WILEY Core and metro networks User Manual
CORE AND METRO
NETWORKS
WILEY SERIES IN COMMUNICATIONS NETWORKING
& DISTRIBUTED SYSTEMS
Series Editors: David Hutchison, Lancaster University, Lancaster, UK
Serge Fdida, Universite´Pierre et Marie Curie, Paris, France
Joe Sventek, University of Glasgow, Glasgow, UK
The ‘Wiley Series in Communications Networking & Distributed Systems’ is a series of
expert-level, technically detailed books covering cutting-edge research, and brand new
developments as well as tutorial-style treatments in networking, middleware and software
technologies for communications and distributed systems. The books will provide timely and
reliable information about the state-of-the-art to researchers, advanced students and
development engineers in the Telecommunications and the Computing sectors.
Other titles in the series:
Wright: Voice over Pac ket Networks 0-471-49516-6 (February 2001)
Jepsen: Java for Telecommunications 0-471-49826-2 (July 2001)
Sutton: Secure Communications 0-471-49904-8 (December 2001)
Stajano: Security for Ubiquitous Computing 0-470-84493-0 (February 2002)
Martin-Flatin: Web-Based Management of IP Networks and Systems 0-471-48702-3
(September 2002)
Berman, Fox, Hey: Grid Computing. Making the Global Infrastructure a Reality
0-470-85319-0 (March 2003)
Turner, Magill, Marples: Service Provision. Technologies for Next Generation
Communications 0-470-85066-3 (April 2004)
Welzl: Network Congestion Control: Managing Internet Traffic 0-470-02528-X (July 2005)
Raz, Juhola, Serrat-Fernandez, Galis: Fast and Efficient Context-Aware Services
0-470-01668-X (April 2006)
Heckmann: The Competitive Internet Service Provider 0-470-01293-5 (April 2006)
Dressler: Self-Organization in Sensor and Actor Networks 0-470-02820-3 (November 2007)
Berndt: Towards 4G Technologies: Services with Initiative 0-470-0 1031-2 (Ma rch 2008)
Jacquenet, Bourdon, Boucadair: Service Automation and Dynamic Provisioning Techniques in
IP/MPLS Environments 0-470-01829-1 (March 2008)
Minei/Lucek: MPLS-Enabled Applications: Emerging Developments and New Technologies,
Second Edition 0-470-98644-1 (April 2008)
Gurtov: Host Identity Protocol (HIP): Towards the Secure Mobile Internet 0-470-99790-7
(June 2008)
Boucadair: Inter-Asterisk Exchange (IAX): Deployment Scenarios in SIP-enabled Networks
0-470-77072-4 (January 2009)
Fitzek: Mobile Peer to Peer (P2P): A Tutorial Guide 0-470-69992-2 (June 2009)
Shelby: 6LoWPAN: The Wireless Embedded Internet 0-470-74799-4 (November 2009)
CORE AND METRO
NETWORKS
Editor
Alexandros Stavdas
University of Peloponnese, Greece
This edition first published 2010
Ó 2010 John Wiley & Sons Ltd.,
Except for:
Chapter 1, ‘The Emerging Core and Metropolitan Networks’ Ó 2009 Angel Ferreiro and Telecom Italia S.p.A
Chapter 4, Section 4.5.1–4.5.5 and 4.5.7 Ó 2009 Telecom Italia S.p.A
Chapter 5, Section 5.2–5.6 Ó 2009 Telecom Italia S.p.A
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Library of Congress Cataloging-in-Publication Data
Core and metro networks / edited by Alexandros Stavdas.
p. cm.
Includes bibliographical references and index.
ISBN 978-0-470-51274-6 (cloth)
1. Metropolitan area networks (Computer networks) I. Stavdas, Alexandros A.
TK5105.85.C678 2010
004.67–dc22
A catalogue record for this book is available from the British Library.
ISBN 9780470512746 (H/B)
Set in 10/12 pt Times Roman by Thomson Digital, Noida, India
Printed and Bound in Singapore by Markono Pte.
2009044665
Contents
Preface ix
1 The Emerging Core and Metropolitan Networks 1
Andrea Di Giglio, Angel Ferreiro and Marco Schiano
1.1 Introduction 1
1.1.1 Chapter’s Scope and Objectives 1
1.2 General Characteristics of Transport Networks 1
1.2.1 Circuit- and Packet-Based Network Paradigms 2
1.2.2 Network Layering 3
1.2.3 Data Plane, Control Plane, Management Plane 4
1.2.4 Users’ Applications and Network Services 4
1.2.5 Resilience 5
1.2.6 Quality of Service 7
1.2.7 Traffic Engineering 8
1.2.8 Virtual Private Networks 10
1.2.9 Packet Transport Technologies 11
1.3 Future Networks Challenges 12
1.3.1 Network Evolution Drivers 12
1.3.2 Characteristics of Applications and Related Traffic 12
1.3.3 Network Architectural Requirements 17
1.3.4 Data Plane, Control Plane, and Management Plane Requirements 24
1.4 New Transport Networks Architectures 31
1.4.1 Metropolitan Area Network 33
1.4.2 Core Network 36
1.4.3 Metro and Core Network (Ultra-long-term Scenario) 38
1.5 Transport Networks Economics 39
1.5.1 Capital Expenditure Models 39
1.5.2 Operational Expenditure Models 42
1.5.3 New Business Opportunities 44
Acronyms 52
References 54
vi Contents
2 The Advances in Control and Management for Transport Networks 55
Dominique Verchere and Bela Be rde
2.1 Drivers Towards More Uniform Management and Control Networks 55
2.2 Control Plane as Main Enabler to Autonomic Network Integration 58
2.2.1 Generalized Multi-Protocol Label Switching 59
2.2.2 Evolution in Integrated Architectures 71
2.3 Multilayer Interactions and Network Models 74
2.3.1 Introduction 74
2.3.2 Vertical Integration and Models 78
2.3.3 Horizontal Integration and Models 79
2.3.4 Conclusions on UNI Definitions from ITU-T, OIF, IETF,
and OIF UNI: GMPLS UNI Interoperability Issues 104
2.4 Evolution of Connection Services and Special Cases of Optical Networks 105
2.4.1 Evolution in Network Services 105
2.4.2 Virtual Private Networks 106
2.4.3 Layer 1 VPN 109
2.4.4 Layer 2 VPN 118
2.4.5 Layer 3 VPN 122
2.5 Conclusion 123
References 124
3 Elements from Telecommunications Engineering 127
Chris Matrakidis, John Mitchell and Benn Thomsen
3.1 Digital Optical Communication Systems 127
3.1.1 Description of Signals in the Time and Frequency Domains 127
3.1.2 Digital Signal Formats 132
3.2 Performance Estimation 135
3.2.1 Introduction 136
3.2.2 Modeling 141
3.2.3 Comparison of Techniques 146
3.2.4 Standard Experimental Measurement Procedures 149
References 158
4 Enabling Technologies 161
Stefano Santoni, Roberto Cigliutti, Massimo Giltrelli, Pasquale Donadio,
Chris Matrakidis, Andrea Paparella, Tanya Politi, Marcello Potenza,
Erwan Pincemin and Alexandros Stavdas
4.1 Introduction 161
4.2 Transmitters 161
4.2.1 Introduction 161
4.2.2 Overview of Light Sources for Optical Communications 167
4.2.3 Transmitters for High Data-Rate Wavel ength-Division
Multiplexing Systems 178
Contents vii
4.3 Receiver 202
4.3.1 Overview of Common Receiver Compone nts 202
4.4 The Optical Fiber 212
4.4.1 Short Introduction to the Waveguide Principle 213
4.4.2 Description of Optical Single-Mode Fibers 216
4.4.3 Special Fiber Types 222
4.5 Optical Amplifiers 223
4.5.1 Introduction to Optical Amplifiers 225
4.5.2 Principle of Operation 229
4.5.3 Gain Saturation 231
4.5.4 Noise 234
4.5.5 Gain Dynamics 235
4.5.6 Optical Fiber and Semiconductor Optical Amplifiers 236
4.5.7 Raman Amplifiers 239
4.5.8 Lasers and Amplifiers 243
4.6 Optical Filters and Multiplexers 245
4.6.1 Introduction 245
4.6.2 Optical (De-)Multiplexing Devices 246
4.6.3 Overall Assessment of (De-)Multiplexing Techniques 256
4.6.4 Optical Filters 257
4.6.5 Tunable Filters 260
References 263
5 Assessing Physical Layer Degradations 267
Andrew Lord, Marcello Potenza, Marco Forzati and Erwan Pincemin
5.1 Introduction and Scope 267
5.2 Optical Power Budgets, Part I 268
5.2.1 Optical Signal-to-Noise Ratio and Q Factor 268
5.2.2 Noise 273
5.2.3 Performance Param eters. Light Path Evaluation Rules 290
5.2.4 Transmission Impairments and Enhancements: Simple
Power Budgets 295
5.3 System Bandwidth 334
5.3.1 System Bandwidth, Signal Distortion, Intersymbol Interference 334
5.3.2 Fiber-Optical Nonlinear Effects 346
5.3.3 Optical Transients 356
5.4 Comments on Budgets for Nonlinear Effects and Optical Transients 362
5.4.1 Compensators/Equalizers 363
5.4.2 CD Equalization 363
5.4.3 PMD Equalization 364
5.4.4 Simultaneous Presence of Distortions, Electronic Equalization,
and Cumulative Filtering 364
5.4.5 General Features of Different Modulation Formats 368
5.5 Semianalytical Models for Penalties 370
5.6 Translucent or Hybrid Networks 370
5.6.1 Design Rules for Hybrid Networks 371
viii Contents
5.7 Appendix 372
5.7.1 Dispersion Managed Links 372
5.7.2 Intrachannel Nonlinear Effects 374
References 378
6 Combating Physical Layer Degradations 381
Herbert Haunstein, Harald Rohde, Marco Forzati, Erwan Pincemin,
Jonas Martensson, Anders Djupsj€obacka and Tanya Politi
6.1 Introduction 381
6.2 Dispersion-Compensating Components and Methods for CD and PMD 382
6.2.1 Introduction on Optical CD and PMD Compensator
Technology 382
6.2.2 Optical Compensation Schemes 383
6.2.3 Key Parameters of Optical Compensators 387
6.2.4 Compensators Suitable for Translucent Networks 389
6.2.5 Impact of Group-Delay Ripple in Fiber Gratings 391
6.3 Modulation Formats 396
6.3.1 On–Off Keying Modulation Formats 397
6.3.2 Comparison of Basic OOK Modulation Formats: NRZ,
RZ, and CSRZ for 40 Gbit/s Transmission 400
6.3.3 A Power-Tolerant Modulation Format: APRZ-OOK 408
6.3.4 DPSK Modulation Formats 412
6.3.5 Spectrally Efficient Modulation Formats 414
6.4 Electronic Equalization of Optical Transmission Impairments 416
6.4.1 Electronic Equalization Concepts 416
6.4.2 Static Performance Characterization 420
6.4.3 Dynamic Adaptation of FFE- and DFE-Structures 420
6.4.4 General Remarks 423
6.5 FEC in Lightwave Systems 424
6.5.1 Application of FEC in Lightwave Systems 424
6.5.2 Standards for FEC in Lightwave Systems 425
6.5.3 FEC Performance Characterization 426
6.5.4 FEC Application in System Design 429
6.6 Appendix: Experimental Configuration and Measurement Procedure
for Evaluation and Comparison for Different Modulation Formats
for 40 Gbit/s Transmission 431
6.6.1 Simulation Setup 434
Acknowledgments 435
References 435
Dictionary of Optical Networking 441
Didier Colle, Chris Matrakidis and Josep Sole-Pareta
Acronyms 465
Index 477
Preface
It is commonly accepted today that optical fiber communications have revolutionized
telecommunications. Indeed, dramatic changes have been induced in the way we interact
with our relatives, friends, and colleagues: we retrieve information, we entertain and
educate ourselves, we buy and sell, we organize our activities, and so on, in a long list
of activities. Optical fiber systems initially allowed for a significant curb in the cost of
transmission and later on they sparked the process of a major rethinking regarding some,
generation-old, telecommunication concepts like the (OSI)-layer definition, the lack of
cross-layer dependency, the oversegmentation and overfragmentation of telecommunications networks, and so on.
Traditionally, telecommunications are classified based on the physical properties of the
channel; that is, fixed-line/wired-communications and wireless/radio communications.
Following this classification, it can be safely a rgued that today’s core networks and metropolitan area networks (metro networks for simplicity) are almost entirely based on optical
fiber systems. Moreover, the penetration of optical fiber communications in the access segment
is progressing at an astonishing rate, although, quite often, it is the competition between
providers, the quest for higher profits based on the established technological framework, and
the legislative gridlocks that prevent an even faster adoption of this technology. Thus, a fullscale deployment of optical fiber systems in the access networks, through fixed/wireless
convergence, could further reduce the role of wireless technology in transporting bandwidth
over a reasonably long distance. Evidently, optical-fiber-based networks are the dominant
technology, literally the backbone, of the future Internet. The fields of this technology are
diverse and its engineering requires knowledge that extends from layer 1 to layer 3.
Many excellent basic text and specialized books are available today aiming to educate and/or
inform scientists, engineers and technicians on the essentials in the field of optical technology.
However, there is a pressing need for books presenting both comprehensive guidelines for
designing fiber-optic systems and core/metro network architectures and, simultaneously,
illustrating the advances in the state of the art in the respective fields. IST-NOBEL (I and
II) was a large-scale research project funded from the Framework Programme 6 of the
European Commission, incorporating major operators, system vendors and leading European
universities. Employing a large number of experts in several fields, the project decided to
collectively produce such a book as part of the disseminating activities. Thus, a considerable
part of this book is based on the deliverables of IST-NOBEL with significant effort made to
provide the necessary introduction of concepts and notions. The objective was to make it
readable for a non-highly specialized audience, as well as to demystify the necessity behind the
introduction of this or that novelty by clearly stating the underlying “need.” It is left to the
readers to decide whether we have succeeded in our goals.
x Preface
The contributors to this book would like to acknowledge the immense help and support of
their colleagues in the IST-NOBEL project that contributed to the preparation of the
respective d eliverables. A separate, specia l, acknowledgment is for the IST-NOBEL I and
II project leaders and colleagues from Telecom Italia, Antonio Manzalini, Marco Schiano,
and Giuseppe Ferraris. Also, the editor is extremely grateful to Andreas Drakos and Penny
Papageorgopoulou, PhD candidates in the University of Peloponnese, for their help in
preparing the final manuscript.
Alexandros Stavdas
Department of Telecommunications Science and Technology
University of Peloponnese, Greece
1
The Emerging Core and Metropolitan Networks
Andrea Di Giglio, Angel Ferreiro and Marco Schiano
1.1 Introduction
1.1.1 Chapter’s Scope and Objectives
The study of transport networks is a vast and highly multidisciplinary field in the modern
telecommunication world. The beginner who starts studying this technical subject may remain
astonished by the variety and complexity of network architectures and technologies that have
proliferated in the last decade. Even an expert in the field may get disoriented in the huge variety
of networks’ functions and characteristics.
This introductory chapter is devoted to the definition of transport networks’ fundamentals
representing the very basic “toolbox” of any expert in the field. Furthermore, it investigates
transport network architectural evolution in terms of new network services supporting
emerging users’ applications.
The chapter is structured as follows. Section 1.2 contains the definitions of the basic network
concepts used throughout the book. Sections 1.3 and 1.4 describe the requirements and the
architectural evolution roadmap of transport networks based on emerging users’ applications.
Finally, Section 1.5 shows the economic models and analysis techniques that enable the design
and realization of economically sustainable transport services.
1.2 General Characteristics of Transport Networks
For more than a century, the traditional vision of telecommunication networks has been a smart
combinationof transmissionand switching technologies. Even if transmissionand switchingare
still the basic building blocks of any network, telecommunication networks fundamentals cover
a much broader scope nowadays. This new vision is primarily due to the introduction of digital
Chapter 1, ‘The Emerging Core and Metropolitan Networks’, Ó 2009 Angel Ferreiro and Telecom Italia S.p.A from
Core and Metro Networks, edited by A. Stavdas, 2009
2 The Emerging Core and Metropolitan Networks
technologies paving the way to packet-based networks. In contrast to old analog networks,
packet-based digital networks can be either connectionless or connection oriented, can have a
control plane for the automation of some functions, can implement various resilience schemes,
can perform a number of network services supporting users’ applications, and so on.
The essential ideas are explained in this section as a background for the entire chapter.
1.2.1 Circuit- and Packet-Based Network Paradigms
Digital networks can transfer information between nodes by means of two fundamental
paradigms: circuit switching or packet switching.
.
In circuit-switched networks, data are organized in continuous, uninterrupted bit streams.
In this mode of operation, a dedicated physical link between a couple of nodes is established.
Before starting the data transfer on a specific connection, the connection itself must be
“provisioned”; that is, the network switching nodes must be configured to provide the
required physical link. This implies an exclusive allocation of network resources for
the whole duration of the connection. Such a task is usually performed by dedicated
elements belonging to the network control system; network resources are released when
the connection ends.
This is the way that the plain old telephony service (POTS) has been working so far. The
private reservation of network resources prevents other connections from using them while
the first one is working, and may lead to inefficient network use.
.
In packet-switched networks, data are organized in packets of finite length that are processed
one by one in network nodes and forwarded based on the packet header information. In this
network scenario, each packet exploits switching and transmission devices just for the time
of its duration, and these network resources are shared by all packets. This process of packet
forwarding and aggregation is called statistical multiplexing and represents the major benefit
of packet-switched networks with respect to the circuit-switched networks in terms of
network exploitation efficiency.
Typical examples of circuit-switching and packet-switching technologies are synchronous
digital hierarchy (SDH) and Ethernet resp ectively.
Packet-switched networks can, in turn, work in connectionless or connection-oriented
network modes.
.
In the connectionless networ k mode, packets are forwarded hop by hop from source node to
destination node according to packet header information only, and no transfer negotiation
is performed in advance between the network nodes involved in the connection; that is, the
source node, optionally the intermediate node(s) and the destination node.
.
In the connection-oriented network mode, packet transfer from source node to dest ination
node is performed through defined resource negotiation and reservation schemes between the
network nodes; that is, it is preceded by a connection set-up phase and a connection usage
phase, followed by a connection tear-down phase.
Typical examples of packet-switched connectionless and connection-oriented network
protocols are Internet protocol (IP) and asynchronous transfer mode (ATM) respectively.
General Characteristics of Transport Networks 3
The main characteristic of the connectionless network mode is that packets are routed
throughout the network solely on the base of the forwarding algorithms working in each
node; hence, packet routes may vary due to the network status. For instance, cable faults
or traffic overloads are possible causes of traffic reroute: in the connectionless network mode,
the new route of a packet connection is not planned in advance and, in general, is
unpredictable.
On the contrary, in the connection-oriented network mode, the route of any connection is
planned in advance and, in the case of faults, traffic is rerouted on a new path that can be
determined in advance.
Since route and rerouting have strong impacts on the quality of a packet connection, the two
network modes are used for different network services depending on the required quality and
the related cost.
1.2.2 Network Layering
The functions of a telecommunication network have become increasingly complex. They
include information transfer, traffic integrity and survivability aspects, and network management and performance monitoring, just to mention the main ones. To keep this growing
complexity under control and to maintain a clear vision of the network structure, layered
network models have been developed. According to these models, network functions are
subdivided into a hierarchical structure of layers. Each layer encompasses a set of homogeneous network functions duly organized for providing defined services to the upper layer, while
using the services provided by the lower layer. For example, in an Ethernet network, the
physical layer provides data transmission services to the data link layer.
To define transport network architectures, it is essential to start from the description of the
lowest three layers [1]: network, data link, and physical layers:
.
Network layer. The main task of the network layer is to provide routing functions. It also
provides fragmentation and reassembly of data at the endpoints. The most common layer 3
technology is the IP. It manages the connectionless transfer of data across a router-based
network.
.
Data-link layer. This provides frames, synchronization, and flow control. The data link
layer also performs transfer of data coming from the network layer. Typical examples of datalink layers are point-to-point protocol and Ethernet MAC (medium/media access control)
(IEEE 802.1xx).
.
Physical layer. The physical layer defines the transmission media used to connect devices
operating at the upper layer (e.g., data link). Physical media can be, for example, copper-wire
pairs, coaxial cables or, more frequently, single-mode or multimode optical fibers. The
physical layer also defines modulation encoding (e.g., Manchester, 8B/10B) or topology
(e.g., ring, mesh) [2]. Most common technologies implementing layer 1 functionalities are
Ethernet (physical layer, IEEE 802.3xx), SDH and optical transport network (OTN).
It is commonly agreed that the Open System Interconnection (OSI) model is an excellent
place to begin the study of network architecture. Nevertheless, the network technologies
commercially available do not map exactly with the levels described in the OSI basic model.
4 The Emerging Core and Metropolitan Networks
1.2.3 Data Plane, Control Plane, Management Plane
The layered network models encompass all network functions related to data transfer.
However, modern transport networks are often provided with additional functions devoted
to network management and automatic network control. Hence, the totality of network
functions can be classified into three groups named planes: the data plane, the management
plane and the control plane.
The functions that characterize each plane are summarized below.
.
Data plane. The data plane aims at framing and carrying out the physical transportation of
data blocks to the final destination. This operation includes all transmission and switching
functions.
.
Control plane. The control plane performs the basic functions of signaling, routing and
resource discovery. These are essential operations to introduce automation on high level
network functions such as: connection establishment (i.e., path computation, resource
availability verification and connection signaling set-up and tear-down), reconfiguration
of signaled connections and connection restoration in case of network faults.
.
Management plane. The management plane performs management functions like alarm
reporting, systems configuration and connection provisioning for data and control planes.
The complexity of the management plane depends strongly on the availability of a control
plane. For example, the management plane of traditional circuit-switched public switched
telephone networks is more cumbersome than transport networks with a control plane, since,
in the latter case, certain tasks (e.g., connection provisioning and restoration) are carried out
by the control plane itself.
1.2.4 Users’ Applications and Network Services
The current challenge of evolving telephony-dedicated transport networks towards enhanced
communication architectures is set by two fundamental trends.
First, services offered today to final users are much richer than simple telephony. User
services like video telephony, video on demand, and Web browsing require an advanced
terminal, typically a personal computer with dedicated software; for this reason, they will be
called “user applications” or simpl y “applications” from now on.
Second, to convey these end-user applications, transport networks are relying on “network
services,” which effectively refer to a number of transfer modes.
As an example, a point-to-point unprotected circuit connection at 2 Mbit/s represents a
specific transfer mode. Other examples of network services are connections based on packet
paradigms; for example, IP/multi-protocol label switching (MPLS), ATM or Ethernet. Today,
all modern applications make reference to packet-based network services.
The idea of a transport network able to provide many different services is one of the most
challenging of recent years and it will be analyzed in detail in the following chapt ers.
Network services and user applications can be provided by different actors. Network
operators that own and manage the networks are typical providers of network services. Service
providers sell and support user applications by means of network services supplied by network
operators.
General Characteristics of Transport Networks 5
Important user application categories are:
.
multimedia triple play – voice, video and high-speed Internet;
.
data storage for disaster recovery and business continuity;
.
grid computing; that is, computing services delivered from distributed computer
networks.
The last two categories, storage and grid computing, are dedicated to business company
customers and research institutions. On the contrary, multimedia applications address residential customers and the small office, home office.
Examples of network services are:
.
time-division multiplexing (TDM) connections and wavelength connections (e.g., leased
lines);
.
Ethernet point-to-point, point-to-multipoint (p2mp) or rooted multipoint connections;
.
virtual private networks (Section 1.2.8).
Each user application is enabled by a network service characterized by specific attributes. A list
of the most important ones is shown below.
.
Protocols: Ethernet and IP are the most common.
.
Bandwidth: committed peak, committed average bit-rate, excess peak and excess bitrate [3].
.
Quality of service (QoS): regarding transport networks, this is defined by mea ns of the
maximum allowed packet loss rate (PLR), the packet latency (i.e., the packet transmission
delay), and jitter (latency variation); see Section 1.2.6.
.
Resilience: required connection availability (Section 1.2.5).
These service attributes are the main inputs for a network provider to design a multi-service
network, in support of a number of defined applications.
1.2.5 Resilience
One of the most important features of transport networks is their ability to preserve live traffic
even when faults occur. This feature is generally referred to as “resilience.”
In transport networks, resilience is usually achieved by duplication of network resources. For
example, a fiber-optic link between a couple of nodes can be duplicated to assure survivability
to cable breaks. Similarly, the switching matrix of an exchange node can be duplicated to
guarantee service continuity in the case of electronics faults.
The way these extra resources are used depends strongly on networ k topology (rings or
meshed network configurations), equipment technology (packet or circuit switching, network
mode, optical transmission), and traffic protection requirements. However, the following
general definitions help understanding the fundamental resilience schemes.
6 The Emerging Core and Metropolitan Networks
1. If the connections for traffic protection are organized in advance, the resilience mechanism
is called “protection.”
a. 1 þ1 protection (also called dedicated protection). The whole traffic of a connection
is duplicated and transmitted through two disjoint paths: the working and the protection
path simultaneously. The receiving node switches between the two signals in the case
of failure. The trigger of 1 þ1 protection is the received signal quality; for example,
the received power level or the bit error rate (BER). Since no complex network protocols
are needed, 1 þ1 protectio n works very quickly, typically within 50 ms. The drawback of
this protection scheme is duplication of network resources.
b. 1: 1 protection (also called protection with extra traffic). The working connection is
protected with one backup connection using a disjoint path. The working traffic is sent
over only one of the connections at a time; this is in contrast to dedicated protection,
where traffic is always bridged onto two connections simultaneously. Under normal
conditions (no network failure) the protecting connection is either idle or is carrying
some extra traffic (typically best-effort traffic). Configuring 1: 1 protection depends
on the control plane’s ability to handle extra traffic, that is, whether it supports the
preemption of network resources for allocating them to the working traffic once it has
been affected by the failure. The ingress node then feeds the working traffic on the
protecting connection in the case of failure. The trigger of 1: 1 protection is the reception
of network failure notification messages. Protection with extra traffic has two main
drawbacks: the need to duplica te working traffic resources onto the protection path and,
in the case of resource contention, the possibility that extra traffic may be interrupted
without effective need.
c. M: N protection (also called shared protection). M working connections are protected
by N backup connections on a disjoint path (N M). The traffic is no longer duplicated
because backup connections can carry traffic initially transported by any one of the
working connections in the case of fault. Thus, switching to backup connections requires
first knowing their availability and then performing traffic switching. Signaling is needed
for failure notification and backup connection activation. Once failure has been repaired,
traffic is reassigned to the working connection and the resources of the backup
connection are available again for protection. In any case, this protection mechanism
allows resource savings with respect to 1 þ1 protection.
Both protection mechanisms, dedicated and shared, are used in rings and meshed network
configurations. The main advantage of protection is its quick operation, since the backup path is
predefined and network resources are pre-allocated.
2. Alternatively to protection, restoration is the resilience mechanism that sets up new backup
connections after failure eventsby discovering, routing, and setting up new links “on the fly”
among the network resources still available after the failure. This is achieved by the
extension of signaling, routing, and discovery para digms typical of IP networks. In fact,
to restore a connection, switching nodes need to discover the network topology not affected
by the failure, thus allowing one to compute a set of candidate routes, then to select a new
route, and to set up the backup connections. Discovery, routing algorithms, and signaling
functions embedded in commercial IP/MPLS routers can quite easily implement restoration. On the other hand, transport network equipment needs a dedicated control plane to
perform such functions.
General Characteristics of Transport Networks 7
Table 1.1 Indicative figures for network availability
Availability (%) N-Nines Downtime time (minutes/year)
99 2-Nines 5000
99.9 3-Nines 500
99.99 4-Nines 50
99.999 5-Nines 5
99.9999 6-Nines 0.5
Usually, the resilience level of a network service (e.g., a leased line or an Ethernet
connection, as defined in Section 1.2.4) is made precise through a number of parameters; the
most important are:
.
Mean time to failure (MTTF): the reciprocal of the failure rate, for systems being replaced
after a failure.
.
Mean time to repair (MTTR): this depends on the repair time of a network fault.
.
Mean time between failures (MTBF): this is the sum of MTTF and MTTR and defines the
mean time interval between successive failures of a repairable system ; it is a measure of
network component reliability.
.
Maximum recovery time: this is the maximum delay between a failure injuring a network
service and the restoration of the service over another path; in other words, the maximum
time during which the network service is not available. It accounts for MTTR and all other
possible delays affecting complete system recovery (signaling, rerouting).
The same concept can be given a different flavor, insisting on network status instead of
duration:
.
Unavailability: the probability that the network service is not working at a given time and
under specified conditions; it is the ratio MTTR/MTBF. Some indicative numbers for
network availability are illustrated in Table 1.1.
1.2.6 Quality of Service
Network services are characterized by a set of parameters that define their quality (QoS).
.
BER: this is a physical-layer parameter, manifesting the fraction of erroneous bits over the
total number of transmitted bits. It is closely related to design rules applied to the physical
layer transport network. It is studied in detail in Chapter 3.
.
PLR: in packet-switched services, this is the fraction of data packets lost out of the total
number of transmitted packets. Packets can be dropped due to congestion, or due to
transmission errors or faults.
.
Latency: the time needed for carrying data from the source node to the destination node.
Latency is caused by the combination of signal propagation delay, data processing delays,
and queuing delays at the intermediate nodes on the connection [3].
.
Latency variation: the range of variation of the latency mainly due to variable queuing
delays in network nodes or due to data segmentation and routing of data blocks, via different
physical paths (a feature readily available in next-generation (NG)-synchronous optical
network (SONET)/SDH). Also, queuing delay variations may occur in the case of traffic
8 The Emerging Core and Metropolitan Networks
overload in nodes or links. An excess of latency variation can cause quality degradation in
some real-time or interactive applications such as voice over IP (VoIP) and video over IP
(IP television (IPTV)).
.
Service unavailability: this has already been defined in Section 1.2.5.
For connection-oriented network services, the definition of QoS also includes:
.
Blocking probability: the ratio between blocking events (failure of a network to establish a
connection requested by the user, because of lack of resources) and the number of attempts.
.
Set-up time: delay between the user application request time and the network service actual
delivery time.
Current packet-based networks are designed to satisfy the appropriate level of QoS for
different network services. Table 1.2 shows suitable values of QoS parameters for the main
users’ applications. As an example, applications like voice or videoconference need tight
values of latency and latency variation. Video distribution is more tolerant to latency variation,
but it needs low packet loss, since lost packets are not retransmitted. File transfer (e.g., backup)
does not have strong requirements about any QoS parameters, since the only requirement is to
transfer a pre-established amount of data in a fixed time interval.
1.2.7 Traffic Engineering
In complex meshed networks, careful traffic engineering (TE) and resource optimization is a
mandatory requirement providing network management and operation functions at reasonable
capital expenditure (CAPEX) and operational expenditure (OPEX). Towards this end, the use
of conventional algorithms to set up the working and protection (backup) paths and for traffic
routing within the network is insufficient. Toaddress this problem, use is made of TE, which is a
network engineering mechanism allowing for network performance optimization by means of
leveraging traffic allocation in conjunction with the available network resources.
The purpose of TE is to optimize the use of network resources and facilitate reliable network
operations. The latter aspect is pursued with mechanisms enhancing network integrity and
by embracing policies supporting network survivability. The overall operation leads to the
minimizations of network vulnerability, service outages due to errors, and congestions and
failures occurring during daily network operations. TE makes it possible to transport traffic via
reliable network resources, minimizing the risk of losing any fraction of this traffic.
TE leverages on some instruments that are independent of the network layer and technology:
.
A set of policies, objectives, and requirements (which may be context dependent) for
network performance evaluation and performance optimization.
.
A collection of mechanisms and tools for measuring, characterizing, modeling, and
efficiently handling the traffic. These tools allow the allocation and control of network
resources where these are needed and/or the allocation of traffic chunks to the appropriate
resources.
.
A set of administrative control parameters, necessary to manage the connec tions for reactive
reconfigurations.
General Characteristics of Transport Networks 9
Table 1.2 QoS characterization of users’ applications
User application QoS
Max.
latency
(ms)
Storage
Backup/restore N.A. N.A. 0.1 min 99.990
Storage on demand 10 1 0.1 s 99.999
Asyncrhonous mirroring 100 10 0.1 s 99.999
Synchronous mirroring 3 1 min 99.999
Grid computing
Compute grid 100 20 0.0 s 99.990
Data grid 500 100 0.1 s 99.990
Utility grid 200 50 0.0 s 99.999
Multimedia
Video on demand (enter-
tainment quality, similar to
DVD)
Video broadcast (IP-TV),
entertainment quality
similar to DVD
Video download 2–20 s 1000 1.0 s 99.990
Video chat (SIF quality, no
real-time coding penalty)
Narrowband voice, data
(VoIP, ...)
Telemedicine (diagnostic) 40–250 5-40 0.5 ms 99.999
Gaming 50–75 10 5.0 s 99.500
Digital distribution, digital
cinema
Video conference (PAL
broadcast quality 2.0
real-time coding penalty)
Note: latency is expressed in milliseconds with the exception of video on demand, video broadcast, and
video download, where seconds are the unit.
2–20 s 50 0.5 s 99.500%
2–20 s 50 0.5 s 99.500
400 10 5.0 s 99.500
100–400 10 0.5 ms 99.999
120 80 0.5 s 99.990
100 10 0.5 99.990
Max. latency
variation (ms)
Packet loss
(layer 3)
(%)
Max.
set-up
time
Min.
availability
(%)
The process of TE can be divided into four phases that may be applied both in core and in
metropolitan area networks, as described by the Internet Engineering Task Force (IETF) in
RFC 2702 [4]:
.
Definition of a relevant control policy that governs network operations (depe nding on many
factors like business model, network cost structure, operating constraints, etc.).
.
Monitoring mechanism, involving the acquisition of measurement data from the actual
network.
.
Evaluation and classification of network status and traffic load. The performance analysis
may be either proactive (i.e., based on estimates and predictions for the traffic load, scenarios
10 The Emerging Core and Metropolitan Networks
for the scheduling of network resources in order to prevent network disruptions like
congestion) or reactive (a set of measures to be taken to handle unforese en circumstances;
e.g., in- progress congestion).
.
Performance optimization of the network. The performance optimization phase involves
a decision process, which selects and implements a set of actions from a set of
alternatives.
1.2.8 Virtual Private Networks
Avirtual private network (VPN) is a logical representation of the connections that makes use of
a physical telecommunication infrastructure shared with other VPNs or services, but maintaining privacy through the use of tunneling protocols (Section 1.2.9) and security procedures.
The idea of the VPN is to give a user the same services accessible in a totally independent
network, but at much lower cost, thanks to the use of a shar ed infrastructure, rather than a
dedicated one [5].
In fact, a common VPN application is to segregate the traffic from different user communities over the public Internet, or to separate the traffic of different service providers sharing the
same physical infrastructure of a unique network provider.
VPNs are a hot topic also in the discussion within standardization bodies: different views
exist on what a VPN truly is.
According to ITU-T recommendation Y.1311 [6] a VPN “provides connectivity amongst
a limited and specific subset of the total set of users served by the network provider. A VPN
has the appearance of a network that is dedicated specifically to the users within the subset.”
The restricted group of network users that can exploit the VPN services is called a closed user
group.
The other standardization approach, used by the IETF, is to define a VPN’s components and
related functions (RFC 4026, [7]):
.
Customer edge (CE) device: this is the node that provides access to the VPN service,
physically located at the customer’s premises.
.
Provider edge (PE) device: a device (or set of devices) at the edge of the provider network
that makes available the provider’s view of the customer site. PEs are usually aware of the
VPNs, and do maintain a VPN state.
.
Provider (P) device: a device inside the provider’s core network; it does not directly
interface to any customer endpoint, but it can be used to provide routing for many provideroperated tunnels belonging to different customers’ VPNs.
Standardization bodies specified VPNs for different network layers. For example, a transport
layer based on SDH can be used to provide a layer 1 VPN [8, 9]. Layer 2, (e.g., Ethernet) allows
the possibility to implement L2-VPN, also called virtual LAN (VLAN). Layer 3 VPNs are very
often based on IP, and this is the first and the most common VPN concept.
In some situations, adaptation funct ions between the bit-stream that is provided from the
“source” (of the applications) and the VPN are required. An example of an adaptation data
protocol function is the mapping of Ethernet frames in NG-SDH containers.
General Characteristics of Transport Networks 11
1.2.9 Packet Transport Technologies
Packet technologies have been dominating the local area network (LAN) scenario for more
than 25 years, and nowadays they are widely used also in transport networks, where many
network services are based on packet paradigms. The main reason for this success is twofold:
first, the superior efficiency of packet networks in traffic grooming due to the statistical
aggregation of packet-based traffic; second, the inherent flexibility of packet networks that can
support an unlimited variety of users’ applications with a few fundamental network services,
as shown in Section 1.2.4.
However, until now, the transport of packe t traffic has been based on the underlying circuitswitch ed technology already available for telephony. A typical example is represented
by Ethernet transport over NG-SDH networks. This solution is justified by the widespread
availability of SDH equipment in already-installed transport networks, and by the
excellent operation, administration, and maintenance (OAM) features of such technology.
These features are fundamental for provisioning packet network services with the quality
required for most users’ applications, but they are not supported by the LAN packet
technologies.
This situation is changi ng rapidly, because a new generation of packet-based network
technologies is emerging. These new scenarios combine the efficiency and flexibility of packet
networks with the effective network control and management features of circuit-based
networks. These new technologies are referred to as packet transport technologies packe t
transport technology (PTTs).
There are proposals for introducing tunnels
engineering features rendering it into a connection-oriented platform. These developments are
currently under standardization at IEEE and ITU-T where is known as Provider Backbone
Bridge with Traffic Engineering (or simply PBB-TE).
An alternative approach under standardization at the ITU-T and IETF is to evolve the
IP/MPLS protocol suites to integrate OAM functions for carrier-grade packet transport
networks.
This PTT, known as MPLS-TP (MPLS transport profile) includes features traditionally
associated with transport networks, such as protection switching and operation and maintenance (OAM) functions, in order to provide a common operation, control and management
paradigm with other transport technologies (e.g., SDH, optical transport hierarchy (OTH),
wavelength-division multiplexing (WDM)).
The trend imposed by the dramatic increase of packet traffic and the obvious advantages in
evolving existing circuit-switched networks into advanced packet-switched networks is going
to make PTTs a viable solution to building a unified transport infrastructure, as depicted in
Figure 1.1. Incumbent network operators that have already deployed a versatile NG-SDH
network for aggregated traffic may follow conservative migration guidelines for their core
networks and keep circuit solutions based on optical technologies. These plausible solutions
are discussed in Section 1.4.
1
facilitating to allow Ethernet attaining traffic
1
A tunnel is a method of communication between a couple of network nodes via a channel passing through intermediate
nodes with no changes in its information content.
12 The Emerging Core and Metropolitan Networks
Figure 1.1 Unified transport network
1.3 Future Networks Challenges
1.3.1 Network Evolution Drivers
In the past decade, the proliferation of electronic and fiber-optic technologies has allowed
network services to evolve from the exclusive support of plain telephony to an abundance of
services which are transported based on the IP. These advances have had a major impact on the
drivers for network evolution.
Nowadays, network design and planning is the outcome of the interplay between different
technological, legal, and economic drivers:
.
Introduction of new services. A network operator or a service provider can decide to offer
new services based on customers’ requests or market trends.
.
Traffic growth. The growing penetration and the intensive use of new services increase the
network load.
.
Availability of new technologies. Electronic, optical, and software technologies keep on
offering new advances in transmission, switching, and control of information flows based on
circuits and packets.
.
Degree of standardization and interoperability of new network equipment. Modern
networks are very complex systems, requiring interaction of various kinds of equipment by
means of dedicated protocols. Standardization and interoperability are key requirements for
a proper integration of many different network elements.
.
Laws and regulati ons. National laws and government regulations may set limitations and
opportunities defining new business actors for network deployment and usage.
.
Market potential and amount of investments. The financial resource availability and the
potentialof the telecommunicationmarket are thekeyeconomic drivers for networkdevelopment.
1.3.2 Characteristics of Applications and Related Traffic
In this section, the association between applications and network services is presented. The
starting point of the analysis is the bandwidth requirement (traffic) of the various applications
Future Networks Challenges 13
and the subsequent classification of this traffic into classes. Figure 1.2, illustrates a classification of user applications based on the following traffic characteristics:
.
elasticity
.
interactivity
.
degree of resilience (availability)
.
symmetry
.
bandwidth.
Elastic
Traffic Classes
Inelastic
non interactive
interactive
Non interactive
interactive
standard availability
high availability
standard availability
high availability
standard availability
high availability
standard availability
high availability
asymmetrical
symmetrical
asymmetrical
symmetrical
asymmetrical
symmetrical
asymmetrical
symmetrical
asymmetrical
symmetrical
asymmetrical
symmetrical
asymmetrical
symmetrical
downloding
remote backup
P2P file exchange
mail
tele-diagnostics
medical data storage
network supervision
web browsing
compute grid
telnet
data grid
utility grid
gambling
network control
low bandwidth
high bandwidth
low bandwidth
high bandwidth
low bandwidth
high bandwidth
low bandwidth
high bandwidth
radio broadcast
Live radio
video on demand
video broadcast
live TV
asynchronous mirroring
storage on demand
tele-vigilance
voice over IP
video chat
remote surgery
synchronous mirroring
real time compute grid
digital distribution
digital cinema distribution
telephony
IP telephony
gaming
video-conference
paramedic communications
emergency communications
Figure 1.2 Classification of traffic generated by reference applications
14 The Emerging Core and Metropolitan Networks
Table 1.3 Qualitative classification of traffic types
Elastic Inelastic
Interactive Transactional Real time
Noninteractive Best effort Streaming
Elasticity refers to the level up to which the original traffic shape can be modified; the two main
categories are as follows:
.
Inelastic traffic (or stream traffic) is generated by applications whose temporal integrity
overwhelms data integrity because they try to emulate virtual presence.
.
Elastic traffic is generated by applications where data integrity overwhelms temporal
integrity, therefore being rather tolerant to delays and being able to adapt their data
generation rate to network conditions.
The term interactivity refers to a mode of operation characterized by constant feedback and
an interrelated traffic exchange between the two endpoints of the connection.
To map users’ applications traffic into the appropriate network services, it is essential to
define a few classes of traffic patterns that share the main characteristics. For this purpose,
Table 1.3 defines four kinds of traffic patterns in terms of QoS requirements.
Another important task is to assign QoS parameters quantitatively to the traffic classes.
Table 1.4 sets the values of QoS parameters used to define four basic classes as:
.
real-time traffic
.
streaming traffic
.
transactional traffic
.
best-effort traffic.
In connection with Table 1.4, the term dynamicity refers to the ability of a user to modify the
parameters of an existing connection. It is the only important parameter not described in
Section 1.2.6, since it is not addressed directly by the classic QoS definition, but it is anyway an
important quantity for application classification. The dynamicity refers to the time variation
of the following connection characteristics:
.
bandwidth (bit-rate);
.
QoS parameters (latency, availability, data integrity);
.
connectivity (the end-points of the connection).
The level of dynamicity is quantified on a three-state base:
– “none” (it is not possible to modify any parameters of an existing connection);
– “bit-rate and QoS” (when only these two parameters can be altered);
– “full” (bit-rate, QoS parameters, and connectivity modifications are allowed).
As seen in connectio n with Table 1.4, four traffic categories are defined based only on QoS
parameters. Table 1.5 shows examples of applications belonging to each one of the four classes
identified above, having different bandwidth requirements.
Table 1.4 Quantitative classification of QoS for traffic classes
Blocking
probability (%)
Real time <0.1 >99.995 <1 <50 ms
Streaming <0.1 >99.99 <1 <1s
Transactional <1 >99.9 <3 <1s <200 Bit-rate and QoS <1 E-2
Best effort
Network
availability (%)
Set-up
time (s)
Max.
latency
Mean
latency
(ms)
Max.
latency
variation
Dynamicity Packet loss rate
Bit-rate, QoS and
<5 E-5
connectivity
None <1 E-3
Not applicable
Future Networks Challenges 15
16 The Emerging Core and Metropolitan Networks
Table 1.5 Traffic characterization based on bandwidth (BW) and QoS parameters and map of users’
applications
QoS Low BW (tens of kbit/s) Medium BW (<2 Mbit/s) High BW (>2 Mbit/s)
Real time Legacy and IP telephony Gaming Video conference, grid
computing
Streaming UMTS Remote backup, network
supervision
Transactional E-commerce Telnet SAN
Best effort E-mail, domotic, VoIP p2p file exchange, data
acquisition
a
Video on demand.
b
Storage area network.
TV and video broadcast,
a
Vo D
b
p2p file exchange, data
acquisition
Table 1.5 is useful to map most common users’ applications into the four traffic classes (real-
time, streaming, transactional, best-effort), taking also the bandwidth use into account.
Similar to the classification of user applications, network services are classified into five
categories in association with the network services reported in Section 1.2.4. Thus, the network
service map looks as follows:
.
L1 VPN, which provides a physical-layer service between customer sites belonging to the
same closed user group. These VPN connections can be based on physical ports, optical
wavelengths, or TDM timeslots.
.
L2 VPN, which provides a service between customer terminals belonging to the VPN at the
data link layer. Data packet forwarding is based on the information contained in the packets’
data link layer headers (e.g., frame relay data link circuit identifier, ATM virtual circuit
identifier/virtual path identifier, or Ethernet MAC addresses).
.
L3 VPN, which provides a network layer service between customer devices belonging to the
same VPN. Packets are forwarded based on the information contained in the layer 3 headers
(e.g., IPv4 or IPv6 destination address).
.
Public IP, which is considered as the paradigm of best-effort network services. Namely, it is
a generalized L3 VPN without restrictions to the user group, but with a consequently poor
QoS.
.
Business IP, which is included as a higher priority class that, for instance, can efficiently
handle latency
2
in ti me-sensitive applications.
On top of this classification, further “orthogonal” categorizations are often introduced. VPN
services are further subdivided into:
– permanent VPNs, to be provided on a permanent basis by the network service
provider;
– on-demand VPNs, which could be controlled dynamically by the client user/network.
2
See latency and other QoS defining parameters later in this section.
Future Networks Challenges 17
Table 1.6 Mapping network services groups to some applications (BW: bandwidth)
L1 and L2 VPN services are also classified into high- and low-availability services. Table 1.6
provides a mapping between “user applications” and “network services”: in this context,
a stippled box means that that particular application may run over on this network service, but
not very efficiently. The most efficient support to that application is designated with horizontal
rows, whereas a white box should be interpreted as no support at all from this service to that
application.
1.3.3 Network Architectural Requirements
This section gives an overview of the architectural requirements for transport networks
supporting the services described above.
1.3.3.1 Network Functional Requirements
From an architectural point of view, data services have been traditionally transported over a
wide set of protocols and technologies. For example, IP services are transported over the core
network usually relying on SDH, ATM, or Ethernet transmission networks. A widespread
alternative used in current convergent transport networks is to go towards a meshed network of
IP/MPLS routers, interconnected through direct fiber or lambda connections and without any
multilayer interaction.
This “IP-based for everything” approach was proved to be valid for the last decade, but with
current traffic trends it would lead to scalability problems. Currently, backbone nodes need
switching capacities of several terabits per second, and this need is predicted to double every
2 years. Routers are also very expensive and they are not optimized for high-bandwidth traffic
transportation, while transport technologies such as SONET/SDH are not efficient enough for
packet transport, due to a very coarse and not flexible bandwidth granularity.
18 The Emerging Core and Metropolitan Networks
On the other hand, a number of emerging services (e.g., new multimedia applications served
over the Internet; i.e., real-time high-bandwidth video services) are imposing new requirements on the current “IP-based for everything” architecture in terms of bandwidth and QoS
(end-to-end delay and availability). Moreover, mobility of users and devices and new traffic
profiles (due to, for example, flash crowds and streaming services) require a network with an
unprecedented dynamicity that is able to support unpredictable traffic patterns.
1.3.3.2 Network Scalability
The term scalability is a feature of a network architecture designating the ability to
accommodate higher traffic load without requiring large-scale redesign and/or major deployment of resources. A typical (negative) example manifesting lack of scalability is an SDH
ring where additional resources and manual configurations are mandatory in order to increase
the capacity between two nodes. Thus, future transport networks should be scalable in order to
support existing or yet-unknown clients and traffic volumes.
The lack of scalability is demonstrated in two distinctive ways. First, by means of an
excessive deployment of network resources to accommodate higher traffic volumes. This
inefficiency is leading to higher CAPEX and OPEX that are mainly attributed to the enduring
very high cost of switching. Solving this issue requires the deployment of technologies able to
transport traffic with a lower cost per bit. Second, it is associated with architectural and/or
control plane scalability restrictions due to the excessive number of network elements to
control (e.g., the number of paths in the network). To address this issue requires the adoption
of layered architectures and aggregation hierarchies.
1.3.3.3 Network Reconfiguration Ability
Network reconfiguration ability refers to the ability of the network to change the status of some
or all of the established connections, to modify the parameters of these connections (e.g.,
modify the amount of allocated bandwidth) or to modify the way the services are provided (for
instance, changing the routing of a given connection to allow more efficient grooming on a
different route or improve spare capacity sharing).
The interest in having a reconfigurable network comes from the fact that traffic profiles
change very frequently, may be fostered by symmetrical traffic patterns, unexpected traffic
growth, possible mobile data/multimedia services, varied geographic connectivity (e.g., home,
work), andemerging services, suchas user-generated content. All these facts make it reasonable
to think in the future about a highly varying traffic profile in a network, thus meaning that
reconfigurability would be a highly advantageous characteristic in data architectures.
1.3.3.4 Cost Effectiveness
Taking into account the fierce competition and the pressure upon network operators in the
telecommunications market, as well as the descending cost per bit charged to the final user, the
only solution for service providers to keep competitive is to reduce traffic transport costs.
Therefore, cost effectiveness is the obvious requirement for any new technology. Basic
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