FOCUS on CONNECTIVITY
FIBER IN THE DATA CENTER
Ethernet will require a lot of fiber. Indeed, 40GB and 100GB Ethernet will require 12 fibers, not one fiber inside the cable.
But there are some issues with fiber, especially as it can be more tricky than copper to install. Pulling the fiber cable is easy, as it can be pulled at eight times the pulling tension of a Cat 5 cable, for example.
Nowadays, a lot of typical cables that are deployed do have strength members and stiffeners in order to make it harder to kink or damage the cable.
COMPLEX TO TERMINATE Terminating a copper cable is a relatively straightforward process, but it is a bit more complex to terminate fiber optic cable.
Most manufacturers are offering crimp-on connectors, but they can be expensive, have potential reliability issues and suffer from high loss. So it is recommended that adhesives are used for fiber optic connectors in order to ensure reliability and low cost.
And it is worth realising straight away that fiber does not have infinite bandwidth. This is especially the case with the multimode fiber used in most premise networks.
Of course, fiber does offer much greater throughput than copper, but as you approach gigabit speeds, you are limiting the distances available for links to 500 meters or so. And remember that bandwidth depends on the type and speed of transmitters, as well as the fiber being used.
Multimode fiber is commonly used in short reach, high-bandwidth communications networks. Single-mode fiber – as used in telco and CATV networks, for example – does offer practically infinite bandwidth.
Unfortunately, it uses higher cost components and can therefore be pricey for shorter links. This could lead some to think it is not necessary for today’s networks, but it may well be for the next generation.
There are various grades and core counts of fiber optical cable. These can include: •
Standards compliance; and Compatibility with installed fiber types.
Network managers must balance these issues, along with their own individual considerations, to develop low-cost solutions that offer the most efficient, low-cost migration paths to higher data rates for their particular installation.
Another issue for them to consider is making sure the fiber they are choosing is compatible with the fiber that is already installed – so-called legacy fiber.
2, 4, 8, 12, 16 and 24 core. While they are the most common, almost any core count can be achieved;
Standard OM2 MM fiber, suitable for 100Base-FX transmissions over shorter distances (220M);
• OM3 MM fiber, suitable for 100Base-FX transmissions over longer distances (2 kilometres) and 1000Base-SX over shorter distances (550 metres); and
GIGALite III fiber, suitable for 1000Base-SX transmissions over longer distances (2 kilometres).
CONCLUSION Choosing the right fiber type for your installation is not exactly straightforward, and it is recommended that advice is sought from the numerous cable manufacturers and solution providers mentioned elsewhere in this Connectivity supplement. Generally speaking, the main considerations for selecting the fiber type are: • • •
Current applications and data rates; Future applications and data rates; Channel lengths;
Consideration must also be given to standards. Each application standard, such as FDDI, Ethernet and Fiber Channel, have specific requirements on the types of fiber that can be used with it, and the bandwidth performance requirements of each.
The standards also help in that they set the maximum channel lengths and channel power loss values that are acceptable. This means that if the correct fiber type and performance is selected, the fiber-based network can be expected to operate correctly over its operational lifetime – providing it has been installed correctly, of course.
Perhaps the biggest onus on the network manager today, however, is to ensure that the fiber types he or she selects for use in the data center now will be able to cope with the upgrades, advances and new equipment in future.
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