10GbE (Gigabit Ethernet) is no longer enough for the increasing need for high speed transmission with applications like Big Data, Cloud and Internet of Things being introduced in a variety of industries. Transmission network migration to 40/100G has already been the industry consensus. As the cost for 100G is far beyond what most companies can afford and the technology for 100G is still not mature, there is still a gap to reach the transmission speed of 100 Gb/s. However, to satisfy the current need for data rate, 40G could be a better and more economic solution. Currently the servers in many data centers are ready to carry the transmission of 40 Gb/s. The core technologies of 40 Gigabit are gradually mature. In addition, more manufacturers are battling for the 40G market, which drives down the 40G deployment price.
Unlike 1G migrating to 10G, 10G migration to 40 Gigabit get across a much larger span in terms of not only transmission data rate but also technologies. Thus, the deployment of 40G migration is much more complicated than that of 10G. Three factors should be considered to increase the reliability and manageability for 40G migration. They are fiber optic transceiver, transmission media, and pre-terminated MPO assemblies.
Fiber optic interconnection is indispensable in today’s telecommunication network. Photoelectric conversion is a necessary part in fiber optic network. The function of fiber optic transceiver is photoelectric conversion, which makes it one of the most commonly used components in the data center. Without it, the data center cannot run normally.
As for 40G migration, transceivers of two different package forms are commonly used: QSFP+ transceiver (Quad Small Form-factor Pluggable Plus transceiver) and CFP transceiver (C Form-factor Pluggable transceiver). QSFP+transceiver is more popular in 40 Gigabit application. A single 40G fiber optic transceiver may not be expensive. However, to a medium-sized data center, thousand of optical transceivers might be needed. The total cost on optical transceivers is a large sum of money. The switch market has already been monopolized. Luckily, the transceiver market is not. Third party transceivers that are compatible with a variety types of switches can be found in today’s market. They have the same performances that the original brand transceivers have, but cost less money. Selecting compatible transceivers has become the choice of many data centers. Cost is one aspect that should be considered in 40G optical transceiver selection. Quality is also very important. Not all the third party transceivers are created equal. Selecting the compatible 40G transceivers from a company that assures 100% compatibility and interoperability is necessary. The above picture shows the testing of Cisco compatible QSFP-40G-LR4 transceivers on a Cisco switch to ensure its compatibility and interoperability.
40GbE standards of IEEE have already been announced several years ago. To meet various situations, there are standards for different transmission media. Although fiber optic cable is becoming more and more popular, there is still a place for copper cable in data center. Standards for both copper and fiber optic are being used. Commonly used 40 Gigabit Ethernet media systems include the following:
- 40GBASE-CR4: 40Gb/s Ethernet over copper cable in short transmission distance.
- 40GBASE-SR4: 40Gb/s Ethernet over four short-range multimode fiber optic cables.
- 40GBASE-LR4: 40Gb/s Ethernet over four wavelengths carried by a signal long-distance single mode fiber optic cable.
It comes to the old question: fiber optic cable or copper cable, which should be used in 40G migration? Copper is cheaper. But it can only support 40GbE transmission limited to several meters. Single mode fiber optic cable supports the longest 40GbE transmission distance up to 10 km. For multimode fiber optic cables, OM3 and OM4 are suggested to support short distance transmission. The longest distance that OM3 can support for 40G transmission is 100 m. OM4 can support a longest 40G transmission distance of 150 m. The selection of transmission media should depend on the specific applications.
According to the IEEE standards, the 40G multimode Ethernet transmission uses four multimode fiber optic cables. The IEEE 802.3ba standard also specifies multi-fiber push-on (MPO) connectors for standard-length multimode fiber connectivity. Most of the 40G multimode Ethernet transceivers are based on the MPO technology. It is wise to increase fiber optic density by using MPO technology, but a new problem is coming up. As the fiber number increased, the cabling and splicing difficulty in data center increased. Unlike traditional two-strand fiber connections, MPO connectors cannot be field terminated easily. Most of the data centers choose the pre-terminated MPO assemblies (as shown in the above picture) in 40G deployment, which is more reliable and can save more human labor. Before cabling, determine the cabling lengths and customized pre-terminated MPO assemblies with manufacturers would save a lot of time and money.
Selecting a compatible third party transceiver of high quality in 40 Gigabit transmission would save a lot of money. Combining specific applications and characteristics of 40G transmission media, would help to determine the most economic and reliable 40G deployment plan. Pre-terminated MPO assemblies are necessary for flexible and manageable cabling in 40G deployment. 40G migration is happening now and it will become a milestone in the history of network transmission.
Source：http://www.fs.com/blog/three-factors-to-consider-for-smooth-migration-to-40g.html