SDH_PDH_GE_DWDM

8/7/2019 SDH_PDH_GE_DWDM

1/17

DWDM Technology. Global Network Hierarchy. SONET and TDM. Wavelength Division Multiplexing. TDM and WDM

Compared. SONET with DWDM. Introduction to DWDM Technology. Single-Mode Fiber Designs. Attenuation.

Dispersion. Light Sources and Detectors. Light Detectors. Optical Amplifiers. Erbium-Doped Fiber Amplifier.

Multiplexers and Demultiplexers. Techniques for Multiplexing and Demultiplexing. SONET/SDH. ATM. Gigabit

Ethernet.Introduction to DWDM Technology. Optical Power Budget.

64 DWDM Technology -

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Synchronous Digital Hierarchy (SDH or SONET)

The introduction of any new technology is usually preceded by much hyperbole and

rhetoric. In many cases, the revolution predicted never gets beyond this. In many more, it

never achieves the wildly over optimistic growth forecasted by market specialists - home

computing and the paperless office to name but two. It is fair to say, however, by whatever

method you use to evaluate a new technology, that synchronous d igital transmission does

not fall into this category. The fundame ntal benefits to be ga ined from its deployment by

PTOs seem to be so overwhelming that, bar a catastrophe, the bulk of today's

plesiochronous transmission systems used for high speed backbone links will be pushed

aside in the nex t few years. To quote Dataquest:, "It has been claimed by many industry

experts that the impact of synchronous technology will equal that of the transition from

analogue to digital technology or from copper to fibre optic based transmission."

For the first time in telecommunications history there will be a world-wide, uniform and

seamless transmission standard for service delivery. Synchronous digital hierarchy (SDH)

provides the capability to se nd da ta at m ulti-gigabit rates over today's single-mode fibre-

optics links. This first issue of Technology Watch looks at synchronous digital transmission

and evaluates its potential impact. Following issues of TW will look at customer oriented

broad-band services that will ride on the back of SDH deployment by PTOs. These will

include:

Frame relay

SMDS (Switched Multi-Megabit Data Service)

ATM (asynchronous transfer m ode)

High speed LAN services such as FDDI

Figure 1 shows the relationship between these technologies and services.

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Figure 1 - The Relationship Between Services

The use of synchronous digital transmission by PTO s in their backbone fibre-optic and

radio network will put in place the enabling technology that will support many new broad-

band data services demanded by the new breed of computer user. However, the

deployment of synchronous digital transmission is not only concerned with the provision of

high-speed gigabit networks. It has as much to do with simplifying access to links and with

bringing the full benefits of software control in the form of flexibility and introduction of

network mana geme nt.

In many respects, the benefits to the PTO will be the sam e as those brought to the

electronics industry when hard wired logic was replaced by the microprocess or. As with tha t

revolution, synchronous digital transmission will not take hold overnight, but deployment

will be spread over a decade, with the technology first appearing on new backbone links.

The first to feel the be nefits will be the PTO s themse lves, as dem onstrated by the

technology's early uptake by many operators including BT. Only later will customers directly

bene fit with the introduction of ne w services such as connectionless LAN-to-LAN

transmission capability.

According to one market research company it will take until the mid or late 1990s before

70% of revenue for network equipment manufacturers will be derived from synchronous

systems. Remembering that this is a multi-billion $ market, this constitutes a radical

change by a ny standard (Figure 2).

Users who extensively use PCs and workstations with LANs, graphic layout, CAD and

remote database applications are now looking to the telecommunication service suppliers

to provide the means of interlinking these now powerful machines at data rates

commensurable with those achieved by their own in-house LANs. They also want to be able

to transfer information to other metropolitan and international sites as easily and asquickly as they can to a colleague sitting at the nex t desk.

Figure 2 - European Revenue Growth of Transmiss ion Equipment

Digital data and voice transmission is bas ed on a 2.048Mbit/s bearer consisting of 30 time

division multiplexed (TDM) voice channels, each running at 64Kbps (known as E1 and

described by the CCITT G.703 specification). At the E1 level, timing is controlled to an

accuracy of 1 in 1011 by synchronising to a master Caesium clock. Increasing traffic over

the past decade has dema nded that more and m ore of these basic E1 bearers be

multiplexed together to provide increased capacity. During this time rates have increased

through 8, 34, and 140Mbit/s. The highest capacity commonly encountered today for inter-

city fibre optic links is 565Mbit/s, with each link carrying 7,680 base channels, and now

even this is insufficient.

Unlike E1 2.048Mbit/s bearers, higher rate bearers in the hierarchy are operatedplesiochronously, with tolerances on an absolute bit-rate ranging from 30ppm (parts per

million) at 8Mbit/s to 15ppm at 140Mbit/s. Multiplexing such bearers (known as tributaries

in SDH speak) to a higher aggregate rate (e.g. 4 x 8Mbit/s to 1 x 34Mbit/s) requires the

padding of each tributary by adding bits such that their combined rate together with the

addition of control bits matches the final aggregate rate. Plesiochronous transmission is

now often referred to as plesiochronous digital hierarchy (PDH).

Overview

Plesiochronous Transmission.

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Synchronous Digital Hierarchy (SDH or SONET)

What is Gigabit Ethernet?

Core DWDM network protection

Time Division Multiplexing (TDM) versusWavelength...

Marking SDH and DWDM packet friendly

CWDM, DWDM & ROADM

Using Ethernet over PDH in SONET/SDHNetworks

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Figure 3 - A typical Plesiochronous Drop & Insert

Because of the large investment in e arlier generations of ple siochronous transmission

equipment, each step increase in capacity has necessitated maintaining compatibility with

what was already installed by adding yet another layer of multiplexing. This has created

the situation where each data link has a rigid physical and electrical multiplexing hierarchy

at either end. Once multiplexed, there is no simple way an individual E1 bearer can be

identified in a PDH hierarchy, let alone extracted, without fully demultiplexing down to the

E1 level again as shown in Figure 3.

The limitations of P DS multiplexing a re:

A hierarchy of multiplexers at either end of the link can lead to reduced

reliability and resilience, minimum flexibility, long reconfiguration turn-around

times, large equipment volume, and high capital-equipment and maintenancecosts.

PDH links are generally limited to point-to-point configurations with full

demultiplexing at each switching or cross connect node.

Incompatibilities at the optical interfaces of two different suppliers can cause

major system integration p roblems.

To add o r drop an individualchannel or add a lower rate branch to a backbone

link a complete hierarchy of MUXs is required as shown in figure 3.

Because of these limitations of PDH, the introduction of an acceptable world-

wide synchronous transmission standard called SDH is welcomed by all.

In the USA in the early 1980s, it was clear that a new standard was required to overcome

the limitations presented by PDH networks, so the ANSI (American National Standards

Institute) SONET (synchronous optical network) standard was born in 1984. By 1988,

collaboration between ANSI and CCITT produced an international standard, a superset of

SONET, called synchronous dig ital hierarchy (SDH).

US SONET standards are based on STS-1 (synchronous transport signal) equivalent to

51.84Mbit/s. When encoded and modulated onto a fibre optic carrier STS-1 is known as

OC-1. This particular rate was chosen to accommodate a US T-3 plesiochronous payload to

maintain backwards compatibility with PDH. Higher data rates are multiples of this up to

STS-48, which is 2,488Gbit/s.

SDH is based on an STM-1 (155.52Mbit/s) rate, which is identical to the SONET STS-3 rate.

Some higher bearer rates coincide with SONET rates such as: STS-12 and STM-4 =

622Mbit/s, and STS-48 and STM-16 = 2.488Gbit/s. Mercury is currently trialing STM-1 and

STM-16 rate eq uipment.

SDH supports the transmission of all PDH payloads, other than 8Mbit/s, and ATM, SMDS

and MAN data. Most importantly, because ea ch type of pa yload is transmitted in containers

synchronous with the STM-1 frame, selected payloads may be inserted or extracted from

the STM-1 or STM-N aggregate without the need to fully hierarchically de-multiplex as with

PDH systems.

Further, all SDH equipment is software controlled, even down to the individual chip,

allowing centralised management of the network configuration, and largely obviates the

need for plugs and sockets. A future SDH network could look like Figure 4.

Synchronous Transmission

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Figure 4- An Example Future SDH Digital Network

SDH transmission systems have m any benefits over PDH:

Software Control allows e xtensive use of intelligent network ma nageme nt

software for high flexibility, fast and easy re-configurability, and efficient

network mana geme nt.

Survivability. With SDH, ring networks become practicable and their use

enables automatic reconfiguration and traffic rerouting when a link is damaged.

End-to-end monitoring will allow full management and maintenance of the

whole network.

Efficient drop and insert. SDH allows simple and efficient cross-connect withoutfull hierarchical multiplexing or de-multiplexing. A single E1 2.048Mbit/s tail can

be dropped or inserted with relative ease even on Gbit/s links.

Standardisation enables the interconnection of equipment from different

suppliers through suppo rt of common digital and optical standards a nd

interfaces.

Robustness and resilience of installed networks is increased.

Equipment size and operating costs are reduced by removing the need for

banks of multiplexers and de-multiplexers. Follow-on ma intenance costs a re

also reduced.

Backwards compatibly will enable SDH links to support PDH traffic.

Future proof. SDH forms the basis, in partnership with ATM (asynchronous

transfer mode), of broad-band transmission, otherwise known as B-ISDN or the

precursor of this service in the form of Switched Multimegabit Data Service,

(SMDS).

The introduction of synchronous digital transmission in the form of SDH will eventually

revolutionise all aspects of public data communication from individual leased lines through

to trunk networks. Because of the state-of-the-art nature of SDH and SONET technology,

there are extensive field trials taking place in 1992 throughout the world prior to

introduction in the 1993 - 1995 time scale.

There is still a lack of understanding of the ramifications of the introduction of SDH within

telecommunications operations. In practice, the use of extensive software control will

impact positively all parts of the business. It is not so much a que stion ofwhetherthe

technology will be taken up, but when.

Introduction of SDH will lead to the availability of many new broad-band data services

providing users with increased flexibility. It is in this area where confusion reigns with

potential technologies vying for supremacy. These will be discussed in future issues of

Technology Watch.

Importantly for PTOs, SDH will bring about more competition between equipment suppliers

designing essentially to a common standard. One practical effect could be to force

equipment p rices down, brought about by the larger volumes engendered by access to

world rather than local markets. At least one manufacturer is currently stating that they will

be spe nding up to 80% of their SDH development budge ts on ma nagem ent software

rather than hardware. Such was the situation in the computer industry in the early 1980s.

Not least, it will have a great impact on such issues as staffing levels and required

personal skills of personnel within PT Os.

SDH deployment will take a great deal of investment and effort since it replaces the very

infrastructure of the world's core communications networks. But it must not be forgotten

that there are still many issues to be resolved.

The be nefits to be ga ined in terms of improving operator profitability, and helping them to

compete in the ne w markets of the 1990s, are so high that deployment of SDH is just a

question of time.

Benefits of SDH Transmission

Conclusions

What is Gigabit Ethernet?

Gigabit Ethernet is an extension of the highly successful 10 Mbps (10BASE-T) Ethernet and




5/17

100 Mbps (100BASE-T) Fast Ethernet standards for network connectivity (see Figure 2).

IEEE has given approval to the Gigabit Ethernet project as the IEEE 802.3z Task Force, and

the specification is exp ected to be complete in ea rly 1998. There have been more than

200 individuals representing more than 50 companies involved in the specification

activities to date.

Figure 2. Functional elements of Gigabit Ethernet technology.

Gigabit Ethernet is fully compatible with the huge installed base of Ethernet and Fast

Ethernet nodes. The original Ethernet specification was defined by the frame format andsupport for CSMA/CD (Carrier Sense Multiple Access with Collision Detection) protocol, full

duplex, flow control, and mana geme nt objects a s de fined by the IEEE 802.3 standard.

Gigabit Ethernet will employ all of these specifications.

In short, Gigabit Ethernet is the same Ethernet that managers already know and use, but

10 times faster than Fast Ethernet and 100 times faster than Ethernet. It also supports

additional features that a ccommo date today's bandwidth-hungry applications and match

the increasing power of the server and desktop.

The Benefits of Gigabit Ethernet To support increasing bandwidth ne eds,Gigabit Ethernet incorporates enhancements that enable fast optical fiber connections at

the physical layer of the network. It provides a tenfold increase in MAC (Media Access

Control) layer data rates to support video conferencing, complex imaging a nd other data-

intensive applications.

Gigabit Ethernet has the advantage of being compatible with the most popular networking

architecture, Ethernet. Since its introduction in the early 1980s, Ethernet deployment has

been rapid, quickly overshadowing networking connection choices such as Token Ring and

ATM.

Gigabit Ethernet compatibility with Ethernet preserves investments in administrator

expertise and support staff training, while taking advantage of user familiarity. There is no

need to purchase additional protocol stacks or invest in new middleware. Just as 100 Mbps




6/17

Fast Ethernet provided a low-cost, incremental migration from 10 Mbps Ethernet, Gigabit

Ethernet will provide the next logical migration to 1000 Mbps bandwidth.

By 1996, according to IDC research projections, more than 80 percent of installed

connections were Ethernet. The dominance of Ethernet is expected to continue beyond

1998, particularly as this compa tible and scalable standard moves to gigabit speeds . In

addition to a wider choice of products and vendors, this market dominance has brought

with it a steady decrease in Ethernet hardware costs (see Figure 3).

Figure 3. Ethernet and Fast Ethernet products have shown steady cost reductions over time.

Similar trends are anticipated for Gigabit Ethernet products. (Source: Dell Oro Group)

As Information Technology (IT) depa rtments a dopt Fast Ethernet, and eventually Gigabit

Ethernet to enhance network performance to support robust desktop needs, they will see:

Increased network performance levels, including traffic localization and high-

speed cross segment movement

Increased network scaleability it will be easier to add and manage more

users and "hungrier" applications

Decreased overall costs over time

Fast Ethernet Paves the Way to Gigabit Ethernet Theproliferation of Intel Pentium, Pentium Pro and P entium II processor-based desktops

in corporate networks, combined with new bandwidth-intensive operating systems and

applications, has already influenced many LAN decision make rs to migrate to Fast

Ethernet. First proposed in 1993, Fast Ethernet is quickly becoming the high-speed

technology for today's LANs and corporate desktop users. It enjoys broad multi-vendor

support and brisk m igration interest among customers.

Intel believes Gigabit Ethernet will enjoy rapid deployment, following the proven track




7/17

records of Ethernet and Fast Ethernet. It addresses the bandwidth dilemma without

requiring costly protocol changes.

Most important, Gigabit Ethernet promises to efficiently match the power of high-

performance PCs that increasingly populate the LAN. As businesses go to these more

powerful processors, they need a high-performance infrastructure all the way from the

desktop to the backbone.

How Will Gigabit Ethernet be Deployed? Gigabit Ethernet deploymentscenarios will most likely mirror the model of Fast Ethernet, though the new technology is

expe cted to become standardized and impleme nted at an even faster rate. The

transformation will be driven by several factors:

The established popularity of Ethernet and the compatibility offered by Gigabit

Ethernet solutions

The e xperience and m omentum already garnered in bringing Fast Ethernet to

market

The commitment and expe rtise of the vendors involved

Deployment Scenarios

Scenario 1: Gigabit Ethernet will be switched and routed at the network backbone with

switch-to-switch connections. The first installations will use optical fibe r for long connections

between buildings and copper links for shorter connections.

Scenario 1

Scenario 2: Next, switch-to-server deployments will be implemented to boost access to

critical se rver resources. Man y 100 Mbps s witches contain m odule slots that will

accommodate Gigabit Ethernet so they will be able to uplink to server connections at

1000 Mbps.

Scenario 2

Scenario 3: Finally, as desktop costs come down and user network dema nds increase ,

Gigabit Ethernet will move to the workgroup and desktop level; Gigabit Ethernet switches

will enter the backbone as older switches are replaced and Gigabit Ethernet will take over

the switch fabric. This evolution will be driven by the increasing installation of 100 Mbps

PCs a s the standa rd desktop, and the migration of power users to switched 100 Mbps, and

switch-to-switch uplink conne ctions will advance to 1000 Mbps. At this time, custom ers will

see gigabit links that are compliant with the installed b ase of UTP Category 5 cabling.

(Over copper media, the Gigabit Ethernet Standards Committee has proposed two distance

options: 25 meters and 100 m eters.)




8/17

Scenario 3

Figure 4. Strong growth is predicted for Gigabit Ethernet products. ( Source: IDC #12382, Nov. 96)

Intel's Plans for Gigabit Ethernet Intel is uniquely positioned in the

emerging market for Gigabit Ethernet products. With strengths in chip design, technology

development a nd volume manufacturing, Intel will be ab le to give customers be st-of-class

products and comprehensive solutions at the be st value.

Intel has established itself as a leader in the transition to Fast Ethernet, with its family of

Fast Ethernet desktop, server and mobile adapters, print servers, hubs and switches. The

PCI bus for Intel architecture PCs and servers is tailor-made for today's power users. A 32-

bit PCI implementation already pumps out data in the multi-hundred m egabits range. In

the future, a 64-bit PCI bus will easily handle Gigabit Ethernet throughput at the desktop.

Adaptive Te chnology is one e xam ple of how Intel's silicon expertise has helped to boost

network performance and extend the product life of both network adapters and switches.

That sam e e xpertise will keep Intel a t the forefront of Gigabit chip spe ed e nhancements,

as well.

Ongoing relationships with key industry leaders Cisco, Microsoft and others reflect

Intel's commitment to extending and supporting industry standards by working with these

leaders to provide e nd-to-end, desk top-to-campus solutions. This cooperation will assurecompatibility with Gigabit Ethernet products that emerge from other vendors.

Intel intends to bring the same commitment to Gigabit Ethernet solutions as it has to Fast

Ethernet, initially focusing o n uplink s to the backbo ne, s witch-to-switch links, a nd s witch-to-

server connections. The strategy will be extended as needed to other high-bandwidth

networking products, in order to provide complete, cost-effective solutions, from the

desktop to the backbone.

Hernandez Caba llero Indiana M. CI: 15.242.745

Asignatura: SCO

Fuente:http://images.google.co.ve/imgres?

imgurl=http://www.intel.com/network/conne ctivity/reso urces/doc_library/tech_brief/pix /gigab it_ethern

et_fig1.gif&imgrefurl=http://www.intel.com/network/connectivity/resources/doc_library/tech_brief/giga

bit_ethernet.htm&usg=__LuFuk8i3jhDtKFNvALBeP4ecAeI=&h=270&w=410&sz=10&hl=es&start=18&um

=1&itbs=1&tbnid=JpUR eJ_rIZeIkM:&tbnh=82&tbnw=125&prev=/images %3Fq%3DGigabit%2BEthernet

%26um%3D1%26hl%3Des%26client%3Dfirefox-a%26sa%3DG%26rls%3Dorg.mozilla:es-

ES:official%26channel%3Ds%26tbs%3Disch:1




9/17



Core DWDM network protection

Figure 1 shows a typ ical DWDM link

Figure 1: Typ ical unpr otected DWDM link

Some of the wavelengths in the link may be sections of a larger single wavelength network such as a Sonet/SDH ring

or IP mesh. Services transported over this wavelength (T1 service in the diagram), may be pr otected by the

network's inherent recovery mechanism. Other wavelengths within the link may car ry high-speed p oint-to-point

traffic as a "leased line" service. Services of this type may be combined to use one DWDM wavelength. These are

called "sub-lambda services". If a single service utilizes a dedicated DWDM wavelength, it is r eferred to as a

"wavelength service". As can be seen from the figure above, clients of these services are not pr otected and any

failure in the DWDM link will interr upt their tr affic.

The high availability of these cr itical services is achieved thr ough the use of redundant r esources (equipment and

fiber ) and pr otection systems that perform automatic pr otection switching (APS) when failure of a working

resource is detected. There ar e several solutions for protection of DWDM networks. The choice of solution

depends on the redundant resources being used as well as the requir ed pr otection scheme. Resource redundancy

may vary according to var ious factors: cost and geographical limitations, detection and repair time, etc. The

protection scheme is determined by d eployment considerations. For example, paths in which there ar e large

length dif ferences between the working and protection links may requir e a "dual-ended" protection scheme, to

avoid problems associated with latency imbalance.

Lynx pr ovides the following solutions for DWDM network protection:

Optical channel/path protection

DWDM line protection

1:n DWDM tributary protection

In-line amplifier protection

Optical Channel /Path Protection

This mechanism provides end-to-end pr otection of an entir e DWDM channel, from one client site to the other. It is

based on complete channel redundancy, including fibers, inline equipment and transponder line-cards that

interface with the CPE.

Figure 2 shows an example of optical channel protection.

Figure 2: Optical channel/path protection

In some optical channels, which contain transport equipment and interconnecting fibers, failures can be detected

by monitoring the optical signal. I n such cases, performing 1+1 single-ended pr otection can be done by fiber




10/17

protection systems. For other pr otection schemes, such as dual-ended p rotection, Lynx pr ovides special in-band

signaling solutions. I n cases where the transport equipment does not suppor t shut-off during failure, but sends AIS

signals instead, failure detection must be done at the pr otocol level. Lynx off ers Op tical Failure M onitoring (OFM)

modules, capable of detecting f ailures in all these situations. Lynx has also developed a unique technology,

LynxSense, to ensure that pr otection switches will indeed switch immediately when required.

Some Lynx pr otection systems allow users to car ry extra traffic, thereby improving the utilization of the network

redundancy. This extr a tr affic is car ried over the pr otection channel while both channels are operational.

DWDM Line Protection

In some cases, deploying a redundant DWDM line may be more cost-effective than using several redundant

channels: this depends on the number of act ive channels in a DWDM link that requir e protection (e.g., not

segments of SDH/Sonet rings), and the amount of in-line transport equipment. Assuming that the terminal

transponders can be p rotected thr ough a 1+N pr otection scheme (Figure 3), and that the passive Mux/Demux is

highly reliable, carr iers may choose to protect only the DWDM line. Figure 4 shows such an application.

One direction depicted (client Tx)

Upon failure of the blue transponder the backup tr anspoder is configures to Blue and the

client and network fib ers p reviously connected to the blue transponder are switched to the

backup one.

Figure 3: 1-N protection scheme

Figure 4: DWDM line protection

As in the case of 1+1 single-ended optical channel protection, simple DWDM lines (such as clear fiber) can be

protected by fiber protection systems. DWDM lines where in-line equipment such as EDFA is used, may be

subjected to noisy optical signals dur ing failures. Opt ical power monitoring may not be sufficient, and Lynx's

Optical Failure M onitor (OFM) for DWDM lines is r ecommended for effective and comprehensive failure detection.

Compared to electro-optical (OEO) p rotection mechanisms, optical switching is a far more cost-effective way ofprotecting DWDM lines. Electro-optical protection requires double multiplexing/demultiplexing, and N termination

and pr otection systems (where N is the number of potential wavelengths over the line).

In-line Amplifier Protection

In some cases, due to cost or geographical limitations, the DWDM link cannot be redundantly diverse; and the

pr otection solutions descr ibed above cannot be used. In other cases, where some form of link protection exists,

there may be long lag times in identifying and repairing in-line amplifiers, leaving the network vulnerable for

unacceptably long per iods. In such cases, car r ier s can use Lynx's EDFA systems to pr otect some of the in-line

amplifiers locally, pr oviding an option for immediate recovery while repair crews are dispatched. Lynx 1:n (2+1)

add-on protecti on systems are used to protect an EDFA node (two EDFAs, one in each direction) with the use of a

single spare EDFA. A special EDFA failure monitor ing module, built into the protection system, is capable of

detecting EDFA failuresincluding those in which the EDFA continues to transmit optical power.

Figure 5 shows an example of EDFA pr otection.




11/17



Figure 5: In-line amplifier (EDFA) pr otection

Time Division Multiplexing (TDM) versus Wavelength

Division Multiplexing (WDM)

Ultrahigh-speed photonic networks capable of accommodating the increase

in Internet data traffic will form the infrastructure of the information society

of the next generation. There are two types of multiplexing schemes to

accommodate such large amount of information: wavelength division

multiplexing (WDM), which multiplexes signals using lightwaves with different

wavelengths, and time division multiplexing (TDM), which multiplexes signals

in different bit slots in the t ime domain. In WDM systems, t ransmitters and

receivers in each channel work independently, and thus WDM allows signalswith different format to be accommodated in one network. In this sense,

WDM is an "analog" multiplexing scheme. In constrast, TDM requires

sophisticated signal processing employing, for example, multiplexers,

demultiplexers, clock recovery, and network synchronization. Nevertheless it

supports "digital" multiplexing, where synchronized high speed signals are

processed together. Optical TDM (OTDM) makes the most of these

advantages in the optical domain and is another important technique for the

construction of photonic networks in addition to the development of

highspeed signal processing.




12/17

Fig. 1 TDM versus WDM

1.28 Tbit/s OTDM signal transmission

Fig. 2 Optical transmission systems and signal pulse interval.

Figure 2 shows the improvement in the T DM transmission sp eed in backbone terrestial

optical transmission systems in Japan. The transmission spe ed ha s increase d from 400

Mbit/s to 2.4 Gbit/s and 10 Gbit/s. With the help of WDM, the capacity can be increased

further. Work on a 40 Gbit/s system is currently in progress and it will be installed in the

backbone system in the ne ar future. This system be nefits from the de velopment of high

speed electronic devices.

The next research target is ultrahigh-speed OTDM transmission with a bit rate of 160

Gbit/s or even 1 Tbit/s, where highspeed signals are multiplexed in the optical domain

alone, without the need for any electronic devices. OTDM transmission operates in a

regime far beyond the capability of electronic devices. In this regime ultra short pulses are

transmitted with pulse widths of pico second to a few hundred femto second order. Thiswould be impossible without the development of advanced technologies such as the

generation of fem to-second pulses, higher-order dispersion compensation, and all-optical

demultiplexers.

Fig. 3 Experimental setup for 1.28 Tbit/s OTDM signal transmission.

Figure 3 shows our setup for a 1.28 Tbit/s-70 km OTDM transmission experiment, which

was successfully achieved for the first time in the world. A 3 ps, 10 GHz regeneratively and

harmonically mode-locked fiber laser operating at 1.544 m was used a s the original pulse

source. The output laser pulse was intensity-modulated at 10 Gbit/s and the pulse train

was coupled into a d ispersion-flattened dispersion decreasing fiber. This realized adia batic

soliton compression to less than 200 fs. We incorporated a phase modulation technique

that compensated for the third- and fourth-order dispersion of the transmission fiber. The

pre-chirped 10 GHz pulse train was optically multiplexed to 640 Gbit/s by using a planar

lightwave circuit (PLC). We obtained a 1.28 Tbit/s signal by polarization multiplexing two

640 Gbit/s pulse trains.




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Fig. 4 Optical signal waveform in 1.28 Tbit/s OTDM signal transmission.

Fugure 4 shows the input and output data patterns. Clean 640 Gbit/s signals were

obtained in ea ch channel. The pulse broadening a fter 70 km transmission was o nly 20 fs.

We obta ined a bit error rate of 109 was achieved for all the channels.


Asignatura: SCO


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Marking SDH and DWDM packet friendly

Back in 1993, I wrote about the advances taking pace in fiber optic technologies and

optical amplifiers. At that time, technology development was principally concerned with

improving transmission distances using optical amplifier technology and increasing data

rates. Thes e op tical cables a single wavelength and he nce provided provided a single data

channel.Wide area traffic in the early 1990s was principally dominated by Public Switched

Telephone Network (PSTN) telephony traffic as this was well before the explosion in data

traffic caused by the Internet. When additional throughput was required, it was relatively

simple to lay down additional fibres in a terrestrial environment. Indeed, this became

standard procedure to the extent that many fibres were laid in a single pipe with only a few

being used or lit as it was kn own. Unlit fibre strand s were called dark fibre. For terrestrial

networks when increasing traffic demanded additional bandwidth on a link, it was simple

job to simply add a dditional ports the a ppropriate SDH equipment and light up an

additional dark fibre.

Wave Division Multiplexing

(Picture credit: photeon)

In undersea cables adding

additional fibres to support traffic

growth was not so easy so the

concept ofWave Division

Multiplexing (WDM) came into

common usag e for point to point

links (the laboratory development

of WDM actually went back to the

1970s). The use of WDM enabled

transoceanic carriers to upgrade

the bandwidths of their undersea

cables without the need to lay

additional cables which would cost

multiple billions of Dollars.

As shown in the picture, a WDM based system uses multiple wavelengths thus multiplying

the available ba ndwidth by the number wavelengths that could be supported. The num ber

of wavelengths that could be used a nd the d ata rate on e ach wavelength were limited by

the quality of the optical fibre that was being upgraded and the current state-of-the-art of

the optical termination electronics. Multiplexers and de-multiplexers at either end of the

cable aggregated and split the combined d ata into separate channels by converted to a nd

from electrical signals.

A number ofWDM technologies or architectures were standardised over time. In the early

days, Course Wavelength Division Multiplexing (CWDM) was relatively proprietary in

nature a nd me ant different things to different companies. CWDM combines up to 16

wavelengths onto a single fibre and use s an ITU standard 20nm spacing between the

wavelengths of 1310nm to 1610nm. With CWDM technology, since the wavelengths are

relatively far apart compared to DWDM, the are generally relatively cheap.

One of the major issues at the time was that Erbium Doped Fibre Amplifiers (EDFAs) as

described in optical amplifierscould not be utilised due to the wavelengths selected or the

frequency stability required to be able de-multiplex the multiplexed signals




14/17

In the late 1990s there was an

explosion of development

activity aimed at deriving

benefit of the concept of

Dense Wavelength Division

Multiplexing (DWDM) to be

able to utilise EDFA amplifiers

that operated in 1550nm

window. EDFAs will amplify any

number of wavelengths

modulated at any data rate as

long as they are within its

amplification bandwidth.

DWDM combines up to 64

wavelengths onto a single fibre and use s an ITU standard that specifies 100GHz or

200GHz spacing between the wavelengths, arranged in several bands around 1500-

1600nm. With DWDM technology, the wavelengths are close together than used in CWDM,

resulting in the multiplexing equipment being m ore complex and expe nsive than CWDM.

However, DWDM allowed a much higher density of wavelengths and enabled longer

distances to be covered through the use of EDFAs. DWDM systems were developed that

could de liver tens of Te rabits of d ata over a single fibre using up to 40 or 80 simultaneous

wavelengths e.g. Lucent 1998.

I wouldn't claim to be an expert in the subject, but I would expect that in dense urban

environments or over longer runs where access is available to the fibre runs, it is

considerably cheaper to install additional runs of fibre than to install expensive DWDM

systems. An exception to this would be a carrier installing cables across a continent. Ifdark fibre is available then it's an e ven simpler decision.

Although considerable advances were taking place at optical transport with the advent of

DWDM systems, e xistingSONET and SDH standards of the time were limited to working

with a single wavelength per fibre and were also limited to working with single optical links

in the physical layer. SDH could cope with astounding data rates on a single wavelengths,

but could not be used with emerging DWDM optical equipment.

Optical Transport Hierarchy

This major deficiency in SDH / SONET led to further standards development initiatives to

bring it "up to date". These are known as the Optical Transport Network (OTN)working in

an Optical Transport Hierarchy (OTH) world. OTH is the same nomenclature as used for

PDH and SDH networks.

The ITU-T G.709 (released be tween 1999 2003) standard Interfaces for the OTN is a

standardised set of methods for transporting wavelengths in a DWDM optical network that

allows the use of completely optical switches known as Optical Cross Connects that does

not require expensive optical-electrical-optical conversions. In effect G.709 provides a

service abstraction layer between services such as standard SDH, IP, MPLS or Ethernet

and the physical DWDM optical transport layer. This capability is also known as OTN/WDH

in a similar way that the term IP/M PLS is used. Optical signals with bit rates of 2.5, 10, and 40

Gbits/s were standardised in G.709 (G.709 overview presentation) (G.709 tutorial).

The functionality added to SDH in G.709 is:

Managem ent of optical channels in the optical domain

Forward error correction (FEC) to improve error performance and enable

longer optical spans

Provides standard methods for managing e nd to e nd optical wavelengths

Other SDH extensions to bring SDH up to date and make it 'packet friendly'

Almost in parallel with the development of G.709 standards a number of o ther extensions

were ma de to SDH to m ake it more packet friendly.

Generic Framing Procedure (GFP): The ITU , ANSI, and IETF have spe cified standards for

transporting various services such as IP, ATM and Ethernet over SONET/SDH networks. GFP

is a protocol for encapsulating packets over SONET/SDH networks.

Virtual Concatenation (VCAT): Packets in data traffic such as Packet over SONET (POS) are

concatenated into larger SONET / SDH payloads to transport them more efficiently.

Link Capacity Adjustment Scheme (LCAS): When customers' needs for capacity change,

they want the change to occur without any d isruption in the s ervice. LCAS a VCAT control

mechanism, provides this capability.

These s tandards have helped SDH / SONET to adap t to an IP or Ethernet packet based

world which was missing in the original protocol standards of the early 1990s.

Next Generation SDH (NG-SDH)

If a SONET or SDH network is deployed with all the extensions that make it packet friendly

is deployed it is commo nly called a Next Generation SDH (NG-SDH). The diagram be low,

shows the different ages of SDH concluding in the latest ITU standards work called T-MPLS

( I cover T-MPLS in: PBT PBB-TE or will it be T-MPLS?




15/17



Transport Ages (Picture credit: TPACK)

Multiservice provisioning platform (MSPP)

Another term in widespread use with advanced optical networks is MSPP.

SONET / SDH equipment use what are known as add / drop multiplexers (ADMs) to insert

or extract data from an optical link. Technology improvements enabled ADMs to include

cross-connect functionality to manage multiple fibre rings and DWDM in a single chassis.

These new devices replaced multiple legacy ADMs and also allow connections directly from

Ethernet LANs to a service provider's optical backbone. This capability was a real benefit to

Metro networks sitting between enterprise LANs and long distance carriers.

There are ma ny variant acronyms in use as there are e quipment vendors:

Multiservice provisioning platform (MSPP): includes SDH multiplexing,

sometimes with add-drop, plus Ethernet ports, sometimes packet m ultiplexing

and switching, sometimes WDM.

Multiservice switching platform (MSSP): an MSPP with a large capacity for TDM

switching.

Multiservice transport node (MSTN): an MSPP with feature-rich packet switching.

Multiservice access node (MSAN): an MSPP d esigned fo r customer access,

largely via coppe r pairs carrying Digital-Subscriber Line (DSL) se rvices.

Optical edge device (OED): an MSSP with no WDM functions.

This has been an interesting post in that it has brought together many of the technologies

and protocols discussed in the previous posts, in particular SDH, Ethernet and MPLS and

joined them to optical networks. It seem strange to say on o ne hand that the main

justification of deploying converged Next Generat ion Networks (NGNs) based on IP is to

simplify existing networks and hence reduce costs, but then consider the complexity and

plethora of acronyms and standards associated with that!


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CWDM, DWDM & ROADM

Primarily driven by Ethernet and packet-based services, the need for bandwidth has

exploded. Even m id-sized network operators are dema nding multiple 10 Gbps pipes to

In a typical fiber optic network, the data signal is transmitted using single

light pulse at e ither 1310 nm or 1550 nm wavelengths. Historically, the way

to increase the capacity of a single fiber is to increase the bit rate of the

signal (1 Mbps to 10 Mbps to 100 Mbps). Throughout the last 30 years,

optical systems have increased their capacity regularly, allowing for

bandwidth upgrades that outpaced the growth in bandwidth demands.




16/17

accommodate large increases for growing and diverse applications such as surveillance,

ITV, and data-center connections. This growth requires transport that is flexible and

scalable

Wavelength division multiplexing (WDM) is now a cost-effective, flexible and scalable

technology for increasing capacity of a fiber network. WDM architecture is based a simple

concept instead of transmitting a single signal on a single wavelength, transmit multiple

signals, each with a different wavelength. Each remains a separate data signal, at any bit

rate with any protocol, unaffected by other signal on the fiber.

Wave Division Multiplexing

There are two types of WDM: Coarse and Dense W avelength Division Multiplexing (CWDM

and DWDM).

CWDMuses a wide spectrum a nd accommodates e ight channels. This wide spacing of

channels allows for the use of mo derate ly priced optics, but limits capa city. CWDM is

typically use d f or lower-cost, lower-capacity, shorter-distance ap plications where cost is the

paramount decision criteria.

DWDMsystems pack 16 or more channels into a narrow spectrum window very near the

1550 nm local attenuation minimum. Decreasing channel spacing requires the use of

more precise an d costly optics, but allows for significantly more scala bility. Typical DWDM

systems provide 1-44 channels of capacity, with some new systems, offering up to 80-160

channels. DWDM is typically used where high capacity is needed over a limited fiber

resource or where it is cost prohibitive to deploy more fiber.

As with most transport systems, there are requirements to add and drop traffic along ring

and tapered ne tworks. WDM systems support two types of add/drop Fixed and

Reconfigurable Optical Add/Drop Multiplexers (FOADM and ROADM).

FOADMs are base d on simple static fibers that permit add/drop of p redefined wavelengths.

These systems a re fully integrated and mana geable a nd provide a fine ba lance of

features and cost.

ROADMs add the ability to remotely switch traffic from a WDM system at the wavelength

layer. While more expensive than FOADMs, ROADMs are used in application where traffic

patterns are not fully known or change frequently.

The ke y features a nd benefits of W DM include:

Protocol and Bit Rate A gnostic wavelengths can accept virtually any services

Fiber Capacity Expansion WDM adds up to 160X bandwidth to a single fiber

Hi Cap/Long Haul and Lo Cap/Short Haul Applications CWDM and DWDM

provide price pe rformance fo r virtually any ne twork

Remotely Provisionable ROADMs provide the flexibility to change with

changing network requirements

WDM Network

CWDM and DWDM

ROADM and FOADM




17/17

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