Ekinops Application Note - Cost Effective ROADM Solution

Figure 1. Examples of 2 and 4 Degree ROADM Network Elements with local add-drop traffic

LocalAdd/Drop

Degree 1 Degree 2

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E K I N O P S P R O P R I E T A R Y I N F O R M A T I O N : : A L L R I G H T S R E S E R V E D

•••BUILDING A COST EFFECTIVE,AFFORDABLE, AND SCALABLE

ROADM BASED OPTICALNETWORK

ROADMs are a disruptive technology that have and will

continue to benefit the industry in many ways. ROADM

technology allows Service Providers network flexibility

without major up front planning or future reconstruction of

the network to accommodate unforeseen service demand.

In addition, ROADM technology holds a very promising

future in the realization of all optical switching and protection.

ROADMs do still have one inhibitor to ubiquitous deployment

in all networks however. This inhibitor is up front cost. Most

ROADM solutions available in the industry today are many

times more expensive than fixed filter solutions and whether or

not this extra cost is worth the investment is still in debate.

There are some lower cost older generation ROADM solutions

available (like Planar Lightwave Circuit, PLC ROADMs for

instance) but these solutions have often fallen short in

scalability or functionality to the extent that newer WSS (Wave

Selective Switch) based ROADMs are preferred. For instance,

many of the PLC based ROADMs had limitations in the number

of degrees supported or in their ability to transport and switch

40Gig wavelengths.

:: So, is there a compromise between cost andflexibility that can be achieved?

The answer is yes. Although, ROADMs will likely be more

expensive than fixed filters for a very long time, the answer to

allowing a ROADM solution to scale in cost with the service

provider’s needs lies in the implementation of ROADM network

elements using available off-the-shelf WSS ROADM technologies.

To understand this better, let’s talk a little about WSS ROADM

technology choices that ROADM solution providers offer. First

to level set, let’s be clear on what we mean by a 2 degree or

3 degree ROADM network elements. The diagram below shows

an example of 2 and 4 degree ROADM network elements with

local add drop traffic.

In the figure 1 above, a 2 degree ROADM network element is a network node that can add and drop traffic locally to or from 2 directions

in the network (right and left in the diagram above). A four degree ROADM network element is a network node that can add and drop

traffic locally to or from 4 directions in the network (right, left, up, and down in the diagram above). In the industry, it is now generally

accepted that any ROADM network element should be able to scale to 8 degrees and drop any channel from any degree locally with

no limitation.

APPLICATION NOTE

LocalAdd/Drop

Degree 1 Degree 2

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Degree 4 ROADM

EKINOPS_WP_ROADM:Mise en page 1 19/01/09 12:21



APPLICATION NOTE


The key in scaling cost lies in the ROADM components used

by the ROADM network element manufacturer given that the

ROADM components used make up the majority of the cost of

the ROADM network element. There are a number of ROADM

optical components that could be used by transport vendors to

produce the 2 ROADM examples above. ROADM components

are classified by the number of degrees that they support.

For instance, a ROADM component that can support up to

2 degrees with local add drop of any channel coming from or

going to any of those degrees would be called a 1x2 ROADM.

Typically, one ROADM component is necessary for each

degree in a ROADM network element so, a 2 degree ROADM

network element would require 2 1x2 ROADM components.

A ROADM component that can support up to 4 degrees with

local add drop of any channels coming from or going to any of

those 4 degrees would be called a 1x4. A four degree

ROADM network element built with this component would

require 4 ROADM components, one for each degree.

As an example, the figure below shows how a 2 degree ROADM

network element is built from 1x2 ROADM components.

LocalAdd/Drop

Degree 1 Degree 2

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1 x 2 WSS1 x 2 WSS

In a ROADM network element, each ROADM component is

used to add and drop channels from a single degree. The

ROADM components are then interconnected to allow

channels to be connected from one degree to the other.

ROADM components have ports that allow for this optical inter-

connection as well as for the dropping of local channels. The

number of ports that a ROADM component has determines

how many degrees it can be interconnected with. In the example

above, the 1x2 ROADM component has 2 ports, one for local

add drop and one for interconnection to the 2nd ROADM

component necessary to support 2 degrees. So, the ROADM

network element in the example above has no more ports for

expansion and will forever be limited to 2 degrees unless traffic

is taken down and the ROADM components are replaced with

higher degree ROADM components. In order to allow for future

expansion, the above ROADM network element can be built

with 2 1x4 ROADM components that have 2 additional ports

each . This would allow for the addition of 2 more ROADM

components in the ROADM network element and upgrade the

ROADM network element from 2 degrees to 4 degrees. The

figures below show a 2 degree ROADM network element built

with 1x4 ROADM components and that same ROADM network

element upgraded to 4 degrees with the addition of two more

1x4 ROADM components.

LocalAdd/Drop


LocalAdd/Drop

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1 x 4 WSS1 x 4 WSS

Figure 2, A 2 Degree ROADM Network Element Built Using 1x2 WSS ROADM Components


LocalAdd/Drop

Degree 1 Degree 2

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Degree 2 ROADM




APPLICATION NOTE


Notice that in the 4 Degree ROADM network element, each

ROADM component uses all 4 of its ports. One port for local

add drop and the other 3 ports to interconnect with the other

ROADM components representing the other degrees of the

ROADM network element. So, why would one ever build a

2 degree ROADM network element with 1x2 ROADMs as

shown in figure 2 when the ROADM network element could

be built to be scalable as shown in figure 3 by using 1x4

ROADM components? This is where the dilemma arises when

designing ROADM network elements. The tradeoff is cost vs.

scalability. Of course, a 1x2 ROADM component is cheaper

than a 1x4 ROADM component so, scalability comes with a

price. The 2 degree ROADM network element is cheaper when

built with 1x2 ROADM components than it is when built with

1x4 ROADM components but, the 2 Degree ROADM network

element is scalable to 4 degrees when built with 1x4 ROADM

components whereas the 2 degree ROADM network element

built with 1x2 ROADM components is not.

Because the primary benefit of a ROADM network element is

to allow flexibility and scalability without planning, most transport

system vendors default to utilizing larger ROADM components

to build even lower degree ROADMs. The generally accepted

requirement for a ROADM network element is to allow for

8 degrees or more of expansion without traffic interruption.

Because of this, many system suppliers opt for utilizing 1x8

or larger ROADM components for all of their ROADM network

elements. This means that lower degree ROADM network

elements are more expensive than they need to be as most

ROADM network elements will always remain 4 degrees or

fewer and in fact many will always remain 2 degrees.

Another alternative would be to allow the service provider to

pick from a number of different ROADM network element

choices that are built from various degree ROADM components

allowing the customer to choose his own price vs. scalability

tradeoff. There is, however, a better solution. A solution that

allows for an optimal tradeoff of flexibility and price, regardless

of the size of the ROADM network element. What one can do

is utilize optical splitters/couplers to allow for the addition of

new ROADM components even if the ROADM component

initially used does not have any remaining ports. What an optical

splitter/coupler does is replicate all of the channels on a fiber

onto another fiber that can then be used to transfer all channels

to another ROADM component. The optical splitter is placed

in front of the existing ROADM component allowing for all

channels being received by that ROADM component to be

replicated and fed to a future ROADM component that will be

used to accommodate future degrees in the ROADM network

element. The figure below shows an example of a 1x2 network

element with optical Couplers/Splitters.

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Figure 5, A 2 Degree ROADM Network Element BuiltUsing 1x2 WSS ROADM Components with a Splitter/Coupler

for future expansion

LocalAdd/Drop

Degree 1 Degree 2

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Degree 2 ROADM




APPLICATION NOTE


The figure below shows how additional 1x2 ROADM components

can be coupled into the ROADM network element to provide

additional ROADM ports for connectivity to future ROADM

network element degrees. The coupler replicates all channels

to this additional ROADM component so it can be used to

switch any channels to future degrees.

And finally, the figure below shows how the additional 1x2

ROADM components can be used to interconnect the existing

2 degrees to an additional 2 degrees making this ROADM

network element 4 degrees.

Note that the 2 1x2 WSS ROADM components coupled together

for each degree now have a combined 4 ports allowing them

to act as a virtual 1x4 ROADM component. The first 1x2

ROADM component of each degree is used to add and drop

channels for that degree as well as connect to one other

degree and the second 1x2 ROADM component is used to

provide a path for all channels to the other 2 degrees not

connected to by the first 1x2 ROADM component. In a real

system, each ROADM component would be encapsulated in

a module and the Splitter/Coupler would be encapsulated in

a module. This architecture allows Service Providers to

incrementally add these components and the ability to scale

their ROADM capability and cost as necessary to accommodate

revenue bearing traffic.

This technique of coupling together ROADM components

works quite well but there is a point where the number of smaller

ROADM components necessary to emulate a larger ROADM

component costs more than the larger ROADM component.

But in most cases the benefits of being able to scale cost far

outweigh that risk. The figures 8 and 9 show an example (using

the Ekinops 360 scalable ROADM architecture) of the number

of ROADM components needed to achieve 1 through 8 degree

ROADM network elements as it relates to the type of ROADM

component used and the relative cost of each solution

(1 through 8 degree ROADM network elements).

BuildModules Modules Modules Modules Modules Modules Modules

Usingneeded at needed at needed at needed at needed at needed at needed at

2 degrees 3 degrees 4 degrees 5 degrees 6 degrees 7 degrees 8 degrees

ROADM 1x2 2 6 8 15 18 28 32

ROADM 1x4 2 3 4 10 12 14 16

ROADM 1x8 2 3 4 5 6 7 8

LocalAdd/Drop


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1 x 2 WSS1 x 2 WSS

Figure 6, A 2 Degree ROADM Network Element BuiltUsing 1x2 WSS ROADM Components with additional 1x2 ROAD

components coupled in for future expansion

Figure 8, Scalability of ROADM, Number of components necessary to construct various size ROADM network elements

LocalAdd/Drop

Degree 1 Degree 2

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Degree 4 ROADM

Figure 7, A 4 Degree ROADM Network Element BuiltUsing 1x2 WSS ROADM Components





APPLICATION NOTE

When looking at the cost of a single ROADM network element

as depicted in the chart above, one might deduce that it is best

to always use 1x2 ROADM components to build a network. It

scales the most incrementally and only presents risk if the

ROADM network element is more than 6 degrees which will

likely be a small percentage of the time. What the chart does

not show however is that with the splitter/coupler technique,

different ROADM components can be mixed. So for instance,

based on the data above, one might want to start with a 1x4

ROADM component and scale it using 1x2 ROADM components

in the case that the ROADM network element is initially

4 degrees. In addition, one must consider the average ROADM

network element size in a network when selecting the ROADM

component to build with. The following chart shows how different

distributions of ROADM network elements of different degrees

effect cost of ROADM components in the network:

One can see from the figure 10 that if the network leans heavily

toward lower degree, ROADM network elements, one should

build with 1x2 ROADM components, if the network leans

toward higher degree network elements, one should build with

1x4 degree ROADM network elements. It is also apparent that

building with 1x8 ROADM components will rarely make sense.

When making the decision to build out a network, one must

also consider how long it will take to build ROADM network

elements to higher degrees and therefore how long it will take

for having utilized a higher degree ROADM component to pay-

off (i.e. to get to the size where having utilized the larger

ROADM component is cheaper than having built with smaller

ROADM components). This is particularly important given that

cost of money declines over time (which is not reflected in the

chart) meaning that if one chooses to build more incrementally

using smaller ROADM components, incremental ROADM

components actually cost less at a later date even if the price

remains the same given that the value of money declines.

In addition, differed payment means the money can be used

for other investments that provide return or money can sit in

the bank and earn interest. One can see that the 1x2 and 1x4

ROADM components provide a far better incremental growth

strategy. The splitter/coupler technique for building ROADMs

is clearly a “Pay as you Grow” strategy. Even if there is some

risk that the network will in the end have a larger distribution of

high degree ROADM network elements than expected causing

additional cost, the benefit of the ability to invest incrementally as

the network returns revenue and the ability to defer purchases

to a later date far outweigh the risk. This type of incremental

investment certainly makes sense from the stand point of

return on investment in your business.

Figure 9, Relative cost of ROADM components in different degree ROADM network elements

when using various ROADM components to build them

Figure 10, Comparative cost of ROADM components based on distribution of ROADM Network Elements

Degrees

ROADM 1x2

ROADM 1x4

ROADM 1x8

2 3 4 5 6 7 8

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Mix of ROADM network elements

Using 1x2 ROADMComponents



5% at 8 degrees, 15% at 8 degrees, 40% at 8 degrees,25% at 4 degrees, 45% at 4 degrees, 50% at 4 degrees,70% at 2 degrees, 40% at 2 degrees, 10% at 2 degrees,

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APPLICATION NOTE

And finally, the splitter/coupler technique can also be optimized

per ROADM network element given that different size ROADM

components can be mixed and that one can tactically make

decisions on what ROADM component to use next as ROADM

network elements add degrees based on the cost of adding the

incremental degree vs. the latest knowledge on how big the

ROADM network element is likely to grow.

Another implementation of the splitter/coupler technique is for

future proofing fixed filter and fixed OADM drop sites so that

they can later be upgraded, in service, to ROADM sites. This

is useful if the use of ROADMs is cost prohibitive for a service

provider but the service provider wants the option to install

them in the future, perhaps when the price comes down. The

figure below shows a fixed filter site and that same fixed filter

site upgraded to a ROADM network element utilizing our

splitter/coupler design.

The above figure 12 provides a service provider the option to upgrade to a ROADM network element at a later date deferring the cost of

installing the expensive ROADM components. This upgrade is not service-disruptive and is particularly useful if the route is not protected.

In this example, 1x2 ROADM components are utilized to upgrade a fixed filter to a 2 Degree ROADM. Higher degree ROADM components

could have been utilized to make this a higher degree ROADM network element if desired. Just like in the previous examples, ROADM

components can also be built with splitters/couplers in order to allow this ROADM network element to be upgraded to a higher number of

degrees in the future.

Figure 11, Add Drop Site using fixed filters with Splitter/Couplersin place for future ROADM upgrade

Figure 12, Add Drop Site upgraded to 2 degree ROADM using Splitter/Couplers

LocalAdd/Drop


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Balance of channels not droppeddiverted to 1 x 2 ROADM components

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Degree 2 ROADM

2 degree Fixed Filter SiteUpgraded to ROADM network element




APPLICATION NOTE

C O P Y R I G H T © 2 0 0 9 E K I N O P S S . A . S . : : A L L R I G H T S R E S E R V E D

IN CONCLUSIONROADM technology is extremely flexible and offers a number of values such as eliminating up front complex planning and the

future promise for true optical mesh protection. But while it offers these benefits, ROADM technology is still relatively expensive

compared to traditional add drop technology. It is important for Service Providers to be able to scale their investment in technology

as revenue bearing traffic pays for it. In addition, by implementing the splitter/combiner technique, Service Providers can easily

maintain the option to deploy and benefit from ROADMs even if they choose not to deploy them initially. This technique offers a

remarkable balance of cost vs. flexibility with virtually no limit on scalability ■

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About EkinopsEkinops is a leading designer and supplier of next generation

optical transport equipment for service providers and

enterprise customers. The Ekinops 360 Dynamic, Multi-

Reach Transport System provides DWDM and CWDM on

a single platform that addresses Metro, Regional, and Long

Haul applications. The Ekinops 360 system relies on the

innovative, programmable Ekinops T-Chip® (TRANSPORT ON A

CHIP TECHNOLOGY) that enables Fast, Flexible, and Cost-effective

service delivery for building high speed optical networks.

Using the Ekinops 360 carrier-grade system, operators can

increase transport capacity of their networks — CWDM,

DWDM, Ethernet, ESCON, Fiber Channel, SONET/SDH, and

uncompressed video (HD-SDI, SD-SDI, ASI) – through the

industry’s most efficient aggregation of services.

The company is headquartered in Lannion, France, with

offices in Europe, the USA and Asia.

Ekinops EMEA Ekinops APAC Ekinops Americas+33 (0) 149 970 404 +65 6829 2156 +1 (310) 494 [email protected] [email protected] [email protected]

:: To learn more about Ekinops solutions, please visit www.ekinops.net


Ekinops Application Note - Cost Effective ROADM Solution

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Transcript of Ekinops Application Note - Cost Effective ROADM Solution