Some enterprises have built 10G network links. But one can never imagine how fast the network traffic is growing. There are many factors influencing the needs for high bandwidth, such as the rising populations of network subscribers, business and personal competitiveness, and the use of more video. In that way, 10G network is not able to meet the increasing needs. Then it pushes optical backbones and metro core networks to move to 40G network. However, to move to the high capacity network, many difficulties must be encountered in optical fiber networks. The question is to upgrade to 40G or not?
Cost Increases
The first challenge some service providers face when they consider moving to 40G technology is the cost of equipment. That’s the same when considering upgrading from 2.5G to 10G. The price of a 40G link is expensive than that of 4*10G links (as shown in Figure1). Equipment is one of the price determining factors. For example, a QSFP transceiver (the average market price of a JNP-QSFP-40G-LX4, Juniper Compatible 40GBASE-LX4 QSFP+ Transceiver, is more than US$ 2000.00) is more expensive than 4 SFP+ transceivers. And some equipment may not be suitable for 40G networks, which means brand-new expensive equipment are needed.
Figure1. 10G to 40G
Optical Signal to Noise Ratio (OSNR) Drops
A unit of information, called a symbol, transmitted at 10G takes 100 pico seconds (100ps), and that symbol transmitted at 40G takes 25ps. This means the receiver translating the light back into a symbol deals with only 25% of the light of a 10G symbol. It causes 6 dB OSNR to drop. The OSNR is a measure of the strength of the signal. So the drop of 6dB means the link length will be decreased by 75%.
Chromatic Dispersion (CD) Increases
When a signal travels through a fiber, CD causes the pulses constituting the signal to spread in time. If this spreading is not compensated, these pulses will overlap. It means the signal is unusable. Comparing to 10G, this effect is 16 times more obvious at 40G. This creates a serious roadblock for 40G system operating.
Polarization Mode Dispersion (PMD) Increases
PMD is another problem which may be the most difficult to solve. This occurs due to infinitesimal imperfections in the circularity of the core of a fiber, which may be caused by the material itself, manufacturing process, or stress in the field created by bending or twisting. PMD is more capricious than predictable, and is very dependent on the qualities of the fiber. PMD can be influenced by factors including cable age or vintage, temperature of cable, cable design and cable manufacturer, etc.
To achieve 40G, new modulation schemes and approaches are being developed. The following tells about methods to overcome those difficulties.
Save Cost
We can discuss it from two sides: to buy or not to buy new equipment. First, to buy new equipment. As mentioned above, some optical equipment like transceivers from Google searching result are quite expensive. Thanks to the fast developed technology, manufacturers like Fiberstore (FS.COM) produce many compatible brands of which the price is quite low. The price of FS.COM JNP-QSFP-40G-LX4 is US$ 400.00. Compared with the average market price, it’s obvious that FS.COM products have advantages on price. Now you may doubt that transceivers with such a low price will not have good quality. Then you don’t need to worry about it when you see FS.COM test assured program which provides world-class customer confidence in each fiber optics. Except transceiver optics module, FS.COM also has other cost-effective optical products for you to upgrade to 40G network.
Second, not to buy new equipment. Consider that many enterprises have spent a lot investments in 10G networks, many carriers would like to upgrade to 40G by just inserting new 40G cards into their existing 10G WDM systems to save cost. Here are three advisable strategies moving from 10G to 40G: Use the current fiber plant of the 10G routes, and not invest in expensive deployments of new fiber for 40G; Add 40G to currently installed equipment, so additional equipment is not required to sit alongside the 10G gear; Keep the network robustness and architecture intact, that is, the current line design, so that the numbers of OADM and ROADM nodes on any pathway in a ring or mesh do not need to be reduced.
Improve OSNR, CD, PMD
Problems related to OSNR, CD and PMD are caused by optics, the fiber quality and other optical equipment on one side. So you should better choose high quality equipment. On the other side, it depends on advanced optical technology bringing about simplified materials and better methods.
Although there are many challenges, the trend of upgrading from 10G to 40G is inevitable. With the above methods and more advanced fiber optical technologies, you should upgrade to 40G network without any hesitation. Besides, to help customers to achieve 40G smoothly, FS.COM researches and develops high-quality products with favorable price. And FS.COM will keep providing customers with more cost-effective equipment and better solutions to realize 40G upgrading.