Description
Research Study on SDH-SONET Core Network and Photonic Switching:- The science of photonics[1] includes the generation, emission, transmission, modulation, signal processing, switching, amplification, and detection/sensing of light. The term photonics thereby emphasizes that photons are neither particles nor waves — they have both particle and wave nature.
Research Study on SDH-SONET Core Network and Photonic Switching
Table of Contents 1 1.1 1.2 2 2.1 3 3.1 ................................................. Introduction ................................................. Research Motivation ................................................. Project Structure ................................................. Evolution of SDH/SONET Core Network ................................................. Integrated Network Architecture ................................................. Designing the Transmission Layer ................................................. Using SDM
3.1.1 ................................................. Using TDM 3.1.2 ................................................. Using WDM 4 4.1 ................................................. Unidirectional Versus Bidirectional WDM Systems ..................................................Long-Haul Networks
4.1.1 ................................................. Long-Haul Undersea Networks 5 6 ................................................. Metro Networks ................................................. From Opaque Links to Agile All-Optical Networks
Conclusion References
ABSTRACT The transportation system model is modifying as confirmed by IP unity and the divergence of architectures and technological innovation. Utilizing the full power of light will encourage the development of new communication and ubiquitous network systems. To obtain this, however, not only must photonic technological innovation be enhanced, but they must also be synchronized with contrasting electrical technological innovation. With regards to photonic system style technological innovation, further improvements are necessary such as very large system style, quasi-dynamic system style, and multi-layer visual direction system style.
CHAPTER 1:
INTRODUCTION
In recent years, we are seeing dramatic changes in the telecommunications industry that have farreaching implications for our lifestyles. There are many drivers for these changes. First and foremost is the continuing, relentless need for more capacity in the network. This demand is fuelled by many factors. The tremendous growth of the Internet and the World Wide Web, both in terms of number of users as well as the amount of time and thus bandwidth taken by each user, is a major factor. At the same time, business these days depends on high-speed systems to perform their organizational tasks. These systems are used to interconnect several places within a company as well as between organizations for business-to-business dealings. Large organizations that used to rental 1.5 Mb/s collections to interconnect their inner websites are generally renting 155 Mb/s relationships today. The predominant client layers in backbone networks today are SONET/SDH, IP, and ATM. SONET/SDH is particularly adept at dealing with lower-speed time division multiplexed streams, whereas IP and ATM are adept at dealing with statistically multiplexed packet streams. In many cases, IP and ATM use SONET/SDH as the underlying transport mechanism. With the emergence of high-speed interfaces on IP and ATM equipment, we are also seeing IP and ATM mapped directly into the optical layer, without requiring separate SONET/SDH equipment. In the metro network, we are seeing a proliferation of several types of client layers, such as Gigabit Ethernet, ESCON, and Fibre Channel. Many of the latter networks are used to interconnect computers and their peripherals in so-called storage-area networks.
1.1
RESEACRH MOTIVATION
The motivation behind this work is to outline the advancement in optical device technologies for photonic networks, focusing on integrated optical device technologies for digital coherent optical transmission technologies. Most of the data traffics are due to IP traffic where existing transmission technique in the Fiber backbone is not giving Optimal Multiplexing. The synchronous multiplexing structure of SONET/SDH provides significant reduction in the cost of multiplexing and de-multiplexing.
1.2
PROJECT OUTLINE
This project is outlined as follow; Chapter two enlighten us about the evolution of SONET/SDH core architectures of network and architectural choices for next general transport network. Chapter three addresses the formation in designing the transmission layer using SDM, TDM and WDM. Chapter four introduces the protection of SDH/SONET through Unidirectional versus Bidirectional WDM systems. Chapter five narrowed to photonic bundles changing provides high-speed, information rate/format visibility, and configurability, which is some of the important features, required later on systems supporting different types of information. In this paper, we existing some of the crucial concerns engaged in developing and applying all-optical packet-switched systems. Chapter six of this paper highlights the metro networks from opaque links to agile all-optical access networks that are expected to enhance the emerging applications.
CHAPTER 2:EVOLUTION OF SDH/SONET CORE NETWORK Since the turn of the last millennium, telecommunication has moved from conventional speech transportation to information transportation, although scanned speech is still a large factor. Instead of a progress of current transportation requirements, a trend was necessary in order to allow additional data-related transportation. Next Creation SDH/SONET provides specific information of the enablers of effective information transportation over any synchronous system. These include virtual concatenation (VCAT), the function to offer more granularities, and the
link capacity adjustment scheme (LCAS), and an expansion of VCAT that provides more versatility [1]. Similarly, generic frame procedure (GFP), the technique that properly conveys
asynchronous or varying bit-rate information alerts over a synchronous or continuous bit-rate, is researched in details. However, to deal with the increasing number of information traffic, providers are quickly using up any extra information they might have on the speech side of the system. Offering a sleek migration from a voice-centric system to a data-centric system is crucial for founded providers with present facilities based on present technology such as Tl/El [1], synchronous electronic hierarchy synchronous visual system (SDH/SONET), and so on. Although they cannot manage to sustain two individual infrastructures, recommended network planners know they must increase system potential to provide new services. Any new equipment set ups must assist both speech and information programs. The current switch toward a data-centric system is creating a new model in how organizers view the growing systems. No longer are systems being designed around huge changing facilities that contain either huge local return changes or huge conjunction (transit) changes or both. Rather, the new networks are being designed to utilize the key benefits of bundle information transportation [2]. These new systems support more common service, call control, allocated system connections, and information managing.
Figure1. Evolution of SDH/SONET Core Network [2] From Figure 1, highlights customer expectancy from the operator: Quality of service & higher bandwidth at lower costs. On the other hand operator wants: reduce operational costs, realize revenue-earning service, use bandwidth of core network, low investment, immediate ROI and close the edge bottleneck. So, to solve all these problem of customers and operator is to make SDH/SONET flexible and data aware at the edge and still use the existing core [1]. Furthermore, choices have been made on integrated architectural next-generation transport network;
2.1
Integrated Network Architecture
The high-level view of a solution for a fully integrated voice connectivity and service delivery capability between the PSTN and IP networks is shown in Figure 2. A packet network solution will provide the basic protocol translation between the networks, transport and end-user services, and network- and service- level management, as well as interoperability with legacy operation support systems, all in a secure environment [3].
Figure2. Integrated High-Level Data View [3]
The gateway (GW) translates between the PSTN and the IP network with call control managed through the media GW control interface. The gatekeeper provides transport services and is extended through the A1 135 service management center (SMC) to support enhanced services via a TCP/IP interface [3]. The service control point (SCP) executes data-driven logic that has been generated via the service creation environment (SCE) and deployed via the service management platform (SMP). These NEs are managed primarily via Simple Network Management Protocol (SNMP) interfaces from an integrated management system that today includes the SMC and the network management centre (NMC) [3].
Figure3. Overview of Product Deployment for Next Generation Networks [3]
As a minimum initial new product offering for the media transport layer, a vendor providing a network solution will have to deploy at least three new functional elements; namely, a multiservice GW device, an edge switched router, and a core switched router. The required control layer support associated with each of these functions must also be provided. This scenario is represented in Figure 3. The multiservice GW is intended to be a device that will support several network services, such as VoIP, remote access node (RAN), and circuit
emulation (CES), simultaneously in the same physical product [4]. Initially, this device will be deployed in a standalone configuration; however, a long-term goal would require the integration of the functionality of this multiservice GW into existing edge and CPE devices to move these new packet services further out into the edges of the network. The multiservice GW is designed for use in the interexchange environment. It can terminate inband MF and SS7, trunks and provides all necessary tandem switch-like functions. The multiservices GW will also support primary rate integrated services digital network (ISDN) interfaces, and can serve as a remote network access server for routing ISP-bound connections around the circuit switch infrastructure [4]. Like the access GW, the multiservices GW extracts the payload from the TDM or SDH/SONET pipe and recodes it for delivery to the IP WAN. These gateways are designed as carrier grade, focusing on carrier scale by allowing the carrier to grow the network based on traffic requirements rather than in predetermined units as defined by existing data products [4]. The distributed architecture ensures the ability to grow termination and processing capacity independent of one another. These units are fully NEBS-compliant and designed to traditional PSTN NE standards.
CHAPTER 3:
DESIGNING THE TRANSMISSION LAYER
The historical trend in designing transmission layer has been to increase capacity in the network and at the same time cut down the cost per bit of bandwidth. Service providers most often look for at least a fourfold increase in capacity when planning their networks. As a rule of thumb, they expect to get this fourfold increase in capacity at about 2-2.5 times the cost of current equipment [5]. There are fundamentally three ways of increasing transmission capacity. 1. The first approach is lighting up additional fibers or to deploy additional fibers as needed. We can think of this as the space division multiplexing (SDM) approach: keep the bit rate the same but use more fibers. 2. The other traditional approach is by increasing the transmission bit rate on the fiber. This is the TDM approach. 3. The third approach is to add additional wavelengths over the same fiber. This is the WDM approach. The three methods are complementary to each other and are all necessary in the system for a wide range of factors. For example, using SDM, particularly when existing fibers are near to being worn-out, can be considered as a long-term way of developing up infrastructure; WDM and TDM can be considered as offering the capability to provide services quickly over current fiber infrastructure [5]. Electronic TDM is necessary for grooming traffic at lower speeds in the system, where optics is not cost-effective. WDM provides the capability to range the potential of the facilities in a different aspect.
3.1
Using SDM
Using extra fibers is a simple upgrade substitute. The practicality of this strategy is determined by a few factors. If the route length is short (typically a few tens of kilometers) and no regenerators or amplifiers are necessary along the path, then this is a good option. However, if amplifiers or regenerators are necessary, then this becomes a high-priced undertaking because each fiber needs individual set of amplifiers or regenerators [5]. However, it may be value shelling out the price to lighting up a new fiber if the new device to be implemented over the fiber provides considerably decreased transmission expenditures when in comparison to existing devices on the already-lit fiber. If no fibers are available on the path, then we need to look at the price associated with laying new fiber. This differs commonly. If there is place in current conduits, fiber can be drawn through relatively at low costs and easily. However, if new conduits must be set, the price can be very costly, even over short ranges if the path is in a dense urban place. If new conduits are to be set, then the link can be booming with a large-count fiber wire. Today's current fiber bundles come with hundreds of fibers [5]. The other element of this issue is the time it needs to lay new fiber. Developing new fiber links needs several months to years and needs right-of-way permits from cities where the new link is set. These permits may not be easy to acquire in dense places, due to the extensive effect caused by digging up the roads. In comparison, improving a current fiber link using either TDM or WDM can be done within time [5]. Although it is necessary in some conditions to lay new fibers, this is not a good procedure for fast reaction to service needs.
3.1.1 Using TDM Clearly, TDM is necessary for self-care traffic at the reduced bit rates where optics is not costeffective. Today's current long-haul hyperlinks operate mostly at rates of 2.5 GB/s, 10 GB/s, or 40 GB/s. urban interoffice hyperlinks work mostly at 2.5 GB/s, and accessibility hyperlinks work at even reduced connections [5]. At the greater bit rate, we have to cope with more serious indication problems over the fibre, particularly chromatic dispersion, polarization-mode dispersal (PMD), and fibre nonlinearities. With conventional single-mode fibre, from Determine 5.19, the chromatic dispersal restrict is about 60 km at 10 Gb/s and about 1000 km at 2.5 Gb/s, supposing indication around 1550 nm [5]. With realistic transmitters, the distance is even lesser. The 10 Gb/s restriction can be further decreased in the use of self-phase modulation. Beyond these distances, the indication must be digitally regenerated, or some way of chromatic dispersion compensation must be applied. Practical 10 GB/s systems being deployed today commonly use some form of chromatic dispersion compensation. This is usually cheaper than using regeneration, particularly when combined with WDM [5]. Electronic regeneration is required for longer distances. The PMD-induced distance restrict may be even reduced because of extra PMD due to connections, and other elements along the indication direction. PMD does not present an issue in recently designed hyperlinks where the PMD value can be kept as low as 0.1ps/?km [5]. Finally, nonlinear results such as self-phase modulation restrict the maximum possible indication power per channel, resulting in a need for closer firm space, and thus more amplifiers in the link, resulting in somewhat greater cost [5]. At 10 GB/s, indication abilities are usually restricted to less than 5 dBm per route. Today 10 Gb/s TDM systems are widely deployed in long-haul networks, mostly in conjunction with WDM, and 40 Gb/s TDM systems will soon become commercially available [6].
3.1.2 Using WDM It may be much better to sustain a minimal indication bit rate, say, 10 Gb/s and have several wavelengths over the fibre, than to go to a greater bit amount and have few wavelengths. Maintaining the low bit amount creates the program less susceptible to chromatic dispersal, polarization-mode dispersal, and some kinds of nonlinearities, such as self-phase modulation [5]. However, WDM techniques are usually not appropriate for implementation over dispersionshifted fibre because of the restrictions charged by four-wave preparing. WDM techniques can be developed to be translucent techniques. This allows different wavelengths to bring information at different bit rates and protocol formats. This can be significant benefits in some situations [5]. Lastly, WDM provides great flexibility in building networks. For example, if there is a network node at which most of the traffic is to be passed through and a small fraction is to be dropped and added, it may be more cost-effective to use a WDM optical add/drop factor than ending all the traffic and doing the add/drop in the electric domain.
Figure4. (a) Unidirectional and (b) bidirectional transmission system [5]
Today's state-of-the-art long-haul techniques bring about 100 programs at 10 GB/s each and have regenerator spacing's of 600 to 1500 km. The ultra-long-haul techniques increase space between regenerators to about 4000 km but have somewhat reduced capacities than the long-haul systems [6].
CHAPTER4: UNIDIRECTIONAL VERSUS BIDIRECTIONAL WDM SYSTEMS A unidirectional WDM system uses two fibres, one for each route of traffic. While a bidirectional program, however, needs only one fibre and generally uses 50 per cent of the wavelengths for sending information in one route and the other 50 per cent for sending information in the other on the same fibre [6]. Both kinds of techniques are being implemented and have their benefits and drawbacks. unidirectional system is capable of handling W full-duplex channels over two fibers. A bidirectional system handles W/2 full-duplex channels over one fibre [6]. The bidirectional system, therefore, has half the total capacity, but allows a user to build capacity more gradually than a unidirectional system. Thus it may have a slightly lower initial cost.
systems. Implementing 1:1 configurations with unidirectional WDM systems requires a minimum of two pairs of fibers routed separately, but only requires two fibers with bidirectional systems, as shown in Figure 5. Note, however, that as mentioned above, the bidirectional systems provide half as much capacity [5,6].
Figure5. Implementing 1:1 protected configurations using unidirectional and bidirectional transmission systems; (a) two unidirectional systems using four fibers, (b) two bidirectional systems using two fibers [5].
do not require an automatic protection switching (APS) protocol between the two ends of the link, since both ends detect a fiber cut simultaneously [6].
total number of wavelengths in the fiber, more wavelengths could be used in one direction compared to the other [6]. Although this may be easy to do for unamplified systems, it is more difficult to do in amplified systems because these systems typically use separate amplifiers for each direction. guard band between the two sets of wavelengths traveling in opposite directions to avoid crosstalk penalties. However, high-channel-count unidirectional systems may also require guard bands due to the hierarchical nature of the multiplexing and de-multiplexing in these systems [6].
4.1
Long-Haul Networks
The long-haul providers in Northern America have links comprising several number of a few thousand kilometers. In European countries the links are somewhat reduced but still several hundred kilometers in total [6]. The business economics for implementing WDM on these links is quite powerful, based on the tremendous benefits in regenerator costs permitted by the use of optical amplifiers, as well as the time to market to set up new services. Thus most long-haul providers have applied WDM considerably in their networks. The particular combination of WDM and TDM is based very much upon the provider's set up platform of fiber and the type of alternatives provided [5]. Among the significant established providers, AT&T and Sprint have mainly set up conventional single-mode fiber. Thus WDM is an eye-catching option for them, and they have definitely applied WDM methods on many of their paths [6]. A number of newer carriers have built long-haul networks worldwide. In the United States, these include Qwest and Level 3 Communications. When these carriers laid new fiber routes, many decided to install nonzero-dispersion fiber or the large effective area fiber (LEAF). Systems operating in the C-band and L-band are available [6]. The L-band needs an individual firm and is relatively more costly than the C-band to set up, due to the more costly of the L-band amplifiers, as opposed to C-band amplifiers (this is partly because L-band amplifiers need greater push abilities than their C-band counterparts) [6]. Although most long-haul providers have implemented C-band WDM systems, they have been slow to look at L-band systems. This is because it is usually cheaper to deploy another C-band system over a new pair of fibers rather than add the L-band to an existing C-band system. Some of the newer service providers that have built new fiber networks particularly have a large number of excess fibers and use this approach. Providers that have deployed dispersion-shifted fibers are likely to be early adopters of the L-band for WDM (and other fiber bands besides the C-band) due to the difficulties associated with four-wave mixing and other nonlinearities in the C-band on this type of fiber [7].
4.1.1 Long-Haul Undersea Networks The economics of long-haul undersea links is just like that of the long-haul terrestrial links, but with a few simple versions. First, there are several types of undersea links generally applied. One type spans over several thousands of kilometres across the ocean to interconnect North America with Europe or Asia, as proven in Figure 6. Another type tends to be relatively decrease take (a few hundred kilometres), internally connected nations either in a festoon type of design or by immediate links across short span of water [7]. The term festoon means a sequence revoked in a cycle between two points. In this perspective, it represents an undersea wire used to hook up two places that are not divided by a lake, usually nearby nations [7]. A trunk-and-branch setting is also popular, where an undersea trunk cable assists several nations. Each country is linked with the trunk cable by a branching wire, with passive optical elements used to perform.
Figure6. Different types of undersea networks, showing a couple of ultra-long-haul transAtlantic links, shorter-haul direct repeaters links, a trunk-and-branch configuration, and a festoon [7].
WDM is widely deployed in all these types of links. The long-haul undersea systems tend to operate at the leading edge of technology and have to overcome significant impairments to attain the distances involved. The links use the dispersion management technique having alternating spans with positive and negative dispersion fiber to realize a total chromatic dispersion of zero but at the same time have finite chromatic dispersion at all points along the link [6]. The shorter-distance undersea links also expand design goals but in a different way. Primarily the links remove any undersea amplifiers or repeater programs, due to their relatively high expense of set up and servicing. Consequently, these techniques use relatively high-power transmitters [6]. The trunk-and-branch setting is also evolving. The early branching units included passive splitters and combiners, but optical add/drop multiplexers are now being used to precisely drop and add particular wavelengths at different places. Undersea systems are designed to provide very high levels of reliability and availability due to the high cost of servicing or replacing failed parts of the network. Optical amplifiers with redundant pumping arrangements have confirmed to be extremely efficient devices, and their failure rates are much reduced than those of electronic regenerators [7]. Furthermore, optical add/drop multiplexers using passive WDM gadgets have been certified for use in undersea branching adjustments. Undersea networks are very costly to develop, and the potential on these networks is distributed among various customers. WDM allows traffic from different customers to be separated by holding them on different channels as useful function [6, 7]. One key difference between undersea links and terrestrial links is that, in most cases, undersea links are implemented from the beginning with new fibers rather than over current fiber plant. It is unusual to update a current long-haul amplified undersea link, as the price of laying a new link is not considerably higher than the price of improving a current link [6]. This provides more flexibility in design options.
CHAPTER5:
METRO NETWORKS
The metro network can be broken up into two parts. The first aspect is the metro access network and expands from the provider's main workplace to the provider's customer places, providing to gather visitors from them into the provider's system. The second part of this system is the community interoffice network. The accessibility system today typically includes a few kilometres to a few thousands of kilometres across, and traffic is mainly hubbed into the main workplace [4]. The interoffice system tends to be several to a few hundreds of miles between sites, and traffic tends to be more allocated. Because of the shorter spans involved, the case for WDM links is less compelling in metro networks. The other alternatives, namely, using multiple fibres or using higher-speed TDM, are quite viable in many situations. Nonetheless, there has been no widespread deployment of OC192 in the metro network [5]. One reason is that OC-192 interfaces have only recently appeared on metro systems. Another reason is that carriers in this part of the network are interested in delivering low-speed services at DS1 (1.5 Mb/s) or DS3 (45 Mb/s) rates and OC-192 equipment is only now becoming a cost-effective alternative for this application [8]. On the other hand, reasons other than pure capacity growth are driving the deployment of WDM in these networks. Metro carriers need to provide a variety of different types of connections to their customers. The service mix includes leased private-line services and statistical multiplexing types of services such as IP, Ethernet, Gigabit Ethernet, and Fibre Channel. In many cases, this service mix is supported by having a set of overlay networks, each dedicated to supporting a different service [4]. Another factor is that the traffic distribution changes much more rapidly in metro networks than in long-haul networks. This drives the need to be able to rearrange network capacity quickly and efficiently as needed [4]. Reconfigurable WDM networks allow capacity to be provided as needed in an efficient manner. A big driver for WDM deployment in metro networks has been the need for large enterprises to interconnect their data centers. These data centers are separated by several kilometers to a few tens of kilometers. All transactions are mirrored at both sites. This allows the enterprise to recover quickly from a disaster when one of the centres fails [8]. There may be other reasons to have separate data centers, such as lower real estate costs at one location than at the other. The bandwidth requirement for such applications is large. The large mainframes at these data centers
need to be interconnected by several hundred channels, each up to several gigabits per second. Typically, these data centers tend to be located in dense metropolitan areas where most of the installed fiber is already in use [8]. Moreover, these networks use a large variety of protocols and bit rates. These two factors make WDM an attractive option for these types of networks. These networks are sometimes called storage-area networks. This is the primary application for most of the WDM networks deployed in metro networks today. There has been widespread deployment of private WDM links for enterprise applications in the metro network. Several carriers in the United States have deployed WDM in their metro networks, but many are still considering the relative benefits of WDM versus other alternatives in this part of the network. As such, the deployment is not yet widely implemented as it is in the long-haul network [4].
Figure7. Using WDM to upgrade a four-node access ring; one additional ring is added at a different wavelength (a) The physical topology, and (b) the light path topology which showing the connectivity between the SONET ADMs [8].
CHAPTER6: FROM OPAQUE LINKS TO AGILE ALL-OPTICAL NETWORKS The optical layer itself is increasing, not just with regards to raw potential, but also with regards to performance. The visual system initially contains WDM links, with all the features at the end of the link conducted in the electric powered sector [2]. These techniques are sometimes known as solid techniques. Due to the expensive cost of optical-to-electrical (O/E) alterations, particularly at the higher bit rates, it is practical to reduce the number of these converters in the network. The first thing in this route was the growth of ultra-long-haul techniques, which offered longer arrival between regenerators. The second phase was to deal with as much of the traffic moving through a node in the optical sector as possible. An all-optical OADM or OXC features this operation [7]. Having optical pass-through instead of electrical processing can lead to an order of magnitude savings in the cost, and given that the cost of O/E conversions dominates the cost of the node itself. There are associated savings in power and floor space as well, given that the O/E devices consume most of the power and occupy most of the floor space in WDM equipment [2]. Even further cost savings can be realized by passing signals through in bands of wavelengths, instead of individual wavelengths. These networks are called all-optical or transparent networks [7]. The next step in the evolution of the optical layer was to add agility. An agile network provides the ability to set up and take down light-paths as needed and allows providers to provide and deploy services rapidly [7]. This can be realized with optical cross connects and reconfigurable optical add/drop multiplexers. Although an all-optical network provides significant advantages, it also has its limitations.Certain functions, such as wavelength conversion, regeneration, and traffic grooming at fine granularities (for example, at STS-1 or 51 Mb/s) will need to be done in the electrical domain [2]. We sometimes may not be able to completely handle all the pass-through traffic in the optical domain, due to inefficiencies in how traffic is groomed in the network. For these reasons, a practical node will end up using a combination of all-optical and electrical cross connects. The all-optical cross connects can be used to switch signals through in the optical domain as much as possible, and signals needing to be regenerated, converted from one wavelength to another, or groomed will be handed down to the electrical layer [2].
Another subtle element of the all-optical network is related to interoperability between systems from several distributors. It is challenging for devices from different distributors to interoperate at the wave length part. Interoperability between distributors needs to be done through regenerators/transponders [4]. What this means is that the all-optical system by itself is a singlevendor system. Transponders are required at the sides of this system to offer interoperability with other all-optical techniques. A genuine network will therefore contain all-optical destinations or subnets, connected with other such subnets through transponders at the limitations [4].
Conclusion In approaching the structural solutions for the new creation of service provider systems, their designs are motivated by the popularity of information over voice data and the emergence of new providers with greatly different business approach providing various kinds of services. The optical layer is becoming popular in both long-haul and metro-networks. The optical layer provides circuit-switched light-paths to the higher layers. Optical packet-switching technological innovation is still in research procedure. The next generation network is moving away from a SONET ring-based structure to a meshed optical-layer-based structure, with security features applied in optical layer or client layer. Within the optical layer, TDM, WDM, and SDM are all used to provide capacity. All types of system could possibly be applied, with regards to the individual conditions. The right combination of these techniques is complicated and is determined by a variety of factors such as the length of the link, the availability of extra fibers. The optical layer itself is moving from an opaque network, made up of WDM links with electric powered handling at the ends of the link, to an all-optical network, where traffic is passed through in the optical sector at advanced nodes. At the same time, the optical network is moving from a fixed network to an agile network, where light-paths can be set up and taken down as required.
Reference:
1 V. Poudyal, R. H. Cardwell, O. J. Wasem, J. E. Baran, and A. Rajan. Comparison of network alternatives for transporting high capacity tributaries for IP router interconnection. In Proceedings of National Fiber Optic Engineers Conference, 2000. 2 J. M. Simmons. Optical Network Design and Planning. Springer, New York, NY, 2008. 3 Y. Maeno et al. Cost comparison of an IP/OTN integrated node against a pure IP routing node. In proceedings of National Fiber Optic Engineers Conference, 2000. 4 G. N. S. Prasanna, E. A. Caridi, and R. M. Krishnaswamy. Metropolitan IP-optical networks: A systematic case study. In Proceedings of National Fiber Optic Engineers Conference, 2000. 5 H. K. Cook. The economics of metro DWDM deployment. In Proceedings ofNational Fiber Optic Engineers Conference, 2000. 6 A. Dwiwedi, M. Sharma, J. M. Grochocinski, and R. E. Wagner. Value of reach extension in long-distance networks. In Proceedings of National Fiber Optic Engineers Conference, 2000. 7 B. Doshi et al. Ultra-long-reach systems, optical transparency and networks. In OFC 2001 Technical Digest, 2001. Paper TuG4. 8 G. Ocakoglu, K. Struyve, and P. Falcao. The business case for DWDM metro systems in a panEuropean carrier environment. In Proceedings of National Fiber Optic Engineers Conference, 2000
doc_821799373.docx
Research Study on SDH-SONET Core Network and Photonic Switching:- The science of photonics[1] includes the generation, emission, transmission, modulation, signal processing, switching, amplification, and detection/sensing of light. The term photonics thereby emphasizes that photons are neither particles nor waves — they have both particle and wave nature.
Research Study on SDH-SONET Core Network and Photonic Switching
Table of Contents 1 1.1 1.2 2 2.1 3 3.1 ................................................. Introduction ................................................. Research Motivation ................................................. Project Structure ................................................. Evolution of SDH/SONET Core Network ................................................. Integrated Network Architecture ................................................. Designing the Transmission Layer ................................................. Using SDM
3.1.1 ................................................. Using TDM 3.1.2 ................................................. Using WDM 4 4.1 ................................................. Unidirectional Versus Bidirectional WDM Systems ..................................................Long-Haul Networks
4.1.1 ................................................. Long-Haul Undersea Networks 5 6 ................................................. Metro Networks ................................................. From Opaque Links to Agile All-Optical Networks
Conclusion References
ABSTRACT The transportation system model is modifying as confirmed by IP unity and the divergence of architectures and technological innovation. Utilizing the full power of light will encourage the development of new communication and ubiquitous network systems. To obtain this, however, not only must photonic technological innovation be enhanced, but they must also be synchronized with contrasting electrical technological innovation. With regards to photonic system style technological innovation, further improvements are necessary such as very large system style, quasi-dynamic system style, and multi-layer visual direction system style.
CHAPTER 1:
INTRODUCTION
In recent years, we are seeing dramatic changes in the telecommunications industry that have farreaching implications for our lifestyles. There are many drivers for these changes. First and foremost is the continuing, relentless need for more capacity in the network. This demand is fuelled by many factors. The tremendous growth of the Internet and the World Wide Web, both in terms of number of users as well as the amount of time and thus bandwidth taken by each user, is a major factor. At the same time, business these days depends on high-speed systems to perform their organizational tasks. These systems are used to interconnect several places within a company as well as between organizations for business-to-business dealings. Large organizations that used to rental 1.5 Mb/s collections to interconnect their inner websites are generally renting 155 Mb/s relationships today. The predominant client layers in backbone networks today are SONET/SDH, IP, and ATM. SONET/SDH is particularly adept at dealing with lower-speed time division multiplexed streams, whereas IP and ATM are adept at dealing with statistically multiplexed packet streams. In many cases, IP and ATM use SONET/SDH as the underlying transport mechanism. With the emergence of high-speed interfaces on IP and ATM equipment, we are also seeing IP and ATM mapped directly into the optical layer, without requiring separate SONET/SDH equipment. In the metro network, we are seeing a proliferation of several types of client layers, such as Gigabit Ethernet, ESCON, and Fibre Channel. Many of the latter networks are used to interconnect computers and their peripherals in so-called storage-area networks.
1.1
RESEACRH MOTIVATION
The motivation behind this work is to outline the advancement in optical device technologies for photonic networks, focusing on integrated optical device technologies for digital coherent optical transmission technologies. Most of the data traffics are due to IP traffic where existing transmission technique in the Fiber backbone is not giving Optimal Multiplexing. The synchronous multiplexing structure of SONET/SDH provides significant reduction in the cost of multiplexing and de-multiplexing.
1.2
PROJECT OUTLINE
This project is outlined as follow; Chapter two enlighten us about the evolution of SONET/SDH core architectures of network and architectural choices for next general transport network. Chapter three addresses the formation in designing the transmission layer using SDM, TDM and WDM. Chapter four introduces the protection of SDH/SONET through Unidirectional versus Bidirectional WDM systems. Chapter five narrowed to photonic bundles changing provides high-speed, information rate/format visibility, and configurability, which is some of the important features, required later on systems supporting different types of information. In this paper, we existing some of the crucial concerns engaged in developing and applying all-optical packet-switched systems. Chapter six of this paper highlights the metro networks from opaque links to agile all-optical access networks that are expected to enhance the emerging applications.
CHAPTER 2:EVOLUTION OF SDH/SONET CORE NETWORK Since the turn of the last millennium, telecommunication has moved from conventional speech transportation to information transportation, although scanned speech is still a large factor. Instead of a progress of current transportation requirements, a trend was necessary in order to allow additional data-related transportation. Next Creation SDH/SONET provides specific information of the enablers of effective information transportation over any synchronous system. These include virtual concatenation (VCAT), the function to offer more granularities, and the
link capacity adjustment scheme (LCAS), and an expansion of VCAT that provides more versatility [1]. Similarly, generic frame procedure (GFP), the technique that properly conveys
asynchronous or varying bit-rate information alerts over a synchronous or continuous bit-rate, is researched in details. However, to deal with the increasing number of information traffic, providers are quickly using up any extra information they might have on the speech side of the system. Offering a sleek migration from a voice-centric system to a data-centric system is crucial for founded providers with present facilities based on present technology such as Tl/El [1], synchronous electronic hierarchy synchronous visual system (SDH/SONET), and so on. Although they cannot manage to sustain two individual infrastructures, recommended network planners know they must increase system potential to provide new services. Any new equipment set ups must assist both speech and information programs. The current switch toward a data-centric system is creating a new model in how organizers view the growing systems. No longer are systems being designed around huge changing facilities that contain either huge local return changes or huge conjunction (transit) changes or both. Rather, the new networks are being designed to utilize the key benefits of bundle information transportation [2]. These new systems support more common service, call control, allocated system connections, and information managing.
Figure1. Evolution of SDH/SONET Core Network [2] From Figure 1, highlights customer expectancy from the operator: Quality of service & higher bandwidth at lower costs. On the other hand operator wants: reduce operational costs, realize revenue-earning service, use bandwidth of core network, low investment, immediate ROI and close the edge bottleneck. So, to solve all these problem of customers and operator is to make SDH/SONET flexible and data aware at the edge and still use the existing core [1]. Furthermore, choices have been made on integrated architectural next-generation transport network;
2.1
Integrated Network Architecture
The high-level view of a solution for a fully integrated voice connectivity and service delivery capability between the PSTN and IP networks is shown in Figure 2. A packet network solution will provide the basic protocol translation between the networks, transport and end-user services, and network- and service- level management, as well as interoperability with legacy operation support systems, all in a secure environment [3].
Figure2. Integrated High-Level Data View [3]
The gateway (GW) translates between the PSTN and the IP network with call control managed through the media GW control interface. The gatekeeper provides transport services and is extended through the A1 135 service management center (SMC) to support enhanced services via a TCP/IP interface [3]. The service control point (SCP) executes data-driven logic that has been generated via the service creation environment (SCE) and deployed via the service management platform (SMP). These NEs are managed primarily via Simple Network Management Protocol (SNMP) interfaces from an integrated management system that today includes the SMC and the network management centre (NMC) [3].
Figure3. Overview of Product Deployment for Next Generation Networks [3]
As a minimum initial new product offering for the media transport layer, a vendor providing a network solution will have to deploy at least three new functional elements; namely, a multiservice GW device, an edge switched router, and a core switched router. The required control layer support associated with each of these functions must also be provided. This scenario is represented in Figure 3. The multiservice GW is intended to be a device that will support several network services, such as VoIP, remote access node (RAN), and circuit
emulation (CES), simultaneously in the same physical product [4]. Initially, this device will be deployed in a standalone configuration; however, a long-term goal would require the integration of the functionality of this multiservice GW into existing edge and CPE devices to move these new packet services further out into the edges of the network. The multiservice GW is designed for use in the interexchange environment. It can terminate inband MF and SS7, trunks and provides all necessary tandem switch-like functions. The multiservices GW will also support primary rate integrated services digital network (ISDN) interfaces, and can serve as a remote network access server for routing ISP-bound connections around the circuit switch infrastructure [4]. Like the access GW, the multiservices GW extracts the payload from the TDM or SDH/SONET pipe and recodes it for delivery to the IP WAN. These gateways are designed as carrier grade, focusing on carrier scale by allowing the carrier to grow the network based on traffic requirements rather than in predetermined units as defined by existing data products [4]. The distributed architecture ensures the ability to grow termination and processing capacity independent of one another. These units are fully NEBS-compliant and designed to traditional PSTN NE standards.
CHAPTER 3:
DESIGNING THE TRANSMISSION LAYER
The historical trend in designing transmission layer has been to increase capacity in the network and at the same time cut down the cost per bit of bandwidth. Service providers most often look for at least a fourfold increase in capacity when planning their networks. As a rule of thumb, they expect to get this fourfold increase in capacity at about 2-2.5 times the cost of current equipment [5]. There are fundamentally three ways of increasing transmission capacity. 1. The first approach is lighting up additional fibers or to deploy additional fibers as needed. We can think of this as the space division multiplexing (SDM) approach: keep the bit rate the same but use more fibers. 2. The other traditional approach is by increasing the transmission bit rate on the fiber. This is the TDM approach. 3. The third approach is to add additional wavelengths over the same fiber. This is the WDM approach. The three methods are complementary to each other and are all necessary in the system for a wide range of factors. For example, using SDM, particularly when existing fibers are near to being worn-out, can be considered as a long-term way of developing up infrastructure; WDM and TDM can be considered as offering the capability to provide services quickly over current fiber infrastructure [5]. Electronic TDM is necessary for grooming traffic at lower speeds in the system, where optics is not cost-effective. WDM provides the capability to range the potential of the facilities in a different aspect.
3.1
Using SDM
Using extra fibers is a simple upgrade substitute. The practicality of this strategy is determined by a few factors. If the route length is short (typically a few tens of kilometers) and no regenerators or amplifiers are necessary along the path, then this is a good option. However, if amplifiers or regenerators are necessary, then this becomes a high-priced undertaking because each fiber needs individual set of amplifiers or regenerators [5]. However, it may be value shelling out the price to lighting up a new fiber if the new device to be implemented over the fiber provides considerably decreased transmission expenditures when in comparison to existing devices on the already-lit fiber. If no fibers are available on the path, then we need to look at the price associated with laying new fiber. This differs commonly. If there is place in current conduits, fiber can be drawn through relatively at low costs and easily. However, if new conduits must be set, the price can be very costly, even over short ranges if the path is in a dense urban place. If new conduits are to be set, then the link can be booming with a large-count fiber wire. Today's current fiber bundles come with hundreds of fibers [5]. The other element of this issue is the time it needs to lay new fiber. Developing new fiber links needs several months to years and needs right-of-way permits from cities where the new link is set. These permits may not be easy to acquire in dense places, due to the extensive effect caused by digging up the roads. In comparison, improving a current fiber link using either TDM or WDM can be done within time [5]. Although it is necessary in some conditions to lay new fibers, this is not a good procedure for fast reaction to service needs.
3.1.1 Using TDM Clearly, TDM is necessary for self-care traffic at the reduced bit rates where optics is not costeffective. Today's current long-haul hyperlinks operate mostly at rates of 2.5 GB/s, 10 GB/s, or 40 GB/s. urban interoffice hyperlinks work mostly at 2.5 GB/s, and accessibility hyperlinks work at even reduced connections [5]. At the greater bit rate, we have to cope with more serious indication problems over the fibre, particularly chromatic dispersion, polarization-mode dispersal (PMD), and fibre nonlinearities. With conventional single-mode fibre, from Determine 5.19, the chromatic dispersal restrict is about 60 km at 10 Gb/s and about 1000 km at 2.5 Gb/s, supposing indication around 1550 nm [5]. With realistic transmitters, the distance is even lesser. The 10 Gb/s restriction can be further decreased in the use of self-phase modulation. Beyond these distances, the indication must be digitally regenerated, or some way of chromatic dispersion compensation must be applied. Practical 10 GB/s systems being deployed today commonly use some form of chromatic dispersion compensation. This is usually cheaper than using regeneration, particularly when combined with WDM [5]. Electronic regeneration is required for longer distances. The PMD-induced distance restrict may be even reduced because of extra PMD due to connections, and other elements along the indication direction. PMD does not present an issue in recently designed hyperlinks where the PMD value can be kept as low as 0.1ps/?km [5]. Finally, nonlinear results such as self-phase modulation restrict the maximum possible indication power per channel, resulting in a need for closer firm space, and thus more amplifiers in the link, resulting in somewhat greater cost [5]. At 10 GB/s, indication abilities are usually restricted to less than 5 dBm per route. Today 10 Gb/s TDM systems are widely deployed in long-haul networks, mostly in conjunction with WDM, and 40 Gb/s TDM systems will soon become commercially available [6].
3.1.2 Using WDM It may be much better to sustain a minimal indication bit rate, say, 10 Gb/s and have several wavelengths over the fibre, than to go to a greater bit amount and have few wavelengths. Maintaining the low bit amount creates the program less susceptible to chromatic dispersal, polarization-mode dispersal, and some kinds of nonlinearities, such as self-phase modulation [5]. However, WDM techniques are usually not appropriate for implementation over dispersionshifted fibre because of the restrictions charged by four-wave preparing. WDM techniques can be developed to be translucent techniques. This allows different wavelengths to bring information at different bit rates and protocol formats. This can be significant benefits in some situations [5]. Lastly, WDM provides great flexibility in building networks. For example, if there is a network node at which most of the traffic is to be passed through and a small fraction is to be dropped and added, it may be more cost-effective to use a WDM optical add/drop factor than ending all the traffic and doing the add/drop in the electric domain.
Figure4. (a) Unidirectional and (b) bidirectional transmission system [5]
Today's state-of-the-art long-haul techniques bring about 100 programs at 10 GB/s each and have regenerator spacing's of 600 to 1500 km. The ultra-long-haul techniques increase space between regenerators to about 4000 km but have somewhat reduced capacities than the long-haul systems [6].
CHAPTER4: UNIDIRECTIONAL VERSUS BIDIRECTIONAL WDM SYSTEMS A unidirectional WDM system uses two fibres, one for each route of traffic. While a bidirectional program, however, needs only one fibre and generally uses 50 per cent of the wavelengths for sending information in one route and the other 50 per cent for sending information in the other on the same fibre [6]. Both kinds of techniques are being implemented and have their benefits and drawbacks. unidirectional system is capable of handling W full-duplex channels over two fibers. A bidirectional system handles W/2 full-duplex channels over one fibre [6]. The bidirectional system, therefore, has half the total capacity, but allows a user to build capacity more gradually than a unidirectional system. Thus it may have a slightly lower initial cost.
systems. Implementing 1:1 configurations with unidirectional WDM systems requires a minimum of two pairs of fibers routed separately, but only requires two fibers with bidirectional systems, as shown in Figure 5. Note, however, that as mentioned above, the bidirectional systems provide half as much capacity [5,6].
Figure5. Implementing 1:1 protected configurations using unidirectional and bidirectional transmission systems; (a) two unidirectional systems using four fibers, (b) two bidirectional systems using two fibers [5].
do not require an automatic protection switching (APS) protocol between the two ends of the link, since both ends detect a fiber cut simultaneously [6].
total number of wavelengths in the fiber, more wavelengths could be used in one direction compared to the other [6]. Although this may be easy to do for unamplified systems, it is more difficult to do in amplified systems because these systems typically use separate amplifiers for each direction. guard band between the two sets of wavelengths traveling in opposite directions to avoid crosstalk penalties. However, high-channel-count unidirectional systems may also require guard bands due to the hierarchical nature of the multiplexing and de-multiplexing in these systems [6].
4.1
Long-Haul Networks
The long-haul providers in Northern America have links comprising several number of a few thousand kilometers. In European countries the links are somewhat reduced but still several hundred kilometers in total [6]. The business economics for implementing WDM on these links is quite powerful, based on the tremendous benefits in regenerator costs permitted by the use of optical amplifiers, as well as the time to market to set up new services. Thus most long-haul providers have applied WDM considerably in their networks. The particular combination of WDM and TDM is based very much upon the provider's set up platform of fiber and the type of alternatives provided [5]. Among the significant established providers, AT&T and Sprint have mainly set up conventional single-mode fiber. Thus WDM is an eye-catching option for them, and they have definitely applied WDM methods on many of their paths [6]. A number of newer carriers have built long-haul networks worldwide. In the United States, these include Qwest and Level 3 Communications. When these carriers laid new fiber routes, many decided to install nonzero-dispersion fiber or the large effective area fiber (LEAF). Systems operating in the C-band and L-band are available [6]. The L-band needs an individual firm and is relatively more costly than the C-band to set up, due to the more costly of the L-band amplifiers, as opposed to C-band amplifiers (this is partly because L-band amplifiers need greater push abilities than their C-band counterparts) [6]. Although most long-haul providers have implemented C-band WDM systems, they have been slow to look at L-band systems. This is because it is usually cheaper to deploy another C-band system over a new pair of fibers rather than add the L-band to an existing C-band system. Some of the newer service providers that have built new fiber networks particularly have a large number of excess fibers and use this approach. Providers that have deployed dispersion-shifted fibers are likely to be early adopters of the L-band for WDM (and other fiber bands besides the C-band) due to the difficulties associated with four-wave mixing and other nonlinearities in the C-band on this type of fiber [7].
4.1.1 Long-Haul Undersea Networks The economics of long-haul undersea links is just like that of the long-haul terrestrial links, but with a few simple versions. First, there are several types of undersea links generally applied. One type spans over several thousands of kilometres across the ocean to interconnect North America with Europe or Asia, as proven in Figure 6. Another type tends to be relatively decrease take (a few hundred kilometres), internally connected nations either in a festoon type of design or by immediate links across short span of water [7]. The term festoon means a sequence revoked in a cycle between two points. In this perspective, it represents an undersea wire used to hook up two places that are not divided by a lake, usually nearby nations [7]. A trunk-and-branch setting is also popular, where an undersea trunk cable assists several nations. Each country is linked with the trunk cable by a branching wire, with passive optical elements used to perform.
Figure6. Different types of undersea networks, showing a couple of ultra-long-haul transAtlantic links, shorter-haul direct repeaters links, a trunk-and-branch configuration, and a festoon [7].
WDM is widely deployed in all these types of links. The long-haul undersea systems tend to operate at the leading edge of technology and have to overcome significant impairments to attain the distances involved. The links use the dispersion management technique having alternating spans with positive and negative dispersion fiber to realize a total chromatic dispersion of zero but at the same time have finite chromatic dispersion at all points along the link [6]. The shorter-distance undersea links also expand design goals but in a different way. Primarily the links remove any undersea amplifiers or repeater programs, due to their relatively high expense of set up and servicing. Consequently, these techniques use relatively high-power transmitters [6]. The trunk-and-branch setting is also evolving. The early branching units included passive splitters and combiners, but optical add/drop multiplexers are now being used to precisely drop and add particular wavelengths at different places. Undersea systems are designed to provide very high levels of reliability and availability due to the high cost of servicing or replacing failed parts of the network. Optical amplifiers with redundant pumping arrangements have confirmed to be extremely efficient devices, and their failure rates are much reduced than those of electronic regenerators [7]. Furthermore, optical add/drop multiplexers using passive WDM gadgets have been certified for use in undersea branching adjustments. Undersea networks are very costly to develop, and the potential on these networks is distributed among various customers. WDM allows traffic from different customers to be separated by holding them on different channels as useful function [6, 7]. One key difference between undersea links and terrestrial links is that, in most cases, undersea links are implemented from the beginning with new fibers rather than over current fiber plant. It is unusual to update a current long-haul amplified undersea link, as the price of laying a new link is not considerably higher than the price of improving a current link [6]. This provides more flexibility in design options.
CHAPTER5:
METRO NETWORKS
The metro network can be broken up into two parts. The first aspect is the metro access network and expands from the provider's main workplace to the provider's customer places, providing to gather visitors from them into the provider's system. The second part of this system is the community interoffice network. The accessibility system today typically includes a few kilometres to a few thousands of kilometres across, and traffic is mainly hubbed into the main workplace [4]. The interoffice system tends to be several to a few hundreds of miles between sites, and traffic tends to be more allocated. Because of the shorter spans involved, the case for WDM links is less compelling in metro networks. The other alternatives, namely, using multiple fibres or using higher-speed TDM, are quite viable in many situations. Nonetheless, there has been no widespread deployment of OC192 in the metro network [5]. One reason is that OC-192 interfaces have only recently appeared on metro systems. Another reason is that carriers in this part of the network are interested in delivering low-speed services at DS1 (1.5 Mb/s) or DS3 (45 Mb/s) rates and OC-192 equipment is only now becoming a cost-effective alternative for this application [8]. On the other hand, reasons other than pure capacity growth are driving the deployment of WDM in these networks. Metro carriers need to provide a variety of different types of connections to their customers. The service mix includes leased private-line services and statistical multiplexing types of services such as IP, Ethernet, Gigabit Ethernet, and Fibre Channel. In many cases, this service mix is supported by having a set of overlay networks, each dedicated to supporting a different service [4]. Another factor is that the traffic distribution changes much more rapidly in metro networks than in long-haul networks. This drives the need to be able to rearrange network capacity quickly and efficiently as needed [4]. Reconfigurable WDM networks allow capacity to be provided as needed in an efficient manner. A big driver for WDM deployment in metro networks has been the need for large enterprises to interconnect their data centers. These data centers are separated by several kilometers to a few tens of kilometers. All transactions are mirrored at both sites. This allows the enterprise to recover quickly from a disaster when one of the centres fails [8]. There may be other reasons to have separate data centers, such as lower real estate costs at one location than at the other. The bandwidth requirement for such applications is large. The large mainframes at these data centers
need to be interconnected by several hundred channels, each up to several gigabits per second. Typically, these data centers tend to be located in dense metropolitan areas where most of the installed fiber is already in use [8]. Moreover, these networks use a large variety of protocols and bit rates. These two factors make WDM an attractive option for these types of networks. These networks are sometimes called storage-area networks. This is the primary application for most of the WDM networks deployed in metro networks today. There has been widespread deployment of private WDM links for enterprise applications in the metro network. Several carriers in the United States have deployed WDM in their metro networks, but many are still considering the relative benefits of WDM versus other alternatives in this part of the network. As such, the deployment is not yet widely implemented as it is in the long-haul network [4].
Figure7. Using WDM to upgrade a four-node access ring; one additional ring is added at a different wavelength (a) The physical topology, and (b) the light path topology which showing the connectivity between the SONET ADMs [8].
CHAPTER6: FROM OPAQUE LINKS TO AGILE ALL-OPTICAL NETWORKS The optical layer itself is increasing, not just with regards to raw potential, but also with regards to performance. The visual system initially contains WDM links, with all the features at the end of the link conducted in the electric powered sector [2]. These techniques are sometimes known as solid techniques. Due to the expensive cost of optical-to-electrical (O/E) alterations, particularly at the higher bit rates, it is practical to reduce the number of these converters in the network. The first thing in this route was the growth of ultra-long-haul techniques, which offered longer arrival between regenerators. The second phase was to deal with as much of the traffic moving through a node in the optical sector as possible. An all-optical OADM or OXC features this operation [7]. Having optical pass-through instead of electrical processing can lead to an order of magnitude savings in the cost, and given that the cost of O/E conversions dominates the cost of the node itself. There are associated savings in power and floor space as well, given that the O/E devices consume most of the power and occupy most of the floor space in WDM equipment [2]. Even further cost savings can be realized by passing signals through in bands of wavelengths, instead of individual wavelengths. These networks are called all-optical or transparent networks [7]. The next step in the evolution of the optical layer was to add agility. An agile network provides the ability to set up and take down light-paths as needed and allows providers to provide and deploy services rapidly [7]. This can be realized with optical cross connects and reconfigurable optical add/drop multiplexers. Although an all-optical network provides significant advantages, it also has its limitations.Certain functions, such as wavelength conversion, regeneration, and traffic grooming at fine granularities (for example, at STS-1 or 51 Mb/s) will need to be done in the electrical domain [2]. We sometimes may not be able to completely handle all the pass-through traffic in the optical domain, due to inefficiencies in how traffic is groomed in the network. For these reasons, a practical node will end up using a combination of all-optical and electrical cross connects. The all-optical cross connects can be used to switch signals through in the optical domain as much as possible, and signals needing to be regenerated, converted from one wavelength to another, or groomed will be handed down to the electrical layer [2].
Another subtle element of the all-optical network is related to interoperability between systems from several distributors. It is challenging for devices from different distributors to interoperate at the wave length part. Interoperability between distributors needs to be done through regenerators/transponders [4]. What this means is that the all-optical system by itself is a singlevendor system. Transponders are required at the sides of this system to offer interoperability with other all-optical techniques. A genuine network will therefore contain all-optical destinations or subnets, connected with other such subnets through transponders at the limitations [4].
Conclusion In approaching the structural solutions for the new creation of service provider systems, their designs are motivated by the popularity of information over voice data and the emergence of new providers with greatly different business approach providing various kinds of services. The optical layer is becoming popular in both long-haul and metro-networks. The optical layer provides circuit-switched light-paths to the higher layers. Optical packet-switching technological innovation is still in research procedure. The next generation network is moving away from a SONET ring-based structure to a meshed optical-layer-based structure, with security features applied in optical layer or client layer. Within the optical layer, TDM, WDM, and SDM are all used to provide capacity. All types of system could possibly be applied, with regards to the individual conditions. The right combination of these techniques is complicated and is determined by a variety of factors such as the length of the link, the availability of extra fibers. The optical layer itself is moving from an opaque network, made up of WDM links with electric powered handling at the ends of the link, to an all-optical network, where traffic is passed through in the optical sector at advanced nodes. At the same time, the optical network is moving from a fixed network to an agile network, where light-paths can be set up and taken down as required.
Reference:
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