Summary on Results from EURESCOM P615 Project Tivadar Jakab Technical University of Budapest Dept. of Telecommunications E-mail:
[email protected] Phone: +36 1 463 1010 Fax: +36 1 463 3263 Abstract
1 Introduction 1.1 EURESCOM – A brief Introduction 1.2 Optical Networks Related EURESCOM Projects
2 Evolution Towards an Optical Network Layer The EURESCOM Project P615 is entitled “Evolution towards an optical network layer”. In today’s national transport networks, optical communication systems are only used for point-to-point connections. The networking is done in the electrical (SDH) domain, see Figure 1.a). A huge amount of fiber has been installed as it is obvious that any network operator is highly interested in exploiting this potential. WDM has been recognized as the key technology to upgrade existing fiber plants to real optical networks. This technology evolution offers additional functionalities due to the application of optical nodes, see [i]. The work of P615 is closely linked with standardization activities by ETSI and ITU-T [ii]-[iv] and can be considered as a logical continuation of the work recently finished in the EURESCOM Project P413 entitled “Optical Networking” [v]. The entire project has three phases, or so called Tasks. In Task 1 a pre-study on possible architectures is made as start-up of the project. Activities elsewhere on the world and benefits expected from the optical network layer are reviewed. Descriptions are given of the functionalities that are introduced in the optical layer, see [i]. Basic network architectures are identified and the OAM requirement of the three sublayers are refined. Furthermore, a study is made on possible physical implementations and evaluation parameters are identified for the evaluation of optical networks. Below, the Tasks 2 and 3 are described in further details. The main purpose of Task 2 is to describe network scenarios with the aim of comparing different generic optical network architectures. Task 2 evaluates then different generic network architectures in details according to the specified criteria. Further, Task 2 identifies relative advantages and drawback of generic architectures in comparison with each other. Finally, Task 3 finishes the project. Task 3 will provide guidelines for the introduction of the an optical network layer, as well as it will describe growth scenarios of the different evaluated network architectures.
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opto-electronic conversion
optical node
electrical networking element (ADM, cross-connect) a)
b)
Figure 1: a) today’s transport networks b) future transport networks Task 1: Pre-study and definition of optical network architectures Main scope of the second phase Task 2: Comparison of reference configurations Main scope of the second phase In the first phase of the EURESCOM P615 project the description of different optical architectures and their detailed functional models are elaborated. The architectures to be studied in detail are specified as well. The main objective in the second phase of the work is the analysis, evaluation and comparison of the specified optical architectures (and at least one standard SDH architecture as a reference). The study of the architectures are performed on two different levels. A general evaluation based on the description and modeling of the architecture is elaborated first, then a more detailed analysis based on relevant networking applications of the architecture are performed.
Methods applied to analyze and evaluate different architecture The aspects of the analysis, evaluation and comparison of different architectures cover a wide range: • Economical aspects: installation, operational, extension and upgrade costs, • Operational aspects: availability on the market, maturity, interworking, complexity, manageability, complexity of OAM functions (e.g. fault localization), • Physical and technical aspects: scalability (extension of network size in terms of number of nodes and/or total amount of carried traffic), flexibility, reliability, survivability, availability, transport capacity, upgradability (changing for higher bitrates). To study these aspects a list of relevant parameters has been developed. Weights and desired (optimal) values of the different parameters have also been specified to support a quantitative evaluation. The specification of such parameters is done independently from and prior to the comparison work. During
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the general analysis, the architectures are evaluated according to the parameter list and a characteristic figure of merit is calculated for each architecture. Based on this first evaluation, realistic and relevant network examples (core, regional or metropolitan area networks) are assigned to each architecture. It is expected that the network examples are chosen in order to highlight the limitations and potential of the architectures. The network examples are specified in terms of: • number of nodes and links • link length • transmission demands and traffic pattern (amount, bandwidth, granularity, growth, service related specifications) • protection and/or restoration policy applied in the network • general network structure (clustered or not, flat, hierarchically layered, etc.) In this second analysis and evaluation phase, the specified network examples are dimensioned applying different network architectures to realize the network. The network dimensioning is performed with help of software tools. Based on the detailed description of the dimensioned network, cost and reliability analyses are elaborated, and network statistics are obtained as background information to support the evaluation of not directly measurable parameters (e.g. complexity). Based on the elaborated analysis results (characteristic parameters), the techno-economical comparison of different architectures is obtained.
Results achieved Based on the detailed analysis results and the comparison, the benefits and drawbacks of different optical architectures and their applications in some realistic cases can be identified in the second phase of the work. The results of the analysis and comparison work can point out the most promising optical architectures and their relevant networking applications. These detailed results and the comparison serve as an input for the third phase of the project work devoted to the elaboration of guidelines for the introduction of optical networking functions.
Task 3: Guidelines for the Introduction of Optical Networking Functions General The objective of the third task of the EURESCOM Project P615 is to evaluate and to define guidelines for the practical introduction of an optical network layer in the national wide transport networks, given today’s fiber plant, see Figure 1.b). This EURESCOM P615 Task 3 will provide the network operators with guidelines for the introduction of optical networking functions, i.e. the purpose is to clarify the big arrow between a) and b) in Figure 1. These guidelines will point out, first of all, the possibilities made available by today’s fiber optical technologies, but the guidelines will also describe aspects related to the difficulties of various solutions. The purpose of EURESCOM P615 is also to establish sets of decision criteria focusing on questions like how, when and in which time the introduction of optical networking functions can be implemented in the transport network. Starting from the results of the preceding task in the project (see Section 2), different scenarios for the introduction of the evaluated network architectures will be assessed in detail. Further interest is devoted to possible growth scenarios, i.e. the practical scalability will be investigated. Important aspects when introducing new technologies are also cost and OAM issues. The final output of Task 3, the deliverable to be distributed to the EURESCOM shareholders, is in principle the most relevant part of the EURESCOM Project P615. This deliverable will be accessible to the general public, also outside of EURESCOM.
Identification and Discussion of Introduction Scenarios for Optical Network Architectures The work within Task 3 will be the outcome of several actions. In a first action, introduction/migration scenarios for optical architectures are identified. The starting point for this identification are the results coming out of Task 2, where a finite set of architectures has been evaluated for further, detailed study. For these selected architectures, possible introduction and migration scenarios of the evaluated network architectures will now be provided. One very important aspect of these evaluated scenarios is their time frame and their impact on existing networks. That means that the interworking possibilities and problems between the new optical network layer and the existing (SDH) networks have to be
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considered in detail. The various scenarios have also to be compared and advantages and drawbacks of the different introduction scenarios have to be itemized. As a continuation of the second task in the EURESCOM Project P615, the work in Task 3 will also assess economical aspects of the introduction scenarios for the selected optical architectures. It is of great importance for a network operator to know how the cost of the introduction scenarios of the various proposed architectures will be distributed over the introduction period. For comparison, a scenario based on a pure capacity upgrade of existing SDH networks (space division multiplexing and/or increasing of the line bit rate, time division multiplexing) will be investigated too. The identification of growth scenarios for the selected optical network architectures is another important issue in the project. We are not interested in general growth aspects but rather assessing the possibilities of a stepwise introduction of a new network layer. Therefore, different growth scenarios for the evaluated optical network architectures will be identified, evaluated and compared. The outcome of this action will provide answers to the following questions: • Where are the critical points for growth of the optical network layer? • How fast can the architecture grow? • How to add new nodes into the architecture? • How to add new wavelengths?
SDH protection available Electrical Protection and Electrical Routing (e.g.: present-day SDH systems) SDH protection not available
Electrical Protection and Optical Routing (e.g.: Coloured Section Rings) Optical Protection and Optical Routing (e.g.: all-optical network) Optical Protection and Electrical Routing (e.g.: optically protected ring)
Present
Figure 2: Time scale for the introduction of optical functionalities Operation, Administration and Maintenance (OAM) Functions and Methods In future networks, whether transport networks or access networks, the OAM aspects will be the key issues for any operator. Therefore, the EURESCOM Project P615 also considers aspects of OAM specific to the optical network architectures under study. The point of view for this assessment will be “high level” questions like • How do the PNOs change from today’s OAM routines to the new OAM routines specific to optical networking architectures? • Where are the most important changes concerning OAM to be expected? • What aspects of training on the new OAM systems have to be planned? The actions in this work will involve the definition and functional description of OAM functions specific to optical networking architectures. However, before really going into detailed studies about the need of new OAM functions, it has to be examined whether new OAM functions in the optical network are necessary, or whether those functions are already specified in the electrical domain and just need to be realized in the optical transport network.
Main achievements Architecture under study Studied architecture In EURESCOM P615 project the evolution of the optical network layer is interpreted as the step by step introduction and implementation of the fundamental networking functionalities like routing and protection in the optical network layer. Architectures representing solution of different combinations for electrical/optical routing and protection were selected for detailed modeling and analysis. A brief
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summary on the selected architectures is given in this section. Table 1 summarizes the main features of the studied architecture.
Table 1
Overview of studied architectures
Architecture
Routing
Protection
SDH MSSP Ring
electrical
CS Ring
optical + elect. optical + electrical electrical optical + electrical
electrical multiplex section shared protection electrical linear MSP improved with logical node reordering optical multiplex section shared protection DXC based restoration (electrical) OXC based restoration (optical)
OMSSP Ring SDH DXC Mesh MWTN Mesh
Key equipments Electrical Optical ADM not present ADM
OADM
ADM or DXC DXC DXC
OADM and optical switches not present OXC
Ring architectures Two promising optical ring architectures and the standard SDH Multiplex Section Shared Protected (MSSP) ring - for reference - are studied in this paper. One optical ring architecture realizes routing and protection partially in the electrical and partially in the optical domain (Colored Section Ring) reutilising standard SDH equipment. Both the routing and the protection are realised in the optical domain for the other optical architecture (Optical Multiplex Section Shared Protected Ring).
Colored Section Ring The basic idea of the Colored Section Ring (CS ring) architecture is to take advantage of the well known linear multiplex section protection (MSP) protocol available in standard SDH ADMs and the wavelength routing in a two-fibber bi-directional optical ring to increase the transmission capacity [3]. CS ring is installed on two fibres, the nodes are equipped with optical add-drop multiplexers (OADM) and standard SDH ADMs, however there are duplicated aggregate units (optical line terminations) in SDH ADMs due to the applied protection. Different wavelengths are assigned to each multiplex section interconnecting the SDH ADMs. Based on wavelength routing logical ring with node order different from the physical (cabling) one can be realised. Additional electrical routing to realise transmission demands between nodes not neighbouring on the logical layer are provided in SDH ADMs. Linear MSP is applied to protect the architecture against cable cuts: aggregate signals are splitted and routed via complementary arcs of the ring. Proper node order depending on the realised demand pattern can be established on the logical network layer to eliminate the need of electrical routing in intermediate nodes. In such a case node failures affect only originating and terminating traffic, thus the performance of linear MSP is significantly improved [4].
Optical Multiplex Section Shared Protected Ring Optical Multiplex Section (OMS) Protection involves the simultaneous switching of wavelength multiplexed traffic from one fibre to another to avoid a broken fibre or a line amplifier failure. In general it should be more cost effective than Optical Channel Protection where optical switches have to be provided for each individual connection. The idea of the OMS protection ring architecture has been elaborated in frames of EURESCOM P615 project from the functional modeling to the physical implementation [2, 5]. Nodes in OMSSP ring are equipped either with SDH DXC or ADM besides the optical add-drop multiplexer. With an OMS protection ring architecture, traffic is switched at both ends of the broken Optical Multiplex Section from one fibre to the another counter-propagating fibre so that it goes around the ring to avoid the break. Note that dual-ended switching is required for any practical OMS Protection ring. In the two-fibre OMSSP ring the capacity of each fibre is divided approximately equally between wavelengths which support working optical channels and wavelengths reserved for protection purposes. Protection wavelengths on the clockwise fibre provide protection capacity for the working optical channels on the counter-clockwise fibre and vice versa. If working optical channels do not occupy the same wavelengths on both fibres then optical protection switching can be achieved without resorting to wavelength conversion. Note that a two-way pair of connections between two nodes will use different wavelengths if they use different fibres. This configuration means that in general any pair of nodes on the ring can be interconnected so that both connections can use the same route (but different fibres). This will normally be the shortest route
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in terms of number of en-route nodes, and hence this scheme frees capacity at the same wavelengths for other connections on the ring, i.e. the wavelengths may be reused for other connections. By comparison, in a two-fibre OMS Dedicated Protection ring working traffic is restricted to one fibre, so that each pair of connections between any two nodes requires an exclusive wavelength. Therefore the OMSSP ring generally offers a higher capacity than the OMSDP ring, all other conditions being equal.
Mesh architectures Two mesh architectures, an optical and a standard SDH mesh architecture (DXC based mesh) are selected for detailed analysis. The Multi-Wavelength Transport Network (MWTN) project, part of the RACE program, set out to develop ideas for a future broad-band flexible transport network employing the optical network layers. The fundamental building block of the MWTN architecture is the Optical Cross-Connect (OXC). The MWTN OXC node has the ability to route traffic according to wavelength. Inbound traffic is selected first by its incoming route, and second by wavelength. Optical crossconnects are then used to redirect this traffic onto outgoing routes. Therefore each optical channel can be selected and redirected as required. In addition, optical channels may be added or dropped using a standard SDH cross-connect.
Results from the techno-economical analyis Introduction Numerous partly or fully optical network architectures based on different optical node configurations can be specified. EURESCOM P615 project titled Evolution towards an optical network layer is focused to study the evolutionary path in the core and metropolitan area networks towards an optical network layer, describe, model and analyse optical network architectures in details. To identify most promising networking applications and the expected benefits of these optical architectures detailed techno-economical analysis and comparison of candidate optical and existing SDH architectures (for reference) were elaborated [1]. Based on the analysis results, background of the differences in the performance of the architectures are identified. Comparisons provide information on the best fit of the architectures to different networking applications and helps to select candidate architectures for the introduction and development of the optical network layer [2].
Aspects and general approaches of the analysis Several aspects like physical size, cost, availability, OAM are covered in the analysis. A set of realistic small network examples (with different topologies and demand patterns) were specified to support the analysis. Typical services and network structures has been taken into account specifying the demand patterns. Typical patterns with normal and high values are specified to evaluate both the traffic capacities and the suitability to different traffic patterns of the different architecture.In the specification of topologies (assumed existing fibre infrastructure) the typical sub-network (cluster) sizes and span length in metropolitan area and long distance networks were taken into account. Two topologies have been specified for the general study cases (rings and meshes), a 5 node topology with 10 km length for each span and a 8 node topology for with span lengths vary from 40 up to 100 km.
Analysis results For about one hundred small network study cases were analyzed and a large amount of detailed results were elaborated in frames of EURESCOM P615 project. In this paper only some selected results are presented to illustrate the achievements major conclusions are based on. For detailed results see [1].
Dimensioning In network dimensioning the two optical rings (OMSSP ring and CS ring) are considered with STM-16 line systems, however, besides STM-16 MSSP rings, STM-64 MSSP ring is studied, as well. Fibre length need of different ring architectures (in km) can be depicted on Chart 1 in a five node network example with different demand patterns. As it is expected due to WDM technique optical rings are with significant optical fibres savings compared with STM-16 MSSP ring. STM-64 MSSP ring is with similar fibre needs in most cases then optical ones, however this high speed SDH ring needs
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slightly less fibre in case of some specific demand patterns. (In the fibre savings calculation maximum 16 wavelengths per fibre is supposed for optical rings.) Both optical rings provide significant fibre savings compared with STM-16 MSSP ring, in some cases depending on the traffic patterns OMSSP ring (equipped with SDH DXC) is much more powerful in routing then CS ring with SDH ADM. Thus, OMSSP is with slightly better performance from fibre savings point of view in these cases. Fibre length savings (normal traffic, 5 nodes) 1200
1000
800 CSR OMSSP
600
MSSP (16) MSSP (64)
400
200
0 near.neigh.
Chart 1
hubbed
uniform
Fibre lengths need for rings in a 5- node network example with normal traffic
Fibre savings performance of CS ring can be improved with help of the extra flexibility provided by the logical ring layer (node reordering with node duplications) [3].
Cost analysis Based on the results of detailed network dimensioning first investment costs for different network examples are calculated. In general electrical equipment cost savings are expected first of all in the intermediate nodes due to the optical routing, and optical restoration in meshed networks applying optical network architectures. Further saving can be achieved with help of the additional flexibility provided by the optical network layer, and the wavelength routing. As it can be depicted on Chart 2 CS ring is less expensive then OMSSP, however OMSSP much more flexible for network growth (DXC, logical mesh). Since network elements realized with passive optics (splitters, filters, etc.) are with low costs the contribution of electrical equipments dominates in the total equipment cost of the optical architectures. Since routing and protection partially or total realized in the optical domain the dominating electrical equipment are the termination equipment interfacing the network with the sources of the signals to be transmitted. Architecture overall cost comparison (normal capacity, 5 nodes) 1400
1200
1000
800
MSSP (16) CSR OMSSP
600
400
200
0 near.neigh.
hubbed
uniform
Traffic pattern
Chart 2
Total equipment cost for rings with different traffic patterns in a 5-node network example
Only equipment costs are presented in this study, because it is not obvious how to calculate cost savings on less utilisation of already installed optical fibres (fibre savings).
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Overall Cost Comparison (KECU) for a 5 node ring with uniform traffic 6000 Fibres Optical equipment Electrical equipment 4000
2000
0 SDH
CSR
OMS-SP
SDH
OMS-SP
5 times Normal traffic demand
Normal traffic demand
Chart 3
CSR
Investment cost of three architectures for normal and high capacity uniform traffic.
Studying the cost breakdown of the total equipment installation costs (including fibre costs) the tradeoff between fibre costs and optical equipment costs can be identified. As it can be depicted on Chart 3 for high capacity demands comparing the SDH MSSP ring with optical rings the fibre costs significantly decreased, and the cost of needed optical equipment to install WDM systems are less then the fibre cost savings: thus it is clear that less expensive to install WDM systems then to install new fibres (infrastructure costs - like duct - are not included in the fibre cost). The reason behind the relatively high electrical equipments for OMSSP is SDH DXC in the nodes, which equipment is more expensive then the SDH ADMs in CS ring. CS ring is with less electrical equipment costs, because of effective capacity utilization due to the minimized transit traffic in the intermediate nodes. Comparing the mesh architectures (Chart 4) MWTN less expensive then the SDH DXC mesh for study cases with high capacity demands (STM-16 line systems are supposed in both architecture). The cost breakdown of MWTN (Chart 5) shows similar picture that for the optical rings. However, a relatively higher contribution of optical equipments can be identified because of the applied optical cross-connect switch is a more expensive network element then the optical add-drop multiplexers applied in optical ring architectures. 5 nodes SDH-MWTN total cost 14000
12000
Total cost (kECU)
10000
8000 SDH MWTN 6000
4000
2000
0 5 nn_n
Chart 4
5 nn_h
5 h_n
5 h_h
5 u_n
5 u_h
Total cost comparison of mesh architecture in a 5 nodes example
Availability analysis From the results of the availability analysis the study on two single STM1 demands routed on single and double span routes in 5 node network example are presented. The availability is evaluated calculating the down time ratio of the studied transmission routes. The results are presented on Chart 6. The presented study cases are (from left to right): MSSP ring, basic CS ring, CS ring with node reordering, basic OMSSP ring, OMSSP ring with 1+1 HW protected tributaries, OMSSP ring with 1+1 HW protected aggregates, OMSSP ring with 1+1 HW protected optical line terminations, and OMSSP ring with 1+1 HW protected aggregates, tributaries and line terminations. The two bars per cases represent single and double span routes, respectively.
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Availability performance of basic CS ring is sensitive for the number of hops on the transmission path because of the non-protected intermediate node failures. Additional flexibility based on wavelength routing provides good feature to improve standard linear MSP protection scheme implemented in the electrical domain. electrical / optical / infrastructure breakdown of MWTN architecture 100% 90% 80% 70% 60% infr. 50%
opt. int. elect.eq.
40% 30% 20% 10% 0% 5 nn_n
Chart 5
5 nn_h
5 h_n
5 h_h
5 u_n
5 u_h
8 nn_n
8 nn_h
8 h_n
8 h_h
8 u_n
8 u_h
Electrical / infrastructure / Optical equipment breakdown of installation costs for MWTN
Simple and effective optical protection against fibre cuts and line amplifier failures in OMSSP is realized in the optical domain on architectural level. However, there is no protection against the failures of the electrical network elements, thus any electyrical failure is critical for the basic OMSSP ring. Applying 1+1 HW protection on electrical equipment level to complete protection significantly improves the availability performance of the architecture [6]. Based on detailed studies electrical equipments are the dominating elements defining the availability performance of the optical architectures. For a single STM-1 demand MSSP and improved optical architectures with same availability performance, for higher capacity demands the optical rings are with better availability then the SDH ring. DRT results of different study cases with an STM1 demand 7.0000E-05
6.0000E-05
5.0000E-05
4.0000E-05
DTR
1span 2span 3.0000E-05
2.0000E-05
1.0000E-05
0.0000E+00 MSSP
CSR
CSRREO
OMSSP
OMSSP t
OMSSP a
OMSSP lte
OMSSP all
study cases
Chart 6 Availability of a single span and a double span 1 STM-1 capacity transmission routes on different optical ring architectures (5 node example) Operation Administration and Maintenance The main drawback of WDM based transmission network from OAM point of view that these type of networks need extra spare parts due to the different wavelengths applied in WDM technique. Two detailed studies were elaborated in frames of EURESCOM P615 project from OAM point of view. One study was focused on the possible application of distributed restoration algorithms in optical mesh networks. Simulation has been performed to calculated the restoration times can be achieved in optical mesh networks. Restoration with and without wavelength conversions were analyzed. The restoration mechanisms for the SDH and MWTN networks differ in the following ways: For the SDH mesh, restoration is done by the digital cross connects at a STM-1 granularity. Normally spare timeslots in point-to-point links between two nodes are used to reroute interrupted traffic in the event of a failure. For the MWTN network, the re-routing of optical channels is performed by optical cross-
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connects, with an STM-16 granularity. Cases with and without wavelength conversion have been considered. Globally, and for the various network scenarios considered, the ranges of restoration times were obtained. The total (100%) restoratrion of the interrupted traffic for a 5 node SDH mesh needs 86-175 ms, in a 8 node SDH mesh 80-313 ms depending on the failure case. The same results for the MWTN without wavelength conversion in a 5 node network 122-166 ms, in a 8 node network 116-263 ms. Restoration times for the same cases with wavelength conversion are 80-94 ms and 82-92 ms, respectively. From achieved results it can be concluded that there is no significant difference in the restoration speed between SDH and WDM mesh networks. The cases without wavelength conversion show that 100% restoration was not possible in some failure cases, and so the extra degrees of freedom provided by wavelength conversion are important in allowing a higher degree of restoration based on the same amount of stand-by capacities. A study was focused on the extension of standard MSSP protocol for optical multiplex section and compare the switching performance of the optical and SDH implementation (Chart 8). The SDH ring protection is found to be faster than for the OMS-SPRing, due mainly to the slower switching speed of opto-mechanical 2x2 switches compared to the SDH electronics, but in all cases the switching times are less than the 50 ms currently the standard for SDH networks. Protection switching times for SDH MSSP and OMSSP 14
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SDH MSSP OMSSP
Time [ms]
10
8
6
4
2
0
Node failure
Bidirectional signal fail
Unidirectional signal fail
Unidirectional signal degrade
Failure cases
Chart 8
MSSP switching times for SDH and optical implementations in case of different failure cases
Summary and conclusions Based on the detailed results of the analysis work performance in frames of EURESCOM P615 project some promising optical architecture were identified. Optical ring architectures seem to be much more mature then optical meshes.Reduction of first investment costs of optical architecture compared with SDH architectures can run up to 70%. This reduction of investment costs caused by fibre reduction and replacement of electrical equipment by low-cost optical equipment. Savings on investments costs of optical architectures are increasing with an increasing traffic demand.The modeling of several performance parameters have shown, that there are no significant difference between optical and SDH architectures. Architectures with protection realized in the optical domain may need extra hardware protection to improve the availability of the applied (not protected) electrical network elements. 6 Acknowledgements The authors wish to thank the valuable comments of the contributors of EURESCOM P615 project from the participating companies: British Telecom, Swisscom, Tele Danmark A/S, France Télécom, MATÁV Hungarian Telecommunications Company Ltd, Koninklijke PTT Nederland N.V., Hellenic Telecommunications Organisation S.A. (OTE), Portugal Telecom S.A., Telefónica de España S.A.. 7 Note This document is based on results achieved in a EURESCOM Project. It is not a document approved by EURESCOM, and may not reflect the technical position of all the EURESCOM Shareholders. The contents and the specifications given in this document may be subject to further changes without prior notification. Neither the Project participants nor EURESCOM warrant that the information contained in
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the report is capable of use, or that use of the information is free from risk, and accept neither liability for loss or damage suffered by any person using this information nor for any damage which may be caused by the modification of a specification. This document contains material which is the copyright of some EURESCOM Project Participants and may not be reproduced or copied without permission. The commercial use of any information contained in this document may require a license from the proprietor of that information.
References: [1]
EURESCOM Project P615 Evolution towards an optical network layer see EURESCOM Web Site: www.eurescom.de
[2]
M. Schiess, R. S. Grant, L. Cucala, J. van der Tol, Chr. Zimmer: Introduction Scenarios for Optical Network Architectures - Results from EURESCOM P615, accepted paper for European Conference on Networks and Optical Communications June 1998, Machester, UK
[3]
L. Blain, A. Hamel, T. Jakab and A. Sutter: "Comparison of classical and WDM based ring Architecture" Proc. of NETWORKS'96, Vol 2 pp. 607-612 , November 1996, Sydney, Australia.
[4]
T. Jakab, D. Arato, A. Hamel: Availability Modelling and Analysis of Optical Transmission Network Architecture, 6th Int. Conf. on Telecomm.Systems, Proceedings pp 372-387, March 58 1998, Nashville, TN, USA
[5]
R. Grant: “Optical protection in a WDM ring: from functional model to implementation” accepted for DRCN'98, 17-20 May, 1998, Brugge, Belgium
[6]
T. Jakab, D. Arató, D. D. Marcenac: “Availability Analysis of Some Optical Ring Network Architectures - Results from EURESCOM P615 Project accepted for DRCN'98, 17-20 May, 1998, Brugge, Belgium
Acknowledgments The authors acknowledge all the participants in the EURESCOM P615 project for contributions to the work in Task 2 and Task 3. These are: Hellenic Telecommunication Organisation, Portugal Telecom Group (CPRM-Marconi and Portugal Telecom), Telefónica de España, France Telecom, British Telecom, KPN Research, Tele Denmark, Hungarian Telecommunications Co., Swiss Telecom PTT References See footnote at the end of the document.
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4 Summary [i] [ii] [iii] [iv] [v]
M.O. van Deventer et al., Node functionalities and architectures for the optical network layer, Results from EURESCOM P615, NOC ’97, Antwerp, Belgium, 1997. Draft ITU-T Rec. G.otn, “Architecture of Optical Transport Networks”, version 1, 21 Oct. 1996 ITU-T Rec. G.805, “Generic Functional Architecture of Transport Networks”, ITU, Nov. 1995. ITU-T Rec. G.681, “Functional Characteristics of Inter-Office and Long-Haul Line Systems Using Optical Amplifiers, Including Optical Multiplexing”, ITU COM 15-R 55-E, Aug. 1996. L. Blain et al., Comparison of classical and WDM based ring architecture, NOC ’96, Conf. Digest pp. 261-268, Heidelberg, Germany, 1996.
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