From once being passive deposit boxes for documents, spreadsheets, and personnel files, the role of data centres has shifted, in recent times, to become something more dynamic, central to all aspects of life and an increasingly critical foundation for society as a whole.
However as data centres have become an increasingly critical part of everyday life, their responsiveness, or latency, has proven detrimental to their general usefulness. To address this problem the industry has taken steps to minimise the impact of latency on the user experience. As a result, rigid hierarchical data centre switching, in which each layer increased latency, is rapidly becoming obsolete.
In its place, the data centre industry is adopting a new approach to switching, designed to reduce latency. Fabric-based networks comprised of leaves - every switch at the edge of the architecture - which are connected to every switch in along the spine - or core. The resemblance of the resulting cabling arrangement to clothing material gives the fabric network its name.
Many combinations and permutations
Despite this being a significant step in the right direction, however, the issue of latency is still yet to be fully resolved.
When you consider the physical layer cabling requirements that an “any-to-any” architecture might bring to a fabric network, it soon becomes clear just how unimaginably complex the many combinations and permutations of cable media, channel length, and transmission standards can become. Indeed, moving from a traditional three-tier approach to a flat network fabric only serves to highlight the number of issues around designing the cabling needed to support such a network. This is further emphasised by the need for the fabric to be flexible, growing as required to cope with any additional demand placed on it in the future.
As the switching hierarchy becomes increasingly less rigid, there is a temptation to move away from structured cabling altogether. Realistically though, this is the time for structured cabling, focused on highly available system designs. For network fabric to be truly agile and efficient, it should be based on the solid foundation that the physical layer offers. After all, a house is only as strong as its foundation.
Points for consideration
Before embarking on a fabric network design, there are a number of factors that should be considered.
First of these is the emergence of new 25G and 50G data rates which are set to appear alongside 10G, 40G and 100G over the next 18 months, enabled by developments in technologies such as 25Gb/s SERDES (serialiser/de-serialiser) and VCSEL (vertical cavity surface emitting laser). Consideration should be given to supporting these technologies using LC, BASE “X” MPO, or an altogether new connector interface, and whether the aggregation of fibre channels over high fibre count MPO connectors could lead to significant savings resulting from reduced pathways, installation and testing.
According to current IEEE classification, the fabric between a leaf and its corresponding spine switch can be anywhere up to 500 metres in length, which can present a significant challenge when selecting the most appropriate media to use. A zone of huge complexity exists between cable lengths of 100 to 400 metres, within which a trade-off can be made between single mode fibre, which offers long reach at a higher price point for the transceivers, and multi-mode fibre, which offers good coverage at lower price points. One size won’t fit all in this situation, so it’s important to choose a vendor that has pedigree in both single and multi-mode fibre. Some manufacturers are currently working to extend the distance of which multi-mode fibre works, and can offer application-specific guarantees, aiding the decision-making process.
While the choice between the alternatives of a simple interconnect or cross-connect path is currently the subject of some debate, some of the world’s leading data centre operators discovered early on in the development of their networks that cross-connect paths make greater sense, as they allow more flexibility within a network.
By using simple patching schemes and cable routing on a well-designed optical distribution frame, these operators realised how it was possible for connections to be made, quickly and efficiently, between different channels in the fabric, or between different data connect halls and rooms.
Illustrating the importance of this realisation, a standard, CEN50600-2-4, has already been created in Europe which makes mandatory the use of cross-connects in European data centre design. Despite not having a global mandate, the fundamental tenets of the standard could be applied to help the wider industry build better data centres for the future.
Finally, some consideration should be given to automation, the latest trend to hit the data centre and its fabric. Traditional networking software/hardware-only designs for controlling the flow of information to the data centre are being replaced by tools such as software-defined networking (SDN) and network function virtualisation (NFV), dynamically directing the flow of traffic across the fabric and reconfiguring hardware on the fly, as they optimise the network’s function to meet the needs of the applications it supports, at any given time.
Supporting SDN or NFV requires new technologies that can be employed in the physical layer fabric design, such as connection point ID technology, which allows the status and ability of a cabled channel to be reported back to the management software, in real time via the cabling itself, in order to support its required functionality.
Increasingly complex
Somewhat paradoxically, it’s clear that the network fabric environment will constantly expand the capacity of latency issues despite being designed to consign them to the past. The growing complexity regarding capacity, network size and component costs means that questions and decisions around cabling are likely to become increasingly difficult to answer without any real certainty.
It’s important that networking IT departments are specific about their business’s future requirements, speeds, media, and the distances data will have to be carried within the facility, otherwise they risk choosing an incorrectly structured cabling architecture. From the outset, careful consideration must be given to all of these factors, or else the issues presented in deploying a fabric design may ultimately outweigh the benefits.
