Technology aligns to raise physical layer performance
Mon 26 Jun 2017 | Michael Adams
Latest high-density fibre raises the performance game for data centres
The rate of change within the data centre sector has been tremendously fast as cloud services have multiplied exponentially. Data centre operators have often had to second guess the standards guidelines for infrastructure to achieve operational and economically viable sites.
Although not immediately apparent, these decisions often have knock-on costs in terms of installation and MAC expenditure. The physical layer represents around 5 percent of data centre project spend and accounts for 59 percent of downtown once operational. The numbers indicate that numerous installations have been found wanting as the infrastructure performance requirements have increased. If we consider that 76 percent of data centre traffic is East to West – machine to machine – within the data centre, then cable infrastructure rationalisation is imperative, whether as an upgrade path or new build site.
Fibre technology for informed data centre managers is a key building block to future higher performance topologies. Simplifying the infrastructure architecture and longer cable reach fibre technology will provide technological and financial benefits to the data centre operators and customers.
Let us consider the use of 10Gb/s switch to switch connections today, and the need for 40Gb/s in the imminent future. To upgrade from 10GBASE-SR to 40GBASE-SR4, the duplex fibre pairs must be replaced with four duplex pairs (8 fibres) terminated with MPO connectors. In addition, only 8 of the 12 fibres in a typical 12 fibre cable are utilised leaving 4 to remain dark.
To fully utilise all fibre strands, the data centre infrastructure must be carefully designed with an upgrade path in mind. A more efficient upgrade path would be to replace 10GBASE-SR transceivers with next generation 50GBASE-SR transceivers (to be ratified in 2018), which exploits the same duplex fibre structured cabling. The higher speed 50Gb/s solution is projected to be lower cost and employs an advanced modulation scheme which can be extended with future 200 Gb/s transceivers.
A key challenge for the date centre operator is understanding what type of fibre to install; single-mode or multimode and if multimode, which Category: OM3, OM4, or OM5. Selecting a fibre type depends on cost, future data rate needs, and maximum channel reach.
Single-Mode Fibre (SMF) will support all future data rates and channel reaches, but the performance comes at a cost premium on the order of 3 to 5 times that of multimode channels. For SWDM, wide band fibre such as Signature Core or OM5 will be required to guarantee performance over the specified channel reaches with a high confidence level.
For data rates up to 400Gb/s, there is little if any risk using existing structured cabling comprising OM3 and OM4 fibre types. However, in the event the cabling contains marginally compliant fibres it is possible the channel efficiency would be reduced due to occasional frame errors.
As data rates increase and technology evolves, lower data rates will become obsolete, as did 50 and 200 megabit per second optical data links. Therefore, the structured cabling should be capable of supporting future specified higher data rates network infrastructure. This suggests the deployment of parallel OM3 or OM4 fibres for short channel reaches less than 75 meters and SigCore or OM5 for reaches up to 150m. Single-mode will likely continue to be more expensive for at least 5 to 10 more years.
Today the discussion is framed around increased bandwidth, reduced latency, and energy concerns including lower power usage and reduced heat generated by the system. Viewed against the alternative cabling systems, fibre offers benefits as a solution to the high-performance requirements of data centres now and in the long-term future.