Introduction to WDM Transponders

With the development of wavelength-division multiplexing (WDM) technology, the network traffic volume is increasing and the demand for more network bandwidth is also on the rise. By converting the operating wavelength of the incoming bitstream to an ITU-compliant wavelength, WDM transponder serves as a key component in WDM system. As an important technology in the fiber optical network, WDM is moving beyond transport to become the basis of all-optical networking. And how to optimize WDM network has always been a hot topic. The transponder is a device to optimize the performance of WDM network, which plays an important in the whole system of WDM network. This article will introduce you the information on WDM transponders.

What Is a WDM Transponder?

Also called as an OEO (optical-electrical-optical) transponder, a WDM transponder is an optical-electrical-optical wavelength converter, which has been widely adopted in a variety of networks and applications. The picture below shows us how a bidirectional transponder works. In this picture, the transponder is located between a client device and a DWDM system. And we can see clearly that, from left to right, the transponder receives an optical bitstream operating at one particular wavelength (1310 nm), and then converts the operating wavelength of the incoming bitstream to an ITU-compliant wavelength and transmits its output into a DWDM system. On the receive side (right to left), the process is reversed. The transponder receives an ITU-compliant bit stream and converts the signals back to the wavelength used by the client device.

WDM transponder

The Application of a WDM Transponder

According to its function, the application of a WDM transponders can be classified into the following types.

  • Wavelength Conversion. It is known to us that when a CWDM Mux/Demux or DWDM Mux/Demux is added into a WDM network, there is a requirement to convert optical wavelengths like 850nm, 1310nm and 1550nm to CWDM or DWDM wavelengths. Then the OEO transponder comes to assist. The OEO transponder receives, amplifies and re-transmits the signal on a different wavelength without changing the signal content.
  • Fiber Mode Conversion. Multimode fiber optic cables (MMF) are often used in short distance transmission, while single-mode fiber optic cables (SMF) are applied in long optical transmission. Therefore, in some network deployment, considering the transmission distances, MMF to SMF or SMF to MMF conversions are needed. WDM transponders can convert both multimode fiber to single-mode fiber and dual fiber to single fiber.
  • Signal Repeating. In long haul fiber optic transmission, WDM transponder also can work as repeaters to extend network distance by converting wavelengths (1310nm to 1550nm) and amplifying optical power. The OEO converters convert the weak optical signals from the fiber into electrical signals, and regenerate or amplify, then recover them into strong optical signals for continuous transmission.
WDM Transponder and FMT Solution

At FS, OEO transponders are made into small plug-in cards to be used on the FMT platform. FMT platform makes devices like EDFA, OEO, DCM, OLP and VOA into plug-in cards and provides standard rack units as well as free software to achieve better management and monitoring. In addition, FMT series products like OEO, DCM and OLP also have higher performance than that of old ones. FMT series OEO transponder can convert optical signals into DWDM wavelengths, reducing the fault risk caused by high power consumption of DWDM fiber optic transceiver. Since the OEO transponder is made into small plug-in card in the FMT platform, it only occupies one slot in the special designed chassis when installed, thus saving a lot of space. In addition, all these FMT plug-in cards, including OEO, in a rack unit share the same power source and support hot plug & play operation. And they can be inserted or removed flexibly in the racks for DWDM networking.

FMT

Conclusion

Since the OEO transponder plays an important role in WDM network, such as receiving, amplifying and re-transmitting the signal on a different wavelength, adding an OEO transponder into the WDM network is very essential. The OEO transponders in our FMT series are made into small plug-in cards with high quality to ensure good transmission performance. For more information on our FMT system, please visit www.fs.com.

Data Centers: Say Hello to White Box Switch

Today, nearly all mainstream organizations use traditional (integrated) switches from vendors like Cisco, HP, Arista and Juniper. However, hyperscale folks such as Google, Amazon and Facebook are taking the lead to use white box switch in the portion of their networks, operating the system in a different manner. So what is the magic behind that? Are these OTTs the only customers of white box switch? You may find some hints in this article.

White Box Switch

What Makes White Box Switch Special?
White box switches consists of generic and inexpensive hardware and a preload network operating system (NOS) that can be purchased and installed separately. Often the hardware and software come from different vendors. This is in contrast to a traditional switch that comes as one package including the hardware and the software. For example, when you buy a catalyst switch from Cisco, you are obliged to use Cisco IOS as its operating system. But with white box switch, you are allowed to buy hardware and software separately.

Except offering increased software flexibility/programmability and reduced vendor lock-in, white box switch enables users to have multiple choices on hardware, network operating system (NOS) and applications. The impact of which is profound when it comes to network orchestration, routing, automation, monitoring and network overlay.
White Box Switch NOS

What About the Target Market of White Box Switch?
White box switch is initially designed for data centers. Companies that operating mega data centers are especially prefer white box switch for at least two reasons: these companies generally demand for massive deployment of switches and the port density of each switch needs to be high. White boxes are cheaper while offering high-density ports, hence proven to be an optimal alternative. On the other hand, these large-scale companies also value the flexibility and openness of the switch platform, besides CAPEX savings. As an open platform to offer broader flexibility, white box switch free them from traditional L2/L3 protocols, enabling more possibilities to develop and support any SDN based networking.

So, are these large-scale OTTs the only target market for the white box switch? Definitely No!

Any small or medium-sized cloud based providers, or data center of service providers can consider deploy white box switches in data centers, concerning the cost savings and enhanced flexibilities compared with traditional switches. Also because of the familiar IT tools/ commands their technicians are used to. However, white box switches are not yet ready to offer all features and services that a service provider needs to offer, and not yet for deployment in non data center environments.

The Potential of White Box Switch
Based on an open platform, white box switch offers greater possibilities for innovation when compared with traditional networking gears. As the number of vendors that specialized in developing software began to soar, customers can choose from a range of software solutions with added functionality and reduced price.

White box switch becomes even popular in this age of SDN. In traditional switches, software and hardware are integrated into one package, which limits the network innovation greatly. SDN is here to decouple the software from hardware, helping speed shifts in networking. It resembles the standpoint of white box switching. Moreover, the advert of SDN also drives white box forward: when combined with SDN-centric designs, these deployments have resulted in dramatic improvements in automation, operational simplification, and faster innovation. These benefits are now being realized by enterprises of all sizes via commercially available SDN solutions.

Conclusion
Despite the fact that white box switches cannot be applied in non-data center environment for the time being, they are meeting their target market requirements successfully. The potential of white box switch cannot easily be underestimate, it is an ideal alternative that worth to be seriously considered at least for data center applications.

Brief Introduction to EDFA

In fiber optic communication systems, problems arise from the fact that no fiber material is perfectly transparent. The visible-light or infrared beams carried by a fiber are attenuated as they travel through the material. This necessitates the use of optical amplifiers. And EDFA (Erbium Doped Fiber Amplifier) is a representative one in the optical amplifier. There is one saying that EDFA is the most popular optical amplifier in optical network communications. Next, we will begin with the definition of EDFA.

The Definition of EDFA

An EDFA, also called optical amplifier or an erbium-doped fiber amplifier or erbium amplifier, is an optical or IR (Infrared Radiation) repeater that amplifies a modulated laser beam directly, without opto-electronic and electro-optical conversion. The device uses a short length of optical fiber doped with the rare-earth element erbium. When the signal-carrying laser beams pass through this fiber, external energy is applied, usually at IR wavelengths. This so-called pumping excites the atoms in the erbium-doped section of optical fiber, increasing the intensity of the laser beams passing through. The beams emerging from the EDFA retain all of their original modulation characteristics, but are brighter than the input beams.

Three Major Applications for Optical AmplifierThree Major Applications for Optical Amplifier

The above picture illustrates the three major applications for optical fiber amplifiers: booster, in-line amplifier, and pre-amplifier. These applications are described in more details below:

Booster Amplifier

Booster amplifiers are placed directly after the optical transmitter. In this application, booster amplifier is adopted to compensate for the losses of optical elements between the laser and optical fibers so that the increased transmitter power can be used to go further in the link.

In-line Amplifier

In-line amplifiers or in-line repeaters are placed along the transmission link to compensate for the losses incurred during propagation of optical signal. They take a small input signal and boost it for re-transmission down the fiber. Here it should also be pointed out that to control the signal performance and the noise added by the EDFA is important, because noise added by amplifier will limit the system length.

Pre-amplifier

Pre-amplifiers are placed just before the receiver to increase the signal level before the photodetection takes place in an ultra-long haul system so as to improve receiver sensitivity. By placing a pre-amplifier, a much larger signal can be presented to the receiver, thus easing the demands of the receiver design.

Top EDFA Products Overview

By now, you should have a basic idea of what an EDFA is and what it is used for, next I will introduce you some truly excellent EDFA products on the market.

Type
Description
22dBm Output Booster DWDM EDFA C-band 24dB Gain, 1U Rack Mount
16dBm Output Mid-stage DWDM EDFA C-band 26dB Gain, Plug-in Card for FMT Multi-Service Transport System
17dBm Output Mid-stage DWDM EDFA C-band 17dB Gain, Plug-in Card for FMT Multi-Service Transport System
Conclusion

Of the various technologies available for optical amplifiers, EDFA technology is the most advanced, and consequently the vast majority of optical amplifiers are designed based on this technology. In addition, the combination of reliable performance and relatively low cost allows EDFA to be widely deployed in modern optical networks.

The Rise of White Box Switch

White-box switching is nothing new to us. ODMs (original design manufacturers) have been building hardware for well-known vendors for many years. These vendors take the ODM hardware, install their operating system, and sell the unit as a bundle, often attaching a support contract. Until now many companies like FS are also getting into the game of producing white-box switches. White-box switches look just like any other switch, which are gaining increasing attention in next generation data center deployments, with many software-defined networking (SDN) startups offering solutions that include them. Enterprises are wondering how white-box switches will impact their data center plans. So what is a white box switch?

What Is a White Box Switch?

white box switch

A white box switch is a network switch which comes with an installed operating system. It can be used as a standard for the base of hardware system elements. In the case of operating systems, white box switches are generally preinstalled on the system, or can be installed later. Loading of the white box switch is not difficult and can be done in a short period of time. They are generally used with SDNs and particularly useful in terms of a networking approach where the control is generated from the physical infrastructure after decoupling it. It can act as an efficient open-source tool for management of materials and information on a device.

And the major difference between traditional black box switch and white box switch is that the first one can’t be programmed but the later one can be programmed. With white box switches, a service can be programmed by using switch controller like ONOS while traditional black box switch provides very limited features and every time when you need to update something you have to log into switches and then change the rules. The white box switches are flexible, fast and inexpensive, which is why many opt for this type of switch.

Reasons for Buying White Boxes

Although white box switches have been around for years, the adoption has been limited to niche companies that have large engineering departments. The rise of software-defined networking (SDN) has brought them into the public eye, though, as a lower-cost alternative to traditional network hardware. In fact, some of the early messaging around SDN revolved around using white boxes as a complete replacement for all network hardware. Besides, many improvements have been made in white boxes during the past few years. So if you ask me why it is the time of white box switches and why you should buy white box switches. Here I’ve got a number of reasons for you:

  • 3-year ROI. A low-cost product can get ROI (return on investment) in less time and be replaced sooner. Faster hardware rotation equals more innovation/feature adoption.
  • Software bugs. Vendors take months to locate, accept, and fix bugs, which has enormous impact on your business. With OCP-compliant white boxes, you can switch software and keep your business alive, or work around slow vendor support.
  • Self-sparing. For some/most use cases, self-sparing is better than relying on vendor inventory. When products are cheap, you can hold inventory in your data center and bring MTTR down to hours instead of days.
  • Cost and reliability. What the customer is often paying for is the software that rides on top of the hardware and the logo. From a reliability standpoint, white boxes are on par with brand-name systems because they are actually the same hardware.
  • SDN. Move your operational focus from a vendor-specific CLI to an SDN solution. If you’re concerned about having multiple vendors to operate, then buy a SDN solution that is device independent.
  • Network operations. Many engineers may ask questions like “Do I have to write my own operating system?” “How do I install a network operating system” “What do I buy?” when considering a white box switch. Now, they can be reassured because white boxes can now be purchased from mainstream network vendors such as FS and HP. Also, when one purchases a white box, those suppliers will offer the kind of technical support most engineers need.
Conclusion

White boxes are certainly ready for mainstream adoption. Although they aren’t for every use case, but in the right situation, like an SDN deployment, they can be as good or better than traditional switches with a much lower price point and equivalent operational costs. If you want to purchase one, you may visit FS.COM where you can find the best-value and cost-efficient white box switch.

Optical Facility Protection for WDM Network

Wavelength-division multiplexing (WDM) is nothing new to us. It is a technology that multiplexes multiple optical signal on a single optical fiber by using different wavelengths of laser light. The multiple transmission paths involved in WDM network effectively relieve fiber exhaustion and extend link capacity, but they also make facility protection more essential than ever, because solid facility protection is the key to the availability of the link and the data being transmitted. This article introduces two methodologies that proven to be valid for optical link protection: electrical switching and optical switching.

Why Facility Protection is Essential to WDM Network?

With the explosion of information, the demand for extremely high-capacity data transmission began to soar. Enterprises and companies were asked to deliver greater volumes of traffic at much higher rates. Which spurs the need to store data in different facilities and to transport these data over different paths, so that if any network failure or downtime occurs, they can soon recover and keep the business running. In a properly protected WDM network, customers will have two or more sites that are connected to each other by diver paths, ensuring the availability and reliability of the network all the time. But fiber may break for many reasons including damage from the physical environment and human faults. Thus facility protection becomes vitally important.

Effective Facility Protection Methods for WDM Network

There are basically two methods for optical facility protection: one is electrical switching which adopts a cross connect to duplicate and select the working or protecting path, with two independent optics involved per each path and two Mux/Demux. And the other is optical switching, unlike electrical switching, it typically uses an optical switch to select the working or protected path.

Electrical Switching

In electrical switching, each service is simultaneously transmitted and received from two dark fibers. The signal from the device on the left side is transmitted to both working and protecting fiber, then it is delivered to the end device on the right side.

facility protection with electrical switching

So how the cross connect duplicates the Tx signals and selects the working and protecting path (Rx) for the receiving signal? In fact, the Tx signal is sent through the cross connect and duplicated through both transponders. On the Rx direction, the cross connect switches the signal to the receiving optical power of the transponder.

electrical switching details

Optical Switching

An optical switch is involved in this method to duplicate the data to the working and protecting fiber with an optical splitter, and selecting the operating fiber according to the optical power signals of all the services. One of the distinct differences between optical switching and electrical switching is that it simply offers no protection for the WDM optic.

facility protection with optical switching

Electrical Switching vs. Optical Switching: How to Choose?

When applied for optical facility protection, both methods have their benefits and drawbacks. For electrical switching, the WDM optic is better protected since it uses two uplink transponders per service – one for working and the other for protecting. Since protection is delivered per service, once a single service needs to be switched, the other service won’t be disturbed. Moreover, electrical switching is suited for any network topologies, and no power budget loss is associated with this method. However, electrical switching generally adopted more WDM optics and an additional Mux/Demux, hence fewer services are available through each unit, and it inevitably increases total costs.

While for optical switching which does not offer protection for WDM optic, more ports are available to transport services on each unit. Besides, no additional Mux/Demux is required in this method, so the overall cost of the solution can be decreased. The drawbacks of this method are that the optical switch lowers the optical power budget of the link. And optical switching is not suited for ring topologies for the fact that add and drop functionality is not available per wavelength.

Conclusion

Optical facility protection impacts the link availability, performance and reliability to a large extent. Your choice on facility protection method should always base on your specific needs, and taking power budget, network topology and cost into consideration. I hope this article would be helpful for you to make an informed decision.