves as an Internet gateway for long hauls. Now, the growing demand for high-speed services is prompting service providers to transform the POP into a dynamic service-delivery center. As a result, it is increasingly likely that a customer now obtains many high-speed services directly from the POP, without ever using the core segment of the Internet.
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A quantum jump in bandwidth in achieved by using a technique called Dense Wave Division Multiplexing (DWDM). This can be explained as thus:
Suppose you had a one lane HW, only one vehicle could run at a time. If you needed more vehicles to run simultaneously you will have to add more lanes. But there would be practical limitations like space & money. Now suppose we equate each lane with a colour of light (violet, blue, green, yellow, orange, red, etc.) to apply this theory to OFC transmission, then we could several vehicles in separate colours, pass them through a prism and get white light. This can be passed through a single fibre (single lane of a HW) and at the destination we can break it up into different colours using another prism.
DWDM uses the above phenomenon, but uses Laser and IR light instead of visible light. The result is the same, only that we can multiplex many more wavelengths (different wavelength stands for different colour in visible spectrum) and demultiplex them at the receiving end. So while we can achieve say 10 Gbps with one wavelength, we can go upto 400 Gbps by using DWDM! That too with a single core of OFC. And we have 48 cores in one cable and 6 such cables that can be laid in our NBB!! How much bandwidth does that come to – calculate during the break!!!
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The early 1990s saw a second generation of WDM, sometimes called narrowband WDM, in which two to eight channels were used. These channels were now spaced at an interval of about 400 GHz in the 1550-nm window. By the mid-1990s, dense WDM (DWDM) systems were emerging with 16 to 40 channels and spacing from 100 to 200 GHz. By the late 1990s DWDM systems had evolved to the point where they were capable of 64 to 160 parallel channels, densely packed at 50 or even 25 GHz intervals.
As the slideshows, the progression of the technology can be seen as an increase in the number of wavelengths accompanied by a decrease in the spacing of the wavelengths. Along with increased density of wavelengths, systems also advanced in their flexibility of configuration, through add-drop functions, and management capabilities.
Increases in channel density resulting from DWDM technology have had a dramatic impact on the carrying capacity of fiber. In 1995, when the first 10 Gbps systems were demonstrated, the rate of increase in capacity went from a linear multiple of four every four years to four every year
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DWDM Records!
1×40 G up to 65 km (Alcatel’98). PMD Limited.
32× 5 G to 9300 km (1998)
64× 5 G to 7200 km (Lucent’97)
100×10 G to 400 km (Lucent’97)
16×10 G to 6000 km (1998)
132×20 G to 120 km (NEC’96)
70×20 G to 600 km (NTT’97)
1022 Wavelengths on one fiber (Lucent 99)
Ref: OFC’9x
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The early 1990s saw a second generation of WDM, sometimes called narrowband WDM, in which two to eight channels were used. These channels were now spaced at an interval of about 400 GHz in the 1550-nm window. By the mid-1990s, dense WDM (DWDM) systems were emerging with 16 to 40 channels and spacing from 100 to 200 GHz. By the late 1990s DWDM systems had evolved to the point where they were capable of 64 to 160 parallel channels, densely packed at 50 or even 25 GHz intervals.
As the slideshows, the progression of the technology can be seen as an increase in the number of wavelengths accompanied by a decrease in the spacing of the wavelengths. Along with increased density of wavelengths, systems also advanced in their flexibility of configuration, through add-drop functions, and management capabilities.
Increases in channel density resulting from DWDM technology have had a dramatic impact on the carrying capacity of fiber. In 1995, when the first 10 Gbps systems were demonstrated, the rate of increase in capacity went from a linear multiple of four every four years to four every year
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DWDM
Standard support 1000 colors of light, only 160 colors supported today
Key players - Ciena, Cerent (Cisco), Lucent, Marconi, Nortel, Siemens, Sycamore
Supports PoS – packet over Sonet to Wavelength
Supports LAMBDA routing
The system performs the following main functions:
• Generating the signal—The source, a solid-state laser, must provide stable light within a specific, narrow bandwidth that carries the digital data, modulated as an analog signal.
• Combining the signals—Modern DWDM systems employ multiplexers to combine the signals. There is some inherent loss associated with multiplexing and demultiplexing. This loss is dependent upon the number of channels but can be mitigated with optical amplifiers, which boost all the wavelengths at once without electrical conversion.
• Transmitting the signals—The effects of crosstalk and optical signal degradation or loss must be reckoned with in fiber optic transmission. These effects can be minimized by controlling variables such as channel spacings, wavelength tolerance, and laser power levels. Over a transmission link, the signal may need to be optically amplified.
• Separating the received signals—At the receiving end, the multiplexed signals must be separated out. Although this task would appear to be simply the opposite of combining the signals, it is actually more technically difficult.
• Receiving the signals—The demultiplexed signal is received by a photodetector.
In addition to these functions, a DWDM system must also be equipped with client-side interfaces to receive the input signal.
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Fiber Optics
Serves as the transmission medium for most carrier’s “backbone” network
Physically links every major metropolitan area in the United States, Canada, and the United Kingdom
Now deployed in The Reliance Network
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Four Way Mixing
Caused when multiple wavelengths travel in the same phase for long time
New signals are generated at the same frequency spacing as original: f1,f2 2f2-f1, 2f1-f2
Closer channels More FWM
More power More FWM
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Þ 4 ps/nm/km near 1530-1570nm band
Avoids four-way mixing
Dispersion Compensating Fiber:
Standard fiber has 17 ps/nm/km. DCF -100 ps/nm/km
100 km of standard fiber followed by 17 km of DCF Þ zero dispersion
Standard Fiber Dispersion Compensating Fiber
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1. The transponder accepts input in the form of standard single-mode or multimode laser. The input can come from different physical media and different protocols and traffic types.
2. The wavelength of each input signal is mapped to a DWDM wavelength.
3. DWDM wavelengths from the transponder are multiplexed into a single optical signal and launched into the fiber. The system might also include the ability to accept direct optical signals to the multiplexer; such signals could come, for example, from a satellite node.
4. A post-amplifier boosts the strength of the optical signal as it leaves the system (optional).
5. Optical amplifiers are used along the fiber span as needed (optional).
6. A pre-amplifier boosts the signal before it enters the end system (optional).
7. The incoming signal is demultiplexed into individual DWDM lambdas (or wavelengths).
8. The individual DWDM lambdas are mapped to the required output type (for example, OC-48 single-mode fiber) and sent out through the transponder.
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1. The transponder accepts input in the form of standard single-mode or multimode laser. The input can come from different physical media and different protocols and traffic types.
2. The wavelength of each input signal is mapped to a DWDM wavelength.
3. DWDM wavelengths from the transponder are multiplexed into a single optical signal and launched into the fiber. The system might also include the ability to accept direct optical signals to the multiplexer; such signals could come, for example, from a satellite node.
4. A post-amplifier boosts the strength of the optical signal as it leaves the system (optional).
5. Optical amplifiers are used along the fiber span as needed (optional).
6. A pre-amplifier boosts the signal before it enters the end system (optional).
7. The incoming signal is demultiplexed into individual DWDM lambdas (or wavelengths).
8. The individual DWDM lambdas are mapped to the required output type (for example, OC-48 single-mode fiber) and sent out through the transponder.
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A simple form of multiplexing or demultiplexing of light can be done using a prism. The slide demonstrates the demultiplexing case. A parallel beam of polychromatic light impinges on a prism surface; each component wavelength is refracted differently. This is the “rainbow” effect. In the output light, each wavelength is separated from the next by an angle. A lens then focuses each wavelength to the point where it needs to enter a fiber. The same components can be used in reverse to multiplex different wavelengths onto one fiber.
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Another technology is based on the principles of diffraction and of optical interference. When a polychromatic light source impinges on a diffraction grating (see slide), each wavelength is diffracted at a different angle and therefore to a different point in space. Using a lens, these wavelengths can be focused onto individual fibers.
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It is often desirable to be able to remove or insert one or more wavelengths at some point along this span. An optical add/drop multiplexer (OADM) performs this function. Rather than combining or separating all wavelengths, the OADM can remove some while passing others on. OADMs are a key part of moving toward the goal of all-optical networks.
OADMs are similar in many respects to SONET ADM, except that only optical wavelengths are added and dropped, and no conversion of the signal from optical to electrical takes place. Slide above is a schematic representation of the add-drop process. This example includes both pre- and post-amplification; these components that may or may not be present in an OADM, depending upon its design.
There are two general types of OADMs. The first generation is a fixed device that is physically configured to drop specific predetermined wavelengths while adding others. The second generation is reconfigurable and capable of dynamically selecting which wavelengths are added and dropped.
Thin-film filters have emerged as the technology of choice for OADMs in current metropolitan DWDM systems because of their low cost and stability. For the emerging second generation of OADMs, other technologies, such as tunable fiber gratings and circulators, will come into prominence.
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OPTICAL AMPLIFICATION
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The explosion of dense wavelength-division multiplexing (DWDM) applications make these optical amplifiers an essential fiber optic system building block. EDFAs allow information to be transmitted over longer distances without the need for conventional repeaters. The fiber is doped with erbium, a rare earth element, that has the appropriate energy levels in their atomic structures for amplifying light. EDFAs are designed to amplify light at 1550 nm. The device utilizes a 980 nm or 1480nm pump laser to inject energy into the doped fiber. When a weak signal at 1310 nm or 1550 nm enters the fiber, the light stimulates the rare earth atoms to release their stored energy as additional 1550 nm or 1310 nm light. This process continues as the signal passes down the fiber, growing stronger and stronger as it goes.
The input coupler, Coupler #1, allows the microcontroller to monitor the input light via detector #1. The input isolator, isolator #1 is almost always present. WDM #1 is always present, and provides a means of injecting the 980 nm pump wavelength into the length of erbium-doped fiber. WDM #1 also allows the optical input signal to be coupled into the erbium-doped fiber with minimal optical loss. The erbium-doped optical fiber is usually tens of meters long. The 980 nm energy pumps the erbium atom into a slowly decaying, excited state. When energy in the 1550 nm band travels through the fiber it causes stimulated emission of radiation, much like in a laser, allowing the 1550 nm signal to gain strength. The erbium fiber has relatively high optical loss, so its length is optimized to provide maximum power output in the desired 1550 nm band. WDM #2 is present only in dual pumped EDFAs. It couples additional 980 nm energy from Pump Laser #2 into the other end of the erbium-doped fiber, increasing gain and output power. Isolator #3 is almost always present. Coupler #2 is optional and may have only one of the two ports shown or may be omitted altogether. The tap that goes to Detector #3 is used to monitor the optical output power. The tap that goes to Detector #2 is used to monitor reflections back into the EDFA. This feature can be used to detect if the connector on the optical output has been disconnected. This increases the backreflected signal, and the microcontrolled can set to disable the pump lasers in this event, providing a measure of safety for technicians working with EDFAs.
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Raman Amplifier
RFAs use the Raman effect – or Stimulated Raman scattering (SRS) – to transfer power from the pump laser at a shorter wavelength to the optical signal.
It uses either the embedded fiber as the active medium (distributed Raman amplification), or a part of the fiber inside a structure (discrete Raman amplification).
The optical fiber is commonly counter pumped (pumped backwards) with a 600 mW laser which is most efficient with a wavelength difference of 100 nm (13.2 THz) to the signal.
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Unidirectional two-fiber arrangements can support up to 80 wavelengths over both the C- and L-Bands.
This offering corresponds to up to 0.8 Tbps (or 800Gbps) aggregate traffic capacity at 10 Gbps.
OPTera LH Release 3 introduces the OPTera 1600G C-Band unidirectional application.
OPTera LH Release 3 supports up to 40 wavelengths in the C-Band (or 400 Gbps).
Unidirectional topology
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80 wavelengths on each fiber
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Unidirectional two-fiber arrangements can support up to 80 wavelengths over both the C- and L-Bands. This offering corresponds to up to 0.8 Tbit/s
aggregate traffic capacity at 10 Gbit/s.
OPTera LH Release 3 introduces the OPTera 1600G C-Band unidirectional
application. OPTera LH Release 3 supports up to 40 wavelengths in the
C-Band (or 400 Gbit/s).
OPTera LH Release 5 will provide an additional 40 wavelengths in the L-Band.
The L-Band Amplifier overlay is supported as an in-service expansion that
shares the same optical fiber as the C-Band. Wavelengths are spaced on a
100-GHz grid.
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Bi-directional single-fiber arrangements can support up to 160 wavelengths or 80 channels over both the C and L-Bands.
A future release of OPTera 1600G configured as bi-directional will employ up to 80 wavelengths in the C-Band with an additional 80 wavelengths in the L-Band when required. These channels are designed to co-propagate and counter-propagate in each band.
Bi-directional topology
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Bi-directional topology (future release)
Bi-directional single-fiber arrangements can support up to 160 wavelengths or 80 channels over both the C- and L-Bands. You can scale systems up to 1.6Tbit/s aggregate fiber span capacity as shown in Figure 3-3.
A future release of OPTera 1600G configured as bi-directional will employ up to 80 wavelengths in the C-Band with an additional 80 wavelengths in the L-Band when required. These channels are designed to co propagate and
counter-propagate in each band.To ensure robust bi-directional performance, wavelengths are interleaved on a
50 GHz grid to provide effective 100-GHz spacing for wavelengths traveling in the same direction.
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The infrastructure
Reliance will use to support low data rates (below 80gbps)
G.655
Reliance will use for high traffic areas
Can support 80gbps
WDM/DWDM
DWDM (Phase I) – 40 channels of 10gbps
DWDM (Phase II) – 80 channels of 10gbps
DWDM (Phase III) – 160 channels of 10gbps
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20 Gbps bandwidth used
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This is our Reliance India Roadmap. It’s a mega network of 60.000 km of OFC highway connecting 227 LDCA, 565 SDCA, covering 18 telecom circles, extending wireline connectivity to 138 cities and wireless connectivity in 578 cities. Business conducted in these cities constitutes 80% of India’s GDP.
The core rings connect 22 Core MCN’s with 17 ILT’s at this moment. These are our Life-lines. The subtended rings interconnect some of these MCN’s and function like the Bypasses.
Like how healthy you are in indicated by how well your heart is functioning and how good is your blood circulation, similarly the health of a telecom network can be measured by how much bandwidth these transport network can handle and how well they do so. Like multiple lanes of Highways, Transport network provide bandwidth which decides how much traffic (read how many calls) can be carried. To the user it translates into how much she/ he pays for a short distance or long distance call or how fast is the download of an interesting article or favorite song. This module we will see how we live up to that challenge.
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22 Countries, 44 PoP’s, 180 Carriers connected world over
42,000 km route length
India - Presently: 15 STM-1’s, Mar. ’05: 39 STM-1’s
SA NY LN, PR, FR
AL JD, TH, MU HK
SG TY
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FLAG Telecom develops and operates advanced fibre-optic global cable systems over which it offers a growing range of value-added network services. It operates a global network and provides customers with connectivity to most of the major business centres around the world.
FLAG Europe-Asia is the world's longest privately funded undersea fibre-optic cable system stretching more than 28,000km from the UK to Japan with landing sites in 13 countries
FLAG Atlantic-1 is the world's first multi-terabit transoceanic dual cable system providing a fully protected city-to-city service between London, Paris and New York.
FLAG North Asian Loop has been designed to support the strong growth in intra-Asia Internet traffic and provides intra-regional, city-to-city connectivity between Hong Kong, Seoul, Tokyo and Taipei.
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At the National level RIC has established 7 very high bandwidth Transport Rings, called National BackBone/ Long Distance Rings. Practically there are 11 rings as Ring 1 and 3 comprise 3 rings each (1A, 1B, 1C & 3A, 3B, 3C). These Rings are so designed that all major cities get enough bandwidth and not too many cities come on the same ring. Also having these 11 rings provide enough alternative routes in case of failure in one section. These rings traverse all the 18 circles, touch all major cities and cover about 90% of Indian population.
Established (read utilised) Bandwidth of these rings are at 10 Gbps, but that’s just tip of the iceberg compared to what we can achieve. What gives these rings such gargantuan bandwidth – OFC. How – we will see later in this module.
As stated earlier, these rings connect 22 Core MCN’s with 17 ILT’s at this moment. From these rings, at these 22 MCN’s, emerges several Metro Access Rings, which connect other small cities and towns to the NBB.
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The backbone transport provides for connectivity between different LDCAs, SDCAs and cities. In addition interconnect is extended for other NLD, CSP and FSP networks.
The core network comprises fully meshed, 7 primary and 14 secondary nodes. Physical architecture of the Core Network comprises of two-tier ring network – Express Ring & Collector Ring. Traffic between major metros and all major node cities is transported on the high capacity transport path – The Express Ring. Traffic from the other LDCA’s (Long Distance Charging Areas) is transported on The Collector Ring. The ring topology provides necessary protection to traffic in terms of alternate path in case of breakage of the optical fibre or equipment failure thus ensuring smooth undisrupted operation of the network.
The functions of the Core-Backbone Network are as follows:
Provide connections, either on permanent basis or temporary basis for the transfer of information in a cost effective, reliable and speedy manner
· Routing – which way to send the information
· Transport – how the information is carried
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Standard OPTera 1600G shelf configurations
Standard shelf configurations supported in OPTera LH Release 3 are as follows:
C-Band Dual Amplifier followed by Booster18 C-Band. This configuration provides a single Mid Stage Access point (Single MSA).
C-Band Dual Amplifier followed by Booster21 C-Band (Single MSA).
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OPTera LH Release 3 supports the extension shelf 2 with the following restrictions:
All slots must be equipped with NTCA49AA filler circuit packs.
The system provides no alarming for the second extension shelf.
A future OPTera LH software release will fully support the second extension shelf for L-Band applications.
Extension shelf 2 Equipping rules
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Single MSA in C-Band supporting up to 30 wavelengths for each group (limited OADM)
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Single MSA in C-Band supporting up to 40 wavelengths for each group (limited OADM/DSCM)
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Dual MSA in C-Band supporting up to 40 wavelengths for each group (full OADM/DSCM)
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DWDM passive bay
The DWDM passive bay can store passive components such as Mux and Demux couplers, OADM filters, and DSCMs.
This bay supports Mux, Demux, DSCMs at Terminal or ADM sites. At Line amplifier sites, the bay supports DSCMs and OADM filters as required.
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The DWDM passive bay has a 24-module capacity.
The DWDM passive bay contains six shelves that can each house up to four modules.
The top two shelves house DSCMs and DCMs, if required.
One shelf can house two Mux and two Demux couplers. Since each coupler consists of 10 ports (10 channels), each shelf can support 40 wavelengths: 20 wavelengths Mux and 20 wavelengths Demux.
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This deals with the multiplexer (Mux) and demultiplexer (Demux) couplers that are required for the OPTera 1600G Amplifier application.
OPTera 1600G requires a new architecture for passive Mux and Demux modules to enable unidirectional amplifier configurations.
The C-Band wavelength plan is mapped into 2 grids:
C-Band Grid 1, and
C-Band Grid 2.
Grid 1 is based on 100-GHz ITU-T wavelength plan. Grid 2 is also based on a 100-GHz spacing with a 50-GHz offset from Grid 1. In a typical unidirectional application, the Mux and Demux would be based on the same grid.
OPTera 1600G DWDM filter Architecture
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Up to four modules (Mux or Demux) are interconnected in cascade to support up to 40 wavelengths, plus 1 spare, in each wavelength grid.
Each module carries 10 wavelengths except for the first module that contains the spare wavelength.
Future releases of OPTera 1600G will introduce two additional grids to support L-Band applications.
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Each Demux module can support up to 10 wavelengths and contains a miniature variable optical attenuator (mVOA) for each wavelength.
Module 1 (first module of the four interconnected modules) includes a monitor port and a spare wavelength port.
Two patchcords (A and B) as shown are used to interconnect the modules.
Demux Modules
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Mux modules
Each Mux module can support up to 10 wavelengths. Module 1 (first module of the four interconnected modules) includes a monitor port and spare wavelength port. The Mux modules are a mirror image of the Demux modules. Two patchcords (A and B) are used to interconnect the modules.
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The wavelength upgrade plans for OPTera 1600G C-Band are shown in (Grid 1) and (Grid 2). The tables specify the channel wavelength-to-DWDM Mux/Demux module mapping.
Engineering rules for module deployment sequence
For all fiber types, the engineering rules for DWDM Mux/Demux module deployment sequence are:
Deploy Module 1 until all the capacity is exhausted for all fiber types.
Deploy Module 2 next for all fiber types except certain types of NZ-SF fiber.
Deploy Module 3 next for all fiber types.
Finally, deploy Module 4 for all fiber types except TrueWaveTM Classic.
Wavelength Plans
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For OADM applications, choose the wavelengths according to 1-channel, 2-channel, or Band OADM drop recommendations. OADM modules will be introduced in 1-channel, 2-channel, or multichannel band drop.
Channels designated to support express or OADM channels need to be correctly assigned to either express or OADM applications.
As a result, careful planning of wavelengths before deployment is required.
For example, if all wavelengths from Module 1 are to be deployed as express channels, the wavelengths on that module must remain as express wavelengths.
In case an OADM is required at a later date, the OADM wavelengths from modules 2, 3, or 4 must be used for providing that the OADM wavelengths
OADM applications
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• Wavelength Translator
• Dense regenerator
• Wavelength Combiner
• MOR Plus amplifier
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Note 1: A network element equipped with at least one Wavelength Combiner circuit pack group requires two ESI and two half-height TD circuit packs.
Note 2: Do not mix circuit pack traffic mode (REGEN for XR or 3R for WT) within the same ODPR circuit pack group.
Note 3: ODPR does not support 2.5 Gbit/s circuit packs.
Note 4: Equip one or two Ethernet Wayside circuit packs in slot 16 (G5) and slot 17 (G6) of the control shelf for point-to-point and continuity of Ethernet communication. The network element must also be equipped with MOR Plus amplifier circuit packs.
Note 5: Be sure to follow the appropriate equipping rules when you equip MOR Plus amplifier circuit packs in the first four slots of the main shelf.
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Dense regenerator application in a network
Note: The client-facing equipment's TFEC setting must be turned off for correct interoperability with other vendors.
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An optical signal can pass through a maximum of 30 WT, XR, or combination of WT and XR circuit packs on an optical link. This maximum complies with the Telcordia (formerly Bellcore) specifications for jitter outlined in the following documents:
• For jitter generation: GR-1377 Section 5.6.5 requirement, R5-20, R5-23
• For jitter tolerance: GR-1377 requirement, R5-22
• For jitter transfer: GR-1377 requirement, R5-21
Dense regenerator circuit packs extend system reach by reconstituting the optical signal in each direction at an intermediate point between two service-terminating locations. If required, multiple-cascaded Dense regenerator circuit packs are deployed along with optical amplifiers to extend system reach by hundreds of kilometers. Unlike traditional SONET/SDH regenerator network elements, OPTera Long Haul 1600 supports as many as 30 Dense regenerator circuit packs in a single seven-foot bay. This efficient use of space yields substantial savings in capital equipment costs, operational costs, and footprint requirements when compared to traditional solutions.
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Note: The client-facing equipment's forward error correction setting must be turned off for correct interoperability with other vendors.
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A Wavelength Translator (also known as a transponder) is a circuit pack that translates one wavelength into another. This capability is useful for mapping legacy wavelengths onto the ITU-T compliant dense-wavelength division multiplexing (DWDM) wavelength grid. Wavelength Translators reshape, reamplify, and retime (3R regeneration) a signal without regenerating the entire SONET/SDH overhead. Release 1.2 and 1.5 supported 3R Wavelength Translators only. Because of its minimal overhead (OH) processing and monitoring capability, a Wavelength Translator is also known as a thin SONET/SDH regenerator. Wavelength Translators provide an enhanced level of transparency for wavelength leasing alternatives.
The Wavelength Translator does not terminate section/RS or line/MS data communications channel (DCC) (D1 to D3 and D4 to D12, respectively). You must use the optical service channel (OSC) to support full DCC-like operations, administration, maintenance, and provisioning (OAM&P) access to all network elements on the optical line/MS.
Some regenerator sites are deployed with thin 3R functionality (without TriFEC functionality). Therefore, when you use circuit packs in Wavelength Translator mode, overhead bytes are passed through transparently.
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Fault sectionalization
Fault sectionalization refers to the process of detecting errors and their location. The fastest method of sectionalizing faults in a Wavelength Translator application or ODPR application is by disabling transparency across the optical line/MS.
B1 byte provisioning functionality for Wavelength Translator applications If the B1 byte is provisioned as pass-through for Wavelength Translator applications, the error count increases every time a fault occurs and the total number of error counts reaches the subtending equipment
The B1 byte is set to recalculated for Dense regenerator applications. As a result, the Dense regenerator application cannot provide pass-through capability. You cannot provision the Dense regenerator application to provide B1 transparency.
To sectionalize faults when B1 is set to pass-through, you must log in to each Repeater network element in the link and analyze the PM screens. This method allows you to determine where the counts have started to increase. Provisioning the B1 byte to pass-through meets the need of some customers for total service transparency, while still signaling faults to the subtending equipment. The subtending equipment can then handle the protection switching. However, in this scenario, sectionalization of faults is a laborious process.
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The Wavelength Combiner application, introduced in Release 2, aggregates up to four 2.5 Gbit/s services into one 10 Gbit/s line signal while maintaining service transparency.
A Repeater network element can house up to five Wavelength Combiner circuit pack groups, for a total of 50 Gbit/s of aggregated 2.5 Gbit/s services. Since the optical line signal is managed by its overhead, the tributary services are transparent to the 10 Gbit/s SONET/SDH line/MS. This arrangement allows the use of forward error correction (FEC) and communication channels on the line side. The Wavelength Combiner application supports ITU-T standard wavelengths.
Compared to a transponder-based solution, the Wavelength Combiner offers service granularity on the access space, while maximizing wavelength traffic capacity on the transport medium. The Wavelength Translator acts as a transparent interface. The Wavelength Combiner acts as an open optical interface and provides at least four times the effective channel count on the fiber plant.
Similar to the transparent Mux (TMux) application on the 10 Gbit/s S/DMS TransportNode platform, the Wavelength Combiner distributes its tributary service signals onto the 10 Gbit/s line/MS signal through a fixed mapping scheme. This mapping is executed through the OPTera Long Haul 1600 platform backplane bus signals, therefore eliminating the need for switch module circuit packs or bandwidth management core.
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The Wavelength Combiner application, introduced in Release 2, aggregates up to four 2.5 Gbit/s services into one 10 Gbit/s line signal while maintaining service transparency.
A Repeater network element can house up to five Wavelength Combiner circuit pack groups, for a total of 50 Gbit/s of aggregated 2.5 Gbit/s services. Since the optical line signal is managed by its overhead, the tributary services are transparent to the 10 Gbit/s SONET/SDH line/MS. This arrangement allows the use of forward error correction (FEC) and communication channels on the line side. The Wavelength Combiner application supports ITU-T standard wavelengths.
Compared to a transponder-based solution, the Wavelength Combiner offers service granularity on the access space, while maximizing wavelength traffic capacity on the transport medium. The Wavelength Translator acts as a transparent interface. The Wavelength Combiner acts as an open optical interface and provides at least four times the effective channel count on the fiber plant.
Similar to the transparent Mux (TMux) application on the 10 Gbit/s S/DMS TransportNode platform, the Wavelength Combiner distributes its tributary service signals onto the 10 Gbit/s line/MS signal through a fixed mapping scheme. This mapping is executed through the OPTera Long Haul 1600 platform backplane bus signals, therefore eliminating the need for switch module circuit packs or bandwidth management core.
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Each tributary interface circuit pack is assigned to a reserved block in the OC-192/STM-64 frame. Timeslot alignment on the Wavelength Combiner is as listed below.
• tributary circuit pack A is mapped to STS timeslots 97 to 144
• tributary circuit pack B is mapped to STS timeslots 49 to 96
• tributary circuit pack C is mapped to STS timeslots 1 to 48 (see Note)
Note: For Wavelength Combiners equipped with a non-TriFEC OC-192/STM-64 T/R circuit pack, the STS timeslot 1 overhead of the C channel tributary is mapped to the STS timeslot 1 of the 10 Gbit/s Combiner line/MS. For Wavelength Combiners equipped with a TriFEC-capable OC-192/STM-64 T/R circuit pack, the STS timeslot 1 overhead of the C channel tributary is mapped to the STS timeslot 13 of the 10 Gbit/s Combiner line/MS. All C channel transparency issues that exist on the non-TriFEC T/R circuit pack do not exist on the TriFEC-capable T/R circuit pack.
• tributary circuit pack D is mapped to STS timeslots 145 to 192
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Note: The Wavelength Combiner circuit pack groups at both terminals
must be originally equipped with the same type of T/R circuit packs,
either TriFEC-capable or non-TriFEC. Failure in following this rule
will probably cause a "Protection scheme mismatch" or "Channel ID
mismatch" alarm to be raised on the subtending OC-48 or TN-16X
equipment and cause subsequent protection path failures.
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The ODPR application provides the following:
• a 1+1 protection scheme at the optical level over a separate optical fiber (a second wavelength protects a working wavelength)
• a unidirectional switching scheme that provides optical switching between traffic in the receive (off ramp) direction, but not in the transmit (on ramp) direction
• a nonrevertive switching mode: traffic does not automatically return to its working channel when the condition fault that caused the switch is corrected
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The OSM circuit pack has six optical interfaces:
• one input connection to the customer equipment on the client side (in the extendable panel on the right)
• one output connection to the customer equipment on the client side (in the extendable panel on the right)
• two input (working and protection) connections to the network interface equipment on the carrier side (in the extendable panel on the left)
• two output (working and protection) connections to the network interface equipment on the carrier side (in the extendable panel on the left)
If an optical fiber cut or any failure at an intermediate Repeater network element site occurs, all downstream Repeater network elements send a failed SONET/SDH signal that
reach the far-end off-ramp 10 Gbit/s optical interface. The off-ramp circuit pack detects the failure and sends information to the OSM circuit pack through GraceLAN messages by way of the Repeater network element backplane.
These GraceLAN transmissions contain protection status messages that are processed and decoded by the OSM circuit pack. The OSM circuit pack always evaluates the signal quality of both working and protection signals before performing switching operations. An optical protection switch occurs when a signal failure or a signal degrade alarm is raised. These conditions are monitored using the B2 byte of the OC-192/STM-64 line/MS overhead. The signal degrade threshold is user-provisionable. If any or both of these conditions are detected by the OSM circuit pack, tail-end switching occurs. These two conditions are monitored by the off-ramp 10 Gbit/s optical interfaces.
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Optical Dedicated Protection Ring (ODPR)
FUNDAMENTALS OF TELECOM FOR NON-EXPERTS
shows the concept of an ODPR application in a network that contains three terminal sites. Each terminal site includes an ODPR circuit pack group. The connection between each terminal site that includes an ODPR
circuit pack group is a point-to-point line connection. An ODPR application is therefore a collapsed ring that consists of multiple point-to-point line connections. The channel type (working or protection) that passes through a node depends on the node position in the network. For the network shown, the pass-through path at the node in City B is a protection channel, and the pass-through path at the nodes in City A and City C are working channels.
Pass-through connectivity is achieved using a regenerating device such as a Wavelength Translator or a Dense regenerator.
The optical switching in an ODPR application is performed on a wavelength by wavelength basis at a specific line rate, therefore providing protected carrier grade wavelength services. The ODPR application is beneficial mainly for the Internet backbone router market and allows protection for unprotected OC-192c/STM-64c router interfaces (see next slide). The ODPR application supports only SONET or SDH traffic at 10 Gbit/s.
Next slide also shows the connectivity between two unprotected client routers and the ODPR application terminals. The ODPR application is deployed at terminal sites, preferably co-located with router interfaces. Route the working line and the protection line separately to prevent double-failure scenarios. The line systems are Repeater network elements with Wavelength Translator or Dense regenerator circuit packs and line amplifiers that can carry the working and protection channels across a carrier network.
RELIANCE INFOCOMM For internal use only
Proprietary & Confidential
Optical Dedicated Protection Ring (ODPR)
FUNDAMENTALS OF TELECOM FOR NON-EXPERTS
The main advantage of the ODPR application is the ability to decouple the service layer from the transport layer by allowing transparent protection switching on the line system. Protection is therefore non-intrusive and does not affect traffic performance or wavelength availability at the end-user level.
Note: Optical switching is performed within 50 ms after fault detection. Failures are detected within 10 ms.
The ODPR application also addresses a problem where a ring carries unbalanced traffic. In such a scenario, providing protection bandwidth all the way around the ring is inefficient. If traffic between cities is distributed unevenly and shared protection is the available protection scheme, reserving ring protection wastes bandwidth.
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Proprietary & Confidential
G.681 Functional characteristics of interoffice and long-haul line systems using optical amplifiers including optical multiplexing
G.692 Optical Interfaces for multichannel systems with optical amplifiers (Oct 98): 50 and 100 GHz spacing centered at 193.1 THz (1553.5 nm)
G.872 Architecture for Optical Transport Networks, 1999
ANSI T1X1.5: http://www.t1.org/t1x1/_x1-grid.htm
Started April 1998 by CISCO, Ciena, ...Now over 128 members
Working groups on Architecture, Physical and Link Layer, OAM&P
Signaling protocols for rapid provisioning and restoration
FUNDAMENTALS OF TELECOM FOR NON-EXPERTS
Suggested Reading:
Dense Wave Division Multiplexing IEC www.iec.org
Optical Add-drop Multiplexers Meriton www.iec.org
Introduction to DWDM Nortel 55216a
RELIANCE INFOCOMM For internal use only
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