Alien Channel and Alien Spectrum ( The new weapon for the wholesale business)

The key to a sustainable business is the ability to understand its most simplest demands. 

-------- Gujarati Proverb

1. The scaling dilemma of wholesale

Wholesale bandwidth provider, although does not have the kind of growth and visibility of traffic like the mobile backhaul provider, has the ambition and vision to grow even beyond them. However, their business is always on a catch 22 scenario where they are always in a dilemma of growing their infrastructure or expanding their coverage in the area. Capacity and coverage have always dominated the scale of the telecom business and this is not new even today. While the methods have changed with respect to deploying the telecom services the fundamentals of growth have not changed at all. There is still this old dilemma of whether to increase the capacity of a small sector or increase the coverage of the area so that more of the geography could be covered. 

If we are considering a common DWDM oriented network in the telecom sector and especially for the wholesale bandwidth provider then the most important factor that dominates the allocation of CAPEX is the traffic matrix. In case we have 100 dollars for spending then 70 dollars are actually attributed to the traffic cards or the traffic section of the network. Let us understand that these traffic cards or the traffic elements can be IP, OTN-Transport or even the ODU-XC. 

Therefore, let us understand that for the entire capex that includes the infrastructure of layer-0 as well as the traffic there can be a limited coverage of the are, especially when the amount of traffic is not known. The planning department of a wholesale entity relies on the business forecasting group to tell them about the planned capacity and then the back-calculation of CAPEX is done. In this back-calculation many things are actually missed out and one of the most primary things out of them is the ability of the DWDM infrastructure (30% of the CAPEX) to act as a primary infrastructure provider that can accommodate the demands of the bandwidth should the end customer also have a tunable service device that can ride on the wavelength of the wholesale bandwidth provider. 

This particular thought process can save almost 50% to 60% of the CAPEX that the wholesale BW provider is trying to put in and can improve bottom-lines considerably. 

2. What is Alien Channel? 

We discussed above as to how the CAPEX can be optimized to the level of 50% to 60% based on the availability of the tunable interface in the end customer devices. Alien channel actually enables the same thing in a wholesale BW infrastructure. 

Basic concept of Alien channel

The figure above shows the basic concept of the transmission of Alien Channel. Here we see that the network and its cost entities are demarcated in two sections altogether. 

1. The OLS (Optical Line System)

2. The Service (Traffic) 

Generally when the wholesale entity plans the network it plans for both the components of traffic and for the OLS. The OLS is the infrastructure portion of the network, while the service part is the part of the network that is consisting of the traffic generation and distribution. The OLS part of the network is the most certain part of the network where the provider knows which are the sites that could be potential traffic sites and which ones are only there for amplification .

The entire coverage of the network is dependent on the planning of the OLS. Therefore, this can be called as the infrastructure layer or the skeleton of the network on which the traffic rides. 

Let us understand that a provider on day-1 only has the OLS and does not have the visibility of the traffic that it wants to carry. Now another operator comes and asks if it can lease capacity from the provider. The conventional answer is that the wholesale will provision OTN traffic across the two points and then provide the pricing for the bandwidth. However, if the end operator already has the relevant transceivers that can run traffic on a C-Band or L-Band network then it becomes technically easy to accommodate these traffic demands to the existing OLS that has been already created. 

So the bandwidth provider now needs to provision a OCH path in the OLS and then this can carry the signal of the operator as an "alien" channel, meaning a wavelength of a different vendor in the optical line system. In case the OLS is able to carry the signal of the other operator then it is called an alien channel enabled OLS. 

3. How is Alien Channel a benefit for wholesale? 

While one may come up with the fact that there are so many moving parts in this solution and so much of dependency involved, one has to understand the commercial benefit of this solution that is a driving factor for the wholesale business. When we talk about the commercial benefits we are talking about two basic things over here. Money and time. So let us cross analyze what are the benefits in each aspects. 

3.1 The money benefit:

The costliest part of the establishing a  multi terabit network is not the OLS it is actually the provisioning of the traffic card. The transponders, ODU-XC, IP routers etc are the larger part of the CAPEX pie. In the case of alien channel this huge portion is taken out from the wholesale bandwidth provider side. This means more room for savings and bring in the customer. The money benefit also translates to improving the margins to a great extent. 

3.2 The expansion benefit:

As discussed before, the wholesale provider should focus in the coverage of the territory. This is also CAPEX dependent in many terms. If the focus is shifted to Alien Channels then the provider, without locking its CAPEX to the service cards and other traffic generating devices can focus on expanding the Flex-Grid network across the territory and thus can cover more part of it. 

3.3 The delivery benefit: 

Today the wholesale industry is totally dependent on the time to delivery. The alien channel helps the provider to immediately activate the bandwidth required without any kind of additional hassles of integration with the grey interfaces and power requirements. The approach is direct and provides immediate activation of the bandwidth with respect to the ordered date. This provides a good level of comfort to the end customer for their services to be started asap. 

3.4 A Win-Win situation:

Frankly speaking, every telecom operator, big or small, would be keen to have a dark fiber to their own disposal so that they can have a better control over the traffic devices. Although this is ideal, it is not possible to achieve in the real world. Alien channel provides this comfort, especially to the end customers/operators who are desiring of controlling their own traffic but do not want to invest on optical infrastructure. The wholesale provider over here provides a slice of the fiber, which the end customer gladly accepts running their own network on it. This gives them better options of leveraging their bandwidth and capacity within the prescribed channel OSNR that they have got. On the other hand it provides the wholesale bandwidth provider a sort of relaxation of not requiring to maintain inventories for different kind of cards and having a liability of the same. 

4. Alien Spectrum

In continuation with the Alien-Channel where we are talking about just one wavelength that can be a carrier for any kind of throughput rates we are now progressing towards a concept that is called as Alien Spectrum also sometimes referred to as Shared Spectrum. 

Alien Spectrum is a new concept where it is possible to provide the end user a bigger slice of the spectrum on which based on the requirement the end user can provision multiple lines or throughput. In order to understand this concept let us take an example below. 

A Hyper-scaler named A wants to have its terrestrial bandwidth across a region. A CoC named X has already got its flex-grid network deployed in that region. The Hyper-scaler desires to have bandwidth from point -1 to point-2 in the region. However, the contention here is that the hyper-scaler has two data centers with different kind of traffic profiles from different end routers. Some routers are emanating the 400Gbps line with a need of 75GHz width while some are giving out line bandwidth with 100Gbps on 50GHz, some need 800Gbps with 150GHz spacing and so on. 

Here the common approach can be the Hyper-scaler coming to the CoC and asking for different channels each of say 50Ghz, 100GHz and so on. However, the CoC here proposes a smart plan for the hyper-scaler. The CoC tells the hyperscaler to take a common shared spectrum of 500Ghz on its network and provide the flexibility to the hyper-scaler to split it in the way it wants. 

Hyper-scalers asking for Alien Spectrum

The hyper-scaler sees a very good value over here as this provides the essential control of spectrum and channel width allocation that it wants in order to have complete flexibility with the bandwidth. On the other hand the CoC is also sanguine that most of the demands of the hyper-scaler can be met in a flexible manner while its main focus would be to control the shared spectrum from one point to another point. 

This particular arrangement is called Shared Spectrum or Alien Spectrum. Here as we can see the service is not limited to a wavelength or a channel but it is a collection of channel that can be provided to the end user where the end user has the control over the channel and the width allocation. 

5. And Finally: 

Alien channel and spectrum are very good tools for a CoC to sustain a healthy business while giving proper freedom to the end customer. This also removes a lot of liability from the head of the CoC and helps it to focus on the aspect of connectivity delivery that is a core objective of a CoC or a wholesale bandwidth provider. 

This concept provides the freedom to the wholesale provider to scale up and spread across the region so that the coverage of the region can be achieved in lower time-frame. 

If you are a part of a wholesale bandwidth provider and you are also a part of the planning department, do consider this option so that the spread of the network can be accelerated. 

Do give me your inputs in the comments. 

Cheers, 

Kalyan

Building the new wholesale network (Planning)

 

If an entity stays in this world beyond the fulfilment of its purpose it will only cause imbalance and anarchy.

 

-------Old Proverb

1. Introduction

In the last blog that I wrote about ODU-XC and how it is fading and giving way to OTN-Transport and IPoDWDM I mentioned the shortcomings and the reasons why ODU-XC in now a non-viable solution. This is especially to those who are in the bandwidth leasing business or in the CoC business. The wholesale business is marred with margins and ODU-XC does not provide a suitable option over economical options like OTN-Transport and IPoDWDM. In this blog we are going to talk about especially the nuances of planning of the wholesale network for the new telecom era.

The fact that we are trying to establish in this section of the blog is related to the planning part of the wholesale network. A wholesale network is very different from that of a mobile back-haul or an ISP backbone. A wholesale network is supposed to serve many functions and many kinds of network. This is why the planning of such a network that is business oriented is extremely complex and has a lot of challenges. We will explore the requirements, the challenges and the new aspects of planning that goes into building this wholesale telecom network.

2. The requirements of a wholesale bandwidth provider

It needs to be clear that a wholesale bandwidth provider is not the owner of the content or is not generating any revenue from the content delivery. They are just pipes  or media who carry the traffic from one point to another with a standardized SLA. They are not owners of QoS or QoE, they are channelizers or media enablers and they are also paid in the same way. Thus the requirements of a wholesale provider is extremely flat and bland (if I am excused to say so)

2.1 Optimized bandwidth infrastructure

The wholesale provider has to play between the CAPEX and the OPEX of the solution that is implemented. The biggest asset it has is the fiber and that it has to capitalize to great extent. This capitalization comes from being able to have an infrastructure layer that will be able to carry large amounts of channels across the distance by consuming least pairs of fiber. Here we are focussing on delivery of bandwidth rather than the QoS of it, which is generally controlled by the end user. Thus the infrastructure is more important. Flex Grid systems with the ability to carry more bandwidth in flexible channels is definitely the good way to go forward. Flex Grid infrastructure provides that quintessential platform on which the premise of a wholesale business in the modern era can be based on.

 2.2 Cost effective transport modules

After the flex-grid ecosystem is created there needs to be a focus on cost effective transport modules that need to be provided in order to carry the traffic from one point to another. In this regard the focus should be on having modules that can aggregate more number of high bandwidth clients in a higher rate line output. This will result into the optimization of the revenue. Most of the times due to the ODU-XC and its inherent separation of the client and the line modules the cost of the solution increases, however if we look at the efficient muxponders that can provide the same solution at a lesser cost then it becomes very cost effective. 

Muxponders serving as simple transport modules

The muxponder that we see in the picture is a clear depiction of how the entire functioning of the ODU-XC can be compressed to a single module that can fit as a service card in the optical photonic shelf. This is an ideal situation for the wholesale bandwidth provider. The muxponder provider the end to end services for the wholesale provider to an extent that the CAPEX is kept minimal and the photonic shelves, that are extremely efficient in power and space, can handle the services. 

2.3 OPEX Efficiency

Another very important need for the wholesale bandwidth provider is the OPEX efficiency of the solution. The wholesale provider makes a full account of the cost that includes CAPEX and OPEX and the latter is a very important aspect as it is recurring in nature. Costs such as power, space, maintenance etc is a major part of the OPEX of the solution. OPEX efficiency, thus, forms an integral part of offering for the wholesale provider. Studies reflect the fact that the classical ODU-XC is extremely OPEX hungry and does not justify the RoI for the wholesale provider. In some cases the OPEX runs out to be more than three times of what it ideally needs to be. For wholesale bandwidth providers this situation is no less than a nightmare where the bandwidth has to be delivered in a wafer-thin margin cost structure. So definitely there have to be alternatives for the ODU-XC for such purposes so that economical ways of bandwidth delivery can be achieved. 

3. Why MNO requirements cannot be imposed on a wholesale network? 

Under normal circumstances it is always seen that the planning philosophy of MNOs often hijack the requirement scene of the wholesale bandwidth provider. This is the first step towards creating a loss-making network for the wholesale bandwidth provider. The wholesale bandwidth environment needs a network planning structure that is very different from the MNO planning structure.  There are certain factors which necessitate a separate design philosophy for the wholesale networks. 

3.1 Wholesale providers are not owners of the end-service

In the case of MNO the ownership of the end service and to an extent the content access lies with the MNO. The MNO is supposed to be the end to end provider of the service whether it is the wireless access or the back-haul. In the case of the wholesale bandwidth provider, this is not the case. The wholesale provider only owns the path and that too a part of the path than owning the entire service. The wholesale provider is like that of an active wire on which the service needs to pass. Since the ownership is limited the revenue expectancy is also of that category.  Therefore the technology that needs to be chosen under this case has to be extremely efficient in terms of cost whether it is CAPEX or OPEX. 

3.2 There are diverse routes in place of complex protection schemes

You agree or you do not agree the end customer will not solely depend on one wholesale network for the carriage of the bandwidth. The premium thus a customer will pay to you for a service that is protected by your network will be negligible in this respect. The focus should rather be on selling diverse routes that are unprotected while letting the protection mechanism work on the end customer. Diverse routes lead to a situation where the spectrum of the DWDM is more optimized and more static. Contrary to the cases of WSON or ASON where most of the resources are used up in protection. If we talk about WSON then there is a bit of economic sense involved as the resources are only blocked on the virtual channel level, however the ODU-XC ASON is of a really different level. Here we can see that the resources are pre-reserved in terms of hardware and interfaces. This increases the CAPEX dramatically.

The end customer on the other hand also ensures that there is enough diversity in the level of wholesale providers also. This is to ensure that if there is a major problem in the network of one wholesale provider the other wholesale provider can carry this bandwidth. This is a common phenomenon observed in the hyper-scaler sector where diversity is a key issue. 

Example of diverse route by the same provider

As seen in the figure above, we see that the diverse routes are provided here but the provider is the same for the wholesale bandwidth. The onus of the protection however is lying with the end service provider who does the switch between the main and the alternate path. Here the situation is a kind of a win-win.

For the wholesale bandwidth operator it is a sale of 2X bandwidth with low consumption of resources as there is no complexities of protection involved in the provisioning of the bandwidth. 

For the end customer there is a control of the main and the alternate path with full transparency. In addition to that the say 2X bandwidth can be used for passing best effort traffic when both the paths are available.

There is also a situation which is more ideal for the end service provider. Here the service provider does not rely on one wholesale entity but has two entities for the diverse carriage of the bandwidth. The diversity is more robust over here because here there is less reliance of the efficacy on one operator. 

Diverse route provided by diverse provider to the end customer

If we see the picture above then the situation is more pragmatic as now there are diverse routes provided by diverse providers. So for the end service provider instead of having an independent network of its own it can have a platter of bandwidths provided by different wholesale provider. The wholesale provider on the other side can be less robust and focus more on spectrum optimization rather than on the protection path.

Generally the end customer would seek such an arrangement with the wholesale provider(s) in order to maintain proper robustness in the network. This in a way lowers the load of onus on the wholesale network and thus can provide a more price optimized offer for the end customer from the wholesale side. 

3.3 Cost sensitivity is at its peak

As we can see from the above section that wholesale bandwidth is an extremely cost sensitive business, so the planning also needs to be cost sensitive. While the demands of technologies like WSON, ODU-Flex can be a sort of a wish-list, they do not have any kind of commercial leverage. So with the dwindling margins of bandwidth delivery there needs to be an innovative approach and cost effective approach in planning that is very much different from the planning that is involved to build a mobile network backhaul. A wholesale network will need to eliminate most of the features that are bulky in nature and are not required into the network. Focus has to be for delivering good quality bandwidth from point A to point B with all the SLA covered.

The planner has to realize that the margins in the wholesale network is less and it is more of a volume game. So, the mandatory aspect of a network needs to be covered for the wholesale network. More and more bandwidth is disposed off as a commercial entity in less and less cost incurred that will sustain the business to a greater level than creating space for more wishlists for the future. 

4. New aspects in the planning of the wholesale network

Now that we have understood the challenges that lure for the planning of the wholesale network let us delve into some points that consider the new aspects that are involved in the planning of the wholesale network. These new points will be extremely essential to build up wholesale networks rapidly and with extremely less cost. Before we venture into the building of the wholesale network we need to consider two fundamental principles on building it.

1. Faster network roll-out and faster delivery

2. Less CAPEX and OPEX involved in building the network. 

3. Prioritize service from the business point of view. 

Considering these fundamental principles we will explore some of the points that will make wholesale network building extremely efficient and cost effective. 

4.1 Build the infrastructure

The biggest requirement for a wholesale network is to secure the infrastructure. This forms almost 80-90 percent of the effort of building the wholesale network. More the delay in building the infrastructure more will be the delay in the delivery of the services. When we talk about the infrastructure we are talking about the following things. 

1. Fiber network readiness. 

2. Flex-Grid DWDM network with OTDR monitoring and fiber health monitoring. 

3. Proper channel/grid planning. 

4. Provision for the Alien wavelength/Spectrum on the network. 

This actually wins most of the battle. It enables the wholesale entity to start providing services on the day one with wavelength or spectrum basis. 

4.2 Identify high-bandwidth services

In a business of wholesale to sustain and to grow it is important to have an outlook and outreach towards cherry-picking the profitable kind of bandwidth deliveries that provide immediate revenue with minimal capex and opex. Our infrastructure is already done and ready. We can already provide spectrum and thus bandwidth on this logical infrastructure with minimal movement of CAPEX and OPEX. However, if there are operators who insist us to take ownership of the traffic segment also, the key guys would be the ones who are demanding bulk bandwidth. Let us take the example of an operator that is demanding bulk bandwidth across two points of 4X100G or more. Now for this the investment is quite small. 

We can assign muxponders that will aggregate this over a 400G or a 800G wavelength and provision across the two ports and be done with. This just is a module addition in the existing OLS not affecting the CAPEX and the OPEX as opposed to a full fledged system addition.

Thus, it becomes a very gradual addition to the infrastructure that we already have built without any additional hassle. Identifying the inventory is also easy as this mapped to the end user. Operations are not a hassle. 

4.3 Looking for those important low-rate subscribers

It is not rocket-science to understand that when you build an information superhighway then looking for a low-rate subscriber who wants the traffic also to be a part of your solution is a much expensive affair. For one such 10G there needs to be a line out towards 100G line or more and this built up can be a hassle for the network. Low rate customers can be the most expensive ones when it comes to the cost of delivery and the cost of maintenance. There cannot be a parallel line network for the 10G and for the 100G+. Therefore it is necessary to find the customers that are more suited to the network. A low-rate customer can be a very good strategic acquisition considering that there will be expansion in the future with growth of experience and the growth of the customers that the end customer has in this aspect. 

Generally low rate customers are coming from the enterprise sectors and more than the bandwidth what they require are. 

1. Reliability

2. Quality

3. Value addition

While the reliability and the quality part is already covered in the equipment and delivery of the wholesale provider the part of value addition is often missed out. Let us take some examples of the value addition that can be done for these enterprise customers. 

1. Customer network management (CNM)

2. Bundled services (Voice+Data Breakout)

3. SDWAN

4. Data monitoring and security. 

5. Encryption. 

Generally, when these value add services are provided with the wholesale bandwidth provider then there is a great deal of attraction for the enterprise services. 

4.4 Alien is very friendly these days

Today there are many service providers, MNOs, MVNOs, ISPs, MSOs etc who have the end device that can support the coherent but do not have either the DWDM infrastructure or the dark fiber. Under these circumstances they are looking for an infrastructure that can carry their traffic, which is already coherent in nature, on a specific wavelength or a spectrum. Hyperscalers, especially make a demand for such a service where they want just a chunk of the spectrum that is available in the DWDM infrastructure.

It is very important thus to plan for the alien spectrum and services like that because these are extremely quick and low maintenance businesses that a wholesale bandwidth provider can achieve. 

4.5 Automation is the key

Quick delivery, Express provisioning, Flexible BwoD and Self Healing networks. These are some of the important buzzwords that are in the market. The answer to all these buzzwords is “Automation”.  The automation has to be primarily in the network management system that the provider is choosing to manage the network. 

• Configuration automation to ease the delivery of the services. 
• Bandwidth on demand
• Fault automation with AI/ML to have a more self-healing network. 

All these aspects are to be seen when planning for a proper management system for a wholesale bandwidth ecosystem

5. Summary

Thus, we understand that the planning of the wholesale network cannot be congruent to the planning of the MNO network. There has to be expertise involved considering all the new aspects of network building.

To cut a long story short. The planner of a Mobile Back-haul is Network-centric but the planner of a wholesale network is network-centric and business-centric. So, in order to get into the planning of a profitable and revenue yielding wholesale network such attitudes have to be developed.

 

I will be adding more of wholesale networks in my next blogs. Keep watching. 

Cheers, 

Kalyan

OTN-Transport or OTN-Cross connect, What to choose in modern times?

 

Fortune favors the brave

------- Old proverb

1       Introduction:

In the optical world there has been a lot of dilemma these days about the validity of the ODU-XC or the OTN cross connect. Considering the rise of the packet traffic and the steady decline of the TDM traffic the purpose of a comprehensive cross connect device that is aggregating both TDM traffic and the packet traffic in a particular single line is slowly getting past its expiration date. Many geographies have actually moved on from the concept of OTN-XC while in some parts of the world OTN-XC is still the easiest and simplest way to groom traffic. This especially is the case when we are talking of a multi direction meshy site where the optical traffic needs to be routed in multiple directions.

1.1    Background of the OTN – XC:

In the early 2010s where in most of the areas of the world there was an explosion in the traffic requirement due to rise of data consumption there needed to be a technology that can deal with a combination of IP and traditional TDM at the same time. It was difficult and almost commercially inviable to have parallel transmission network for TDM and IP at the same time. Two parallel networks meant

1.     Higher CAPEX

2.     More maintenance.

3.     More usage of fiber cores or Channels.

4.     More manpower.

 

Arresting all these issues there was a standard quite similar to the levels of SDH multiplexing but with higher line rates. This technology was termed as OTN, Optical Transport Network. OTN has a similar hierarchal structure like that of the SDH but then there is no use of pointers over here rather it uses overheads. The understanding and the basic operations of these devices were more SDH like and thus were very appealing to the people who are especially in the transmission section of the network and are used to working with legacy, SDH like networks.

 

The OTN device has one more very unique characteristic and that is, it can aggregate several signals like IP, TDM, FC, HDI, SDI etc. and can line out this from a higher bandwidth line. This line can also be a coherent DWDM compliant interface that can easily be put as an optical channel in a WSS or in a MUX-DEMUX system. Thus, with the availability of one box the problems of multiple signal rates from different sources can be managed and multiple devices are not required for different technology. With the use of the OTN technology the transmission capabilities of a network are made more homogeneous and accommodative towards many technologies. Whatever the client rate maybe, it can be put in a OTN device and these can be aggregated and segregated at the same time.

 

There is also this good ability to add and drop multiple clients of different characteristics and switch directions of these clients by the introduction of OTN cross connects or OTN switches.

1.1.1   Structure of OTN:

The OTN, just like SDH, is very structured and this can be demonstrated in the figure below

Structure of the OTN-Frame as it evolves

 The building block and the progression from the client signal to the final Optical transport unit is somewhat similar to what is done in SDH. The difference over here is the pointers which is not existent in the OTN framework. However, if we inspect in details then the flexibility of OTN is to a great degree than that of SDH with respect to carrying of traffic. This is because of the flexibility in the number of interfaces that can be carried out with respect to client is much better than SDH.

1.1.2   The OTN Cross connect Device:

The OTN cross connect device or in short OTN-XC is a device that has the capability to have several clients converted to the OTN frame and then switch them to multiple directions. Just like the SDH cross connect this also depends on several unit of cross connections which are in the form of ODU (Optical Data Unit). This is why it is often referred to as ODU cross connect as well. In SDH the cross connects used to happen in the level of VC-12/VC-3/VC-4 and in the OTN cross connect they happen in the level of ODU0, ODU1, ODU2, ODU4 etc.

 

The ODU-XC consists of line cards that are usually coherent modules of 100G/200G/400G. These can be in the form of cards or pluggable CFP2/QSFPDD on the line cards. In addition it contains the client modules that are grey interfaces of STM1/4/16/64 1G/10G/100G FC etc. There is a back-plane connectivity and a ODU-matrix. This matrix is usually ODU-k (where k can be 0,1,2,3 and 4) or this can also be a ODU-Flex matrix where we can have several combinations of ODU in the system.

Structure of the ODU-XC device

The figure shows the flexibility of the OTN cross connect device in a similar fashion as it used to be for the SDH devices. There is a concept to cross connects that can be translated into trails in the level of topology and network. There can be a protected segment just like the SNCP-I that was there in SDH. Thus in many ways the OTN-XC resembles, operationally, the workings of the SDH cross connect albeit for higher line rates and for multiple client rates.

1.1.3   How the OTN-XC is operationally easy to use

 For a person who is coming from the traditional SDH/TDM background the OTN XC is definitely a  gradual and a comfortable method of evolution. The OTN-XC does not bring in drastic complications for the person who is into planning, provisioning and maintenance of the transmission network, as it is a gradual upgrade of the previous SDH network that was prevalent. Essentially the complications of several protocols and different service types are avoided in the transmission layer keeping it as simple as it can be.

 

On top of that the OTN-XC can do the same kind of provisioning which is closely aligned with the processes of the erstwhile TDM architecture. This is extremely important when a planning team and an operational team in the system is generally evolving from the SDH architecture. 

2       Challenges with the OTN – XC

It may be very easy operationally to scale from the SDH network to the OTN-XC network as a natural choice to increase the bandwidth and accommodate changes but OTN-XC comes with its set of challenges and this need to be really considered when considering OTN-XC for a long term solution for the network.

2.1    Bulky:

The OTN-XC can be extremely bulky resulting to heavy footprints in the network. The general consensus over here is that with the increase in the bandwidth in the access there will be requirement to increase of the OTN-XC capacity. From 2T, to 4T to 16T to 32 T and so on. As the access bandwidth increases in meshy sites and the line bandwidth increases it results to bulky OTN-XCs and thus make the solution not really OPEX efficient.

2.2    Heavy consumption of Power:

With the increase in the size of the OTN-XC there is also a demand of increase in the power consumption. The OTN – XC has the cross connect component and the combination of line cards and client cards that make the solution extremely power inefficient. Networks where there are requirements of power efficiency due to frequent outages in the system and heavy battery backup, the OTN-XC solution can become extremely Opex hungry. In the later sections we will come across the understanding of the comparison of power consumption against alternative solutions like OTN transport.

2.3    Not efficient for point-to-point traffic

Generally, when we talk about wholesale bandwidth providers in the industry most of the nature of their traffic is point to point. The traffic is either between two data center points or specific leas of bandwidth, protected or unprotected across two different endpoints. Realizing an OTN-XC under such a condition is extremely expensive option.

Let us assume that there is a requirement of 4x100G across two points that are 500kms apart. The most efficient way would be to have a Muxponder with 4x100G groomed to a 400G QPSK line.

OTN on Card for Point to Point traffic

 

As we can see in the figure the Muxponder card provides a localized OTN – XC on a  card function and the traffic can be groomed in one unit and provide the aggregate traffic to the two different points.

The same system can also be used for 800G wavelengths and for 1.2Tb/s wavelengths as well. Here the main thing is that we are saving a lot of Opex when it comes to service delivery and cost by introducing the concept of Muxponder.

2.4    Not suitable for a full packet environment

As we have seen from 2017 there has been a consistent decline in the traditional TDM traffic that used to ride on SDH. Even international connectivity is now no more on SDH but on pure ethernet or IP peering. If we analyze the data from 2017 to 2023 then we will see that today almost 95% of the traffic that is there in the network is IP or Ethernet.

The utility of the OTN-XC was when we had a mixture of clients that were from the ethernet zone and the traditional SDH zone with some elements of fiber channel as well. However, with most of the traffic migrating to IP/Ethernet this mixture is becoming far from homogenous. The ethernet share of the traffic is increasing to a great extent.

This has further led to a thought process which mandates the coherent interfaces of 100G/200G/400G and even 800G to be used as a pluggable in the router itself which totally eliminates the need for the OTN-XC and to some extent even transponders and muxponders. The coherent interfaces can directly interact with the WSS or the Optical line system.

In the later section as we study the IPoDWDM system this is explained better.

3       OTN – Transport system

A possible alternative that is low cost on the CAPEX and OPEX is the OTN -Transport system. Basically this consists of grooming of bandwidth by means of transponder and Muxponder. The OTN-TX as it is called with abbreviation can eliminate the need of a back-plane based OTN-XC and can be accommodated in the optical photonic user shelf itself that is used for the optical line system.

3.1    Understanding the OTN-TX components:

In order to delve more into the OTN – TX we need to first understand the components of the OTN-Transport. There are many elementary components that comprise of the OTN-Transport and this is what we are exploring in the sections below. 

3.1.1   Transponder:

A transponder is the simplest form of a service card that can be realized in a OTN – Transport scenario. The basic work of a transponder is to take in a signal of a particular rate (Eth/OTU etc.) and then provide the OTN wrapping in addition to tuning this signal to a particular wavelength and frequency of a particular width.  Transponders are used generally in network when we have a situation where the line and the client need to be of the same rate.

The structure of a Transponder

As we can see in the picture this is a module where the input is essentially a signal of 100G / 400G and the output is a colored signal of OTU4/OTUC4.

The concept of transponder is slowly getting faded away with the arrival of IPoDWDM devices, which we will discuss later. However, transponder have a very good case where we need to connect third party grey interfaces to an optical line system of the same line rate. Eg. Say all the routers in the data center have 400G line out and this needs to be put on different wavelengths of 400G in the optical line system. Here the routers do not have colored interfaces and we need a device to convert the 400G to a proper coherent OTUC4 that can ride on the optical line system. This is where we take the help of a transponder.

 

3.1.2   Muxponder:

As the name suggests a Muxponder is a device that does multiplexing of signals of lower rates to a line of higher rate. In a very layman language we can imagine this as an OTN-XC on a card where the card has 1 line output of a particular line rate and several clients of lower client rates. The Muxponder enables to create ODU-XC trails across several clients and lines in the same subsystem of the card.

Structure of a Muxponder

As we can see in the figure this is a simple layout of a Muxponder that can be inserted on one of the slots of the Optical photonic user shelf. Here we can see an example of a Muxponder that has a 400G/OTUC4 line out and 2x100G and 20x10G interfaces thus giving the flexibility to the user of having several clients of several rates groomed to a particular Muxponder. The Muxponder makes traffic grooming, if it is pre-planned and predetermined, extremely efficient and provides the right mix of low order and high order traffic especially for the whole-sale bandwidth environment.

3.1.3   ADM on Card (AoC)

As we see the structure of the Muxponder a question arises. “How can we use the muxponder in sites that are add drop in nature?” The Muxponder is having only one-line out port so how can we have a east west kind of a scenario where we can add and drop traffic and do a bit of 1+1 electrical protection as well. Here comes the concept of ADM on a card. The ADM on a card stands for Add drop multiplexer on a card, in short in can be called as AoC as well.

The concept remains same as the Muxponder, however, there is also an ability to do east west routing of traffic using protected cross connect. There can be Y type of protected cross connect form using the ADM on card. The ADM on card can actually solve the problem of several add and drop over a particular channel and can also provide ring protection with east-west kind of cross connection.

Structure of the ADM on a Card (AoC)

The picture shows an extension of the concept of Muxponder to a system that can be providing an east-west kind of a topology. The AoC concept is extremely beneficial to use if we know the proper drop points and plan the traffic in a way that it will properly adhere to the traffic matrix with a growth margin. The AoC in a way simulates the multi directional attribute of the OTN-XC in a very compact manner and gets accommodated in one of the slots of the photonic shelf. The AoC can seamlessly interoperate with a OTN-XC on a mesh side and a Muxponder on a terminal site and this can provide a comprehensive way of dealing with networks that have multiple layers. In the later sections it will be more apparent to understand how the traffic can be groomed across different kinds of the networks. 

3.1.4   Transponder/Muxponder:

In some scenarios a particular card can perform the dual role of a Transponder and a Muxponder. This can be considered to have a sort of dual function in multiple directions. A reason for this is also to save the amount of slot space for grooming more traffic. Taking one such example is a card/module that has two-line interfaces of OTUC4 however on the client side it can be 1 client interface of 400GE or 4 client interfaces of 100GE. When the mapping is from 400GE to the OTUC4 it is working as a transponder. When the mapping is from 4x100GE to a OTUC4 it is working as a Muxponder.

Layout of a Transponder/Muxponder 

As we can see in the picture here, we have an example of a transponder/Muxponder. Another thing to note down is the 4x100GE realization on a single port. Here we use a concept that is called the fan-out. The fanout takes the advantage of grooming lanes of 100G on a 400G DR4/LR4 mapping. Generally, the QSFP slot of a 400GE takes the LR4/DR4 of 400G. This essentially means 4 lanes of 100G combining to make the 400Ge interface. Now this can be further distributed using a MPO cable and a passive fanout device to 4x100GE separate inputs. However, here the thing needs to be noted that the router should have the 100GE LR1 instead of the conventional 100GE LR4.

3.2    How the protection works?

It may be a common argument from the operator side that the realization of a simple level protection is difficult in the OTN-TX scenario as compared to a full-Fledged OTN cross connect device. There may be arguments that the OTN-XC has redundant mechanisms like the ASON in the electrical level and the SNCP when it comes to 1+1.  As these arguments are true, a point needs to be considered that with the inclusion of more an more electrical protection layers the cost increases drastically. This is because the most expensive component in a optical scenario is the Optical line transceiver. While providing multiple transceiver for the line is a solution to enhance protection but then it increases the cost to exorbitant levels. This is why alternative protection schemes should be envisaged looking at the MTBF of the line transceivers.

3.2.1   OLP Level Protection:

One of the basic levels of protection that can be achieved while keeping the service intact is the OLP level protection. Here we are looking at the protection only at the fiber level to provide a 1+1 protection at sub 50ms. OLP level protection is very easy to configure as the protection works at Layer – 0. This saves the idea of keeping redundant line interfaces that is extremely costly.  A general OLP level protection can work perfectly well if we are considering a point-to-point bandwidth between two different locations.

Below is an example of an OLP based configuration on one side of the network. The similar configuration is replicated on the other side of the network also. Please note that since this is using the collector and the ROADM network the OLP mechanism can also be implemented in a network that consists of a WSS Mesh and is not limited only to a network that is traditionally point to point.

 

With the introduction of OLP level protection we can provide

1.     1+1 protection for multiple number of client services with less cost.

2.     Optimize the number of line coherent interfaces.

3.     Reduce a lot of cost on the footprint by providing the same amount of redundancy on the line.

4.     Provide business services in a converged meshy network with desired amount of protection.

 

OLP level protection setup with dual collector

 

3.2.2  WSON (Wavelength Switched Optical Networks)

There would be a lot of demand that is based on multiple restoration if more paths are available in the network. A network that is complex and meshy demands multiple switching paths of the traffic with respect to the availability of paths after a failure event occurs on multiple sections. This also takes into account the availability of resources along the path. A classical way to achieving this in the OTN based network is ASON (Automatic switched optical network) that is based on the GMPLS protocol. A similar extension of this in the layer-0 is WSON. In the case of ASON it is the ODU that is the main unit of switching and there needs to be several electrical options and line interface availability for the switching of the network. This, however, is eliminated in the WSON network.

 

The WSON enabled network can do multiple level restoration and switching at layer-0 but switching wavelengths. This however needs at least a colorless-directionless configuration in the nodes or best a CDC configuration that makes the switching of wavelength easy for the traffic.

 

For networks that are metro level and connecting to several of data centers and traffic aggregation points over a region say spanning around 400-500 kms, WSON is a very good solution to provide cost effective services with multiple restoration. Here the requirement of line interfaces are less as there is no O-E-O switching and the cost of the infrastructure is one time.

Example of a WSON Network

 In the picture above we see an example of a WSON network that is built out of the CDC ROADMs. There are multiple paths for the restoration of the main path and here three options of the alternate paths are shown. A Thing to note over here is that the WSON restoration paths do not need any additional line interface hardware to be constructed or generated. On the basis of availability, the system will create optical cross connects at the OCh level in the system. These OCH level cross connects will lead to the creation of new paths.

So to summarize when we do the network using OTN-Transport and WSON the following are the advantages of WSON

1.   

1.     1. Economical to implement in the network.

2.    2.  Does the restoration at the OCH level so there is no need for additional hardware.

3.    3. In the event more services are added extra line cards need not be added in the transit as the network is self-healing in the optical mode.

4.     4. GMPLS infrastructure has to be developed only once and not again and again. 

3.2.3   OLP + WSON

As we know that GMPLS restoration has its challenges or restoration times that can exceed the limit of 50ms. This is the reason why in ASON also we combine it with the protection of SNCP where there is a pre-provisioned protection path so that we have 50ms switching always.  In the case of WSON also we can combine this with OLP protection, and this can provide the 50ms switching always.

In the ROADM-CDC sites we need to ensure dual collector and ensure that the OLP connectivity is done properly along the lines. In case we use the CDC-collector, this will be better as we will have more flexibility in the wavelength re-usage in the whole network.

 

In the OLP+WSON mechanism we have complete end to end protection mechanism that is carrier grade in nature.

4       The trend to choose OTN- transport over OTN-XC

As we see the operator network from end to end today there is more trend to choose the OTN-Transport solution over a bulky OTN-XC solution. The question is why? There needs to be a close examination on this aspect that leads to this choice for the operator network and the below sections reveal the rationale behind this choice that the operator networks are making.

4.1    Comparison over cost and power

When a network is constructed plainly to provide bandwidth as a service then the primary question that comes into the mind of an operator is how much would be the CAPEX and OPEX load on the system? This figure is a major factor that ultimately provides the figures for pricing of the bandwidth and determines the profitability of the service over the years. If we compare the OTN-XC cost with the cost involved in providing a service of the same bandwidth with OTN-Transport then the OTN-Transport wins hands down. Same happens when the comparison is made on the basis of power consumption.

Statistically speaking the following inferences can be drawn

1.     The OTN-XC for a 400G lambda is 3 times as costly than the OTN – Transport.
2.     In case we are introducing ASON in the OTN-XC then the cost jumps 6 times.
3.     Power consumption is 4 times in the OTN-XC than the OTN-Transport.
4.     With ASON the power consumption is around 10 times more for the OTN-XC.

5.   As we increase the lambdas from 400G to 800G the cost even goes up.

 

CAPEX and Power consumption is extremely high as we go more towards the OTN-XC. Here this is the case because there will be expansion on the line side and the client side separately. On the other side there will be a good amount of increase on the line side when ASON is added. OTN – XC expansion will create more number of cards and line modules. In addition, it will increase the load on the matrix and the cross connect. These more modules and more number of processes increase the power consumption to a great deal.

4.2    Comparison on Space and Density:

Another very important part of the OPEX is the space and density. Most of the operators who have their networks running leased space environment. Space comes at a premium in some of the cases just like power. Space prices appreciate over the years, and it is very imminent to have efficiency on the space and increase the density of the product to have more interfaces packed in less of a footprint. In this case the OTN-Transport, especially the compact modular version comes of a greater use.

A thing to note is that more density means less space consumed and thus less OPEX. 

4.3    Services types

The services types are also a candidate for the operators to choose the OTN-Tranport over the OTN-XC. As we go to the level of multiples of 100G services it is important to note that in the case of OTN-XC the space consumption and the power consumption will be very high. In case most of the services are point to point bandwidth delivery and grooming kind of services the OTN-Tranport makes a much better solution option than the OTN-XC. There can be in the network some services that are completely based on 10G and lower rates and for them a separate channel of 400G + can be used for small OTN-XC devices giving them a sort of diversity in the network.

Blending the OTN-Transport and the OTN-XC making an efficient solution

The figure above represents a comprehensive device for the OTN-XC and the OTN-Transport blending. For the present case of services which the customers have, especially in the region of wholesale bandwidth and providing bandwidth as a service, this model can be extremely efficient based on services.

5       IPoDWDM (IP over DWDM)

The purpose of the OTN-XC as we discussed before is more when there is a mix of services that are having legacy TDM and modern IP. However, if we consider the present situation that is prevalent in the market then we will see that most of the services are ethernet/ip natured and the demands are also going to those levels.

So, there is a maximum need to have a system that has most of the clients of the IP nature. This is the router. However, today we have a router connected to an OTN-XC and then connected to an Optical line system. 

How the combination of transport and IP is in most of the cases today

The figure above was pertinent if there is a proper mix of the TDM clients and the IP clients. TDM aggregation coming from the legacy TDM mux while the IP clients coming from the IP interfaces. Both of them merging to the OTN-XC and then further the OTN-Wrapping is done to take this over the optical line system. Here we have a complete segregation of network and services. There is a layer of TDM, IP, OTN and Optical separately.

Today, however, the situation is different. The number of TDM-Mux in the network has reduced substantially and there is a good amount of increase in the IP-Traffic in the network. Most of the services are IP oriented so the relevance of the TDM device has reduced considerably. On top of that the bandwidth requirements have increased to a great extent. The need is thus of a router that can have line interfaces as coherent line.

How the IPoDWDM is setup

 

In the IPoDWDM structure we are able to groom the services of IP on a line that is coherent in nature. This line can be C-band or L-Band and thus can be integrated directly to the Optical Line system. Here, the OTN-XC and the OTN-Tranport both are eliminated from the network and the network becomes even more economical.

 

The carriage of the legacy bandwidth of TDM can be done over CES, Circuit emulated service. The CES can carry E-1, STM1/4/16 over encapsulation when needed and the IP services go as it is.

The line interfaces can be 100G/200G/400G coherent. The protection can also be based out of LDP-FRR and other IP protection mechanisms.

6      Conclusion

As we look at the various aspects of the network that the operator takes into account the following points come out as inferences.

1.     OTN-Transport solutions involving transponders, muxponders, compact-modular serve to be much economical and efficient ways of delivering bandwidth especially in a wholesale bandwidth scenario. 

2.     OTN-Transport solutions have much higher densities, especially when we go to the options of compact modular to delivery high amounts of bandwidth with better efficiency. 

3.     The protection mechanisms and the reliability of the network is hardly compromised with options like OLP and WSON also in the offering. 

4.   The deployment ease and upgrade in an OTN transport network is much higher than the OTN-XC.

5.     IPoDWDM devices can be a better option considering the futuristic growth of the network. 

And Finally:

      So friends, fairly long article and the article is put up after a lot of research and observation. Hope all of you will like it. Please comment, share and like.... 

Cheers, 

Kalyan.....