EXTENDED ABSTRACT
1.1 Background
The Internet that was once described as the backbone of the information age, it is now
becoming the nervous system of the information hungry age and the knowledge era. The
Internet as a communication network based on the Internet Protocol (IP) has experienced
tremendous growth over the last decade. This growth was a natural response to the everincreasing demands for more bandwidth, and speed. Additionally, these demands
invoked the needs for reliability, and high quality services that are expected to become
more intense in the future, which makes the need for a reliable, efficient, and feasible
network infrastructure more evident and complex to achieve. Such a network
infrastructure does not only support the user demands, but it provides a full range of new
opportunities and services.
Three network generations can be distinguished, depending on the deployed physical
technology. The first-generation networks were based on copper wire or radio,
subsequently; the copper wire (around 10 Gigabits per Second) was replaced by a more
sophisticated transmission medium, which is the optical fiber. The optical fiber offers an
immense bandwidth (Theoretically, 50 Terabits per Second), low error rate, high
reliability, availability, and maintainability. Additionally, optical fibers feature many
other advantages, e.g., lightweight and small space requirements, resistance to corrosive
materials; and less signal attenuation and high immunity to tapping. Having optical fiber
as the transmission medium in the second-generation networks enhanced the network
performance and throughput, however, this improvement was restricted by the so-called
Electronic Bottleneck. Electronic bottleneck phenomenon is caused by the limited
processing speed of electronic components (a few gigabits per second) deployed in
switches/routers, multiplexers, and end-nodes in the network. Since the electronic
processing speed is at its peak, the ultimate solution is to move the switching and routing
functions from the electronic domain to the optical domain. However, due to the optical
technology restrictions, another solution is adopted. The solution is to divide the huge
bandwidth of the fiber among multiple wavelength channels with the appropriate data
rates, which will allow the use of relatively low-speed electrical circuits. The
wavelength channels are then multiplexed simultaneously over a single fiber using a
parallel transmission technology that is referred to as Wavelength-Division Multiplexing
(WDM). Therefore, the third generation networks will be designed as all-optical
networks, where the data are transmitted all-optically through the network from source
to destination, over WDM infrastructure.
1.2 IP and WDM convergence
The success of the Internet and its omnipresence has made the Internet Protocol (IP) a de
facto standard, thus the demand for IP network solutions has increased exponentially.
With the Internet protocol, voice and video as well as real-time multimedia traffic could
be integrated and transmitted with the data traffic over a single network infrastructure,
providing unprecedented opportunity for businesses to improve their services, reduce
expenses, and increase their revenues. With the technological evolution, IP waned the
boundaries between the computing, entertainment, and the telecom industries, which led
to more customer centric business models. IP being an intermediate layer between an
immense variety of IP-based services and almost all the layer 2 technologies, it is more
than revenue-generating integration layer. IP convergence is not merely an option; it is
inevitably becoming a business necessity in the Internet-dependent era. Such
convergence is best supported by the Wavelength-Division Multiplexing (WDM)
technology. WDM relieves the effect of electronic bottleneck by dividing the optical
transmission spectrum into a number of non-overlapping channels; thus, the electronic
components would only work at their own speed (few gigabits per second) and not at the
aggregated transmission rate. IP/WDM convergence will eventually be translated to an
efficient, robust, reliable, and feasible all-optical network.
1.2.1 Internet Protocol (IP)
The Internet Protocol (IP) is the dominant network layer protocol in the current public
Internet. IP was designed for use in packet-switched communication networks,
correspondingly, IP provides for transmitting blocks of data called packets/datagrams
from sources to destinations. As a lower layer protocol, the datagrams are encapsulated
in a data link layer protocol in an abstracted manner that allows the use of IP over a
heterogonous network. IP also provides for fragmentation and reassembly of long
datagrams, if necessary, for transmission through small-packet switching networks.
The Internet Protocol is a best effort delivery protocol, which means that IP is unreliable
and does not provide any special features that handle or manage data corruption,
duplicate/out of order packets arrival, or lost/discarded packets. However, IP does
ensure that the IP packet's header is error-free through the use of a checksum.
The current IP version is version 4 (IPv4); Versions 0 through 3 were either reserved or
unused. IPv4 uses 32-bit addresses (more than 4 billion addresses). Another version is
IPv5, which was not a successor to IPv4. IPv5 is an experimental flow-oriented
streaming protocol intended to support video and audio. However, IPv4 is followed by
IPv6 to deal with the address space exhaustion problem by using 128-bit addresses, thus
offering around 3.4×1038 addresses.
1.2.2 Wavelength-Division Multiplexing (WDM)
Wavelength-Division Multiplexing (WDM) is a multiplexing technique by which
separate optical carrier signals, distinguished by wavelength, are combined and
simultaneously transmitted down the core of a single optical fiber. This allows for a
multiplication in the fibre’s capacity without deploying additional optical fibers.
A WDM system uses a multiplexer at the source side (transmitter) to combine the
signals and a Demultiplexer at the destination side (receiver) to split them apart. These
two functions are usually combined in what is referred to as Optical Add-Drop
Multiplexer (OADM).
The first WDM systems only combined two signals, which are demultiplexed, at the
destination, by a dichroic (two-wavelength) filter with a cutoff wavelength
approximately midway between the wavelengths of the two signals. Soon, it became
apparent that, using cascaded dichroic filters, more than two multiplexed wavelengths
could be demultiplexed. Currently, up to 160 parallel wavelengths with up to 80 Gbps
per wavelength can be transmitted using WDM systems, which are ranked as Dense
WDM (DWDM) systems, while those with fewer than eight active wavelengths are
considered as Coarse WDM (CWDM). DWDM and CWDM technologies are based on
the same concept of using multiple wavelengths of light on a single optical fiber, but the
two technologies differ in the wavelengths’ spacing, channels’ number, and the ability to
amplify signals in the optical domain.
1.3 IP over WDM layering
The Internet Protocol (IP) has prevailed, and the advantages of WDM technology are by
and large undisputable. Therefore, Integrating the IP layer directly onto the WDM layer
is the natural choice to lower the cost, simplify the management and the control; and to
reduce the signaling overhead. Unfortunately, such a direct integration is not that
comprehensible and straightforward, because the needs for functionalities like framing
and synchronization between IP and the optical layer. Many solutions were proposed to
transport IP traffic over WDM starting with multilayer architecture (e.g. IP over
SONET/SDH over WDM) and gradually eliminating the intermediate layers. Thus,
moving toward a tighter integration between IP and the optical layer, that is the twolayer model. Below, different approaches of transporting IP traffic over WDM are
briefly presented.
WDM System
IP
ATM
IP
IP
SONET
SONET
ATM
Optical Wavelength Layer
Optical Multiplexing Layer
Optical Transmission Layer
Overhead || Complexity || CAPEX || OPEX
IP over WDM layering
IP
IP over ATM over SONET over WDM
In the IP over ATM over SONET over WDM mechanism, IP traffic is carried by ATM
connections that are multiplexed into SONET connections, which call upon the services
of the optical layer. In other words, IP packets are segmented and encapsulated into
ATM Adaptation Layer type 5 (AAL-5) Protocol Data Units (PDUs) and assigned
different virtual connections by the SONET/ATM line card in the IP router. The ATM
cells are then packed into an SONET frame, which can be sent either to an ATM switch
or directly to a WDM transponder.
The SONET infrastructure provides high resilience against fiber cuts, and the use of the
ATM layer is attractive mainly because of the ATM’s bandwidth allocation flexibility
and its traffic engineering capabilities. ATM can also provide the desired QoS to the
various connections, which complements the conventional IP best effort traffic routing.
However, in addition to the overhead due to the process of mapping variable-length IP
packets onto fixed-length ATM cells, using ATM to transport IP over SONET incurs
extra overhead because the idle ATM cells that have to be inserted as dummy data into
SONET frames during the periods where there are no ATM cells for transmission; this is
because SONET links operate at fixed rate.
IP over ATM over WDM
A similar approach is to maintain only the ATM layer as an intermediate layer between
IP and the WDM layer, therefore, eliminating the SONET layer with its high initial
equipment cost and high operational costs. In this scenario, using an ATM Cell-Based
physical layer, the ATM cells are transported directly on a WDM channel, without being
encapsulated into SONET frames. The Cell-Based physical layer specification defines
the function to transport ATM cells without using a frame structure.
In addition to its aptness in handling high amount of layer 2 services, e.g., leased lines
and voice services; this approach lowers the physical layer overhead (around 16 times
lower than SONET) and simplifies the ATM cells transmission technique as they are
directly sent over the optical layer. Furthermore, since ATM is asynchronous, the
synchronization difficulties associated with SONET networks are alleviated.
Despite the fact that ATM enhances the bandwidth utilization through statistical
multiplexing and provides certain QoS functionality, the drawback of this approach is,
again, the introduced high ATM overhead including AAL5 and ATM cell overhead.
IP over SONET/SDH over WDM
To reduce the transmission inefficiency of the ATM layer, the IP packets are
encapsulated into Point-to-Point Protocol (PPP)/High-Level Data Link Control (HDLC)
frames or into Simple Data Link (SDL) frames. The PPP/HDLC frames or SDL frames
are then encapsulated into SONET frames and directly transmitted over WDM. There
are different types of interfaces used to interface IP and SONET/SDH; for example:

STS-3c/VC-4, which provides aggregate bandwidth without any separation between
different IP services.

Channelized interfaces, where STS-48/STM16 optical output may contain 16
individual STS-3c/VC-4, with a possible service differentiation for each STS-3/VC4.
SONET/SDH can be used to provide protection functionality against cable cuts by
Automatic Protection Switching (APS) in a variety of configurations; in addition to its
ability to transport legacy voice traffic. On the other hand, all the previously mentioned
disadvantages associated with the SONET/SDH layer, such as the high operational costs,
remain.
IP over WDM
In contrast to the earlier approaches, an optimized approach is to deliver IP services
directly over the Optical/WDM layer by eliminating both the SONET/SDH and ATM
layer. The transport efficiency is optimized because the ATM layer is removed. The
initial equipment is reduced because no SONET/SDH equipment is used.
Research Objectives
Currently, storing and manipulating data in the optical domain is difficult, and
wavelength conversion is costly and quite limited. Under these constraints, Burst
Switching has been demonstrated as a promising and rational switching strategy for
directly transporting IP over the optical layer. In this thesis, WDM burst switching is
described, investigated, and analyzed. New approaches and strategies, to streamline the
transmission of IP traffic in a WDM-enabled optical network, are introduced based on
the simplicity principle; where the complexity is moved from the network core to the
edges of the network. Thus, providing intelligent edges (for robustness) and preserving
simple network core (for scalability).
In this thesis, firstly, a detailed survey on WDM Burst Switching is provided. Burst
Switching network architecture, burst assembly, signaling and reservation protocols;
QoS support and contention resolution techniques are discussed. Furthermore, based on
the review of the burst segmentation techniques, a new Staged Reservation Scheme
(SRS) is introduced. With SRS the network core nodes are supplied with manageable
data bursts and the implementation of the existing burst segmentation techniques is
streamlined. Additionally, SRS simplifies the QoS provisioning and significantly
improves the TCP performance. Novel control packet format, burst assembly, and
wavelengths reservation schemes are presented; and a new burst-segments dropping
policy is devised.
Secondly, a new optical burst switching strategy named Parallel Optical Burst-Switching
(POBS) is proposed. POBS is designed for Ultra-Dense WDM transmission systems in
which an appropriate transmission granularity is maintained while the transmission data
rate is increased by increasing the number of wavelengths. POBS is flexible, simple, and
reliably allows constructing manageable data bursts. Furthermore, POBS requires less
switching elements and successfully lowers the burst-scheduling complexity. In
addition, the potential of POBS in providing differentiated services is investigated, and a
new QoS mechanism is introduced.
Finally, due to the important effect of nonlinearities on WDM systems even at moderate
powers and bit rates, the performance of POBS network system is investigated and
evaluated in term of blocking probability, considering two major optical nonlinearity
induced penalties, namely, the Four-Wave-Mixing (FWM) and the Cross-PhaseModulation (XPM).