ECE 678

Integrated Telecommunications Networks

Project Report

Design of Optical Switch Router

Professor: Dr. Martinez

Group Member: Yun ZhaoYeliang Zhang

Department of Electrical and Computer Engineering

University of Arizona

Spring 2002

Content

Abstract................................................................................................................................31. Introduction..................................................................................................................32. Optical Communication System..................................................................................4

2.1 Overview of Optical Communication System.....................................................42.2 Advantage of Optical Communication System...................................................5

3. Optical Communication System..................................................................................63.1 Overview of All-Optical Network.......................................................................63.2 Dense Wavelength Division Multiplexing (DWDM)..........................................73.3 Generalized Multi-protocol Label Switch (GMPLS)..........................................93.4 Optical Switching Router..................................................................................12

4. Optical Switching Technology..................................................................................134.1 Switch versus Route..........................................................................................134.2 O-E-O Switch....................................................................................................134.3 O-O-O Switch....................................................................................................13

5. Optical Components/Elements..................................................................................145.1 Optical Component Characteristics...................................................................145.2 Micro Electro-mechanical System (MEMS).....................................................165.3 Tunable Laser....................................................................................................175.4 Tunable Filter.....................................................................................................185.5 Wavelength Converter.......................................................................................195.6 Optical Amplifier...............................................................................................20

5.6.1 Erbium Doped Fiber Amplifier (EDFA)...................................................205.6.2 Semiconductor Optical Amplifier (SOA)..................................................21

5.7 Optical Cross Connect (OXC)...........................................................................235.8 Tunable Optical Add-Drop Multiplexer (TOADM)..........................................23

6. Optical Switching Router Design..............................................................................246.1 LSR Forwarding Plane Design #1.....................................................................246.2 LSR Forwarding Plane Design #2.....................................................................266.3 LSR Control Plane Design.................................................................................27

7. Conclusion.................................................................................................................28Reference...........................................................................................................................29

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Abstract

This paper deals with the design of optical switching router. The paper talks about the

concepts of all-optical network, dense wavelength division multiplexing and generalized multi-

protocol label switching, optical switching technology. The various optical components and

elements like Optical Amplifiers, Optical Add/Drop Multiplexers and tunable lasers are

described. Some sample optical products are listed on the paper. Finally, several draft designs of

optical switching router architecture are proposed in this paper.

1. Introduction

One of the major issues in the networking industry today is tremendous demand for more

and more bandwidth. With the development of Internet technology, a wide variety of

applications, such as multimedia communications (audio and video streams), database

applications, etc., have been deployed on Internet. All these applications need much more high

bandwidth. Before the introduction of optical networks, the reduced availability of fibers became

a big problem for the network providers. However, with the development of optical networks and

the use of Dense Wavelength Division Multiplexing (DWDM) technology, a new and probably, a

very crucial milestone is being reached in network evolution.

Optical fiber has significant advantages compared with the electrical transmission line. It is

no doubt that the future of the network infrastructure lies in the field of fiber optics. Optical fiber

is significantly smaller and lighter than electrical cables. Optical fiber provides the huge

bandwidth, low loss rate, and cost effectiveness to enable this emerging network backbone.

Optical fiber is more secure than copper wire. Given that fiber has a potential bandwidth of

approximately 50 Tb/s [1], nearly four orders of magnitude higher than peak electronic data rates.

Therefore, every effort should be made to maximize the capabilities of the fiber optic network.

DWDM technology supports multiple simultaneous channels (of different wavelengths) on

a single fiber. In DWDM, the optical transmission spectrum is divided into a number of non-

overlapping wavelength, and with each wavelength supporting a single communication channel.

Thus, by allowing multiple DWDM channels to coexist on a single fiber, we can tap into the huge

fiber bandwidth and throughput. This simple concept has changed the landscape of

telecommunication. DWDM telecommunication systems have the transmission capability that

exceeds terabits per second; and systems supporting hundreds of gigabits per second are

becoming commercially available. Unfortunately, since much of today’s network infrastructure

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was developed to support voice traffic, an efficient and ultra-high backbone networks based on

DWDM is yet to be realized.

Meanwhile, Multi-protocol label switching (MPLS), a new network protocol is emerging.

MPLS is growing in popularity as a set of protocols for provisioning and managing core

networks. The networks may be data-centric like those of ISPs, voice-centric like those of

traditional telecommunications companies, or a converged network that combines voice and data.

At least around the edges, all these networks are converging on a model that uses the Internet

Protocol (IP) to transport data.

Generalized MPLS (GMPLS) is proposed shortly after MPLS. The premise of GMPLS is

that the idea of a label can be generalized to be anything that is sufficient to identify a traffic

flow. For example, in an optical fiber whose bandwidth is divided into wavelengths, the whole of

one wavelength could be allocated to a requested flow. The Label Switch Router (LSR) at either

end of the fiber simply have to agree on which frequency to use. Unlike with non-generalized

labels, the data inside the requested flow does not need to be marked at all with a label value;

instead, the label value is implicit in the fact that the data is being transported within the agreed

frequency band. On the other hand, some representation of the label value is needed in the

signaling protocol so that control messages between the LSRs can agree on the value to use.

The tremendous bandwidth of DWDM technology and devices and the innovative GMPLS

gives us a chance to step into All-Optical Network. Optical Switching Router is going to be a

very important and core part of All-Optical Network.

In this paper, we are focused on the design of Optical Switching Router and the optical

components.

2. Optical Communication System

2.1 Overview of Optical Communication System

The basic concept of an optical communication system is illustrated in figure 1. To begin, a

serial/parallel bit stream in electrical form from electrical storage medium is presented to a

modulator, which encodes the data appropriately for fiber transmission. A light source (laser or

Light Emitting Diode - LED) is driven by the modulator and the light focused into the fiber. The

light travels down the fiber will be amplified or regenerated by the repeater/amplifier during

which time it may experience dispersion and loss of strength. At the receiver end the light is fed

to a detector and converted to electrical form. The signal is then amplified and fed to another

detector, which isolates the individual state changes and their timing. It then decodes the

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sequence of state changes and reconstructs the original bit stream. The received electrical bit

stream may then be fed to a using device.

Optical sources

(Laser/LED)

E/Omodulator

Electrical Information

Repeater/Amplifier

Photodetector

Decision Device(Error-Checking)

Informationsink/storage

Amplifier/equalizer

fiber fiber

transmitter(electrical)

receiver(electrical)(light)

Figure 1 Block diagram of basic optical communication system [2].

2.2 Advantage of Optical Communication System

Optical communication has significant advantages compared to electrical communication.

First, optical fiber is significantly smaller, lighter and cheaper than electrical cables for the same

capacity of cables. In the wide area environment a large coaxial cable system can easily involve a

cable of several inches in diameter and weighing many pounds per foot. A fiber cable to do the

same job could be less than one half an inch in diameter and weigh a few ounces per foot. This

means that the cost of laying the cable is dramatically reduced.

Figure 2 The capacity of fiber over the years [3].

Second, the data transmission rate of optical communication is tremendous. Figure 2 shows

that the data rate of a single fiber (TDM) in use in 1998 is about 10 Gbps. This is very high in

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digital transmission terms. In telephone transmission terms the very best coaxial cable systems

give about 2,000 analog voice circuits. A 150 Mbps fiber connection gives just over 2,000 digital

telephone (64 Kbps) connections [4]. By sending many (“wavelength division multiplexed”)

channels on a single fiber, we can increase this capacity a hundred and perhaps a thousand times.

Third, optical communication does not have electrical connections. Data are transmitted via

different channel. Each channel has its own wavelength. There is no electromagnetic effect

during transmission. Because the connection is not electrical, you can neither pick up nor create

electrical interference (the major source of noise). Thus the signal interference is almost reduced

since each channel is independent to another. This is one reason that optical communication has

so few errors. There are very few sources of things that can distort or interfere with the signal. In

a building this means that fiber cables can be placed almost anywhere electrical cables would

have problems, (for example near a lift motor or in a cable duct with heavy power cables). In an

industrial plant such as a steel mill, this gives much greater flexibility in cabling than previously

available. In the wide area network environment there is much greater flexibility in route

selection. Cables may be located near water or power lines without risk to people or equipment.

Also, the optical communication is more secure than copper wire.

3. Optical Communication System

3.1 Overview of All-Optical Network

It is predictable that the current Internet is evolving to an All-Optical network in the nearby

future. With the developments in DWDM technology, All-Optical Network offers an almost

unlimited potential for bandwidth. There is no O/E or E/O conversion in the optical core network.

With DWDM as the optical backbone, GMPLS as the control plane, and optical switching router

as the router in the optical core network, All-Optical Network is the most exciting network

technology. All-Optical Network increases network throughput, provides high transmission rate

and low loss rate, provides Quality of Service (QoS) and Class of Service (CoS). Video on

Demand (VOD) and long haul broadband transmission is not a dream in the future. All-Optical

Network can achieve terabit-per-second bandwidth easily. We know the highest speed of

electrical signal is about 2.5~4 Gbps. Bandwidth bottleneck of electrical signal is removed once

All-Optical Network is implemented. Figure 3 shows a picture of All-Optical Network.

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Figure 3 All-Optical Networks

3.2 Dense Wavelength Division Multiplexing (DWDM)

First, Let’s take a look at Wavelength Division Multiplexing (WDM). WDM is the basic

technology of optical networking. It is a technique for using a fiber (or optical device) to carry

many separate and independent optical channels. Each channel is transmitted at a different

wavelength (or frequency). Each channel can be view as a lightpath. Multiple wavelengths are

multiplexed into a single optical fiber and multiple lightpath data are transmitted. Because each

channel is independent, there is no interference. It is the cost effective technology and is used

widely in long haul network. In fact, WDM is one type of FDM. Another way of envisaging

WDM is to consider that each channel consists of light of a different color. Thus a WDM system

transmits a “rainbow”. Actually at the wavelengths involved the light is invisible but it's a good

way of describing the principle.

1

2

3

4

1

2

3

4

Fiber link

multiplexer demultiplexer

Figure 4 WDM scheme

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Figure 5 shows there are three wavelength windows in optical communications: 850nm,

1310nm and 1550 nm. One simple form of WDM is using 1310 nm as one wavelength and 1550

nm as the other or 850 nm and 1310 nm.

Figure 5 Wavelength Window of Optical Transmission

This type of WDM can be built using relatively simple and inexpensive components and

some applications have been in operation for a number of years using this principle. Dense WDM

however is an evolution of WDM. Dense WDM refers to the close spacing of channels. There is

no accurate and unanimous definition of DWDM. To some, a series of WDM channels spaced at

3.6 nm apart qualifies for the description. Someone define DWDM if the number of multiplexing

wavelengths are larger than 40. Others use the term to distinguish systems where the wavelength

spacing is 1 nm per channel or less [5].

fiber plantTx

Rx

Rx

Tx

1533nm

1557nm 1557nm

1533nm

1533nm / 1557nm WDM Coupler

Figure 5 Sparse WDM.

Figure 5 shows an example of a very simple WDM system. Wavelength selective couplers

are used both to mix (multiplex) and to separate (demultiplex) the signals. The distinguishing

characteristic here is the very wide separation of wavelengths used (different bands rather than

different wavelengths in the same band). There are many variations around on this very simple

theme. Some systems use a single fiber bi-directionally while others use separate fibers for each

direction (as illustrated). Other systems use different wavelength bands from those illustrated in

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the figure (1310 and 1550 for example). The most common systems run at very low data rates (by

today's standards). Common application areas are in video transport for security monitoring and

in plant process control [6].

Tx1

Tx2

. .

Tx1

Tx2

TxN

Rx1

Rx2

RxN

. .. .

Rx1

Rx2

RxN

TxN

1 , 2 . . . N

Figure 6 Dense WDM

Figure 6 shows how a DWDM system works. Ns share one optical fiber link. Each optical

channel is allocated its own wavelength or a small range of wavelengths. A typical optical

channel might be 1 nm wide. This channel is really a wavelength range within which the signal

must stay. It is normally much wider than the signal itself. The width of a channel depends on

many things such as the modulated bandwidth of the transmitter, its stability and the tolerances of

the other components in the system.

3.3 Generalized Multi-protocol Label Switch (GMPLS)

Multi-Protocol Label Switching (MPLS) is growing in popularity as a set of protocols for

provisioning and managing core networks [17]. The networks may be data-centric like those of

ISPs, voice-centric like those of traditional telecommunications companies, or a converged

network that combines voice and data. At least around the edges, all these networks are

converging on a model that uses the Internet Protocol (IP) to transport data.

Non-generalized MPLS overlays a packet switched IP network to facilitate traffic

engineering and allow resources to be reserved and routes pre-determined. It provides virtual

links or tunnels through the network to connect nodes that lie at the edge of the network. For

packets injected into the ingress of an established MPLS tunnel, normal IP routing procedures are

suspended; instead the packets are label switched so that they automatically follow the tunnel to

its egress.

Traditionally, provisioning in optical networks has required manual planning and

configuration resulting in setup times of days or even weeks and a marked reluctance amongst

network managers to de-provision resources in case doing so impacts other services. Where

control protocols have been deployed to provision optical networks they have been proprietary

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and have suffered from interoperability problems. With the success of MPLS in packet switched

IP networks, optical network providers have driven a process to generalize the applicability of

MPLS to cover optical networks as well, the result of which is the set of internet drafts that

collectively describe “Generalized MPLS” (GMPLS). These drafts generalize:

the MPLS data forwarding model . such that it includes current practice in optical

networks

the MPLS control protocols . so that they can be used as a standardized and interoperable

way of provisioning optical networks

Other, related work to standardize the management and configuration of optical networks is

ongoing in the development of the Link Management Protocol (LMP) [8] and of optical

extensions to OSPF.

Figure 7 shows application of MPLS.

Figure 7 MPLS Application (from Trillium®)

MPLS uses a technique known as label switching to forward data through the network.

Before data packet traversing MPLS network, the Label Edge Router (LER) will partition each

incoming data packet into a set of “Forwarding Equivalence Classes (FECs)” and assign each

FEC with a small and fixed-format label. When a packet is forwarded to its next hop, the label is

sent along with it. At each hop across the network, the label on the incoming packet is used as the

index in the forwarding table that contains the outgoing interface and a new label that are to

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replace the incoming label before it is transmitted to the next hop. When a packet reaches the

egress router, the label is removed and the packet is forwarded according to the original network-

layer routing scheme.

As a packet traverses a MPLS enabled network it must make three transitions. First, it must

go from its native layer 3 forwarding into labeled MPLS forwarding. This process entails the

adding of a label to the head of the packet. Second, a labeled packet must be able to traverse an

MPLS path. This path consists of all the devices that know how this particular packet (and

packets like it) needs to traverse a network. This path is called a Label Switch Path (LSP). It is a

connection-oriented path that is setup ahead of the forwarding of any packets. Finally a packet

must make its way back into layer 3 forwarding. This process consists of removing the label

from the head of the packet and then sending it to the appropriate layer 3 protocol for additional

handling. In a MPLS enabled network, layer 3 forwarding is used by the edges of the network,

and MPLS forwarding is used in the core of the network. Figure 8 shows a two LSPs in a MPLS

network.

Figure 8 Two LSPs in an MPLS Packet-Switched Network

The path that data traverses through a network is defined by the transition in label values,

as the label is swapped at each LSR. Since the mapping between labels is constant at each LSR,

the path LSP is determined by the initial label value. The decision that each packet is examined to

determine which LSP it should use and hence what label to assign to it is a local matter to each

LER. But it is likely to be based on factors including the destination address, the quality of

service requirements and the current sate of the network. This flexibility is one of the key features

that make MPLS useful.

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The premise of Generalized MPLS is that the idea of a label can be generalized to be

anything that is sufficient to identify a traffic flow. For example, in an optical fiber whose

bandwidth is divided into wavelengths, the whole of one wavelength could be allocated to a

requested flow. The LSRs at either end of the fiber simply have to agree on which frequency to

use. Unlike with non-generalized labels, the data inside the requested flow does not need to be

marked at all with a label value; instead, the label value is implicit in the fact that the data is

being transported within the agreed frequency band. On the other hand, some representation of

the label value is needed in the signaling protocol so that control messages between the LSRs can

agree on the value to use.

Generalized MPLS extends the representation of a label from a single 32-bit number to an

arbitrary length byte array and introduces the Generalized Label object (in RSVP) and

Generalized Label TLV (in CR-LDP) to carry both the label itself and related information. The

following subsections describe how the switching quantities used in optical networks are

represented as GMPLS labels.

3.4 Optical Switching Router

Optical Switching Router is such kind of router that switch labeled packet directly inside

the optical core network, not route the packet hop by hop based on the packet head information.

Traditionally, router is built to route packet according the routing table, which resident in the

router. This kind of routing is a hop-by-hop routing. GMPLS provide a simple and fast way to

switch the labeled packet, if packet is labeled at the edge LSR.

Optical Switching Route has the following parts:

Data Forwarding Plane — the functions are label attaching, label switching and

forwarding.

Control Plane — the functions are table lookup, processing, wavelength assignment,

queuing decisions, etc.

Interface with other legacy network such as ATM, Gigabit Ethernet, SONET.

We will discuss the detail of Optical Switching Router later after introduction of optical

components and elements.

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4. Optical Switching Technology

4.1 Switch versus Route

Basically, there is no apparent way to distinguish which technology is switching or routing.

According to the OSI/ISO network reference model, a network device forward an IP packet

directly from one to the other, such device is a layer 2 switch. If a network device dynamically

route a IP packet based on the routing table, which is a collection of network information with all

other routers, such device is called router or layer 3 switch. Switch is fast and simple, it forwards

packet directly. Router is much more complicated, slower. Usually backbone network router is a

kind of super computer.

4.2 O-E-O Switch

Currently most of Optical Switch is O-E-O switch. Incoming signals are converted from

Optical domain to Electrical domain, then signals are switched electrically. Once finishing

switch, outgoing signals are converted back to optical domain. Figure 9 shows structure of O-E-O

optical switch. From the figure, we can see a optical signal from 1290 nm to 1570 nm wavelength

is switched to a fixed 1.3 m output.

Figure 9 O-E-O Switch

If we need high bandwidth beyond 10 Gbps, O-E-O switch is not a ideal candidate due to

its bandwidth bottleneck. Thus, we need O-O-O switch.

4.3 O-O-O Switch

All-Optical switch (O-O-O switch) has advantages over O-E-O switch. Its complexity is a

flat function and is independent of bit rate, it can get up to 20 Tbps bandwidth. But its

implementation is not easy. Currently, O-O-O switch is in the research lab and its application is

in the near future.

CDR Clock and Data RecoveryP Header ProcessingACS Automatic Crosspoint Selection

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5. Optical Components/Elements

Optical components and elements used to build a Optical Switching Router include Micro

Electro-mechanical System (MEMS), Tunable Laser, Wavelength Converter, Optical Amplifier,

Optical Cross Connect (OXC), Tunable Optical Add-Drop Multiplexer (TOADM), etc. We will

first look through the component characteristics.

5.1 Optical Component Characteristics

In order to describe optical component characteristics, we categorize the components to

three categories [10]:

Interconnection: Optical Cross Connect, Optical Add-Drop Mulitplexer, Wavelength

Converter

Optical Amplifier: Semiconductor Optical Amplifier (SOA), Erbium Doped Fiber

Amplifier (EDFA)

Light Source: Laser, LED

Interconnection Characteristics:

Insertion loss: the difference in power levels between the input and output of the device

under test

Crosstalk: indicates the amount of power that enters a channel form neighboring

channels. Typically, it is around 25 dB.

Repeatability and Switch time:

Polarization dependent loss (PDL): the peak-to peak output power variation when the

input is exposed to all possible polarization states

Center Wavelength: A demultiplexer's output center wavelength must coincide with the

channel center wavelength

Fresnel Reflection: Fresnel reflection results from boundary interfaces between two

materials with different refractive indices.

Optical Amplifier Characteristics:

Noise: Optical Amplifiers introduce noise. This becomes significant as more and more

amplifiers are cascaded in the system.

Gain: The gain varies with wavelength

Gain Flatness: measure of the difference in gain over the range of wavelengths. The gain

differences is small for one fiber amplifier, but becomes more substantial over longer

links due to the cascade of amplifiers. These gain differences promote linear crosstalk.

Bandwidth

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Saturation Level: The upper limit of linear range.

Dynamic Nonlinearity: Channels are sometimes added or dropped, and the number and

position of the channels in use changes. These changes affects the amplifier response.

Light Source Characteristics:

Peak Wavelength: The peak wavelength is the wavelength at which the source emits the

most power. Since the peak wavelength is the operating wavelength, we choose those that

can be transmitted with the least attenuation over optical fiber. Thus, 780, 850, 1300, and

1550 nm are usually used. Saturation Level: The upper limit of linear range.

Spectral Width: Ideally, the light transmitted by light emitters is concentrated at the peak

wavelength. In practice, the light is emitted in a range of wavelengths centered at the

peak wavelength. The spectral width is the width of this range. The smaller the spectral

width, the better the system performance, as chromatic dispersion is minimized

Power: The output power of the source must be large enough to provide sufficient power

at the detector after fiber attenuation and other losses are taken into account.

Speed: The more quickly the source can turn on and off, the greater the bit rate and

bandwidth possible.

Another Characteristics is the fiber band. From Table 1, we can see C, L and U bands are

commonly used [7].

Table 1 Fiber Band

5.2 Micro Electro-mechanical System (MEMS)

MEMS device is a mechanical integrated circuit where the actuation force required moving

the parts may be electrostatic, electro-magnetic or thermal. These silicon micromachines are built

just the same way as a silicon integrated circuit. Starting with a silicon wafer, one deposits and

patterns materials such as polysilicon, silicon nitride, silicon dioxide and gold in a sequence of

Band Descriptor Range (nm)

O bandOriginal 1260 to 1360

E band Extended 1360 to 1460

S band Short wavelength 1460 to 1530

C band Conventional 1530 to 1565

L band Long wavelength 1565 to 1625

U bandUltralong wavelength 1625 to 1675

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steps, producing a complicated three-dimensional structure. However, unlike an integrated

circuit, at the end one releases the devise or etches pats of it away, leaving pieces free to move.

Because they are built using IC batch-processing techniques, these devices, albeit complicated,

are inexpensive to produce because many are fabricated in parallel [8].

VLSI fabrication techniques also allow designers to integrate micromechnical, analog, and

digital microelectronic devices on the same chip, producing multifunctional integrated systems.

Contrary to intuition, MEMS devices have proven to be robust and long-lived, especially ones

whose parts flex without microscopic wear points. MEMS devices have a number of desirable

attributes to offer to the systems architect such as small size, high speed, low power, and a high

degree of functionality. In particular, many of us believe that the size scale at which these

machines work well make them a particularly good match to optics problems where the devices,

structures, and relevant wavelengths range in size from one to several hundred microns. MEMS

allow the device to be high port count and data-rate independent.

The possible application area range from data modulators, variable attenuators, active

remote odes, active equalizers, add/drop multiplexers, optical switches, power limiters and

MEMS-based Optical Cross connect (OXC).

There are two types of MEMS: 2D MEMS and 3D MEMS. Figure 10 and 11 shows the 2D

and 3D MEMS architectures.

Figure 10 2D MEMS for optical crossconnect switching[8]

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Figure 11 3D MEMS architecture [8]

Mirror control for 2D MEMS switch is binary: on(1) and off(0). 2D MEMS is simple and

mature technology. 3D MEMS provides very large port count up to over 1000 input and output

ports. The drawback of 3D MEMS is its complexity and is still in the research lab.

5.3 Tunable Laser

Tunable laser is an important light emitter. The tuning methods are mechanical tuning,

acousto-optical tuning, electro-optical tuning and injection current tuning, etc. Table 2 summarize

the tunable laser[7].

Nortel has a 8 channel LCW508ET tunable DFB laser. It is a InGaAsP DFB laser, tunable

wavelength from 1528 nm to 1605 nm, with 20 mW output power. Figure 12 shows the product

and its features.

(a) 3D MEMS switching(b) Beam steering using a two-axis mirror(c) Fabricated MEMS mirror array

Table 2 Tunable laser summary

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Figure 12 Nortel LCW508ET Tunable DFB laser – 8 channel [15]

5.4 Tunable Filter

Tunable Filter can filter the input frequency. Table 3 summarize the features of tunable

filter. Figure 13 shows the JDS Uniphase polarization independent tunable bandpass filter—TB4

series. Table 3 Tunable Filter summary

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Figure 13 JDS Uniphase Polarization Independent tunable Bandpass filters – TB4 series[11]

5.5 Wavelength Converter

Wavelength Converter converts radiation at one wavelength to radiation at another

wavelength. Traditional product is O/E/O wavalength converter. The new generation is All-

optical wavelength converter. Table 4 shows the Optovation™ AOWC All Optical Wavelength

Converter features and applications.

Table 4 Optovation™ AOWC All Optical Wavelength Converter Features[16]

5.6 Optical Amplifier

Optical Amplifier is a device that amplifies an optical signal directly, without the need to

convert it to an electrical signal, amplify it electrically, and reconvert it to an optical signal. There

are several kinds of Optical Amplifier:

Erbium Doped Fiber Amplifier (EDFA)

Praseodymium Doped Fluoride Amplifier (PDFA)

Telluride Based Erbium Doped Optical Amplifier

Semiconductors Optical Amplifier (SOA)

Raman Amplifier

Application: Wavelength conversion Relieve wavelength blocking Dynamic provisioning/lambda management Bit rate/ protocol transparent regeneration Optical Cross Connects Optical Add Drop Muliplexeers

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Planar Waveguide Optical Amplifier

Among these OA, EDFA and SOA are the most widely used OA.

5.6.1 Erbium Doped Fiber Amplifier (EDFA)

EDFA is working around the 1550 nm window. It is transparent to modulation format and

is extremely low polarization sensitivity. EDFA can get high gain (50 dB) over 80 nm wide

bandwidth, and low noise. The disadvantage is the bad gain flatness. Figure 14 shows the

principle of EDFA.

Figure 14 EDFA Principle

Figure 15 shows the Nortel MGMFL-1AWC28 Multiwavelength Gain Module EDFA

product and features.

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Figure 15 Nortel MGMFL-1AWC28 Multiwavelength Gain Module EDFA product and features[15]

5.6.2 Semiconductor Optical Amplifier (SOA)

SOA is working at both 1330 nm and 1550 nm windows. It is small and compact. It can be

integrated with other devices. It has flat gain. The disadvantage is that it cannot do multiple

wavelength amplification. Figure 16 shows SOA scheme and Table 5 shows typical SOA

characteristics [9][14].

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Figure 16 SOA Scheme

Table 5 Typical SOA Characteristics

5.7 Optical Cross Connect (OXC)

As we mention earlier, MEMS-based OXC is in research stage. There is no commercial

product available. Other OXC is not suitable for Optical Switching Router.

5.8 Tunable Optical Add-Drop Multiplexer (TOADM)

TOADM is a flexible optical component. Figure 17 shows cascade Add/Drop can add or

drop multiple channels simultaneously. Figure 18 shows lambda Crossing™ LambdaFlow

Tunable OADM [13].

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Figure 17 Multiple OADM

Figure 18 Lambda Crossing™ LambdaFlow Tunable OADM [13]

6. Optical Switching Router Design

GMPLS network has two types of Optical Switching Routers:

Label Switching Router (LSR): LSR interacts and links with other LSRs

Label Edge Router (LER): LER serves as the “interface” between the LSR and the legacy

networks such as ATM, SONET and Ethernet.

Optical Switching Router Design has two parts:

Label Switching Router Forwarding Plane (LSR-FP) Design

Label Switching Router Control Plane Design

This methodology is consistent with the IETF GMPLS standard draft.

The LSR Forwarding Plane needs to perform:

LambdaFlow is a 40 channel tunable OADM with 4 Add/Drop ports. The OADM is tunable over the C band and is capable of adding and dropping data at a rate of 10 Gbps.

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— Data Routing t oappropriate ports (data forwarding)

— Channel add/drop to label Edge Router

— Label Swapping

Figure 19 shows the architecture of a LSR.

Figure 19 Architecture of LSR

6.1 LSR Forwarding Plane Design #1

Figure 20 shows LSR Forwarding Plane Design #1. Figure 21 and 22 shows the working

principle of Design #1.

Figure 20 LSR Forwarding Plane Design #1

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Figure 21 Design #1 Working Principle A

In working principle A, LSR #1 comprises of an array of demultiplexers, label swappers,

optical crossconnects, optical amplifiers and multiplexers. Demux separates incoming N from 1

port into individual . Label swapper will swap the label based on the instruction from control

plane. In the side view example, the red label green label, black purple, green black, and

cyan remains.

In working plane B, the cross connect redirects the wavelength into appropriate output

ports. The multiplexers group the signals from multiple layers of cross connects. There is one

input port and output ports that adds and drops from the LER.

Figure 22 Design #1 Working Principle B

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The advantages of Design #1 are:

–Fully connected

–Suitable for backbone

–For mesh connection

–Multiple input ports and multiple output ports

The disadvantages are:

–Expensive

–Require a lot of components

6.2 LSR Forwarding Plane Design #2

Figure 23 LSR Forwarding Plane Design #2

Figure 24 Design # 2 Working Principle

Figure 23 and 24 show the LSR Forwarding Plane Design #2 and its working principle.

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The advantages of Design #2 are:

–Cheaper and simpler

–For Ring Networks

–Suitable for metro or smaller networks

–Lower Insertion loss

The disadvantages of Design #2 are:

–Only 2 Nl input and output ports

–Not as flexible

–Extra add/drop switches are need if the number of wavelengths is increased.

6.3 LSR Control Plane Design

The proposed LSR-CP has to perform the following in order to set up the LSP routing and

resource table:

–Wavelength Assignment & Routing Management at each link.

–Traffic Engineering to set up the LSP (Protocol & Algorithm used: OSPF & RSVP)

–Link Management between LSRs

The incoming data has to check its label against the routing table to determine the next

destination hop. Hence, our first proposed optical processing is to perform table lookup. Figure

25 shows the structure of LSR Control Plane Design.

Figure 25 LSR Control Plane Design

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7. Conclusion

In this project, optical communication technology is reviewed. All-Optical Network,

DWDM, GMPLS and optical switching technology are discussed. The optical components

features and the characteristics are studied. Based on these information, the Optical Switching

Router Design draft are proposed.

Reference

[1] B. E. A. Saleh, and M. C. Teich, Fundamentals of Photonics, John Wiley & Sons Inc., 1991.[2] L. Kazovsky, S. Benedetto, and A. Willner, Optical Fiber Communication Systems, Artech House Inc.,

1996.[3] http://commsci.usc.edu/Willner.NSF/pdf/peter-kaiser-technology-roadmap.pdf[4] A. S. Tanenbaum, Computer Networks, Prentice Hall PTR, 1996.[5] R. Ramaswami, K. N. Sivarajan, Optical Networks: A Practical Perspective, Morgan Kaufmann

Publishers, 1998.[6] Nortal Networks Tutorials on WDM, CD version.[7] R.Martinez, P.Y.Choo, “ECE678 Class LectureNotes”, http://www.ece.arizona.edu/~ece678[8] P.B.Chu, et., “MEMS: The Path to Large Optical Crossconnects”, IEEE Commu. Mag., Mar.2002, pp.

80-87.[9] “Overview of Optical Amplifiers:Technology and Systems”,

http://www.gii.co.jp/english/gi4433_mn_optical_amplifiers.html[10] J. Hsu, “DWDM/Fiber Optic Technology”, http://jhsu.www3.50megs.com/tech-dwdm.html[11] “Optical Amplificatioin”, JDS Unifaphse,

http://www.jdsu.com/Presentations/Jennifer_Aspell_Optical_Amplification.pdf [12] “Kailight Photonics All-Optical Wavelength Converter”, http://www.kailight.com/[13] “LambdaFlow – Tunable Optical Add Drop Multiplexer (OADM) “,

http://www.lambdax.com/pages/LambdaFlow.asp[14] T. Kelly, I Andonovic, et., “Role of semiconductor optical amplifiers in advanced networking”,

http://lw.pennnet.com/Articles/Article_Display.cfm?Section=Articles&Subsection=Display&ARTICLE_I D=94177

[15] Nortel Optical Components Datasheets, http://www126.nortelnetworks.com/datasheets/

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[16] Optovation Product Fact Sheet, http://www.optovation.com/pdf/OPM3D.pdf[17] E. Rosen, A. Viswanathan, R. Callon, “Multiprotocol Label Switching Architecture”, Request for

Comments 3031, Network Working Group, January 2001.

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