Quality-of-Service Provisioning
in IP/WDM Networks
with Dynamic Lightpath Allocation
Eugene Kozlovski
Submitted to the University o f London for the degree o f
DOCTOR
o f Philosophy
UCL
Department o f Electronic and Electrical Engineering
University College London
ProQuest Number: U642985
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Abstract
This thesis is focused on the investigation of Quality-of-Service (QoS) provisioning in fast-switched IP/WDM optical network architectures, supporting mission-critical service-differentiated Internet applications.
First, drawbacks associated with QoS provisioning in currently proposed fast- switched optical networks, including those based on re-configurable optical core, optical burst switching (OBS) and optical packet switching (OPS), are discussed. To overcome these drawbacks, a novel approach, namely, the wavelength-routed optical burst-switched architecture (WR-OBS) is proposed and comprehensively investigated throughout this work. Contrarily to existing OBS approaches, WR-OBS bypasses opto electronic buffering/processing o f bursts in the optical domain, using connection- oriented, two-way lightpath reservation mechanism.
A general framework for explicit QoS provisioning in WR-OBS is discussed and the design of the key WR-OBS network components, the control node and the edge-router, is presented. The QoS framework is based on a set o f new burst scheduling algorithms that effectively maintain the required burst blocking probability for a given number o f supported wavelengths, whilst bounding burst end-to-end delays. Novel network parameters, key to ensuring the QoS performance in WR-OBS, are introduced. In particular, the burst maximum scheduling delay, which governs the maximum time allowed for a burst to request a lightpath before being blocked, is shovm to be critical in bounding the burst blocking probability. Furthermore, the WR- OBS restoration model, based on a novel failure-compensating burst scheduling technique, is presented. It is then successfully applied to the case o f single link failures, for the first time analysing the implications of resource failures in OBS in terms of wavelength restoration over-provisioning.
The trade-offs are quantified between the burst end-to-end delays and WR-OBS wavelength requirements, maintaining the bounded blocking probability. This analysis, carried out as a function of network physical connectivity, traffic loads and service differentiation, identifies the conditions, allowing the proposed architecture to operate with higher bandwidth utilisation with respect to that in statically-routed WDM networks. For both failure-free and link-failure cases, the WR-OBS wavelength savings are shown to be especially significant in sparsely connected network physical topologies.
Finally, the design o f a novel inter-domain network management system for automatic, QoS-capable IP service provisioning over the re-configurable WDM networks is investigated. The concept o f the integrated IP/WDM network management is devised as a shorter-term solution to automating the network provisioning with respect to those, supporting finer switching granularities, including WR-OBS. A key component o f this solution, the WDM routing manager, carrying out near real-time lightpath setup on-demand, is implemented using novel component-oriented and object-oriented software programming techniques. A detailed experimental scenario is then developed and the system successfully tested on a representative network set-up.
Acknowledgments
This thesis could not be successfully completed without the help o f many people, whom I would like to express my sincere gratitude.
First and foremost, I would like to thank my supervisor. Prof. Polina Bayvel, for introducing to me the exciting world o f advanced optical networking, and for the continuous support and guidance throughout the course o f this project. Her comments were critical to shaping most of the problems investigated in this work.
I would like to thank Prof. Chris Todd and Prof. Alex Galis for their interest in my research work, and encouragement o f my activities in the EU 1ST WINMAN Consortium.
I am deeply grateful to Dr. Mark Searle, INSIG Ltd, for fhiitful discussions on the WR-OBS simulation system and the burst scheduler implementation that were used in Chapters 3-5.
I would like to express my gratitude to Prof. Jon Crowcroft, Dr. Richard Gibbens and Dr. Sven Ostring, University of Cambridge, as well as Dr. Stefano Baroni, UCL/Corvis (USA), for helpful comments in the area o f QoS provisioning.
I would like to acknowledge Dr. Naohide Nagatsu, NTT (Japan), for taking time to read my thesis and providing valuable comments and suggestions, especially in the area of WR-OBS restoration techniques.
I am grateful to all WINMAN colleagues for sharing with me their expert knowledge of both network management and large-scale software systems development. The collaboration with Lucent (the Netherlands), Telefonica-ID, UPC (Spain), PTI (Portugal), TTI (Israel), Felix Telecom (Romania) and OTE, NTUA and Ellemedia Technologies (Greece), was equally enjoyable and invaluable experience. This collaboration led to the results discussed in Chapter 6. And the time spent in working meetings on those Greek islands was unforgettable!
ACKNOWLEDGMENTS
fruitful collaboration on the WR-OBS modelling. I would like to thank Dr. Jorge Castro for numerous helpful discussions on the evolution o f IP/WDM network architectures, and for the collaborative work on the WDM routing manager component, which led to the results presented in Chapter 6.
I would also like to thanks all my colleagues and friends in the Optical Networks Group and the Ultrafast Photonics Group. These people are always “on the same wavelength”, both for brilliant research ideas and for going out. I can now say “Cheers!” in almost any language spoken in office 808.
I would like to gratefully acknowledge the ORS and UCL Graduate School Research Award Schemes, as well as the Ian Karten Foundation and the Wingate Foundation, for their fellowships and generous funding.
I am really grateful to Prof. Gregory Z. Gutin, Royal Holloway, University of London, for the vital support in my first academic endeavours when in London.
I would like to thank Dr. Marco Bojcun, London Metropolitan University, for the supervision o f my initial academic visit to the UK, under the British Foreign and Commonwealth Office Chevening Award.
I would also like to acknowledge Alexander Litvin, Pivden-Informatika Ltd, Dr. Evgeni Snezhko, Dnepropetrovsk National University (Ukraine), as well as many other people from my home town, for fostering my computer and networking experience, and general research aptitude.
Table of Contents
Abstract 1
Acknowledgements 2
Table of Contents 4
List of Tables 8
List of Figures 10
List of Abbreviations 16
List of Symbols 20
Chapter 1 Introduction 23
1.1 Thesis objectives and structure...24
1.2 References... 27
Chapter 2 Challenges in QoS provisioning in Internet-over-optical network architectures 28 2.1 Introduction... 28
2.2 QoS in static wavelength-routed optical networks (W RON)... 32
2.3 QoS in networks with re-configurable optical core... 36
2.4 QoS in optical packet-switched networks...43
2.5 QoS in optical burst-switched networks...47
2.6 QoS in the wavelength-routed optical burst-switched networks (WR-OBS).... 56
2.7 Summary and conclusions... 58
2.8 References... 60
Chapter 3 The design of wavelength-routed optical burst-switched networks 69 3.1 Introduction... 69
3.2 The concept of wavelength-routed optical burst switching (W R-OBS)...70
3.3 Centralised WR-OBS network m odel... 74
TABLE OF CONTENTS
3.5 Metrics of WR-OBS wavelength assignment efficiency with respect to
statically-routed WDM networks... 81
3.5.1 WR-OBS wavelength gain... 81
3.5.2 WR-OBS wavelength gain in sparsely-connected physical topologies ... 82
3.6 Simulation model and network configuration...84
3.7 Lower limit on the burst aggregation delay...88
3.8 WR-OBS QoS performance without request scheduling capability... 95
3.9 Impact o f request scheduling on WR-OBS QoS performance...99
3.9.1 Request scheduling algorithm... 99
3.9.2 The provision of end-to-end guarantees with fairness... 102
3.9.3 Maximum scheduling d elay ...105
3.9.4 Impact of traffic load... 108
3.10 QoS provisioning in WR-OBS with service differentiation... I l l 3.10.1 Impact o f request scheduling... 113
3.10.2 Impact of traffic load... 116
3.11 Summary and conclusions...118
3.12 References...121
Chapter 4 The impact of network physical connectivity on WR-OBS QoS performance 124 4.1 Introduction... 124
4.2 Randomly-connected network topologies... 125
4.3 A remark on the scalability of centralised WR-OBS architecture...133
4.4 Burst aggregation delay... 134
4.5 Maximum scheduling delay as a function o f connectivity...137
4.6 QoS provisioning with service differentiation...147
4.7 Real networks as W R-OBS... 152
4.8 Summary and conclusions...157
TABLE OF CONTENTS
Chapter 5 Survivability of WR-OBS architecture against single link
failures 163
5.1 Introduction... 163
5.2 Impact o f single link failures on burst blocking probability in WR-OBS 164 5.3 WR-OBS restoration m odel... 166
5.4 Wavelength restoration over-provisioning in W R-OBS...169
5.5 WR-OBS restoration in randomly-connected networks...173
5.6 WR-OBS restoration in real networks... 185
5.7 Summary and conclusions... 191
5.8 References... 195
Chapter 6 Integrated management of end-to-end IP services over re-configurable WDM networks 197 6.1 Introduction... 197
6.2 WINMAN system architecture... 200
6.2.1 Functionality o f the WINMAN system... 200
6.2.2 Generic architecture o f network management system...205
6.2.3 The design of the WDM routing component...207
6.2.4 End-to-end IP connectivity service provisioning... 211
6.3 The validation o f the WINMAN system ...213
6.3.1 Testbed set-up for WINMAN evaluation... 214
6.3.2 Integrated experimental scenario for validation of the WINMAN functionality...218
6.3.3 Evaluation results and discussion...221
6.4 Management of WR-OBS networks... 225
6.5 Summary and conclusions... 229
6.6 References... 232
Chapter 7 Summary and conclusions 234 7.1 Thesis summary...234
7.2 Original contributions... 239
TABLE OF CONTENTS
7.4 List of publications...242
Appendix A ILP formulation of the dynamic wavelength allocation to bursts 245 Appendix B Verification of the dynamic wavelength routing and assignment algorithm 248 Appendix C Control plane approach to the IP and WDM integration in re-configurable optical networks 252 C. 1 Control plane models... 252
C.2 Frameworks for the unified control plane...254
C.2.1 MPlambdaS and Generalized MPLS...255
C.2.2 The ASON/ASTN framework... 256
List of Tables
2.1 QoS performance targets in some audio/video applications [C o v l], [M irl]. 30
2.2 QoS performance targets in some data applications [C o v l], [M irl]. 30
2.3 Elements o f the optical transport layer hierarchy with expected deployment scenarios [Ser2]. Number o f wavelengths in global and wide-area networks is not expected to grow significantly due limited regeneration capabilities, combined with non-linearities, associated with long-distance transmission. 31
2.4 Dynamic routing strategies. 38
2.5 Comparison o f heuristics for the dynamic wavelength assignment. Heuristics are presented in the order o f decreasing request blocking probability [Z anl]. L - number o f links; - number o f wavelengths per link; N - number o f nodes. 38
2.6 Signalling protocols in OBS. The typical burst sizes are given wherever specified in the literature. Toffset - the offset time between the transmissions o f control packet and the corresponding data burst, 7^eiay,mio - burst minimum end-to-end delay (excluding burst aggregation time), Tprop - end-to-end propagation time, H - the number o f hops in the end-to-end path, /node - control packet processing delay per node, /trans - burst transmission delay, C\ - high-priority traffic class, C] - low-priority traffic class, Zburst(C2) - average size o f low-priority bursts. 49
2.7 Channel scheduling in OBS. Unscheduled timeis the instant after the latest burst reservation in a given channel. Unused time is the duration o f a void tim e-slot between tw o successively scheduled bursts and after the latest burst reservation in a given channel. The performance is evaluated using a standalone O BS node [X io l]. The considered node configuration assumes 8 ports, 15 data optical channels (wavelengths), 1 signalling channel, buffer size o f 2 slots (14 ps each), and traffic loads o f 0.76. N ote that the blocking probability values are shown for a particular node configuration and may vary depending on different network
parameters. 54
4.1 RCNs representing upper limit on W ROBS wavelength requirement, a -network physical connectivity, L - number o f links in topology, A^wRON -WRON wavelength requirement, D- network diameter, (ômm, 6max) - min. and max. nodal degree.
129
4.2 RCNs representing lower limit on WR-OBS wavelength requirementa- network physical connectivity, L - number o f links in topology, Wx,wron - WRON wavelength requirement, D - network diameter, (ômin, Smax) - min. and max.
LIST OF TABLES
4.3 Topological parameters o f real networks, a - network physical connectivity, L
-number o f links in topology, A 'x .w ro n - WRON wavelength requirement, D
-network diameter, (ômin, ômax) - min. and max. nodal degree. 153
5.1 RCNs representing upper limit on W R-OBS wavelength requirement under the worst case o f the link failure in terms o f the blocking probability. In each topology, a link w hose failure causes a maximum increase in the burst blocking probability, is shown by the dotted line, a - network physical connectivity, ^r%TtON" bound on WRON restoration capacity, Aest - network diameter
under the failure. 175
5.2 RCNs representing lower limit on WR-OBS wavelength requirement under the worst case o f the link failure in terms o f the blocking probability. In each topology, a link whose failure causes a maximum increase in the burst blocking probability, is shown by the dotted line, a - network physical connectivity, ^ r ^ o N " bound on WRON restoration capacity, Aest - network diameter
under the failure. 177
5.3 Real networks under the worst case o f the link failure in terms o f the blocking probability. In each topology, a link w hose failure causes a maximum increase in the burst blocking probability, is shown by the dotted line, a - network physical connectivity, bound on W RON restoration capacity,
Aest - network diameter under the failure. 186
6.1 Functional requirements o f W INMAN N M Ss 203
6.2 The components o f the generic NM S, supporting the provision o f IP services,
and their functionality [Ser2]. 206
6.3 The generic functionality o f the End-to-end routing component 208
6.4 Functional characteristics o f the W DM routing component in W INM AN (Release 0), and the guidelines for further enhancements in the auto-routing functionality, supporting the wavelength switching capability. 211
6.5 Results o f the experiments with operational W INM AN system. The execution time, estimated to be achieved after the optimisation o f system code, is shown in
parentheses. 222
C. 1 The comparison between different IP/WDM interconnection m odels (n - number
o f routers) [C hal]. 254
List of Figures
2.1 IP over static WRONs. An example o f two fixed lightpaths, (R2-^R4) and
(R]—^R]), sharing the same fibre between nodes R] and R3. For simplicity, the
case o f uni-directional connectivity is shown. 33
2.2 IP over optical networks with re-configurable W DM core. An exam ple o f two dynamically re-configurable lightpaths, (R2—>Rt) and (R2—^Rs). Dashed line
shows an alternative in provisioning the lightpath (R2—>R|) in response to
changes in network operational conditions or traffic pattern. For simplicity, the
case o f uni-directional connectivity is shown. 36
2.3 IP over OPS networks. An example o f tw o optical packets, (R2—>R|) and
(R2—>Ra), sharing the same wavelength in the fibre between nodes R2 and R3.
W avelength conversion capability is supported to route packets between nodes R2 and R3, as w ell as between nodes R3 and R$. For simplicity, the case o f uni
directional connectivity is shown. 43
2.4 Generic architecture o f an optical packet switch. Input FDLs delay payloads for the duration o f header processing, whilst output FDLs are used for contention
resolution. 44
2.5 IP over O BS networks. Control packet configures resources ahead o f the data burst (R2->R4), such that it w ill be routed via between nodes R2 and R3, and
via X.2 between nodes R3 and R4. At the same time, data burst (R3—>R,) is routed
via Xy between nodes R3 and R4, and via between nodes R$ and Ri. For
simplicity, signalling for the burst (R2—>R,) only is depicted, and the case o f uni
directional connectivity is shown. 48
2.6 Timing diagrams o f the conventional OBS protocols, (a) IBT, (b) JET. Toffset -offset time between the control packet and the data burst, tp^p - propagation time per hop, tnode - control packet processing delay per node. 51
2.7 IP over W R-OBS networks. First, control packet configures resources for the burst (R2—>R4), such that it w ill be routed end-to-end via A,i. Then,
acknowledgement packet is signalled back to R2. Once it has been received, the
burst (R2—>R4) is sent. At the same time, the burst (R3-> R i) is routed end-to-end
via X,2. For simplicity, signalling for the burst (R2—>R$) only is depicted, and the
case o f uni-directional connectivity is shown. 57
LIST OF FIGURES I I
3.2 Timing diagram o f the centralised WR-OBS architecture [Diis4]. The case o f limited burst size (L B S) aggregation method [M ig3] is considered. The parameters that determine the burst end-to-end delay are discussed in section 3.3. 73
3.3 Centralised WR-OBS architecture. An example o f wavelengths X-i and A,2,
sharing the same link. 74
3.4 Edge-router architecture in W R-OBS 75
3.5 Architecture o f the request server residing in W R-OBS control node 75
3.6 ARPA Net as centralised W R-OBS. Dashed lines show an example o f the control topology with links assumed to have equal propagation delay. 88
3.7 Impact o f /gggr on the increase o f the overhead involved in the lighpath set-up. It is assumed that /tuning = 0. For the same period o f time, 160 ms, the overhead is tw ice higher when /aggr = 40 ms with respect to /aggr = 80 ms. 89
3.8 Burst blocking probability vs. burst aggregation delay. Shaded area indicates /aggr values affecting the burst blocking, (a) W\^ = A(Rjn.max) = 19; (b) Wi =
Ax.,wron“ 33. 91
3.9 Relationship between burst blocking probability and traffic load. Dotted line shows limiting values o f /aggr- (a) = M^in.max) = 19; (b) = A^wRON = 33 93
3.10 Relationship between burst blocking probability and the number o f wavelengths for different values o f /aggr under the traffic load o f 0.7. Dotted line shows
limiting values o f /aggr. 94
3.11 Burst blocking probability vs. number o f wavelengths (/sched.max = 0). 97
3.12 Burst blocking probability vs. traffic load (/sched,max = 0). 97
3.13 The trade-off between traffic load and the wavelength requirement maintaining the required burst blocking probability. Shaded area indicates Pbiocking < 10"^. 99
3.14 Flow-chart o f the request scheduling (Algorithm 3.4). 101
3.15 Timing diagram o f the burst end-to-end delay under the request scheduling
policy (scenario B). 105
Burst blocking probability vs. /sched,max for different Ct^ .obs • Traffic load is 0.7,
/a g g r = 40 ms. 106
3.17 Burst blocking probability vs. the number o f wavelengths for different /sched,max- 107
3.18 Burst blocking probability vs. traffic load for different values o f
/schcd,max-4ggr— 40 ms. (a) G wR-oBS“ 100% ( ) T l = 19); (b) G wR.0BS~ 0 ( ^ L ~ 3 3 ). 109
3.19 The trade-off between maximum schedulimg delay and the wavelength
LIST OF FIGURES 12
3.20 Burst blocking probability vs. the number o f wavelengths for both CoS. Traffic
load is 0.7, C\ = 50% o f total traffic load. 113
3.21 Burst blocking probability o f the best-effort traffic vs. /sched,max(C2). Maximum
scheduling delay /sched.max(Ci) = 10 ms. Dashed line denotes fbiockmg(Ci) (burst blocking probability o f premium traffic) with Wi = 50. Dotted lines represent the ^biockingCCi) for different Wi and enable to determine appropriate values o f
^ sch cd ,m ax (C 2 ) reaching P b io c k in g ( C 2 ) = f b i o c k m g ( C i ) . Traffic load is 0.7, C i = 50% o f
total traffic load. 114
3.22 The trade-off between maximum scheduling delay and the wavelength requirement for the ARPA Net physical topology. Pbiocking < 10"^ for both traffic classes. Traffic load is 0.7, C, = 50% o f total traffic load. 115
3.23 Burst blocking probability vs. traffic load for fsched,max(Ci) = /scbed.njax(C2) = 10 ms
and G*wr-obs = 100%. C\ = 50% o f total traffic load. 117
3.24 The trade-off between traffic load and maximum scheduling delay allow ing for both traffic classes to achieve Pbiocking < 10*^ for G*wr-obs = 100%. C\ = 50% o f
total traffic load. 117
3.25 Relationship between the wavelength requirement and traffic load ensuring
P b i o c k in g < 10"^ for various fixed values o f / s c h e d , m a x ( C i ) and / s c h e d . m a x ( C2) . C l = 50%
o f total traffic load. 118
4.1 WRON wavelength requirements in the case o f the limiting topologies. The
limits on A^x,wron are given with 95% degree o f confidence. 132
4.2 Network diameter in the limiting topologies.
(Since there is a small variation in the network diameter in RCNs with the same value o f a , [B ari], the diameter occurred to be the same in both limiting topologies with a = 0.18. ) The limits on A^jl,wron are given with 95% degree o f
confidence. 133
4.3 Burst blocking probability vs. network physical connectivity at different values o f the burst aggregation delay. Dotted line shows values o f /aggr at which the blocking probability saturates, (a) T opologies A-E (upper limit on the wavelength requirement), (b) Topologies F-J (low er limit on the wavelength
requirement). 136
4.4 Burst blocking probability vs. network physical connectivity. Traffic load: 0.7, ^sched,max = 0. (a) Topologics A-E (uppcr limit on the wavelength requirement), (b) T opologies F-J (lower limit on the wavelength requirement). 139
4.5 Maximum scheduling delay vs. network physical connectivity at different wavelength gains. Pbiocking <10*^, traffic load: 0.7.
(a) T opologies A-E (upper limit on the wavelength requirement).
LIST OF FIGURES B
4.6 Maximum scheduling delay vs. network physical connectivity at different traffic loads. Pb lo c k in g ^10 .
(a) Topologies A-E (upper limit on the wavelength requirement).
(b) Topologies F-J (low er limit on the wavelength requirement). 144
4.7 W R-OBS wavelength requirement vs. network physical connectivity at different maximum scheduling delays. Pbiocking <10'^, traffic load: 0.7. Dotted lines represent wavelength requirements in W RONs [B ari].
(a) Topologies A-E (upper limit on the wavelength requirement).
(b) Topologies F-J (low er limit on the wavelength requirement). 145
4.8 Maximum scheduling delay vs. W R-OBS wavelength gain at different a . Pbiocking <10^, traffic load: 0.7.
(a) Topologies A-E (upper limit on the wavelength requirement).
(b) Topologies F-J (low er limit on the wavelength requirement). 146
4.9 Maximum scheduling delay vs. network physical connectivity for the tw o CoS at OwR^BS= 30%. P b io c k in g <10'^, traffic load: 0.7.
(a) Topologies A-E (upper limit on the wavelength requirement).
(b) Topologies F-J (low er limit on the wavelength requirement). 150
4.10 Maximum scheduling delay vs. network physical connectivity for the tw o CoS at GwROBS= 20%. P b io c k in g <10'^, traffic load: 0.7.
(a) Topologies A-E (upper limit on the wavelength requirement).
(b) Topologies F-J (lower limit on the wavelength requirement). 151
4.11 Lower limit on the aggregation delay in the real network physical topologies.
Traffic load: 0.7 155
4.12 W R-OBS wavelength requirement in the real network physical topologies at different 4ched.max. blocking < 10"^, Traffic load: 0.7 156
4.13 W R-OBS wavelength gain in the real network physical topologies at different
^ sc h e d ,m a x ' -P b io c k in g ^ 1 0 , Traffic load. 0.7 156
4.14 Maximum packet end-to-end delays vs. network physical connectivity in classless W R-OBS, operating with Gwr-obs= 20%. Traffic load: 0.5. /aggr = 43 ms for networks A-C, and /aggr = 40 ms for networks D-J. /prop.s-d = 6 ms (max. shortest path + 1 extra hop). /ack,ctri-s = 2.5 ms, /caic = /tuning = 0. Bars represent ranges o f T’EEdeiay.max due to the distribution o f /trans, the latter determined by the distribution o f Zburst for 95% o f bursts (/trans ^ /aggr for 100% o f bursts when 6in,max = 6core). Dotted lines show maximum burst scheduling delay, bounding the burst blocking probability to Pbiocking < 10"^. (a) Topologies A-E (upper limit on the wavelength requirement), (b) Topologies F-J (lower limit on the wavelength
requirement). 159
LIST OF FIGURES 14
5.2 Burst blocking probability vs. A^wR-oBs = 27, /sched.max= 12 ms. Traffic load:
0.7, /aggr = 40 ms. 166
5.3 Burst blocking probability vs. failure-compensating scheduling delay. A^wROBS
= 27, /sched.max= 12 ms. Traffic load: 0.7 170
5.4 Restoration to f blocking < 10'^. A^x.wr^bs = 27, /sched,max = 12 ms. Traffle load: 0.7 171
5.5 Trade-off between maximum scheduling delay and wavelength requirement for f blocking < 10"^. A^,WR-OBS = 27, /sched.max = 12 ms. Traffic load: 0.7 172
5.6 Failure-compensating scheduling 172
5.7 Average number o f bursts per failed link vs. network physical connectivity, (a) Networks representing the upper limit on wavelength requirements, (b) Networks representing the lower limit on wavelength requirements 179
5.8 Network diameter under the failure and in no-failure case vs. network physical connectivity, (a) Networks representing the upper limit on wavelength requirements, (b) Networks representing the lower limit on wavelength
requirements 180
5.9 Lower limit on burst aggregation delay vs. network physical connectivity under
the failure 181
5.10 W avelength requirements under the failure vs. network physical connectivity, (a) Upper limit on WRON wavelength requirement, (b) Lower limit on WRON
wavelength requirement. Traffic load: 0.7 182
5.11 W R-OBS restoration gain vs. network physical connectivity. Traffic load: 0.7. (a) Networks representing the upper limit on wavelength requirements, (b) Networks representing the lower limit on wavelength requirements. 184
5.12 W R-OBS restoration gain vs. network physical connectivity. For comparison, GwR.oBs.rest undcr the load o f 0.7 from Figure 5.11 is shown by the dotted line, (a) Upper limit on wavelength requirements, (b) Lower limit on wavelength
requirements. /sched.rest = 16 ms. 185
5.13 Network diameter under the failure in real network physical topologies 188
5.14 Lower limit on the burst aggregation delay in real network physical topologies 189
5.15 W avelength requirements under the failure vs. network physical connectivity.
Traffic load: 0.7 190
LIST OF FIGURES 15
5.17 Maximum packet end-to-end delays vs. network physical connectivity in classless WR-OBS, operating under failure with GwR.oBS.rest = 20%. Traffic load: 0.5. /'aggr = 43 ms for networks A-C, and /'aggr = 40 ms for networks D-J. /'sched,max = 1 ms for networks A-H, and /'sched.max = 3 ms for networks I-J. /ack,ctri-s = 2.5 ms, /calc = /turning = 0. Bars represent ranges o f 2EEdeiay.max due to the distribution o f /trans, the latter determined by the distribution o f Zburst for 95% o f bursts (/trans ^ /aggr for 100% o f bursts when 6m,max = ^core). Dotted lines show maximum failure-compensating scheduling delay, bounding the burst blocking probability to ^blocking < lO’^ under failure, (a) Topologies A-E (upper limit on the wavelength requirement), (b) Topologies F-J (lower limit on the wavelength requirement). 193
6.1 W INM AN high-level functional architecture 201
6.2 W INM AN positioning in the TM N management layers [K arl]. 204
6.3 Architecture o f the generic W INM AN N M S [K arl]. For simplicity, some interactions, such as those related to the Policy Manager and the supporting
components, are not shown. 206
6.4 Class diagram o f the WDM routing component. Base classes related to the
generic end-to-end routing component are shaded. 209
6.5 W INM AN validation test-bed. (See Figure 6.8 for the com plete experimental
set-up.) 215
6.6 The IP layer o f the W INM AN test-bed 216
6.7 IP/WDM integration 217
6.8 Integrated scenario set-up for WINMAn functional validation 219
6.9 W INM AN GUI screenshot, demonstrating a fraction o f the service setup sequence diagram, showing the creation o f an IP/LSP path. 223
6.10 Generic N M S, extended to support the W R-OBS N M S fault management functionality. For simplicity, only tw o extended components, the Restoration
manager and Alarm correlator, are shown. 226
6.11 Sequence diagram o f communications between the W R-OBS N M S, I-NM S and IP-NM S, involved in link failure restoration according to the W R-OBS failure-compensating scheduling (section 5.3). /rest is the time, required for setting ^sched,max, re-configurating the OXCs and updating routing tables within the control node, as w ell as for the updating /aggr within the edge-routers according to the Algorithm 5.1 (RSU). Algorithm 5.2 (FOBS) is carried out by W R-OBS control plane. It is assumed that both control planes interwork with their corresponding N M Ss through proper information m odels, translating the proprietary control plane functionality to N M S southbound interfaces. 227
B. 1 Portion o f blocked requests vs. the number o f wavelengths. For all three
networks, the entire set o f requests is accommodated when IFl = Ax,wron. 251
C .l Generalised MPLS Hierarchy 256
List of Abbreviations
ASON Automatically-Switched Optical Network
ASTN Automatically-Switched Transport Network
ATM Asynchronous Transfer Mode
AUR Adaptive Unconstraint Routing
AWG Arrayed Waveguide Grating
BBP Burst Blocking Probability
BER Bit Error Rate
CaSMIM Connection and Service Management Information Model
CE Customer Edge router
CLI Command-Line Interface
CORBA Common Object Request Broker Architecture
CoS Class of Service
CR-LDP Constraint-based Routed Link Distribution Protocol
DCN Data Communication Network
DiffServ Differentiated Services
DOS Differentiated Optical Services
DRWA Dynamic Routing and Wavelength Assignment
DSC Distributed Component Software
EDF Earliest Deadline First
EML Element Management Layer
EMS Element Management System
E-NNI Exterior N etwork-to-N etwork Interface
FBAT Fixed Burst Aggregation Time
FCAPS Fault, Configuration, Accounting, Performance, Security
FCBS Failure-Compensating Burst Scheduling
FDL Fibre Delay Line
FF First-Fit
FFUC First-Fit Unscheduled Channel
FF-VF F irst-F it-with-V oid-F illing FFWAB
FIFO First-In-First-Out
FLA Fault Location Algorithm
FRR Forward Resource Reservation
FSC Fibre Switch Capable
G-LAUC-VF Generalised Latest-Available-Unscheduled-Channel-with GMPLS Generalised Multi-Protocol Label Switching
GUI Graphical User Interface
LIST OF ABBRE VIA TIONS 1 7
IBT In-Band-Terminator
ICS IP Connectivity Service
IETF Internet Engineering Task Force
ILP Integer Linear Programming
I-NMS Inter-domain Network Management System
I-NNI Internal Network-to-Network Interface IntServ Integrated Services
IP Internet Protocol
IP-NMS IP Network Management System
IS-IS Intermediate System to Intermediate System
1ST Information Society Technologies
ITU International Telecommunications Union
JET Just-Enough-Time
JIT Just-In-Time
LAUC-VF Latest-Available-Unscheduled-Channel-with-Void-Filling
LBS Limited Burst Size
LCP Least-Congested Path
LDP Label Distribution Protocol
LL Least-Loaded
LSC Lambda Switch Capable
LSP Label Switched Path
LSR Label Switch Router
LU Least-Used
MEDFR Modified-Earliest-Deadline-First-witb-Re-attempts
MEMS Micro Electro Mechanical System
MP Min-Product
MPEG Motion Pictures Experts Group
MPLambdaS Multi-Protocol Lambda Switching
MPLS Multi-Protocol Label Switching
MTNM Multi-Technology Network Management
MU Most-Used
MX Maximum Sum
NE Network Element
NMA-A Network Management Interface - ASON
NMA-T Network Management Interface - Transport
NML Network Management Layer
NMS Network Management System
NNI Network-to-Network Interface
GADM Optical Add-Drop Multiplexer
OBS Optical Burst Switching
OIF Optical Interworking Forum
0-PNNI Optical Private Network-to-Network Interface
OPS Optical Packet Switching
LIST OF ABBREVIA TIONS 18
OTN Optical Transport Network
OXC Optical Cross-Connect
PDF Probability Density Function
PLR Packet Loss Rate
PNNI Private Network-to-Network Interface
PON Passive Optical Network
PRS Proactive Reservation-based Scheduling
PSC Packet Switch Capable
PTP Physical Termination Point
QoS Quality o f Service
RA Random Assignment
RAM Random Access Memory
RCL Relative Capacity Loss
RON Randomly-Connected Network
RFD Reserve-a-F ixed-Duration
RSU Restoration Scheduler Update
RSVP Resource Reservation Protocol
RSVP-TE Resource Reservation Protocol with Traffic Engineering
RWA Routing and Wavelength Assignment
SCM Sub-Carrier Multiplexing
SDH Synchronous Digital Hierarchy
SLA Service Level Agreement
SML Service Management Layer
SMS Service Management System
SNC SubNetwork Connection
SNR Signal-to-Noise Ratio
SOA Semiconductor Optical Amplifier
SRWA Static Routing and Wavelength Assignment
TAG Tell-And-Go
TCP Transmission Control Protocol
TDM Time Division Multiplexing
TMF Tele Management Forum
TMN Telecommunication Management Network
TOM Telecom Operations Map
UNI User-to-Network Interface
VIP Video over IP
VoIP Voice over IP
VPN Virtual Private Network
WA Wavelength Allocation
WAS Wavelength Allocation with Scheduling
WATD Wavelength Allocation and Threshold Dropping
WDM Wavelength Division Multiplexing
WDM-NMS WDM Network Management System
LIST OF ABBREVIA TIONS 7 p
WR-OBS Wavelength-Routed Optical Burst-Switched Network
WRON Wavelength-Routed Optical Network
WRR Weighted-Round-Robin
List of Symbols
t^core ■^in.max
^ in .m a x
Bl
c
C l C 2 C i D Dqyv C>ON ^rest CwR-OBS CwR-OBSC w R -O B S ,rest H H k L ■^burst L?c N n ■^(■^in,max)
M ,, WR-OBS
M -,W R0N
■ rest
'^X.WRON
P
B blocking
core bit-rate
maximum bit-rate of the total traffic, arriving an edge-router node maximum bit-rate o f the traffic arriving at a buffer
average number of bursts simultaneously routed through the same link from different source-destination pairs in failure-free case
number of classes of service premium traffic class
best-effort traffic class service class i
network diameter
number of void bits in the inter-arrival time packet size in bits
network diameter under the failure WR-OBS wavelength gain
WR-OBS wavelength gain in sparsely-connected network physical topologies
WR-OBS restoration gain number of hops
average inter-nodal distance link
number of links burst size
number of bi-directional links in the fully-connected network number o f nodes/edge-routers
number of re-attempts o f a request for a lightpath
minimum number of the wavelengths required to accommodate all traffic from one edge router, if this traffic has to be transmitted over the same optical link
wavelength requirement in WR-OBS wavelength requirement in WRON
wavelength restoration over-provisioning in WRON
LIST OF SYMBOLS 21 -^blocking,alIowed <li Qmdx R Si T ^ack,ctri-s ^aggr ^aggr,rest ^calc ^delay,m in Tedge ^edge.itiax "T rest edge, max ^edge_elapsed ^EEdelay ^EEdelay.max jirest
I EEdeIay,max
^node ^offset ^prop ^prop,s-ctrl ^prop,s-d ^sched,max ^sched,max ^sched,rest ^trans ^tuning
w a itin g ZwHT
W
maximum burst blocking probability allowed by QoS requirements value o f a QoS metric for a service class i
maximum number o f the requests held in one queue o f the request server
number o f requests to route a burst between a source-destination pair arrived at time t
request for a lightpath between a source-destination pair arrived at time t
differentiation factor for the class i
request generation time
one-way acknowledgement propagation delay between the control node and source
burst aggregation delay
increase in the burst aggregation delay under the failure
calculation delay o f DRWA algorithm per one assignment attempt burst minimum end-to-end delay, excluding the aggregation time burst edge delay
maximum burst edge delay
maximum burst edge delay in the failure-compensating mode highest elapsed edge delay
burst end-to-end delay
maximum burst end-to-end delay
maximum burst end-to-end delay in the failure-compensating mode control packet processing delay per node
offset time between control packet and the corresponding burst end-to-end propagation time
one-way request propagation delay between the source and control node
one-way burst propagation delay between source and destination maximum burst scheduling delay
maximum burst scheduling delay in the failure-free case failure-compensating scheduling delay
burst transmission delay
time of laser tuning and OXC re-configuration in source-destination path
waiting time of a request Ri in the control node wavelength holding time
LIST OF SYMBOLS 2 2
Wl number of wavelengths per fibre
^ 0 minimum packet size in bits
a network physical connectivity
^E E delay,s-d bounded burst end-to-end delay
Sm ax maximum nodal degree
Smin minimum nodal degree
^ p h ,s-d location-dependent delay
r network graph
A set of links
N set of network edge-routers
Q set of wavelengths per link in a single-fibre network set of source-destination pairs
source-destination pair
Chapter 1
Introduction
The potential of Internet Protocol (IP) technology, coupled with high-capacity wavelength division multiplexing (WDM) optical transport networks, appears to offer the most efficient platform for transmitting Terabit traffic over long distances in the next-generation Internet. The WDM-based transport layer has proved to reduce the cost of core network equipment, whilst significantly increasing transmission capacity [Stel]. At the same time, the IP-over-WDM networking is gradually evolving from static wavelength-routed optical networks (WRONs) towards a fast-switched WDM transport layer, ensuring the increased flexibility and throughput of optical backbones [Weil]. The first breakthrough in the provision of IP services over WDM networks will be the support o f wavelength switching capability, ensuring automatic re configurability of the optical core in response to changes in traffic pattern or network operational conditions [Ser2]. On the longer perspective, optical transport layer is expected to provide further improvement in network resource utilisation and throughput by supporting switching granularity below that of the wavelength level. This can be achieved by employing technologies, based on optical packet switching and/or optical burst switching (e.g., see [Hun2], [Qial]).
INTRODUCTION___________________________________________________________________ 2 ^
1.1 Thesis objectives and structure
Driven by the motivation to overcome the limitations o f existing approaches to QoS provisioning in the IP/WDM architectures, the main objective o f this thesis is the design and detailed investigation of new network models and algorithms, enabling the QoS provisioning framework in fast-switched optical networks. To offer telecom operators a viable solution to the analysis and optimisation of network performance, this framework must effectively support the following functionality:
• The explicit control of QoS parameters, such as burst blocking probability and end- to-end delays, in a given case o f network operational conditions. The latter are determined by a given network physical topology, bandwidth (i.e. the number o f wavelengths per fibre) and traffic loads.
• The support of service differentiation between high-priority and low-priority traffic, whilst bounding the blocking probability of both traffic classes, as well as minimising network wavelength requirements.
• The support of new restoration strategies after the resource failures, to guarantee the required QoS performance under the failure. These restoration strategies should exploit the fast-switching properties o f the optical core to efficiently re-configure active network connections such that the bandwidth restoration capacity is minimised.
This thesis investigates the provision of the above functionality in networks with both the burst-switched core and re-configurable optical core, and is organised as follows. Chapter 2 reviews the evolution path o f the IP/WDM network architectures, classifies approaches, currently proposed for QoS provisioning in each o f these architectures, and discusses their fundamental limitations. To overcome these limitations, this chapter also briefly introduces the concept o f wavelength-routed optical burst switching (WR-OBS).
INTRODUCTION___________________________________________________________________ ^
delivering QoS-guaranteed performance, is proposed. These algorithms are comprehensively evaluated on a realistic network physical topology in terms o f both burst blocking probability and burst end-to-end delays, as well as a function o f traffic load and wavelength requirement. The investigation o f the centralised network model pursues a twofold objective. First, such a model maintains global knowledge on the network state and, hence, gives an upper bound on the performance o f any WR-OBS architecture with the incomplete knowledge, including the distributed WR-OBS. Second, using this model, the advantages and limitations o f the centralised control in terms of QoS provisioning and network resilience are studied in the subsequent chapters. Optimal values o f two WR-OBS controllable parameters, namely, burst aggregation delay and request scheduling delay, are studied under different network operational conditions. The trade-offs between the maximum scheduling delay and burst blocking probability are analysed, whilst taking into account QoS differentiation and fairness strategies for burst servicing. To investigate WR-OBS feasibility in terms of bandwidth utilisation, a comparison between wavelength requirements in WR-OBS, maintaining a given QoS performance, and WRONs, is presented.
Chapter 4 systematically studies, for the first time, WR-OBS QoS performance as a function of network physical connectivity. Upper and lower bounds on WR-OBS wavelength gain over WRONs at a given value o f connectivity are obtained using two sets o f randomly-connected physical mesh topologies, representing, respectively, upper and lower bounds on WRON wavelength requirements (referred to as limiting topologies). Additionally, the WR-OBS QoS performance is investigated when applied to a number o f real optical backbone topologies. The impact o f network physical connectivity is studied in terms of the lower limit on burst aggregation delay, and as a function o f the burst maximum scheduling delay. WR-OBS QoS performance is investigated in both classless and multi-service operational modes, whilst taking into account WR-OBS wavelength gain over WRON architecture.
INTRODUCTION___________________________________________________________________ 2 ^
restoration to pre-defined QoS performance under single link failures, is introduced and thoroughly investigated, again, in terms o f both QoS parameters, and network physical connectivity. Wavelength restoration requirements in WR-OBS are compared with those in WRONs, to identify feasibility o f WR-OBS architecture in the presence of resource failures. The investigation has been carried out using both randomly- connected limiting topologies and real optical backbone networks.
Chapter 6 represents the experimental part of this thesis, which describes the original contributions to the design and implementation o f an integrated IP/WDM network management system (WINMAN software^) for QoS-capable networks with re- configurable optical core, supporting the wavelength switching capability. Architecture of the proposed system is first presented, and the design o f WINMAN WDM routing component, a central part of end-to-end IP service provisioning with QoS guarantees, is discussed. A scenario, which can be used as a framework for rigorous evaluation of the functionality o f any network management system, is described. The outcome of experiments with operational WINMAN system is also discussed.
Finally, Chapter 7 summarises main conclusions of this research work and outlines future directions of investigation.
INTRODUCTION 27
1.2 References
[Hun2] D. Hunter, M. Chia, I. Andonovic, “Buffering in optical packet switches,”
lEEE/OSA lEEE/OSA lEEE/OSA J. Lightwave Technol, Vol. 16, No. 12,
Dec. 1998, pp. 2081-2094
[Kahl] A. Kaheel, T. Khattab, A. Mohamed and H. Alnuweiri, “Quality-of-service mechanisms in IP-over-WDM networks,” IEEE Comm. M ag, Vol. 40, No.
12, Dec. 2002
[Qial] C. Qiao, M. Yoo, “Choices, features and issues in optical burst switching,”
Optical Networks M ag, Vol. 1, No. 2, Apr. 2000, pp. 36-44
[Ser2] J. Serrât, et al., co-edited/co-authored by E. Kozlovski, “Deployment o f IP over WDM networks”, ARTECH House Books, June 2003
[Stel] T. E. Stem, K. Bala, “Multiwavelength Optical Networks: A Layered Approach,” Addison-Wesley, 1999
[Weil] J. Y. Wei, “Advances in the management and control of optical Internet,”
Chapter 2
Challenges in QoS provisioning in
Internet-over-optical network
architectures
2.1 Introduction
The level o f service, maintained by a given traffic transport environment, is the most critical characteristic of network performance from an end-user point o f view. This characteristic imposes a range of stringent requirements on all the functional components involved in the provision of end-to-end IP traffic delivery, including the management software and network hardware capabilities, resource reservation strategies, and underlying network infrastructure. The term '‘quality o f service ’ can be defined as the bounded worst-case of network performance, measured in terms of certain metrics, affecting the end-to-end quality o f IP network applications [Mirl]. The most important network QoS metrics are as follows [Covl], [Mirl]:
• Bandwidth defines the portion of available capacity on an end-to-end network path, which is accessible to an application or a data flow. It imposes a constraint on the amount of bits, admitted by the network from a given application at a given time period. The volume of bandwidth, available to a given application, is governed by the network control/management protocols, as will be shown in chapter 6. At the same time, this parameter is determined by the overall network transport throughput, which motivates the need o f throughput maximisation.
CHALLENGES IN QOS PRO VISIONING IN INTERNET-O VER-OPTICAL NETWORK ARCHITECTURES
This parameter is derived from the combination o f network propagation delay, processing delays, variable queuing delays at intermediate routers on the end-to-end path [Alml], as well as by certain delays, associated with network signalling protocols, as will be discussed in sections 2.5 and 3.3.
• Packet loss, which is caused by the contention o f packets, competing for the same bandwidth. Packet loss rate (PLR) is measured as the fraction o f packets, out of the total number of transmitted packets, which are dropped in the end-to-end path during the transmission.
• Delay variation, or jitter, is the time determined by the variation in delays experienced by individual packets. Jitter is o f special importance at the transport layer, due to the inherent variability in arrival times o f individual packets.
• Loss pattern, or loss period, is determined by the packet loss distribution over time. It has been observed to have a bursty nature, and can be taken into account by the application codecs and error correction mechanisms to reduce QoS deterioration [Yajl]. Since this parameter is mostly dealt with by the application-level protocols, it is not considered in this thesis.
CHALLENGES IN QOS PROVISIONING IN INTERNET-OVER-OPTICAL NETWORK
ARCHITECTURES 30
different types of modem Internet applications, as well as their QoS requirements and supporting high-level protocols, can be found, for instance, in [Mirl].
Application Directio nality
Typical data rates
Upper limit on key performance parameters
One-way delay
PLR Jitter
with no smoothing technique Conversational
voice
Two-way 4-64 kb/s 150ms, preferred
400 ms, limit
1 0% 1 ms
Voice messaging
One-way 4-32 kb/s 1 sec 1 0% 1 ms
Streaming audio
One-way 16-128 kb/s 1 0 sec 1% 1 ms
Video conference
Two-way 5 kb/s-4 Mb/s, MPEG4
28 kb/s-1 Mb/s, H.323
150ms, preferred 400 ms, limit
1 % 1 ms
Streaming video
One-way 5 kb/s-4 Mb/s. MPEG4
28 kb/s-1 Mb/s, H.323
1 0 sec 1 % 1 ms
Table 2.2. QoS performance targets in some data applications [Covl], [Mirll. Zero PLR
Application Directio nality
Typical amount of
data
Upper limit on key performance parameters One-way delay PLR
Web browsing - HTML One-way 10 kB/page 4 sec per page Zero
E-business transactions, e.g. ATM
Two-way 10 kB 2 sec Zero
Command/control, games, telnet
Two way 1 kB 2 0 0 ms Zero
Bulk data transfer One way 100 MB 30 sec Zero
E-mail (server to server) One way 10 k B - 10 MB Several min Zero
Low priority transactions One way 10 k B - 50 MB 30 sec Zero
CHALLENGES IN QOS PROVISIONING IN INTERNET-OVER-OPTICAL NETWORK
ARCHITECTURES 31
behaviour, which packet flows receive at a network node. The DiffServ is implemented using packet scheduling and buffer management techniques that allow different packet classes to be processed according to their QoS characteristics.
At the same time, optical transport layer, rather than pure electronic transport layer, is becoming a global carrier o f the bulk o f Internet traffic. High-capacity WDM transport platforms will be based on the hierarchical model [Butl], interconnecting local-area, wide-area and national/global transport networks, with each layer in the hierarchy having specific transport characteristics [Ser2], shown in Table 2.3.
Table 23. Elements of the optical transport layer hierarchy with expected deployment scenarios [Ser2|. Number of wavelengths in global and wide-area networks is not expected to grow significantly due limited regeneration capabilities, combined with
non-5-10 years > 10 years
Global Area Network Capacity: 4 Tbit/s/fibre Channel speed: 20 - 40 Gbit/s Number o f wavelengths: <200
Unregenerated distance: > 10 000 km OADM & switched nodes: small number
Global Area Network Capacity: 16 Tbit/s/fibre
Channel speed: 8 0 - 100 Gbit/s Number of wavelengths: <200
Unregenerated distance: > 10 000 km Increased number of OXCs & OADMs Wide Area Network
Capacity: 10 Tbit/s/fibre Channel speed: 2.5 - 40 Gbit/s Number of wavelengths: 100 - 256 Unregenerated distance: 500 - 4 500 km 0 X 0 1 0 0 0 X 1000
Wide Area Network Capacity: 20 Tbit/s/fibre
Channel speed: 4 0 - 1 6 0 Gbit/s Number of wavelengths: 200 - 500 Unregenerated distance: 500 - 5 500 km OXC >5000 X 5000
Metropolitan Area Network Capacity: 10 Tbit/s/fibre Channel speed: 2.5 - 40 Gbit/s Number of wavelengths: 10 - 1000 Distance 20 - 200 km
Metropolitan Area Network Capacity: 40 Tbit/s/fibre
Channel speed: 10 - 640 Gbit/s Number o f wavelengths: 100 - 500 Distance 100 - 200 km
Access Network Capacity:
rings <1 Tbit/s/fibre PONs < 1 /2 5 0 Gbit/s/fibre (down/up)
Channel speed:
meshed < 1 0 Gbit/s
PONs < 1 0 /2 .5 Gbit/s (down/up) Number of wavelengths: < 100
Distance: < 20 km
Access Network Capacity:
rings <10 Tbit/s/fibre PONs < 1 0 /2 .5 Tbit/s/fibre (down/up)
Channel speed:
meshed < 40 Gbit/s
PONs < 4 0 /1 0 Gbit/s (down /up) Number o f wavelengths: < 250
CHALLENGES IN QOS PROVISIONING IN INTERNET-OVER-OPTICAL NETWORK ARCHITECTURES
As evidenced by extensive research (e.g., see [Weil] and references therein), to deliver a next-generation platform, optimised in terms o f QoS provisioning, optical transport layer should natively support high level networking functionality. The latter includes the dynamic adaptability of the optical core to changes in traffic pattern, the provision o f prioritised traffic routing, as well as the real-time execution of protection/restoration schemes. As discussed in sections 2.3-2.S, the main challenge in the development o f such functionality is the introduction o f new IP-over-WDM switching technologies. This is because these technologies must allow for smooth integration of the IP and WDM network layers, whilst maximising the overall network throughput and ensuring QoS performance in the WDM domain. Such technologies can be classified according to the supported switching time-scales in the optical domain that are gradually progressing from pure static point-to-point WDM connections to dynamically-switched optical core [Ser2], as discussed in the subsequent sections. However, the QoS provisioning in WDM networks cannot be based on the frameworks proposed for the implementation in IP networks. This is because at present, there is no optical counterpart to the store-and-forward model, which is based on random access memory (RAM), used for packet scheduling and contention resolution in electronic IP routers (as discussed, for instance, in [Hun2], [Kahl]). Hence, there is a motivation to devise new QoS provisioning models in IP/WDM networks that adapt to the limitations and functional characteristics of the optical domain.
The reminder o f this chapter reviews the evolution o f the IP-over-WDM switching technologies and analyses the associated open issues in addressing the problem of QoS provisioning in the optical domain.
2.2 QoS in static wavelength-routed optical networks
(WRON)
C H ALLEN G ES IN QO S PROVISIONIN G IN INTERN ET-OVER-OPTIC AL N E T W O R K
ARC H ITE C T U RE S 33
relies on SDH layer, which takes care of both packet framing and operations associated
with network management [Weil]. In quasi-static WRONs, the IP routers are directly
interconnected with each other via multi-wavelength links, and the neighbouring router
for each router interface is fixed, as shown in Figure 2.1. Hence, the entire network
logical topology is also fixed, and the network connections are quasi-static.
En d-to-end IP connectivity
IP layer
fixed lightpath (R .-^ R .) fixed lightpath (R .-^R ^)
WDM layer
Electronic IP router with underlying SDH equipment
^ Static OXC
Figure 2.1. IP over static WRONs. An example of two fixed lightpaths, (R2—>R4) and
(Rz-^Rj), sharing the same fibre between nodes Rzand R3. For simplicity, the case of uni
directional connectivity is shown.
WRONs are based on the wavelength-routing within the nodes, as was
suggested in [KobI], [Hill], which enables high-capacity optical signals to be routed
via the dedicated wavelengths [Youl]. The wavelength routing provides network
node-pairs with end-to-end optical channels, known as optical paths, or lightpaths,
[Chl2], that maintain the full-mesh network logical topology.
The network nodes in WRONs are referred to as wavelength-routing nodes, or
optical cross-connects (OXCs) [ChiI], [Youl]. A single-hop network logical topology
ensures that each connection request is serviced by a dedicated lightpath, which is
established from source to destination (end-to-end) and maintained quasi-permanently
[Mukl]. This approach eliminates processing at intermediate nodes, as opposed to a
CHALLENGES IN QOS PRO VISIONING IN INTERNET-O VER-OPTICAL NETWORK ARCHITECTURES
wavelengths, does not provision an entire lightpath for all the node-pairs, and, hence, requires processing to share the available optical bandwidth.
The problem o f setting up lightpaths by means of routing and assigning a wavelength to each connection is referred to as the routing and wavelength assignment
(RWA) problem [Bar4], [Zanl], [Nagl]. Because in static WRONs, the requests for lightpath connections are assumed to be known a-priori, the routing and wavelength assignment can be carried out off-line. The objective o f this procedure is to minimise the number of wavelengths needed to support a given set o f lightpaths for a given physical topology (e.g., see [Bari]).
The wavelength routing and assignment problem can be formulated as an integer linear programme (ILP) [Rami], which was shown to be NP-complete [Chl2], [Bar4]. The initially proposed efficient heuristic approaches to RWA solution in WRONs, mostly applied to either ring or regular network physical topologies, can be found in [Stel], [Bar4] and in references therein.
To make the problem more tractable, it can be divided into two sub-problems, specifically, the sub-problem of routing and the sub-problem o f wavelength assignment, with each o f them to be solved separately. Near-optimal heuristic algorithms, based on such separation technique, have been proposed and investigated in [Bari], [Bar2] and [Bar3], together with the relationship between WRON wavelength requirements and network physical connectivity. It was also shown that networks with
wavelength conversion capability, (i.e. the ability o f a lightpath to use different wavelengths in each of the links on its path [Subl], [Ram2]), do not significantly outperform networks with wavelength continuity constraint in terms of wavelength requirements under static wavelength assignment [Bari]. This behaviour was observed for a number o f single-fibre real network physical topologies with values o f network physical connectivity ranging from 0.07 to 0.45, and full wavelength interchange supported in each node [Bari], [Bar4].